Copyright (C) 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
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This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.
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If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.
one line to give the program's name and an idea of what it does. Copyright (C) 19yy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere "extension language"; it is a full computer programming language in its own right. You can use it as you would any other programming language.
Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables.
This manual describes Emacs Lisp, presuming considerable familiarity with the use of Emacs for editing. (See The GNU Emacs Manual, for this basic information.) Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing.
This is edition 2.1.
This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few sections which are not included, either because we consider them secondary (such as most of the individual modes) or because they are yet to be written.
Because we are not able to deal with them completely, we have left out several parts intentionally. This includes most references to VMS and all information relating Sunview. (The Free Software Foundation expends no effort on support for Sunview, since we believe users should use the free X window system rather than proprietary window systems.)
The manual should be fully correct in what it does cover, and it is therefore open to criticism on anything it says--from specific examples and descriptive text, to the ordering of chapters and sections. If something is confusing, or you find that you have to look at the sources or experiment to learn something not covered in the manual, then perhaps the manual should be fixed. Please let us know.
As you use the manual, we ask that you mark pages with corrections so you can later look them up and send them in. If you think of a simple, real life example for a function or group of functions, please make an effort to write it up and send it in. Please reference any comments to the chapter name, section name, and function name, as appropriate, since page numbers and chapter and section numbers will change. Also state the number of the edition which you are criticizing.
Please mail comments and corrections to
bug-lisp-manual@prep.ai.mit.edu
--Bil Lewis, Dan LaLiberte, Richard Stallman
Lisp (LISt Processing language) was first developed in the late 1950s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it superior for other purposes as well, such as writing editing commands.
Dozens of Lisp implementations have been built over the years, each with its own idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960's at MIT's Project MAC. Eventually the implementors of the descendents of Maclisp came together and developed a standard for Lisp systems, called Common Lisp.
GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you know Common Lisp, you will notice many similarities. However, many of the features of Common Lisp have been omitted or simplified in order to reduce the memory requirements of GNU Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might be very confused. We will occasionally point out how GNU Emacs Lisp differs from Common Lisp. If you don't know Common Lisp, don't worry about it; this manual is self-contained.
This section explains the notational conventions that are used in this manual. You may want to skip this section and refer back to it later.
Throughout this manual, the phrases "the Lisp reader" and "the Lisp printer" are used to refer to those routines in Lisp that convert textual representations of Lisp objects into actual objects, and vice versa. See section Printed Representation and Read Syntax, for more details. You, the person reading this manual, are thought of as "the programmer" and are addressed as "you". "The user" is the person who uses Lisp programs including those you write.
Examples of Lisp code appear in this font or form: (list 1 2
3). Names that represent arguments or metasyntactic variables appear
in this font or form: first-number.
nil and t
In Lisp, the symbol nil is overloaded with three meanings: it
is a symbol with the name `nil'; it is the logical truth value
false; and it is the empty list--the list of zero elements.
When used as a variable, nil always has the value nil.
As far as the Lisp reader is concerned, `()' and `nil' are
identical: they stand for the same object, the symbol nil. The
different ways of writing the symbol are intended entirely for human
readers. After the Lisp reader has read either `()' or `nil',
there is no way to determine which representation was actually written
by the programmer.
In this manual, we use () when we wish to emphasize that it
means the empty list, and we use nil when we wish to emphasize
that it means the truth value false. That is a good convention to use
in Lisp programs also.
(cons 'foo ()) ; Emphasize the empty list (not nil) ; Emphasize the truth value false
In contexts where a truth value is expected, any non-nil value
is considered to be true. However, t is the preferred way
to represent the truth value true. When you need to choose a
value which represents true, and there is no other basis for
choosing, use t. The symbol t always has value t.
In Emacs Lisp, nil and t are special symbols that always
evaluate to themselves. This is so that you do not need to quote them
to use them as constants in a program. An attempt to change their
values results in a setting-constant error. See section Accessing Variable Values.
A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with `=>':
(car '(1 2))
=> 1
You can read this as "(car '(1 2)) evaluates to 1".
When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with `==>'. We may or may not show the actual result of the evaluation of the expanded form.
(third '(a b c))
==> (car (cdr (cdr '(a b c))))
=> c
Sometimes to help describe one form we show another form which produces identical results. The exact equivalence of two forms is indicated with `=='.
(make-sparse-keymap) == (list 'keymap)
Many of the examples in this manual print text when they are
evaluated. If you execute the code from an example in a Lisp
Interaction buffer (such as the buffer `*scratch*'), the printed
text is inserted into the buffer. If the example is executed by other
means (such as by evaluating the function eval-region), the text
printed is usually displayed in the echo area. You should be aware that
text displayed in the echo area is truncated to a single line.
In examples that print text, the printed text is indicated with
`-|', irrespective of how the form is executed. The value
returned by evaluating the form (here bar) follows on a separate
line.
(progn (print 'foo) (print 'bar))
-| foo
-| bar
=> bar
Some examples cause errors to be signaled. In them, the error message (which always appears in the echo area) is shown on a line starting with `error-->'. Note that `error-->' itself does not appear in the echo area.
(+ 23 'x) error--> Wrong type argument: integer-or-marker-p, x
Some examples show modifications to text in a buffer, with "before" and "after" versions of the text. In such cases, the entire contents of the buffer in question are included between two lines of dashes containing the buffer name. In addition, the location of point is shown as `-!-'. (The symbol for point, of course, is not part of the text in the buffer; it indicates the place between two characters where point is located.)
---------- Buffer: foo ----------
This is the -!-contents of foo.
---------- Buffer: foo ----------
(insert "changed ")
=> nil
---------- Buffer: foo ----------
This is the changed -!-contents of foo.
---------- Buffer: foo ----------
Functions, variables, macros, commands, user options, and special forms are described in this manual in a uniform format. The first line of a description contains the name of the item followed by its arguments, if any. The category--function, variable, or whatever--is printed next to the right margin. The description follows on succeeding lines, sometimes with examples.
In a function description, the name of the function being described appears first. It is followed on the same line by a list of parameters. The names used for the parameters are also used in the body of the description.
The appearance of the keyword &optional in the parameter list
indicates that the arguments for subsequent parameters may be omitted
(omitted parameters default to nil). Do not write
&optional when you call the function.
The keyword &rest (which will always be followed by a single
parameter) indicates that any number of arguments can follow. The value
of the single following parameter will be a list of all these arguments.
Do not write &rest when you call the function.
Here is a description of an imaginary function foo:
Function: foo integer1 &optional integer2 &rest integers
The function foo subtracts integer1 from integer2,
then adds all the rest of the arguments to the result. If integer2
is not supplied, then the number 19 is used by default.
(foo 1 5 3 9)
=> 16
(foo 5)
=> 14
More generally,
(foo w x y...) == (+ (- x w) y...)
Any parameter whose name contains the name of a type (e.g., integer, integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers) often means a list of objects of that type. Parameters named object may be of any type. (See section Lisp Data Types, for a list of Emacs object types.) Parameters with other sorts of names (e.g., new-file) are discussed specifically in the description of the function. In some sections, features common to parameters of several functions are described at the beginning.
See section Lambda Expressions, for a more complete description of optional and rest arguments.
Command, macro, and special form descriptions have the same format, but the word `Function' is replaced by `Command', `Macro', or `Special Form', respectively. Commands are simply functions that may be called interactively; macros process their arguments differently from functions (the arguments are not evaluated), but are presented the same way.
Special form descriptions use a more complex notation to specify
optional and repeated parameters because they can break the argument
list down into separate arguments in more complicated ways.
`[optional-arg]' means that optional-arg is
optional and `repeated-args...' stands for zero or more
arguments. Parentheses are used when several arguments are grouped into
additional levels of list structure. Here is an example:
Special Form: count-loop (var [from to [inc]]) body...
This imaginary special form implements a loop that executes the body forms and then increments the variable var on each iteration. On the first iteration, the variable has the value from; on subsequent iterations, it is incremented by 1 (or by inc if that is given). The loop exits before executing body if var equals to. Here is an example:
(count-loop (i 0 10) (prin1 i) (princ " ") (prin1 (aref vector i)) (terpri))
If from and to are omitted, then var is bound to
nil before the loop begins, and the loop exits if var is
non-nil at the beginning of an iteration. Here is an example:
(count-loop (done)
(if (pending)
(fixit)
(setq done t)))
In this special form, the arguments from and to are optional, but must both be present or both absent. If they are present, inc may optionally be specified as well. These arguments are grouped with the argument var into a list, to distinguish them from body, which includes all remaining elements of the form.
A variable is a name that can hold a value. Although any variable can be set by the user, certain variables that exist specifically so that users can change them are called user options. Ordinary variables and user options are described using a format like that for functions except that there are no arguments.
Here is a description of the imaginary electric-future-map
variable.
Variable: electric-future-map
The value of this variable is a full keymap used by electric command future mode. The functions in this map will allow you to edit commands you have not yet thought about executing.
User option descriptions have the same format, but `Variable' is replaced by `User Option'.
This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc.
Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom, David Boyes, Alan Carroll, David A. Duff, Beverly Erlebacher, David Eckelkamp, Eirik Fuller, Eric Hanchrow, George Hartzell, Nathan Hess, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, K. Richard Magill, Brian Marick, Roland McGrath, Skip Montanaro, John Gardiner Myers, Arnold D. Robbins, Raul Rockwell, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn.
A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes, a type or data type is a set of possible objects.
Every object belongs to at least one type. Objects of the same type have similar structures and may usually be used in the same contexts. Types can overlap, and objects can belong to two or more types. Consequently, we can ask whether an object belongs to a particular type, but not for "the" type of an object.
A few fundamental object types are built into Emacs. These, from which all other types are constructed, are called primitive types. Each object belongs to one and only one primitive type. These types include integer, float, cons, symbol, string, vector, subr, byte-code function, and several special types, such as buffer, that are related to editing. (See section Editing Types.)
Each primitive type has a corresponding Lisp function that checks whether an object is a member of that type.
Note that Lisp is unlike many other languages in that Lisp objects are self-typing: the primitive type of the object is implicit in the object itself. For example, if an object is a vector, it cannot be treated as a number because Lisp knows it is a vector, not a number.
In most languages, the programmer must declare the data type of each variable, and the type is known by the compiler but not represented in the data. Such type declarations do not exist in Emacs Lisp. A Lisp variable can have any type of value, and remembers the type of any value you store in it.
This chapter describes the purpose, printed representation, and read syntax of each of the standard types in GNU Emacs Lisp. Details on how to use these types can be found in later chapters.
The printed representation of an object is the format of the
output generated by the Lisp printer (the function print) for
that object. The read syntax of an object is the format of the
input accepted by the Lisp reader (the function read) for that
object. Most objects have more than one possible read syntax. Some
types of object have no read syntax; except for these cases, the printed
representation of an object is also a read syntax for it.
In other languages, an expression is text; it has no other form. In Lisp, an expression is primarily a Lisp object and only secondarily the text that is the object's read syntax. Often there is no need to emphasize this distinction, but you must keep it in the back of your mind, or you will occasionally be very confused.
Every type has a printed representation. Some types have no read
syntax, since it may not make sense to enter objects of these types
directly in a Lisp program. For example, the buffer type does not have
a read syntax. Objects of these types are printed in hash
notation: the characters `#<' followed by a descriptive string
(typically the type name followed by the name of the object), and closed
with a matching `>'. Hash notation cannot be read at all, so the
Lisp reader signals the error invalid-read-syntax whenever a
`#<' is encountered.
(current-buffer)
=> #<buffer objects.texi>
When you evaluate an expression interactively, the Lisp interpreter
first reads the textual representation of it, producing a Lisp object,
and then evaluates that object (see section Evaluation). However,
evaluation and reading are separate activities. Reading returns the
Lisp object represented by the text that is read; the object may or may
not be evaluated later. See section Input Functions, for a description of
read, the basic function for reading objects.
A comment is text that is written in a program only for the sake of humans that read the program, and that has no effect on the meaning of the program. In Lisp, a comment starts with a semicolon (`;') if it is not within a string or character constant, and continues to the end of line. Comments are discarded by the Lisp reader, and do not become part of the Lisp objects which represent the program within the Lisp system.
See section Tips on Writing Comments, for conventions for formatting comments.
There are two general categories of types in Emacs Lisp: those having to do with Lisp programming, and those having to do with editing. The former are provided in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp.
Integers are the only kind of number in GNU Emacs Lisp, version 18.
The range of values for integers is -8388608 to
8388607 (24 bits; i.e.,
to
on most machines, but is 25 or 26 bits on some systems. It is important
to note that the Emacs Lisp arithmetic functions do not check for
overflow. Thus (1+ 8388607) is -8388608 on 24-bit
implementations.
The read syntax for numbers is a sequence of (base ten) digits with an optional sign. The printed representation produced by the Lisp interpreter never has a leading `+'.
-1 ; The integer -1.
1 ; The integer 1.
+1 ; Also the integer 1.
16777217 ; Also the integer 1!
; (on a 24-bit or 25-bit implementation)
See section Numbers, for more information.
Emacs version 19 supports floating point numbers, if compiled with the
macro LISP_FLOAT_TYPE defined. The precise range of floating
point numbers is machine-specific.
The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4' are five ways of writing a floating point number whose value is 1500. They are all equivalent.
See section Numbers, for more information.
A character in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character A is represented as the integer 65.
Individual characters are not often used in programs. It is far more common to work with strings, which are sequences composed of characters. See section String Type.
Characters in strings, buffers, and files are currently limited to the range of 0 to 255. If an arbitrary integer is used as a character for those purposes, only the lower eight bits are significant. Characters that represent keyboard input have a much wider range.
Since characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is a very bad idea. You should always use the special read syntax formats that Emacs Lisp provides for characters. These syntax formats start with a question mark.
The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, `?A' for the character A, `?B' for the character B, and `?a' for the character a.
For example:
?Q => 81 ?q => 113
You can use the same syntax for punctuation characters, but it is often a good idea to add a `\' to prevent Lisp mode from getting confused. For example, `?\ ' is the way to write the space character. If the character is `\', you must use a second `\' to quote it: `?\\'.
You can express the characters control-g, backspace, tab, newline, vertical tab, formfeed, return, and escape as `?\a', `?\b', `?\t', `?\n', `?\v', `?\f', `?\r', `?\e', respectively. Those values are 7, 8, 9, 10, 11, 12, 13, and 27 in decimal. Thus,
?\a => 7 ; C-g ?\b => 8 ; backspace, BS, C-h ?\t => 9 ; tab, TAB, C-i ?\n => 10 ; newline, LFD, C-j ?\v => 11 ; vertical tab, C-k ?\f => 12 ; formfeed character, C-l ?\r => 13 ; carriage return, RET, C-m ?\e => 27 ; escape character, ESC, C-[ ?\\ => 92 ; backslash character, \
These sequences which start with backslash are also known as escape sequences, because backslash plays the role of an escape character, but they have nothing to do with the character ESC.
Control characters may be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, either `?\^I' or `?\^i' may be used as the read syntax for the character C-i, the character whose value is 9.
Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to `?\^I' and to `?\^i':
?\^I => 9
?\C-I => 9
For use in strings and buffers, you are limited to the control characters that exist in ASCII, but for keyboard input purposes, you can turn any character into a control character with `C-'. The character codes for these characters include the 2**22 bit as well as the code for the non-control character. Ordinary terminals have no way of generating non-ASCII control characters, but you can generate them straightforwardly using an X terminal.
The DEL key can be considered and written as Control-?:
?\^? => 127
?\C-? => 127
When you represent control characters to be found in files or strings, we recommend the `^' syntax; but when you refer to keyboard input, we prefer the `C-' syntax. This does not affect the meaning of the program, but may guide the understanding of people who read it.
A meta character is a character typed with the META key. The integer that represents such a character has the 2**23 bit set (which on most machines makes it a negative number). We use high bits for this and other modifiers to make possible a wide range of basic character codes.
In a string, the 2**7 bit indicates a meta character, so the meta characters that can fit in a string have codes in the range from 128 to 255, and are the meta versions of the ordinary ASCII characters. (In Emacs versions 18 and older, this convention was used for characters outside of strings as well.)
The read syntax for meta characters uses `\M-'. For example, `?\M-A' stands for M-A. You can use `\M-' together with octal codes, `\C-', or any other syntax for a character. Thus, you can write M-A as `?\M-A', or as `?\M-\101'. Likewise, you can write C-M-b as `?\M-\C-b', `?\C-\M-b', or `?\M-\002'.
The shift modifier is used in indicating the case of a character in special circumstances. The case of an ordinary letter is indicated by its character code as part of ASCII, but ASCII has no way to represent whether a control character is upper case or lower case. Emacs uses the 2**21 bit to indicate that the shift key was used for typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary terminals do not indicate the distinction to the computer in any way.
The X Window system defines three other modifier bits that can be set in a character: hyper, super and alt. The syntaxes for these bits are `\H-', `\s-' and `\A-'. Thus, `?\H-\M-\A-x' represents Alt-Hyper-Meta-x. Numerically, the bit values are 2**18 for alt, 2**19 for super and 2**20 for hyper.
Finally, the most general read syntax consists of a question mark
followed by a backslash and the character code in octal (up to three
octal digits); thus, `?\101' for the character A,
`?\001' for the character C-a, and ?\002 for the
character C-b. Although this syntax can represent any ASCII
character, it is preferred only when the precise octal value is more
important than the ASCII representation.
?\012 => 10 ?\n => 10 ?\C-j => 10 ?\101 => 65 ?A => 65
A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, `?\A' is equivalent to `?A'. There is no reason to use a backslash before most such characters. However, any of the characters `()\|;'`"#.,' should be preceded by a backslash to avoid confusing the Emacs commands for editing Lisp code. Whitespace characters such as space, tab, newline and formfeed should also be preceded by a backslash. However, it is cleaner to use one of the easily readable escape sequences, such as `\t', instead of an actual control character such as a tab.
A sequence is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in Emacs Lisp, lists and arrays. Thus, an object of type list or of type array is also considered a sequence.
Arrays are further subdivided into strings and vectors. Vectors can hold elements of any type, but string elements must be characters in the range from 0 to 255. However, the characters in a string can have text properties; vectors do not support text properties even when their elements happen to be characters.
Lists, strings and vectors are different, but they have important
similarities. For example, all have a length l, and all have
elements which can be indexed from zero to l minus one. Also,
several functions, called sequence functions, accept any kind of
sequence. For example, the function elt can be used to extract
an element of a sequence, given its index. See section Sequences, Arrays, and Vectors.
It is impossible to read the same sequence twice, in the sense of
eq (see section Equality Predicates), since sequences are always
created anew upon reading. There is one exception: the empty list
() always stands for the same object, nil.
A list is a series of cons cells, linked together. A cons cell is an object comprising two pointers named the CAR and the CDR. Each of them can point to any Lisp object, but when the cons cell is part of a list, the CDR points either to another cons cell or to the empty list. See section Lists, for functions that work on lists.
The names CAR and CDR have only historical meaning now. The
original Lisp implementation ran on an IBM 704 computer which
divided words into two parts, called the "address" part and the
"decrement"; CAR was an instruction to extract the contents of
the address part of a register, and CDR an instruction to extract
the contents of the decrement. By contrast, "cons cells" are named
for the function cons that creates them, which in turn is named
for its purpose, the construction of cells.
Because cons cells are so central to Lisp, we also have a word for "an object which is not a cons cell". These objects are called atoms.
The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis.
Upon reading, any object inside the parentheses is made into an
element of the list. That is, a cons cell is made for each element.
The CAR of the cons cell points to the element, and its CDR
points to the next cons cell which holds the next element in the list.
The CDR of the last cons cell is set to point to nil.
A list can be illustrated by a diagram in which the cons cells are
shown as pairs of boxes. (The Lisp reader cannot read such an
illustration; unlike the textual notation, which can be understood both
humans and computers, the box illustrations can only be understood by
humans.) The following represents the three-element list (rose
violet buttercup):
___ ___ ___ ___ ___ ___
|___|___|--> |___|___|--> |___|___|--> nil
| | |
| | |
--> rose --> violet --> buttercup
In the diagram, each box represents a slot that can refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow is a reference to a Lisp object, either an atom or another cons cell.
In this example, the first box, the CAR of the first cons cell,
refers to or "contains" rose (a symbol). The second box, the
CDR of the first cons cell, refers to the next pair of boxes, the
second cons cell. The CAR of the second cons cell refers to
violet and the CDR refers to the third cons cell. The
CDR of the third (and last) cons cell refers to nil.
Here is another diagram of the same list, (rose violet
buttercup), sketched in a different manner:
--------------- ---------------- ------------------- | car | cdr | | car | cdr | | car | cdr | | rose | o-------->| violet | o-------->| buttercup | nil | | | | | | | | | | --------------- ---------------- -------------------
A list with no elements in it is the empty list; it is identical
to the symbol nil. In other words, nil is both a symbol
and a list.
Here are examples of lists written in Lisp syntax:
(A 2 "A") ; A list of three elements.
() ; A list of no elements (the empty list).
nil ; A list of no elements (the empty list).
("A ()") ; A list of one element: the string "A ()".
(A ()) ; A list of two elements: A and the empty list.
(A nil) ; Equivalent to the previous.
((A B C)) ; A list of one element
; (which is a list of three elements).
Here is the list (A ()), or equivalently (A nil),
depicted with boxes and arrows:
___ ___ ___ ___
|___|___|--> |___|___|--> nil
| |
| |
--> A --> nil
Dotted pair notation is an alternative syntax for cons cells
that represents the CAR and CDR explicitly. In this syntax,
(a . b) stands for a cons cell whose CAR is
the object a, and whose CDR is the object b. Dotted
pair notation is therefore more general than list syntax. In the dotted
pair notation, the list `(1 2 3)' is written as `(1 . (2 . (3
. nil)))'. For nil-terminated lists, the two notations produce
the same result, but list notation is usually clearer and more
convenient when it is applicable. When printing a list, the dotted pair
notation is only used if the CDR of a cell is not a list.
Box notation can also be used to illustrate what dotted pairs look
like. For example, (rose . violet) is diagrammed as follows:
___ ___
|___|___|--> violet
|
|
--> rose
Dotted pair notation can be combined with list notation to represent a
chain of cons cells with a non-nil final CDR. For example,
(rose violet . buttercup) is equivalent to (rose . (violet
. buttercup)). The object looks like this:
___ ___ ___ ___
|___|___|--> |___|___|--> buttercup
| |
| |
--> rose --> violet
These diagrams make it evident that (rose . violet .
buttercup) must have an invalid syntax since it would require that a
cons cell have three parts rather than two.
The list (rose violet) is equivalent to (rose . (violet))
and looks like this:
___ ___ ___ ___
|___|___|--> |___|___|--> nil
| |
| |
--> rose --> violet
Similarly, the three-element list (rose violet buttercup)
is equivalent to (rose . (violet . (buttercup))).
An association list or alist is a specially-constructed list whose elements are cons cells. In each element, the CAR is considered a key, and the CDR is considered an associated value. (In some cases, the associated value is stored in the CAR of the CDR.) Association lists are often used to implement stacks, since new associations may easily be added to or removed from the front of the list.
For example,
(setq alist-of-colors
'((rose . red) (lily . white) (buttercup . yellow)))
sets the variable alist-of-colors to an alist of three elements. In the
first element, rose is the key and red is the value.
See section Association Lists, for a further explanation of alists and for functions that work on alists.
An array is composed of an arbitrary number of other Lisp objects, arranged in a contiguous block of memory. Any element of an array may be accessed in constant time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.)
Emacs defines two types of array, strings and vectors. A string is an array of characters and a vector is an array of arbitrary objects. Both are one-dimensional. (Most other programming languages support multidimensional arrays, but we don't think they are essential in Emacs Lisp.) Each type of array has its own read syntax; see section String Type, and section Vector Type.
An array may have any length up to the largest integer; but once created, it has a fixed size. The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3.
The array type is contained in the sequence type and contains both strings and vectors.
A string is an array of characters. Strings are used for many purposes in Emacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants; evaluation of a string returns the same string.
The read syntax for strings is a double-quote, an arbitrary number of
characters, and another double-quote, "like this". The Lisp
reader accepts the same formats for reading the characters of a string
as it does for reading single characters (without the question mark that
begins a character literal). You can enter a nonprinting character such
as tab, C-a or M-C-A using the convenient escape sequences,
like this: "\t, \C-a, \M-\C-a". You can include a double-quote
in a string by preceding it with a backslash; thus, "\"" is a
string containing just a single double-quote character.
(See section Character Type, for a description of the read syntax for
characters.)
If you use the `\M-' syntax to indicate a meta character in a string constant, this sets the 2**7 bit of the character in the string. This is not the same representation that the meta modifier has in a character regarded as a simple integer. See section Character Type.
Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no others. They do not distinguish case in ASCII control characters.
In contrast with the C programming language, Emacs Lisp allows newlines in string literals. But an escaped newline--one that is preceded by `\'---does not become part of the string; i.e., the Lisp reader ignores an escaped newline in a string literal.
"It is useful to include newlines
in documentation strings,
but the newline is \
ignored if escaped."
=> "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."
The printed representation of a string consists of a double-quote, the
characters it contains, and another double-quote. However, any
backslash or double-quote characters in the string are preceded with a
backslash like this: "this \" is an embedded quote".
A string can hold properties of the text it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to preserve the properties with no special effort. See section Text Properties. Strings with text properties have a special read and print syntax:
#("characters" property-data...)
where property-data is zero or more elements in groups of three as follows:
beg end plist
The elements beg and end are integers, and together specify a portion of the string; plist is the property list for that portion.
See section Strings and Characters, for functions that work on strings.
A vector is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.)
The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation.
[1 "two" (three)] ; A vector of three elements.
=> [1 "two" (three)]
See section Vectors, for functions that work with vectors.
A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the name is unique--no two symbols have the same name.
A symbol may be used in programs as a variable, as a function name, or to hold a list of properties. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended.
A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters `-+=*/'. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a `\' at the beginning of the name to force interpretation as a symbol.) The characters `_~!@$%^&:<>{}' are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol quotes the single character that follows the backslash, without conversion. For example, in a string, `\t' represents a tab character; in the name of a symbol, however, `\t' merely quotes the letter t. To have a symbol with a tab character in its name, you must actually type an tab (preceded with a backslash). But you would hardly ever do such a thing.
Common Lisp note: in Common Lisp, lower case letters are always "folded" to upper case, unless they are explicitly escaped. This is in contrast to Emacs Lisp, in which upper case and lower case letters are distinct.
Here are several examples of symbol names. Note that the `+' in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the last example because the rest of the name makes it invalid as a number.
foo ; A symbol named `foo'.
FOO ; A symbol named `FOO', different from `foo'.
char-to-string ; A symbol named `char-to-string'.
1+ ; A symbol named `1+'
; (not `+1', which is an integer).
\+1 ; A symbol named `+1'
; (not a very readable name).
\(*\ 1\ 2\) ; A symbol named `(* 1 2)' (a worse name).
+-*/_~!@$%^&=:<>{} ; A symbol named `+-*/_~!@$%^&=:<>{}'.
; These characters need not be escaped.
Just as functions in other programming languages are executable,
Lisp function objects are pieces of executable code. However,
functions in Lisp are primarily Lisp objects, and only secondarily the
text which represents them. These Lisp objects are lambda expressions:
lists whose first element is the symbol lambda (see section Lambda Expressions).
In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression is also called an anonymous function (see section Anonymous Functions). A named function in Lisp is actually a symbol with a valid function in its function cell (see section Defining Named Functions).
Most of the time, functions are called when their names are written in
Lisp expressions in Lisp programs. However, a function object found or
constructed at run time can be called and passed arguments with the
primitive functions funcall and apply. See section Calling Functions.
A Lisp macro is a user-defined construct that extends the Lisp
language. It is represented as an object much like a function, but with
different parameter-passing semantics. A Lisp macro has the form of a
list whose first element is the symbol macro and whose CDR
is a Lisp function object, including the lambda symbol.
Lisp macro objects are usually defined with the built-in
defmacro function, but any list that begins with macro is
a macro as far as Emacs is concerned. See section Macros, for an explanation
of how to write a macro.
A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions. (The word "subr" is derived from "subroutine".) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a special form (see section Special Forms).
It does not matter to the caller of a function whether the function is primitive. However, this does matter if you are trying to substitute a function written in Lisp for a primitive of the same name. The reason is that the primitive function may be called directly from C code. When the redefined function is called from Lisp, the new definition will be used; but calls from C code may still use the old definition.
The term function is used to refer to all Emacs functions, whether written in Lisp or C. See section Lisp Function Type, for information about the functions written in Lisp.
Primitive functions have no read syntax and print in hash notation with the name of the subroutine.
(symbol-function 'car) ; Access the function cell
; of the symbol.
=> #<subr car>
(subrp (symbol-function 'car)) ; Is this a primitive function?
=> t ; Yes.
The byte compiler produces byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. See section Byte Compilation, for information about the byte compiler.
The printed representation for a byte-code function object is like that for a vector, with an additional `#' before the opening `['.
An autoload object is a list whose first element is the symbol
autoload. It is stored as the function definition of a symbol to
say that a file of Lisp code should be loaded when necessary to find the
true definition of that symbol. The autoload object contains the name
of the file, plus some other information about the real definition.
After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user's point of view, the function call works as expected, using the function definition in the loaded file.
An autoload object is usually created with the function
autoload, which stores the object in the function cell of a
symbol. See section Autoload, for more details.
The types in the previous section are common to many Lisp-like languages. But Emacs Lisp provides several additional data types for purposes connected with editing.
A buffer is an object that holds text that can be edited (see section Buffers). Most buffers hold the contents of a disk file (see section Files) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (see section Windows). But a buffer need not be displayed in a window.
The contents of a buffer are much like a string, but buffers are not used like strings in Emacs Lisp, and the available operations are different. For example, text can be inserted into a buffer very quickly, while "inserting" text into a string is accomplished by concatenation and the result is an entirely new string object.
Each buffer has a designated position called point (see section Positions). And one buffer is the current buffer. Most editing commands act on the contents of the current buffer in the neighborhood of point. Many other functions manipulate or test the characters in the current buffer and much of this manual is devoted to describing these functions (see section Text).
Several other data structures are associated with each buffer:
The local keymap and variable list contain entries which individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs.
Buffers have no read syntax. They print in hash notation with the buffer name.
(current-buffer)
=> #<buffer objects.texi>
A window describes the portion of the terminal screen that Emacs uses to display a buffer. Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows.
Though many windows may exist simultaneously, one window is designated the selected window. This is the window where the cursor is (usually) displayed when Emacs is ready for a command. The selected window usually displays the current buffer, but this is not necessarily the case.
Windows are grouped on the screen into frames; each window belongs to one and only one frame. See section Frame Type.
Windows have no read syntax. They print in hash notation, giving the window number and the name of the buffer being displayed. The window numbers exist to identify windows uniquely, since the buffer displayed in any given window can change frequently.
(selected-window)
=> #<window 1 on objects.texi>
See section Windows, for a description of the functions that work on windows.
A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows.
Frames have no read syntax. They print in hash notation, giving the frame's title, plus its address in core (useful to identify the frame uniquely).
(selected-frame)
=> #<frame xemacs@mole.gnu.ai.mit.edu 0xdac80>
See section Frames, for a description of the functions that work on frames.
A window configuration stores information about the positions and sizes of windows at the time the window configuration is created, so that the screen layout may be recreated later.
Window configurations do not have a read syntax. They print as `#<window-configuration>'. See section Window Configurations, for a description of several functions related to window configurations.
A marker denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. The position value is changed automatically as necessary as text is inserted into or deleted from the buffer. This is to ensure that the marker always points between the same two characters in the buffer.
Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer.
(point-marker)
=> #<marker at 10779 in objects.texi>
See section Markers, for information on how to test, create, copy, and move markers.
The word process means a running program. Emacs itself runs in a process of this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocess created by Emacs process. External subprocesses, such as shells, GDB, ftp, and compilers, may be used to extend the processing capability of Emacs.
A process takes input from Emacs and returns output to Emacs for further manipulation. Both text and signals can be communicated between Emacs and a subprocess.
Processes have no read syntax. They print in hash notation, giving the name of the process:
(process-list)
=> (#<process shell>)
See section Processes, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes.
A stream is an object that can be used as a source or sink for characters--either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a `*Help*' buffer, or to the echo area.
The object nil, in addition to its other meanings, may be used
as a stream. It stands for the value of the variable
standard-input or standard-output. Also, the object
t as a stream specifies input using the minibuffer
(see section Minibuffers) or output in the echo area (see section The Echo Area).
Streams have no special printed representation or read syntax, and print as whatever primitive type they are.
See section Reading and Printing Lisp Objects, for a description of various functions related to streams, including various parsing and printing functions.
A keymap maps keys typed by the user to functions. This mapping
controls how the user's command input is executed. A keymap is actually
a list whose CAR is the symbol keymap.
See section Keymaps, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings.
A syntax table is a vector of 256 integers. Each element of the vector defines how one character is interpreted when it appears in a buffer. For example, in C mode (see section Major Modes), the `+' character is punctuation, but in Lisp mode it is a valid character in a symbol. These different interpretations are effected by changing the syntax table entry for `+', i.e., at index 43.
Syntax tables are only used for scanning text in buffers, not for reading Lisp expressions. The table the Lisp interpreter uses to read expressions is built into the Emacs source code and cannot be changed; thus, to change the list delimiters to be `{' and `}' instead of `(' and `)' would be impossible.
See section Syntax Tables, for details about syntax classes and how to make and modify syntax tables.
A display table specifies how to display each character code. Each buffer and each window can have its own display table. A display table is actually a vector of length 261. See section Display Tables.
An overlay specifies temporary alteration of the display appearance of a part of a buffer. It contains markers delimiting a range of the buffer, plus a property list (a list whose elements are alternating property names and values). Overlays are used to present parts of the buffer temporarily in a different display style.
See section Overlays, for how to create and use overlays.
The Emacs Lisp interpreter itself does not perform type checking on the actual arguments passed to functions when they are called. It could not do otherwise, since variables in Lisp are not declared to be of a certain type, as they are in other programming languages. It is therefore up to the individual function to test whether each actual argument belongs to a type that can be used by the function.
All built-in functions do check the types of their actual arguments
when appropriate and signal a wrong-type-argument error if an
argument is of the wrong type. For example, here is what happens if you
pass an argument to + which it cannot handle:
(+ 2 'a)
error--> Wrong type argument: integer-or-marker-p, a
Many functions, called type predicates, are provided to test whether an object is a member of a given type. (Following a convention of long standing, the names of most Emacs Lisp predicates end in `p'.)
Here is a table of predefined type predicates, in alphabetical order, with references to further information.
atom
arrayp
bufferp
byte-code-function-p
case-table-p
char-or-string-p
commandp
consp
floatp
frame-live-p
framep
integer-or-marker-p
integerp
keymapp
listp
markerp
natnump
nlistp
numberp
number-or-marker-p
overlayp
processp
sequencep
stringp
subrp
symbolp
syntax-table-p
user-variable-p
vectorp
window-configuration-p
window-live-p
windowp
Here we describe two functions that test for equality between any two objects. Other functions test equality between objects of specific types, e.g., strings. See the appropriate chapter describing the data type for these predicates.
Function: eq object1 object2
This function returns t if object1 and object2 are
the same object, nil otherwise. The "same object" means that a
change in one will be reflected by the same change in the other.
eq returns t if object1 and object2 are
integers with the same value. Also, since symbol names are normally
unique, if the arguments are symbols with the same name, they are
eq. For other types (e.g., lists, vectors, strings), two
arguments with the same contents or elements are not necessarily
eq to each other: they are eq only if they are the same
object.
(The make-symbol function returns an uninterned symbol that is
not interned in the standard obarray. When uninterned symbols
are in use, symbol names are no longer unique. Distinct symbols with
the same name are not eq. See section Creating and Interning Symbols.)
(eq 'foo 'foo)
=> t
(eq 456 456)
=> t
(eq "asdf" "asdf")
=> nil
(eq '(1 (2 (3))) '(1 (2 (3))))
=> nil
(eq [(1 2) 3] [(1 2) 3])
=> nil
(eq (point-marker) (point-marker))
=> nil
Function: equal object1 object2
This function returns t if object1 and object2 have
equal components, nil otherwise. Whereas eq tests if its
arguments are the same object, equal looks inside nonidentical
arguments to see if their elements are the same. So, if two objects are
eq, they are equal, but the converse is not always true.
(equal 'foo 'foo)
=> t
(equal 456 456)
=> t
(equal "asdf" "asdf")
=> t
(eq "asdf" "asdf")
=> nil
(equal '(1 (2 (3))) '(1 (2 (3))))
=> t
(eq '(1 (2 (3))) '(1 (2 (3))))
=> nil
(equal [(1 2) 3] [(1 2) 3])
=> t
(eq [(1 2) 3] [(1 2) 3])
=> nil
(equal (point-marker) (point-marker))
=> t
(eq (point-marker) (point-marker))
=> nil
Comparison of strings is case-sensitive.
(equal "asdf" "ASDF")
=> nil
The test for equality is implemented recursively, and circular lists may therefore cause infinite recursion (leading to an error).
GNU Emacs supports two numeric data types: integers and floating point numbers. Integers are whole numbers such as -3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as -4.5, 0.0, or 2.71828. They can also be expressed in an exponential notation as well: thus, 1.5e2 equals 150; in this example, `e2' stands for ten to the second power, and is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision.
Support for floating point numbers is a new feature in Emacs 19, and it is controlled by a separate compilation option, so you may encounter a site where Emacs does not support them.
The range of values for an integer depends on the machine. The range is -8388608 to 8388607 (24 bits; i.e., to ) on most machines, but on others it is -16777216 to 16777215 (25 bits), or -33554432 to 33554431 (26 bits). All of the examples shown below assume an integer has 24 bits.
The Lisp reader reads numbers as a sequence of digits with an optional sign.
1 ; The integer 1. +1 ; Also the integer 1. -1 ; The integer -1. 16777217 ; Also the integer 1, due to overflow. 0 ; The number 0. -0 ; The number 0. 1. ; The integer 1.
To understand how various functions work on integers, especially the bitwise operators (see section Bitwise Operations on Integers), it is often helpful to view the numbers in their binary form.
In 24 bit binary, the decimal integer 5 looks like this:
0000 0000 0000 0000 0000 0101
(We have inserted spaces between groups of 4 bits, and two spaces between groups of 8 bits, to make the binary integer easier to read.)
The integer -1 looks like this:
1111 1111 1111 1111 1111 1111
-1 is represented as 24 ones. (This is called two's complement notation.)
The negative integer, -5, is creating by subtracting 4 from -1. In binary, the decimal integer 4 is 100. Consequently, -5 looks like this:
1111 1111 1111 1111 1111 1011
In this implementation, the largest 24 bit binary integer is the decimal integer 8,388,607. In binary, this number looks like this:
0111 1111 1111 1111 1111 1111
Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 8,388,607, the value is negative integer -8,388,608:
(+ 1 8388607)
=> -8388608
=> 1000 0000 0000 0000 0000 0000
Many of the following functions accept markers for arguments as well as integers. (See section Markers.) More precisely, the actual parameters to such functions may be either integers or markers, which is why we often give these parameters the name int-or-marker. When the actual parameter is a marker, the position value of the marker is used and the buffer of the marker is ignored.
Emacs version 19 supports floating point numbers, if compiled with the
macro LISP_FLOAT_TYPE defined. The precise range of floating
point numbers is machine-specific; it is the same as the range of the C
data type double on the machine in question.
The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4' are five ways of writing a floating point number whose value is 1500. They are all equivalent. You can also use a minus sign to write negative floating point numbers, as in `-1.0'.
You can use logb to extract the binary exponent of a floating
point number (or estimate the logarithm of an integer):
Function: logb number
This function returns the binary exponent of number. More precisely, the value is the logarithm of number base 2, rounded down to an integer.
The functions in this section test whether the argument is a number or
whether it is a certain sort of number. The functions integerp
and floatp can take any type of Lisp object as argument (the
predicates would not be of much use otherwise); but the zerop
predicate requires a number as its argument. See also
integer-or-marker-p and number-or-marker-p, in
section Predicates on Markers.
Function: floatp object
This predicate tests whether its argument is a floating point
number and returns t if so, nil otherwise.
floatp does not exist in Emacs versions 18 and earlier.
Function: integerp object
This predicate tests whether its argument is an integer, and returns
t if so, nil otherwise.
Function: numberp object
This predicate tests whether its argument is a number (either integer or
floating point), and returns t if so, nil otherwise.
Function: natnump object
The natnump predicate (whose name comes from the phrase
"natural-number-p") tests to see whether its argument is a nonnegative
integer, and returns t if so, nil otherwise. 0 is
considered non-negative.
Markers are not converted to integers, hence natnump of a marker
is always nil.
People have pointed out that this function is misnamed, because the term "natural number" is usually understood as excluding zero. We are open to suggestions for a better name to use in a future version.
Function: zerop number
This predicate tests whether its argument is zero, and returns t
if so, nil otherwise. The argument must be a number.
These two forms are equivalent: (zerop x) == (= x 0).
Floating point numbers in Emacs Lisp actually take up storage, and
there can be many distinct floating point number objects with the same
numeric value. If you use eq to compare them, then you test
whether two values are the same object. If you want to compare
just the numeric values, use =.
If you use eq to compare two integers, it always returns
t if they have the same value. This is sometimes useful, because
eq accepts arguments of any type and never causes an error,
whereas = signals an error if the arguments are not numbers or
markers. However, it is a good idea to use = if you can, even
for comparing integers, just in case we change the representation of
integers in a future Emacs version.
There is another wrinkle: because floating point arithmetic is not exact, it is often a bad idea to check for equality of two floating point values. Usually it is better to test for approximate equality. Here's a function to do this:
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor))
Common Lisp note: because of the way numbers are implemented in
Common Lisp, you generally need to use `=' to test for
equality between numbers of any kind.
Function: = number-or-marker1 number-or-marker2
This function tests whether its arguments are the same number, and
returns t if so, nil otherwise.
Function: /= number-or-marker1 number-or-marker2
This function tests whether its arguments are not the same number, and
returns t if so, nil otherwise.
Function: < number-or-marker1 number-or-marker2
This function tests whether its first argument is strictly less than
its second argument. It returns t if so, nil otherwise.
Function: <= number-or-marker1 number-or-marker2
This function tests whether its first argument is less than or equal
to its second argument. It returns t if so, nil
otherwise.
Function: > number-or-marker1 number-or-marker2
This function tests whether its first argument is strictly greater
than its second argument. It returns t if so, nil
otherwise.
Function: >= number-or-marker1 number-or-marker2
This function tests whether its first argument is greater than or
equal to its second argument. It returns t if so, nil
otherwise.
Function: max number-or-marker &rest numbers-or-markers
This function returns the largest of its arguments.
(max 20)
=> 20
(max 1 2)
=> 2
(max 1 3 2)
=> 3
Function: min number-or-marker &rest numbers-or-markers
This function returns the smallest of its arguments.
To convert an integer to floating point, use the function float.
Function: float number
This returns number converted to floating point.
If number is already a floating point number, float returns
it unchanged.
There are four functions to convert floating point numbers to integers; they differ in how they round. You can call these functions with an integer argument also; if you do, they return it without change.
Function: truncate number
This returns number, converted to an integer by rounding towards zero.
Function: floor number &optional divisor
This returns number, converted to an integer by rounding downward (towards negative infinity).
If divisor is specified, number is divided by divisor
before the floor is taken; this is the division operation that
corresponds to mod. An arith-error results if
divisor is 0.
Function: ceiling number
This returns number, converted to an integer by rounding upward (towards positive infinity).
Function: round number
This returns number, converted to an integer by rounding towards the nearest integer.
Emacs Lisp provides the traditional four arithmetic operations: addition, subtraction, multiplication, and division. Remainder and modulus functions supplement the division functions. The functions to add or subtract 1 are provided because they are traditional in Lisp and commonly used.
All of these functions except % return a floating point value
if any argument is floating.
It is important to note that in GNU Emacs Lisp, arithmetic functions
do not check for overflow. Thus (1+ 8388607) may equal
-8388608, depending on your hardware.
Function: 1+ number-or-marker
This function returns number-or-marker plus 1. For example,
(setq foo 4)
=> 4
(1+ foo)
=> 5
This function is not analogous to the C operator ++---it does
not increment a variable. It just computes a sum. Thus,
foo
=> 4
If you want to increment the variable, you must use setq,
like this:
(setq foo (1+ foo))
=> 5
Function: 1- number-or-marker
This function returns number-or-marker minus 1.
Function: abs number
This returns the absolute value of number.
Function: + &rest numbers-or-markers
This function adds its arguments together. When given no arguments,
+ returns 0. It does not check for overflow.
(+)
=> 0
(+ 1)
=> 1
(+ 1 2 3 4)
=> 10
Function: - &optional number-or-marker &rest other-numbers-or-markers
The - function serves two purposes: negation and subtraction.
When - has a single argument, the value is the negative of the
argument. When there are multiple arguments, each of the
other-numbers-or-markers is subtracted from number-or-marker,
cumulatively. If there are no arguments, the result is 0. This
function does not check for overflow.
(- 10 1 2 3 4)
=> 0
(- 10)
=> -10
(-)
=> 0
Function: * &rest numbers-or-markers
This function multiplies its arguments together, and returns the
product. When given no arguments, * returns 1. It does
not check for overflow.
(*)
=> 1
(* 1)
=> 1
(* 1 2 3 4)
=> 24
Function: / dividend divisor &rest divisors
This function divides dividend by divisors and returns the quotient. If there are additional arguments divisors, then dividend is divided by each divisor in turn. Each argument may be a number or a marker.
If all the arguments are integers, then the result is an integer too.
This means the result has to be rounded. On most machines, the result
is rounded towards zero after each division, but some machines may round
differently with negative arguments. This is because the Lisp function
/ is implemented using the C division operator, which has the
same possibility for machine-dependent rounding. As a practical matter,
all known machines round in the standard fashion.
If you divide by 0, an arith-error error is signaled.
(See section Errors.)
(/ 6 2)
=> 3
(/ 5 2)
=> 2
(/ 25 3 2)
=> 4
(/ -17 6)
=> -2
Since the division operator in Emacs Lisp is implemented using the
division operator in C, the result of dividing negative numbers may in
principle vary from machine to machine, depending on how they round the
result. Thus, the result of (/ -17 6) could be -3 on some
machines. In practice, all known machines round the quotient towards
0.
Function: % dividend divisor
This function returns the integer remainder after division of dividend by divisor. The arguments must be integers or markers.
For negative arguments, the value is in principle machine-dependent since the quotient is; but in practice, all known machines behave alike.
An arith-error results if divisor is 0.
(% 9 4)
=> 1
(% -9 4)
=> -1
(% 9 -4)
=> 1
(% -9 -4)
=> -1
For any two integers dividend and divisor,
(+ (% dividend divisor) (* (/ dividend divisor) divisor))
always equals dividend.
Function: mod dividend divisor
This function returns the value of dividend modulo divisor; in other words, the remainder after division of dividend by divisor, but with the same sign as divisor. The arguments must be numbers or markers.
Unlike %, the result is well-defined for negative arguments.
Also, floating point arguments are permitted.
An arith-error results if divisor is 0.
(mod 9 4)
=> 1
(mod -9 4)
=> 3
(mod 9 -4)
=> -3
(mod -9 -4)
=> -1
For any two numbers dividend and divisor,
(+ (mod dividend divisor) (* (floor dividend divisor) divisor))
always equals dividend, subject to rounding error if either argument is floating point.
In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern "moved over".
The bitwise operations in Emacs Lisp apply only to integers.
Function: lsh integer1 count
lsh, which is an abbreviation for logical shift, shifts the
bits in integer1 to the left count places, or to the
right if count is negative. If count is negative,
lsh shifts zeros into the most-significant bit, producing a
positive result even if integer1 is negative. Contrast this with
ash, below.
Thus, the decimal number 5 is the binary number 00000101. Shifted once to the left, with a zero put in the one's place, the number becomes 00001010, decimal 10.
Here are two examples of shifting the pattern of bits one place to the
left. Since the contents of the rightmost place has been moved one
place to the left, a value has to be inserted into the rightmost place.
With lsh, a zero is placed into the rightmost place. (These
examples show only the low-order eight bits of the binary pattern; the
rest are all zero.)
(lsh 5 1)
=> 10
;; Decimal 5 becomes decimal 10.
00000101 => 00001010
(lsh 7 1)
=> 14
;; Decimal 7 becomes decimal 14.
00000111 => 00001110
As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.
Note, however that functions do not check for overflow, and a returned value may be negative (and in any case, no more than a 24 bit value) when an integer is sufficiently left shifted.
For example, left shifting 8,388,607 produces -2:
(lsh 8388607 1) ; left shift
=> -2
In binary, in the 24 bit implementation, the numbers looks like this:
;; Decimal 8,388,607 0111 1111 1111 1111 1111 1111
which becomes the following when left shifted:
;; Decimal -2 1111 1111 1111 1111 1111 1110
Shifting the pattern of bits two places to the left produces results like this (with 8-bit binary numbers):
(lsh 3 2)
=> 12
;; Decimal 3 becomes decimal 12.
00000011 => 00001100
On the other hand, shifting the pattern of bits one place to the right looks like this:
(lsh 6 -1)
=> 3
;; Decimal 6 becomes decimal 3.
00000110 => 00000011
(lsh 5 -1)
=> 2
;; Decimal 5 becomes decimal 2.
00000101 => 00000010
As the example illustrates, shifting the pattern of bits one place to the right divides the value of the binary number by two, rounding downward.
Function: ash integer1 count
ash (arithmetic shift) shifts the bits in integer1
to the left count places, or to the right if count
is negative.
ash gives the same results as lsh except when
integer1 and count are both negative. In that case,
ash puts a one in the leftmost position, while lsh puts
a zero in the leftmost position.
Thus, with ash, shifting the pattern of bits one place to the right
looks like this:
(ash -6 -1)
=> -3
;; Decimal -6
;; becomes decimal -3.
1111 1111 1111 1111 1111 1010
=>
1111 1111 1111 1111 1111 1101
In contrast, shifting the pattern of bits one place to the right with
lsh looks like this:
(lsh -6 -1)
=> 8388605
;; Decimal -6
;; becomes decimal 8,388,605.
1111 1111 1111 1111 1111 1010
=>
0111 1111 1111 1111 1111 1101
In this case, the 1 in the leftmost position is shifted one place to the right, and a zero is shifted into the leftmost position.
Here are other examples:
; 24-bit binary values
(lsh 5 2) ; 5 = 0000 0000 0000 0000 0000 0101
=> 20 ; 20 = 0000 0000 0000 0000 0001 0100
(ash 5 2)
=> 20
(lsh -5 2) ; -5 = 1111 1111 1111 1111 1111 1011
=> -20 ; -20 = 1111 1111 1111 1111 1110 1100
(ash -5 2)
=> -20
(lsh 5 -2) ; 5 = 0000 0000 0000 0000 0000 0101
=> 1 ; 1 = 0000 0000 0000 0000 0000 0001
(ash 5 -2)
=> 1
(lsh -5 -2) ; -5 = 1111 1111 1111 1111 1111 1011
=> 4194302 ; 0011 1111 1111 1111 1111 1110
(ash -5 -2) ; -5 = 1111 1111 1111 1111 1111 1011
=> -2 ; -2 = 1111 1111 1111 1111 1111 1110
Function: logand &rest ints-or-markers
This function returns the "logical and" of the arguments: the nth bit is set in the result if, and only if, the nth bit is set in all the arguments. ("Set" means that the value of the bit is 1 rather than 0.)
For example, using 4-bit binary numbers, the "logical and" of 13 and 12 is 12: 1101 combined with 1100 produces 1100.
In both the binary numbers, the leftmost two bits are set (i.e., they are 1's), so the leftmost two bits of the returned value are set. However, for the rightmost two bits, each is zero in at least one of the arguments, so the rightmost two bits of the returned value are 0's.
Therefore,
(logand 13 12)
=> 12
If logand is not passed any argument, it returns a value of
-1. This number is an identity element for logand
because its binary representation consists entirely of ones. If
logand is passed just one argument, it returns that argument.
; 24-bit binary values
(logand 14 13) ; 14 = 0000 0000 0000 0000 0000 1110
; 13 = 0000 0000 0000 0000 0000 1101
=> 12 ; 12 = 0000 0000 0000 0000 0000 1100
(logand 14 13 4) ; 14 = 0000 0000 0000 0000 0000 1110
; 13 = 0000 0000 0000 0000 0000 1101
; 4 = 0000 0000 0000 0000 0000 0100
=> 4 ; 4 = 0000 0000 0000 0000 0000 0100
(logand)
=> -1 ; -1 = 1111 1111 1111 1111 1111 1111
Function: logior &rest ints-or-markers
This function returns the "inclusive or" of its arguments: the nth bit
is set in the result if, and only if, the nth bit is set in at least
one of the arguments. If there are no arguments, the result is zero,
which is an identity element for this operation. If logior is
passed just one argument, it returns that argument.
; 24-bit binary values
(logior 12 5) ; 12 = 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0101
=> 13 ; 13 = 0000 0000 0000 0000 0000 1101
(logior 12 5 7) ; 12 = 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0101
; 7 = 0000 0000 0000 0000 0000 0111
=> 15 ; 15 = 0000 0000 0000 0000 0000 1111
Function: logxor &rest ints-or-markers
This function returns the "exclusive or" of its arguments: the
nth bit is set in the result if, and only if, the nth bit
is set in an odd number of the arguments. If there are no arguments,
the result is 0. If logxor is passed just one argument, it returns
that argument.
; 24-bit binary values
(logxor 12 5) ; 12 = 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0101
=> 9 ; 9 = 0000 0000 0000 0000 0000 1001
(logxor 12 5 7) ; 12 = 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0101
; 7 = 0000 0000 0000 0000 0000 0111
=> 14 ; 14 = 0000 0000 0000 0000 0000 1110
Function: lognot integer
This function returns the logical complement of its argument: the nth bit is one in the result if, and only if, the nth bit is zero in integer, and vice-versa.
;; 5 = 0000 0000 0000 0000 0000 0101
;; becomes
;; -6 = 1111 1111 1111 1111 1111 1010
(lognot 5)
=> -6
These mathematical functions are available if floating point is supported. They allow integers as well as floating point numbers as arguments.
Function: sin arg
Function: cos arg
Function: tan arg
These are the ordinary trigonometric functions, with argument measured in radians.
Function: asin arg
The value of (asin arg) is a number between - pi / 2
and pi / 2 (inclusive) whose sine is arg; if, however, arg
is out of range (outside [-1, 1]), then the result is a NaN.
Function: acos arg
The value of (acos arg) is a number between 0 and pi
(inclusive) whose cosine is arg; if, however, arg
is out of range (outside [-1, 1]), then the result is a NaN.
Function: atan arg
The value of (atan arg) is a number between - pi / 2
and pi / 2 (exclusive) whose tangent is arg.
Function: exp arg
This is the exponential function; it returns e to the power arg.
Function: log arg &optional base
This function returns the logarithm of arg, with base base. If you don't specify base, the base e is used. If arg is negative, the result is a NaN.
Function: log10 arg
This function returns the logarithm of arg, with base 10. If arg is negative, the result is a NaN.
Function: expt x y
This function returns x raised to power y.
Function: sqrt arg
This returns the square root of arg.
In a computer, a series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series.
In Emacs, pseudo-random numbers are generated from a "seed" number.
Starting from any given seed, the random function always
generates the same sequence of numbers. Emacs always starts with the
same seed value, so the sequence of values of random is actually
the same in each Emacs run! For example, in one operating system, the
first call to (random) after you start Emacs always returns
-1457731, and the second one always returns -7692030. This is helpful
for debugging.
If you want truly unpredictable random numbers, execute (random
t). This chooses a new seed based on the current time of day and on
Emacs' process ID number.
Function: random &optional limit
This function returns a pseudo-random integer. When called more than once, it returns a series of pseudo-random integers.
If limit is nil, then the value may in principle be any
integer. If limit is a positive integer, the value is chosen to
be nonnegative and less than limit (only in Emacs 19).
If limit is t, it means to choose a new seed based on the
current time of day and on Emacs's process ID number.
On some machines, any integer representable in Lisp may be the result
of random. On other machines, the result can never be larger
than a certain maximum or less than a certain (negative) minimum.
A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files, to send messages to users, to hold text being copied between buffers, and for many other purposes. Because strings are so important, many functions are provided expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters.
See section Putting Keyboard Events in Strings, for special considerations when using strings of keyboard character events.
Strings in Emacs Lisp are arrays that contain an ordered sequence of characters. Characters are represented in Emacs Lisp as integers; whether an integer was intended as a character or not is determined only by how it is used. Thus, strings really contain integers.
The length of a string (like any array) is fixed and independent of the string contents, and cannot be altered. Strings in Lisp are not terminated by a distinguished character code. (By contrast, strings in C are terminated by a character with ASCII code 0.) This means that any character, including the null character (ASCII code 0), is a valid element of a string.
Since strings are considered arrays, you can operate on them with the
general array functions. (See section Sequences, Arrays, and Vectors.) For
example, you can access or change individual characters in a string
using the functions aref and aset (see section Functions that Operate on Arrays).
Each character in a string is stored in a single byte. Therefore, numbers not in the range 0 to 255 are truncated when stored into a string. This means that a string takes up much less memory than a vector of the same length.
Sometimes key sequences are represented as strings. When a string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are extremely large integers) rather than keyboard events in the range 128 to 255.
Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no others. They do not distinguish case in ASCII control characters. See section Character Type, for more information about representation of meta and other modifiers for keyboard input characters.
Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See section Text Properties.
See section Text, for information about functions that display strings or copy them into buffers. See section Character Type, and section String Type, for information about the syntax of characters and strings.
For more information about general sequence and array predicates, see section Sequences, Arrays, and Vectors, and section Arrays.
Function: stringp object
This function returns t if object is a string, nil
otherwise.
Function: char-or-string-p object
This function returns t if object is a string or a
character (i.e., an integer), nil otherwise.
The following functions create strings, either from scratch, or by putting strings together, or by taking them apart.
Function: make-string count character
This function returns a string made up of count repetitions of character. If count is negative, an error is signaled.
(make-string 5 ?x)
=> "xxxxx"
(make-string 0 ?x)
=> ""
Other functions to compare with this one include char-to-string
(see section Conversion of Characters and Strings), make-vector (see section Vectors), and
make-list (see section Building Cons Cells and Lists).
Function: substring string start &optional end
This function returns a new string which consists of those characters from string in the range from (and including) the character at the index start up to (but excluding) the character at the index end. The first character is at index zero.
(substring "abcdefg" 0 3)
=> "abc"
Here the index for `a' is 0, the index for `b' is 1, and the index for `c' is 2. Thus, three letters, `abc', are copied from the full string. The index 3 marks the character position up to which the substring is copied. The character whose index is 3 is actually the fourth character in the string.
A negative number counts from the end of the string, so that -1 signifies the index of the last character of the string. For example:
(substring "abcdefg" -3 -1)
=> "ef"
In this example, the index for `e' is -3, the index for `f' is -2, and the index for `g' is -1. Therefore, `e' and `f' are included, and `g' is excluded.
When nil is used as an index, it falls after the last character
in the string. Thus:
(substring "abcdefg" -3 nil)
=> "efg"
Omitting the argument end is equivalent to specifying nil.
It follows that (substring string 0) returns a copy of all
of string.
(substring "abcdefg" 0)
=> "abcdefg"
But we recommend copy-sequence for this purpose (see section Sequences).
A wrong-type-argument error is signaled if either start
or end are non-integers. An args-out-of-range error is
signaled if start indicates a character following end, or if
either integer is out of range for string.
Contrast this function with buffer-substring (see section Examining Buffer Contents), which returns a string containing a portion of the text in
the current buffer. The beginning of a string is at index 0, but the
beginning of a buffer is at index 1.
Function: concat &rest sequences
This function returns a new string consisting of the characters in the
arguments passed to it. The arguments may be strings, lists of numbers,
or vectors of numbers; they are not themselves changed. If no arguments
are passed to concat, it returns an empty string.
(concat "abc" "-def")
=> "abc-def"
(concat "abc" (list 120 (+ 256 121)) [122])
=> "abcxyz"
(concat "The " "quick brown " "fox.")
=> "The quick brown fox."
(concat)
=> ""
The second example above shows how characters stored in strings are taken modulo 256. In other words, each character in the string is stored in one byte.
The concat function always constructs a new string that is
not eq to any existing string.
When an argument is an integer (not a sequence of integers), it is
converted to a string of digits making up the decimal printed
representation of the integer. This special case exists for
compatibility with Mocklisp, and we don't recommend you take advantage
of it. If you want to convert an integer in this way, use format
(see section Formatting Strings) or int-to-string (see section Conversion of Characters and Strings).
(concat 137)
=> "137"
(concat 54 321)
=> "54321"
For information about other concatenation functions, see the
description of mapconcat in section Mapping Functions,
vconcat in section Vectors, and append in section Building Cons Cells and Lists.
Function: char-equal character1 character2
This function returns t if the arguments represent the same
character, nil otherwise. This function ignores differences
in case if case-fold-search is non-nil.
(char-equal ?x ?x)
=> t
(char-to-string (+ 256 ?x))
=> "x"
(char-equal ?x (+ 256 ?x))
=> t
Function: string= string1 string2
This function returns t if the characters of the two strings
match exactly; case is significant.
(string= "abc" "abc")
=> t
(string= "abc" "ABC")
=> nil
(string= "ab" "ABC")
=> nil
Function: string-equal string1 string2
string-equal is another name for string=.
Function: string< string1 string2
This function compares two strings a character at a time. First it
scans both the strings at once to find the first pair of corresponding
characters that do not match. If the lesser character of those two is
the character from string1, then string1 is less, and this
function returns t. If the lesser character is the one from
string2, then string1 is greater, and this function returns
nil. If the two strings match entirely, the value is nil.
Pairs of characters are compared by their ASCII codes. Keep in mind that lower case letters have higher numeric values in the ASCII character set than their upper case counterparts; numbers and many punctuation characters have a lower numeric value than upper case letters.
(string< "abc" "abd")
=> t
(string< "abd" "abc")
=> nil
(string< "123" "abc")
=> t
When the strings have different lengths, and they match
up to the length of string1, then the result is t. If they
match up to the length of string2, the result is nil.
A string without any characters in it is the smallest possible string.
(string< "" "abc")
=> t
(string< "ab" "abc")
=> t
(string< "abc" "")
=> nil
(string< "abc" "ab")
=> nil
(string< "" "")
=> nil
Function: string-lessp string1 string2
string-lessp is another name for string<.
See compare-buffer-substrings in section Comparing Text, for a
way to compare text in buffers.
Characters and strings may be converted into each other and into
integers. format and prin1-to-string
(see section Output Functions) may also be used to convert Lisp objects into
strings. read-from-string (see section Input Functions) may be used
to "convert" a string representation of a Lisp object into an object.
See section Documentation, for a description of functions which return a
string representing the Emacs standard notation of the argument
character (single-key-description and
text-char-description). These functions are used primarily for
printing help messages.
Function: char-to-string character
This function returns a new string with a length of one character. The value of character, modulo 256, is used to initialize the element of the string.
This function is similar to make-string with an integer argument
of 1. (See section Creating Strings.) This conversion can also be done with
format using the `%c' format specification.
(See section Formatting Strings.)
(char-to-string ?x)
=> "x"
(char-to-string (+ 256 ?x))
=> "x"
(make-string 1 ?x)
=> "x"
Function: string-to-char string
This function returns the first character in string. If the string is empty, the function returns 0. The value is also 0 when the first character of string is the null character, ASCII code 0.
(string-to-char "ABC")
=> 65
(string-to-char "xyz")
=> 120
(string-to-char "")
=> 0
(string-to-char "\000")
=> 0
This function may be eliminated in the future if it does not seem useful enough to retain.
Function: number-to-string number
Function: int-to-string number
This function returns a string consisting of the printed representation of number, which may be an integer or a floating point number. The value starts with a sign if the argument is negative.
(int-to-string 256)
=> "256"
(int-to-string -23)
=> "-23"
(int-to-string -23.5)
=> "-23.5"
See also the function format in section Formatting Strings.
Function: string-to-number string
Function: string-to-int string
This function returns the integer value of the characters in string, read as a number in base ten. It skips spaces at the beginning of string, then reads as much of string as it can interpret as a number. (On some systems it ignores other whitespace at the beginning, not just spaces.) If the first character after the ignored whitespace is not a digit or a minus sign, this function returns 0.
(string-to-number "256")
=> 256
(string-to-number "25 is a perfect square.")
=> 25
(string-to-number "X256")
=> 0
(string-to-number "-4.5")
=> -4.5
Formatting means constructing a string by substitution of computed values at various places in a constant string. This string controls how the other values are printed as well as where they appear; it is called a format string.
Formatting is often useful for computing messages to be displayed. In
fact, the functions message and error provide the same
formatting feature described here; they differ from format only
in how they use the result of formatting.
Function: format string &rest objects
This function returns a new string that is made by copying string and then replacing any format specification in the copy with encodings of the corresponding objects. The arguments objects are the computed values to be formatted.
A format specification is a sequence of characters beginning with a
`%'. Thus, if there is a `%d' in string, the
format function replaces it with the printed representation of
one of the values to be formatted (one of the arguments objects).
For example:
(format "The value of fill-column is %d." fill-column)
=> "The value of fill-column is 72."
If string contains more than one format specification, the format specifications are matched with successive values from objects. Thus, the first format specification in string is matched with the first such value, the second format specification is matched with the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause unpredictable behavior. Any extra values to be formatted will be ignored.
Certain format specifications require values of particular types. However, no error is signaled if the value actually supplied fails to have the expected type. Instead, the output is likely to be meaningless.
Here is a table of the characters that can follow `%' to make up a format specification:
If there is no corresponding object, the empty string is used.
If there is no corresponding object, the empty string is used.
(format "%%
%d" 30) returns "% 30".
Any other format character results in an `Invalid format operation' error.
Here are several examples:
(format "The name of this buffer is %s." (buffer-name))
=> "The name of this buffer is strings.texi."
(format "The buffer object prints as %s." (current-buffer))
=> "The buffer object prints as #<buffer strings.texi>."
(format "The octal value of 18 is %o,
and the hex value is %x." 18 18)
=> "The octal value of 18 is 22,
and the hex value is 12."
All the specification characters allow an optional numeric prefix between the `%' and the character. The optional numeric prefix defines the minimum width for the object. If the printed representation of the object contains fewer characters than this, then it is padded. The padding is on the left if the prefix is positive (or starts with zero) and on the right if the prefix is negative. The padding character is normally a space, but if the numeric prefix starts with a zero, zeros are used for padding.
(format "%06d will be padded on the left with zeros" 123)
=> "000123 will be padded on the left with zeros"
(format "%-6d will be padded on the right" 123)
=> "123 will be padded on the right"
format never truncates an object's printed representation, no
matter what width you specify. Thus, you can use a numeric prefix to
specify a minimum spacing between columns with no risk of losing
information.
In the following three examples, `%7s' specifies a minimum width
of 7. In the first case, the string inserted in place of `%7s' has
only 3 letters, so 4 blank spaces are inserted for padding. In the
second case, the string "specification" is 13 letters wide but is
not truncated. In the third case, the padding is on the right.
(format "The word `%7s' actually has %d letters in it." "foo"
(length "foo"))
=> "The word ` foo' actually has 3 letters in it."
(format "The word `%7s' actually has %d letters in it."
"specification"
(length "specification"))
=> "The word `specification' actually has 13 letters in it."
(format "The word `%-7s' actually has %d letters in it." "foo"
(length "foo"))
=> "The word `foo ' actually has 3 letters in it."
The character case functions change the case of single characters or of the contents of strings. The functions convert only alphabetic characters (the letters `A' through `Z' and `a' through `z'); other characters are not altered. The functions do not modify the strings that are passed to them as arguments.
The examples below use the characters `X' and `x' which have ASCII codes 88 and 120 respectively.
Function: downcase string-or-char
This function converts a character or a string to lower case.
When the argument to downcase is a string, the function creates
and returns a new string in which each letter in the argument that is
upper case is converted to lower case. When the argument to
downcase is a character, downcase returns the
corresponding lower case character. This value is an integer. If the
original character is lower case, or is not a letter, then the value
equals the original character.
(downcase "The cat in the hat")
=> "the cat in the hat"
(downcase ?X)
=> 120
Function: upcase string-or-char
This function converts a character or a string to upper case.
When the argument to upcase is a string, the function creates
and returns a new string in which each letter in the argument that is
lower case is converted to upper case.
When the argument to upcase is a character, upcase
returns the corresponding upper case character. This value is an integer.
If the original character is upper case, or is not a letter, then the
value equals the original character.
(upcase "The cat in the hat")
=> "THE CAT IN THE HAT"
(upcase ?x)
=> 88
Function: capitalize string-or-char
This function capitalizes strings or characters. If string-or-char is a string, the function creates and returns a new string, whose contents are a copy of string-or-char in which each word has been capitalized. This means that the first character of each word is converted to upper case, and the rest are converted to lower case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent category in the current syntax table (See section Table of Syntax Classes).
When the argument to capitalize is a character, capitalize
has the same result as upcase.
(capitalize "The cat in the hat")
=> "The Cat In The Hat"
(capitalize "THE 77TH-HATTED CAT")
=> "The 77th-Hatted Cat"
(capitalize ?x)
=> 88
You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the string and character case conversion functions (see the previous section) and those that apply to text in the buffer (see section Case Changes). Use case table if you are using a language which has letters that are not the standard ASCII letters.
A case table is a list of this form:
(downcase upcase canonicalize equivalences)
where each element is either nil or a string of length 256. The
element downcase says how to map each character to its lower-case
equivalent. The element upcase maps each character to its
upper-case equivalent. If lower and upper case characters are in
one-to-one correspondence, use nil for upcase; then Emacs
deduces the upcase table from downcase.
For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both directions.
The element canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character.
The element equivalences is a map that cyclicly permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ASCII, this would map `a' into `A' and `A' into `a', and likewise for each set of equivalent characters.)
You can provide nil for both canonicalize and
equivalences, in which case both are deduced from downcase
and upcase. Normally, that's what you should do, when you
construct a case table. Alternatively, you can provide suitable strings
for both canonicalize and equivalences. When you look at
the case table that's in use, you will find non-nil values for
those components. Do not try to make just one of these components
nil; that is not meaningful.
Each buffer has a case table. Emacs also has a standard case table which is copied into each buffer when you create the buffer. (Changing the standard case table doesn't affect any existing buffers.)
Here are the functions for working with case tables:
Function: case-table-p object
This predicate returns non-nil if object is a valid case
table.
Function: set-standard-case-table table
This function makes table the standard case table, so that it will apply to any buffers created subsequently.
Function: standard-case-table
This returns the standard case table.
Function: current-case-table
This function returns the current buffer's case table.
Function: set-case-table table
This sets the current buffer's case table to table.
The following three functions are convenient subroutines for packages that define non-ASCII character sets. They modify a string downcase-table provided as an argument; this should be a string to be used as the downcase part of a case table. They also modify two syntax tables, the standard syntax table and the Text mode syntax table. (See section Syntax Tables.)
Function: set-case-syntax-pair uc lc downcase-table
This function specifies a pair of corresponding letters, one upper case and one lower case.
Function: set-case-syntax-delims l r downcase-table
This function makes characters l and r a matching pair of case-invariant delimiters.
Function: set-case-syntax char syntax downcase-table
This function makes char case-invariant, with syntax syntax.
Command: describe-buffer-case-table
This command displays a description of the contents of the current buffer's case table.
You can load the library `iso-syntax' to set up the syntax and case table for the 256 bit ISO Latin 1 character set.
A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list.
Lists in Lisp are not a primitive data type; they are built up from cons cells. A cons cell is a data object which represents an ordered pair. It records two Lisp objects, one labeled as the CAR, and the other labeled as the CDR. (These names are traditional.)
A list is made by chaining cons cells together, one cons cell per
element. By convention, the CARs of the cons cells are the
elements of the list, and the CDRs are used to chain the list: the
CDR of each cons cell is the following cons cell. The CDR of
the last cons cell is nil. This asymmetry between the CAR
and the CDR is entirely a matter of convention; at the level of
cons cells, the CAR and CDR slots have the same
characteristics.
The symbol nil is considered a list as well as a symbol; it is
the list with no elements. For convenience, the symbol nil is
considered to have nil as its CDR (and also as its
CAR).
The CDR of any nonempty list l is a list containing all the elements of l except the first.
A cons cell can be illustrated as a pair of boxes. The first box
represents the CAR and the second box represents the CDR.
Here is an illustration of the two-element list, (tulip lily),
made from two cons cells:
--------------- --------------- | car | cdr | | car | cdr | | tulip | o---------->| lily | nil | | | | | | | --------------- ---------------
Each pair of boxes represents a cons cell. Each box "refers to",
"points to" or "contains" a Lisp object. (These terms are
synonymous.) The first box, which is the CAR of the first cons
cell, contains the symbol tulip. The arrow from the CDR of
the first cons cell to the second cons cell indicates that the CDR
of the first cons cell points to the second cons cell.
The same list can be illustrated in a different sort of box notation like this:
___ ___ ___ ___
|___|___|--> |___|___|--> nil
| |
| |
--> tulip --> lily
Here is a more complex illustration, this time of the three-element
list, ((pine needles) oak maple), the first element of which is
a two-element list:
___ ___ ___ ___ ___ ___
|___|___|--> |___|___|--> |___|___|--> nil
| | |
| | |
| --> oak --> maple
|
| ___ ___ ___ ___
--> |___|___|--> |___|___|--> nil
| |
| |
--> pine --> needles
The same list is represented in the first box notation like this:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| o | o------->| oak | o------->| maple | nil |
| | | | | | | | | |
-- | --------- -------------- --------------
|
|
| -------------- ----------------
| | car | cdr | | car | cdr |
------>| pine | o------->| needles | nil |
| | | | | |
-------------- ----------------
See section List Type, for the read and print syntax of lists, and for more "box and arrow" illustrations of lists.
The following predicates test whether a Lisp object is an atom, is a cons
cell or is a list, or whether it is the distinguished object nil.
(Many of these tests can be defined in terms of the others, but they are
used so often that it is worth having all of them.)
Function: consp object
This function returns t if object is a cons cell, nil
otherwise. nil is not a cons cell, although it is a list.
Function: atom object
This function returns t if object is an atom, nil
otherwise. All objects except cons cells are atoms. The symbol
nil is an atom and is also a list; it is the only Lisp object
which is both.
(atom object) == (not (consp object))
Function: listp object
This function returns t if object is a cons cell or
nil. Otherwise, it returns nil.
(listp '(1))
=> t
(listp '())
=> t
Function: nlistp object
This function is the opposite of listp: it returns t if
object is not a list. Otherwise, it returns nil.
(listp object) == (not (nlistp object))
Function: null object
This function returns t if object is nil, and
returns nil otherwise. This function is identical to not,
but as a matter of clarity we use null when object is
considered a list and not when it is considered a truth value
(see not in section Constructs for Combining Conditions).
(null '(1))
=> nil
(null '())
=> t
Function: car cons-cell
This function returns the value pointed to by the first pointer of the cons cell cons-cell. Expressed another way, this function returns the CAR of cons-cell.
As a special case, if cons-cell is nil, then car
is defined to return nil; therefore, any list is a valid argument
for car. An error is signaled if the argument is not a cons cell
or nil.
(car '(a b c))
=> a
(car '())
=> nil
Function: cdr cons-cell
This function returns the value pointed to by the second pointer of the cons cell cons-cell. Expressed another way, this function returns the CDR of cons-cell.
As a special case, if cons-cell is nil, then cdr
is defined to return nil; therefore, any list is a valid argument
for cdr. An error is signaled if the argument is not a cons cell
or nil.
(cdr '(a b c))
=> (b c)
(cdr '())
=> nil
Function: car-safe object
This function lets you take the CAR of a cons cell while avoiding
errors for other data types. It returns the CAR of object if
object is a cons cell, nil otherwise. This is in contrast
to car, which signals an error if object is not a list.
(car-safe object)
==
(let ((x object))
(if (consp x)
(car x)
nil))
Function: cdr-safe object
This function lets you take the CDR of a cons cell while
avoiding errors for other data types. It returns the CDR of
object if object is a cons cell, nil otherwise.
This is in contrast to cdr, which signals an error if
object is not a list.
(cdr-safe object)
==
(let ((x object))
(if (consp x)
(cdr x)
nil))
Function: nth n list
This function returns the nth element of list. Elements
are numbered starting with zero, so the CAR of list is
element number zero. If the length of list is n or less,
the value is nil.
If n is less than zero, then the first element is returned.
(nth 2 '(1 2 3 4))
=> 3
(nth 10 '(1 2 3 4))
=> nil
(nth -3 '(1 2 3 4))
=> 1
(nth n x) == (car (nthcdr n x))
Function: nthcdr n list
This function returns the nth cdr of list. In other words, it removes the first n links of list and returns what follows.
If n is less than or equal to zero, then all of list is
returned. If the length of list is n or less, the value is
nil.
(nthcdr 1 '(1 2 3 4))
=> (2 3 4)
(nthcdr 10 '(1 2 3 4))
=> nil
(nthcdr -3 '(1 2 3 4))
=> (1 2 3 4)
Many functions build lists, as lists reside at the very heart of Lisp.
cons is the fundamental list-building function; however, it is
interesting to note that list is used more times in the source
code for Emacs than cons.
Function: cons object1 object2
This function is the fundamental function used to build new list structure. It creates a new cons cell, making object1 the CAR, and object2 the CDR. It then returns the new cons cell. The arguments object1 and object2 may be any Lisp objects, but most often object2 is a list.
(cons 1 '(2))
=> (1 2)
(cons 1 '())
=> (1)
(cons 1 2)
=> (1 . 2)
cons is often used to add a single element to the front of a
list. This is called consing the element onto the list. For
example:
(setq list (cons newelt list))
Note that there is no conflict between the variable named list
used in this example and the function named list described below;
any symbol can serve both functions.
Function: list &rest objects
This function creates a list with objects as its elements. The
resulting list is always nil-terminated. If no objects
are given, the empty list is returned.
(list 1 2 3 4 5)
=> (1 2 3 4 5)
(list 1 2 '(3 4 5) 'foo)
=> (1 2 (3 4 5) foo)
(list)
=> nil
Function: make-list length object
This function creates a list of length length, in which all the
elements have the identical value object. Compare
make-list with make-string (see section Creating Strings).
(make-list 3 'pigs)
=> (pigs pigs pigs)
(make-list 0 'pigs)
=> nil
Function: append &rest sequences
This function returns a list containing all the elements of sequences. The sequences may be lists, vectors, strings, or integers. All arguments except the last one are copied, so none of them are altered.
The final argument to append may be any object but it is
typically a list. The final argument is not copied or converted; it
becomes part of the structure of the new list.
Here is an example:
(setq trees '(pine oak))
=> (pine oak)
(setq more-trees (append '(maple birch) trees))
=> (maple birch pine oak)
trees
=> (pine oak)
more-trees
=> (maple birch pine oak)
(eq trees (cdr (cdr more-trees)))
=> t
You can see what happens by looking at a box diagram. The variable
trees is set to the list (pine oak) and then the variable
more-trees is set to the list (maple birch pine oak).
However, the variable trees continues to refer to the original
list:
more-trees trees
| |
| ___ ___ ___ ___ -> ___ ___ ___ ___
--> |___|___|--> |___|___|--> |___|___|--> |___|___|--> nil
| | | |
| | | |
--> maple -->birch --> pine --> oak
An empty sequence contributes nothing to the value returned by
append. As a consequence of this, a final nil argument
forces a copy of the previous argument.
trees
=> (pine oak)
(setq wood (append trees ()))
=> (pine oak)
wood
=> (pine oak)
(eq wood trees)
=> nil
This once was the standard way to copy a list, before the function
copy-sequence was invented. See section Sequences, Arrays, and Vectors.
With the help of apply, we can append all the lists in a list of
lists:
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
If no sequences are given, nil is returned:
(append)
=> nil
In the special case where one of the sequences is an integer
(not a sequence of integers), it is first converted to a string of
digits making up the decimal print representation of the integer. This
special case exists for compatibility with Mocklisp, and we don't
recommend you take advantage of it. If you want to convert an integer
in this way, use format (see section Formatting Strings) or
number-to-string (see section Conversion of Characters and Strings).
(setq trees '(pine oak))
=> (pine oak)
(char-to-string 54)
=> "6"
(setq longer-list (append trees 6 '(spruce)))
=> (pine oak 54 spruce)
(setq x-list (append trees 6 6))
=> (pine oak 54 . 6)
See nconc in section Functions that Rearrange Lists, for another way to join lists
without copying.
Function: reverse list
This function creates a new list whose elements are the elements of list, but in reverse order. The original argument list is not altered.
(setq x '(1 2 3 4))
=> (1 2 3 4)
(reverse x)
=> (4 3 2 1)
x
=> (1 2 3 4)
You can modify the CAR and CDR contents of a cons cell with the
primitives setcar and setcdr.
Common Lisp note: Common Lisp uses functionsrplacaandrplacdto alter list structure; they change structure the same way assetcarandsetcdr, but the Common Lisp functions return the cons cell whilesetcarandsetcdrreturn the new CAR or CDR.
setcar
Changing the CAR of a cons cell is done with setcar and
replaces one element of a list with a different element.
Function: setcar cons object
This function stores object as the new CAR of cons, replacing its previous CAR. It returns the value object. For example:
(setq x '(1 2))
=> (1 2)
(setcar x '4)
=> 4
x
=> (4 2)
When a cons cell is part of the shared structure of several lists, storing a new CAR into the cons changes one element of each of these lists. Here is an example:
;; Create two lists that are partly shared.
(setq x1 '(a b c))
=> (a b c)
(setq x2 (cons 'z (cdr x1)))
=> (z b c)
;; Replace the CAR of a shared link.
(setcar (cdr x1) 'foo)
=> foo
x1 ; Both lists are changed.
=> (a foo c)
x2
=> (z foo c)
;; Replace the CAR of a link that is not shared.
(setcar x1 'baz)
=> baz
x1 ; Only one list is changed.
=> (baz foo c)
x2
=> (z foo c)
Here is a graphical depiction of the shared structure of the two lists
x1 and x2, showing why replacing b changes them both:
___ ___ ___ ___ ___ ___
x1---> |___|___|----> |___|___|--> |___|___|--> nil
| --> | |
| | | |
--> a | --> b --> c
|
___ ___ |
x2--> |___|___|--
|
|
--> z
Here is an alternative form of box diagram, showing the same relationship:
x1:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| a | o------->| b | o------->| c | nil |
| | | -->| | | | | |
-------------- | -------------- --------------
|
x2: |
-------------- |
| car | cdr | |
| z | o----
| | |
--------------
The lowest-level primitive for modifying a CDR is setcdr:
Function: setcdr cons object
This function stores object into the cdr of cons. The value returned is object, not cons.
Here is an example of replacing the CDR of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the CAR of the list, and is not reached via the CDR.
(setq x '(1 2 3))
=> (1 2 3)
(setcdr x '(4))
=> (4)
x
=> (1 4)
You can delete elements from the middle of a list by altering the
CDRs of the cons cells in the list. For example, here we delete
the second element, b, from the list (a b c), by changing
the CDR of the first cell:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cdr (cdr x1)))
=> (c)
x1
=> (a c)
Here is the result in box notation:
--------------------
| |
-------------- | -------------- | --------------
| car | cdr | | | car | cdr | -->| car | cdr |
| a | o----- | b | o-------->| c | nil |
| | | | | | | | |
-------------- -------------- --------------
The second cons cell, which previously held the element b, still
exists and its CAR is still b, but it no longer forms part
of this list.
It is equally easy to insert a new element by changing CDRs:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cons 'd (cdr x1)))
=> (d b c)
x1
=> (a d b c)
Here is this result in box notation:
-------------- ------------- -------------
| car | cdr | | car | cdr | | car | cdr |
| a | o | -->| b | o------->| c | nil |
| | | | | | | | | | |
--------- | -- | ------------- -------------
| |
----- --------
| |
| --------------- |
| | car | cdr | |
-->| d | o------
| | |
---------------
Here are some functions that rearrange lists "destructively" by modifying the CDRs of their component cons cells. We call these functions "destructive" because the original lists passed as arguments to them are chewed up to produce a new list that is subsequently returned.
Function: nconc &rest lists
This function returns a list containing all the elements of lists.
Unlike append (see section Building Cons Cells and Lists), the lists are
not copied. Instead, the last CDR of each of the
lists is changed to refer to the following list. The last of the
lists is not altered. For example:
(setq x '(1 2 3))
=> (1 2 3)
(nconc x '(4 5))
=> (1 2 3 4 5)
x
=> (1 2 3 4 5)
Since the last argument of nconc is not itself modified, it is
reasonable to use a constant list, such as '(4 5), as is done in
the above example. For the same reason, the last argument need not be a
list:
(setq x '(1 2 3))
=> (1 2 3)
(nconc x 'z)
=> (1 2 3 . z)
x
=> (1 2 3 . z)
A common pitfall is to use a quoted constant list as a non-last
argument to nconc. If you do this, your program will change
each time you run it! Here is what happens:
(defun add-foo (x) ; This function should add
(nconc '(foo) x)) ; foo to the front of its arg.
(symbol-function 'add-foo)
=> (lambda (x) (nconc (quote (foo)) x))
(setq xx (add-foo '(1 2))) ; It seems to work.
=> (foo 1 2)
(setq xy (add-foo '(3 4))) ; What happened?
=> (foo 1 2 3 4)
(eq xx xy)
=> t
(symbol-function 'add-foo)
=> (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
Function: nreverse list
This function reverses the order of the elements of list.
Unlike reverse, nreverse alters its argument destructively
by reversing the CDRs in the cons cells forming the list. The cons
cell which used to be the last one in list becomes the first cell
of the value.
For example:
(setq x '(1 2 3 4))
=> (1 2 3 4)
x
=> (1 2 3 4)
(nreverse x)
=> (4 3 2 1)
;; The cell that was first is now last.
x
=> (1)
To avoid confusion, we usually store the result of nreverse
back in the same variable which held the original list:
(setq x (nreverse x))
Here is the nreverse of our favorite example, (a b c),
presented graphically:
Original list head: Reversed list:
------------- ------------- ------------
| car | cdr | | car | cdr | | car | cdr |
| a | nil |<-- | b | o |<-- | c | o |
| | | | | | | | | | | | |
------------- | --------- | - | -------- | -
| | | |
------------- ------------
Function: sort list predicate
This function sorts list stably, though destructively, and returns the sorted list. It compares elements using predicate. A stable sort is one in which elements with equal sort keys maintain their relative order before and after the sort. Stability is important when successive sorts are used to order elements according to different criteria.
The argument predicate must be a function that accepts two
arguments. It is called with two elements of list. To get an
increasing order sort, the predicate should return t if the
first element is "less than" the second, or nil if not.
The destructive aspect of sort is that it rearranges the cons
cells forming list by changing CDRs. A nondestructive sort
function would create new cons cells to store the elements in their
sorted order. If you wish to sort a list without destroying the
original, copy it first with copy-sequence.
The CARs of the cons cells are not changed; the cons cell that
originally contained the element a in list still has
a in its CAR after sorting, but it now appears in a
different position in the list due to the change of CDRs. For
example:
(setq nums '(1 3 2 6 5 4 0))
=> (1 3 2 6 5 4 0)
(sort nums '<)
=> (0 1 2 3 4 5 6)
nums
=> (1 2 3 4 5 6)
Note that the list in nums no longer contains 0; this is the same
cons cell that it was before, but it is no longer the first one in the
list. Don't assume a variable that formerly held the argument now holds
the entire sorted list! Instead, save the result of sort and use
that. Most often we store the result back into the variable that held
the original list:
(setq nums (sort nums '<))
See section Sorting Text, for more functions that perform sorting.
See documentation in section Access to Documentation Strings, for a
useful example of sort.
The function delq in the following section is another example
of destructive list manipulation.
A list can represent an unordered mathematical set--simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list. To form the union of two sets, use append (as
long as you don't mind having duplicate elements). Other useful
functions for sets include memq and delq, and their
equal versions, member and delete.
Common Lisp note: Common Lisp has functionsunion(which avoids duplicate elements) andintersectionfor set operations, but GNU Emacs Lisp does not have them. You can write them in Lisp if you wish.
Function: memq object list
This function tests to see whether object is a member of
list. If it is, memq returns a list starting with the
first occurrence of object. Otherwise, it returns nil.
The letter `q' in memq says that it uses eq to
compare object against the elements of the list. For example:
(memq 2 '(1 2 3 2 1))
=> (2 3 2 1)
(memq '(2) '((1) (2))) ; (2) and (2) are not eq.
=> nil
Function: delq object list
This function removes all elements eq to object from
list. The letter `q' in delq says that it uses
eq to compare object against the elements of the list, like
memq.
When delq deletes elements from the front of the list, it does so
simply by advancing down the list and returning a sublist that starts
after those elements:
(delq 'a '(a b c)) == (cdr '(a b c))
When an element to be deleted appears in the middle of the list, removing it involves changing the CDRs (see section Altering the CDR of a List).
(setq sample-list '(1 2 3 (4)))
=> (1 2 3 (4))
(delq 1 sample-list)
=> (2 3 (4))
sample-list
=> (1 2 3 (4))
(delq 2 sample-list)
=> (1 3 (4))
sample-list
=> (1 3 (4))
Note that (delq 2 sample-list) modifies sample-list to
splice out the second element, but (delq 1 sample-list) does not
splice anything--it just returns a shorter list. Don't assume that a
variable which formerly held the argument list now has fewer
elements, or that it still holds the original list! Instead, save the
result of delq and use that. Most often we store the result back
into the variable that held the original list:
(setq flowers (delq 'rose flowers))
In the following example, the (4) that delq attempts to match
and the (4) in the sample-list are not eq:
(delq '(4) sample-list)
=> (1 3 (4))
The following two functions are like memq and delq but use
equal rather than eq to compare elements. They are new in
Emacs 19.
Function: member object list
The function member tests to see whether object is a member
of list, comparing members with object using equal.
If object is a member, member returns a list starting with
its first occurrence in list. Otherwise, it returns nil.
Compare this with memq:
(member '(2) '((1) (2))) ;(2)and(2)areequal. => ((2)) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. => nil ;; Two strings with the same contents areequal. (member "foo" '("foo" "bar")) => ("foo" "bar")
Function: delete object list
This function removes all elements equal to object from
list. It is to delq as member is to memq: it
uses equal to compare elements with object, like
member; when it finds an element that matches, it removes the
element just as delq would. For example:
(delete '(2) '((2) (1) (2)))
=> '((1))
Common Lisp note: The functionsmemberanddeletein GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not useequalto compare elements.
An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the CAR of each cell is the key, and the CDR is the associated value. (This usage of "key" is not related to the term "key sequence"; it means any object which can be looked up in a table.)
Here is an example of an alist. The key pine is associated with
the value cones; the key oak is associated with
acorns; and the key maple is associated with seeds.
'((pine . cones) (oak . acorns) (maple . seeds))
The associated values in an alist may be any Lisp objects; so may the
keys. For example, in the following alist, the symbol a is
associated with the number 1, and the string "b" is
associated with the list (2 3), which is the CDR of
the alist element:
((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated value in the CAR of the CDR of the element. Here is an example:
'((rose red) (lily white) (buttercup yellow)))
Here we regard red as the value associated with rose. One
advantage of this method is that you can store other related
information--even a list of other items--in the CDR of the
CDR. One disadvantage is that you cannot use rassq (see
below) to find the element containing a given value. When neither of
these considerations is important, the choice is a matter of taste, as
long as you are consistent about it for any given alist.
Note that the same alist shown above could be regarded as having the
associated value in the CDR of the element; the value associated
with rose would be the list (red).
Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one.
In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases.
Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See section Property Lists, for a comparison of property lists and association lists.
Function: assoc key alist
This function returns the first association for key in
alist. It compares key against the alist elements using
equal (see section Equality Predicates). It returns nil if no
association in alist has a CAR equal to key.
For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
=> ((pine . cones) (oak . acorns) (maple . seeds))
(assoc 'oak trees)
=> (oak . acorns)
(cdr (assoc 'oak trees))
=> acorns
(assoc 'birch trees)
=> nil
Here is another example in which the keys and values are not symbols:
(setq needles-per-cluster
'((2 . ("Austrian Pine" "Red Pine"))
(3 . "Pitch Pine")
(5 . "White Pine")))
(cdr (assoc 3 needles-per-cluster))
=> "Pitch Pine"
(cdr (assoc 2 needles-per-cluster))
=> ("Austrian Pine" "Red Pine")
Function: assq key alist
This function is like assoc in that it returns the first
association for key in alist, but it makes the comparison
using eq instead of equal. assq returns nil
if no association in alist has a CAR eq to key.
This function is used more often than assoc, since eq is
faster than equal and most alists use symbols as keys.
See section Equality Predicates.
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
(assq 'pine trees)
=> (pine . cones)
On the other hand, assq is not usually useful in alists where the
keys may not be symbols:
(setq leaves
'(("simple leaves" . oak)
("compound leaves" . horsechestnut)))
(assq "simple leaves" leaves)
=> nil
(assoc "simple leaves" leaves)
=> ("simple leaves" . oak)
Function: rassq value alist
This function returns the first association with value value in
alist. It returns nil if no association in alist has
a CDR eq to value.
rassq is like assq except that the CDR of the
alist associations is tested instead of the CAR. You can
think of this as "reverse assq", finding the key for a given
value.
For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
(rassq 'acorns trees)
=> (oak . acorns)
(rassq 'spores trees)
=> nil
Note that rassq cannot be used to search for a value stored in
the CAR of the CDR of an element:
(setq colors '((rose red) (lily white) (buttercup yellow)))
(rassq 'white colors)
=> nil
In this case, the CDR of the association (lily white) is not
the symbol white, but rather the list (white). This can
be seen more clearly if the association is written in dotted pair
notation:
(lily white) == (lily . (white))
Function: copy-alist alist
This function returns a two-level deep copy of alist: it creates a new copy of each association, so that you can alter the associations of the new alist without changing the old one.
(setq needles-per-cluster
'((2 . ("Austrian Pine" "Red Pine"))
(3 . "Pitch Pine")
(5 . "White Pine")))
=>
((2 "Austrian Pine" "Red Pine")
(3 . "Pitch Pine")
(5 . "White Pine"))
(setq copy (copy-alist needles-per-cluster))
=>
((2 "Austrian Pine" "Red Pine")
(3 . "Pitch Pine")
(5 . "White Pine"))
(eq needles-per-cluster copy)
=> nil
(equal needles-per-cluster copy)
=> t
(eq (car needles-per-cluster) (car copy))
=> nil
(cdr (car (cdr needles-per-cluster)))
=> "Pitch Pine"
(eq (cdr (car (cdr needles-per-cluster)))
(cdr (car (cdr copy))))
=> t
Recall that the sequence type is the union of three other Lisp types: lists, vectors, and strings. In other words, any list is a sequence, any vector is a sequence, and any string is a sequence. The common property that all sequences have is that each is an ordered collection of elements.
An array is a single primitive object directly containing all its elements. Therefore, all the elements are accessible in constant time. The length of an existing array cannot be changed. Both strings and vectors are arrays. A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Therefore, elements farther from the beginning of the list take longer to access, but it is possible to add elements to the list or remove elements. The elements of vectors and lists may be any Lisp objects. The elements of strings are all characters.
The following diagram shows the relationship between these types:
___________________________________
| |
| Sequence |
| ______ ______________________ |
| | | | | |
| | List | | Array | |
| | | | ________ _______ | |
| |______| | | | | | | |
| | | String | | Vector| | |
| | |________| |_______| | |
| |______________________| |
|___________________________________|
The Relationship between Sequences, Arrays, and Vectors
In Emacs Lisp, a sequence is either a list, a vector or a string. The common property that all sequences have is that each is an ordered collection of elements. This section describes functions that accept any kind of sequence.
Function: sequencep object
Returns t if object is a list, vector, or
string, nil otherwise.
Function: copy-sequence sequence
Returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order.
Storing a new element into the copy does not affect the original
sequence, and vice versa. However, the elements of the new
sequence are not copies; they are identical (eq) to the elements
of the original. Therefore, changes made within these elements, as
found via the copied sequence, are also visible in the original
sequence.
If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original's property list. However, the actual values of the properties are shared. See section Text Properties.
See also append in section Building Cons Cells and Lists, concat in
section Creating Strings, and vconcat in section Vectors, for others
ways to copy sequences.
(setq bar '(1 2))
=> (1 2)
(setq x (vector 'foo bar))
=> [foo (1 2)]
(setq y (copy-sequence x))
=> [foo (1 2)]
(eq x y)
=> nil
(equal x y)
=> t
(eq (elt x 1) (elt y 1))
=> t
;; Replacing an element of one sequence.
(aset x 0 'quux)
x => [quux (1 2)]
y => [foo (1 2)]
;; Modifying the inside of a shared element.
(setcar (aref x 1) 69)
x => [quux (69 2)]
y => [foo (69 2)]
Function: length sequence
Returns the number of elements in sequence. If sequence is
a cons cell that is not a list (because the final CDR is not
nil), a wrong-type-argument error is signaled.
(length '(1 2 3))
=> 3
(length ())
=> 0
(length "foobar")
=> 6
(length [1 2 3])
=> 3
Function: elt sequence index
This function returns the element of sequence indexed by
index. Legitimate values of index are integers ranging from
0 up to one less than the length of sequence. If sequence
is a list, then out-of-range values of index return nil;
otherwise, they produce an args-out-of-range error.
(elt [1 2 3 4] 2)
=> 3
(elt '(1 2 3 4) 2)
=> 3
(char-to-string (elt "1234" 2))
=> "3"
(elt [1 2 3 4] 4)
error-->Args out of range: [1 2 3 4], 4
(elt [1 2 3 4] -1)
error-->Args out of range: [1 2 3 4], -1
This function duplicates aref (see section Functions that Operate on Arrays) and
nth (see section Accessing Elements of Lists), except that it works for any kind of
sequence.
An array object refers directly to a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, an element of a list requires access time that is proportional to the position of the element in the list.
When you create an array, you must specify how many elements it has. The amount of space allocated depends on the number of elements. Therefore, it is impossible to change the size of an array once it is created. You cannot add or remove elements. However, you can replace an element with a different value.
Emacs defines two types of array, both of which are one-dimensional: strings and vectors. A vector is a general array; its elements can be any Lisp objects. A string is a specialized array; its elements must be characters (i.e., integers between 0 and 255). Each type of array has its own read syntax. See section String Type, and section Vector Type.
Both kinds of arrays share these characteristics:
aref and aset, respectively (see section Functions that Operate on Arrays).
In principle, if you wish to have an array of characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons:
In this section, we describe the functions that accept both strings and vectors.
Function: arrayp object
This function returns t if object is an array (i.e., either a
vector or a string).
(arrayp [a]) => t (arrayp "asdf") => t
Function: aref array index
This function returns the indexth element of array. The first element is at index zero.
(setq primes [2 3 5 7 11 13])
=> [2 3 5 7 11 13]
(aref primes 4)
=> 11
(elt primes 4)
=> 11
(aref "abcdefg" 1)
=> 98 ; `b' is ASCII code 98.
See also the function elt, in section Sequences.
Function: aset array index object
This function sets the indexth element of array to be object. It returns object.
(setq w [foo bar baz])
=> [foo bar baz]
(aset w 0 'fu)
=> fu
w
=> [fu bar baz]
(setq x "asdfasfd")
=> "asdfasfd"
(aset x 3 ?Z)
=> 90
x
=> "asdZasfd"
If array is a string and object is not a character, a
wrong-type-argument error results.
Function: fillarray array object
This function fills the array array with pointers to object, replacing any previous values. It returns array.
(setq a [a b c d e f g])
=> [a b c d e f g]
(fillarray a 0)
=> [0 0 0 0 0 0 0]
a
=> [0 0 0 0 0 0 0]
(setq s "When in the course")
=> "When in the course"
(fillarray s ?-)
=> "------------------"
If array is a string and object is not a character, a
wrong-type-argument error results.
The general sequence functions copy-sequence and length
are often useful for objects known to be arrays. See section Sequences.
Arrays in Lisp, like arrays in most languages, are blocks of memory whose elements can be accessed in constant time. A vector is a general-purpose array; its elements can be any Lisp objects. (The other kind of array provided in Emacs Lisp is the string, whose elements must be characters.) The main uses of vectors in Emacs are as syntax tables (vectors of integers) and keymaps (vectors of commands). They are also used internally as part of the representation of a byte-compiled function; if you print such a function, you will see a vector in it.
The indices of the elements of a vector are numbered starting with zero in Emacs Lisp.
Vectors are printed with square brackets surrounding the elements
in their order. Thus, a vector containing the symbols a,
b and c is printed as [a b c]. You can write
vectors in the same way in Lisp input.
A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. The elements of the vector are not evaluated. See section Self-Evaluating Forms.
Here are examples of these principles:
(setq avector [1 two '(three) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(eval avector)
=> [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
=> t
Here are some functions that relate to vectors:
Function: vectorp object
This function returns t if object is a vector.
(vectorp [a])
=> t
(vectorp "asdf")
=> nil
Function: vector &rest objects
This function creates and returns a vector whose elements are the arguments, objects.
(vector 'foo 23 [bar baz] "rats")
=> [foo 23 [bar baz] "rats"]
(vector)
=> []
Function: make-vector integer object
This function returns a new vector consisting of integer elements, each initialized to object.
(setq sleepy (make-vector 9 'Z))
=> [Z Z Z Z Z Z Z Z Z]
Function: vconcat &rest sequences
This function returns a new vector containing all the elements of the sequences. The arguments sequences may be lists, vectors, or strings. If no sequences are given, an empty vector is returned.
The value is a newly constructed vector that is not eq to any
existing vector.
(setq a (vconcat '(A B C) '(D E F)))
=> [A B C D E F]
(eq a (vconcat a))
=> nil
(vconcat)
=> []
(vconcat [A B C] "aa" '(foo (6 7)))
=> [A B C 97 97 foo (6 7)]
When an argument is an integer (not a sequence of integers), it is
converted to a string of digits making up the decimal printed
representation of the integer. This special case exists for
compatibility with Mocklisp, and we don't recommend you take advantage
of it. If you want to convert an integer in this way, use format
(see section Formatting Strings) or int-to-string (see section Conversion of Characters and Strings).
For other concatenation functions, see mapconcat in section Mapping Functions, concat in section Creating Strings, and append
in section Building Cons Cells and Lists.
The append function may be used to convert a vector into a list
with the same elements (see section Building Cons Cells and Lists):
(setq avector [1 two (quote (three)) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(append avector nil)
=> (1 two (quote (three)) "four" [five])
A symbol is an object with a unique name. This chapter describes symbols, their components, and how they are created and interned. Property lists are also described. The uses of symbols as variables and as function names are described in separate chapters; see section Variables, and section Functions. For the precise syntax for symbols, see section Symbol Type.
You can test whether an arbitrary Lisp object is a symbol
with symbolp:
Function: symbolp object
This function returns t if object is a symbol, nil
otherwise.
Each symbol has four components (or "cells"), each of which references another object:
symbol-name in section Creating and Interning Symbols.
symbol-value in
section Accessing Variable Values.
symbol-function in section Accessing Function Cell Contents.
symbol-plist in section Property Lists.
The print name cell always holds a string, and cannot be changed. The other three cells can be set individually to any specified Lisp object.
The print name cell holds the string that is the name of the symbol. Since symbols are represented textually by their names, it is important not to have two symbols with the same name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing symbol with the specified name before it creates a new one. (In GNU Emacs Lisp, this is done with a hashing algorithm that uses an obarray; see section Creating and Interning Symbols.)
In normal usage, the function cell usually contains a function or
macro, as that is what the Lisp interpreter expects to see there
(see section Evaluation). Keyboard macros (see section Keyboard Macros),
keymaps (see section Keymaps) and autoload objects (see section Autoloading) are
also sometimes stored in the function cell of symbols. We often refer
to "the function foo" when we really mean the function stored
in the function cell of the symbol foo. We make the distinction
only when necessary.
Similarly, the property list cell normally holds a correctly formatted property list (see section Property Lists), as a number of functions expect to see a property list there.
The function cell or the value cell may be void, which means
that the cell does not reference any object. (This is not the same
thing as holding the symbol void, nor the same as holding the
symbol nil.) Examining the value of a cell which is void results
in an error, such as `Symbol's value as variable is void'.
The four functions symbol-name, symbol-value,
symbol-plist, and symbol-function return the contents of
the four cells. Here as an example we show the contents of the four
cells of the symbol buffer-file-name:
(symbol-name 'buffer-file-name)
=> "buffer-file-name"
(symbol-value 'buffer-file-name)
=> "/gnu/elisp/symbols.texi"
(symbol-plist 'buffer-file-name)
=> (variable-documentation 29529)
(symbol-function 'buffer-file-name)
=> #<subr buffer-file-name>
Because this symbol is the variable which holds the name of the file
being visited in the current buffer, the value cell contents we see are
the name of the source file of this chapter of the Emacs Lisp Manual.
The property list cell contains the list (variable-documentation
29529) which tells the documentation functions where to find
documentation about buffer-file-name in the `DOC' file.
(29529 is the offset from the beginning of the `DOC' file where the
documentation for the function begins.) The function cell contains the
function for returning the name of the file. buffer-file-name
names a primitive function, which has no read syntax and prints in hash
notation (see section Primitive Function Type). A symbol naming a function
written in Lisp would have a lambda expression (or a byte-code object)
in this cell.
A definition in Lisp is a special form that announces your intention to use a certain symbol in a particular way. In Emacs Lisp, you can define a symbol as a variable, or define it as a function (or macro), or both independently.
A definition construct typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable.
defvar and defconst are special forms that define a
symbol as a global variable. They are documented in detail in
section Defining Global Variables.
defun defines a symbol as a function, creating a lambda
expression and storing it in the function cell of the symbol. This
lambda expression thus becomes the function definition of the symbol.
(The term "function definition", meaning the contents of the function
cell, is derived from the idea that defun gives the symbol its
definition as a function.) See section Functions.
defmacro defines a symbol as a macro. It creates a macro
object and stores it in the function cell of the symbol. Note that a
given symbol can be a macro or a function, but not both at once, because
both macro and function definitions are kept in the function cell, and
that cell can hold only one Lisp object at any given time.
See section Macros.
In GNU Emacs Lisp, a definition is not required in order to use a
symbol as a variable or function. Thus, you can make a symbol a global
variable with setq, whether you define it first or not. The real
purpose of definitions is to guide programmers and programming tools.
They inform programmers who read the code that certain symbols are
intended to be used as variables, or as functions. In addition,
utilities such as `etags' and `make-docfile' can recognize
definitions, and add the appropriate information to tag tables and the
`emacs/etc/DOC-version' file. See section Access to Documentation Strings.
To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion.
When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it "hashes" those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J's and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name's hash code.
If a symbol with the desired name is found, then it is used. If no such symbol is found, then a new symbol is created and added to the obarray bucket. Adding a symbol to an obarray is called interning it, and the symbol is then called an interned symbol. In Emacs Lisp, a symbol may be interned in only one obarray--if you try to intern the same symbol in more than one obarray, you will get unpredictable results.
It is possible for two different symbols to have the same name in
different obarrays; these symbols are not eq or equal.
However, this normally happens only as part of abbrev definition
(see section Abbrevs And Abbrev Expansion).
Common Lisp note: in Common Lisp, a symbol may be interned in several obarrays at once.
If a symbol is not in the obarray, then there is no way for Lisp to find it when its name is read. Such a symbol is called an uninterned symbol relative to the obarray. An uninterned symbol has all the other characteristics of symbols.
In Emacs Lisp, an obarray is represented as a vector. Each element of
the vector is a bucket; its value is either an interned symbol whose
name hashes to that bucket, or 0 if the bucket is empty. Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket. Because these links are invisible, there is no way to
scan the symbols in an obarray except using mapatoms (below).
The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, and you can create an obarray
with (make-vector length 0). This is the only
valid way to create an obarray. Prime numbers as lengths tend
to result in good hashing; lengths one less than a power of two are also
good.
Do not try to create an obarray that is not empty. This
does not work--only intern can enter a symbol in an obarray
properly. Also, don't try to put into an obarray of your own
a symbol that is already interned in the main obarray, because in
Emacs Lisp a symbol cannot be in two obarrays at once.
Most of the functions below take a name and sometimes an obarray as
arguments. A wrong-type-argument error is signaled if the name
is not a string, or if the obarray is not a vector.
Function: symbol-name symbol
This function returns the string that is symbol's name. For example:
(symbol-name 'foo)
=> "foo"
Changing the string by substituting characters, etc, does change the name of the symbol, but fails to update the obarray, so don't do it!
Function: make-symbol name
This function returns a newly-allocated, uninterned symbol whose name is
name (which must be a string). Its value and function definition
are void, and its property list is nil. In the example below,
the value of sym is not eq to foo because it is a
distinct uninterned symbol whose name is also `foo'.
(setq sym (make-symbol "foo"))
=> foo
(eq sym 'foo)
=> nil
Function: intern name &optional obarray
This function returns the interned symbol whose name is name. If
there is no such symbol in the obarray, a new one is created, added to
the obarray, and returned. If obarray is supplied, it specifies
the obarray to use; otherwise, the value of the global variable
obarray is used.
(setq sym (intern "foo"))
=> foo
(eq sym 'foo)
=> t
(setq sym1 (intern "foo" other-obarray))
=> foo
(eq sym 'foo)
=> nil
Function: intern-soft name &optional obarray
This function returns the symbol whose name is name, or nil
if a symbol with that name is not found in the obarray. Therefore, you
can use intern-soft to test whether a symbol with a given name is
interned. If obarray is supplied, it specifies the obarray to
use; otherwise the value of the global variable obarray is used.
(intern-soft "frazzle") ; No such symbol exists.
=> nil
(make-symbol "frazzle") ; Create an uninterned one.
=> frazzle
(intern-soft "frazzle") ; That one cannot be found.
=> nil
(setq sym (intern "frazzle")) ; Create an interned one.
=> frazzle
(intern-soft "frazzle") ; That one can be found!
=> frazzle
(eq sym 'frazzle) ; And it is the same one.
=> t
Variable: obarray
This variable is the standard obarray for use by intern and
read.
Function: mapatoms function &optional obarray
This function applies function to every symbol in obarray.
It returns nil. If obarray is not supplied, it defaults to
the value of obarray, the standard obarray for ordinary symbols.
(setq count 0)
=> 0
(defun count-syms (s)
(setq count (1+ count)))
=> count-syms
(mapatoms 'count-syms)
=> nil
count
=> 1871
See documentation in section Access to Documentation Strings, for another
example using mapatoms.
A property list (plist for short) is a list of paired elements stored in the property list cell of a symbol. Each of the pairs associates a property name (usually a symbol) with a property or value. Property lists are generally used to record information about a symbol, such as how to compile it, the name of the file where it was defined, or perhaps even the grammatical class of the symbol (representing a word) in a language understanding system.
Character positions in a string or buffer can also have property lists. See section Text Properties.
The property names and values in a property list can be any Lisp
objects, but the names are usually symbols. They are compared using
eq. Here is an example of a property list, found on the symbol
progn when the compiler is loaded:
(lisp-indent-function 0 byte-compile byte-compile-progn)
Here lisp-indent-function and byte-compile are property
names, and the other two elements are the corresponding values.
Association lists (see section Association Lists) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant since the property names must be distinct.
Property lists are better than association lists when it is necessary
to attach information to various Lisp function names or variables. If
all the pairs are recorded in one association list, the program will
need to search that entire list each time a function or variable is to
be operated on. By contrast, if the information is recorded in the
property lists of the function names or variables themselves, each
search will scan only the length of one property list, which is usually
short. For this reason, the documentation for a variable is recorded in
a property named variable-documentation. The byte compiler
likewise uses properties to record those functions needing special
treatment.
However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to use property names that are probably unique, such as by including the name of the library in the property name.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list.
Function: symbol-plist symbol
This function returns the property list of symbol.
Function: setplist symbol plist
This function sets symbol's property list to plist. Normally, plist should be a well-formed property list, but this is not enforced.
(setplist 'foo '(a 1 b (2 3) c nil))
=> (a 1 b (2 3) c nil)
(symbol-plist 'foo)
=> (a 1 b (2 3) c nil)
For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see section Abbrevs And Abbrev Expansion).
Function: get symbol property
This function finds the value of the property named property in
symbol's property list. If there is no such property, nil
is returned. Thus, there is no distinction between a value of
nil and the absence of the property.
The name property is compared with the existing property names
using eq, so any object is a legitimate property.
See put for an example.
Function: put symbol property value
This function puts value onto symbol's property list under the property name property, replacing any previous value.
(put 'fly 'verb 'transitive)
=>'transitive
(put 'fly 'noun '(a buzzing little bug))
=> (a buzzing little bug)
(get 'fly 'verb)
=> transitive
(symbol-plist 'fly)
=> (verb transitive noun (a buzzing little bug))
The evaluation of expressions in Emacs Lisp is performed by the
Lisp interpreter---a program that receives a Lisp object as input
and computes its value as an expression. The value is computed in
a fashion that depends on the data type of the object, following rules
described in this chapter. The interpreter runs automatically
to evaluate portions of your program, but can also be called explicitly
via the Lisp primitive function eval.
A Lisp object which is intended for evaluation is called an expression or a form. The fact that expressions are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often.
It is very common to read a Lisp expression and then evaluate the
expression, but reading and evaluation are separate activities, and
either can be performed alone. Reading per se does not evaluate
anything; it converts the printed representation of a Lisp object to the
object itself. It is up to the caller of read whether this
object is a form to be evaluated, or serves some entirely different
purpose. See section Input Functions.
Do not confuse evaluation with command key interpretation. The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses call-interactively to invoke the command. The execution of
the command itself involves evaluation if the command is written in
Lisp, but that is not a part of command key interpretation itself.
See section Command Loop.
Evaluation is a recursive process. That is, evaluation of a form may
cause eval to be called again in order to evaluate parts of the
form. For example, evaluation of a function call first evaluates each
argument of the function call, and then evaluates each form in the
function body. Consider evaluation of the form (car x): the
subform x must first be evaluated recursively, so that its value
can be passed as an argument to the function car.
The evaluation of forms takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables.(1) Whenever the form refers to a variable without creating a new binding for it, the value of the binding in the current environment is used. See section Variables.
Evaluation of a form may create new environments for recursive
evaluation by binding variables (see section Local Variables). These
environments are temporary and will be gone by the time evaluation of
the form is complete. The form may also make changes that persist;
these changes are called side effects. An example of a form that
produces side effects is (setq foo 1).
Finally, evaluation of one particular function call, byte-code,
invokes the byte-code interpreter on its arguments. Although the
byte-code interpreter is not the same as the Lisp interpreter, it uses
the same environment as the Lisp interpreter, and may on occasion invoke
the Lisp interpreter. (See section Byte Compilation.)
The details of what evaluation means for each kind of form are described below (see section Kinds of Forms).
Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run. On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list. On these occasions, use the eval function.
The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see section Loading).
Function: eval form
This is the basic function for performing evaluation. It evaluates form in the current environment and returns the result. How the evaluation proceeds depends on the type of the object (see section Kinds of Forms).
Since eval is a function, the argument expression that appears
in a call to eval is evaluated twice: once as preparation before
eval is called, and again by the eval function itself.
Here is an example:
(setq foo 'bar)
=> bar
(setq bar 'baz)
=> baz
;; eval receives argument bar, which is the value of foo
(eval foo)
=> baz
The number of currently active calls to eval is limited to
max-lisp-eval-depth (see below).
Command: eval-current-buffer &optional stream
This function evaluates the forms in the current buffer. It reads
forms from the buffer and calls eval on them until the end of the
buffer is reached, or until an error is signaled and not handled.
If stream is supplied, the variable standard-output is
bound to stream during the evaluation (see section Output Functions).
eval-current-buffer always returns nil.
Command: eval-region start end &optional stream
This function evaluates the forms in the current buffer in the region
defined by the positions start and end. It reads forms from
the region and calls eval on them until the end of the region is
reached, or until an error is signaled and not handled.
If stream is supplied, standard-output is bound to it
for the duration of the command.
eval-region always returns nil.
Variable: max-lisp-eval-depth
This variable defines the maximum depth allowed in calls to
eval, apply, and funcall before an error is
signaled (with error message "Lisp nesting exceeds
max-lisp-eval-depth"). eval is called recursively to evaluate
the arguments of Lisp function calls and to evaluate bodies of
functions.
This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.
The default value of this variable is 200. If you set it to a value less than 100, Lisp will reset it to 100 if the given value is reached.
max-specpdl-size provides another limit on nesting.
See section Local Variables.
Variable: values
The value of this variable is a list of values returned by all expressions which were read from buffers (including the minibuffer), evaluated, and printed. The elements are in order, most recent first.
(setq x 1)
=> 1
(list 'A (1+ 2) auto-save-default)
=> (A 3 t)
values
=> ((A 3 t) 1 ...)
This variable is useful for referring back to values of forms recently
evaluated. It is generally a bad idea to print the value of
values itself, since this may be very long. Instead, examine
particular elements, like this:
;; Refer to the most recent evaluation result.
(nth 0 values)
=> (A 3 t)
;; That put a new element on,
;; so all elements move back one.
(nth 1 values)
=> (A 3 t)
;; This gets the element that was next-to-last
;; before this example.
(nth 3 values)
=> 1
A Lisp object that is intended to be evaluated is called a form. How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and "all other types". All three kinds are described in this section, starting with "all other types" which are self-evaluating forms.
A self-evaluating form is any form that is not a list or symbol.
Self-evaluating forms evaluate to themselves: the result of evaluation
is the same object that was evaluated. Thus, the number 25 evaluates to
25, and the string "foo" evaluates to the string "foo".
Likewise, evaluation of a vector does not cause evaluation of the
elements of the vector--it returns the same vector with its contents
unchanged.
'123 ; An object, shown without evaluation.
=> 123
123 ; Evaluated as usual--result is the same.
=> 123
(eval '123) ; Evaluated "by hand"---result is the same.
=> 123
(eval (eval '123)) ; Evaluating twice changes nothing.
=> 123
It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because it is inconvenient and not very useful; however, it is possible to put them inside Lisp programs when they are constructed from subexpressions rather than read. Here is an example:
;; Build such an expression.
(setq buffer (list 'print (current-buffer)))
=> (print #<buffer eval.texi>)
;; Evaluate it.
(eval buffer)
-| #<buffer eval.texi>
=> #<buffer eval.texi>
When a symbol is evaluated, it is treated as a variable. The result is the variable's value, if it has one. If it has none (if its value cell is void), an error is signaled. For more information on the use of variables, see section Variables.
In the following example, we set the value of a symbol with
setq. When the symbol is later evaluated, that value is
returned.
(setq a 123)
=> 123
(eval 'a)
=> 123
a
=> 123
The symbols nil and t are treated specially, so that the
value of nil is always nil, and the value of t is
always t. Thus, these two symbols act like self-evaluating
forms, even though eval treats them like any other symbol.
A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The rest of the list consists of arguments for the function, macro or special form.
The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects including Scheme.
If the first element of the list is a symbol then evaluation examines the symbol's function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until a non-symbol is obtained. See section Naming a Function, for more information about using a symbol as a name for a function stored in the function cell of the symbol.
One possible consequence of this process is an infinite loop, in the
event that a symbol's function cell refers to the same symbol. Or a
symbol may have a void function cell, causing a void-function
error. But if neither of these things happens, we eventually obtain a
non-symbol, which ought to be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro, a
special form, or an autoload object. Each of these types is a case
described in one of the following sections. If the object is not one of
these types, the error invalid-function is signaled.
The following example illustrates the symbol indirection process. We
use fset to set the function cell of a symbol and
symbol-function to get the function cell contents
(see section Accessing Function Cell Contents). Specifically, we store the symbol car
into the function cell of first, and the symbol first into
the function cell of erste.
;; Build this function cell linkage: ;; ------------- ----- ------- ------- ;; | #<subr car> | <-- | car | <-- | first | <-- | erste | ;; ------------- ----- ------- -------
(symbol-function 'car)
=> #<subr car>
(fset 'first 'car)
=> car
(fset 'erste 'first)
=> first
(erste '(1 2 3)) ; Call the function referenced by erste.
=> 1
By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol.
((lambda (arg) (erste arg))
'(1 2 3))
=> 1
After that function is called, its body is evaluated; this does
involve symbol function indirection when calling erste.
The built-in function indirect-function provides an easy way to
perform symbol function indirection explicitly.
Function: indirect-function function
This function returns the meaning of function as a function. If function is a symbol, then it finds function's function definition and starts over with that value. If function is not a symbol, then it returns function itself.
Here is how you could define indirect-function in Lisp:
(defun indirect-function (function)
(if (symbolp function)
(indirect-function (symbol-function function))
function))
If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a function call. For example, here is a call to the function
+:
(+ 1 x)
When a function call is evaluated, the first step is to evaluate the
remaining elements of the list in the order they appear. The results
are the actual argument values, one argument from each element. Then
the function is called with this list of arguments, effectively using
the function apply (see section Calling Functions). If the function
is written in Lisp, the arguments are used to bind the argument
variables of the function (see section Lambda Expressions); then the forms
in the function body are evaluated in order, and the result of the last
one is used as the value of the function call.
If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, which is evaluated in place of the original form. The expansion may be any sort of form: a self-evaluating constant, a symbol or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results.
Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are evaluated when the expansion is evaluated.
For example, given a macro defined as follows:
(defmacro cadr (x) (list 'car (list 'cdr x)))
an expression such as (cadr (assq 'handler list)) is a macro
call, and its expansion is:
(car (cdr (assq 'handler list)))
Note that the argument (assq 'handler list) appears in the
expansion.
See section Macros, for a complete description of Emacs Lisp macros.
A special form is a primitive function specially marked so that its arguments are not all evaluated. Special forms define control structures or perform variable bindings--things which functions cannot do.
Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.
Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described.
and
catch
catch and throw
cond
condition-case
defconst
defmacro
defun
defvar
function
if
interactive
let
let*
or
prog1
prog2
progn
quote
save-excursion
save-restriction
save-window-excursion
setq
setq-default
track-mouse
unwind-protect
while
with-output-to-temp-buffer
Common Lisp note: here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp.setq,if, andcatchare special forms in both Emacs Lisp and Common Lisp.defunis a special form in Emacs Lisp, but a macro in Common Lisp.save-excursionis a special form in Emacs Lisp, but doesn't exist in Common Lisp.throwis a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn't have multiple values).
The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. When an autoload object appears as a symbol's function definition and that symbol is used as a function, Emacs will automatically install the real definition (plus other associated code) and then call that definition. (See section Autoload.)
The special form quote returns its single argument
"unchanged".
Special Form: quote object
This special form returns object, without evaluating it. This allows symbols and lists, which would normally be evaluated, to be included literally in a program. (It is not necessary to quote numbers, strings, and vectors since they are self-evaluating.)
Because quote is used so often in programs, Lisp provides a
convenient read syntax for it. An apostrophe character (`'')
followed by a Lisp object (in read syntax) expands to a list whose first
element is quote, and whose second element is the object. Thus,
the read syntax 'x is an abbreviation for (quote x).
Here are some examples of expressions that use quote:
(quote (+ 1 2))
=> (+ 1 2)
(quote foo)
=> foo
'foo
=> foo
"foo
=> (quote foo)
'(quote foo)
=> (quote foo)
['foo]
=> [(quote foo)]
Other quoting constructs include function (see section Anonymous Functions), which causes an anonymous lambda expression written in Lisp
to be compiled, and ` (see section Backquote), which is used to quote
only part of a list, while computing and substituting other parts.
A Lisp program consists of expressions or forms (see section Kinds of Forms). We control the order of execution of the forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain.
The simplest control structure is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code--the forms are executed in the order they are written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b, and the function's value is the value of b.
Naturally, Emacs Lisp has many kinds of control structures, including other varieties of sequencing, function calls, conditionals, iteration, and (controlled) jumps. The built-in control structures are special forms since their subforms are not necessarily evaluated. You can use macros to define your own control structure constructs (see section Macros).
Evaluating forms in the order they are written is the most common
control structure. Sometimes this happens automatically, such as in a
function body. Elsewhere you must use a control structure construct to
do this: progn, the simplest control construct of Lisp.
A progn special form looks like this:
(progn a b c ...)
and it says to execute the forms a, b, c and so on, in
that order. These forms are called the body of the progn form.
The value of the last form in the body becomes the value of the entire
progn.
When Lisp was young, progn was the only way to execute two or
more forms in succession and use the value of the last of them. But
programmers found they often needed to use a progn in the body of
a function, where (at that time) only one form was allowed. So the body
of a function was made into an "implicit progn": several forms
are allowed just as in the body of an actual progn. Many other
control structures likewise contain an implicit progn. As a
result, progn is not used as often as it used to be. It is
needed now most often inside of an unwind-protect, and, or
or.
Special Form: progn forms...
This special form evaluates all of the forms, in textual order, returning the result of the final form.
(progn (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The third form"
Two other control constructs likewise evaluate a series of forms but return a different value:
Special Form: prog1 form1 forms...
This special form evaluates form1 and all of the forms, in textual order, returning the result of form1.
(prog1 (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The first form"
Here is a way to remove the first element from a list in the variable
x, then return the value of that former element:
(prog1 (car x) (setq x (cdr x)))
Special Form: prog2 form1 form2 forms...
This special form evaluates form1, form2, and all of the following forms, in textual order, returning the result of form2.
(prog2 (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The second form"
Conditional control structures choose among alternatives. Emacs Lisp
has two conditional forms: if, which is much the same as in other
languages, and cond, which is a generalized case statement.
Special Form: if condition then-form else-forms...
if chooses between the then-form and the else-forms
based on the value of condition. If the evaluated condition is
non-nil, then-form is evaluated and the result returned.
Otherwise, the else-forms are evaluated in textual order, and the
value of the last one is returned. (The else part of if is
an example of an implicit progn. See section Sequencing.)
If condition has the value nil, and no else-forms are
given, if returns nil.
if is a special form because the branch which is not selected is
never evaluated--it is ignored. Thus, in the example below,
true is not printed because print is never called.
(if nil
(print 'true)
'very-false)
=> very-false
Special Form: cond clause...
cond chooses among an arbitrary number of alternatives. Each
clause in the cond must be a list. The CAR of this
list is the condition; the remaining elements, if any, the
body-forms. Thus, a clause looks like this:
(condition body-forms...)
cond tries the clauses in textual order, by evaluating the
condition of each clause. If the value of condition is
non-nil, the body-forms are evaluated, and the value of the
last of body-forms becomes the value of the cond. The
remaining clauses are ignored.
If the value of condition is nil, the clause "fails", so
the cond moves on to the following clause, trying its
condition.
If every condition evaluates to nil, so that every clause
fails, cond returns nil.
A clause may also look like this:
(condition)
Then, if condition is non-nil when tested, the value of
condition becomes the value of the cond form.
The following example has four clauses, which test for the cases where
the value of x is a number, string, buffer and symbol,
respectively:
(cond ((numberp x) x)
((stringp x) x)
((bufferp x)
(setq temporary-hack x) ; multiple body-forms
(buffer-name x)) ; in one clause
((symbolp x) (symbol-value x)))
Often we want the last clause to be executed whenever none of the
previous clauses was successful. To do this, we use t as the
condition of the last clause, like this: (t
body-forms). The form t evaluates to t, which
is never nil, so this clause never fails, provided the
cond gets to it at all.
For example,
(cond ((eq a 1) 'foo)
(t "default"))
=> "default"
This expression is a cond which returns foo if the value
of a is 1, and returns the string "default" otherwise.
Both cond and if can usually be written in terms of the
other. Therefore, the choice between them is a matter of taste and
style. For example:
(if a b c) == (cond (a b) (t c))
This section describes three constructs that are often used together
with if and cond to express complicated conditions. The
constructs and and or can also be used individually as
kinds of multiple conditional constructs.
Function: not condition
This function tests for the falsehood of condition. It returns
t if condition is nil, and nil otherwise.
The function not is identical to null, and we recommend
using null if you are testing for an empty list.
Special Form: and conditions...
The and special form tests whether all the conditions are
true. It works by evaluating the conditions one by one in the
order written.
If any of the conditions evaluates to nil, then the result
of the and must be nil regardless of the remaining
conditions; so the remaining conditions are ignored and the
and returns right away.
If all the conditions turn out non-nil, then the value of
the last of them becomes the value of the and form.
Here is an example. The first condition returns the integer 1, which is
not nil. Similarly, the second condition returns the integer 2,
which is not nil. The third condition is nil, so the
remaining condition is never evaluated.
(and (print 1) (print 2) nil (print 3))
-| 1
-| 2
=> nil
Here is a more realistic example of using and:
(if (and (consp foo) (eq (car foo) 'x))
(message "foo is a list starting with x"))
Note that (car foo) is not executed if (consp foo) returns
nil, thus avoiding an error.
and can be expressed in terms of either if or cond.
For example:
(and arg1 arg2 arg3) == (if arg1 (if arg2 arg3)) == (cond (arg1 (cond (arg2 arg3))))
Special Form: or conditions...
The or special form tests whether at least one of the
conditions is true. It works by evaluating all the
conditions one by one in the order written.
If any of the conditions evaluates to a non-nil value, then
the result of the or must be non-nil; so the remaining
conditions are ignored and the or returns right away. The
value it returns is the non-nil value of the condition just
evaluated.
If all the conditions turn out nil, then the or
expression returns nil.
For example, this expression tests whether x is either 0 or
nil:
(or (eq x nil) (= x 0))
Like the and construct, or can be written in terms of
cond. For example:
(or arg1 arg2 arg3)
==
(cond (arg1)
(arg2)
(arg3))
You could almost write or in terms of if, but not quite:
(if arg1 arg1
(if arg2 arg2
arg3))
This is not completely equivalent because it can evaluate arg1 or
arg2 twice. By contrast, (or arg1 arg2
arg3) never evaluates any argument more than once.
Iteration means executing part of a program repetitively. For example,
you might want to repeat some expressions once for each element of a list,
or once for each integer from 0 to n. You can do this in Emacs Lisp
with the special form while:
Special Form: while condition forms...
while first evaluates condition. If the result is
non-nil, it evaluates forms in textual order. Then it
reevaluates condition, and if the result is non-nil, it
evaluates forms again. This process repeats until condition
evaluates to nil.
There is no limit on the number of iterations that may occur. The loop
will continue until either condition evaluates to nil or
until an error or throw jumps out of it (see section Nonlocal Exits).
The value of a while form is always nil.
(setq num 0)
=> 0
(while (< num 4)
(princ (format "Iteration %d." num))
(setq num (1+ num)))
-| Iteration 0.
-| Iteration 1.
-| Iteration 2.
-| Iteration 3.
=> nil
If you would like to execute something on each iteration before the
end-test, put it together with the end-test in a progn as the
first argument of while, as shown here:
(while (progn
(forward-line 1)
(not (looking-at "^$"))))
This moves forward one line and continues moving by lines until an empty line is reached.
A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited.
catch and throw
Most control constructs affect only the flow of control within the
construct itself. The function throw is the exception to this
rule for of normal program execution: it performs a nonlocal exit on
request. (There are other exceptions, but they are for error handling
only.) throw is used inside a catch, and jumps back to
that catch. For example:
(catch 'foo
(progn
...
(throw 'foo t)
...))
The throw transfers control straight back to the corresponding
catch, which returns immediately. The code following the
throw is not executed. The second argument of throw is used
as the return value of the catch.
The throw and the catch are matched through the first
argument: throw searches for a catch whose first argument
is eq to the one specified. Thus, in the above example, the
throw specifies foo, and the catch specifies the
same symbol, so that catch is applicable. If there is more than
one applicable catch, the innermost one takes precedence.
All Lisp constructs between the catch and the throw,
including function calls, are exited automatically along with the
catch. When binding constructs such as let or function
calls are exited in this way, the bindings are unbound, just as they are
when these constructs are exited normally (see section Local Variables).
Likewise, the buffer and position saved by save-excursion
(see section Excursions) are restored, and so is the narrowing status
saved by save-restriction and the window selection saved by
save-window-excursion (see section Window Configurations). Any
cleanups established with the unwind-protect special form are
executed if the unwind-protect is exited with a throw.
The throw need not appear lexically within the catch
that it jumps to. It can equally well be called from another function
called within the catch. As long as the throw takes place
chronologically after entry to the catch, and chronologically
before exit from it, it has access to that catch. This is why
throw can be used in commands such as exit-recursive-edit
which throw back to the editor command loop (see section Recursive Editing).
Common Lisp note: most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially:return,return-from, andgo, for example. Emacs Lisp has onlythrow.
Special Form: catch tag body...
catch establishes a return point for the throw function. The
return point is distinguished from other such return points by tag,
which may be any Lisp object. The argument tag is evaluated normally
before the return point is established.
With the return point in effect, the forms of the body are evaluated
in textual order. If the forms execute normally, without error or nonlocal
exit, the value of the last body form is returned from the catch.
If a throw is done within body specifying the same value
tag, the catch exits immediately; the value it returns is
whatever was specified as the second argument of throw.
Function: throw tag value
The purpose of throw is to return from a return point previously
established with catch. The argument tag is used to choose
among the various existing return points; it must be eq to the value
specified in the catch. If multiple return points match tag,
the innermost one is used.
The argument value is used as the value to return from that
catch.
If no return point is in effect with tag tag, then a no-catch
error is signaled with data (tag value).
catch and throw
One way to use catch and throw is to exit from a doubly
nested loop. (In most languages, this would be done with a "go to".)
Here we compute (foo i j) for i and j
varying from 0 to 9:
(defun search-foo ()
(catch 'loop
(let ((i 0))
(while (< i 10)
(let ((j 0))
(while (< j 10)
(if (foo i j)
(throw 'loop (list i j)))
(setq j (1+ j))))
(setq i (1+ i))))))
If foo ever returns non-nil, we stop immediately and return a
list of i and j. If foo always returns nil, the
catch returns normally, and the value is nil, since that
is the result of the while.
Here are two tricky examples, slightly different, showing two
return points at once. First, two return points with the same tag,
hack:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'hack))
'no)
-| yes
=> no
Since both return points have tags that match the throw, it goes to
the inner one, the one established in catch2. Therefore,
catch2 returns normally with value yes, and this value is
printed. Finally the second body form in the outer catch, which is
'no, is evaluated and returned from the outer catch.
Now let's change the argument given to catch2:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'quux))
'no)
=> yes
We still have two return points, but this time only the outer one has the
tag hack; the inner one has the tag quux instead. Therefore,
the throw returns the value yes from the outer return point.
The function print is never called, and the body-form 'no is
never evaluated.
When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error.
When an error is signaled, Emacs's default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer.
In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers which should be deleted before
the program is finished. In such cases, you would use
unwind-protect to establish cleanup expressions to be
evaluated in case of error. Occasionally, you may wish the program to
continue execution despite an error in a subroutine. In these cases,
you would use condition-case to establish error handlers to
recover control in case of error.
Resist the temptation to use error handling to transfer control from
one part of the program to another; use catch and throw.
See section Explicit Nonlocal Exits: catch and throw.
Most errors are signaled "automatically" within Lisp primitives
which you call for other purposes, such as if you try to take the
CAR of an integer or move forward a character at the end of the
buffer; you can also signal errors explicitly with the functions
error and signal.
Quitting, which happens when the user types C-g, is not considered an error, but it handled almost like an error. See section Quitting.
Function: error format-string &rest args
This function signals an error with an error message constructed by
applying format (see section Conversion of Characters and Strings) to
format-string and args.
Typical uses of error is shown in the following examples:
(error "You have committed an error.
Try something else.")
error--> You have committed an error.
Try something else.
(error "You have committed %d errors." 10)
error--> You have committed 10 errors.
error works by calling signal with two arguments: the
error symbol error, and a list containing the string returned by
format.
If you want to use a user-supplied string as an error message verbatim,
don't just write (error string). If string contains
`%', it will be interpreted as a format specifier, with undesirable
results. Instead, use (error "%s" string).
Function: signal error-symbol data
This function signals an error named by error-symbol. The argument data is a list of additional Lisp objects relevant to the circumstances of the error.
The argument error-symbol must be an error symbol---a symbol
bearing a property error-conditions whose value is a list of
condition names. This is how different sorts of errors are classified.
The number and significance of the objects in data depends on
error-symbol. For example, with a wrong-type-arg error,
there are two objects in the list: a predicate which describes the type
that was expected, and the object which failed to fit that type.
See section Error Symbols and Condition Names, for a description of error symbols.
Both error-symbol and data are available to any error
handlers which handle the error: a list (error-symbol .
data) is constructed to become the value of the local variable
bound in the condition-case form (see section Writing Code to Handle Errors). If
the error is not handled, both of them are used in printing the error
message.
The function signal never returns (though in older Emacs versions
it could sometimes return).
(signal 'wrong-number-of-arguments '(x y))
error--> Wrong number of arguments: x, y
(signal 'no-such-error '("My unknown error condition."))
error--> peculiar error: "My unknown error condition."
Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors.
When an error is signaled, Emacs searches for an active handler
for the error. A handler is a specially marked place in the Lisp code
of the current function or any of the functions by which it was called.
If an applicable handler exists, its code is executed, and control
resumes following the handler. The handler executes in the environment
of the condition-case which established it; all functions called
within that condition-case have already been exited, and the
handler cannot return to them.
If no applicable handler is in effect in your program, the current command is terminated and control returns to the editor command loop, because the command loop has an implicit handler for all kinds of errors. The command loop's handler uses the error symbol and associated data to print an error message.
When an error is not handled explicitly, it may cause the Lisp debugger
to be called. The debugger is enabled if the variable
debug-on-error (see section Entering the Debugger on an Error) is non-nil.
Unlike error handlers, the debugger runs in the environment of the
error, so that you can examine values of variables precisely as they
were at the time of the error.
The usual effect of signaling an error is to terminate the command that
is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler with the special form
condition-case. A simple example looks like this:
(condition-case nil
(delete-file filename)
(error nil))
This deletes the file named filename, catching any error and
returning nil if an error occurs.
The second argument of condition-case is called the
protected form. (In the example above, the protected form is a
call to delete-file.) The error handlers go into effect when
this form begins execution and are deactivated when this form returns.
They remain in effect for all the intervening time. In particular, they
are in effect during the execution of subroutines called by this form,
and their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
signal and error) called by the protected form, not by the
protected form itself.
The arguments after the protected form are handlers. Each handler
lists one or more condition names (which are symbols) to specify
which errors it will handle. The error symbol specified when an error
is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example
above, there is one handler, and it specifies one condition name,
error, which covers all errors.
The search for an applicable handler checks all the established handlers
starting with the most recently established one. Thus, if two nested
condition-case forms try to handle the same error, the inner of
the two will actually handle it.
When an error is handled, control returns to the handler. Before this
happens, Emacs unbinds all variable bindings made by binding constructs
that are being exited and executes the cleanups of all
unwind-protect forms that are exited. Once control arrives at
the handler, the body of the handler is executed.
After execution of the handler body, execution continues by returning
from the condition-case form. Because the protected form is
exited completely before execution of the handler, the handler cannot
resume execution at the point of the error, nor can it examine variable
bindings that were made within the protected form. All it can do is
clean up and proceed.
condition-case is often used to trap errors that are
predictable, such as failure to open a file in a call to
insert-file-contents. It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.
Error signaling and handling have some resemblance to throw and
catch, but they are entirely separate facilities. An error
cannot be caught by a catch, and a throw cannot be handled
by an error handler (though using throw when there is no suitable
catch signals an error which can be handled).
Special Form: condition-case var protected-form handlers...
This special form establishes the error handlers handlers around
the execution of protected-form. If protected-form executes
without error, the value it returns becomes the value of the
condition-case form; in this case, the condition-case has
no effect. The condition-case form makes a difference when an
error occurs during protected-form.
Each of the handlers is a list of the form (conditions
body...). conditions is an error condition name to be
handled, or a list of condition names; body is one or more Lisp
expressions to be executed when this handler handles an error. Here are
examples of handlers:
(error nil) (arith-error (message "Division by zero")) ((arith-error file-error) (message "Either division by zero or failure to open a file"))
Each error that occurs has an error symbol which describes what
kind of error it is. The error-conditions property of this
symbol is a list of condition names (see section Error Symbols and Condition Names). Emacs
searches all the active condition-case forms for a handler which
specifies one or more of these names; the innermost matching
condition-case handles the error. The handlers in this
condition-case are tested in the order in which they appear.
The body of the handler is then executed, and the condition-case
returns normally, using the value of the last form in the body as the
overall value.
The argument var is a variable. condition-case does not
bind this variable when executing the protected-form, only when it
handles an error. At that time, var is bound locally to a list of
the form (error-symbol . data), giving the
particulars of the error. The handler can refer to this list to decide
what to do. For example, if the error is for failure opening a file,
the file name is the second element of data---the third element of
var.
If var is nil, that means no variable is bound. Then the
error symbol and associated data are not made available to the handler.
Here is an example of using condition-case to handle the error
that results from dividing by zero. The handler prints out a warning
message and returns a very large number.
(defun safe-divide (dividend divisor)
(condition-case err
;; Protected form.
(/ dividend divisor)
;; The handler.
(arith-error ; Condition.
(princ (format "Arithmetic error: %s" err))
1000000)))
=> safe-divide
(safe-divide 5 0)
-| Arithmetic error: (arith-error)
=> 1000000
The handler specifies condition name arith-error so that it will handle only division-by-zero errors. Other kinds of errors will not be handled, at least not by this condition-case. Thus,
(safe-divide nil 3)
error--> Wrong type argument: integer-or-marker-p, nil
Here is a condition-case that catches all kinds of errors,
including those signaled with error:
(setq baz 34)
=> 34
(condition-case err
(if (eq baz 35)
t
;; This is a call to the function error.
(error "Rats! The variable %s was %s, not 35." 'baz baz))
;; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))
2))
-| The error was: (error "Rats! The variable baz was 34, not 35.")
=> 2
When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Lisp language.
These narrow classifications are grouped into a hierarchy of wider
classes called error conditions, identified by condition
names. The narrowest such classes belong to the error symbols
themselves: each error symbol is also a condition name. There are also
condition names for more extensive classes, up to the condition name
error which takes in all kinds of errors. Thus, each error has
one or more condition names: error, the error symbol if that
is distinct from error, and perhaps some intermediate
classifications.
In order for a symbol to be usable as an error symbol, it must have an
error-conditions property which gives a list of condition names.
This list defines the conditions which this kind of error belongs to.
(The error symbol itself, and the symbol error, should always be
members of this list.) Thus, the hierarchy of condition names is
defined by the error-conditions properties of the error symbols.
In addition to the error-conditions list, the error symbol
should have an error-message property whose value is a string to
be printed when that error is signaled but not handled. If the
error-message property exists, but is not a string, the error
message `peculiar error' is used.
Here is how we define a new error symbol, new-error:
(put 'new-error
'error-conditions
'(error my-own-errors new-error))
=> (error my-own-errors new-error)
(put 'new-error 'error-message "A new error")
=> "A new error"
This error has three condition names: new-error, the narrowest
classification; my-own-errors, which we imagine is a wider
classification; and error, which is the widest of all.
Naturally, Emacs will never signal a new-error on its own; only
an explicit call to signal (see section Errors) in your code can do
this:
(signal 'new-error '(x y))
error--> A new error: x, y
This error can be handled through any of the three condition names.
This example handles new-error and any other errors in the class
my-own-errors:
(condition-case foo
(bar nil t)
(my-own-errors nil))
The significant way that errors are classified is by their condition
names--the names used to match errors with handlers. An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names. If signal were given a list of
condition names rather than one error symbol, that would be cumbersome.
By contrast, using only error symbols without condition names would
seriously decrease the power of condition-case. Condition names
make it possible to categorize errors at various levels of generality
when you write an error handler. Using error symbols alone would
eliminate all but the narrowest level of classification.
See section Standard Errors, for a list of all the standard error symbols and their conditions.
The unwind-protect construct is essential whenever you
temporarily put a data structure in an inconsistent state; it permits
you to ensure the data are consistent in the event of an error or throw.
Special Form: unwind-protect body cleanup-forms...
unwind-protect executes the body with a guarantee that the
cleanup-forms will be evaluated if control leaves body, no
matter how that happens. The body may complete normally, or
execute a throw out of the unwind-protect, or cause an
error; in all cases, the cleanup-forms will be evaluated.
Only the body is actually protected by the unwind-protect.
If any of the cleanup-forms themselves exit nonlocally (e.g., via
a throw or an error), it is not guaranteed that the rest
of them will be executed. If the failure of one of the
cleanup-forms has the potential to cause trouble, then it should
be protected by another unwind-protect around that form.
The number of currently active unwind-protect forms counts,
together with the number of local variable bindings, against the limit
max-specpdl-size (see section Local Variables).
For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing:
(save-excursion
(let ((buffer (get-buffer-create " *temp*")))
(set-buffer buffer)
(unwind-protect
body
(kill-buffer buffer))))
You might think that we could just as well write (kill-buffer
(current-buffer)) and dispense with the variable buffer.
However, the way shown above is safer, if body happens to get an
error after switching to a different buffer! (Alternatively, you could
write another save-excursion around the body, to ensure that the
temporary buffer becomes current in time to kill it.)
Here is an actual example taken from the file `ftp.el'. It creates
a process (see section Processes) to try to establish a connection to a remote
machine. As the function ftp-login is highly susceptible to
numerous problems which the writer of the function cannot anticipate, it is
protected with a form that guarantees deletion of the process in the event
of failure. Otherwise, Emacs might fill up with useless subprocesses.
(let ((win nil))
(unwind-protect
(progn
(setq process (ftp-setup-buffer host file))
(if (setq win (ftp-login process host user password))
(message "Logged in")
(error "Ftp login failed")))
(or win (and process (delete-process process)))))
This example actually has a small bug: if the user types C-g to
quit, and the quit happens immediately after the function
ftp-setup-buffer returns but before the variable process is
set, the process will not be killed. There is no easy way to fix this bug,
but at least it is very unlikely.
A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text for a Lisp program, variables are written using the syntax for symbols.
In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of whether the same symbol has a function definition. See section Symbol Components.
The textual form of a program is determined by its Lisp object representation; it is the read syntax for the Lisp object which constitutes the program. This is why a variable in a textual Lisp program is written as the read syntax for the symbol that represents the variable.
The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq. For example,
(setq x '(a b))
gives the variable x the value (a b). Note that the
first argument of setq, the name of the variable, is not
evaluated, but the second argument, the desired value, is evaluated
normally.
Once the variable has a value, you can refer to it by using the symbol by itself as an expression. Thus,
x
=> (a b)
assuming the setq form shown above has already been executed.
If you do another setq, the new value replaces the old one:
x
=> (a b)
(setq x 4)
=> 4
x
=> 4
Emacs Lisp has two special symbols, nil and t, that
always evaluate to themselves. These symbols cannot be rebound, nor can
their value cells be changed. An attempt to change the value of
nil or t signals a setting-constant error.
nil == 'nil
=> nil
(setq nil 500)
error--> Attempt to set constant symbol: nil
Global variables are given values that last until explicitly superseded with new values. Sometimes it is useful to create variable values that exist temporarily--only while within a certain part of the program. These values are called local, and the variables so used are called local variables.
For example, when a function is called, its argument variables receive
new local values which last until the function exits. Similarly, the
let special form explicitly establishes new local values for
specified variables; these last until exit from the let form.
When a local value is established, the previous value (or lack of one) of the variable is saved away. When the life span of the local value is over, the previous value is restored. In the mean time, we say that the previous value is shadowed and not visible. Both global and local values may be shadowed (see section Scope).
If you set a variable (such as with setq) while it is local,
this replaces the local value; it does not alter the global value, or
previous local values that are shadowed. To model this behavior, we
speak of a local binding of the variable as well as a local value.
The local binding is a conceptual place that holds a local value.
Entry to a function, or a special form such as let, creates the
local binding; exit from the function or from the let removes the
local binding. As long as the local binding lasts, the variable's value
is stored within it. Use of setq or set while there is a
local binding stores a different value into the local binding; it does
not create a new binding.
We also speak of the global binding, which is where (conceptually) the global value is kept.
A variable can have more than one local binding at a time (for
example, if there are nested let forms that bind it). In such a
case, the most recently created local binding that still exists is the
current binding of the variable. (This is called dynamic
scoping; see section Scoping Rules for Variable Bindings.) If there are no local bindings,
the variable's global binding is its current binding. We also call the
current binding the most-local existing binding, for emphasis.
Ordinary evaluation of a symbol always returns the value of its current
binding.
The special forms let and let* exist to create
local bindings.
Special Form: let (bindings...) forms...
This function binds variables according to bindings and then
evaluates all of the forms in textual order. The let-form
returns the value of the last form in forms.
Each of the bindings is either (i) a symbol, in which case
that symbol is bound to nil; or (ii) a list of the form
(symbol value-form), in which case symbol is
bound to the result of evaluating value-form. If value-form
is omitted, nil is used.
All of the value-forms in bindings are evaluated in the
order they appear and before any of the symbols are bound. Here
is an example of this: Z is bound to the old value of Y,
which is 2, not the new value, 1.
(setq Y 2)
=> 2
(let ((Y 1)
(Z Y))
(list Y Z))
=> (1 2)
Special Form: let* (bindings...) forms...
This special form is like let, except that each symbol in
bindings is bound as soon as its new value is computed, before the
computation of the values of the following local bindings. Therefore,
an expression in bindings may reasonably refer to the preceding
symbols bound in this let* form. Compare the following example
with the example above for let.
(setq Y 2)
=> 2
(let* ((Y 1)
(Z Y)) ; Use the just-established value of Y.
(list Y Z))
=> (1 1)
Here is a complete list of the other facilities which create local bindings:
condition-case (see section Errors).
Variable: max-specpdl-size
This variable defines the limit on the total number of local variable
bindings and unwind-protect cleanups (see section Nonlocal Exits)
that are allowed before signaling an error (with data "Variable
binding depth exceeds max-specpdl-size").
This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.
The default value is 600.
max-lisp-eval-depth provides another limit on depth of nesting.
See section Eval.
If you have never given a symbol any value as a global variable, we
say that that symbol's global value is void. In other words, the
symbol's value cell does not have any Lisp object in it. If you try to
evaluate the symbol, you get a void-variable error rather than
a value.
Note that a value of nil is not the same as void. The symbol
nil is a Lisp object and can be the value of a variable just as any
other object can be; but it is a value. A void variable does not
have any value.
After you have given a variable a value, you can make it void once more
using makunbound.
Function: makunbound symbol
This function makes the current binding of symbol void. This
causes any future attempt to use this symbol as a variable to signal the
error void-variable, unless or until you set it again.
makunbound returns symbol.
(makunbound 'x) ; Make the global value
; of x void.
=> x
x
error--> Symbol's value as variable is void: x
If symbol is locally bound, makunbound affects the most
local existing binding. This is the only way a symbol can have a void
local binding, since all the constructs that create local bindings
create them with values. In this case, the voidness lasts at most as
long as the binding does; when the binding is removed due to exit from
the construct that made it, the previous or global binding is reexposed
as usual, and the variable is no longer void unless the newly reexposed
binding was void all along.
(setq x 1) ; Put a value in the global binding.
=> 1
(let ((x 2)) ; Locally bind it.
(makunbound 'x) ; Void the local binding.
x)
error--> Symbol's value as variable is void: x
x ; The global binding is unchanged.
=> 1
(let ((x 2)) ; Locally bind it.
(let ((x 3)) ; And again.
(makunbound 'x) ; Void the innermost-local binding.
x)) ; And refer: it's void.
error--> Symbol's value as variable is void: x
(let ((x 2))
(let ((x 3))
(makunbound 'x)) ; Void inner binding, then remove it.
x) ; Now outer let binding is visible.
=> 2
A variable that has been made void with makunbound is
indistinguishable from one that has never received a value and has
always been void.
You can use the function boundp to test whether a variable is
currently void.
Function: boundp variable
boundp returns t if variable (a symbol) is not void;
more precisely, if its current binding is not void. It returns
nil otherwise.
(boundp 'abracadabra) ; Starts out void.
=> nil
(let ((abracadabra 5)) ; Locally bind it.
(boundp 'abracadabra))
=> t
(boundp 'abracadabra) ; Still globally void.
=> nil
(setq abracadabra 5) ; Make it globally nonvoid.
=> 5
(boundp 'abracadabra)
=> t
You may announce your intention to use a symbol as a global variable
with a definition, using defconst or defvar.
In Emacs Lisp, definitions serve three purposes. First, they inform
the user who reads the code that certain symbols are intended to be
used as variables. Second, they inform the Lisp system of these things,
supplying a value and documentation. Third, they provide information to
utilities such as etags and make-docfile, which create data
bases of the functions and variables in a program.
The difference between defconst and defvar is primarily
a matter of intent, serving to inform human readers of whether programs
will change the variable. Emacs Lisp does not restrict the ways in
which a variable can be used based on defconst or defvar
declarations. However, it also makes a difference for initialization:
defconst unconditionally initializes the variable, while
defvar initializes it only if it is void.
One would expect user option variables to be defined with
defconst, since programs do not change them. Unfortunately, this
has bad results if the definition is in a library that is not preloaded:
defconst would override any prior value when the library is
loaded. Users would like to be able to set the option in their init
files, and override the default value given in the definition. For this
reason, user options must be defined with defvar.
Special Form: defvar symbol [value [doc-string]]
This special form informs a person reading your code that symbol
will be used as a variable that the programs are likely to set or
change. It is also used for all user option variables except in the
preloaded parts of Emacs. Note that symbol is not evaluated;
the symbol to be defined must appear explicitly in the
defvar.
If symbol already has a value (i.e., it is not void), value is not even evaluated, and symbol's value remains unchanged. If symbol is void and value is specified, it is evaluated and symbol is set to the result. (If value is not specified, the value of symbol is not changed in any case.)
If symbol has a buffer-local binding in the current buffer,
defvar sets the default value, not the local value.
If the doc-string argument appears, it specifies the documentation
for the variable. (This opportunity to specify documentation is one of
the main benefits of defining the variable.) The documentation is
stored in the symbol's variable-documentation property. The
Emacs help functions (see section Documentation) look for this property.
If the first character of doc-string is `*', it means that
this variable is considered to be a user option. This affects commands
such as set-variable and edit-options.
For example, this form defines foo but does not set its value:
(defvar foo)
=> foo
The following example sets the value of bar to 23, and
gives it a documentation string:
(defvar bar 23
"The normal weight of a bar.")
=> bar
The following form changes the documentation string for bar,
making it a user option, but does not change the value, since bar
already has a value. (The addition (1+ 23) is not even
performed.)
(defvar bar (1+ 23)
"*The normal weight of a bar.")
=> bar
bar
=> 23
Here is an equivalent expression for the defvar special form:
(defvar symbol value doc-string)
==
(progn
(if (not (boundp 'symbol))
(setq symbol value))
(put 'symbol 'variable-documentation 'doc-string)
'symbol)
The defvar form returns symbol, but it is normally used
at top level in a file where its value does not matter.
Special Form: defconst symbol [value [doc-string]]
This special form informs a person reading your code that symbol
has a global value, established here, that will not normally be changed
or locally bound by the execution of the program. The user, however,
may be welcome to change it. Note that symbol is not evaluated;
the symbol to be defined must appear explicitly in the defconst.
defconst always evaluates value and sets the global value
of symbol to the result, provided value is given. If
symbol has a buffer-local binding in the current buffer,
defconst sets the default value, not the local value.
Please note: don't use defconst for user option
variables in libraries that are not normally loaded. The user should be
able to specify a value for such a variable in the `.emacs' file,
so that it will be in effect if and when the library is loaded later.
Here, pi is a constant that presumably ought not to be changed
by anyone (attempts by the Indiana State Legislature notwithstanding).
As the second form illustrates, however, this is only advisory.
(defconst pi 3 "Pi to one place.")
=> pi
(setq pi 4)
=> pi
pi
=> 4
Function: user-variable-p variable
This function returns t if variable is a user option,
intended to be set by the user for customization, nil otherwise.
(Variables other than user options exist for the internal purposes of
Lisp programs, and users need not know about them.)
User option variables are distinguished from other variables by the
first character of the variable-documentation property. If the
property exists and is a string, and its first character is `*',
then the variable is a user option.
Note that if the defconst and defvar special forms are
used while the variable has a local binding, the local binding's value
is set, and the global binding is not changed. This would be confusing.
But the normal way to use these special forms is at top level in a file,
where no local binding should be in effect.
The usual way to reference a variable is to write the symbol which
names it (see section Symbol Forms). This requires you to specify the
variable name when you write the program. Usually that is exactly what
you want to do. Occasionally you need to choose at run time which
variable to reference; then you can use symbol-value.
Function: symbol-value symbol
This function returns the value of symbol. This is the value in the innermost local binding of the symbol, or its global value if it has no local bindings.
(setq abracadabra 5)
=> 5
(setq foo 9)
=> 9
;; Here the symbol abracadabra
;; is the symbol whose value is examined.
(let ((abracadabra 'foo))
(symbol-value 'abracadabra))
=> foo
;; Here the value of abracadabra,
;; which is foo,
;; is the symbol whose value is examined.
(let ((abracadabra 'foo))
(symbol-value abracadabra))
=> 9
(symbol-value 'abracadabra)
=> 5
A void-variable error is signaled if symbol has neither a
local binding nor a global value.
The usual way to change the value of a variable is with the special
form setq. When you need to compute the choice of variable at
run time, use the function set.
Special Form: setq [symbol form]...
This special form is the most common method of changing a variable's value. Each symbol is given a new value, which is the result of evaluating the corresponding form. The most-local existing binding of the symbol is changed.
The value of the setq form is the value of the last form.
(setq x (1+ 2))
=> 3
x ; x now has a global value.
=> 3
(let ((x 5))
(setq x 6) ; The local binding of x is set.
x)
=> 6
x ; The global value is unchanged.
=> 3
Note that the first form is evaluated, then the first symbol is set, then the second form is evaluated, then the second symbol is set, and so on:
(setq x 10 ; Notice thatxis set before y (1+ x)) ; the value ofyis computed. => 11
Function: set symbol value
This function sets symbol's value to value, then
returns value. Since set is a function, the expression
written for symbol is evaluated to obtain the symbol to be
set.
The most-local existing binding of the variable is the binding that is
set; shadowed bindings are not affected. If symbol is not
actually a symbol, a wrong-type-argument error is signaled.
(set one 1)
error--> Symbol's value as variable is void: one
(set 'one 1)
=> 1
(set 'two 'one)
=> one
(set two 2) ; two evaluates to symbol one.
=> 2
one ; So it is one that was set.
=> 2
(let ((one 1)) ; This binding of one is set,
(set 'one 3) ; not the global value.
one)
=> 3
one
=> 2
Logically speaking, set is a more fundamental primitive that
setq. Any use of setq can be trivially rewritten to use
set; setq could even be defined as a macro, given the
availability of set. However, set itself is rarely used;
beginners hardly need to know about it. It is needed only when the
choice of variable to be set is made at run time. For example, the
command set-variable, which reads a variable name from the user
and then sets the variable, needs to use set.
Common Lisp note: in Common Lisp,setalways changes the symbol's special value, ignoring any lexical bindings. In Emacs Lisp, all variables and all bindings are special, sosetalways affects the most local existing binding.
A given symbol foo may have several local variable bindings,
established at different places in the Lisp program, as well as a global
binding. The most recently established binding takes precedence over
the others.
Local bindings in Emacs Lisp have indefinite scope and dynamic extent. Scope refers to where textually in the source code the binding can be accessed. Indefinite scope means that any part of the program can potentially access the variable binding. Extent refers to when, as the program is executing, the binding exists. Dynamic extent means that the binding lasts as long as the activation of the construct that established it.
The combination of dynamic extent and indefinite scope is called dynamic scoping. By contrast, most programming languages use lexical scoping, in which references to a local variable must be textually within the function or block that binds the variable.
Common Lisp note: variables declared "special" in Common Lisp are dynamically scoped like variables in Emacs Lisp.
Emacs Lisp uses indefinite scope for local variable bindings. This means that any function anywhere in the program text might access a given binding of a variable. Consider the following function definitions:
(defun binder (x) ;xis bound inbinder. (foo 5)) ;foois some other function. (defun user () ;xis used inuser. (list x))
In a lexically scoped language, the binding of x from
binder would never be accessible in user, because
user is not textually contained within the function
binder. However, in dynamically scoped Emacs Lisp, user
may or may not refer to the binding of x established in
binder, depending on circumstances:
user directly without calling binder at all,
then whatever binding of x is found, it cannot come from
binder.
foo as follows and call binder, then the
binding made in binder will be seen in user:
(defun foo (lose) (user))
foo as follows and call binder, then the
binding made in binder will not be seen in user:
(defun foo (x) (user))
Here, when foo is called by binder, it binds x.
(The binding in foo is said to shadow the one made in
binder.) Therefore, user will access the x bound
by foo instead of the one bound by binder.
Extent refers to the time during program execution that a variable name is valid. In Emacs Lisp, a variable is valid only while the form that bound it is executing. This is called dynamic extent. "Local" or "automatic" variables in most languages, including C and Pascal, have dynamic extent.
One alternative to dynamic extent is indefinite extent. This means that a variable binding can live on past the exit from the form that made the binding. Common Lisp and Scheme, for example, support this, but Emacs Lisp does not.
To illustrate this, the function below, make-add, returns a
function that purports to add n to its own argument m.
This would work in Common Lisp, but it does not work as intended in
Emacs Lisp, because after the call to make-add exits, the
variable n is no longer bound to the actual argument 2.
(defun make-add (n)
(function (lambda (m) (+ n m)))) ; Return a function.
=> make-add
(fset 'add2 (make-add 2)) ; Define function add2
; with (make-add 2).
=> (lambda (m) (+ n m))
(add2 4) ; Try to add 2 to 4.
error--> Symbol's value as variable is void: n
A simple sample implementation (which is not how Emacs Lisp actually works) may help you understand dynamic binding. This technique is called deep binding and was used in early Lisp systems.
Suppose there is a stack of bindings: variable-value pairs. At entry
to a function or to a let form, we can push bindings on the stack
for the arguments or local variables created there. We can pop those
bindings from the stack at exit from the binding construct.
We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable. To set the variable, we search for the current binding, then store the new value into that binding.
As you can see, a function's bindings remain in effect as long as it continues execution, even during its calls to other functions. That is why we say the extent of the binding is dynamic. And any other function can refer to the bindings, if it uses the same variables while the bindings are in effect. That is why we say the scope is indefinite.
The actual implementation of variable scoping in GNU Emacs Lisp uses a technique called shallow binding. Each variable has a standard place in which its current value is always found--the value cell of the symbol.
In shallow binding, setting the variable works by storing a value in the value cell. When a new local binding is created, the local value is stored in the value cell, and the old value (belonging to a previous binding) is pushed on a stack. When a binding is eliminated, the old value is popped off the stack and stored in the value cell.
We use shallow binding because it has the same results as deep binding, but runs faster, since there is never a need to search for a binding.
Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand. There are two clean ways to use this technique:
You should write comments to inform other programmers that they can see all uses of the variable before them, and to advise them not to add uses elsewhere.
case-fold-search is defined as "non-nil means ignore case
when searching"; various search and replace functions refer to it
directly or through their subroutines, but do not bind or set it.
Then you can bind the variable in other programs, knowing reliably what the effect will be.
Global and local variable bindings are found in most programming languages in one form or another. Emacs also supports another, unusual kind of variable binding: buffer-local bindings, which apply only to one buffer. Emacs Lisp is meant for programming editing commands, and having different values for a variable in different buffers is an important customization method.
A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so the global binding is unchanged; this means that the change is visible in that buffer alone.
A variable may have buffer-local bindings in some buffers but not in
others. The global binding is shared by all the buffers that don't have
their own bindings. Thus, if you set the variable in a buffer that does
not have a buffer-local binding for it, the new value is visible in all
buffers except those with buffer-local bindings. (Here we are assuming
that there are no let-style local bindings to complicate the issue.)
The most common use of buffer-local bindings is for major modes to change
variables that control the behavior of commands. For example, C mode and
Lisp mode both set the variable paragraph-start to specify that only
blank lines separate paragraphs. They do this by making the variable
buffer-local in the buffer that is being put into C mode or Lisp mode, and
then setting it to the new value for that mode.
The usual way to make a buffer-local binding is with
make-local-variable, which is what major mode commands use. This
affects just the current buffer; all other buffers (including those yet to
be created) continue to share the global value.
A more powerful operation is to mark the variable as
automatically buffer-local by calling
make-variable-buffer-local. You can think of this as making the
variable local in all buffers, even those yet to be created. More
precisely, the effect is that setting the variable automatically makes
the variable local to the current buffer if it is not already so. All
buffers start out by sharing the global value of the variable as usual,
but any setq creates a buffer-local binding for the current
buffer. The new value is stored in the buffer-local binding, leaving
the (default) global binding untouched. The global value can no longer
be changed with setq; you need to use setq-default to do
that.
Warning: when a variable has local values in one or more
buffers, you can get Emacs very confused by binding the variable with
let, changing to a different current buffer in which a different
binding is in effect, and then exiting the let. To preserve your
sanity, it is wise to avoid such situations. If you use
save-excursion around each piece of code that changes to a
different current buffer, you will not have this problem. Here is an
example of incorrect code:
(setq foo 'b)
(set-buffer "a")
(make-local-variable 'foo)
(setq foo 'a)
(let ((foo 'temp))
(set-buffer "b")
...)
foo => 'a ; The old buffer-local value from buffer `a'
; is now the default value.
(set-buffer "a")
foo => 'temp ; The local value that should be gone
; is now the buffer-local value in buffer `a'.
But save-excursion as shown here avoids the problem:
(let ((foo 'temp))
(save-excursion
(set-buffer "b")
...))
Local variables in a file you edit are also represented by buffer-local bindings for the buffer that holds the file within Emacs. See section How Emacs Chooses a Major Mode.
Command: make-local-variable variable
This function creates a buffer-local binding in the current buffer for variable (a symbol). Other buffers are not affected. The value returned is variable.
The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.
;; In buffer `b1':
(setq foo 5) ; Affects all buffers.
=> 5
(make-local-variable 'foo) ; Now it is local in `b1'.
=> foo
foo ; That did not change
=> 5 ; the value.
(setq foo 6) ; Change the value
=> 6 ; in `b1'.
foo
=> 6
;; In buffer `b2', the value hasn't changed.
(save-excursion
(set-buffer "b2")
foo)
=> 5
Command: make-variable-buffer-local variable
This function marks variable (a symbol) automatically buffer-local, so that any attempt to set it will make it local to the current buffer at the time.
The value returned is variable.
Function: buffer-local-variables &optional buffer
This function tells you what the buffer-local variables are in buffer buffer. It returns an association list (see section Association Lists) in which each association contains one buffer-local variable and its value. When a buffer-local variable is void in buffer, then it appears directly in the resulting list. If buffer is omitted, the current buffer is used.
(make-local-variable 'foobar)
(makunbound 'foobar)
(make-local-variable 'bind-me)
(setq bind-me 69)
(setq lcl (buffer-local-variables))
;; First, built-in variables local in all buffers:
=> ((mark-active . nil)
(buffer-undo-list nil)
(mode-name . "Fundamental")
...
;; Next, non-built-in local variables.
;; This one is local and void:
foobar
;; This one is local and nonvoid:
(bind-me . 69))
Note that storing new values into the CDRs of cons cells in this list does not change the local values of the variables.
Command: kill-local-variable variable
This function deletes the buffer-local binding (if any) for variable (a symbol) in the current buffer. As a result, the global (default) binding of variable becomes visible in this buffer. Usually this results in a change in the value of variable, since the global value is usually different from the buffer-local value just eliminated.
It is possible to kill the local binding of a variable that automatically becomes local when set. This causes the variable to show its global value in the current buffer. However, if you set the variable again, this will once again create a local value.
kill-local-variable returns variable.
Function: kill-all-local-variables
This function eliminates all the buffer-local variable bindings of the current buffer except for variables marker as "permanent". As a result, the buffer will see the default values of most variables.
This function also resets certain other information pertaining to the
buffer: its local keymap is set to nil, its syntax table is set
to the value of standard-syntax-table, and its abbrev table is
set to the value of fundamental-mode-abbrev-table.
Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.
kill-all-local-variables returns nil.
A local variable is permanent if the variable name (a symbol) has a
permanent-local property that is non-nil. Permanent
locals are appropriate for data pertaining to where the file came from
or how to save it, rather than with how to edit the contents.
The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect except when specifically overridden.
The functions default-value and setq-default allow you
to access and change the default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
setq-default to change the default setting of
paragraph-start for most buffers; and this would work even when
you are in a C or Lisp mode buffer which has a buffer-local value for
this variable.
The special forms defvar and defconst also set the
default value (if they set the variable at all), rather than any local
value.
Function: default-value symbol
This function returns symbol's default value. This is the value
that is seen in buffers that do not have their own values for this
variable. If symbol is not buffer-local, this is equivalent to
symbol-value (see section Accessing Variable Values).
Function: default-boundp variable
The function default-boundp tells you whether variable's
default value is nonvoid. If (default-boundp 'foo) returns
nil, then (default-value 'foo) would get an error.
default-boundp is to default-value as boundp is to
symbol-value.
Special Form: setq-default symbol value
This sets the default value of symbol to value.
symbol is not evaluated, but value is. The value of the
setq-default form is value.
If a symbol is not buffer-local for the current buffer, and is not
marked automatically buffer-local, this has the same effect as
setq. If symbol is buffer-local for the current buffer,
then this changes the value that other buffers will see (as long as they
don't have a buffer-local value), but not the value that the current
buffer sees.
;; In buffer `foo':
(make-local-variable 'local)
=> local
(setq local 'value-in-foo)
=> value-in-foo
(setq-default local 'new-default)
=> new-default
local
=> value-in-foo
(default-value 'local)
=> new-default
;; In (the new) buffer `bar':
local
=> new-default
(default-value 'local)
=> new-default
(setq local 'another-default)
=> another-default
(default-value 'local)
=> another-default
;; Back in buffer `foo':
local
=> value-in-foo
(default-value 'local)
=> another-default
Function: set-default symbol value
This function is like setq-default, except that symbol is
evaluated.
(set-default (car '(a b c)) 23)
=> 23
(default-value 'a)
=> 23
A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them.
In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures.
Here are important terms for functions in Emacs Lisp and for other function-like objects.
car or append. These functions are also called
built-in functions or subrs. (Special forms are also
considered primitives.)
Usually the reason that a function is a primitives is because it is fundamental, or provides a low-level interface to operating system services, or because it needs to run fast. Primitives can be modified or added only by changing the C sources and recompiling the editor. See section Writing Emacs Primitives.
command-execute can invoke; it
is a possible definition for a key sequence. Some functions are
commands; a function written in Lisp is a command if it contains an
interactive declaration (see section Defining Commands). Such a function
can be called from Lisp expressions like other functions; in this case,
the fact that the function is a command makes no difference.
Strings are commands also, even though they are not functions. A symbol is a command if its function definition is a command; such symbols can be invoked with M-x. The symbol is a function as well if the definition is a function. See section Command Loop Overview.
Function: subrp object
This function returns t if object is a built-in function
(i.e. a Lisp primitive).
(subrp 'message) ; message is a symbol,
=> nil ; not a subr object.
(subrp (symbol-function 'message))
=> t
Function: byte-code-function-p object
This function returns t if object is a byte-code
function. For example:
(byte-code-function-p (symbol-function 'next-line))
=> t
A function written in Lisp is a list that looks like this:
(lambda (arg-variables...) [documentation-string] [interactive-declaration] body-forms...)
(Such a list is called a lambda expression for historical reasons, even though it is not really an expression at all--it is not a form that can be evaluated meaningfully.)
The first element of a lambda expression is always the symbol
lambda. This indicates that the list represents a function. The
reason functions are defined to start with lambda is so that
other lists, intended for other uses, will not accidentally be valid as
functions.
The second element is a list of argument variable names (symbols). This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See section Local Variables.
The documentation string is an actual string that serves to describe the function for the Emacs help facilities. See section Documentation Strings of Functions.
The interactive declaration is a list of the form (interactive
code-string). This declares how to provide arguments if the
function is used interactively. Functions with this declaration are called
commands; they can be called using M-x or bound to a key.
Functions not intended to be called in this way should not have interactive
declarations. See section Defining Commands, for how to write an interactive
declaration.
The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, "a list of Lisp forms to evaluate"). The value returned by the function is the value returned by the last element of the body.
Consider for example the following function:
(lambda (a b c) (+ a b c))
We can call this function by writing it as the CAR of an expression, like this:
((lambda (a b c) (+ a b c)) 1 2 3)
The body of this lambda expression is evaluated with the variable
a bound to 1, b bound to 2, and c bound to 3.
Evaluation of the body adds these three numbers, producing the result 6;
therefore, this call to the function returns the value 6.
Note that the arguments can be the results of other function calls, as in this example:
((lambda (a b c) (+ a b c)) 1 (* 2 3) (- 5 4))
Here all the arguments 1, (* 2 3), and (- 5 4) are
evaluated, left to right. Then the lambda expression is applied to the
argument values 1, 6 and 1 to produce the value 8.
It is not often useful to write a lambda expression as the CAR of
a form in this way. You can get the same result, of making local
variables and giving them values, using the special form let
(see section Local Variables). And let is clearer and easier to use.
In practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
arguments to other functions (see section Anonymous Functions).
However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form let was invented. At
that time, they were the only way to bind and initialize local
variables.
Our simple sample function, (lambda (a b c) (+ a b c)),
specifies three argument variables, so it must be called with three
arguments: if you try to call it with only two arguments or four
arguments, you get a wrong-number-of-arguments error.
It is often convenient to write a function that allows certain arguments
to be omitted. For example, the function substring accepts three
arguments--a string, the start index and the end index--but the third
argument defaults to the end of the string if you omit it. It is also
convenient for certain functions to accept an indefinite number of
arguments, as the functions and and + do.
To specify optional arguments that may be omitted when a function
is called, simply include the keyword &optional before the optional
arguments. To specify a list of zero or more extra arguments, include the
keyword &rest before one final argument.
Thus, the complete syntax for an argument list is as follows:
(required-vars... [&optional optional-vars...] [&rest rest-var])
The square brackets indicate that the &optional and &rest
clauses, and the variables that follow them, are optional.
A call to the function requires one actual argument for each of the
required-vars. There may be actual arguments for zero or more of the
optional-vars, and there cannot be any more actual arguments than
these unless &rest exists. In that case, there may be any number of
extra actual arguments.
If actual arguments for the optional and rest variables are omitted,
then they always default to nil. However, the body of the function
is free to consider nil an abbreviation for some other meaningful
value. This is what substring does; nil as the third argument
means to use the length of the string supplied. There is no way for the
function to distinguish between an explicit argument of nil and
an omitted argument.
Common Lisp note: Common Lisp allows the function to specify what
default value to use when an optional argument is omitted; GNU Emacs
Lisp always uses nil.
For example, an argument list that looks like this:
(a b &optional c d &rest e)
binds a and b to the first two actual arguments, which are
required. If one or two more arguments are provided, c and
d are bound to them respectively; any arguments after the first
four are collected into a list and e is bound to that list. If
there are only two arguments, c is nil; if two or three
arguments, d is nil; if four arguments or fewer, e
is nil.
There is no way to have required arguments following optional
ones--it would not make sense. To see why this must be so, suppose
that c in the example were optional and d were required.
If three actual arguments are given; then which variable would the third
argument be for? Similarly, it makes no sense to have any more
arguments (either required or optional) after a &rest argument.
Here are some examples of argument lists and proper calls:
((lambda (n) (1+ n)) ; One required:
1) ; requires exactly one argument.
=> 2
((lambda (n &optional n1) ; One required and one optional:
(if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments.
1 2)
=> 3
((lambda (n &rest ns) ; One required and one rest:
(+ n (apply '+ ns))) ; 1 or more arguments.
1 2 3 4 5)
=> 15
A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See section Documentation, for how the documentation-string is accessed.
It is a good idea to provide documentation strings for all commands, and for all other functions in your program that users of your program should know about; internal functions might as well have only comments, since comments don't take up any room when your program is loaded.
The first line of the documentation string should stand on its own,
because apropos displays just this first line. It should consist
of one or two complete sentences that summarize the function's purpose.
The start of the documentation string is usually indented, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up. This is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands.
You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation.
In most computer languages, every function has a name; the idea of a
function without a name is nonsensical. In Lisp, a function in the
strictest sense has no name. It is simply a list whose first element is
lambda, or a primitive subr-object.
However, a symbol can serve as the name of a function. This happens when you put the function in the symbol's function cell (see section Symbol Components). Then the symbol itself becomes a valid, callable function, equivalent to the list or subr-object that its function cell refers to. The contents of the function cell are also called the symbol's function definition. When the evaluator finds the function definition to use in place of the symbol, we call that symbol function indirection; see section Symbol Function Indirection.
In practice, nearly all functions are given names in this way and
referred to through their names. For example, the symbol car works
as a function and does what it does because the primitive subr-object
#<subr car> is stored in its function cell.
We give functions names because it is more convenient to refer to them
by their names in other functions. For primitive subr-objects such as
#<subr car>, names are the only way you can refer to them: there
is no read syntax for such objects. For functions written in Lisp, the
name is more convenient to use in a call than an explicit lambda
expression. Also, a function with a name can refer to itself--it can
be recursive. Writing the function's name in its own definition is much
more convenient than making the function definition point to itself
(something that is not impossible but that has various disadvantages in
practice).
Functions are often identified with the symbols used to name them. For
example, we often speak of "the function car", not distinguishing
between the symbol car and the primitive subr-object that is its
function definition. For most purposes, there is no need to distinguish.
Even so, keep in mind that a function need not have a unique name. While
a given function object usually appears in the function cell of only
one symbol, this is just a matter of convenience. It is easy to store
it in several symbols using fset; then each of the symbols is
equally well a name for the same function.
A symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict.
We usually give a name to a function when it is first created. This
is called defining a function, and it is done with the
defun special form.
Special Form: defun name argument-list body-forms
defun is the usual way to define new Lisp functions. It
defines the symbol name as a function that looks like this:
(lambda argument-list . body-forms)
This lambda expression is stored in the function cell of name.
The value returned by evaluating the defun form is name,
but usually we ignore this value.
As described previously (see section Lambda Expressions),
argument-list is a list of argument names and may include the
keywords &optional and &rest. Also, the first two forms
in body-forms may be a documentation string and an interactive
declaration.
Note that the same symbol name may also be used as a global variable, since the value cell is independent of the function cell.
Here are some examples:
(defun foo () 5)
=> foo
(foo)
=> 5
(defun bar (a &optional b &rest c)
(list a b c))
=> bar
(bar 1 2 3 4 5)
=> (1 2 (3 4 5))
(bar 1)
=> (1 nil nil)
(bar)
error--> Wrong number of arguments.
(defun capitalize-backwards ()
"Upcase the last letter of a word."
(interactive)
(backward-word 1)
(forward-word 1)
(backward-char 1)
(capitalize-word 1))
=> capitalize-backwards
Be careful not to redefine existing functions unintentionally.
defun redefines even primitive functions such as car
without any hesitation or notification. Redefining a function already
defined is often done deliberately, and there is no way to distinguish
deliberate redefinition from unintentional redefinition.
Defining functions is only half the battle. Functions don't do anything until you call them, i.e., tell them to run. This process is also known as invocation.
The most common way of invoking a function is by evaluating a list. For
example, evaluating the list (concat "a" "b") calls the function
concat. See section Evaluation, for a description of evaluation.
When you write a list as an expression in your program, the function
name is part of the program. This means that the choice of which
function to call is made when you write the program. Usually that's
just what you want. Occasionally you need to decide at run time which
function to call. Then you can use the functions funcall and
apply.
Function: funcall function &rest arguments
funcall calls function with arguments, and returns
whatever function returns.
Since funcall is a function, all of its arguments, including
function, are evaluated before funcall is called. This
means that you can use any expression to obtain the function to be
called. It also means that funcall does not see the expressions
you write for the arguments, only their values. These values are
not evaluated a second time in the act of calling function;
funcall enters the normal procedure for calling a function at the
place where the arguments have already been evaluated.
The argument function must be either a Lisp function or a
primitive function. Special forms and macros are not allowed, because
they make sense only when given the "unevaluated" argument
expressions. funcall cannot provide these because, as we saw
above, it never knows them in the first place.
(setq f 'list)
=> list
(funcall f 'x 'y 'z)
=> (x y z)
(funcall f 'x 'y '(z))
=> (x y (z))
(funcall 'and t nil)
error--> Invalid function: #<subr and>
Compare this example with that of apply.
Function: apply function &rest arguments
apply calls function with arguments, just like
funcall but with one difference: the last of arguments is a
list of arguments to give to function, rather than a single
argument. We also say that this list is appended to the other
arguments.
apply returns the result of calling function. As with
funcall, function must either be a Lisp function or a
primitive function; special forms and macros do not make sense in
apply.
(setq f 'list)
=> list
(apply f 'x 'y 'z)
error--> Wrong type argument: listp, z
(apply '+ 1 2 '(3 4))
=> 10
(apply '+ '(1 2 3 4))
=> 10
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
An interesting example of using apply is found in the description
of mapcar; see the following section.
It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using funcall or apply. Functions
that accept function arguments are often called functionals.
Sometimes, when you call such a function, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function:
Function: identity arg
This function returns arg and has no side effects.
Function: ignore &rest args
This function ignores any arguments and returns nil.
A mapping function applies a given function to each element of a
list or other collection. Emacs Lisp has three such functions;
mapcar and mapconcat, which scan a list, are described
here. For the third mapping function, mapatoms, see
section Creating and Interning Symbols.
Function: mapcar function sequence
mapcar applies function to each element of sequence in
turn. The results are made into a nil-terminated list.
The argument sequence may be a list, a vector or a string. The result is always a list. The length of the result is the same as the length of sequence.
For example:
(mapcar 'car '((a b) (c d) (e f)))
=> (a c e)
(mapcar '1+ [1 2 3])
=> (2 3 4)
(mapcar 'char-to-string "abc")
=> ("a" "b" "c")
;; Call each function in my-hooks.
(mapcar 'funcall my-hooks)
(defun mapcar* (f &rest args)
"Apply FUNCTION to successive cars of all ARGS, until one
ends. Return the list of results."
;; If no list is exhausted,
(if (not (memq 'nil args))
;; Apply function to CARs.
(cons (apply f (mapcar 'car args))
(apply 'mapcar* f
;; Recurse for rest of elements.
(mapcar 'cdr args)))))
(mapcar* 'cons '(a b c) '(1 2 3 4))
=> ((a . 1) (b . 2) (c . 3))
Function: mapconcat function sequence separator
mapconcat applies function to each element of
sequence: the results, which must be strings, are concatenated.
Between each pair of result strings, mapconcat inserts the string
separator. Usually separator contains a space or comma or
other suitable punctuation.
The argument function must be a function that can take one argument and returns a string.
(mapconcat 'symbol-name
'(The cat in the hat)
" ")
=> "The cat in the hat"
(mapconcat (function (lambda (x) (format "%c" (1+ x))))
"HAL-8000"
"")
=> "IBM.9111"
In Lisp, a function is a list that starts with lambda (or
alternatively a primitive subr-object); names are "extra". Although
usually functions are defined with defun and given names at the
same time, it is occasionally more concise to use an explicit lambda
expression--an anonymous function. Such a list is valid wherever a
function name is.
Any method of creating such a list makes a valid function. Even this:
(setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x))))
=> (lambda (x) (+ 12 x))
This computes a list that looks like (lambda (x) (+ 12 x)) and
makes it the value (not the function definition!) of
silly.
Here is how we might call this function:
(funcall silly 1)
=> 13
(It does not work to write (silly 1), because this function
is not the function definition of silly. We have not given
silly any function definition, just a value as a variable.)
Most of the time, anonymous functions are constants that appear in
your program. For example, you might want to pass one as an argument
to the function mapcar, which applies any given function to each
element of a list. Here we pass an anonymous function that multiplies
a number by two:
(defun double-each (list)
(mapcar '(lambda (x) (* 2 x)) list))
=> double-each
(double-each '(2 11))
=> (4 22)
In such cases, we usually use the special form function instead
of simple quotation to quote the anonymous function.
Special Form: function function-object
This special form returns function-object without evaluating it.
In this, it is equivalent to quote. However, it serves as a
note to the Emacs Lisp compiler that function-object is intended
to be used only as a function, and therefore can safely be compiled.
See section Quoting, for comparison.
Using function instead of quote makes a difference
inside a function or macro that you are going to compile. For example:
(defun double-each (list)
(mapcar (function (lambda (x) (* 2 x))) list))
=> double-each
(double-each '(2 11))
=> (4 22)
If this definition of double-each is compiled, the anonymous
function is compiled as well. By contrast, in the previous definition
where ordinary quote is used, the argument passed to
mapcar is the precise list shown:
(lambda (arg) (+ arg 5))
The Lisp compiler cannot assume this list is a function, even though it
looks like one, since it does not know what mapcar does with the
list. Perhaps mapcar will check that the CAR of the third
element is the symbol +! The advantage of function is
that it tells the compiler to go ahead and compile the constant
function.
We sometimes write function instead of quote when
quoting the name of a function, but this usage is just a sort of
comment.
(function symbol) == (quote symbol) == 'symbol
See documentation in section Access to Documentation Strings, for a
realistic example using function and an anonymous function.
The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.
Function: symbol-function symbol
This returns the object in the function cell of symbol. If the
symbol's function cell is void, a void-function error is
signaled.
This function does not check that the returned object is a legitimate function.
(defun bar (n) (+ n 2))
=> bar
(symbol-function 'bar)
=> (lambda (n) (+ n 2))
(fset 'baz 'bar)
=> bar
(symbol-function 'baz)
=> bar
If you have never given a symbol any function definition, we say that
that symbol's function cell is void. In other words, the function
cell does not have any Lisp object in it. If you try to call such a symbol
as a function, it signals a void-function error.
Note that void is not the same as nil or the symbol
void. The symbols nil and void are Lisp objects,
and can be stored into a function cell just as any other object can be
(and they can be valid functions if you define them in turn with
defun); but nil or void is an object. A
void function cell contains no object whatsoever.
You can test the voidness of a symbol's function definition with
fboundp. After you have given a symbol a function definition, you
can make it void once more using fmakunbound.
Function: fboundp symbol
Returns t if the symbol has an object in its function cell,
nil otherwise. It does not check that the object is a legitimate
function.
Function: fmakunbound symbol
This function makes symbol's function cell void, so that a
subsequent attempt to access this cell will cause a void-function
error. (See also makunbound, in section Local Variables.)
(defun foo (x) x)
=> x
(fmakunbound 'foo)
=> x
(foo 1)
error--> Symbol's function definition is void: foo
Function: fset symbol object
This function stores object in the function cell of symbol. The result is object. Normally object should be a function or the name of a function, but this is not checked.
There are three normal uses of this function:
defun. See section Classification of List Forms, for an
example of this usage.
defun
were not a primitive, it could be written in Lisp (as a macro) using
fset.
Here are examples of the first two uses:
;; Givefirstthe same definitioncarhas. (fset 'first (symbol-function 'car)) => #<subr car> (first '(1 2 3)) => 1 ;; Make the symbolcarthe function definition ofxfirst. (fset 'xfirst 'car) => car (xfirst '(1 2 3)) => 1 (symbol-function 'xfirst) => car (symbol-function (symbol-function 'xfirst)) => #<subr car> ;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") => "\^u2\^k"
When writing a function that extends a previously defined function, the following idiom is often used:
(fset 'old-foo (symbol-function 'foo)) (defun foo () "Just like old-foo, except more so." (old-foo) (more-so))
This does not work properly if foo has been defined to autoload.
In such a case, when foo calls old-foo, Lisp attempts
to define old-foo by loading a file. Since this presumably
defines foo rather than old-foo, it does not produce the
proper results. The only way to avoid this problem is to make sure the
file is loaded before moving aside the old definition of foo.
See also the function indirect-function in section Symbol Function Indirection.
You can define an inline function by using defsubst instead
of defun. An inline function works just like an ordinary
function except for one thing: when you compile a call to the function,
the function's definition is open-coded into the caller.
Making a function inline makes explicit calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them. Since the flexibility of redefining functions is an important features of Emacs, you should not make a function inline unless its speed is really crucial.
Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the advantages of inline functions are greatest for small functions, you generally should not make large functions inline.
It's possible to define a macro to expand into the same code that an
inline function would execute. But the macro would have a limitation:
you can use it only explicitly--a macro cannot be called with
apply, mapcar and so on. Also, it takes some work to
convert an ordinary function into a macro. (See section Macros.) To convert
it into an inline function is very easy; simply replace defun
with defsubst.
Inline functions can be used and open coded later on in the same file, following the definition, just like macros.
Emacs versions prior to 19 did not have inline functions.
Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here.
apply
autoload
call-interactively
commandp
documentation
eval
funcall
ignore
indirect-function
interactive
interactive.
interactive-p
mapatoms
mapcar
mapconcat
undefined
Macros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro.
Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them.
If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See section Inline Functions.
Suppose we would like to define a Lisp construct to increment a
variable value, much like the ++ operator in C. We would like to
write (inc x) and have the effect of (setq x (1+ x)).
Here's a macro definition that does the job:
(defmacro inc (var) (list 'setq var (list '1+ var)))
When this is called with (inc x), the argument var has
the value x---not the value of x. The body
of the macro uses this to construct the expansion, which is (setq
x (1+ x)). Once the macro definition returns this expansion, Lisp
proceeds to evaluate it, thus incrementing x.
A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list.
Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked. The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a &rest argument. And the macro body executes and
returns its value just as a function body does.
The second crucial difference between macros and functions is that the value returned by the macro body is not the value of the macro call. Instead, it is an alternate expression for computing that value, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro.
Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual.
You can see the expansion of a given macro call by calling
macroexpand.
Function: macroexpand form &optional environment
This function expands form, if it is a macro call. If the result
is another macro call, it is expanded in turn, until something which is
not a macro call results. That is the value returned by
macroexpand. If form is not a macro call to begin with, it
is returned as given.
Note that macroexpand does not look at the subexpressions of
form (although some macro definitions may do so). Even if they
are macro calls themselves, macroexpand does not expand them.
The function macroexpand does not expand calls to inline functions.
Normally there is no need for that, since a call to an inline function is
no harder to understand than a call to an ordinary function.
If environment is provided, it specifies an alist of macro definitions that shadow the currently defined macros. This is used by byte compilation.
(defmacro inc (var)
(list 'setq var (list '1+ var)))
=> inc
(macroexpand '(inc r))
=> (setq r (1+ r))
(defmacro inc2 (var1 var2)
(list 'progn (list 'inc var1) (list 'inc var2)))
=> inc2
(macroexpand '(inc2 r s))
=> (progn (inc r) (inc s)) ; inc not expanded here.
You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation.
When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself--they would be computed at compile time, which is not useful.
In order for compilation of macro calls to work, the macros must be
defined in Lisp when the calls to them are compiled. The compiler has a
special feature to help you do this: if a file being compiled contains a
defmacro form, the macro is defined temporarily for the rest of
the compilation of that file. To use this feature, you must define the
macro in the same file where it is used and before its first use.
While byte-compiling a file, any require calls at top-level are
executed. One way to ensure that necessary macro definitions are
available during compilation is to require the file that defines them.
See section Features.
A Lisp macro is a list whose CAR is macro. Its CDR should
be a function; expansion of the macro works by applying the function
(with apply) to the list of unevaluated argument-expressions
from the macro call.
It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to pass
an anonymous macro to mapping functions such as mapcar. In
practice, all Lisp macros have names, and they are usually defined with
the special form defmacro.
Special Form: defmacro name argument-list body-forms...
defmacro defines the symbol name as a macro that looks
like this:
(macro lambda argument-list . body-forms)
This macro object is stored in the function cell of name. The
value returned by evaluating the defmacro form is name, but
usually we ignore this value.
The shape and meaning of argument-list is the same as in a
function, and the keywords &rest and &optional may be used
(see section Advanced Features of Argument Lists). Macros may have a documentation string, but
any interactive declaration is ignored since macros cannot be
called interactively.
It could prove rather awkward to write macros of significant size,
simply due to the number of times the function list needs to be
called. To make writing these forms easier, a macro ``'
(often called backquote) exists.
Backquote allows you to quote a list, but selectively evaluate
elements of that list. In the simplest case, it is identical to the
special form quote (see section Quoting). For example, these
two forms yield identical results:
(` (a list of (+ 2 3) elements))
=> (a list of (+ 2 3) elements)
(quote (a list of (+ 2 3) elements))
=> (a list of (+ 2 3) elements)
By inserting a special marker, `,', inside of the argument to backquote, it is possible to evaluate desired portions of the argument:
(list 'a 'list 'of (+ 2 3) 'elements)
=> (a list of 5 elements)
(` (a list of (, (+ 2 3)) elements))
=> (a list of 5 elements)
It is also possible to have an evaluated list spliced into the
resulting list by using the special marker `,@'. The elements of
the spliced list become elements at the same level as the other elements
of the resulting list. The equivalent code without using ` is
often unreadable. Here are some examples:
(setq some-list '(2 3))
=> (2 3)
(cons 1 (append some-list '(4) some-list))
=> (1 2 3 4 2 3)
(` (1 (,@ some-list) 4 (,@ some-list)))
=> (1 2 3 4 2 3)
(setq list '(hack foo bar))
=> (hack foo bar)
(cons 'use
(cons 'the
(cons 'words (append (cdr list) '(as elements)))))
=> (use the words foo bar as elements)
(` (use the words (,@ (cdr list)) as elements (,@ nil)))
=> (use the words foo bar as elements)
The reason for (,@ nil) is to avoid a bug in Emacs version 18.
The bug occurs when a call to ,@ is followed only by constant
elements. Thus,
(` (use the words (,@ (cdr list)) as elements))
would not work, though it really ought to. (,@ nil) avoids the
problem by being a nonconstant element that does not affect the result.
Macro: ` list
This macro returns list as quote would, except that the
list is copied each time this expression is evaluated, and any sublist
of the form (, subexp) is replaced by the value of
subexp. Any sublist of the form (,@ listexp)
is replaced by evaluating listexp and splicing its elements
into the containing list in place of this sublist. (A single sublist
can in this way be replaced by any number of new elements in the
containing list.)
There are certain contexts in which `,' would not be recognized and should not be used:
;; Use of a `,' expression as the CDR of a list. (` (a . (, 1))) ; Not(a . 1)=> (a \, 1) ;; Use of `,' in a vector. (` [a (, 1) c]) ; Not[a 1 c]error--> Wrong type argument ;; Use of a `,' as the entire argument of ``'. (` (, 2)) ; Not 2 => (\, 2)
Common Lisp note: in Common Lisp, `,' and `,@' are implemented as reader macros, so they do not require parentheses. Emacs Lisp implements them as functions because reader macros are not supported (to save space).
The basic facts of macro expansion have all been described above, but there consequences are often counterintuitive. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.
When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple "for" loop such as one might find in Pascal.
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop, e.g.,
(for i from 1 to 10 do (print i))."
(list 'let (list (list var init))
(cons 'while (cons (list '<= var final)
(append body (list (list 'inc var)))))))
=> for
(for i from 1 to 3 do
(setq square (* i i))
(princ (format "\n%d %d" i square)))
==>
(let ((i 1))
(while (<= i 3)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
-|1 1
-|2 4
-|3 9
=> nil
(The arguments from, to, and do in this macro are
"syntactic sugar"; they are entirely ignored. The idea is that you
will write noise words (such as from, to, and do)
in those positions in the macro call.)
This macro suffers from the defect that final is evaluated on
every iteration. If final is a constant, this is not a problem.
If it is a more complex form, say (long-complex-calculation x),
this can slow down the execution significantly. If final has side
effects, executing it more than once is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the for macro:
(let ((i 1)
(max 3))
(while (<= i max)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
Here is a macro definition that creates this expansion:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(` (let (((, var) (, init))
(max (, final)))
(while (<= (, var) max)
(,@ body)
(inc (, var))))))
Unfortunately, this introduces another problem.
The new definition of for has a new problem: it introduces a
local variable named max which the user does not expect. This
causes trouble in examples such as the following:
(let ((max 0))
(for x from 0 to 10 do
(let ((this (frob x)))
(if (< max this)
(setq max this)))))
The references to max inside the body of the for, which
are supposed to refer to the user's binding of max, really access
the binding made by for.
The way to correct this is to use an uninterned symbol instead of
max (see section Creating and Interning Symbols). The uninterned symbol can be
bound and referred to just like any other symbol, but since it is created
by for, we know that it cannot appear in the user's program.
Since it is not interned, there is no way the user can put it into the
program later. It will never appear anywhere except where put by
for. Here is a definition of for which works this way:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(let ((tempvar (make-symbol "max")))
(` (let (((, var) (, init))
((, tempvar) (, final)))
(while (<= (, var) (, tempvar))
(,@ body)
(inc (, var)))))))
This creates an uninterned symbol named max and puts it in the
expansion instead of the usual interned symbol max that appears
in expressions ordinarily.
Another problem can happen if you evaluate any of the macro argument
expressions during the computation of the expansion, such as by calling
eval (see section Eval). If the argument is supposed to refer to the
user's variables, you may have trouble if the user happens to use a
variable with the same name as one of the macro arguments. Inside the
macro body, the macro argument binding is the most local binding of this
variable, so any references inside the form being evaluated do refer
to it. Here is an example:
(defmacro foo (a)
(list 'setq (eval a) t))
=> foo
(setq x 'b)
(foo x) ==> (setq b t)
=> t ; and b has been set.
;; but
(setq a 'b)
(foo a) ==> (setq 'b t) ; invalid!
error--> Symbol's value is void: b
It makes a difference whether the user types a or x,
because a conflicts with the macro argument variable a.
In general it is best to avoid calling eval in a macro
definition at all.
Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded.
In particular, constructing objects is a kind of side effect. If the macro is called once, then the objects are constructed only once. In other words, the same structure of objects is used each time the macro call is executed. In interpreted operation, the macro is reexpanded each time, producing a fresh collection of objects each time. Usually this does not matter--the objects have the same contents whether they are shared or not. But if the surrounding program does side effects on the objects, it makes a difference whether they are shared. Here is an example:
(defmacro new-object ()
(list 'quote (cons nil nil)))
(defun initialize (condition)
(let ((object (new-object)))
(if condition
(setcar object condition))
object))
If initialize is interpreted, a new list (nil) is
constructed each time initialize is called. Thus, no side effect
survives between calls. If initialize is compiled, then the
macro new-object is expanded during compilation, producing a
single "constant" (nil) that is reused and altered each time
initialize is called.
Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file.
The load functions evaluate all the expressions in a file just
as the eval-current-buffer function evaluates all the
expressions in a buffer. The difference is that the load functions
read and evaluate the text in the file as found on disk, not the text
in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code or, optionally, as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions.
A file containing Lisp code is often called a library. Thus, the "Rmail library" is a file containing code for Rmail mode. Similarly, a "Lisp library directory" is a directory of files containing Lisp code.
There are several interface functions for loading. For example, the
autoload function creates a Lisp object that loads a file when it
is evaluated (see section Autoload). require also causes files to be
loaded (see section Features). Ultimately, all these facilities call the
load function to do the work.
Function: load filename &optional missing-ok nomessage nosuffix
This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file.
To find the file, load first looks for a file named
`filename.elc', that is, for a file whose name has
`.elc' appended. If such a file exists, it is loaded. But if
there is no file by that name, then load looks for a file whose
name has `.el' appended. If that file exists, it is loaded.
Finally, if there is no file by either name, load looks for a
file named filename with nothing appended, and loads it if it
exists. (The load function is not clever about looking at
filename. In the perverse case of a file named `foo.el.el',
evaluation of (load "foo.el") will indeed find it.)
If the optional argument nosuffix is non-nil, then the
suffixes `.elc' and `.el' are not tried. In this case, you
must specify the precise file name you want.
If filename is a relative file name, such as `foo' or
`baz/foo.bar', load searches for the file using the variable
load-path. It appends filename to each of the directories
listed in load-path, and loads the first file it finds whose
name matches. The current default directory is tried only if it is
specified in load-path, where it is represented as nil.
All three possible suffixes are tried in the first directory in
load-path, then all three in the second directory in
load-path, etc.
If you get a warning that `foo.elc' is older than `foo.el', it means you should consider recompiling `foo.el'. See section Byte Compilation.
Messages like `Loading foo...' and `Loading foo...done' appear
in the echo area during loading unless nomessage is
non-nil.
Any errors that are encountered while loading a file cause load
to abort. If the load was done for the sake of autoload, certain
kinds of top-level forms, those which define functions, are undone.
The error file-error is signaled (with `Cannot open load
file filename') if no file is found. No error is signaled if
missing-ok is non-nil---then load just returns
nil.
load returns t if the file loads successfully.
User Option: load-path
The value of this variable is a list of directories to search when
loading files with load. Each element is a string (which must be
a directory name) or nil (which stands for the current working
directory). The value of load-path is initialized from the
environment variable EMACSLOADPATH, if it exists; otherwise it is
set to the default specified in `emacs/src/paths.h' when Emacs is
built.
The syntax of EMACSLOADPATH is the same as that of PATH;
fields are separated by `:', and `.' is used for the current
default directory. Here is an example of how to set your
EMACSLOADPATH variable from a csh `.login' file:
setenv EMACSLOADPATH .:/user/bil/emacs:/usr/lib/emacs/lisp
Here is how to set it using sh:
export EMACSLOADPATH EMACSLOADPATH=.:/user/bil/emacs:/usr/local/lib/emacs/lisp
Here is an example of code you can place in a `.emacs' file to add
several directories to the front of your default load-path:
(setq load-path
(append
(list nil
"/user/bil/emacs"
"/usr/local/lisplib")
load-path))
In this example, the path searches the current working directory first, followed then by the `/user/bil/emacs' directory and then by the `/usr/local/lisplib' directory, which are then followed by the standard directories for Lisp code.
When Emacs version 18 processes command options `-l' or
`-load' which specify Lisp libraries to be loaded, it temporarily
adds the current directory to the front of load-path so that
files in the current directory can be specified easily. Newer Emacs
versions also find such files in the current directory, but without
altering load-path.
Variable: load-in-progress
This variable is non-nil if Emacs is in the process of loading a
file, and it is nil otherwise. This is how defun and
provide determine whether a load is in progress, so that their
effect can be undone if the load fails.
To learn how load is used to build Emacs, see section Building Emacs.
The autoload facility allows you to make a function or macro available but put off loading its actual definition. An attempt to call a symbol whose definition is an autoload object automatically reads the file to install the real definition and its other associated code, and then calls the real definition.
To prepare a function or macro for autoloading, you must call
autoload, specifying the function name and the name of the file
to be loaded. A file such as `emacs/lisp/loaddefs.el' usually does
this when Emacs is first built.
The following example shows how doctor is prepared for
autoloading in `loaddefs.el':
(autoload 'doctor "doctor" "\ Switch to *doctor* buffer and start giving psychotherapy." t)
The backslash and newline immediately following the double-quote are a convention used only in the preloaded Lisp files such as `loaddefs.el'; they cause the documentation string to be put in the `etc/DOC' file. (See section Building Emacs.) In any other source file, you would write just this:
(autoload 'doctor "doctor" "Switch to *doctor* buffer and start giving psychotherapy." t)
Calling autoload creates an autoload object containing the name
of the file and some other information, and makes this the function
definition of the specified symbol. When you later try to call that
symbol as a function or macro, the file is loaded; the loading should
redefine that symbol with its proper definition. After the file
completes loading, the function or macro is called as if it had been
there originally.
If, at the end of loading the file, the desired Lisp function or macro
has not been defined, then the error error is signaled (with data
"Autoloading failed to define function function-name").
The autoloaded file may, of course, contain other definitions and may
require or provide one or more features. If the file is not completely
loaded (due to an error in the evaluation of the contents) any function
definitions or provide calls that occurred during the load are
undone. This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file. If not for
this, then some of the functions in the file might appear defined, but
they may fail to work properly for the lack of certain subroutines
defined later in the file and not loaded successfully.
Emacs as distributed comes with many autoloaded functions.
The calls to autoload are in the file `loaddefs.el'.
There is a convenient way of updating them automatically.
Write `;;;###autoload' on a line by itself before the real
definition of the function, in its autoloadable source file; then the
command M-x update-file-autoloads automatically puts the
autoload call into `loaddefs.el'. M-x
update-directory-autoloads is more powerful; it updates autoloads for
all files in the current directory.
You can also put other kinds of forms into `loaddefs.el', by writing `;;;###autoload' followed on the same line by the form. M-x update-file-autoloads copies the form from that line.
The commands for updating autoloads work by visiting and editing the file `loaddefs.el'. To make the result take effect, you must save that file's buffer.
Function: autoload symbol filename &optional docstring interactive type
This function defines the function (or macro) named symbol so as
to load automatically from filename. The string filename is
a file name which will be passed to load when the function is
called.
The argument docstring is the documentation string for the function. Normally, this is the same string that is in the function definition itself. This makes it possible to look at the documentation without loading the real definition.
If interactive is non-nil, then the function can be
called interactively. This lets completion in M-x work without
loading the function's real definition. The complete interactive
specification need not be given here. If type is macro,
then the function is really a macro. If type is keymap,
then the function is really a keymap.
If symbol already has a non-nil function definition that
is not an autoload object, autoload does nothing and returns
nil. If the function cell of symbol is void, or is already
an autoload object, then it is set to an autoload object that looks like
this:
(autoload filename docstring interactive type)
For example,
(symbol-function 'run-prolog)
=> (autoload "prolog" 169681 t nil)
In this case, "prolog" is the name of the file to load, 169681 refers
to the documentation string in the `emacs/etc/DOC'
file (see section Documentation Basics), t means the function is
interactive, and nil that it is not a macro.
You may load a file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file in which it is located.
When you load or reload files, bear in mind that the load and
load-library functions automatically load a byte-compiled file
rather than a non-compiled file of similar name. If you rewrite a file
that you intend to save and reinstall, remember to byte-compile it if
necessary; otherwise you may find yourself inadvertently reloading the
older, byte-compiled file instead of your newer, non-compiled file!
When writing the forms in a library, keep in mind that the library
might be loaded more than once. For example, the choice of
defvar vs. defconst for defining a variable depends on
whether it is desirable to reinitialize the variable if the library is
reloaded: defconst does so, and defvar does not.
(See section Defining Global Variables.)
The simplest way to add an element to an alist is like this:
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist))
But this would add multiple elements if the library is reloaded. To avoid the problem, write this:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
Occasionally you will want to test explicitly whether a library has already been loaded; you can do so as follows:
(if (not (boundp 'foo-was-loaded))
execute-first-time-only)
(setq foo-was-loaded t)
provide and require are an alternative to
autoload for loading files automatically. They work in terms of
named features. Autoloading is triggered by calling a specific
function, but a feature is loaded the first time another program asks
for it by name.
The use of named features simplifies the task of determining whether required definitions have been defined. A feature name is a symbol that stands for a collection of functions, variables, etc. A program that needs the collection may ensure that they are defined by requiring the feature. If the file that contains the feature has not yet been loaded, then it will be loaded (or an error will be signaled if it cannot be loaded). The file thus loaded must provide the required feature or an error will be signaled.
To require the presence of a feature, call require with the
feature name as argument. require looks in the global variable
features to see whether the desired feature has been provided
already. If not, it loads the feature from the appropriate file. This
file should call provide at the top-level to add the feature to
features.
Features are normally named after the files they are provided in
so that require need not be given the file name.
For example, in `emacs/lisp/prolog.el',
the definition for run-prolog includes the following code:
(defun run-prolog () "Run an inferior Prolog process,\ input and output via buffer *prolog*." (interactive) (require 'comint) (switch-to-buffer (make-comint "prolog" prolog-program-name)) (inferior-prolog-mode))
The expression (require 'shell) loads the file `shell.el' if
it has not yet been loaded. This ensures that make-shell is
defined.
The `shell.el' file contains the following top-level expression:
(provide 'shell)
This adds shell to the global features list when the
`shell' file is loaded, so that (require 'shell) will
henceforth know that nothing needs to be done.
When require is used at top-level in a file, it takes effect if
you byte-compile that file (see section Byte Compilation). This is in case
the required package contains macros that the byte compiler must know
about.
Although top-level calls to require are evaluated during
byte compilation, provide calls are not. Therefore, you can
ensure that a file of definitions is loaded before it is byte-compiled
by including a provide followed by a require for the same
feature, as in the following example.
(provide 'my-feature) ; Ignored by byte compiler,
; evaluated by load.
(require 'my-feature) ; Evaluated by byte compiler.
Function: provide feature
This function announces that feature is now loaded, or being loaded, into the current Emacs session. This means that the facilities associated with feature are or will be available for other Lisp programs.
The direct effect of calling provide is to add feature to
the front of the list features if it is not already in the list.
The argument feature must be a symbol. provide returns
feature.
features
=> (bar bish)
(provide 'foo)
=> foo
features
=> (foo bar bish)
During autoloading, if the file is not completely loaded (due to an
error in the evaluation of the contents) any function definitions or
provide calls that occurred during the load are undone.
See section Autoload.
Function: require feature &optional filename
This function checks whether feature is present in the current
Emacs session (using (featurep feature); see below). If it
is not, then require loads filename with load. If
filename is not supplied, then the name of the symbol
feature is used as the file name to load.
If feature is not provided after the file has been loaded, Emacs
will signal the error error (with data `Required feature
feature was not provided').
Function: featurep feature
This function returns t if feature has been provided in the
current Emacs session (i.e., feature is a member of
features.)
Variable: features
The value of this variable is a list of symbols that are the features
loaded in the current Emacs session. Each symbol was put in this list
with a call to provide. The order of the elements in the
features list is not significant.
You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects. To do this, use the function
unload-feature:
Command: unload-feature feature
This command unloads the library that provided feature feature.
It undefines all functions and variables defined with defvar,
defmacro, defconst, defsubst and
defalias by the library which provided feature
feature. It then restores any autoloads associated with those
symbols.
The unload-feature function is written in Lisp; its actions are
based on the variable load-history.
Variable: load-history feature association list
This variable's value is an alist connecting library names with the names of functions and variables they define, the features they provide, and the features they require.
Each element is a list and describes one library. The CAR of the list is the name of the library, as a string. The rest of the list is composed of these kinds of objects:
(require . feature) indicating the
features that are required.
(provide . feature) indicating the
features that are provided.
The value of load-history may have one element whose CAR is
nil. This element describes definitions made with
eval-buffer on a buffer that is not visiting a file.
The command eval-region updates load-history, but does so
by adding the symbols defined to the element for the file being visited,
rather than replacing that element.
You can ask for code to be executed if and when a particular library is
loaded, by calling eval-after-load.
Function: eval-after-load library form
This function arranges to evaluate form at the end of loading the library library, if and when library is loaded.
The library name library must exactly match the argument of
load. To get the proper results when an installed library is
found by searching load-path, you should not include any
directory names in library.
An error in form does not undo the load, but does prevent execution of the rest of form.
Variable: after-load-alist
An alist of expressions to evaluate if and when particular libraries are loaded. Each element looks like this:
(filename forms...)
The function load checks after-load-alist in order to
implement eval-after-load.
GNU Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.
Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code.
In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true. In particular, if you compile a program with Emacs 18, you can run the compiled code in Emacs 19, but not vice versa.
See section Debugging Problems in Compilation, for how to investigate errors occurring in byte compilation.
You can byte-compile an individual function or macro definition with
the byte-compile function. You can compile a whole file with
byte-compile-file, or several files with
byte-recompile-directory or batch-byte-compile.
When you run the byte compiler, you may get warnings in a buffer called `*Compile-Log*'. These report usage in your program that suggest a problem, but are not necessarily erroneous.
Be careful when byte-compiling code that uses macros. Macro calls are expanded when they are compiled, so the macros must already be defined for proper compilation. For more details, see section Macros and Byte Compilation.
While byte-compiling a file, any require calls at top-level are
executed. One way to ensure that necessary macro definitions are
available during compilation is to require the file that defines them.
See section Features.
A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. For a rough comparison, consider the example below:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(silly-loop 100000)
=> ("Thu Jan 12 20:18:38 1989"
"Thu Jan 12 20:19:29 1989") ; 51 seconds
(byte-compile 'silly-loop)
=> [Compiled code not shown]
(silly-loop 100000)
=> ("Thu Jan 12 20:21:04 1989"
"Thu Jan 12 20:21:17 1989") ; 13 seconds
In this example, the interpreted code required 51 seconds to run, whereas the byte-compiled code required 13 seconds. These results are representative, but actual results will vary greatly.
Function: byte-compile symbol
This function byte-compiles the function definition of symbol,
replacing the previous definition with the compiled one. The function
definition of symbol must be the actual code for the function;
i.e., the compiler does not follow indirection to another symbol.
byte-compile does not compile macros. byte-compile
returns the new, compiled definition of symbol.
(defun factorial (integer)
"Compute factorial of INTEGER."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(byte-compile 'factorial)
=>
#[(integer)
"^H\301U\203^H^@\301\207\302^H\303^HS!\"\207"
[integer 1 * factorial]
4 "Compute factorial of INTEGER."]
The result is a compiled function object. The string it contains is the actual byte-code; each character in it is an instruction. The vector contains all the constants, variable names and function names used by the function, except for certain primitives that are coded as special instructions.
Command: compile-defun
This command reads the defun containing point, compiles it, and evaluates the result. If you use this on a defun that is actually a function definition, the effect is to install a compiled version of that function.
Command: byte-compile-file filename
This function compiles a file of Lisp code named filename into a file of byte-code. The output file's name is made by appending `c' to the end of filename.
Compilation works by reading the input file one form at a time. If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read.
This command returns t. When called interactively, it prompts
for the file name.
% ls -l push*
-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
(byte-compile-file "~/emacs/push.el")
=> t
% ls -l push*
-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
-rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc
Command: byte-recompile-directory directory flag
This function recompiles every `.el' file in directory that needs recompilation. A file needs recompilation if a `.elc' file exists but is older than the `.el' file.
If a `.el' file exists, but there is no corresponding `.elc'
file, then flag is examined. If it is nil, the file is
ignored. If it is non-nil, the user is asked whether the file
should be compiled.
The returned value of this command is unpredictable.
Function: batch-byte-compile
This function runs byte-compile-file on the files remaining on
the command line. This function must be used only in a batch execution
of Emacs, as it kills Emacs on completion. An error in one file does
not prevent processing of subsequent files. (The file which gets the
error will not, of course, produce any compiled code.)
% emacs -batch -f batch-byte-compile *.el
Function: byte-code code-string data-vector max-stack
This function actually interprets byte-code. A byte-compiled function
is actually defined with a body that calls byte-code. Don't call
this function yourself. Only the byte compiler knows how to generate
valid calls to this function.
In newer Emacs versions (19 and up), byte-code is usually executed as
part of a compiled function object, and only rarely as part of a call to
byte-code.
These features permit you to write code to be evaluated during compilation of a program.
Special Form: eval-and-compile body
This form marks body to be evaluated both when you compile the containing code and when you run it (whether compiled or not).
You can get a similar result by putting body in a separate file
and referring to that file with require. Using require is
preferable if there is a substantial amount of code to be executed in
this way.
Special Form: eval-when-compile body
This form marks body to be evaluated at compile time only. The result of evaluation by the compiler becomes a constant which appears in the compiled program. When the program is interpreted, not compiled at all, body is evaluated normally.
At top-level, this is analogous to the Common Lisp idiom
(eval-when (compile) ...). Elsewhere, the Common Lisp
`#.' reader macro (but not when interpreting) is closer to what
eval-when-compile does.
Byte-compiled functions have a special data type: they are byte-code function objects.
Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. The printed representation for a byte-code function object is like that for a vector, with an additional `#' before the opening `['.
In Emacs version 18, there was no byte-code function object data type;
compiled functions used the function byte-code to run the byte
code.
A byte-code function object must have at least four elements; there is no maximum number, but only the first six elements are actually used. They are:
nil. For functions
preloaded before Emacs is dumped, this is usually an integer which is an
index into the `DOC' file; use documentation to convert this
into a string (see section Access to Documentation Strings).
nil for a function that isn't interactive.
Here's an example of a byte-code function object, in printed
representation. It is the definition of the command
backward-sexp.
#[(&optional arg) "^H\204^F^@\301^P\302^H[!\207" [arg 1 forward-sexp] 2 254435 "p"]
The primitive way to create a byte-code object is with
make-byte-code:
Function: make-byte-code &rest elements
This function constructs and returns a byte-code function object with elements as its elements.
You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte-compiler to create these objects; it, we hope, always makes the elements consistent.
You can access the elements of a byte-code object using aref;
you can also use vconcat to create a vector with the same
elements.
People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into humanly readable form.
The byte-code interpreter is implemented as a simple stack machine. Values get stored by being pushed onto the stack, and are popped off and manipulated, the results being pushed back onto the stack. When a function returns, the top of the stack is popped and returned as the value of the function.
In addition to the stack, values used during byte-code execution can be stored in ordinary Lisp variables. Variable values can be pushed onto the stack, and variables can be set by popping the stack.
Command: disassemble object &optional stream
This function prints the disassembled code for object. If
stream is supplied, then output goes there. Otherwise, the
disassembled code is printed to the stream standard-output. The
argument object can be a function name or a lambda expression.
As a special exception, if this function is used interactively, it outputs to a buffer named `*Disassemble*'.
Here are two examples of using the disassemble function. We
have added explanatory comments to help you relate the byte-code to the
Lisp source; these do not appear in the output of disassemble.
These examples show unoptimized byte-code. Nowadays byte-code is
usually optimized, but we did not want to rewrite these examples, since
they still serve their purpose.
(defun factorial (integer)
"Compute factorial of an integer."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(factorial 4)
=> 24
(disassemble 'factorial)
-| byte-code for factorial:
doc: Compute factorial of an integer.
args: (integer)
0 constant 1 ; Push 1 onto stack.
1 varref integer ; Get value of integer
; from the environment
; and push the value
; onto the stack.
2 eqlsign ; Pop top two values off stack,
; compare them,
; and push result onto stack.
3 goto-if-nil 10 ; Pop and test top of stack;
; if nil, go to 10,
; else continue.
6 constant 1 ; Push 1 onto top of stack.
7 goto 17 ; Go to 17 (in this case, 1 will be
; returned by the function).
10 constant * ; Push symbol * onto stack.
11 varref integer ; Push value of integer onto stack.
12 constant factorial ; Push factorial onto stack.
13 varref integer ; Push value of integer onto stack.
14 sub1 ; Pop integer, decrement value,
; push new value onto stack.
; Stack now contains:
; - decremented value of integer
; - factorial
; - value of integer
; - *
15 call 1 ; Call function factorial using
; the first (i.e., the top) element
; of the stack as the argument;
; push returned value onto stack.
; Stack now contains:
; - result of result of recursive
; call to factorial
; - value of integer
; - *
16 call 2 ; Using the first two
; (i.e., the top two)
; elements of the stack
; as arguments,
; call the function *,
; pushing the result onto the stack.
17 return ; Return the top element
; of the stack.
=> nil
The silly-loop function is somewhat more complex:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(disassemble 'silly-loop)
-| byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0 constant current-time-string ; Push
; current-time-string
; onto top of stack.
1 call 0 ; Call current-time-string
; with no argument,
; pushing result onto stack.
2 varbind t1 ; Pop stack and bind t1
; to popped value.
3 varref n ; Get value of n from
; the environment and push
; the value onto the stack.
4 sub1 ; Subtract 1 from top of stack.
5 dup ; Duplicate the top of the stack;
; i.e. copy the top of
; the stack and push the
; copy onto the stack.
6 varset n ; Pop the top of the stack,
; and bind n to the value.
; In effect, the sequence dup varset
; copies the top of the stack
; into the value of n
; without popping it.
7 constant 0 ; Push 0 onto stack.
8 gtr ; Pop top two values off stack,
; test if n is greater than 0
; and push result onto stack.
9 goto-if-nil-else-pop 17 ; Goto 17 if n > 0
; else pop top of stack
; and continue
; (this exits the while loop).
12 constant nil ; Push nil onto stack
; (this is the body of the loop).
13 discard ; Discard result of the body
; of the loop (a while loop
; is always evaluated for
; its side effects).
14 goto 3 ; Jump back to beginning
; of while loop.
17 discard ; Discard result of while loop
; by popping top of stack.
18 varref t1 ; Push value of t1 onto stack.
19 constant current-time-string ; Push
; current-time-string
; onto top of stack.
20 call 0 ; Call current-time-string again.
21 list2 ; Pop top two elements off stack,
; create a list of them,
; and push list onto stack.
22 unbind 1 ; Unbind t1 in local environment.
23 return ; Return value of the top of stack.
=> nil
There are three ways to investigate a problem in an Emacs Lisp program, depending on what you are doing with the program when the problem appears.
Another useful debugging tool is a dribble file. When a dribble file is open, Emacs copies all keyboard input characters to that file. Afterward, you can examine the file to find out what input was used. See section Terminal Input.
For debugging problems in terminal descriptions, the
open-termscript function can be useful. See section Terminal Output.
The Lisp debugger provides you with the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See section Recursive Editing.
The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error.
However, entry to the debugger is not a normal consequence of an
error. Many commands frequently get Lisp errors when invoked in
inappropriate contexts (such as C-f at the end of the buffer) and
during ordinary editing it would be very unpleasant to enter the
debugger each time this happens. If you want errors to enter the
debugger, set the variable debug-on-error to non-nil.
User Option: debug-on-error
This variable determines whether the debugger is called when a error is
signaled and not handled. If debug-on-error is t, all
errors call the debugger. If it is nil, none call the debugger.
The value can also be a list of error conditions that should call the
debugger. For example, if you set it to the list
(void-variable), then only errors about a variable that has no
value invoke the debugger.
To debug an error that happens during loading of the `.emacs'
file, use the option `-debug-init', which binds
debug-on-error to t while `.emacs' is loaded.
If your `.emacs' file sets debug-on-error, the effect
lasts only until the end of loading `.emacs'. (This is an
undesirable by-product of the `-debug-init' feature.) If you want
`.emacs' to set debug-on-error permanently, use
after-init-hook, like this:
(add-hook 'after-init-hook
'(lambda () (setq debug-on-error t)))
When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes quit.
Ordinary quitting gives no information about why the program was
looping. To get more information, you can set the variable
debug-on-quit to non-nil. Quitting with C-g is not
considered an error, and debug-on-error has no effect on the
handling of C-g. Contrariwise, debug-on-quit has no effect
on errors.
Once you have the debugger running in the middle of the infinite loop, you can proceed from the debugger using the stepping commands. If you step through the entire loop, you will probably get enough information to solve the problem.
User Option: debug-on-quit
This variable determines whether the debugger is called when quit
is signaled and not handled. If debug-on-quit is non-nil,
then the debugger is called whenever you quit (that is, type C-g).
If debug-on-quit is nil, then the debugger is not called
when you quit. See section Quitting.
To investigate a problem that happens in the middle of a program, one useful technique is to cause the debugger to be entered when a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.
Command: debug-on-entry function-name
This function requests function-name to invoke the debugger each time
it is called. It works by inserting the form (debug 'debug) into
the function definition as the first form.
Any function defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. Even functions that are commands may be debugged--they will enter the debugger when called inside a function, or when called interactively (after the reading of the arguments). Primitive functions (i.e., those written in C) may not be debugged.
When debug-on-entry is called interactively, it prompts
for function-name in the minibuffer.
Caveat: if debug-on-entry is called more than once on the same
function, the second call does nothing. If you redefine a function
after using debug-on-entry on it, the code to enter the debugger
is lost.
debug-on-entry returns function-name.
(defun fact (n)
(if (zerop n) 1
(* n (fact (1- n)))))
=> fact
(debug-on-entry 'fact)
=> fact
(fact 3)
=> 6
------ Buffer: *Backtrace* ------
Entering:
* fact(3)
eval-region(4870 4878 t)
byte-code("...")
eval-last-sexp(nil)
(let ...)
eval-insert-last-sexp(nil)
* call-interactively(eval-insert-last-sexp)
------ Buffer: *Backtrace* ------
(symbol-function 'fact)
=> (lambda (n)
(debug (quote debug))
(if (zerop n) 1 (* n (fact (1- n)))))
Command: cancel-debug-on-entry function-name
This function undoes the effect of debug-on-entry on
function-name. When called interactively, it prompts for
function-name in the minibuffer.
If cancel-debug-on-entry is called more than once on the same
function, the second call does nothing. cancel-debug-on-entry
returns function-name.
You can cause the debugger to be called at a certain point in your
program by writing the expression (debug) at that point. To do
this, visit the source file, insert the text `(debug)' at the
proper place, and type C-M-x. Be sure to undo this insertion
before you save the file!
The place where you insert `(debug)' must be a place where an
additional form can be evaluated and its value ignored. (If the value
isn't ignored, it will alter the execution of the program!) Usually
this means inside a progn or an implicit progn
(see section Sequencing).
When the debugger is entered, it displays the previously selected buffer in one window and a buffer named `*Backtrace*' in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error).
The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (see section Recursive Editing) and it is wise to go back to the backtrace buffer and exit the debugger (with the q command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer.
The contents of the backtrace buffer show you the functions that are executing and the arguments that were given to them. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function. The frame whose line point is on is considered the current frame.) Some of the debugger commands operate on the current frame.
The debugger itself should always be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.
Inside the debugger (in Debugger mode), these special commands are available in addition to the usual cursor motion commands. (Keep in mind that all the usual facilities of Emacs, such as switching windows or buffers, are still available.)
The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source file for the function and type C-M-x on its definition.)
Continuing is possible after entry to the debugger due to function entry or exit, explicit invocation, quitting or certain errors. Most errors cannot be continued; trying to continue an unsuitable error causes the same error to occur again.
The stack frame made for the function call which enters the debugger in this way will be flagged automatically so that the debugger will be called again when the frame is exited. You can use the u command to cancel this flag.
If the debugger was entered due to a C-g but you really want to quit, and not debug, use the q command.
The r command makes a difference when the debugger was invoked due to exit from a Lisp call frame (as requested with b); then the value specified in the r command is used as the value of that frame.
You can't use r when the debugger was entered due to an error.
Here we describe fully the function used to invoke the debugger.
Function: debug &rest debugger-args
This function enters the debugger. It switches buffers to a buffer named `*Backtrace*' (or `*Backtrace*<2>' if it is the second recursive entry to the debugger, etc.), and fills it with information about the stack of Lisp function calls. It then enters a recursive edit, leaving that buffer in Debugger mode and displayed in the selected window.
Debugger mode provides a c command which operates by exiting the
recursive edit, switching back to the previous buffer, and returning to
whatever called debug. The r command also returns from
debug. These are the only ways the function debug can
return to its caller.
If the first of the debugger-args passed to debug is
nil (or if it is not one of the following special values), then
the rest of the arguments to debug are printed at the top of the
`*Backtrace*' buffer. This mechanism is used to display a message
to the user.
However, if the first argument passed to debug is one of the
following special values, then it has special significance. Normally,
these values are passed to debug only by the internals of Emacs
and the debugger, and not by programmers calling debug.
The special values are:
lambda
lambda, the debugger displays
`Entering:' as a line of text at the top of the buffer. This means
that a function is being entered when debug-on-next-call is
non-nil.
debug
debug, the debugger displays
`Entering:' just as in the lambda case. However,
debug as the argument indicates that the reason for entering the
debugger is that a function set to debug on entry is being entered.
In addition, debug as the first argument directs the debugger
to mark the function that called debug so that it will invoke the
debugger when exited. (When lambda is the first argument, the
debugger does not do this, because it has already been done by the
interpreter.)
t
t, the debugger displays the following
as the top line in the buffer:
Beginning evaluation of function call form:
This indicates that it was entered due to the evaluation of a list form
at a time when debug-on-next-call is non-nil.
exit
exit, it indicates the exit of a
stack frame previously marked to invoke the debugger on exit. The
second argument given to debug in this case is the value being
returned from the frame. The debugger displays `Return value:' on
the top line of the buffer, followed by the value being returned.
error
error, the debugger indicates that
it is being entered because an error or quit was signaled and not
handled, by displaying `Signaling:' followed by the error signaled
and any arguments to signal. For example,
(let ((debug-on-error t))
(/ 1 0))
------ Buffer: *Backtrace* ------
Signaling: (arith-error)
/(1 0)
...
------ Buffer: *Backtrace* ------
If an error was signaled, presumably the variable
debug-on-error is non-nil. If quit was signaled,
then presumably the variable debug-on-quit is non-nil.
nil
nil as the first of the debugger-args when you want
to enter the debugger explicitly. The rest of the debugger-args
are printed on the top line of the buffer. You can use this feature to
display messages--for example, to remind yourself of the conditions
under which debug is called.
This section describes functions and variables used internally by the debugger.
Variable: debugger
The value of this variable is the function to call to invoke the
debugger. Its value must be a function of any number of arguments (or,
more typically, the name of a function). Presumably this function will
enter some kind of debugger. The default value of the variable is
debug.
The first argument that Lisp hands to the function indicates why it
was called. The convention for arguments is detailed in the description
of debug.
Command: backtrace
This function prints a trace of Lisp function calls currently active.
This is the function used by debug to fill up the
`*Backtrace*' buffer. It is written in C, since it must have access
to the stack to determine which function calls are active. The return
value is always nil.
In the following example, backtrace is called explicitly in a
Lisp expression. When the expression is evaluated, the backtrace is
printed to the stream standard-output: in this case, to the
buffer `backtrace-output'. Each line of the backtrace represents
one function call. If the arguments of the function call are all known,
they are displayed; if they are being computed, that fact is stated.
The arguments of special forms are elided.
(with-output-to-temp-buffer "backtrace-output"
(let ((var 1))
(save-excursion
(setq var (eval '(progn
(1+ var)
(list 'testing (backtrace))))))))
=> nil
----------- Buffer: backtrace-output ------------
backtrace()
(list ...computing arguments...)
(progn ...)
eval((progn (1+ var) (list (quote testing) (backtrace))))
(setq ...)
(save-excursion ...)
(let ...)
(with-output-to-temp-buffer ...)
eval-region(1973 2142 #<buffer *scratch*>)
byte-code("... for eval-print-last-sexp ...")
eval-print-last-sexp(nil)
* call-interactively(eval-print-last-sexp)
----------- Buffer: backtrace-output ------------
The character `*' indicates a frame whose debug-on-exit flag is set.
Variable: debug-on-next-call
This variable determines whether the debugger is called before the
next eval, apply or funcall. It is automatically
reset to nil when the debugger is entered.
The d command in the debugger works by setting this variable.
Function: backtrace-debug level flag
This function sets the debug-on-exit flag of the eval frame
level levels down to flag. If flag is non-nil,
this will cause the debugger to be entered when that frame exits.
Even a nonlocal exit through that frame will enter the debugger.
The debug-on-exit flag is an entry in the stack frame of a function call. This flag is examined on every exit from a function.
Normally, this function is only called by the debugger.
Variable: command-debug-status
This variable records the debugging status of current interactive
command. Each time a command is called interactively, this variable is
bound to nil. The debugger can set this variable to leave
information for future debugger invocations during the same command.
The advantage of using this variable rather that defining another global variable is that the data will never carry over to a later other command invocation.
Function: backtrace-frame frame-number
The function backtrace-frame is intended for use in Lisp
debuggers. It returns information about what computation is happening
in the eval frame level levels down.
If that frame has not evaluated the arguments yet (or is a special
form), the value is (nil function arg-forms...).
If that frame has evaluated its arguments and called its function
already, the value is (t function
arg-values...).
In the return value, function is whatever was supplied as CAR
of evaluated list, or a lambda expression in the case of a macro
call. If the function has a &rest argument, that is represented
as the tail of the list arg-values.
If the argument is out of range, backtrace-frame returns
nil.
The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error "End of file during parsing" in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, "Invalid read syntax: ")"" indicates an excess close parenthesis or missing open parenthesis, but not where the missing parenthesis belongs. How, then, to find what to change?
If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases.
The first step is to find the defun that is unbalanced. If there is
an excess open parenthesis, the way to do this is to insert a
close parenthesis at the end of the file and type C-M-b
(backward-sexp). This will move you to the beginning of the
defun that is unbalanced. (Then type C-SPC C-_ C-u
C-SPC to set the mark there, undo the insertion of the
close parenthesis, and finally return to the mark.)
The next step is to determine precisely what is wrong. There is no way to be sure of this except to study the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves.
Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use C-M-e to move there, since that too will fail to work until the defun is balanced.
Then go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. It should not change anything, if the problem is really fixed.
To deal with an excess close parenthesis, first insert an open parenthesis at the beginning of the file and type C-M-f to find the end of the unbalanced defun. (Then type C-SPC C-_ C-u C-SPC to set the mark there, undo the insertion of the open parenthesis, and finally return to the mark.)
Then find the actual matching close parenthesis by typing C-M-f at the beginning of the defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity.
If you don't see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q, since the old indentation is probably appropriate to the intended parentheses.
When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the `*Compile-Log*' buffer, and then stops. The message may state a function name in which the error was found, or it may not. Regardless, here is how to find out where in the file the error occurred.
What you should do is switch to the buffer ` *Compiler Input*'. (Note that the buffer name starts with a space, so it does not show up in M-x list-buffers.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read.
If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was detected. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error.
If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, it can't localize the error precisely, but can still show you which function to check.
Edebug is a source-level debugger for Emacs Lisp programs that provides the following features:
The first three sections of this chapter should tell you enough about Edebug to enable you to use it.
To debug a Lisp program with Edebug, you must first prepare the Lisp functions that you want to debug. See section Preparing Functions for Edebug.
Once a function is prepared, any call to the function activates Edebug. This involves entering a recursive edit which is a level of Edebug activation.
Activating Edebug may stop execution and let you step through the function, or it may continue execution while checking for debugging commands, depending on the selected Edebug execution mode. See section Edebug Modes.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp function you are debugging. We call this the Edebug buffer---but note that it is not always the same buffer, and it is not reserved for Edebug use.
An arrow at the left margin indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.
If you prepare the definition of fac (shown below) for Edebug and
then execute (fac 3), here is what you normally see. Point is at
the open-parenthesis before if.
(defun fac (n)
=>-!-(if (< 0 n)
(* n (fac (1- n)))
1))
The places within a function where Edebug can stop execution are called
stop points. These occur both before and after each subexpression
that is a list, and also after each variable reference. Stop points
before variables are optional, under the control of the value of
edebug-stop-before-symbols. Here we show with periods the stop
points normally found in the function fac:
(defun fac (n)
.(if .(< 0 n.).
.(* n. .(fac (1- n.).).).
1).)
While a buffer is the Edebug buffer, the special commands of Edebug are available in it, instead of many usual editing commands. Type ? to display a list of Edebug commands. In particular, you can exit the innermost Edebug activation level with C-], and you can return all the way to top level with q.
For example, you can type the Edebug command SPC to execute until
the next stop point. If you type SPC once after entry to
fac, here is the state that you get:
(defun fac (n)
=>(if -!-(< 0 n)
(* n (fac (1- n)))
1))
When Edebug stops execution after an expression, it displays the expression's value in the echo area. Use the r command to display the value again later.
While Edebug is active, it catches all errors (if debug-on-error is
non-nil) and quits (if debug-on-quit is non-nil)
instead of the standard debugger. When this happens, Edebug displays the
last stop point that it knows about. This may be the location of a call
to a function which was not prepared for Edebug debugging, within which
the error actually occurred.
In order to use Edebug to debug a function, you must first prepare the function. Preparing a function inserts additional code into it which invokes Edebug at the proper places.
Any call to an Edebug-prepared function activates Edebug. This may or
may not stop execution, depending on the Edebug execution mode in use.
Some Edebug modes only update the display to indicate the progress of
the evaluation without stopping execution. The default initial Edebug
mode is step which does stop execution. See section Edebug Modes.
Once you have loaded Edebug, the command C-M-x is redefined so
that when used on a function or macro definition, it prepares the
function or macro if given a prefix argument. If the variable
edebug-all-defuns is non-nil, that inverts the meaning of
the prefix argument: then C-M-x prepares the function or macro
unless it has a prefix argument. The default value of
edebug-all-defuns is nil. The command M-x
edebug-all-defuns toggles the value of the variable
edebug-all-defuns.
If edebug-all-defuns is non-nil, then the commands
eval-region and eval-current-buffer also prepare any
functions and macros whose definitions they evaluate.
Loading a file does not prepare functions and macros for Edebug.
See section Evaluation for discussion of other evaluation functions available inside of Edebug.
Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug modes; do not confuse them with major modes or minor modes. The current Edebug mode determines how Edebug displays the progress of the evaluation, whether it stops at each stop point, or continues to the next breakpoint, for example.
Normally, you specify the Edebug mode for execution by typing a command to continue the program in a certain mode. Here is a table of these commands. All except for S resume execution of the program, at least for a certain distance.
In general, the execution modes earlier in the above list run the program more slowly or stop sooner.
When you enter a new Edebug level, the mode comes from the value of the
variable edebug-initial-mode. By default, this specifies
step mode. If the mode thus specified is not stop mode, then the
Edebug level executes the program (or part of it).
While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command that you typed. For example, typing t during execution switches to trace mode at the next stop point.
You can use the S command to stop execution without doing anything else.
If your function happens to read input, a character you hit intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.
Keyboard macros containing the commands in this section do not completely work: exiting from Edebug, to resume the program, loses track of the keyboard macro. This is not easy to fix.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
Be careful that the position C-M-f finds is a place that the
program will really get to; this may not be true in a
condition-case, for example.
This command does forward-sexp starting at point rather than the
stop point, thus providing more flexibility. If you want to execute one
expression from the current stop point, type w first, to move
point there.
This command does not exit the currently executing function unless you are positioned after the last sexp of the function.
If the program does a non-local exit, it may fail to reach the temporary breakpoint that this command sets.
One undesirable side effect of using edebug-step-in is that the
next time the stepped-into function is called, Edebug will be called
there as well.
The f command runs the program forward over one expression. More precisely, set a temporary breakpoint at the position that C-M-f would reach, then execute in go mode so that the program will stop at breakpoints. See section Breakpoints for the details on breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
Be careful that the position C-M-f finds is a place that the
program will really get to; this may not be true in a
condition-case, for example.
The f command uses the existing value of point as the basis for setting the breakpoint, because that is more flexible. To execute one expression from the current stop point, type w and then f.
The o command continues "out of" an expression. It places a temporary breakpoints at the end of the containing sexp. If the containing sexp is the top level defun, it continues until just before the function returns. If that is where you are now, it returns from the function and then stops.
This command does not exit the currently executing function unless you are positioned after the last sexp of the function.
The i command steps into the function about to be called. Use this command before any of the arguments of the function call are evaluated, since otherwise it is too late.
One undesirable side effect of using i is that the next time the stepped-into function is called, Edebug will be called there as well.
The h command proceeds to the stop point near where point is, using a temporary breakpoint.
All the commands in this section may fail to work as expected in case of nonlocal exit, because a nonlocal exit can bypass the temporary breakpoint where you expected the program to stop.
Some miscellaneous commands are described here.
You cannot use debugger commands in the backtrace buffer in Edebug as you would in the standard debugger.
The backtrace buffer is killed automatically when you continue execution.
While using Edebug, you can specify breakpoints in the program you are testing: points where execution should stop. You can set a breakpoint at any stop point, as defined in section Using Edebug---even before a symbol. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the Edebug buffer. Here are the Edebug commands for breakpoints:
nil value. If you use a prefix argument, the
breakpoint is temporary (it turns off the first time it stops the
program).
While in Edebug, you can set a breakpoint with b
(edebug-set-breakpoint) and unset one with u
(edebug-unset-breakpoint). First you must move point to a
position at or before the desired Edebug stop point, then hit the key to
change the breakpoint. Unsetting a breakpoint that has not been set
does nothing.
Reevaluating the function with edebug-defun clears all
breakpoints in the function.
A conditional breakpoint tests a condition each time the program gets there, to decide whether to stop. To set a conditional breakpoint, use x, and specify the condition expression in the minibuffer.
You can make both conditional and unconditional breakpoints temporary by using a prefix arg to the command to set the breakpoint. After breaking at a temporary breakpoint, it is automatically cleared.
Edebug always stops or pauses at a breakpoint except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B
(edebug-next-breakpoint) command, which moves point to the next
breakpoint in the function following point, or to the first breakpoint
if there are no following breakpoints. This command does not continue
execution--it just moves point in the buffer.
These Edebug commands let you view aspects of the buffer and window status that obtained before entry to Edebug.
edebug-save-windows
variable.
While within Edebug, you can evaluate expressions "as if" Edebug were not running. Edebug tries to be invisible to the expression's evaluation.
You can use the evaluation list buffer, called `*edebug*', to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug is reentered.
In the `*edebug*' buffer you can use the commands of Lisp Interaction as well as these special commands:
You can evaluate expressions in the evaluation list window with LFD or C-x C-e, just as you would in `*scratch*'; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost
when you continue execution of your function unless you add them to the
evaluation list with C-c C-u (edebug-update-eval-list).
This command builds a new list from the first expression of each
evaluation list group. Groups are separated by a line starting
with a comment.
When the evaluation list is redisplayed, each expression is displayed followed by the result of evaluating it, and a comment line. If an error occurs during an evaluation, the error message is displayed in a string as if it were the result. Therefore expressions that use variables not currently valid do not interrupt your debugging.
Here is an example of what the evaluation list window looks like after several expressions have been added to it:
(current-buffer) #<buffer *scratch*> ;--------------------------------------------------------------- (point-min) 1 ;--------------------------------------------------------------- (point-max) 2 ;--------------------------------------------------------------- edebug-outside-point-max "Symbol's value as variable is void: edebug-outside-point-max" ;--------------------------------------------------------------- (recursion-depth) 0 ;--------------------------------------------------------------- this-command eval-last-sexp ;---------------------------------------------------------------
To delete a group, move point into it and type C-c C-d
(edebug-delete-eval-item), or simply delete the text for it and
update the evaluation list with C-c C-u. When you add a new
group, be sure to add a comment at the beginning.
After selecting `*edebug*', you can return to the source code
buffer (the Edebug buffer) with C-c C-w. The *edebug*
buffer is killed when you continue execution of your function, and
recreated next time it is needed.
If the results of your expressions contain circular references to other parts of the same structure, you can print them more usefully with the `custom-print'.
To load the package and activate custom printing only for Edebug, simply
use the command edebug-install-custom-print-funcs. Then set the
variable print-circle to enable special handling of circular
structure. To restore the standard print functions, use
edebug-reset-print-funcs.
Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. In addition, most evaluations you do within Edebug (see section Evaluation) occur in the same outside context which is temporarily restored for the evaluation. This section explains precisely how use Edebug fails to be completely transparent.
Whenever Edebug is entered just to think about whether to take some action, it needs to save and restore certain data.
max-lisp-eval-depth and max-specpdl-size are both
incremented for each edebug-enter call so that your code should
not be impacted by Edebug frames on the stack.
When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from "outside" Edebug (see section Window Configurations). When you exit Edebug (by continuing the program), it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue Edebug, the program comes back into Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the "outside" configuration. What you see is the window configuration for within Edebug, with no interruption.
The window configuration proper does not include which buffer is current or where point and mark are in the current buffer, but Edebug saves and restores these also.
Entry to Edebug for displaying something also saves and restores the following data. (Some of these variables are deliberately not restored if an error or quit signal occurs.)
edebug-save-windows is non-nil.
edebug-save-displayed-buffer-points is non-nil.
overlay-arrow-position and
overlay-arrow-string are saved and restored. This permits
recursive use of Edebug, and use of Edebug while using GUD.
cursor-in-echo-area is locally bound to nil so that
the cursor shows up in the window.
When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:
last-command, this-command, last-command-char, and
last-input-char. Commands used within Edebug do not affect these
variables outside of Edebug.
But note that it is not possible to preserve the status reported by
(this-command-keys) and the variable unread-command-char.
standard-output and standard-input.
Edebug operation unavoidably alters some data in Emacs, and this can interfere with debugging certain programs.
max-lisp-eval-depth and max-specpdl-size, are also
increased proportionally.
this-command-keys is changed by
executing commands within Edebug and there appears to be no way to reset
the key sequence from Lisp.
unread-command-char
or unread-command-events. Entering Edebug while these variables
have nontrivial values can interfere with execution of the program you
are debugging.
command-history. In rare cases this can alter execution.
When Edebug prepares for stepping through an expression that uses a Lisp
macro, it needs additional advice to do the job properly. This is
because there is no way to tell which parts of the macro call are forms
to be evaluated. You must explain the format of calls to each macro to
enable Edebug to handle it. To do this, use def-edebug-form-spec
to define the format of calls to a given macro.
Macro: def-edebug-form-spec macro argpattern
Specify which parts of a call to macro macro are subexpressions to be evaluated. The second argument, argpattern, details what the argument list looks like.
Here is a table of the possibilities for argpattern and its subexpressions:
t
0
sexp
form
symbolp
integerp
stringp
vectorp
atom
function
function
nil.
'object
(patterns)
[patterns]
&optional
[&optional pattern].
&rest
&rest may appear at the same level of a
specification list, and &rest must not be followed by
&optional.
To specify repetition of certain types of arguments, followed by
dissimilar arguments, use [&rest patterns...].
&or
[...]. Only one &or may appear in a list, and it may
not be followed by &optional or &rest. One of the
alternatives must match, unless the &or is preceded by
&optional or &rest.
If the actual arguments of a macro call fail to match the specification, taking account of alternatives, optional arguments and repeated arguments, Edebug reports a syntax error in use of the macro.
The combination of backtracking, &optional, &rest,
&or, and [...] for grouping provides the equivalent of
regular expressions. The (...) lists require balanced
parentheses, which is the only context free (finite state with stack)
construct supported.
Here are some examples of using def-edebug-form-spec. First, for
the let special form:
(def-edebug-form-spec let
'((&rest
&or symbolp (symbolp &optional form))
&rest form))
Here's the spec for the for loop macro (see section Common Problems Using Macros) and for the case and do macros in `cl.el':
(def-edebug-form-spec for
'(symbolp 'from form 'to form 'do &rest form))
(def-edebug-form-spec case
'(form &rest (sexp form)))
(def-edebug-form-spec do
'((&rest &or symbolp (symbolp &optional form form))
(form &rest form)
&rest body))
Finally, the functions mapcar, mapconcat, mapatoms,
apply, and funcall all take function arguments, and Edebug
defines specifications for them. Here's one example:
(def-edebug-form-spec apply '(function &rest form))
The backquote (`) macro results in an expression that is not necessarily evaluated. Edebug cannot step through code generated by use of backquote.
These options affect the behavior of Edebug:
User Option: edebug-all-defuns
If non-nil, normal evaluation of defun and defmacro
forms prepares the functions and macros for stepping with Edebug. This
applies to eval-defun, eval-region and
eval-current-buffer.
The default value is nil.
User Option: edebug-stop-before-symbols
If non-nil, Edebug places stop points before symbols as well as
after.
This option takes effect for a function when you prepare it for stepping with Edebug. Changing the option's value during execution of Edebug has no effect on the functions already set up for Edebug execution.
User Option: edebug-save-windows
If non-nil, save and restore window configuration on Edebug calls.
It takes some time to save and restore, so if your program does not care
what happens to the window configurations, it is better to set this
variable to nil.
The default value is t.
User Option: edebug-save-point
If non-nil, Edebug saves and restores point and the mark in
source code buffers. The default value is t.
User Option: edebug-save-displayed-buffer-points
If non-nil, save and restore point in all buffers when entering
Edebug mode.
Saving and restoring point in other buffers is necessary if you are debugging code that changes the point of a buffer which is displayed in a non-selected window. If Edebug or the user then selects the window, the buffer's point will be changed to the window's point.
Saving and restoring is an expensive operation since it visits each window and each displayed buffer twice for each Edebug call, so it is best to avoid it if you can.
The default value is nil.
User Option: edebug-initial-mode
If this variable is non-nil, it specifies an Edebug mode to start
in each time the program enters a new Edebug recursive-edit level.
Possible values are step, go, Go-nonstop,
trace, Trace-fast, continue, and
Continue-fast.
The default value is step.
User Option: edebug-trace
Non-nil means display a trace of function entry and exit.
Tracing output is displayed in a buffer named `*edebug-trace*', one
function entry or exit per line, indented by the recursion level. You
can customize this display by replacing the functions
edebug-print-trace-entry and edebug-print-trace-exit.
The default value is nil.
Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in section Lisp Data Types.
This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing).
Reading a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
read syntax of the object. For example, reading the text `(a
. 5)' returns a cons cell whose CAR is a and whose
CDR is the number 5.
Printing a Lisp object means producing text that represents that object--converting the object to its printed representation. Printing the cons cell described above produces the text `(a . 5)'.
Reading and printing are more or less inverse operations: printing the
object that results from reading a given piece of text often produces
the same text, and reading the text that results from printing an object
usually produces a similar-looking object. For example, printing the
symbol foo produces the text `foo', and reading that text
returns the symbol foo. Printing a list whose elements are
a and b produces the text `(a b)', and reading that
text produces a list (but not the same list) with elements are a
and b.
However, these two operations are not precisely inverses. There are two kinds of exceptions:
Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream:
Occasionally function is called with one argument (always a character). When that happens, function should save the argument and arrange to return it on the next call. This is called unreading the character; it happens when the Lisp reader reads one character too many and want to "put it back where it came from".
t
t used as a stream means that the input is read from the
minibuffer. In fact, the minibuffer is invoked once and the text
given by the user is made into a string that is then used as the
input stream.
nil
nil used as a stream means that the value of
standard-input should be used instead; that value is the
default input stream, and must be a non-nil input stream.
Here is an example of reading from a stream which is a buffer, showing where point is located before and after:
---------- Buffer: foo ----------
This-!- is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
=> is
(read (get-buffer "foo"))
=> the
---------- Buffer: foo ----------
This is the-!- contents of foo.
---------- Buffer: foo ----------
Note that the first read skips a space at the beginning of the buffer. Reading skips any amount of whitespace preceding the significant text.
In Emacs 18, reading a symbol discarded the delimiter terminating the symbol. Thus, point would end up at the beginning of `contents' rather than after `the'. The Emacs 19 behavior is superior because it correctly handles input such as `bar(foo)' where the delimiter that ends one object is needed as the beginning of another object.
Here is an example of reading from a stream that is a marker,
initialized to point at the beginning of the buffer shown. The value
read is the symbol This.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
=> #<marker at 1 in foo>
(read m)
=> This
m
=> #<marker at 6 in foo> ;; After the first space.
Here we read from the contents of a string:
(read "(When in) the course")
=> (When in)
The following example reads from the minibuffer. The
prompt is: `Lisp expression: '. (That is always the prompt
used when you read from the stream t.) The user's input is shown
following the prompt.
(read t)
=> 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 RET
---------- Buffer: Minibuffer ----------
Finally, here is an example of a stream that is a function, named
useless-stream. Before we use the stream, we initialize the
variable useless-list to a list of characters. Then each call to
the function useless-stream obtains the next characters in the list
or unreads a character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))
=> (88 89 40 41)
(defun useless-stream (&optional unread)
(if unread
(setq useless-list (cons unread useless-list))
(prog1 (car useless-list)
(setq useless-list (cdr useless-list)))))
=> useless-stream
Now we read using the stream thus constructed:
(read 'useless-stream)
=> XY
useless-list
=> (41)
Note that the close parenthesis remains in the list. The reader has read it, discovered that it ended the input, and unread it. Another attempt to read from the stream at this point would get an error due to the unmatched close parenthesis.
Function: get-file-char
This function is used internally as an input stream to read from the
input file opened by the function load. Don't use this function
yourself.
This section describes the Lisp functions and variables that pertain to reading.
In the functions below, stream stands for an input stream (see
the previous section). If stream is nil or omitted, it
defaults to the value of standard-input.
An end-of-file error results if an unterminated list or
vector is found.
Function: read &optional stream
This function reads one textual Lisp expression from stream, returning it as a Lisp object. This is the basic Lisp input function.
Function: read-from-string string &optional start end
This function reads the first textual Lisp expression from the text in string. It returns a cons cell whose CAR is that expression, and whose CDR is an integer giving the position of the next remaining character in the string (i.e., the first one not read).
If start is supplied, then reading begins at index start in the string (where the first character is at index 0). If end is also supplied, then reading stops at that index as if the rest of the string were not there.
For example:
(read-from-string "(setq x 55) (setq y 5)")
=> ((setq x 55) . 11)
(read-from-string "\"A short string\"")
=> ("A short string" . 16)
;; Read starting at the first character.
(read-from-string "(list 112)" 0)
=> ((list 112) . 10)
;; Read starting at the second character.
(read-from-string "(list 112)" 1)
=> (list . 6)
;; Read starting at the seventh character,
;; and stopping at the ninth.
(read-from-string "(list 112)" 6 8)
=> (11 . 8)
Variable: standard-input
This variable holds the default input stream: the stream that
read uses when the stream argument is nil.
An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream:
t
nil
nil specified as an output stream means that the value of
standard-output should be used as the output stream; that value
is the default output stream, and must be a non-nil output
stream.
Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the `h' in `the'. At the end, point is located directly before that same `h'.
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
=> "This is the output"
---------- Buffer: foo ----------
This is t
"This is the output"
-!-he contents of foo.
---------- Buffer: foo ----------
Now we show a use of a marker as an output stream. Initially, the
marker points in buffer foo, between the `t' and the
`h' in the word `the'. At the end, the marker has been
advanced over the inserted text so that it still points before the same
`h'. Note that the location of point, shown in the usual fashion,
has no effect.
---------- Buffer: foo ----------
"This is the -!-output"
---------- Buffer: foo ----------
m
=> #<marker at 11 in foo>
(print "More output for foo." m)
=> "More output for foo."
---------- Buffer: foo ----------
"This is t
"More output for foo."
he -!-output"
---------- Buffer: foo ----------
m
=> #<marker at 35 in foo>
The following example shows output to the echo area:
(print "Echo Area output" t)
=> "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------
Finally, we show an output stream which is a function. The function
eat-output takes each character that it is given and conses it
onto the front of the list last-output (see section Building Cons Cells and Lists).
At the end, the list contains all the characters output, but in reverse
order.
(setq last-output nil)
=> nil
(defun eat-output (c)
(setq last-output (cons c last-output)))
=> eat-output
(print "This is the output" 'eat-output)
=> "This is the output"
last-output
=> (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:
(concat (nreverse last-output))
=> "
\"This is the output\"
"
This section describes the Lisp functions for printing Lisp objects.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are `\' and `"'; they are used to distinguish strings from symbols, and to prevent punctuation characters in strings and symbols from being taken as delimiters. See section Printed Representation and Read Syntax, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then it is best to print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is better to print without quoting.
Printing a self-referent Lisp object requires an infinite amount of text. In certain cases, trying to produce this text leads to a stack overflow. Emacs detects such recursion and prints `#level' instead of recursively printing an object already being printed. For example, here `#0' indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil))
=> (nil)
(setcar foo foo)
=> (#0)
In the functions below, stream stands for an output stream.
(See the previous section for a description of output streams.) If
stream is nil or omitted, it defaults to the value of
standard-output.
Function: print object &optional stream
The print is a convenient way of printing. It outputs the
printed representation of object to stream, printing in
addition one newline before object and another after it. Quoting
characters are used. print returns object. For example:
(progn (print 'The\ cat\ in)
(print "the hat")
(print " came back"))
-|
-| The\ cat\ in
-|
-| "the hat"
-|
-| " came back"
-|
=> " came back"
Function: prin1 object &optional stream
This function outputs the printed representation of object to
stream. It does not print any spaces or newlines to separate
output as print does, but it does use quoting characters just
like print. It returns object.
(progn (prin1 'The\ cat\ in)
(prin1 "the hat")
(prin1 " came back"))
-| The\ cat\ in"the hat"" came back"
=> " came back"
Function: princ object &optional stream
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people,
not by read, so quoting characters are not used and double-quotes
are not printed around the contents of strings. It does not add any
spacing between calls.
(progn
(princ 'The\ cat)
(princ " in the \"hat\""))
-| The cat in the "hat"
=> " in the \"hat\""
Function: terpri &optional stream
This function outputs a newline to stream. The name stands for "terminate print".
Function: write-char character &optional stream
This function outputs character to stream. It returns character.
Function: prin1-to-string object &optional noescape
This function returns a string containing the text that prin1
would have printed for the same argument.
(prin1-to-string 'foo)
=> "foo"
(prin1-to-string (mark-marker))
=> "#<marker at 2773 in strings.texi>"
If noescape is non-nil, that inhibits use of quoting
characters in the output. (This argument is supported in Emacs versions
19 and later.)
(prin1-to-string "foo")
=> "\"foo\""
(prin1-to-string "foo" t)
=> "foo"
See format, in section Conversion of Characters and Strings, for other ways to obtain
the printed representation of a Lisp object as a string.
Variable: standard-output
The value of this variable is the default output stream, used when the
stream argument is omitted or nil.
Variable: print-escape-newlines
If this variable is non-nil, then newline characters in strings
are printed as `\n'. Normally they are printed as actual newlines.
This variable affects the print functions prin1 and print,
as well as everything that uses them. It does not affect princ.
Here is an example using prin1:
(prin1 "a\nb")
-| "a
-| b"
=> "a
=> b"
(let ((print-escape-newlines t))
(prin1 "a\nb"))
-| "a\nb"
=> "a
=> b"
In the second expression, the local binding of
print-escape-newlines is in effect during the call to
prin1, but not during the printing of the result.
Variable: print-length
The value of this variable is the maximum number of elements of a list that will be printed. If the list being printed has more than this many elements, then it is abbreviated with an ellipsis.
If the value is nil (the default), then there is no limit.
(setq print-length 2)
=> 2
(print '(1 2 3 4 5))
-| (1 2 ...)
=> (1 2 ...)
Variable: print-level
The value of this variable is the maximum depth of nesting of
parentheses that will be printed. Any list or vector at a depth
exceeding this limit is abbreviated with an ellipsis. A value of
nil (which is the default) means no limit.
This variable exists in version 19 and later versions.
A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the screen, in the same place as the echo area, but only while it is in use for reading an argument.
In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ` *Minibuf-number', and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometime frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see section Minibuffers and Frames.)
The minibuffers window is normally a single line; you can resize it temporarily with the window sizing commands, but reverts to its normal size when the minibuffer is exited.
A recursive minibuffer may be created when there is an active
minibuffer and a command is invoked that requires input from a
minibuffer. The first minibuffer is named ` *Minibuf-0*'.
Recursive minibuffers are named by incrementing the number at the end of
the name. (The names begin with a space so that they won't show up in
normal buffer lists.) Of several recursive minibuffers, the innermost
(or most recently entered) is the active minibuffer. We usually call
this "the" minibuffer. You can permit or forbid recursive minibuffers
by setting the variable enable-recursive-minibuffers or by
putting properties of that name on command symbols (see section Minibuffer Miscellany).
Like other buffers, a minibuffer may use any of several local keymaps (see section Keymaps); these contain various exit commands and in some cases completion commands. See section Completion.
minibuffer-local-map is for ordinary input (no completion).
minibuffer-local-ns-map is similar, except that SPC exits
just like RET. This is used mainly for Mocklisp compatibility.
minibuffer-local-completion-map is for permissive completion.
minibuffer-local-must-match-map is for strict completion and
for cautious completion.
The minibuffer is usually used to read text which is returned as a
string, but can also be used to read a Lisp object in textual form. The
most basic primitive for minibuffer input is
read-from-minibuffer.
Function: read-from-minibuffer prompt-string &optional initial keymap read hist
This function is the most general way to get input through the
minibuffer. By default, it accepts arbitrary text and returns it as a
string; however, if read is non-nil, then it uses
read to convert the text into a Lisp object (see section Input Functions).
The first thing this function does is to activate a minibuffer and display it with prompt-string as the prompt. This value must be a string.
Then, if initial is a string; its contents are inserted into the minibuffer as initial contents. The text thus inserted is treated as if the user had inserted it; the user can alter it with Emacs editing commands.
The value of initial may also be a cons cell of the form
(string . position). This means to insert
string in the minibuffer but put the cursor position
characters from the beginning, rather than at the end.
If keymap is non-nil, that keymap is the local keymap to
use while reading. If keymap is omitted or nil, the value
of minibuffer-local-map is used as the keymap. Specifying a
keymap is the most important way to customize minibuffer input for
various applications including completion.
The argument hist specifies which history list variable to use
for saving the input and for history commands used in the minibuffer.
It defaults to minibuffer-history. See section Minibuffer History.
When the user types a command to exit the minibuffer, the current
minibuffer contents are usually made into a string which becomes the
value of read-from-minibuffer. However, if read is
non-nil, read-from-minibuffer converts the result to a
Lisp object, and returns that object, unevaluated.
Suppose, for example, you are writing a search command and want to
record the last search string and provide it as a default for the next
search. Suppose that the previous search string is stored in the
variable last-search-string. Here is how you can read a search
string while providing the previous string as initial input to be
edited:
(read-from-minibuffer "Find string: " last-search-string)
Assuming the value of last-search-string is `No', and
the user wants to search for `Nope', the interaction looks
like this:
(setq last-search-string "No")
(read-from-minibuffer "Find string: " last-search-string)
---------- Buffer: Minibuffer ----------
Find string: No-!-
---------- Buffer: Minibuffer ----------
;; The user now types pe RET:
=> "Nope"
This technique is no longer preferred for most applications; it is usually better to use a history list.
Function: read-string prompt &optional initial
This function reads a string from the minibuffer and returns it. The
arguments prompt and initial are used as in
read-from-minibuffer.
This is a simplified interface to the
read-from-minibuffer function:
(read-string prompt initial) == (read-from-minibuffer prompt initial nil nil)
Variable: minibuffer-local-map
This is the default local keymap for reading from the minibuffer. It is
the keymap used by the minibuffer for local bindings in the function
read-string. By default, it makes the following bindings:
exit-minibuffer
exit-minibuffer
abort-recursive-edit
next-history-element and previous-history-element
next-matching-history-element
previous-matching-history-element
Function: read-no-blanks-input prompt &optional initial
This function reads a string from the minibuffer, but does not allow
whitespace characters as part of the input: instead, those characters
terminate the input. The arguments prompt and initial are
used as in read-from-minibuffer.
This is a simplified interface to the read-from-minibuffer
function, and passes the value of the minibuffer-local-ns-map
keymap as the keymap argument for that function. Since the keymap
minibuffer-local-ns-map does not rebind C-q, it is
possible to put a space into the string, by quoting it.
(read-no-blanks-input prompt initial) == (read-from-minibuffer prompt initial minibuffer-local-ns-map)
Variable: minibuffer-local-ns-map
This built-in variable is the keymap used as the minibuffer local keymap
in the function read-no-blanks-input. By default, it makes the
following bindings:
exit-minibuffer
exit-minibuffer
exit-minibuffer
exit-minibuffer
abort-recursive-edit
self-insert-and-exit
next-history-element and previous-history-element
next-matching-history-element
previous-matching-history-element
This section describes functions for reading Lisp objects with the minibuffer.
Function: read-minibuffer prompt &optional initial
This function reads a Lisp object in the minibuffer and returns it,
without evaluating it. The arguments prompt and initial are
used as in read-from-minibuffer; in particular, initial
must be a string or nil.
This is a simplified interface to the
read-from-minibuffer function:
(read-minibuffer prompt initial) == (read-from-minibuffer prompt initial nil t)
Here is an example in which we supply the string "(testing)" as
initial input:
(read-minibuffer "Enter an expression: " (format "%s" '(testing))) ;; Here is how the minibuffer is displayed: ---------- Buffer: Minibuffer ---------- Enter an expression: (testing)-!- ---------- Buffer: Minibuffer ----------
The user can type RET immediately to use the initial input as a default, or can edit the input.
Function: eval-minibuffer prompt &optional initial
This function reads a Lisp expression in the minibuffer, evaluates it,
then returns the result. The arguments prompt and initial
are used as in read-from-minibuffer.
This function simply evaluates the result of a call to
read-minibuffer:
(eval-minibuffer prompt initial) == (eval (read-minibuffer prompt initial))
Function: edit-and-eval-command prompt form
This function reads a Lisp expression in the minibuffer, and then
evaluates it. The difference between this command and
eval-minibuffer is that here the initial form is not
optional and it is treated as a Lisp object to be converted to printed
representation rather than as a string of text. It is printed with
prin1, so if it is a string, double-quote characters (`"')
appear in the initial text. See section Output Functions.
The first thing edit-and-eval-command does is to activate the
minibuffer with prompt as the prompt. Then it inserts the printed
representation of form in the minibuffer, and lets the user edit.
When the user exits the minibuffer, the edited text is read with
read and then evaluated. The resulting value becomes the value
of edit-and-eval-command.
In the following example, we offer the user an expression with initial text which is a valid form already:
(edit-and-eval-command "Please edit: " '(forward-word 1)) ;; After evaluating the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Please edit: (forward-word 1)-!- ---------- Buffer: Minibuffer ----------
Typing RET right away would exit the minibuffer and evaluate the
expression, thus moving point forward one word.
edit-and-eval-command returns nil in this example.
A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. There are many separate history lists which contain different kinds of inputs. The Lisp programmer's job is to specify the right history list for each use of the minibuffer.
The basic minibuffer input functions read-from-minibuffer and
completing-read both accept an optional argument named hist
which is how you specify the history list. Here are the possible
values:
If you specify startpos, then you should also specify that element of the history as initial, for consistency.
If you don't specify hist, then the default history list
minibuffer-history is used. For other standard history lists,
see below. You can also create your own history list variable; just
initialize it to nil before the first use. The value of the
history list variable is a list of strings, most recent first.
Both read-from-minibuffer and completing-read add new
elements to the history list automatically, and provide commands to
allow the user to reuse items on the list. The only thing your program
needs to do to use a history list is to initialize it and to pass its
name to the input functions when you wish. But it is safe to modify the
list by hand when the minibuffer input functions are not using it.
Variable: minibuffer-history
The default history list for minibuffer history input.
Variable: query-replace-history
A history list for arguments to query-replace (and similar
arguments to other commands).
Variable: file-name-history
A history list for file name arguments.
Completion is a feature that fills in the rest of a name starting from an abbreviation for it. Completion works by comparing the user's input against a list of valid names and determining how much of the name is determined uniquely by what the user has typed.
For example, when you type C-x b (switch-to-buffer) and
then type the first few letters of the name of the buffer to which you
wish to switch, and then type TAB (minibuffer-complete),
Emacs extends the name as far as it can. Standard Emacs commands offer
completion for names of symbols, files, buffers, and processes; with the
functions in this section, you can implement completion for other kinds
of names.
The try-completion function is the basic primitive for
completion: it returns the longest determined completion of a given
initial string, with a given set of strings to match against.
The function completing-read provides a higher-level interface
for completion. A call to completing-read specifies how to
determine the list of valid names. The function then activates the
minibuffer with a local keymap that binds a few keys to commands useful
for completion. Other functions provide convenient simple interfaces
for reading certain kinds of names with completion.
Function: try-completion string collection &optional predicate
This function returns the longest common substring of all possible completions of string in collection. The value of collection must be an alist, an obarray, or a function which implements a virtual set of strings.
If collection is an alist (see section Association Lists),
completion compares the CAR of each cons cell in it against
string; if the beginning of the CAR equals string, the
cons cell matches. If no cons cells match, try-completion
returns nil. If only one cons cell matches, and the match is
exact, then try-completion returns t. Otherwise, the
value is the longest initial sequence common to all the matching strings
in the alist.
If collection is an obarray (see section Creating and Interning Symbols), the
names of all symbols in the obarray form the space of possible
completions. They are tested and used just like the CARs of the
elements of an association list. (The global variable obarray
holds an obarray containing the names of all interned Lisp symbols.)
Note that the only valid way to make a new obarray is to create it
empty and then add symbols to it one by one using intern.
Also, you cannot intern a given symbol in more than one obarray.
If the argument predicate is non-nil, then it must be a
function of one argument. It is used to test each possible match, and
the match is accepted only if predicate returns non-nil.
The argument given to predicate is either a cons cell from the alist
(the CAR of which is a string) or else it is a symbol (not a
symbol name) from the obarray.
It is also possible to use a function symbol as collection.
Then the function is solely responsible for performing completion;
try-completion returns whatever this function returns. The
function is called with three arguments: string, predicate
and nil. (The reason for the third argument is so that the same
function can be used in all-completions and do the appropriate
thing in either case.) See section Programmed Completion.
In the first of the following examples, the string `foo' is
matched by three of the alist CARs. All of the matches begin with
the characters `fooba', so that is the result. In the second
example, there is only one possible match, and it is exact, so the value
is t.
(try-completion
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))
=> "fooba"
(try-completion "foo" '(("barfoo" 2) ("foo" 3)))
=> t
In the following example, numerous symbols begin with the characters `forw', and all of them begin with the word `forward'. In most of the symbols, this is followed with a `-', but not in all, so no more than `forward' can be completed.
(try-completion "forw" obarray)
=> "forward"
Finally, in the following example, only two of the three possible
matches pass the predicate test (the string `foobaz' is
too short). Both of those begin with the string `foobar'.
(defun test (s)
(> (length (car s)) 6))
=> test
(try-completion
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
'test)
=> "foobar"
Function: all-completions string collection &optional predicate
This function returns a list of all possible completions, instead of
the longest substring they share. The parameters to this function are
the same as to try-completion.
If collection is a function, it is called with three
arguments: string, predicate and t, and
all-completions returns whatever the function returns.
See section Programmed Completion.
Here is an example, using the function test shown in the
example for try-completion:
(defun test (s)
(> (length (car s)) 6))
=> test
(all-completions
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
(function test))
=> ("foobar1" "foobar2")
Variable: completion-ignore-case
If the value of this variable is
non-nil, Emacs does not consider case significant in completion.
The two functions try-completion and all-completions
have nothing in themselves to do with minibuffers. However,
completion is most often used there, which is why it is described in
this chapter.
Sometimes it is not possible to create an alist or an obarray containing all the intended possible completions. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion.
To use this feature, pass a symbol with a function definition as the
collection argument to completing-read. This command
arranges to pass the function along to try-completion and
all-completions, which will then let your function do all the
work.
The completion function should accept three arguments:
nil if none.
Your function should call the predicate for each possible match and ignore
the possible match if the predicate returns nil.
There are three flag values for three operations:
nil specifies try-completion. The completion function
should return the completion of the specified string, or t if the
string is an exact match already, or nil if the string matches no
possibility.
t specifies all-completions. The completion function
should return a list of all possible completions of the specified
string.
lambda specifies a test for an exact match. The completion
function should return t if the specified string is an exact
match for some possibility; nil otherwise.
It would be consistent and clean for completion functions to allow lambda expressions (lists which are functions) as well as function symbols as collection, but this is impossible. Lists as completion tables are already assigned another meaning--as alists. It would be unreliable to fail to handle an alist normally because it is also a possible function. So you must arrange for any function you wish to use for completion to be encapsulated in a symbol.
Emacs uses programmed completion when completing file names. See section File Name Completion.
This section describes the basic interface for reading from the minibuffer with completion.
Function: completing-read prompt collection &optional predicate require-match initial hist
This function reads a string in the minibuffer, assisting the user by
providing completion. It activates the minibuffer with prompt
prompt, which must be a string. If initial is
non-nil, completing-read inserts it into the minibuffer as
part of the input. Then it allows the user to edit the input, providing
several commands to attempt completion.
The actual completion is done by passing collection and
predicate to the function try-completion. This happens in
certain commands bound in the local keymaps used for completion.
If require-match is t, the user is not allowed to exit
unless the input completes to an element of collection. If
require-match is neither nil nor t, then
completing-read does not exit unless the input typed is itself an
element of collection. To accomplish this, completing-read
calls read-minibuffer. It uses the value of
minibuffer-local-completion-map as the keymap if
require-match is nil, and uses
minibuffer-local-must-match-map if require-match is
non-nil.
The argument hist specifies which history list variable to use for
saving the input and for minibuffer history commands. It defaults to
minibuffer-history. See section Minibuffer History.
Case is ignored when comparing the input against the possible matches
if the built-in variable completion-ignore-case is
non-nil. See section Basic Completion Functions.
For example:
(completing-read
"Complete a foo: "
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
nil t "fo")
;; After evaluating the preceding expression,
;; the following appears in the minibuffer:
---------- Buffer: Minibuffer ----------
Complete a foo: fo-!-
---------- Buffer: Minibuffer ----------
If the user then types DEL DEL b RET,
completing-read returns barfoo.
The completing-read function binds three variables to pass
information to the commands which actually do completion. Here they
are:
minibuffer-completion-table
try-completion function.
minibuffer-completion-predicate
try-completion function.
minibuffer-completion-confirm
minibuffer-complete-and-exit function.
This section describes the keymaps, commands and user options used in the minibuffer to do completion.
Variable: minibuffer-local-completion-map
completing-read uses this value as the local keymap when an
exact match of one of the completions is not required. By default, this
keymap makes the following bindings:
minibuffer-completion-help
minibuffer-complete-word
minibuffer-complete
with other characters bound as in minibuffer-local-map.
Variable: minibuffer-local-must-match-map
completing-read uses this value as the local keymap when an
exact match of one of the completions is required. Therefore, no keys
are bound to exit-minibuffer, the command which exits the
minibuffer unconditionally. By default, this keymap makes the following
bindings:
minibuffer-completion-help
minibuffer-complete-word
minibuffer-complete
minibuffer-complete-and-exit
minibuffer-complete-and-exit
with other characters bound as in minibuffer-local-map.
Variable: minibuffer-completion-table
The value of this variable is the alist or obarray used for completion
in the minibuffer. This is the global variable that contains what
completing-read passes to try-completion. It is used by
all the minibuffer completion functions, such as
minibuffer-complete-word.
Variable: minibuffer-completion-predicate
This variable's value is the predicate that completing-read
passes to try-completion. The variable is also used by the other
minibuffer completion functions.
Command: minibuffer-complete-word
This function completes the minibuffer contents by at most a single
word. Even if the minibuffer contents have only one completion,
minibuffer-complete-word does not add any characters beyond the
first character that is not a word constituent. See section Syntax Tables.
Command: minibuffer-complete
This function completes the minibuffer contents as far as possible.
Command: minibuffer-complete-and-exit
This function completes the minibuffer contents, and exits if
confirmation is not required, i.e., if
minibuffer-completion-confirm is non-nil. If confirmation
is required, it is given by repeating this command immediately.
Variable: minibuffer-completion-confirm
When the value of this variable is non-nil, Emacs asks for
confirmation of a completion before exiting the minibuffer. The
function minibuffer-complete-and-exit checks the value of this
variable before it exits.
Command: minibuffer-completion-help
This function creates a list of the possible completions of the
current minibuffer contents. It works by calling all-completions
using the value of the variable minibuffer-completion-table as
the collection argument, and the value of
minibuffer-completion-predicate as the predicate argument.
The list of completions is displayed as text in a buffer named
`*Completions*'.
Function: display-completion-list completions
This function displays completions to the stream in
standard-output, usually a buffer. (See section Reading and Printing Lisp Objects, for more
information about streams.) The argument completions is normally
a list of completions just returned by all-completions, but it
does not have to be. Each element may be a symbol or a string, either
of which is simply printed, or a list of two strings, which is printed
as if the strings were concatenated.
This function is called by minibuffer-completion-help. The
most common way to use it is together with
with-output-to-temp-buffer, like this:
(with-output-to-temp-buffer " *Completions*"
(display-completion-list
(all-completions (buffer-string) my-alist)))
User Option: completion-auto-help
If this variable is non-nil, the completion commands
automatically display a list of possible completions whenever nothing
can be completed because the next character is not uniquely determined.
This section describes the higher-level convenient functions for reading certain sorts of names with completion.
Function: read-buffer prompt &optional default existing
This function reads the name of a buffer and returns it as a string.
The argument default is the default name to use, the value to
return if the user exits with an empty minibuffer. If non-nil,
it should be a string. It is mentioned in the prompt, but is not
inserted in the minibuffer as initial input.
If existing is non-nil, then the name specified must be
that of an existing buffer. The usual commands to exit the
minibuffer do not exit if the text is not valid, and RET does
completion to attempt to find a valid name. (However, default is
not checked for this; it is returned, whatever it is, if the user exits
with the minibuffer empty.)
In the following example, the user enters `minibuffer.t', and
then types RET. The argument existing is t, and the
only buffer name starting with the given input is
`minibuffer.texi', so that name is the value.
(read-buffer "Buffer name? " "foo" t)
;; After evaluating the preceding expression,
;; the following prompt appears,
;; with an empty minibuffer:
---------- Buffer: Minibuffer ----------
Buffer name? (default foo) -!-
---------- Buffer: Minibuffer ----------
;; The user types minibuffer.t RET.
=> "minibuffer.texi"
Function: read-command prompt
This function reads the name of a command and returns it as a Lisp
symbol. The argument prompt is used as in
read-from-minibuffer. Recall that a command is anything for
which commandp returns t, and a command name is a symbol
for which commandp returns t. See section Interactive Call.
(read-command "Command name? ") ;; After evaluating the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Command name? ---------- Buffer: Minibuffer ----------
If the user types forward-c RET, then this function returns
forward-char.
The read-command function is a simplified interface to the
completing-read function. It uses the commandp
predicate to allow only commands to be entered, and it uses the
variable obarray so as to be able to complete all extant Lisp
symbols:
(read-command prompt) == (intern (completing-read prompt obarray 'commandp t nil))
Function: read-variable prompt
This function reads the name of a user variable and returns it as a symbol.
(read-variable "Variable name? ") ;; After evaluating the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Variable name? -!- ---------- Buffer: Minibuffer ----------
If the user then types fill-p RET, read-variable will
return fill-prefix.
This function is similar to read-command, but uses the
predicate user-variable-p instead of commandp:
(read-variable prompt) == (intern (completing-read prompt obarray 'user-variable-p t nil))
Here is another high-level completion function, designed for reading a file name. It provides special features including automatic insertion of the default directory.
Function: read-file-name prompt &optional directory default existing initial
This function reads a file name in the minibuffer, prompting with
prompt and providing completion. If default is
non-nil, then the function returns default if the user just
types RET.
If existing is non-nil, then the name must refer to an
existing file; then RET performs completion to make the name valid
if possible, and then refuses to exit if it is not valid. If the value
of existing is neither nil nor t, then RET
also requires confirmation after completion.
The argument directory specifies the directory to use for completion of relative file names. Usually it is inserted in the minibuffer as initial input as well. It defaults to the current buffer's default directory.
If you specify initial, that is an initial file name to insert in
the buffer along with directory. In this case, point goes after
directory, before initial. The default for initial is
nil---don't insert any file name. To see what initial
does, try the command C-x C-v.
Here is an example:
(read-file-name "The file is ") ;; After evaluating the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/-!- ---------- Buffer: Minibuffer ----------
Typing manual TAB results in the following:
---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/manual.texi-!- ---------- Buffer: Minibuffer ----------
If the user types RET, read-file-name returns the string
"/gp/gnu/elisp/manual.texi".
User Option: insert-default-directory
This variable is used by read-file-name. Its value controls
whether read-file-name starts by placing the name of the default
directory in the minibuffer, plus the initial file name if any. If the
value of this variable is nil, then read-file-name does
not place any initial input in the minibuffer. In that case, the
default directory is still used for completion of relative file names,
but is not displayed.
For example:
;; Here the minibuffer starts out containing the default directory. (let ((insert-default-directory t)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is ~lewis/manual/-!- ---------- Buffer: Minibuffer ---------- ;; Here the minibuffer is empty and only the prompt ;; appears on its line. (let ((insert-default-directory nil)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is -!- ---------- Buffer: Minibuffer ----------
If you type a part of a symbol, and then type M-TAB
(lisp-complete-symbol), this command attempts to fill in as much
more of the symbol name as it can. Not only does this save typing, but
it can help you with the name of a symbol that you have partially
forgotten.
Command: lisp-complete-symbol
This function performs completion on the symbol name preceding point.
The name is completed against the symbols in the global variable
obarray, and characters from the completion are inserted into the
buffer, making the name longer. If there is more than one completion, a
list of all possible completions is placed in the `*Help*' buffer.
The bell rings if there is no possible completion in obarray.
If an open parenthesis immediately precedes the name, only symbols with function definitions are considered. (By reducing the number of alternatives, this may succeed in completing more characters.) Otherwise, symbols with either a function definition, a value, or at least one property are considered.
lisp-complete-symbol returns t if the symbol had an exact,
and unique, match; otherwise, it returns nil.
In the following example, the user has already inserted `(forwa'
into the buffer `foo.el'. The command lisp-complete-symbol
then completes the name to `(forward-'.
---------- Buffer: foo.el ----------
(forwa-!-
---------- Buffer: foo.el ----------
(lisp-complete-symbol)
=> nil
---------- Buffer: foo.el ----------
(forward--!-
---------- Buffer: foo.el ----------
This section describes functions used to ask the user a yes-or-no
question. The function y-or-n-p can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. yes-or-no-p is suitable for
more momentous questions, since it requires three or four characters to
answer.
Strictly speaking, yes-or-no-p uses the minibuffer and
y-or-n-p does not; but it seems best to describe them together.
Function: y-or-n-p prompt
This function asks the user a question, expecting input in the echo
area. It returns t if the user types y, nil if the
user types n. This function also accepts SPC to mean yes
and DEL to mean no. It accepts C-] to mean "quit", like
C-g, because the question might look like a minibuffer and for
that reason the user might try to use C-] to get out. The answer
is a single character, with no RET needed to terminate it. Upper
and lower case are equivalent.
"Asking the question" means printing prompt in the echo area, followed by the string `(y or n) '. If the input is not one of the expected answers (y, n, SPC, DEL, or something that quits), the function responds `Please answer y or n.', and repeats the request.
This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see section The Echo Area), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.
The meanings of answers, even `y' and `n', are not
hardwired. They are controlled by the keymap query-replace-map.
See section Replacement.
In the following example, the user first types q, which is invalid. At the next prompt the user types n.
(y-or-n-p "Do you need a lift? ") ;; After evaluating the preceding expression, ;; the following prompt appears in the echo area: ---------- Echo area ---------- Do you need a lift? (y or n) ---------- Echo area ---------- ;; If the user then types q, the following appears: ---------- Echo area ---------- Please answer y or n. Do you need a lift? (y or n) ---------- Echo area ---------- ;; When the user types a valid answer, ;; it is displayed after the question: ---------- Echo area ---------- Do you need a lift? (y or n) y ---------- Echo area ----------
Note that we show successive lines of echo area messages here. Only one actually appears on the screen at a time.
Function: yes-or-no-p prompt
This function asks the user a question, expecting input in minibuffer.
It returns t if the user enters `yes', nil if the
user types `no'. The user must type RET to finalize the
response. Upper and lower case are equivalent.
yes-or-no-p starts by displaying prompt in the echo area,
followed by `(yes or no) '. The user must type one of the
expected responses; otherwise, the function responds `Please answer
yes or no.', waits about two seconds and repeats the request.
yes-or-no-p requires more work from the user than
y-or-n-p and is appropriate for more crucial decisions.
Here is an example:
(yes-or-no-p "Do you really want to remove everything? ") ;; After evaluating the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
If the user first types y RET, which is invalid because this function demands the entire word `yes', it responds by displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
Function: map-y-or-n-p prompter actor list &optional help action-alist
This function, new in Emacs 19, asks the user a series of questions, reading a single-character answer in the echo area for each one.
The value of list specifies what varies from question to question
within the series. It should be either a list of objects or a generator
function. If it is a function, it should expect no arguments, and
should return either the next object or nil meaning there are no
more questions.
The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:
(format prompter object)
where object is the next object to ask about (as obtained from list).
If not a string, prompter should be a function of one argument (the next object to ask about) and should return the question text.
The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list.
If the argument help is given, it should be a list of this form:
(singular plural action)
where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does.
If you don't specify help, the default is ("object"
"objects" "act on").
Each time a question is asked, the user may enter y, Y, or
SPC to act on that object; n, N, or DEL to skip
that object; ! to act on all following objects; ESC or
q to exit (skip all following objects); . (period) to act on
the current object and then exit; or C-h to get help. These are
the same answers that query-replace accepts. The keymap
query-replace-map defines their meaning for map-y-or-n-p
as well as for query-replace; see section Replacement.
You can use action-alist to specify additional possible answers
and what they mean. It is an alist of elements of the form
(char function help), each of which defines one
additional answer. In this element, char is a character (the
answer); function is a function of one argument (an object from
list); help is a string.
When the user responds with char, map-y-or-n-p calls
function. If it returns non-nil, the object is considered
"acted upon", and map-y-or-n-p advances to the next object in
list. If it returns nil, the prompt is repeated for the
same object.
The return value of map-y-or-n-p is the number of objects acted on.
This section describes some basic functions and variables related to minibuffers.
Command: exit-minibuffer
This command exits the active minibuffer. It is normally bound to keys in minibuffer local keymaps.
Command: self-insert-and-exit
This command exits the active minibuffer after inserting the last
character typed on the keyboard (found in last-command-char;
see section Information from the Command Loop).
Command: previous-history-element n
This command replaces the minibuffer contents with the value of the nth previous (older) history element.
Command: next-history-element n
This command replaces the minibuffer contents with the value of the nth more recent history element.
Command: previous-matching-history-element pattern
This command replaces the minibuffer contents with the value of the previous (older) history element that matches pattern. At the time of printing, we have not made a final decision about how to get the pattern interactively or how to match it against history elements.
Command: next-matching-history-element pattern
This command replaces the minibuffer contents with the value of the next (newer) history element that matches pattern.
Variable: minibuffer-setup-hook
This is a normal hook that is run whenever the minibuffer is entered.
Variable: minibuffer-help-form
The current value of this variable is used to rebind help-form
locally inside the minibuffer (see section Help Functions).
Function: minibuffer-window &optional frame
This function returns the window that is used for the minibuffer. In Emacs 18, there is one and only one minibuffer window; this window always exists and cannot be deleted. In Emacs 19, each frame can have its own minibuffer, and this function returns the minibuffer window used for frame frame (which defaults to the currently selected frame).
Function: window-minibuffer-p window
This function returns non-nil if window is a minibuffer window.
It is not correct to determine whether a given window is a minibuffer by
comparing it with the result of (minibuffer-window), because
there can be more than one minibuffer window there is more than one
frame.
Function: minibuffer-window-active-p window
This function returns non-nil if window, assumed to be
a minibuffer window, is currently active.
Variable: minibuffer-scroll-window
If the value of this variable is non-nil, it should be a window
object. When the function scroll-other-window is called in the
minibuffer, it scrolls this window.
Finally, some functions and variables deal with recursive minibuffers (see section Recursive Editing):
Function: minibuffer-depth
This function returns the current depth of activations of the minibuffer, a nonnegative integer. If no minibuffers are active, it returns zero.
User Option: enable-recursive-minibuffers
If this variable is non-nil, you can invoke commands (such as
find-file) which use minibuffers even while in the minibuffer
window. Such invocation produces a recursive editing level for a new
minibuffer. The outer-level minibuffer is invisible while you are
editing the inner one.
This variable only affects invoking the minibuffer while the minibuffer window is selected. If you switch windows while in the minibuffer, you can always invoke minibuffer commands while some other window is selected.
If a command name has a property enable-recursive-minibuffers
which is non-nil, then the command can use the minibuffer to read
arguments even if it is invoked from the minibuffer. The minibuffer
command next-matching-history-element (normally bound to
M-s in the minibuffer) uses this feature.
When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them.
The first thing the command loop must do is read a key sequence, which
is a sequence of events that translates into a command. It does this by
calling the function read-key-sequence. Your Lisp code can also
call this function (see section Key Sequence Input). Lisp programs can also
do input at a lower level with read-event (see section Reading One Event) or discard pending input with discard-input
(see section Peeking and Discarding).
The key sequence is translated into a command through the currently
active keymaps. See section Key Lookup, for information on how this is done.
The result should be a keyboard macro or an interactively callable
function. If the key is M-x, then it reads the name of another
command, which is used instead. This is done by the command
execute-extended-command (see section Interactive Call).
Once the command is chosen, it must be executed, which includes
reading arguments to be given to it. This is done by calling
command-execute (see section Interactive Call). For commands written
in Lisp, the interactive specification says how to read the
arguments. This may use the prefix argument (see section Prefix Command Arguments) or may read with prompting in the minibuffer
(see section Minibuffers). For example, the command find-file has an
interactive specification which says to read a file name using
the minibuffer. The command's function body does not use the
minibuffer; if you call this command from Lisp code as a function, you
must supply the file name string as an ordinary Lisp function argument.
If the command is a string or vector (i.e., a keyboard macro) then
execute-kbd-macro is used to execute it. You can call this
function yourself (see section Keyboard Macros).
If a command runs away, typing C-g terminates its execution immediately. This is called quitting (see section Quitting).
Variable: pre-command-hook
The editor command loop runs this normal hook before each command.
Variable: post-command-hook
The editor command loop runs this normal hook after each command, and also when the command loop is entered, or reentered after an error or quit.
A Lisp function becomes a command when its body contains, at top
level, a form which calls the special form interactive. This
form does nothing when actually executed, but its presence serves as a
flag to indicate that interactive calling is permitted. Its argument
controls the reading of arguments for an interactive call.
interactive
This section describes how to write the interactive form that
makes a Lisp function an interactively-callable command.
Special Form: interactive arg-descriptor
This special form declares that the function in which it appears is a command, and that it may therefore be called interactively (via M-x or by entering a key sequence bound to it). The argument arg-descriptor declares the way the arguments to the command are to be computed when the command is called interactively.
A command may be called from Lisp programs like any other function, but then the arguments are supplied by the caller and arg-descriptor has no effect.
The interactive form has its effect because the command loop
(actually, its subroutine call-interactively) scans through the
function definition looking for it, before calling the function. Once
the function is called, all its body forms including the
interactive form are executed, but at this time
interactive simply returns nil without even evaluating its
argument.
There are three possibilities for the argument arg-descriptor:
nil; then the command is called with no
arguments. This leads quickly to an error if the command requires one
or more arguments.
(interactive "bFrobnicate buffer: ")
The code letter `b' says to read the name of an existing buffer, with completion. The buffer name is the sole argument passed to the command. The rest of the string is a prompt.
If there is a newline character in the string, it terminates the prompt. If the string does not end there, then the rest of the string should contain another code character and prompt, specifying another argument. You can specify any number of arguments in this way.
The prompt string can use `%' to include previous argument values
in the prompt. This is done using format (see section Formatting Strings). For example, here is how you could read the name of an
existing buffer followed by a new name to give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
If the first character in the string is `*', then an error is signaled if the buffer is read-only.
If the first character in the string is `@', and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run.
You can use `*' and `@' together; the order does not matter. Actual reading of arguments is controlled by the rest of the prompt string (starting with the first character that is not `*' or `@').
interactiveThe code character descriptions below contain a number of key words, defined here as follows:
completing-read
(see section Completion). ? displays a list of possible completions.
Here are the code character descriptions for use with interactive:
fboundp). Existing,
Completion, Prompt.
commandp). Existing,
Completion, Prompt.
default-directory (see section Operating System Environment).
Existing, Completion, Default, Prompt.
You can use `e' more than once in a single command's interactive specification. If the key sequence which invoked the command has n events with parameters, the nth `e' provides the nth list event. Events which are not lists, such as function keys and ASCII characters, do not count where `e' is concerned.
Even though `e' does not use a prompt string, you must follow it with a newline if it is not the last code character.
default-directory. Existing, Completion, Default,
Prompt.
This kind of input is used by commands such as describe-key and
global-set-key.
nil, then a
number is read as with n. Requires a number. Prompt.
user-variable-p). See section High-Level Completion Functions. Existing,
Completion, Prompt.
interactive
Here are some examples of interactive:
(defun foo1 () ;foo1takes no arguments, (interactive) ; just moves forward two words. (forward-word 2)) => foo1 (defun foo2 (n) ;foo2takes one argument, (interactive "p") ; which is the numeric prefix. (forward-word (* 2 n))) => foo2 (defun foo3 (n) ;foo3takes one argument, (interactive "nCount:") ; which is read with the Minibuffer. (forward-word (* 2 n))) => foo3 (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) => three-b (three-b "*scratch*" "declarations.texi" "*mail*") => nil
After the command loop has translated a key sequence into a
definition, it invokes that definition using the function
command-execute. If the definition is a function that is a
command, command-execute calls call-interactively, which
reads the arguments and calls the command. You can also call these
functions yourself.
Function: commandp object
Returns t if object is suitable for calling interactively;
that is, if object is a command. Otherwise, returns nil.
The interactively callable objects include strings and vectors (treated
as keyboard macros), lambda expressions that contain a top-level call to
interactive, byte-code function objects, autoload objects that
are declared as interactive (non-nil fourth argument to
autoload), and some of the primitive functions.
A symbol is commandp if its function definition is
commandp.
Keys and keymaps are not commands. Rather, they are used to look up commands (see section Keymaps).
See documentation in section Access to Documentation Strings, for a
realistic example of using commandp.
Function: call-interactively command &optional record-flag
This function calls the interactively callable function command, reading arguments according to its interactive calling specifications. An error is signaled if command cannot be called interactively (i.e., it is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands.
If record-flag is non-nil, then this command and its
arguments are unconditionally added to the list command-history.
Otherwise, the command is added only if it uses the minibuffer to read
an argument. See section Command History.
Function: command-execute command &optional record-flag
This function executes command as an editing command. The
argument command must satisfy the commandp predicate; i.e.,
it must be an interactively callable function or a string.
A string or vector as command is executed with
execute-kbd-macro. A function is passed to
call-interactively, along with the optional record-flag.
A symbol is handled by using its function definition in its place. A
symbol with an autoload definition counts as a command if it was
declared to stand for an interactively callable function. Such a
definition is handled by loading the specified library and then
rechecking the definition of the symbol.
Command: execute-extended-command prefix-argument
This function reads a command name from the minibuffer using
completing-read (see section Completion). Then it uses
command-execute to call the specified command. Whatever that
command returns becomes the value of execute-extended-command.
If the command asks for a prefix argument, the value
prefix-argument is supplied. If execute-extended-command
is called interactively, the current raw prefix argument is used for
prefix-argument, and thus passed on to whatever command is run.
execute-extended-command is the normal definition of M-x,
so it uses the string `M-x ' as a prompt. (It would be better
to take the prompt from the events used to invoke
execute-extended-command, but that is painful to implement.) A
description of the value of the prefix argument, if any, also becomes
part of the prompt.
(execute-extended-command 1)
---------- Buffer: Minibuffer ----------
M-x forward-word RET
---------- Buffer: Minibuffer ----------
=> t
Function: interactive-p
This function returns t if the containing function (the one that
called interactive-p) was called interactively, with the function
call-interactively. (It makes no difference whether
call-interactively was called from Lisp or directly from the
editor command loop.) Note that if the containing function was called
by Lisp evaluation (or with apply or funcall), then it was
not called interactively.
The usual application of interactive-p is for deciding whether to
print an informative message. As a special exception,
interactive-p returns nil whenever a keyboard macro is
being run. This is to suppress the informative messages and speed
execution of the macro.
For example:
(defun foo ()
(interactive)
(and (interactive-p)
(message "foo")))
=> foo
(defun bar ()
(interactive)
(setq foobar (list (foo) (interactive-p))))
=> bar
;; Type M-x foo.
-| foo
;; Type M-x bar.
;; This does not print anything.
foobar
=> (nil t)
The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run.
Variable: last-command
This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed.
The value is set by copying the value of this-command when a
command returns to the command loop, except when the command specifies a
prefix argument for the following command.
Variable: this-command
This variable records the name of the command now being executed by
the editor command loop. Like last-command, it is normally a symbol
with a function definition.
This variable is set by the command loop just before the command is run,
and its value is copied into last-command when the command
finishes (unless the command specifies a prefix argument for the
following command).
Some commands change the value of this variable during their execution,
simply as a flag for whatever command runs next. In particular, the
functions that kill text set this-command to kill-region
so that any kill commands immediately following will know to append the
killed text to the previous kill.
Function: this-command-keys
This function returns a string or vector containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command. The value is a string if all those events were characters. See section Input Events.
(this-command-keys)
;; Now type C-u C-x C-e.
=> "^U^X^E"
Variable: last-nonmenu-event
This variable holds the last input event read as part of a key sequence, aside from events resulting from mouse menus.
One use of this variable is to figure out a good default location to pop up another menu.
Variable: last-command-event
Variable: last-command-char
This variable is set to the last input event that was read by the
command loop as part of a command. The principal use of this variable
is in self-insert-command, which uses it to decide which
character to insert.
last-command-char
;; Now type C-u C-x C-e.
=> 5
The value is 5 because that is the ASCII code for C-e.
The alias last-command-char exists for compatibility with
Emacs version 18.
Variable: last-event-frame
This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. See section Input Focus.
Variable: echo-keystrokes
This variable determines how much time should elapse before command characters echo. Its value must be an integer, which specifies the number of seconds to wait before echoing. If the user types a prefix key (say C-x) and then delays this many seconds before continuing, the key C-x is echoed in the echo area. Any subsequent characters in the same command will be echoed as well.
If the value is zero, then command input is not echoed.
The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity. The events for keyboard activity are characters or symbols; mouse events are always lists. This section describes the representation and meaning of input events in detail.
A command invoked using events that are lists can get the full values of
these events using the `e' interactive code. See section Code Characters for interactive.
A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer--that is entirely under the control of the command binding of the key sequence.
Function: eventp object
This function returns non-nil if event is an input event.
There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. In Emacs versions 18 and earlier, characters were the only events.
An input character event consists of a basic code between 0 and 255, plus any or all of these modifier bits:
ASCII control characters such as C-a have special basic codes of their own, so Emacs needs no special bit to indicate them. Thus, the code for C-a is just 1.
But if you type a control combination not in ASCII, such as % with the control key, the numeric value you get is the code for % plus 2**22 (assuming the terminal supports non-ASCII control characters).
For letters, the basic code indicates upper versus lower case; for digits and punctuation, the shift key selects an entirely different character with a different basic code. In order to keep within the ASCII character set whenever possible, Emacs avoids using the 2**21 bit for those characters.
However, ASCII provides no way to distinguish C-A from C-A, so Emacs uses the 2**21 bit in C-A and not in C-a.
In the future, Emacs may support a larger range of basic codes. We
may also move the modifier bits to larger bit numbers. Therefore, you
should avoid mentioning specific bit numbers in your program.
Instead, the way to test the modifier bits of a character is with the
function event-modifiers (see section Classifying Events).
Most keyboards also have function keys---keys which have names or
symbols that are not characters. Function keys are represented in Lisp
as symbols; the symbol's name is the function key's label. For example,
pressing a key labeled F1 places the symbol f1 in the input
stream.
For all keyboard events, the event type (which classifies the event for key lookup purposes) is identical to the event--it is the character or the symbol. See section Classifying Events.
Here are a few special cases in the symbol naming convention for function keys:
backspace, tab, newline, return, delete
In ASCII, C-i and TAB are the same character. Emacs
lets you distinguish them if you wish, by returning the former as the
integer 9, and the latter as the symbol tab.
Most of the time, it's not useful to distinguish the two. So normally
function-key-map is set up to map tab into 9. Thus, a
key binding for character code 9 also applies to tab. Likewise
for the other symbols in this group. The function read-char
also converts these events into characters.
In ASCII, BS is really C-h. But backspace
converts into the character code 127 (DEL), not into code 8
(BS). This is what most users prefer.
kp-add, kp-decimal, kp-divide, ...
kp-0, kp-1, ...
kp-f1, kp-f2, kp-f3, kp-f4
left, up, right, down
You can use the modifier keys CTRL, META, HYPER, SUPER, ALT and SHIFT with function keys. The way to represent them is with prefixes in the symbol name:
Thus, the symbol for the key F3 with META held down is M-F3. When you use more than one prefix, we recommend you write them in alphabetical order (though the order does not matter in arguments to the key-binding lookup and modification functions).
When the user presses a mouse button and releases it at the same location, that generates a click event. Mouse click events have this form:
(event-type (window buffer-pos (column . row) timestamp) click-count)
Here is what the elements normally mean:
mouse-1, mouse-2, ..., where the
buttons are numbered numbered left to right.
You can also use prefixes `A-', `C-', `H-', `M-', `S-' and `s-' for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys.
This symbol also serves as the event type of the event. Key bindings
describe events by their types; thus, if there is a key binding for
mouse-1, that binding would apply to all events whose
event-type is mouse-1.
(0 . 0).
The meanings of buffer-pos, row and column are somewhat different when the event location is in a special part of the screen, such as the mode line or a scroll bar.
If the location is in a scroll bar, then buffer-pos is the symbol
vertical-scroll-bar or horizontal-scroll-bar, and the pair
(column . row) is replaced with a pair
(portion . whole), where portion is the
distance of the click from the top or left end of the scroll bar, and
whole is the length of the entire scroll bar.
If the position is on a mode line or the vertical line separating
window from its neighbor to the right, then buffer-pos is
the symbol mode-line or vertical-line. For the mode line,
row does not have meaningful data. For the vertical line,
column does not have meaningful data.
buffer-pos may be a list containing a symbol (one of the symbols listed above) instead of just the symbol. This is what happens after the imaginary prefix keys for these events are inserted into the input stream. See section Key Sequence Input.
With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this:
(event-type (window1 buffer-pos1 (column1 . row1) timestamp1) (window2 buffer-pos2 (column2 . row2) timestamp2) click-count)
For a drag event, the name of the symbol event-type contains the prefix `drag-'. The second and third elements of the event give the starting and ending position of the drag. Aside from that, the data have the same meanings as in a click event (see section Click Events). You can access the second element of any mouse event in the same way, with no need to distinguish drag events from others.
The `drag-' prefix follows the modifier key prefixes such as `C-' and `M-'.
If read-key-sequence receives a drag event which has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position. This means that you don't have to distinguish between click
and drag events unless you want to.
Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need to handle button-down events.(2). These occur as soon as a button is pressed. They are represented by lists which look exactly like click events (see section Click Events), except that the name of event-type contains the prefix `down-'. The `down-' prefix follows the modifier key prefixes such as `C-' and `M-'.
The function read-key-sequence, and the Emacs command loop,
ignore any button-down events that don't have command bindings. This
means that you need not worry about defining button-down events unless
you want them to do something. The usual reason to define a button-down
event is so that you can track mouse motion (by reading motion events)
until the button is released.
If you press the same mouse button more than once in quick succession without moving the mouse, Emacs uses special repeat mouse events for the second and subsequent presses.
The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events).
The event type of a double-click event contains the prefix
double. Thus, a double click on the second mouse button with
meta held down comes to the Lisp program as
M-double-mouse-2. If a double-click event has no binding, the
binding of the corresponding ordinary click event is used to execute
it. Thus, you need not pay attention to the double click feature
unless you really want to.
When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, the command binding of the double click event must be written to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click.
This means that it is most convenient to give double clicks a meaning that somehow "builds on" the meaning of a single click. This is what user interface experts recommend that double clicks should do.
If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains `double-drag' instead of just `drag'. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary click.
Before the double-click or double-drag event, Emacs generates a double-down event when the button is pressed down for the second time. Its event type contains `double-down' instead of just `down'. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored.
To summarize, when you click a button and then press it again right away, Emacs generates a double-down event, followed by either a double-click or a double-drag.
If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain `triple' instead of `double'. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event.
If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have quadruple, quintuple, etc. events as separate event types. However, you can look at the event list to find out precisely how many times the button was pressed.
Function: event-click-count event
This function returns the number of consecutive button presses that led up to event. If event is a double-down, double-click or double-drag event, the value is 2. If event is a triple event, the value is 3 or greater. If event is an ordinary mouse event (not a repeat event), the value is 1.
Variable: double-click-time
To count as double- and triple-clicks, mouse clicks must be at the same
location as the first click, and the number of milliseconds between the
first release and the second must be less than the value of
double-click-time. Setting double-click-time to
nil disables multi-click detection entirely. Setting it to
t removes the time limit; Emacs then detects multi-clicks by
position only.
Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this:
(mouse-movement (window buffer-pos (column . row) timestamp))
The second element of the list describes the current position of the mouse, just as in a click event (see section Click Events).
The special form track-mouse enables generation of motion events
within its body. Outside of track-mouse forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear.
Special Form: track-mouse body...
This special form executes body, with generation of mouse motion
events enabled. Typically body would use read-event
to read the motion events and modify the display accordingly.
When the user releases the button, that generates a click event. Normally body should return when it sees the click event, and discard the event.
Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See section Input Focus.
Focus events are represented in Lisp as lists that look like this:
(switch-frame new-frame)
where new-frame is the frame switched to.
In X windows, most window managers are set up so that just moving the mouse into a window is enough to set the focus there. Emacs appears to do this, because it changes the cursor to solid in the new frame. However, there is no need for the Lisp program to know about the focus change until some other kind of input arrives. So Emacs generates the focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event.
A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence--that is, after a prefix key--then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it.
If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this:
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320)) (mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
Or, while holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here:
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
(#<window 18 on NEWS> 3510 (0 . 28) -729648))
Or, while holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces the following pair of events:
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
-453816))
Every event has an event type which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events which are lists, the event type is the symbol in the CAR of the list. Thus, the event type is always a symbol or a character.
Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide what text to act on.
Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the META key, regardless of which other key or mouse button was used.
The functions event-modifiers and event-basic-type are
provided to get such information conveniently.
Function: event-modifiers event
This function returns a list of the modifiers that event has.
The modifiers are symbols; they include shift, control,
meta, alt, hyper and super. In addition,
the property of a mouse event symbol always has one of click,
drag, and down among the modifiers. For example:
(event-modifiers ?a)
=> nil
(event-modifiers ?\C-a)
=> (control)
(event-modifiers ?\C-%)
=> (control)
(event-modifiers ?\C-\S-a)
=> (control shift)
(event-modifiers 'f5)
=> nil
(event-modifiers 's-f5)
=> (super)
(event-modifiers 'M-S-f5)
=> (meta shift)
(event-modifiers 'mouse-1)
=> (click)
(event-modifiers 'down-mouse-1)
=> (down)
The modifiers list for a click event explicitly contains click,
but the event symbol name itself does not contain `click'.
Function: event-basic-type event
This function returns the key or mouse button that event describes, with all modifiers removed. For example:
(event-basic-type ?a)
=> 97
(event-basic-type ?A)
=> 97
(event-basic-type ?\C-a)
=> 97
(event-basic-type ?\C-\S-a)
=> 97
(event-basic-type 'f5)
=> f5
(event-basic-type 's-f5)
=> f5
(event-basic-type 'M-S-f5)
=> f5
(event-basic-type 'down-mouse-1)
=> mouse-1
Function: mouse-movement-p object
This function returns non-nil if object is a mouse movement
event.
This section describes convenient functions for accessing the data in an event which is a list.
The following functions return the starting or ending position of a mouse-button event. The position is a list of this form:
(window buffer-position (col . row) timestamp)
Function: event-start event
This returns the starting position of event.
If event is a click or button-down event, this returns the location of the event. If event is a drag event, this returns the drag's starting position.
Function: event-end event
This returns the ending position of event.
If event is a drag event, this returns the position where the user released the mouse button. If event is a click or button-down event, the value is actually the starting position, which is the only position such events have.
These four functions take a position-list as described above, and return various parts of it.
Function: posn-window position
Return the window that position is in.
Function: posn-point position
Return the buffer location in position.
Function: posn-col-row position
Return the row and column in position, as a list (col
. row).
Function: posn-timestamp position
Return the timestamp of position.
Function: scroll-bar-scale ratio total
This function multiples (in effect) ratio by total,
rounding the result to an integer. ratio is not a number,
but rather a pair (num . denom).
This is handy for scaling a position on a scroll bar into a buffer position. Here's how to do that:
(+ (point-min)
(scroll-bar-scale
(posn-col-row (event-start event))
(- (point-max) (point-min))))
In most of the places where strings are used, we conceptualize the string as containing text characters--the same kind of characters found in buffers or files. Occasionally Lisp programs use strings which conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. There are special rules for how to put keyboard characters into a string, because they are not limited to the range of 0 to 255 as text characters are.
A keyboard character typed using the META key is called a
meta character. The numeric code for such an event includes the
2**23 bit; it does not even come close to fitting in a string. However,
earlier Emacs versions used a different representation for these
characters, which gave them codes in the range of 128 to 255. That did
fit in a string, and many Lisp programs contain string constants that
use `\M-' to express meta characters, especially as the argument to
define-key and similar functions.
We provide backward compatibility to run those programs with special rules for how to put a keyboard character event in a string. Here are the rules:
Functions such as read-key-sequence that can construct strings
containing events follow these rules.
When you use the read syntax `\M-' in a string, it produces a code in the range of 128 to 255--the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings.
New programs can avoid dealing with these rules by using vectors instead of strings for key sequences when there is any possibility that these issues might arise.
The reason we changed the representation of meta characters as keyboard events is to make room for basic character codes beyond 127, and support meta variants of such larger character codes.
The editor command loop reads keyboard input using the function
read-key-sequence, which uses read-event. These and other
functions for keyboard input are also available for use in Lisp
programs. See also momentary-string-display in section Temporary Displays, and sit-for in section Waiting for Elapsed Time or Input. See section Terminal Input,
for functions and variables for controlling terminal input modes and
debugging terminal input.
For higher-level input facilities, see section Minibuffers.
The command loop reads input a key sequence at a time, by calling
read-key-sequence. Lisp programs can also call this function;
for example, describe-key uses it to read the key to describe.
Function: read-key-sequence prompt
This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a full key sequence; that is, enough to specify a non-prefix command using the currently active keymaps.
If the events are all characters and all can fit in a string, then
read-key-sequence returns a string (see section Putting Keyboard Events in Strings).
Otherwise, it returns a vector, since a vector can hold all kinds of
events--characters, symbols, and lists. The elements of the string or
vector are the events in the key sequence.
Quitting is suppressed inside read-key-sequence. In other words,
a C-g typed while reading with this function is treated like any
other character, and does not set quit-flag. See section Quitting.
The argument prompt is either a string to be displayed in the echo
area as a prompt, or nil, meaning not to display a prompt.
In the example below, the prompt `?' is displayed in the echo area, and the user types C-x C-f.
(read-key-sequence "?")
---------- Echo Area ----------
?C-x C-f
---------- Echo Area ----------
=> "^X^F"
Variable: num-input-keys
This variable's value is the number of key sequences processed so far in this Emacs session. This includes key sequences read from the terminal and key sequences read from keyboard macros being executed.
If an input character is an upper case letter and has no key binding,
but the lower case equivalent has one, then read-key-sequence
converts the character to lower case. Note that lookup-key does
not perform case conversion in this way.
The function read-key-sequence also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events so that they
never appear in a key sequence with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event itself shows nothing special--only the
symbol that would normally represent that mouse button and modifier
keys. The information about the screen region is kept elsewhere in the
event--in the coordinates. But read-key-sequence translates
this information into imaginary prefix keys, all of which are symbols:
mode-line, vertical-line, horizontal-scroll-bar and
vertical-scroll-bar.
For example, if you call read-key-sequence and then click the
mouse on the window's mode line, this is what happens:
(read-key-sequence "Click on the mode line: ")
=> [mode-line
(mouse-1
(#<window 6 on NEWS> mode-line
(40 . 63) 5959987))]
You can define meanings for mouse clicks in special window regions by defining key sequences using these imaginary prefix keys.
The lowest level functions for command input are those which read a single event.
Function: read-event
This function reads and returns the next event of command input, waiting if necessary until an event is available. Events can come directly from the user or from a keyboard macro.
The function read-event does not display any message to indicate
it is waiting for input; use message first, if you wish to
display one. If you have not displayed a message, read-event
does prompting: it displays descriptions of the events that led to
or were read by the current command. See section The Echo Area.
If cursor-in-echo-area is non-nil, then read-event
moves the cursor temporarily to the echo area, to the end of any message
displayed there. Otherwise read-event does not move the cursor.
Here is what happens if you call read-event and then press the
right-arrow function key:
(read-event)
=> right
Function: read-char
This function reads and returns a character of command input. It discards any events that are not characters until it gets a character.
In the first example, the user types 1 (which is ASCII code
49). The second example shows a keyboard macro definition that calls
read-char from the minibuffer. read-char reads the
keyboard macro's very next character, which is 1. The value of
this function is displayed in the echo area by the command
eval-expression.
(read-char)
=> 49
(symbol-function 'foo)
=> "^[^[(read-char)^M1"
(execute-kbd-macro foo)
-| 49
=> nil
You can use the function read-quoted-char when you want the user
to specify a character, and allow the user to specify a control or meta
character conveniently with quoting or as an octal character code. The
command quoted-insert calls this function.
Function: read-quoted-char &optional prompt
This function is like read-char, except that if the first
character read is an octal digit (0-7), it reads up to two more octal digits
(but stopping if a non-octal digit is found) and returns the
character represented by those digits as an octal number.
Quitting is suppressed when the first character is read, so that the user can enter a C-g. See section Quitting.
If prompt is supplied, it specifies a string for prompting the user. The prompt string is always printed in the echo area and followed by a single `-'.
In the following example, the user types in the octal number 177 (which is 127 in decimal).
(read-quoted-char "What character")
---------- Echo Area ----------
What character-177
---------- Echo Area ----------
=> 127
Variable: unread-command-events
This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list.
The variable is used because in some cases a function reads a event and then decides not to use it. Storing the event in this variable causes it to be processed normally by the command loop or when the functions to read command input are called.
For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events it does not recognize.
Variable: unread-command-char
This variable holds a character to be read as command input. A value of -1 means "empty".
This variable is pretty much obsolete now that you can use
unread-command-events instead; it exists only to support programs
written for Emacs versions 18 and earlier.
Function: listify-key-sequence key
This function converts the string or vector key to a list of
events which you can put in unread-command-events. Converting a
vector is simple, but converting a string is tricky because of the
special representation used for meta characters in a string
(see section Putting Keyboard Events in Strings).
Function: input-pending-p
This function determines whether any command input is currently
available to be read. It returns immediately, with value t if
there is input, nil otherwise. On rare occasions it may return
t when no input is available.
Variable: last-input-event
Variable: last-input-char
This variable records the last terminal input event read, whether as part of a command or explicitly by a Lisp program.
In the example below, a character is read (the character 1,
ASCII code 49). It becomes the value of last-input-char,
while C-e (from the C-x C-e command used to evaluate this
expression) remains the value of last-command-char.
(progn (print (read-char))
(print last-command-char)
last-input-char)
-| 49
-| 5
=> 49
The alias last-input-char exists for compatibility with
Emacs version 18.
Function: discard-input
This function discards the contents of the terminal input buffer and
cancels any keyboard macro that might be in the process of definition.
It returns nil.
In the following example, the user may type a number of characters right
after starting the evaluation of the form. After the sleep-for
finishes sleeping, any characters that have been typed are discarded.
(progn (sleep-for 2)
(discard-input))
=> nil
The waiting commands are designed to make Emacs wait for a certain
amount of time to pass or until there is input. For example, you may
wish to pause in the middle of a computation to allow the user time to
view the display. sit-for pauses and updates the screen, and
returns immediately if input comes in, while sleep-for pauses
without updating the screen.
Function: sit-for seconds &optional millisec nodisp
This function performs redisplay (provided there is no pending input
from the user), then waits seconds seconds, or until input is
available. The result is t if sit-for waited the full
time with no input arriving (see input-pending-p in section Peeking and Discarding). Otherwise, the value is nil.
The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. Not all operating systems support waiting periods other than multiples of a second; on those that do not, you get an error if you specify nonzero millisec.
Redisplay is always preempted if input arrives, and does not happen at
all if input is available before it starts. Thus, there is no way to
force screen updating if there is pending input; however, if there is no
input pending, you can force an update with no delay by using
(sit-for 0).
If nodisp is non-nil, then sit-for does not
redisplay, but it still returns as soon as input is available (or when
the timeout elapses).
The usual purpose of sit-for is to give the user time to read
text that you display.
Function: sleep-for seconds &optional millisec
This function simply pauses for seconds seconds without updating
the display. It pays no attention to available input. It returns
nil.
The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. Not all operating systems support waiting periods other than multiples of a second; on those that do not, you get an error if you specify nonzero millisec.
Use sleep-for when you wish to guarantee a delay.
See section Time of Day, for functions to get the current time.
Typing C-g while the command loop has run a Lisp function causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop.
Typing C-g while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character. In the
simplest case, you cannot tell the difference, because C-g
normally runs the command keyboard-quit, whose effect is to quit.
However, when C-g follows a prefix key, the result is an undefined
key. The effect is to cancel the prefix key as well as any prefix
argument.
In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g quit directly.
C-g causes a quit by setting the variable quit-flag to a
non-nil value. Emacs checks this variable at appropriate times
and quits if it is not nil. Setting quit-flag
non-nil in any way thus causes a quit.
At the level of C code, quits cannot happen just anywhere; only at the
special places which check quit-flag. The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state. Because quitting is delayed until a safe place, quitting
cannot make Emacs crash.
Certain functions such as read-key-sequence or
read-quoted-char prevent quitting entirely even though they wait
for input. Instead of quitting, C-g serves as the requested
input. In the case of read-key-sequence, this serves to bring
about the special behavior of C-g in the command loop. In the
case of read-quoted-char, this is so that C-q can be used
to quote a C-g.
You can prevent quitting for a portion of a Lisp function by binding
the variable inhibit-quit to a non-nil value. Then,
although C-g still sets quit-flag to t as usual, the
usual result of this--a quit--is prevented. Eventually,
inhibit-quit will become nil again, such as when its
binding is unwound at the end of a let form. At that time, if
quit-flag is still non-nil, the requested quit happens
immediately. This behavior is ideal for a "critical section", where
you wish to make sure that quitting does not happen within that part of
the program.
In some functions (such as read-quoted-char), C-g is
handled in a special way which does not involve quitting. This is done
by reading the input with inhibit-quit bound to t and
setting quit-flag to nil before inhibit-quit
becomes nil again. This excerpt from the definition of
read-quoted-char shows how this is done; it also shows that
normal quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)
"...documentation..."
(let ((count 0) (code 0) char)
(while (< count 3)
(let ((inhibit-quit (zerop count))
(help-form nil))
(and prompt (message "%s-" prompt))
(setq char (read-char))
(if inhibit-quit (setq quit-flag nil)))
...)
(logand 255 code)))
Variable: quit-flag
If this variable is non-nil, then Emacs quits immediately,
unless inhibit-quit is non-nil. Typing C-g sets
quit-flag non-nil, regardless of inhibit-quit.
Variable: inhibit-quit
This variable determines whether Emacs should quit when quit-flag
is set to a value other than nil. If inhibit-quit is
non-nil, then quit-flag has no special effect.
Command: keyboard-quit
This function signals the quit condition with (signal 'quit
nil). This is the same thing that quitting does. (See signal
in section Errors.)
You can specify a character other than C-g to use for quitting.
See the function set-input-mode in section Terminal Input.
Most Emacs commands can use a prefix argument, a number
specified before the command itself. (Don't confuse prefix arguments
with prefix keys.) The prefix argument is represented by a value that
is always available (though it may be nil, meaning there is no
prefix argument). Each command may use the prefix argument or ignore
it.
There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation.
Here are the possible values of a raw prefix argument:
nil, meaning there is no prefix argument. Its numeric value is
1, but numerous commands make a distinction between nil and the
integer 1.
-. This indicates that M-- or C-u - was
typed, without following digits. The equivalent numeric value is
-1, but some commands make a distinction between the integer
-1 and the symbol -.
The various possibilities may be illustrated by calling the following function with various prefixes:
(defun display-prefix (arg) "Display the value of the raw prefix arg." (interactive "P") (message "%s" arg))
Here are the results of calling print-prefix with various
raw prefix arguments:
M-x print-prefix -| nil
C-u M-x print-prefix -| (4)
C-u C-u M-x print-prefix -| (16)
C-u 3 M-x print-prefix -| 3
M-3 M-x print-prefix -| 3 ; (Same as C-u 3.)
C-u - M-x print-prefix -| -
M- - M-x print-prefix -| - ; (Same as C-u -.)
C-u -7 M-x print-prefix -| -7
M- -7 M-x print-prefix -| -7 ; (Same as C-u -7.)
Emacs uses two variables to store the prefix argument:
prefix-arg and current-prefix-arg. Commands such as
universal-argument that set up prefix arguments for other
commands store them in prefix-arg. In contrast,
current-prefix-arg conveys the prefix argument to the current
command, so setting it has no effect on the prefix arguments for future
commands.
Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the interactive declaration.
(See section Interactive Call.) Alternatively, functions may look at the
value of the prefix argument directly in the variable
current-prefix-arg, but this is less clean.
Do not call the functions universal-argument,
digit-argument, or negative-argument unless you intend to
let the user enter the prefix argument for the next command.
Command: universal-argument
This command reads input and specifies a prefix argument for the following command. Don't call this command yourself unless you know what you are doing.
Command: digit-argument arg
This command adds to the prefix argument for the following command. The argument arg is the raw prefix argument as it was before this command; it is used to compute the updated prefix argument. Don't call this command yourself unless you know what you are doing.
Command: negative-argument arg
This command adds to the numeric argument for the next command. The argument arg is the raw prefix argument as it was before this command; its value is negated to form the new prefix argument. Don't call this command yourself unless you know what you are doing.
Function: prefix-numeric-value arg
This function returns the numeric meaning of a valid raw prefix argument
value, arg. The argument may be a symbol, a number, or a list.
If it is nil, the value 1 is returned; if it is any other symbol,
the value -1 is returned. If it is a number, that number is
returned; if it is a list, the CAR of that list (which should be a
number) is returned.
Variable: current-prefix-arg
This variable is the value of the raw prefix argument for the
current command. Commands may examine it directly, but the usual
way to access it is with (interactive "P").
Variable: prefix-arg
The value of this variable is the raw prefix argument for the next editing command. Commands that specify prefix arguments for the following command work by setting this variable.
The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop is never exited until the Emacs is killed. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command.
The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when finished. (The special commands for exiting are always available, but do nothing when recursive editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands.
To invoke a recursive editing level, call the function
recursive-edit. This function contains the command loop; it also
contains a call to catch with tag exit, which makes it
possible to exit the recursive editing level by throwing to exit
(see section Explicit Nonlocal Exits: catch and throw). If you throw a value other than t,
then recursive-edit returns normally to the function that called
it. The command C-M-c (exit-recursive-edit) does this.
Throwing a t value causes recursive-edit to quit, so that
control returns to the command loop one level up. This is called
aborting, and is done by C-] (abort-recursive-edit).
Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which has a command to go back to the previous mode. (This technique is used by the w command in Rmail.) Or, if you wish to give the user different text to edit "recursively", create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.)
Recursive edits are useful in debugging. You can insert a call to
debug into a function definition as a sort of breakpoint, so that
you can look around when the function gets there. debug invokes
a recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type C-r in
query-replace or use C-x q (kbd-macro-query).
Function: recursive-edit
This function invokes the editor command loop. It is called automatically by the initialization of Emacs, to let the user begin editing. When called from a Lisp program, it enters a recursive editing level.
In the following example, the function simple-rec first
advances point one word, then enters a recursive edit, printing out a
message in the echo area. The user can then do any editing desired, and
then type C-M-c to exit and continue executing simple-rec.
(defun simple-rec ()
(forward-word 1)
(message "Recursive edit in progress.")
(recursive-edit)
(forward-word 1))
=> simple-rec
(simple-rec)
=> nil
Command: exit-recursive-edit
This function exits from the innermost recursive edit (including
minibuffer input). Its definition is effectively (throw 'exit
nil).
Command: abort-recursive-edit
This function aborts the command that requested the innermost recursive
edit (including minibuffer input), by signaling quit
after exiting the recursive edit. Its definition is effectively
(throw 'exit t). See section Quitting.
Command: top-level
This function exits all recursive editing levels; it does not return a value, as it jumps completely out of any computation directly back to the main command loop.
Function: recursion-depth
This function returns the current depth of recursive edits. When no recursive edit is active, it returns 0.
Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.
The low-level mechanism for disabling a command is to put a
non-nil disabled property on the Lisp symbol for the
command. These properties are normally set up by the user's
`.emacs' file with Lisp expressions such as this:
(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default and may be removed by the `.emacs' file.
If the value of the disabled property is a string, that string
is included in the message printed when the command is used:
(put 'delete-region 'disabled
"Text deleted this way cannot be yanked back!\n")
See section 'Disabling' in The GNU Emacs Manual, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs.
Command: enable-command command
Allow command to be executed without special confirmation from now on. The user's `.emacs' file is optionally altered so that this will apply to future sessions.
Command: disable-command command
Require special confirmation to execute command from now on. The user's `.emacs' file is optionally altered so that this will apply to future sessions.
Variable: disabled-command-hook
This variable is a normal hook that is run instead of a disabled command,
when the user runs the disabled command interactively. The hook functions
can use this-command-keys to determine what the user typed to run
the command, and thus find the command itself.
By default, disabled-command-hook contains a function that asks
the user whether to proceed.
The command loop keeps a history of the complex commands that have
been executed, to make it convenient to repeat these commands. A
complex command is one for which the interactive argument reading
uses the minibuffer. This includes any M-x command, any
M-ESC command, and any command whose interactive
specification reads an argument from the minibuffer. Explicit use of
the minibuffer during the execution of the command itself does not cause
the command to be considered complex.
Variable: command-history
This variable's value is a list of recent complex commands, each represented as a form to evaluate. It continues to accumulate all complex commands for the duration of the editing session, but all but the first (most recent) thirty elements are deleted when a garbage collection takes place (see section Garbage Collection).
command-history
=> ((switch-to-buffer "chistory.texi")
(describe-key "^X^[")
(visit-tags-table "~/emacs/src/")
(find-tag "repeat-complex-command"))
This history list is actually a special case of minibuffer history (see section Minibuffer History), with one special twist: the elements are expressions rather than strings.
There are a number of commands devoted to the editing and recall of
previous commands. The commands repeat-complex-command, and
list-command-history are described in the user manual
(see section 'Repetition' in The GNU Emacs Manual). Within the
minibuffer, the history commands used are the same ones available in any
minibuffer.
A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. Don't confuse keyboard macros with Lisp macros (see section Macros).
Function: execute-kbd-macro macro &optional count
This function executes macro as a sequence of events. If macro is a string or vector, then the events in it are executed exactly as if they had been input by the user. The sequence is not expected to be a single key sequence; normally a keyboard macro definition consists of several key sequences concatenated.
If macro is a symbol, then its function definition is used in place of macro. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled.
The argument count is a repeat count; macro is executed that
many times. If count is omitted or nil, macro is
executed once. If it is 0, macro is executed over and over until it
encounters an error or a failing search.
Variable: last-kbd-macro
This variable is the definition of the most recently defined keyboard
macro. Its value is a string or vector, or nil.
Variable: executing-macro
This variable contains the string or vector that defines the keyboard
macro that is currently executing. It is nil if no macro is
currently executing.
Variable: defining-kbd-macro
This variable indicates whether a keyboard macro is being defined. It
is set to t by start-kbd-macro, and nil by
end-kbd-macro. You can use this variable to make a command
behave differently when run from a keyboard macro (perhaps indirectly by
calling interactive-p). However, do not set this variable
yourself.
The commands are described in the user's manual (see section 'Keyboard Macros' in The GNU Emacs Manual).
The bindings between input events and commands are recorded in data structures called keymaps. Each binding in a keymap associates (or binds) an individual event type either with another keymap or with a command. When an event is bound to a keymap, that keymap is used to look up the next character typed; this continues until a command is found. The whole process is called key lookup.
A keymap is a table mapping event types to definitions (which can be any Lisp objects, though only certain types are meaningful for execution by the command loop). Given an event (or an event type) and a keymap, Emacs can get the event's definition. Events include ordinary ASCII characters, function keys, and mouse actions (see section Input Events).
A sequence of input events that form a unit is called a key sequence, or key for short. A sequence of one event is always a key sequence, and so are some multi-event sequences.
A keymap determines a binding or definition for any key sequence. If the key sequence is a single event, its binding is the definition of the event in the keymap. The binding of a key sequence of more than one event is found by an iterative process: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up.
If the binding of a key sequence is a keymap, we call the key sequence
a prefix key. Otherwise, we call it a complete key (because
no more characters can be added to it). If the binding is nil,
we call the key undefined. Examples of prefix keys are C-c,
C-x, and C-x 4. Examples of defined complete keys are
X, RET, and C-x 4 C-f. Examples of undefined complete
keys are C-x C-g, and C-c 3. See section Prefix Keys, for more
details.
The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit--it is not really a key sequence. In other words, removing one or more events from the end of any valid key must always yield a prefix key. For example, C-f C-f is not a key; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key.
Note that the set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active---that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See section Active Keymaps, for details.
A keymap is a list whose CAR is the symbol keymap. The
remaining elements of the list define the key bindings of the keymap.
Use the function keymapp (see below) to test whether an object is
a keymap.
An ordinary element is a cons cell of the form (type .
binding). This specifies one binding which applies to events of
type type. Each ordinary binding applies to events of a
particular event type, which is always a character or a symbol.
See section Classifying Events.
A cons cell whose CAR is t is a default key binding;
any event not bound by other elements of the keymap is given
binding as its binding. Default bindings allow a keymap to bind
all possible event types without having to enumerate all of them. A
keymap that has a default binding completely masks any lower-precedence
keymap.
If an element of a keymap is a vector, the vector counts as bindings for all the ASCII characters; vector element n is the binding for the character with code n. This is a more compact way to record lots of bindings. A keymap with such a vector is called a full keymap. Other keymaps are called sparse keymaps.
When a keymap contains a vector, it always defines a binding for every
ASCII character even if the vector element is nil. Such a
binding of nil overrides any default binding in the keymap.
However, default bindings are still meaningful for events that are not
ASCII characters. A binding of nil does not
override lower-precedence keymaps; thus, if the local map gives a
binding of nil, Emacs uses the binding from the global map.
Aside from bindings, a keymap can also have a string as an element. This is called the overall prompt string and makes it possible to use the keymap as a menu. See section Menu Keymaps.
Keymaps do not directly record bindings for the meta characters, whose
codes are from 128 to 255. Instead, meta characters are regarded for
purposes of key lookup as sequences of two characters, the first of
which is ESC (or whatever is currently the value of
meta-prefix-char). Thus, the key M-a is really represented
as ESC a, and its global binding is found at the slot for
a in esc-map.
Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for DEL and TAB, plus C-c C-l, M-C-q, and M-C-x.
lisp-mode-map
=>
(keymap
;; TAB
(9 . lisp-indent-line)
;; DEL
(127 . backward-delete-char-untabify)
(3 keymap
;; C-c C-l
(12 . run-lisp))
(27 keymap
;; M-C-q, treated as ESC C-q
(17 . indent-sexp)
;; M-C-x, treated as ESC C-x
(24 . lisp-send-defun)))
Function: keymapp object
This function returns t if object is a keymap, nil
otherwise. Practically speaking, this function tests for a list whose
CAR is keymap.
(keymapp '(keymap))
=> t
(keymapp (current-global-map))
=> t
Here we describe the functions for creating keymaps.
Function: make-keymap &optional prompt
This function creates and returns a new full keymap (i.e., one which
contains a vector of length 128 for defining all the ASCII
characters). The new keymap initially binds all ASCII characters
to nil, and does not bind any other kind of event.
(make-keymap)
=> (keymap [nil nil nil ... nil nil])
If you specify prompt, that becomes the overall prompt string for the keymap. The prompt string is useful for menu keymaps (see section Menu Keymaps).
Function: make-sparse-keymap &optional prompt
This function creates and returns a new sparse keymap with no entries.
The new keymap does not bind any events. The argument prompt
specifies a prompt string, as in make-keymap.
(make-sparse-keymap)
=> (keymap)
Function: copy-keymap keymap
This function returns a copy of keymap. Any keymaps which appear directly as bindings in keymap are also copied recursively, and so on to any number of levels. However, recursive copying does not take place when the definition of a character is a symbol whose function definition is a keymap; the same symbol appears in the new copy.
(setq map (copy-keymap (current-local-map)))
=> (keymap
;; (This implements meta characters.)
(27 keymap
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
(eq map (current-local-map))
=> nil
(equal map (current-local-map))
=> t
A keymap can inherit the bindings of another keymap. Do do this, make a keymap whose "tail" is another existing keymap to inherit from. Such a keymap looks like this:
(keymap bindings... . other-keymap)
The effect is that this keymap inherits all the bindings of other-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with bindings.
If you change the bindings in other-keymap using define-key
or other key-binding functions, these changes are visible in the
inheriting keymap unless shadowed by bindings. The converse is
not true: if you use define-key to change the inheriting keymap,
that affects bindings, but has no effect on other-keymap.
Here is an example showing how to make a keymap that inherits
from text-mode-map:
(setq my-mode-map (cons 'keymap text-mode-map))
A prefix key has an associated keymap which defines what to do
with key sequences that start with the prefix key. For example,
C-x is a prefix key, and it uses a keymap which is also stored in
the variable ctl-x-map. Here is a list of the standard prefix
keys of Emacs and their keymaps:
esc-map is used for events that follow ESC. Thus, the
global definitions of all meta characters are actually found here. This
map is also the function definition of ESC-prefix.
help-map is used for events that follow C-h.
mode-specific-map is for events that follow C-c. This
map is not actually mode specific; its name was chosen to be informative
for the user in C-h b (display-bindings), where it
describes the main use of the C-c prefix key.
ctl-x-map is the variable name for the map used for events
that follow C-x. This map is also the function definition of
Control-X-prefix.
ctl-x-4-map is used for events that follow C-x 4.
ctl-x-5-map used is for events that follow C-x 5.
The binding of a prefix key is the keymap to use for looking up the
events that follow the prefix key. (It may instead be a symbol whose
function definition is a keymap. The effect is the same, but the symbol
serves as a name for the prefix key.) Thus, the binding of C-x is
the symbol Control-X-prefix, whose function definition is the
keymap for C-x commands. (The same keymap is also the value of
ctl-x-map.)
Prefix key definitions of this sort can appear in any active keymap. The definitions of C-c, C-x, C-h and ESC as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See section Active Keymaps.
If a key is defined as a prefix in more than one active map, then the various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then
the binding for C-p C-f is the function find-file, just
like C-x C-f. The key sequence C-p 6 is not found in any
active keymap.
(use-local-map (make-sparse-keymap))
=> nil
(local-set-key "\C-p" ctl-x-map)
=> nil
(key-binding "\C-p\C-f")
=> find-file
(key-binding "\C-p6")
=> nil
Function: define-prefix-command symbol
This function defines symbol as a prefix command: it creates a full keymap and stores it as symbol's function definition. Storing the symbol as the binding of a key makes the key a prefix key which has a name. It also sets symbol as a variable, to have the keymap as its value. The function returns symbol.
In Emacs version 18, only the function definition of symbol was set, not the value as a variable.
A keymap can define a menu as well as ordinary keys and mouse button meanings. Menus are normally actuated with the mouse, but they can work with the keyboard also.
A keymap is suitable for menu use if it has an overall prompt
string, which is a string that appears as an element of the keymap.
(See section Format of Keymaps.) The string should describe the purpose of
the menu. The easiest way to construct a keymap with a prompt string is
to specify the string as an argument when you call make-keymap or
make-sparse-keymap (see section Creating Keymaps).
The individual bindings in the menu keymap should also have prompt strings; these strings become the items displayed in the menu. A binding with a prompt string looks like this:
(string . real-binding)
As far as define-key and lookup-key are concerned, the
string is part of the event's binding. However, only real-binding
is used for executing the key.
You can also supply a second string, called the help string, as follows:
(string help-string . real-binding)
Currently Emacs does not actually use help-string; it knows only how to ignore help-string in order to extract real-binding. In the future we hope to make help-string serve as extended documentation for the menu item, available on request.
The prompt string for a binding should be short--one or two words. It should describe the action of the command it corresponds to.
If real-binding is nil, then string appears in the
menu but cannot be selected.
If real-binding is a symbol, and has a non-nil
menu-enable property, that property is an expression which
controls whether the menu item is enabled. Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-nil. When a
menu item is disabled, it is displayed in a "fuzzy" fashion, and
cannot be selected with the mouse.
The order of items in the menu is the same as the order of bindings in
the keymap. Since define-key puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order.
The way to make a menu keymap produce a menu is to make it the definition of a prefix key.
When the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding which brought about that menu item.
It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.
A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings a prompt string that starts with `@'. The rest of the prompt string becomes the name of the pane. See the file `lisp/mouse.el' for an example of this. Any ordinary bindings with `@'-less prompt strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.
You can also get multiple panes from separate keymaps. The full definition of a prefix key always comes from merging the definitions supplied by the various active keymaps (minor mode, local, and global). When more than one of these keymaps is a menu, each of them makes a separate pane or panes. See section Active Keymaps.
A Lisp program can explicitly pop up a menu and receive the user's choice. You can use keymaps for this also. See section Pop-Up Menus.
When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the user can use the keyboard to choose a menu item.
Emacs displays the menu alternatives (the prompt strings of the bindings) in the echo area. If they don't all fit at once, the user can type SPC to see the next line of alternatives. Successive uses of SPC eventually get to the end of the menu and then cycle around to the beginning.
When the user has found the desired alternative from the menu, he or she should type the corresponding character--the one whose binding is that alternative.
In a menu intended for keyboard use, each menu item must clearly indicate what character to type. The best convention to use is to make the character the first letter of the menu item prompt string. That is something users will understand without being told.
This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.
Variable: menu-prompt-more-char
This variable specifies the character to use to ask to see the next line of a menu. Its initial value is 32, the code for SPC.
Here is a simple example of how to set up a menu for mouse use.
(defvar my-menu-map
(make-sparse-keymap "Key Commands <==> Functions"))
(fset 'help-for-keys my-menu-map)
(define-key my-menu-map [bindings]
'("List all keystroke commands" . describe-bindings))
(define-key my-menu-map [key]
'("Describe key briefly" . describe-key-briefly))
(define-key my-menu-map [key-verbose]
'("Describe key verbose" . describe-key))
(define-key my-menu-map [function]
'("Describe Lisp function" . describe-function))
(define-key my-menu-map [where-is]
'("Where is this command" . where-is))
(define-key global-map [C-S-down-mouse-1] 'help-for-keys)
The symbols used in the key sequences bound in the menu are fictitious
"function keys"; they don't appear on the keyboard, but that doesn't
stop you from using them in the menu. Their names were chosen to be
mnemonic, because they show up in the output of where-is and
apropos to identify the corresponding menu items.
However, if you want the menu to be usable from the keyboard as well, you must use real ASCII characters instead of fictitious function keys.
Under X Windows, each frame can have a menu bar---a permanently
displayed menu stretching horizontally across the top of the frame. The
items of the menu bar are the subcommands of the fake "function key"
menu-bar, as defined by all the active keymaps.
To add an item to the menu bar, invent a fake "function key" of your
own (let's call it key), and make a binding for the key sequence
[menu-bar key]. Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined submenu containing all the subcommands of that item--the global subcommands, the local subcommands, and the minor mode subcommands, all together.
In order for a frame to display a menu bar, its menu-bar-lines
property must be greater than zero. Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame. We
recommend you try one or two as the value of menu-bar-lines.
See section X Window Frame Parameters.
Here's an example of setting up a menu bar item:
(modify-frame-parameters (selected-frame) '((menu-bar-lines . 2)))
;; Make a menu keymap (with a prompt string)
;; to be the menu bar item's definition.
(define-key global-map [menu-bar words]
(cons "Words" (make-sparse-keymap "Words")))
;; Make specific subcommands in the item's submenu.
(define-key global-map
[menu-bar words forward]
'("Forward word" . forward-word))
(define-key global-map
[menu-bar words backward]
'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by
rebinding the same fake function key with undefined as the
binding. For example, this is how Dired suppresses the `Edit' menu
bar item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
edit is the fake function key used by the global map for the
`Edit' menu bar item. The main reason to suppress a global
menu bar item is to regain space for mode-specific items.
Variable: menu-bar-final-items
Normally the menu bar shows global items followed by items defined by the local maps.
This variable holds a list of fake function keys for items to display at
the end of the menu bar rather than in normal sequence. The default
value is (help); thus, the `Help' menu item normally appears
at the end of the menu bar, following local menu items.
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use define-key to add the item, it normally goes at the front of
the menu. To put it elsewhere, use define-key-after:
Function: define-key-after map key binding after
Define a binding in map for key, with value binding,
just like define-key, but position the binding in map after
the binding for the key after. For example,
(define-key my-menu [drink]
'("Drink" . drink-command) [eat])
makes a binding for the fake function key drink and puts it right after the binding for eat.
Emacs normally contains many keymaps; at any given time, just a few of them are active in that they participate in the interpretation of user input. These are the global keymap, the current buffer's local keymap, and the keymaps of any enabled minor modes.
The global keymap holds the bindings of keys that are defined
regardless of the current buffer, such as C-f. The variable
global-map holds this keymap, which is always active.
Each buffer may have another keymap, its local keymap, which may contain new or overriding definitions for keys. At all times, the current buffer's local keymap is active. Text properties can specify an alternative local map for certain parts of the buffer; see section Special Properties.
Each minor mode may have a keymap; if it does, the keymap is active whenever the minor mode is enabled.
All the active keymaps are used together to determine what command to execute when a key is entered. The key lookup proceeds as described earlier (see section Key Lookup), but Emacs first searches for the key in the minor mode maps (one map at a time); if they do not supply a binding for the key, Emacs searches the local map; if that too has no binding, Emacs then searches the global map.
Since every buffer that uses the same major mode normally uses the
very same local keymap, it may appear as if the keymap is local to the
mode. A change to the local keymap of a buffer (using
local-set-key, for example) will be seen also in the other
buffers that share that keymap.
The local keymaps that are used for Lisp mode, C mode, and several
other major modes exist even if they have not yet been used. These
local maps are the values of the variables lisp-mode-map,
c-mode-map, and so on. For most other modes, which are less
frequently used, the local keymap is constructed only when the mode is
used for the first time in a session.
The minibuffer has local keymaps, too; they contain various completion and exit commands. See section Minibuffers.
See section Standard Keymaps, for a list of standard keymaps.
Variable: global-map
This variable contains the default global keymap that maps Emacs
keyboard input to commands. Normally this keymap is the global keymap.
The default global keymap is a full keymap that binds
self-insert-command to all of the printing characters.
Function: current-global-map
This function returns the current global keymap. This is always the
same as the value of global-map unless you change one or the
other.
(current-global-map)
=> (keymap [set-mark-command beginning-of-line ...
delete-backward-char])
Function: current-local-map
This function returns the current buffer's local keymap, or nil
if it has none. In the following example, the keymap for the
`*scratch*' buffer (using Lisp Interaction mode) is a sparse keymap
in which the entry for ESC, ASCII code 27, is another sparse
keymap.
(current-local-map)
=> (keymap
(10 . eval-print-last-sexp)
(9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap
(24 . eval-defun)
(17 . indent-sexp)))
Function: current-minor-mode-maps
This function returns a list of the keymaps of currently enabled minor modes.
Function: use-global-map keymap
This function makes keymap the new current global keymap. It
returns nil.
It is very unusual to change the global keymap.
Function: use-local-map keymap
This function makes keymap the new current local keymap of the
current buffer. If keymap is nil, then there will be no
local keymap. It returns nil. Most major modes use this
function.
Variable: minor-mode-map-alist
This variable is an alist describing keymaps that may or may not be active according to the values of certain variables. Its elements look like this:
(variable . keymap)
The keymap keymap is active whenever variable has a
non-nil value. Typically variable is the variable which
enables or disables a minor mode. See section Keymaps and Minor Modes.
When more than one minor mode keymap is active, their order of priority
is the order of minor-mode-map-alist.
See also minor-mode-key-binding in section Functions for Key Lookup.
Key lookup is the process of finding the binding of a key sequence from a given keymap. Actual execution of the binding is not part of key lookup.
Key lookup uses just the event types of each event in the key
sequence; the rest of the event is ignored. In fact, a key sequence
used for key lookup may designate mouse events with just their types
(symbols) instead of with entire mouse events (lists). See section Input Events. Such a pseudo-key-sequence is insufficient for
command-execute, but it is sufficient for looking up or rebinding
a key.
When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.
Let's use the term keymap entry to describe the value directly associated with an event type in a keymap. While any Lisp object may be stored as a keymap entry, not all make sense for key lookup. Here is a list of the meaningful kinds of keymap entries:
nil
nil means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at all,
that is equivalent to an entry of nil for that type.
keymap, then the list
is a keymap, and is treated as a keymap (see above).
lambda, then the list is a
lambda expression. This is presumed to be a command, and is treated as
such (see above).
(othermap . othertype)
When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that.
This feature permits you to define one key as an alias for another key.
For example, an entry whose CAR is the keymap called esc-map
and whose CDR is 32 (the code for space) means, "Use the global
binding of Meta-SPC, whatever that may be."
Note that keymaps and keyboard macros (strings and vectors) are not
valid functions, so a symbol with a keymap, string or vector as its
function definition is also invalid as a function. It is, however,
valid as a key binding. If the definition is a keyboard macro, then the
symbol is also valid as an argument to command-execute
(see section Interactive Call).
The symbol undefined is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and its
binding is the command undefined; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling ding) but does not signal an error.
undefined is used in local keymaps to override a global key
binding and make the key "undefined" locally. A local binding of
nil would fail to do this because it would not override the
global binding.
In short, a keymap entry may be a keymap, a command, a keyboard macro,
a symbol which leads to one of them, or an indirection or nil.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap. This map is the normal value
of emacs-lisp-mode-map. Note that 9 is the code for TAB,
127 for DEL, 27 for ESC, 17 for C-q and 24 for
C-x.
(keymap (9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap (17 . indent-sexp) (24 . eval-defun)))
Here are the functions and variables pertaining to key lookup.
Function: lookup-key keymap key &optional accept-defaults
This function returns the definition of key in keymap. If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap (which means it is "too long" and has extra events at the end), then the value is a number, the number of events at the front of key that compose a complete key.
If accept-defaults is non-nil, then lookup-key
considers default bindings as well as bindings for the specific events
in key. Otherwise, lookup-key reports only bindings for
the specific sequence key, ignoring default bindings except when
an element of key is t.
All the other functions described in this chapter that look up keys use
lookup-key.
(lookup-key (current-global-map) "\C-x\C-f")
=> find-file
(lookup-key (current-global-map) "\C-x\C-f12345")
=> 2
If key contains a meta character, that character is implicitly
replaced by a two-character sequence: the value of
meta-prefix-char, followed by the corresponding non-meta
character. Thus, the first example below is handled by conversion into
the second example.
(lookup-key (current-global-map) "\M-f")
=> forward-word
(lookup-key (current-global-map) "\ef")
=> forward-word
This function does not modify the specified events in ways that
discard information as read-key-sequence does (see section Key Sequence Input). In particular, it does not convert letters to lower
case and it does not change drag events to clicks.
Command: undefined
Used in keymaps to undefine keys. It calls ding, but does
not cause an error.
Function: key-binding key &optional accept-defaults
This function returns the binding for key in the current
keymaps, trying all the active keymaps. The result is nil if
key is undefined in the keymaps.
The argument accept-defaults controls checking for default
bindings, as in lookup-key.
An error is signaled if key is not a string or a vector.
(key-binding "\C-x\C-f")
=> find-file
Function: local-key-binding key &optional accept-defaults
This function returns the binding for key in the current
local keymap, or nil if it is undefined there.
The argument accept-defaults controls checking for default bindings,
as in lookup-key (above).
Function: global-key-binding key &optional accept-defaults
This function returns the binding for command key in the
current global keymap, or nil if it is undefined there.
The argument accept-defaults controls checking for default bindings,
as in lookup-key (above).
Function: minor-mode-key-binding key &optional accept-defaults
This function returns a list of all the active minor mode bindings of
key. More precisely, it returns an alist of pairs
(modename . binding), where modename is the the
variable which enables the minor mode, and binding is key's
binding in that mode. If key has no minor-mode bindings, the
value is nil.
If the first binding is a non-prefix, all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.
The argument accept-defaults controls checking for default
bindings, as in lookup-key (above).
Variable: meta-prefix-char
This variable is the meta-prefix character code. It is used when translating a meta character to a two-character sequence so it can be looked up in a keymap. For useful results, the value should be a prefix event (see section Prefix Keys). The default value is 27, which is the ASCII code for ESC.
As long as the value of meta-prefix-char remains 27, key
lookup translates M-b into ESC b, which is normally
defined as the backward-word command. However, if you set
meta-prefix-char to 24, the code for C-x, then Emacs will
translate M-b into C-x b, whose standard binding is the
switch-to-buffer command.
meta-prefix-char ; The default value.
=> 27
(key-binding "\M-b")
=> backward-word
?\C-x ; The print representation
=> 24 ; of a character.
(setq meta-prefix-char 24)
=> 24
(key-binding "\M-b")
=> switch-to-buffer ; Now, typing M-b is
; like typing C-x b.
(setq meta-prefix-char 27) ; Avoid confusion!
=> 27 ; Restore the default value!
The way to rebind a key is to change its entry in a keymap. You can
change the global keymap, so that the change is effective in all buffers
(except those that override the global binding with a local one). Or
you can change the current buffer's local map, which usually affects all
buffers using the same major mode. The global-set-key and
local-set-key functions are convenient interfaces for these
operations. Or you can use define-key and specify explicitly
which map to change.
People often use global-set-key in their `.emacs' file for
simple customization. For example,
(global-set-key "\C-x\C-\\" 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
redefines C-x C-\ to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, typed with the Meta key, to set point where you click.
In writing the key sequence to rebind, it is useful to use the special
escape sequences for control and meta characters (see section String Type).
The syntax `\C-' means that the following character is a control
character and `\M-' means that the following character is a meta
character. Thus, the string "\M-x" is read as containing a
single M-x, "\C-f" is read as containing a single
C-f, and "\M-\C-x" and "\C-\M-x" are both read as
containing a single C-M-x.
For the functions below, an error is signaled if keymap is not a keymap or if key is not a string or vector representing a key sequence. However, you can use event types (symbols) as shorthand for events that are lists.
Function: define-key keymap key binding
This function sets the binding for key in keymap. (If
key is more than one event long, the change is actually made
in another keymap reached from keymap.) The argument
binding can be any Lisp object, but only certain types are
meaningful. (For a list of meaningful types, see section Key Lookup.)
The value returned by define-key is binding.
Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled.
If some prefix of key is undefined, then define-key defines
it as a prefix key so that the rest of key may be defined as
specified.
The following example creates a sparse keymap and makes a number of bindings:
(setq map (make-sparse-keymap))
=> (keymap)
(define-key map "\C-f" 'forward-char)
=> forward-char
map
=> (keymap (6 . forward-char))
;; Build sparse submap for C-x and bind f in that.
(define-key map "\C-xf" 'forward-word)
=> forward-word
map
=> (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map "\C-p" ctl-x-map)
;; ctl-x-map
=> [nil ... find-file ... backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map "\C-p\C-f" 'foo)
=> 'foo
map
=> (keymap ; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for C-p C-f actually works by
changing an entry in ctl-x-map, and this has the effect of
changing the bindings of both C-p C-f and C-x C-f in the
default global map.
Function: substitute-key-definition olddef newdef keymap &optional oldmap
This function replaces olddef with newdef for any keys in
keymap that were bound to olddef. In other words,
olddef is replaced with newdef wherever it appears. The
function returns nil.
For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:
(substitute-key-definition 'find-file 'find-file-read-only (current-global-map))
If oldmap is non-nil, then its bindings determine which
keys to rebind. The rebindings still happen in newmap, not in
oldmap. Thus, you can change one map under the control of the
bindings in another. For example,
(substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map)
puts the special deletion command in my-map for whichever keys
are globally bound to the standard deletion command.
Here is an example showing a keymap before and after substitution:
(setq map '(keymap
(?1 . olddef-1)
(?2 . olddef-2)
(?3 . olddef-1)))
=> (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))
(substitute-key-definition 'olddef-1 'newdef map)
=> nil
map
=> (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
Function: suppress-keymap keymap &optional nodigits
This function changes the contents of the full keymap keymap by
replacing the self-insertion commands for numbers with the
digit-argument function, unless nodigits is non-nil,
and by replacing the functions for the rest of the printing characters
with undefined. This means that ordinary insertion of text is
impossible in a buffer with a local keymap on which
suppress-keymap has been called.
The suppress-keymap function does not make it impossible to
modify a buffer, as it does not suppress commands such as yank
and quoted-insert. To prevent any modification of a buffer, make
it read-only (see section Read-Only Buffers).
Since this function modifies keymap, you would normally use it
on a newly created keymap. Operating on an existing keymap
that is used for some other purpose is likely to cause trouble; for
example, suppressing global-map would make it impossible to use
most of Emacs.
Most often, suppress-keymap is used to initialize local
keymaps of modes such as Rmail and Dired where insertion of text is not
desirable and the buffer is read-only. Here is an example taken from
the file `emacs/lisp/dired.el', showing how the local keymap for
Dired mode is set up:
... (setq dired-mode-map (make-keymap)) (suppress-keymap dired-mode-map) (define-key dired-mode-map "r" 'dired-rename-file) (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted) (define-key dired-mode-map "d" 'dired-flag-file-deleted) (define-key dired-mode-map "v" 'dired-view-file) (define-key dired-mode-map "e" 'dired-find-file) (define-key dired-mode-map "f" 'dired-find-file) ...
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling define-key.
Command: global-set-key key definition
This function sets the binding of key in the current global map to definition.
(global-set-key key definition) == (define-key (current-global-map) key definition)
Command: global-unset-key key
This function removes the binding of key from the current global map.
One use of this function is in preparation for defining a longer key which uses it implicitly as a prefix--which would not be allowed if key has a non-prefix binding. For example:
(global-unset-key "\C-l")
=> nil
(global-set-key "\C-l\C-l" 'redraw-display)
=> nil
This function is implemented simply using define-key:
(global-unset-key key) == (define-key (current-global-map) key nil)
Command: local-set-key key definition
This function sets the binding of key in the current local keymap to definition.
(local-set-key key definition) == (define-key (current-local-map) key definition)
Command: local-unset-key key
This function removes the binding of key from the current local map.
(local-unset-key key) == (define-key (current-local-map) key nil)
This section describes functions used to scan all the current keymaps for the sake of printing help information.
Function: accessible-keymaps keymap &optional prefix
This function returns a list of all the keymaps that can be accessed
(via prefix keys) from keymap. The value is an association list
with elements of the form (key . map), where
key is a prefix key whose definition in keymap is
map.
The elements of the alist are ordered so that the key increases
in length. The first element is always ("" . keymap),
because the specified keymap is accessible from itself with a prefix of
no events.
If prefix is given, it should be a prefix key sequence; then
accessible-keymaps includes only the submaps whose prefixes start
with prefix. These elements look just as they do in the value of
(accessible-keymaps); the only difference is that some elements
are omitted.
In the example below, the returned alist indicates that the key
ESC, which is displayed as `^[', is a prefix key whose
definition is the sparse keymap (keymap (83 . center-paragraph)
(115 . foo)).
(accessible-keymaps (current-local-map))
=>(("" keymap
(27 keymap ; Note this keymap for ESC is repeated below.
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
("^[" keymap
(83 . center-paragraph)
(115 . foo)))
In the following example, C-h is a prefix key that uses a sparse
keymap starting with (keymap (118 . describe-variable)...).
Another prefix, C-x 4, uses a keymap which happens to be
ctl-x-4-map. The event mode-line is one of several dummy
events used as prefixes for mouse actions in special parts of a window.
(accessible-keymaps (current-global-map))
=> (("" keymap [set-mark-command beginning-of-line ...
delete-backward-char])
("^H" keymap (118 . describe-variable) ...
(8 . help-for-help))
("^X" keymap [x-flush-mouse-queue ...
backward-kill-sentence])
("^[" keymap [mark-sexp backward-sexp ...
backward-kill-word])
("^X4" keymap (15 . display-buffer) ...)
([mode-line] keymap
(S-mouse-2 . mouse-split-window-horizontally) ...))
These are not all the keymaps you would see in an actual case.
Function: where-is-internal command &optional keymap firstonly
This function returns a list of key sequences (of any length) that are
bound to command in keymap and the global keymap. The
argument command can be any object; it is compared with all keymap
entries using eq. If keymap is not supplied, then the
global map alone is used.
If firstonly is non-nil, then the value is a single
string representing the first key sequence found, rather than a list of
all possible key sequences.
This function is used by where-is (see section 'Help' in The GNU Emacs Manual).
(where-is-internal 'describe-function)
=> ("\^hf" "\^hd")
Command: describe-bindings prefix
This function creates a listing of all defined keys, and their definitions. The listing is put in a buffer named `*Help*', which is then displayed in a window.
A meta character is shown as ESC followed by the corresponding non-meta character. Control characters are indicated with C-.
When several characters with consecutive ASCII codes have the
same definition, they are shown together, as
`firstchar..lastchar'. In this instance, you need to
know the ASCII codes to understand which characters this means.
For example, in the default global map, the characters `SPC
.. ~' are described by a single line. SPC is ASCII 32,
~ is ASCII 126, and the characters between them include all
the normal printing characters, (e.g., letters, digits, punctuation,
etc.); all these characters are bound to self-insert-command.
If prefix is non-nil, it should be a prefix key; then only
keys that start with prefix are described.
A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that may be enabled individually.
This chapter covers both major and minor modes, the way they are indicated in the mode line, and how they run hooks supplied by the user. Related topics such as keymaps and syntax tables are covered in separate chapters. (See section Keymaps, and section Syntax Tables.)
Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time.
The least specialized major mode is called Fundamental mode.
This mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
LFD (eval-print-last-sexp), TAB
(lisp-indent-line), and other keys.
When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter it for its new function. For example, Rmail Edit mode, which is in `emacs/lisp/rmailedit.el', is a major mode that is very similar to Text mode except that it provides three additional commands. Its definition is distinct from that of Text mode, but was derived from it.
Rmail Edit mode is an example of a case where one piece of text is put temporarily into a different major mode so it can be edited in a different way (with ordinary Emacs commands rather than Rmail). In such cases, the temporary major mode usually has a command to switch back to the buffer's usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user's options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using alternative major modes avoids this limitation. See section Recursive Editing.
The standard GNU Emacs Lisp library directory contains the code for several major modes, in files including `text-mode.el', `texinfo.el', `lisp-mode.el', `c-mode.el', and `rmail.el'. You can look at these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a rather complicated, full-featured mode.
The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please keep these conventions in mind when you create a new major mode:
describe-mode) will print this.
The documentation string may include the special documentation
substrings, `\[command]', `\{keymap}', and
`\<keymap>', that enable the documentation to adapt
automatically to the user's own key bindings. See section Substituting Key Bindings in Documentation. The describe-mode function replaces these
special documentation substrings with their current meanings.
See section Access to Documentation Strings.
major-mode to the
major mode command symbol. This is how describe-mode discovers
which documentation to print.
mode-name to the
"pretty" name of the mode, as a string. This appears in the mode
line.
use-local-map to install this local map.
See section Active Keymaps, for more information.
This keymap should be kept in a global variable named
modename-mode-map. Normally the library that defines the
mode sets this variable. Use defvar to set the variable, so that
it is not reinitialized if it already has a value. (Such
reinitialization could discard customizations made by the user.)
modename-mode-syntax-table. The reasons
for this are the same as for using a keymap variable. See section Syntax Tables.
modename-mode-abbrev-table. See section Abbrev Tables.
make-local-variable in the major mode command, not
make-variable-buffer-local. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See section Buffer-Local Variables.
mode-class
with value special, put on as follows:
(put 'funny-mode 'mode-class 'special)
This tells Emacs that new buffers created while the current buffer has Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature.
auto-mode-alist to select the mode for those file names. If you
define the mode command to autoload, you should add this element in the
same file that calls autoload. Otherwise, it is sufficient to
add the element in the file that contains the mode definition.
See section How Emacs Chooses a Major Mode.
autoload form
and an example of how to add to auto-mode-alist, that users can
include in their `.emacs' files.
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from `text-mode.el' that illustrate many of the conventions listed above:
;; Create mode-specific tables.
(defvar text-mode-syntax-table nil
"Syntax table used while in text mode.")
(if text-mode-syntax-table
() ; Do not change the table if it is already set up.
(setq text-mode-syntax-table (make-syntax-table))
(modify-syntax-entry ?\" ". " text-mode-syntax-table)
(modify-syntax-entry ?\\ ". " text-mode-syntax-table)
(modify-syntax-entry ?' "w " text-mode-syntax-table))
(defvar text-mode-abbrev-table nil
"Abbrev table used while in text mode.")
(define-abbrev-table 'text-mode-abbrev-table ())
(defvar text-mode-map nil) ; Create a mode-specific keymap.
(if text-mode-map
() ; Do not change the keymap if it is already set up.
(setq text-mode-map (make-sparse-keymap))
(define-key text-mode-map "\t" 'tab-to-tab-stop)
(define-key text-mode-map "\es" 'center-line)
(define-key text-mode-map "\eS" 'center-paragraph))
Here is the complete major mode function definition for Text mode:
(defun text-mode ()
"Major mode for editing text intended for humans to read.
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map) ; This provides the local keymap.
(setq mode-name "Text") ; This name goes into the mode line.
(setq major-mode 'text-mode) ; This is how describe-mode
; finds the doc string to print.
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(run-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from `lisp-mode.el' that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table
; if it is already set.
(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))
;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is 48 in the ASCII character set.)
(while (< i ?0)
(modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
(setq i (1+ i)))
...
;; Set the syntax for other characters.
(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
...
(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
...))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:
(defun lisp-mode-variables (lisp-syntax) ;; Thelisp-syntaxargument isnilin Emacs Lisp mode, ;; andtin the other two Lisp modes. (cond (lisp-syntax (if (not lisp-mode-syntax-table) ;; The Emacs Lisp mode syntax table always exists, but ;; the Lisp Mode syntax table is created the first time a ;; mode that needs it is called. This is to save space. (progn (setq lisp-mode-syntax-table (copy-syntax-table emacs-lisp-mode-syntax-table)) ;; Change some entries for Lisp mode. (modify-syntax-entry ?\| "\" " lisp-mode-syntax-table) (modify-syntax-entry ?\[ "_ " lisp-mode-syntax-table) (modify-syntax-entry ?\] "_ " lisp-mode-syntax-table))) (set-syntax-table lisp-mode-syntax-table))) (setq local-abbrev-table lisp-mode-abbrev-table) ...)
Functions such as forward-paragraph use the value of the
paragraph-start variable. Since Lisp code is different from
ordinary text, the paragraph-start variable needs to be set
specially to handle Lisp. Also, comments are indented in a special
fashion in Lisp and the Lisp modes need their own mode-specific
comment-indent-function. The code to set these variables is the
rest of lisp-mode-variables.
(make-local-variable 'paragraph-start) (setq paragraph-start (concat "^$\\|" page-delimiter)) ... (make-local-variable 'comment-indent-function) (setq comment-indent-function 'lisp-comment-indent))
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-l to run-lisp, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following function adds these common commands to a given
keymap.
(defun lisp-mode-commands (map) (define-key map "\e\C-q" 'indent-sexp) (define-key map "\177" 'backward-delete-char-untabify) (define-key map "\t" 'lisp-indent-line))
Here is an example of using lisp-mode-commands to initialize a
keymap, as part of the code for Emacs Lisp mode. First we declare a
variable with defvar to hold the mode-specific keymap. When this
defvar executes, it sets the variable to nil if it was
void. Then we set up the keymap if the variable is nil.
This code avoids changing the keymap or the variable if it is already set up. This lets the user customize the keymap if he or she so wishes.
(defvar emacs-lisp-mode-map () "")
(if emacs-lisp-mode-map
()
(setq emacs-lisp-mode-map (make-sparse-keymap))
(define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun)
(lisp-mode-commands emacs-lisp-mode-map))
Finally, here is the complete major mode function definition for Emacs Lisp mode.
(defun emacs-lisp-mode ()
"Major mode for editing Lisp code to run in Emacs.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{emacs-lisp-mode-map}
Entry to this mode runs the hook `emacs-lisp-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map emacs-lisp-mode-map) ; This provides the local keymap.
(set-syntax-table emacs-lisp-mode-syntax-table)
(setq major-mode 'emacs-lisp-mode) ; This is how describe-mode
; finds out what to describe.
(setq mode-name "Emacs-Lisp") ; This goes into the mode line.
(lisp-mode-variables nil) ; This define various variables.
(run-hooks 'emacs-lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited.
Command: fundamental-mode
Fundamental mode is a major mode that is not specialized for anything
in particular. Other major modes are defined in effect by comparison
with this one--their definitions say what to change, starting from
Fundamental mode. The fundamental-mode function does not
run any hooks, so it is not readily customizable.
Command: normal-mode &optional find-file
This function establishes the proper major mode and local variable
bindings for the current buffer. First it calls set-auto-mode,
then it runs hack-local-variables to parse, and bind or
evaluate as appropriate, any local variables.
If the find-file argument to normal-mode is
non-nil, normal-mode assumes that the find-file
function is calling it. In this case, it may process a local variables
list at the end of the file. The variable enable-local-variables
controls whether to do so.
If you run normal-mode yourself, the argument find-file
is normally nil. In this case, normal-mode
unconditionally processes any local variables list. See section 'Local Variables in Files' in The GNU Emacs Manual, for
the syntax of the local variables section of a file.
normal-mode uses condition-case around the call to the
major mode function, so errors are caught and reported as a `File
mode specification error', followed by the original error message.
User Option: enable-local-variables
This variable controls processing of local variables lists in files
being visited. A value of t means process the local variables
lists unconditionally; nil means ignore them; anything else means
ask the user what to do for each file. The default value is t.
User Option: enable-local-eval
This variable controls processing of `Eval:' in local variables
lists in files being visited. A value of t means process them
unconditionally; nil means ignore them; anything else means ask
the user what to do for each file. The default value is maybe.
Function: set-auto-mode
This function selects the major mode that is appropriate for the
current buffer. It may base its decision on the value of the `-*-'
line, on the visited file name (using auto-mode-alist), or on the
value of a local variable). However, this function does not look for
the `mode:' local variable near the end of a file; the
hack-local-variables function does that. See section 'How Major Modes are Chosen' in The GNU Emacs Manual.
User Option: default-major-mode
This variable holds the default major mode for new buffers. The
standard value is fundamental-mode.
If the value of default-major-mode is nil, Emacs uses
the (previously) current buffer's major mode for the major mode of a new
buffer. However, if the major mode symbol has a mode-class
property with value special, then it is not used for new buffers;
Fundamental mode is used instead. The modes that have this property are
those such as Dired and Rmail that are useful only with text that has
been specially prepared.
Variable: initial-major-mode
The value of this variable determines the major mode of the initial
`*scratch*' buffer. The value should be a symbol that is a major
mode command name. The default value is lisp-interaction-mode.
Variable: auto-mode-alist
This variable contains an association list of file name patterns
(regular expressions; see section Regular Expressions) and corresponding
major mode functions. Usually, the file name patterns test for suffixes,
such as `.el' and `.c', but this need not be the case. Each
element of the alist looks like (regexp .
mode-function).
For example,
(("^/tmp/fol/" . text-mode)
("\\.texinfo$" . texinfo-mode)
("\\.texi$" . texinfo-mode)
("\\.el$" . emacs-lisp-mode)
("\\.c$" . c-mode)
("\\.h$" . c-mode)
...)
When you visit a file whose expanded file name (see section Functions that Expand Filenames) matches a regexp, set-auto-mode calls the
corresponding mode-function. This feature enables Emacs to select
the proper major mode for most files.
Here is an example of how to prepend several pattern pairs to
auto-mode-alist. (You might use this sort of expression in your
`.emacs' file.)
(setq auto-mode-alist
(append
;; Filename starts with a dot.
'(("/\\.[^/]*$" . fundamental-mode)
;; Filename has no dot.
("[^\\./]*$" . fundamental-mode)
("\\.C$" . c++-mode))
auto-mode-alist))
Function: hack-local-variables &optional force
This function parses, and binds or evaluates as appropriate, any local variables for the current buffer.
The handling of enable-local-variables documented for
normal-mode actually takes place here. The argument force
reflects the argument find-file given to normal-mode.
The describe-mode function is used to provide information
about major modes. It is normally called with C-h m. The
describe-mode function uses the value of major-mode,
which is why every major mode function needs to set the
major-mode variable.
Command: describe-mode
This function displays the documentation of the current major mode.
The describe-mode function calls the documentation
function using the value of major-mode as an argument. Thus, it
displays the documentation string of the major mode function.
(See section Access to Documentation Strings.)
Variable: major-mode
This variable holds the symbol for the current buffer's major mode. This
symbol should be the name of the function that is called to initialize the
mode. The describe-mode function uses the documentation string
of this symbol as the documentation of the major mode.
A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named "Generally available, optional feature modes" except that such a name is unwieldy.
A minor mode is not usually a modification of single major mode. For example, Auto Fill mode may be used in any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do.
A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to deactivate a minor mode and restore the environment of the major mode to the state it was in before the minor mode was activated.
Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of Emacs. Minor mode keymaps make this easier.
There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, and the use of keymaps and other tables.
In addition, there are several conventions that are specific to minor modes.
nil to
disable; anything else to enable.) We call this the mode
variable.
This variable is used in conjunction with the minor-mode-alist to
display the minor mode name in the mode line. It can also enable
or disable a minor mode keymap. Individual commands or hooks can also
check the variable's value.
If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local.
The command should accept one optional argument. If the argument is
nil, it should toggle the mode (turn it on if it is off, and off
if it is on). Otherwise, it should turn the mode on if the argument is
a positive integer, a symbol other than nil or -, or a
list whose CAR is such an integer or symbol; it should turn the
mode off otherwise.
Here is an example taken from the definition of overwrite-mode.
It shows the use of overwrite-mode as a variable which enables or
disables the mode's behavior.
(setq overwrite-mode
(if (null arg) (not overwrite-mode)
(> (prefix-numeric-value arg) 0)))
minor-mode-alist for each minor mode
(see section Variables Used in the Mode Line). This element should be a list of the
following form:
(mode-variable string)
Here mode-variable is the variable that controls enablement of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once.
When you add an element to minor-mode-alist, use assq to
check for an existing element, to avoid duplication. For example:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
As of Emacs version 19, each minor mode can have its own keymap which is
active when the mode is enabled. See section Active Keymaps. To set up a
keymap for a minor mode, add an element to the alist
minor-mode-map-alist.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. This is the only way to accomplish this in general, since
there is no way to customize what self-insert-command does except
in certain special cases (designed for abbrevs and Auto Fill mode). (Do
not try substituting your own definition of self-insert-command
for the standard one. The editor command loop handles this function
specially.)
Variable: minor-mode-map-alist
This variable is an alist of elements element that look like this:
(variable . keymap)
where variable is the variable which indicates whether the minor
mode is enabled, and keymap is the keymap. The keymap
keymap is active whenever variable has a non-nil
value.
Note that elements of minor-mode-map-alist do not have the same
structure as elements of minor-mode-alist. The map must be the
CDR of the element; a list with the map as the second element will
not do.
What's more, the keymap itself must appear in the CDR. It does not work to store a variable in the CDR and make the map the value of that variable.
When more than one minor mode keymap is active, their order of priority
is the order of minor-mode-map-alist. But you should design
minor modes so that they don't interfere with each other. If you do
this properly, the order will not matter.
Each Emacs window (aside from minibuffer windows) includes a mode line which displays status information about the buffer displayed in the window. The mode line contains information about the buffer such as its name, associated file, depth of recursive editing, and the major and minor modes of the buffer.
This section describes how the contents of the mode line are controlled. It is in the chapter on modes because much of the information displayed in the mode line relates to the enabled major and minor modes.
mode-line-format is a buffer-local variable that holds a
template used to display the mode line of the current buffer. All
windows for the same buffer use the same mode-line-format and the
mode lines will appear the same (except perhaps for the percentage of
the file scrolled off the top).
The mode line of a window is normally updated whenever a different
buffer is shown in the window, or when the buffer's modified-status
changes from nil to t or vice-versa. If you modify any of
the variables referenced by mode-line-format, you may want to
force an update of the mode line so as to display the new information.
Function: force-mode-line-update
Force redisplay of the current buffer's mode line.
The mode line is usually displayed in inverse video; see
mode-line-inverse-video in section Inverse Video.
The mode line contents are controlled by a data structure of lists,
strings, symbols and numbers kept in the buffer-local variable
mode-line-format. The data structure is called a mode line
construct, and it is built in recursive fashion out of simpler mode line
constructs.
Variable: mode-line-format
The value of this variable is a mode line construct with overall responsibility for the mode line format. The value of this variable controls which other variables are used to form the mode line text, and where they appear.
A mode line construct may be as simple as a fixed string of text, but it usually specifies how to use other variables to construct the text. Many of these variables are themselves defined to have mode line constructs as their values.
The default value of mode-line-format incorporates the values
of variables such as mode-name and minor-mode-alist.
Because of this, very few modes need to alter mode-line-format.
For most purposes, it is sufficient to alter the variables referenced by
mode-line-format.
A mode line construct may be a list, cons cell, symbol, or string. If the value is a list, each element may be a list, a cons cell, a symbol, or a string.
string
%-constructs. Decimal digits after the %
specify the field width for space filling on the right (i.e., the data
is left justified). See section %-Constructs in the Mode Line.
symbol
t or nil, or is void, in which case symbol is
ignored.
There is one exception: if the value of symbol is a string, it is
processed verbatim in that the %-constructs are not recognized.
(string rest...) or (list rest...)
(symbol then else)
nil,
the second element of the list (then) is processed recursively as
a mode line element. But if the value of symbol is nil,
the third element of the list (if there is one) is processed
recursively.
(width rest...)
For example, the usual way to show what percentage of a buffer is above
the top of the window is to use a list like this: (-3 . "%p").
If you do alter mode-line-format itself, the new value should
use all the same variables that are used by the default value, rather
than duplicating their contents or displaying the information in another
fashion. This permits customizations made by the user, by libraries
(such as display-time) or by major modes via changes to those
variables remain effective.
Here is an example of a mode-line-format that might be
useful for shell-mode since it contains the hostname and default
directory.
(setq mode-line-format
(list ""
'mode-line-modified
"%b--"
(getenv "HOST") ; One element is not constant.
":"
'default-directory
" "
'global-mode-string
" %[(" 'mode-name
'minor-mode-alist
"%n"
'mode-line-process
")%]----"
'(-3 . "%p")
"-%-"))
This section describes variables incorporated by the
standard value of mode-line-format into the text of the mode
line. There is nothing inherently special about these variables; any
other variables could have the same effects on the mode line if
mode-line-format were changed to use them.
Variable: mode-line-modified
This variable holds the value of the mode-line construct that displays whether the current buffer is modified.
The default value of mode-line-modified is
("--%1*%1*-"). This means that the mode line displays
`--**-' if the buffer is modified, `-----' if the buffer is
not modified, and `--%%-' if the buffer is read only.
Changing this variable does not force an update of the mode line.
Variable: mode-line-buffer-identification
This variable identifies the buffer being displayed in the window. Its default value is `Emacs: %17b', which means that it displays `Emacs:' followed by the buffer name. You may want to change this in modes such as Rmail that do not behave like a "normal" Emacs.
Variable: global-mode-string
This variable holds a string that is displayed in the mode line. The
command display-time puts the time and load in this variable.
The `%M' construct substitutes the value of
global-mode-string, but this is obsolete, since the variable is
included directly in the mode line.
Variable: mode-name
This buffer-local variable holds the "pretty" name of the current buffer's major mode. Each major mode should set this variable so that the mode name will appear in the mode line.
Variable: minor-mode-alist
This variable holds an association list whose elements specify how the
mode line should indicate that a minor mode is active. Each element of
the minor-mode-alist should be a two-element list:
(minor-mode-variable mode-line-string)
The string mode-line-string is included in the mode line when
the value of minor-mode-variable is non-nil and not
otherwise. These strings should begin with spaces so that they don't
run together. Conventionally, the minor-mode-variable for a
specific mode is set to a non-nil value when that minor mode is
activated.
The default value of minor-mode-alist is:
minor-mode-alist
=> ((abbrev-mode " Abbrev")
(overwrite-mode " Ovwrt")
(auto-fill-function " Fill")
(defining-kbd-macro " Def"))
(In earlier Emacs versions, auto-fill-function was called
auto-fill-hook.)
minor-mode-alist is not buffer-local. The variables mentioned
in the alist should be buffer-local if the minor mode can be enabled
separately in each buffer.
Variable: mode-line-process
This buffer-local variable contains the mode line information on process
status in modes used for communicating with subprocesses. It is
displayed immediately following the major mode name, with no intervening
space. For example, its value in the `*shell*' buffer is
(": %s"), which allows the shell to display its status along
with the major mode as: `(Shell: run)'. Normally this variable
is nil.
Variable: default-mode-line-format
This variable holds the default mode-line-format for buffers
that do not override it. This is the same as (default-value
'mode-line-format).
The default value of default-mode-line-format is:
(""
mode-line-modified
mode-line-buffer-identification
" "
global-mode-string
" %[("
mode-name
minor-mode-alist
"%n"
mode-line-process
")%]----"
(-3 . "%p")
"-%-")
%-Constructs in the Mode Line
The following table lists the recognized %-constructs and what
they mean.
%b
buffer-name function.
%f
buffer-file-name function.
%*
buffer-read-only); buffer-modified-p);
%s
process-status.
%p
%n
narrow-to-region in section Narrowing).
%[
%]
%%
%-constructs are allowed.
%-
The following two %-constructs are still supported but are
obsolete since use of the mode-name and
global-mode-string variables will produce the same results.
%m
mode-name.
%M
global-mode-string. Currently, only
display-time modifies the value of global-mode-string.
A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides lots of hooks for the sake of customization. Most often, hooks are set up in the `.emacs' file, but Lisp programs can set them also. See section Standard Hooks, for a list of standard hook variables.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. The reason most hooks are normal hooks is so that you can use them in a uniform way. You can always tell when a hook is a normal hook, because its name ends in `-hook'.
The recommended way to add a hook function to a normal hook is by
calling add-hook (see below). The hook functions may be any of
the valid kinds of functions that funcall accepts (see section What Is a Function?). Most normal hook variables are initially void;
add-hook knows how to deal with this.
As for abnormal hooks, those whose names end in `-function' have a value which is a single function. Those whose names end in `-hooks' have a value which is a list of functions. Any hook which is abnormal is abnormal because a normal hook won't do the job; either the functions are called with arguments, or their values are meaningful. The name shows you that the hook is abnormal and you need to look up how to use it properly.
Most major modes run hooks as the last step of initialization. This
makes it easy for a user to customize the behavior of the mode, by
overriding the local variable assignments already made by the mode. But
hooks may also be used in other contexts. For example, the hook
suspend-hook runs just before Emacs suspends itself
(see section Suspending Emacs).
For example, you can put the following expression in your `.emacs' file if you want to turn on Auto Fill mode when in Lisp Interaction mode:
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
The next example shows how to use a hook to customize the way Emacs formats C code. (People often have strong personal preferences for one format compared to another.) Here the hook function is an anonymous lambda expression.
(add-hook 'c-mode-hook
(function (lambda ()
(setq c-indent-level 4
c-argdecl-indent 0
c-label-offset -4
c-continued-statement-indent 0
c-brace-offset 0
comment-column 40))))
(setq c++-mode-hook c-mode-hook)
Finally, here is an example of how to use the Text mode hook to provide a customized mode line for buffers in Text mode, displaying the default directory in addition to the standard components of the mode line. (This may cause the mode line to run out of space if you have very long file names or display the time and load.)
(add-hook 'text-mode-hook
(function (lambda ()
(setq mode-line-format
'(mode-line-modified
"Emacs: %14b"
" "
default-directory
" "
global-mode-string
"%[("
mode-name
minor-mode-alist
"%n"
mode-line-process
") %]---"
(-3 . "%p")
"-%-")))))
At the appropriate time, Emacs uses the run-hooks function to
run particular hooks. This function calls the hook functions you have
added with add-hooks.
Function: run-hooks &rest hookvar
This function takes one or more hook names as arguments and runs each one in turn. Each hookvar argument should be a symbol that is a hook variable. These arguments are processed in the order specified.
If a hook variable has a non-nil value, that value may be a
function or a list of functions. If the value is a function (either a
lambda expression or a symbol with a function definition), it is
called. If it is a list, the elements are called, in order.
The hook functions are called with no arguments.
For example:
(run-hooks 'emacs-lisp-mode-hook)
Major mode functions use this function to call any hooks defined by the user.
Function: add-hook hook function &optional append
This function is the handy way to add function function to hook variable hook. For example,
(add-hook 'text-mode-hook 'my-text-hook-function)
adds my-text-hook-function to the hook called text-mode-hook.
It is best to design your hook functions so that the order in which they
are executed does not matter. Any dependence on the order is "asking
for trouble." However, the order is predictable: normally,
function goes at the front of the hook list, so it will be
executed first (barring another add-hook call).
If the optional argument append is non-nil, the new hook
function goes at the end of the hook list and will be executed last.
GNU Emacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation.
Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion.
A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable.
When you write a documentation string, make the first line a complete
sentence (or two complete sentences) since some commands, such as
apropos, print only the first line of a multi-line documentation
string. Also, you should not indent the second line of a documentation
string, if you have one, because that looks odd when you use C-h f
(describe-function) or C-h v (describe-variable).
Documentation strings may contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (See section Access to Documentation Strings.)
Within the Lisp world, a documentation string is kept with the function or variable that it describes:
documentation knows how to extract it.
variable-documentation. The
function documentation-property knows how to extract it.
However, to save space, the documentation for preloaded functions and
variables (including primitive functions and autoloaded functions) are
stored in the `emacs/etc/DOC-version' file. The
`emacs/etc/DOC-version' file can be accessed by both the
documentation and the documentation-property functions,
and the process is transparent to the user. In this case, the
documentation string is replaced with an integer offset into the
`emacs/etc/DOC-version' file. Keeping the documentation
strings out of the Emacs core image saves a significant amount of space.
See section Building Emacs.
For information on the uses of documentation strings, see section 'Help' in The GNU Emacs Manual.
The `emacs/etc' directory contains two utilities that you can use to print nice-looking hardcopy for the file `emacs/etc/DOC-version'. These are `sorted-doc.c' and `digest-doc.c'.
Function: documentation-property symbol property &optional verbatim
This function returns the documentation string that is recorded
symbol's property list under property property. This uses
the function get, but does more than that: it also retrieves the
string from the file `emacs/etc/DOC-version' if necessary,
and runs substitute-command-keys to substitute the actual
(current) key bindings.
If verbatim is non-nil, that inhibits running
substitute-command-keys. (The verbatim argument exists
only as of Emacs 19.)
(documentation-property 'command-line-processed
'variable-documentation)
=> "t once command line has been processed"
(symbol-plist 'command-line-processed)
=> (variable-documentation 188902)
Function: documentation function &optional verbatim
This function returns the documentation string of function. This function will access the documentation string if it is stored in the `emacs/etc/DOC-version' file.
In addition, documentation runs substitute-command-keys
on the resulting string, so the value contains the actual (current) key
bindings. (This is not done if verbatim is non-nil; the
verbatim argument exists only as of Emacs 19.)
The function documentation signals a void-function error
unless function has a function definition. However,
function does not need to have a documentation string. If there
is no documentation string, documentation returns nil.
Here is an example of using the two functions, documentation and
documentation-property, to display the documentation strings for
several symbols in a `*Help*' buffer.
(defun describe-symbols (pattern)
"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the `*Help*' buffer."
(interactive "sDescribe symbols matching: ")
(let ((describe-func
(function
(lambda (s)
;; Print description of symbol.
(if (fboundp s) ; It is a function.
(princ
(format "%s\t%s\n%s\n\n" s
(if (commandp s)
(let ((keys (where-is-internal s)))
(if keys
(concat
"Keys: "
(mapconcat 'key-description
keys " "))
"Keys: none"))
"Function")
(or (documentation s)
"not documented"))))
(if (boundp s) ; It is a variable.
(princ
(format "%s\t%s\n%s\n\n" s
(if (user-variable-p s)
"Option " "Variable")
(or (documentation-property
s 'variable-documentation)
"not documented")))))))
sym-list)
;; Build a list of symbols that match pattern.
(mapatoms (function
(lambda (sym)
(if (string-match pattern (symbol-name sym))
(setq sym-list (cons sym sym-list))))))
;; Display the data.
(with-output-to-temp-buffer "*Help*"
(mapcar describe-func (sort sym-list 'string<))
(print-help-return-message))))
The describe-symbols function works like apropos,
but provides more information.
(describe-symbols "goal") ---------- Buffer: *Help* ---------- goal-column Option *Semipermanent goal column for vertical motion, as set by C-x C-n, or nil. set-goal-column Command: C-x C-n Set the current horizontal position as a goal for C-n and C-p. Those commands will move to this position in the line moved to rather than trying to keep the same horizontal position. With a non-nil argument, clears out the goal column so that C-n and C-p resume vertical motion. The goal column is stored in the variable `goal-column'. temporary-goal-column Variable Current goal column for vertical motion. It is the column where point was at the start of current run of vertical motion commands. When the `track-eol' feature is doing its job, the value is 9999. ---------- Buffer: *Help* ----------
Function: Snarf-documentation filename
This function is used only during Emacs initialization, just before the runnable Emacs is dumped. It finds the file offsets of the documentation strings stored in the file filename, and records them in the in-core function definitions and variable property lists in place of the actual strings. See section Building Emacs.
Emacs finds the file filename in the `emacs/etc'
directory. When the dumped Emacs is later executed, the same file is
found in the directory data-directory. Usually filename is
"DOC-version".
Variable: data-directory
This variable holds the name of the directory in which Emacs finds
certain data files that come with Emacs or are built as part of building
Emacs. (In older Emacs versions, this directory was the same as
exec-directory.)
This function makes it possible for you to write a documentation string
that enables a user to display information about the current, actual key
bindings. if you call documentation with non-nil
verbatim, you might later call this function to do the
substitution that you prevented documentation from doing.
Function: substitute-command-keys string
This function returns string with certain special substrings replaced by the actual (current) key bindings. This permits the documentation to be displayed with accurate information about key bindings. (The key bindings may be changed by the user between the time Emacs is built and the time that the documentation is asked for.)
This table lists the forms of the special substrings and what they are replaced with:
\[command]
\{mapvar}
describe-bindings.)
\<mapvar>
substitute-command-keys use the value of
mapvar as the keymap for future `\[command]'
substrings. This special string does not produce any replacement text
itself; it only affects the replacements done later.
Please note: each `\' must be doubled when written in a string in Emacs Lisp.
Here are examples of the special substrings:
(substitute-command-keys
"To abort recursive edit, type: \\[abort-recursive-edit]")
=> "To abort recursive edit, type: C-]"
(substitute-command-keys
"The keys that are defined for the minibuffer here are:
\\{minibuffer-local-must-match-map}")
=> "The keys that are defined for the minibuffer here are:
? minibuffer-completion-help
SPC minibuffer-complete-word
TAB minibuffer-complete
LFD minibuffer-complete-and-exit
RET minibuffer-complete-and-exit
C-g abort-recursive-edit
"
(substitute-command-keys
"To abort a recursive edit from the minibuffer, type\
\\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
=> "To abort a recursive edit from the minibuffer, type C-g."
These functions convert events, key sequences or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing characters to sequences of printing characters. The description of a printing character is the character itself.
Function: key-description sequence
This function returns a string containing the Emacs standard notation
for the input events in sequence. The argument sequence may
be a string, vector or list. See section Input Events, for more information
about valid events. See also the examples for
single-key-description, below.
Function: single-key-description event
This function returns a string describing event in the standard Emacs notation for keyboard input. A normal printing character is represented by itself, but a control character turns into a string starting with `C-', a meta character turns into a string starting with `M-', and space, linefeed, etc. are transformed to `SPC', `LFD', etc. A function key is represented by its name. An event which is a list is represented by the name of the symbol in the CAR of the list.
(single-key-description ?\C-x)
=> "C-x"
(key-description "\C-x \M-y \n \t \r \f123")
=> "C-x SPC M-y SPC LFD SPC TAB SPC RET SPC C-l 1 2 3"
(single-key-description 'C-mouse-1)
=> "C-mouse-1"
Function: text-char-description character
This function returns a string describing character in the
standard Emacs notation for characters that appear in text--like
single-key-description, except that control characters are
represented with a leading caret (which is how control characters in
Emacs buffers are usually displayed).
(text-char-description ?\C-c)
=> "^C"
(text-char-description ?\M-m)
=> "M-m"
(text-char-description ?\C-\M-m)
=> "M-^M"
Emacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see section 'Help' in The GNU Emacs Manual. Here we describe some program-level interfaces to the same information.
Command: apropos regexp &optional do-all predicate
This function finds all symbols whose names contain a match for the regular expression regexp, and returns a list of them. It also displays the symbols in a buffer named `*Help*', each with a one-line description.
If do-all is non-nil, then apropos also shows
key bindings for the functions that are found.
If predicate is non-nil, it should be a function to be
called on each symbol that has matched regexp. Only symbols for
which predicate returns a non-nil value are listed or
displayed.
In the first of the following examples, apropos finds all the
symbols with names containing `exec'. In the second example, it
finds and returns only those symbols that are also commands.
(We don't show the output that results in the `*Help*' buffer.)
(apropos "exec")
=> (Buffer-menu-execute command-execute exec-directory
exec-path execute-extended-command execute-kbd-macro
executing-kbd-macro executing-macro)
(apropos "exec" nil 'commandp)
=> (Buffer-menu-execute execute-extended-command)
The command C-h a (command-apropos) calls apropos,
but specifies a predicate to restrict the output to symbols that
are commands. The call to apropos looks like this:
(apropos string t 'commandp)
Command: super-apropos regexp &optional do-all
This function differs from apropos in that it searches
documentation strings as well as symbol names for matches for
regexp. By default, it searches only the documentation strings,
and only those of functions and variables that are included in Emacs
when it is dumped. If do-all is non-nil, it scans the
names and documentation strings of all functions and variables.
Command: help-command
This command is not a function, but rather a symbol which is
equivalent to the keymap called help-map. It is defined in
`help.el' as follows:
(define-key global-map "\C-h" 'help-command) (fset 'help-command help-map)
Variable: help-map
The value of this variable is a local keymap for characters following the Help key, C-h.
Function: print-help-return-message &optional function
This function builds a string which is a message explaining how to
restore the previous state of the windows after a help command. After
building the message, it applies function to it if function
is non-nil. Otherwise it calls message to display it in
the echo area.
This function expects to be called inside a
with-output-to-temp-buffer special form, and expects
standard-output to have the value bound by that special form.
For an example of its use, see the example in the section describing the
documentation function (see section Access to Documentation Strings).
The constructed message will have one of the forms shown below.
---------- Echo Area ---------- Type C-x 1 to remove help window. ---------- Echo Area ---------- ---------- Echo Area ---------- Type C-x 4 b RET to restore old contents of help window. ---------- Echo Area ----------
Variable: help-char
The value of this variable is the character that Emacs recognizes as
meaning Help. When Emacs reads this character (which is usually 8, the
value of C-h), Emacs evaluates (eval help-form), and
displays the result if it is a string. If help-form's value is
nil, this character is read normally.
Variable: help-form
The value of this variable is a form to execute when the character
help-char is read. If the form returns a string, that string is
displayed. If help-form is nil, then the help character
is not recognized.
Entry to the minibuffer binds this variable to the value of
minibuffer-help-form.
Variable: prefix-help-command
This variable holds a command that prints help for a prefix character.
The command is run when the user types the help character after a prefix
character. The default value of prefix-help-command is
describe-prefix-bindings; that command uses
this-command-keys to find what prefix character was used, then
uses describe-bindings to describe it.
The following two functions are found in the library `helper'.
They are for modes that want to provide help without relinquishing
control, such as the "electric" modes. You must load that library
with (require 'helper) in order to use them. Their names begin
with `Helper' to distinguish them from the ordinary help functions.
Command: Helper-describe-bindings
This command pops up a window displaying a help buffer containing a
listing of all of the key bindings from both the local and global keymaps.
It works by calling describe-bindings.
Command: Helper-help
This command provides help for the current mode. It prompts the user
in the minibuffer with the message `Help (Type ? for further
options)', and then provides assistance in finding out what the key
bindings are, and what the mode is intended for. It returns nil.
This can be customized by changing the map Helper-help-map.
In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in section Buffers, and those related to backups and auto-saving are described in section Backups and Auto-Saving.
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file "the visited file" of the buffer.
A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.
In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, "I am editing a file," rather than, "I am editing a buffer which I will soon save as a file of the same name." Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind.
This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with `find-' rather than `visit-'. See section Buffer File Name, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.
Command: find-file filename
This function reads the file filename into a buffer and displays that buffer in the selected window so that the user can edit it.
The body of the find-file function is very simple and looks
like this:
(switch-to-buffer (find-file-noselect filename))
(See switch-to-buffer in section Displaying Buffers in Windows.)
When find-file is called interactively, it prompts for
filename in the minibuffer.
Function: find-file-noselect filename
This function is the guts of all the file-visiting functions. It reads a file into a buffer and returns the buffer. You may then make the buffer current or display it in a window if you wish, but this function does not do so.
If no buffer is currently visiting filename, then one is created
and the file is visited. If filename does not exist, the buffer
is left empty, and find-file-noselect displays the message
`New file' in the echo area.
If a buffer is already visiting filename, then the
find-file-noselect function uses that buffer rather than creating
a new one. However, it does verify that the file has not changed since
it was last visited or saved in that buffer. If the file has changed,
then this function asks the user whether to reread the changed file. If
the user says `yes', any changes previously made in the buffer are
lost.
The find-file-noselect function calls after-find-file
after the file is read in (see section Subroutines of Visiting). The
after-find-file function sets the buffer major mode, parses local
variables, warns the user if there exists an auto-save file more recent
than the file just visited, and finishes by running the functions in
find-file-hooks.
The find-file-noselect function returns the buffer that is
visiting the file filename.
(find-file-noselect "/etc/fstab")
=> #<buffer fstab>
Command: find-alternate-file filename
This function reads the file filename into a buffer and selects it, killing the buffer current at the time the command is run. It is useful if you have visited the wrong file by mistake, so that you can get rid of the buffer that you did not want to create, at the same time as you visit the file you intended.
When this function is called interactively, it prompts for filename.
Command: find-file-other-window filename
This function visits the file filename and displays its buffer in a window other than the selected window. It may use another existing window or split a window; see section Displaying Buffers in Windows.
When this function is called interactively, it prompts for filename.
Command: find-file-read-only filename
This function visits the file named filename and selects its
buffer, just like find-file, but it marks the buffer as
read-only. See section Read-Only Buffers, for related functions and
variables.
When this function is called interactively, it prompts for filename.
Command: view-file filename
This function views filename in View mode, returning to the previous buffer when done. View mode is a mode that allows you to skim rapidly through the file but does not let you modify it.
After loading the file, view-file runs the normal hook
view-hook using run-hooks. See section Hooks.
When this function is called interactively, it prompts for filename.
Variable: find-file-hooks
The value of this variable is a list of functions to be called after a file is visited. The file's local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run.
This variable could be a normal hook, but we think that renaming it would not be advisable.
Variable: find-file-not-found-hooks
The value of this variable is a list of functions to be called when
find-file or find-file-noselect is passed a nonexistent
filename. These functions are called as soon as the error is
detected. buffer-file-name is already set up. The functions are
called in the order given, until one of them returns non-nil.
This is not a normal hook because the values of the functions are used and they may not all be run.
The find-file-noselect function uses the
create-file-buffer and after-find-file functions as
subroutines. Sometimes it is useful to call them directly.
Function: create-file-buffer filename
This function creates a suitably named buffer for visiting filename, and returns it. The string filename (sans directory) is used unchanged if that name is free; otherwise, a string such as `<2>' is appended to get an unused name. See also section Creating Buffers.
Please note: create-file-buffer does not
associate the new buffer with a file and does not make it the current
buffer.
(create-file-buffer "foo")
=> #<buffer foo>
(create-file-buffer "foo")
=> #<buffer foo<2>>
(create-file-buffer "foo")
=> #<buffer foo<3>>
This function is used by find-file-noselect.
It uses generate-new-buffer (see section Creating Buffers).
Function: after-find-file &optional error warn
This function is called by find-file-noselect and by the
default revert function (see section Reverting). It sets the buffer major
mode, and parses local variables (see section How Emacs Chooses a Major Mode).
If there was an error in opening the file, the calling function
should pass error a non-nil value. In that case,
after-find-file issues a warning: `(New File)'. Note that,
for serious errors, you would not even call after-find-file.
Only "file not found" errors get here with a non-nil
error.
If warn is non-nil, then this function issues a warning
if an auto-save file exists and is more recent than the visited file.
The last thing after-find-file does is call all the functions
in find-file-hooks.
When you edit a file in Emacs, you are actually working on a buffer that is visiting that file--that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
Command: save-buffer &optional backup-option
This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing.
save-buffer is responsible for making backup files. Normally,
backup-option is nil, and save-buffer makes a backup
file only if this is the first save or if the buffer was previously
modified. Other values for backup-option request the making of
backup files in other circumstances:
save-buffer function marks this version of the file to be
backed up when the buffer is next saved.
save-buffer function unconditionally backs up the previous
version of the file before saving it.
Command: save-some-buffers &optional save-silently-p exiting
This command saves some modified file-visiting buffers. Normally it
asks the user about each buffer. But if save-silently-p is
non-nil, it saves all the file-visiting buffers without querying
the user.
The optional exiting argument, if non-nil, requests this
function to offer also to save certain other buffers that are not
visiting files. These are buffers that have a non-nil local
value of buffer-offer-save. (A user who says yes to saving one
of these is asked to specify a file name to use.) The
save-buffers-kill-emacs function passes a non-nil value
for this argument.
Variable: buffer-offer-save
When this variable is non-nil in a buffer, Emacs offers to save
the buffer on exit even if the buffer is not visiting a file. The
variable is automatically local in all buffers. Normally, Mail mode
(used for editing outgoing mail) sets this to t.
Command: write-file filename
This function writes the current buffer into file filename, makes the buffer visit that file, and marks it not modified. The buffer is renamed to correspond to filename unless that name is already in use.
Variable: write-file-hooks
The value of this variable is a list of functions to be called before
writing out a buffer to its visited file. If one of them returns
non-nil, the file is considered already written and the rest of
the functions are not called, nor is the usual code for writing the file
executed.
If a function in write-file-hooks returns non-nil, it
is responsible for making a backup file (if that is appropriate).
To do so, execute the following code:
(or buffer-backed-up (backup-buffer))
You might wish to save the file modes value returned by
backup-buffer and use that to set the mode bits of the file that
you write. This is what basic-save-buffer does when it writes a
file in the usual way.
Here is an example showing how to add an element to
write-file-hooks but avoid adding it twice:
(or (memq 'my-write-file-hook write-file-hooks)
(setq write-file-hooks
(cons
'my-write-file-hook write-file-hooks)))
Variable: local-write-file-hooks
This works just like write-file-hooks, but it is intended
to be made local to particular buffers. It's not a good idea to make
write-file-hooks local to a buffer--use this variable instead.
The variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. This is convenient for packages that read "file" contents in special ways, and set up hooks to save the data in a corresponding way.
Variable: write-contents-hooks
This works just like write-file-hooks, but it is intended to be
used for hooks that pertain to the contents of the file, as opposed to
hooks that pertain to where the file came from.
Variable: after-save-hook
This normal hook runs after a buffer has been saved in its visited file.
Variable: file-precious-flag
If this variable is non-nil, then save-buffer protects
against I/O errors while saving by writing the new file to a temporary
name instead of the name it is supposed to have, and then renaming it to
the intended name after it is clear there are no errors. This procedure
prevents problems such as a lack of disk space from resulting in an
invalid file.
(This feature worked differently in older Emacs versions.)
Some modes set this non-nil locally in particular buffers.
User Option: require-final-newline
This variable determines whether files may be written out that do
not end with a newline. If the value of the variable is
t, then Emacs silently puts a newline at the end of the file
whenever the buffer being saved does not already end in one. If the
value of the variable is non-nil, but not t, then Emacs
asks the user whether to add a newline each time the case arises.
If the value of the variable is nil, then Emacs doesn't add
newlines at all. nil is the default value, but a few major modes
set it to t in particular buffers.
You can copy a file from the disk and insert it into a buffer
using the insert-file-contents function. Don't use the user-level
command insert-file in a Lisp program, as that sets the mark.
Function: insert-file-contents filename &optional visit beg end
This function inserts the contents of file filename into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if filename is not the name of a file that can be read.
If visit is non-nil, it also marks the buffer as
unmodified and sets up various fields in the buffer so that it is
visiting the file filename: these include the buffer's visited
file name and its last save file modtime. This feature is used by
find-file-noselect and you should probably not use it yourself.
If beg and end are non-nil, they should be integers
specifying the portion of the file to insert. In this case, visit
must be nil. For example,
(insert-file-contents filename nil 0 500)
inserts the first 500 characters of a file.
If you want to pass a file name to another process so that another
program can read the file, see the function file-local-copy in
section Making Certain File Names "Magic".
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the append-to-file and
write-region functions. Don't use these functions to write to
files that are being visited; that could cause confusion in the
mechanisms for visiting.
Command: append-to-file start end filename
This function appends the contents of the region delimited by
start and end in the current buffer to the end of file
filename. If that file does not exist, it is created. This
function returns nil.
An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
Command: write-region start end filename &optional append visit
This function writes the region (of the current buffer) delimited by start and end into the file specified by filename.
If start is a string, then write-region writes or appends
that string, rather than text from the buffer.
If append is non-nil, then the region is appended to the
existing file contents (if any).
If visit is t, then Emacs establishes an association
between the buffer and the file: the buffer is then visiting that file.
It also sets the last file modification time for the current buffer to
filename's modtime, and marks the buffer as not modified. This
feature is used by write-file and you should probably not use it
yourself.
If visit is a string, it specifies the file name to visit. This
way, you can write the data to one file (filename) while recording
the buffer as visiting another file (visit). The argument
visit is used in the echo area message and also for file locking;
visit is stored in buffer-file-name. This feature is used
to implement file-precious-flag; don't use it yourself unless you
really know what you're doing.
Normally, write-region displays a message `Wrote file
filename' in the echo area. If visit is neither t
nor nil nor a string, then this message is inhibited. This
feature is useful for programs that use files for internal purposes,
files which the user does not need to know about.
When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do.
File locks do not work properly when multiple machines can share file systems, such as with NFS. Perhaps a better file locking system will be implemented in the future. When file locks do not work, it is possible for two users to make changes simultaneously, but Emacs can still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see section Comparison of Modification Time.
Function: file-locked-p filename
This function returns nil if the file filename is not
locked by this Emacs process. It returns t if it is locked by
this Emacs, and it returns the name of the user who has locked it if it
is locked by someone else.
(file-locked-p "foo")
=> nil
Function: lock-buffer &optional filename
This function locks the file filename, if the current buffer is modified. The argument filename defaults to the current buffer's visited file. Nothing is done if the current buffer is not visiting a file, or is not modified.
Function: unlock-buffer
This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file.
Function: ask-user-about-lock file other-user
This function is called when the user tries to modify file, but it is locked by another user name other-user. The value it returns tells Emacs what to do next:
t tells Emacs to grab the lock on the file. Then
this user may edit the file and other-user loses the lock.
nil tells Emacs to ignore the lock and let this
user edit the file anyway.
file-locked error, in which
case the change to the buffer which the user was about to make does not
take place.
The error message for this error looks like this:
error--> File is locked: file other-user
where file is the name of the file and other-user is the
name of the user who has locked the file.
The default definition of this function asks the user to choose what
to do. If you wish, you can replace the ask-user-about-lock
function with your own version that decides in another way. The code
for its usual definition is in `userlock.el'.
The functions described in this section are similar in as much as they all operate on strings which are interpreted as file names. All have names that begin with the word `file'. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted.
Most of the file-oriented functions take a single argument,
filename, which must be a string. The file name is expanded using
expand-file-name, so `~' is handled correctly, as are
relative file names (including `../'). Environment variable
substitutions, such as `$HOME', are not recognized by these
functions. See section Functions that Expand Filenames.
These functions test for permission to access a file in specific ways.
Function: file-exists-p filename
This function returns t if a file named filename appears
to exist. This does not mean you can necessarily read the file, only
that you can find out its attributes. (On Unix, this is true if the
file exists and you have execute permission on the containing
directories, regardless of the protection of the file itself.)
If the file does not exist, or if fascist access control policies
prevent you from finding the attributes of the file, this function
returns nil.
Function: file-readable-p filename
This function returns t if a file named filename exists
and you can read it. It returns nil otherwise.
(file-readable-p "files.texi")
=> t
(file-exists-p "/usr/spool/mqueue")
=> t
(file-readable-p "/usr/spool/mqueue")
=> nil
Function: file-executable-p filename
This function returns t if a file named filename exists
and you can execute it. It returns nil otherwise. If the file
is a directory, execute permission means you can access files inside
the directory.
Function: file-writable-p filename
This function returns t if filename can be written or
created by you. It is writable if the file exists and you can write it.
It is creatable if the file does not exist, but the specified directory
does exist and you can write in that directory. file-writable-p
returns nil otherwise.
In the third example below, `foo' is not writable because the parent directory does not exist, even though the user could create it.
(file-writable-p "~rms/foo")
=> t
(file-writable-p "/foo")
=> nil
(file-writable-p "~rms/no-such-dir/foo")
=> nil
Function: file-accessible-directory-p dirname
This function returns t if you have permission to open existing
files in directory dirname; otherwise (and if there is no such
directory), it returns nil. The value of dirname may be
either a directory name or the file name of a directory.
Example: after the following,
(file-accessible-directory-p "/foo")
=> nil
we can deduce that any attempt to read a file in `/foo/' will give an error.
Function: file-newer-than-file-p filename1 filename2
This functions returns t if the file filename1 is
newer than file filename2. If filename1 does not
exist, it returns nil. If filename2 does not exist,
it returns t.
You can use file-attributes to get a file's last modification
time as a list of two numbers. See section Other Information about Files.
In the following example, assume that the file `aug-19' was written on the 19th, and `aug-20' was written on the 20th. The file `no-file' doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20")
=> nil
(file-newer-than-file-p "aug-20" "aug-19")
=> t
(file-newer-than-file-p "aug-19" "no-file")
=> t
(file-newer-than-file-p "no-file" "aug-19")
=> nil
This section describes how to distinguish directories and symbolic links from ordinary files.
Function: file-symlink-p filename
If filename is a symbolic link, the file-symlink-p
function returns the file name to which it is linked. This may be the
name of a text file, a directory, or even another symbolic link, or of
no file at all.
If filename is not a symbolic link (or there is no such file),
file-symlink-p returns nil.
(file-symlink-p "foo")
=> nil
(file-symlink-p "sym-link")
=> "foo"
(file-symlink-p "sym-link2")
=> "sym-link"
(file-symlink-p "/bin")
=> "/pub/bin"
Function: file-directory-p filename
This function returns t if filename is the name of an
existing directory, nil otherwise.
(file-directory-p "~rms")
=> t
(file-directory-p "~rms/lewis/files.texi")
=> nil
(file-directory-p "~rms/lewis/no-such-file")
=> nil
(file-directory-p "$HOME")
=> nil
(file-directory-p
(substitute-in-file-name "$HOME"))
=> t
The truename of a file is the name that you get by following symbolic links until none remain, then expanding to get rid of `.' and `..' as components. Strictly speaking, a file need not have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
Function: file-truename filename
The function file-truename returns the true name of the file
filename. This is the name that you get by following symbolic
links until none remain. The argument must be an absolute file name.
See section Buffer File Name, for related information.
This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.
Function: file-modes filename
This function returns the mode bits of filename, as an integer. The mode bits are also called the file permissions, and they specify access control in the usual Unix fashion. If the low-order bit is 1, then the file is executable by all users, if the second lowest-order bit is 1, then the file is writable by all users, etc.
The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the SUID bit is set for both others and group, and that the sticky bit is set.
(file-modes "~/junk/diffs")
=> 492 ; Decimal integer.
(format "%o" 492)
=> 754 ; Convert to octal.
(set-file-modes "~/junk/diffs" 438)
=> nil
(format "%o" 438)
=> 666 ; Convert to octal.
% ls -l diffs
-rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
Function: file-nlinks filename
This functions returns the number of names (i.e., hard links) that
file filename has. If the file does not exist, then this function
returns nil. Note that symbolic links have no effect on this
function, because they are not considered to be names of the files they
link to.
% ls -l foo*
-rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
-rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
(file-nlinks "foo")
=> 2
(file-nlinks "doesnt-exist")
=> nil
Function: file-attributes filename
This function returns a list of attributes of file filename. If
the specified file cannot be opened, it returns nil.
The elements of the list, in order, are:
t for a directory, a string for a symbolic link (the name
linked to), or nil for a text file.
add-name-to-file function
(see section Changing File Names and Attributes).
current-time; see section Time of Day.)
t if the file's GID would change if file were
deleted and recreated; nil otherwise.
For example, here are the file attributes for `files.texi':
(file-attributes "files.texi")
=> (nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252)
and here is how the result is interpreted:
nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252
A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the ls shell command. In
the latter case, it can optionally display information about each file,
depending on the value of switches passed to the ls command.
Function: directory-files directory &optional full-name match-regexp nosort
This function returns a list of the names of the files in the directory directory. By default, the list is in alphabetical order.
If full-name is non-nil, the function returns the files'
absolute file names. Otherwise, it returns just the names relative to
the specified directory.
If match-regexp is non-nil, this function returns only
those file names that contain that regular expression--the other file
names are discarded from the list.
If nosort is non-nil, that inhibits sorting the list, so
you get the file names in no particular order. Use this if you want the
utmost possible speed and don't care what order the files are processed
in. If the order of processing is visible to the user, then the user
will probably be happier if you do sort the names.
(directory-files "~lewis")
=> ("#foo#" "#foo.el#" "." ".."
"dired-mods.el" "files.texi"
"files.texi.~1~")
An error is signaled if directory is not the name of a directory that can be read.
Function: file-name-all-versions file dirname
This function returns a list of all versions of the file named file in directory dirname.
Function: insert-directory file switches &optional wildcard full-directory-p
This function inserts a directory listing for directory dir, formatted according to switches. It leaves point after the inserted text.
The argument dir may be either a directory name or a file
specification including wildcard characters. If wildcard is
non-nil, that means treat file as a file specification with
wildcards.
If full-directory-p is non-nil, that means file is a
directory and switches do not contain `d', so that a full listing
is expected.
This function works by running a directory listing program whose name is
in the variable insert-directory-program. If wildcard is
non-nil, it also runs the shell specified by
shell-file-name, to expand the wildcards.
Variable: insert-directory-program
This variable's value is the program to run to generate a directory listing
for the function insert-directory.
Function: make-directory dirname
This function creates a directory named dirname.
Function: delete-directory dirname
This function deletes the directory named dirname. The function
delete-file does not work for files that are directories; you
must use delete-directory in that case.
The functions in this section rename, copy, delete, link, and set the modes of files.
In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists:
file-already-exists error is signaled if
ok-if-already-exists is nil.
Function: add-name-to-file oldname newname &optional ok-if-already-exists
This function gives the file named oldname the additional name newname. This means that newname becomes a new "hard link" to oldname.
In the first part of the following example, we list two files, `foo' and `foo3'.
% ls -l fo* -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Then we evaluate the form (add-name-to-file "~/lewis/foo"
"~/lewis/foo2"). Again we list the files. This shows two names,
`foo' and `foo2'.
(add-name-to-file "~/lewis/foo1" "~/lewis/foo2")
=> nil
% ls -l fo*
-rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
-rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
-rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Finally, we evaluate the following:
(add-name-to-file "~/lewis/foo" "~/lewis/foo3" t)
and list the files again. Now there are three names for one file: `foo', `foo2', and `foo3'. The old contents of `foo3' are lost.
(add-name-to-file "~/lewis/foo1" "~/lewis/foo3")
=> nil
% ls -l fo*
-rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
-rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
-rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
This function is meaningless on VMS, where multiple names for one file are not allowed.
See also file-nlinks in section Other Information about Files.
Command: rename-file filename newname &optional ok-if-already-exists
This command renames the file filename as newname.
If filename has additional names aside from filename, it
continues to have those names. In fact, adding the name newname
with add-name-to-file and then deleting filename has the
same effect as renaming, aside from momentary intermediate states.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
Command: copy-file oldname newname &optional ok-if-exists time
This command copies the file oldname to newname. An error is signaled if oldname does not exist.
If time is non-nil, then this functions gives the new
file the same last-modified time that the old one has. (This works on
only some operating systems.)
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
Command: delete-file filename
This command deletes the file filename, like the shell command `rm filename'. If the file has multiple names, it continues to exist under the other names.
A suitable kind of file-error error is signaled if the file
does not exist, or is not deletable. (In Unix, a file is deletable if
its directory is writable.)
See also delete-directory in section Creating and Deleting Directories.
Command: make-symbolic-link filename newname &optional ok-if-exists
This command makes a symbolic link to filename, named newname. This is like the shell command `ln -s filename newname'.
In an interactive call, filename and newname are read in the minibuffer, and ok-if-exists is set to the numeric prefix argument.
Function: define-logical-name varname string
This function defines the logical name name to have the value string. It is available only on VMS.
Function: set-file-modes filename mode
This function sets mode bits of filename to mode (which must be an integer). Only the 12 low bits of mode are used.
Function: set-default-file-modes mode
This function sets the default file protection for new files created by Emacs and its subprocesses. Every file created with Emacs initially has this protection. On Unix, the default protection is the bitwise complement of the "umask" value.
The argument mode must be an integer. Only the 9 low bits of mode are used.
Saving a modified version of an existing file does not count as creating the file; it does not change the file's mode, and does not use the default file protection.
Function: default-file-modes
This function returns the current default protection value.
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs often need to operate on the names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.
On VMS, all these functions understand both VMS file name syntax and Unix syntax. This is so that all the standard Lisp libraries can specify file names in Unix syntax and work properly on VMS without change.
The operating system groups files into directories. To specify a file, you must specify the directory, and the file's name in that directory. Therefore, a file name in Emacs is considered to have two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.
On Unix, the directory part is everything up to and including the last slash; the nondirectory part is the rest. The rules in VMS syntax are complicated.
For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On Unix, only backup files have version numbers in their names; on VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number. Version numbers are found mostly in directory lists.
Function: file-name-directory filename
This function returns the directory part of filename (or
nil if filename does not include a directory part). On
Unix, the function returns a string ending in a slash. On VMS, it
returns a string ending in one of the three characters `:',
`]', or `>'.
(file-name-directory "lewis/foo") ; Unix example
=> "lewis/"
(file-name-directory "foo") ; Unix example
=> nil
(file-name-directory "[X]FOO.TMP") ; VMS example
=> "[X]"
Function: file-name-nondirectory filename
This function returns the nondirectory part of filename.
(file-name-nondirectory "lewis/foo")
=> "foo"
(file-name-nondirectory "foo")
=> "foo"
;; The following example is accurate only on VMS.
(file-name-nondirectory "[X]FOO.TMP")
=> "FOO.TMP"
Function: file-name-sans-versions filename
This function returns filename without any file version numbers, backup version numbers, or trailing tildes.
(file-name-sans-versions "~rms/foo.~1~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo")
=> "~rms/foo"
;; The following example applies to VMS only.
(file-name-sans-versions "foo;23")
=> "foo"
A directory name is the name of a directory. A directory is a kind of file, and it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On Unix, this is simple: a directory name ends in a slash, whereas the directory's name as a file lacks that slash. On VMS, the relationship is more complicated.
The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable.
These two functions take a single argument, filename, which must
be a string. Environment variable substitutions such as `$HOME',
and the symbols `~', and `..', are not expanded. Use
expand-file-name or substitute-in-file-name for that
(see section Functions that Expand Filenames).
Function: file-name-as-directory filename
This function returns a string representing filename in a form that the operating system will interpret as the name of a directory. In Unix, this means that a slash is appended to the string. On VMS, the function converts a string of the form `[X]Y.DIR.1' to the form `[X.Y]'.
(file-name-as-directory "~rms/lewis")
=> "~rms/lewis/"
Function: directory-file-name dirname
This function returns a string representing dirname in a form that the operating system will interpret as the name of a file. On Unix, this means removing a final slash from the string. On VMS, the function converts a string of the form `[X.Y]' to `[X]Y.DIR.1'.
(directory-file-name "~lewis/")
=> "~lewis"
Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link's name as "the name" of the directory, and find it annoying to see the directory's "real" name. If you define the link name as an abbreviation for the "real" name, Emacs shows users the abbreviation instead.
If you wish to convert a directory name to its abbreviation, use this function:
Function: abbreviate-file-name dirname
This function applies abbreviations from directory-abbrev-alist
to its argument, and substitutes `~' for the user's home
directory.
Variable: directory-abbrev-alist
The variable directory-abbrev-alist contains an alist of
abbreviations to use for file directories. Each element has the form
(from . to), and says to replace from with
to when it appears in a directory name. The from string is
actually a regular expression; it should always start with `^'.
The function abbreviate-file-name performs these substitutions.
You can set this variable in `site-init.el' to describe the abbreviations appropriate for your site.
Here's an example, from a system on which file system `/home/fsf' and so on are normally accessed through symbolic links named `/fsf' and so on.
(("^/home/fsf" . "/fsf")
("^/home/gp" . "/gp")
("^/home/gd" . "/gd"))
All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called an relative file name. On Unix, an absolute file name starts with a slash or a tilde (`~'), and a relative one does not. The rules on VMS are complicated.
Function: file-name-absolute-p filename
This function returns t if file filename is an absolute
file name, nil otherwise. On VMS, this function understands both
Unix syntax and VMS syntax.
(file-name-absolute-p "~rms/foo")
=> t
(file-name-absolute-p "rms/foo")
=> nil
(file-name-absolute-p "/user/rms/foo")
=> t
Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as `./' and `name/../'.
Function: expand-file-name filename &optional directory
This function converts filename to an absolute file name. If
directory is supplied, it is the directory to start with if
filename is relative. (The value of directory should itself
be an absolute, expanded file name; it should not start with `~'.)
Otherwise, the current buffer's value of default-directory is
used. For example:
(expand-file-name "foo")
=> "/xcssun/users/rms/lewis/foo"
(expand-file-name "../foo")
=> "/xcssun/users/rms/foo"
(expand-file-name "foo" "/usr/spool/")
=> "/usr/spool/foo"
(expand-file-name "$HOME/foo")
=> "/xcssun/users/rms/lewis/$HOME/foo"
Filenames containing `.' or `..' are simplified to their canonical form:
(expand-file-name "bar/../foo")
=> "/xcssun/users/rms/lewis/foo"
`~/' is expanded into the user's home directory. A `/' or `~' following a `/' is taken to be the start of an absolute file name that overrides what precedes it, so everything before that `/' or `~' is deleted. For example:
(expand-file-name
"/a1/gnu//usr/local/lib/emacs/etc/MACHINES")
=> "/usr/local/lib/emacs/etc/MACHINES"
(expand-file-name "/a1/gnu/~/foo")
=> "/xcssun/users/rms/foo"
In both cases, `/a1/gnu/' is discarded because an absolute file name follows it.
Note that expand-file-name does not expand environment
variables; that is done only by substitute-in-file-name.
Function: file-relative-name filename directory
This function does the inverse of expansion--it tries to return a relative name which is equivalent to filename when interpreted relative to directory. (If such a relative name would be longer than the absolute name, it returns the absolute name instead.)
(file-relative-name "/foo/bar" "/foo/")
=> "bar")
(file-relative-name "/foo/bar" "/hack/")
=> "/foo/bar")
Variable: default-directory
The value of this buffer-local variable is the default directory for
the current buffer. It is local in every buffer.
expand-file-name uses the default directory when its second
argument is nil.
On Unix systems, the value is always a string ending with a slash.
default-directory
=> "/user/lewis/manual/"
Function: substitute-in-file-name filename
This function replaces environment variables names in filename with the values to which they are set by the operating system. Following standard Unix shell syntax, `$' is the prefix to substitute an environment variable value.
The environment variable name is the series of alphanumeric characters (including underscores) that follow the `$'. If the character following the `$' is a `{', then the variable name is everything up to the matching `}'.
Here we assume that the environment variable HOME, which holds
the user's home directory name, has value `/xcssun/users/rms'.
(substitute-in-file-name "$HOME/foo")
=> "/xcssun/users/rms/foo"
If a `~' or a `/' appears following a `/', after substitution, everything before the following `/' is discarded:
(substitute-in-file-name "bar/~/foo")
=> "~/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
=> "/xcssun/users/rms/foo"
On VMS, `$' substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.
Some programs need to write temporary files. Here is the usual way to construct a name for such a file:
(make-temp-name (concat "/tmp/" name-of-application))
Here we use the directory `/tmp/' because that is the standard
place on Unix for temporary files. The job of make-temp-name is
to prevent two different users or two different jobs from trying to use
the same name.
Function: make-temp-name string
This function generates string that can be used as a unique name. The name starts with the prefix string, and ends with a number that is different in each Emacs job.
(make-temp-name "/tmp/foo")
=> "/tmp/foo021304"
To prevent conflicts among different application libraries run in the same Emacs, each application should have its own string. The number added to the end of the name distinguishes between the same application running in different Emacs jobs.
This section describes low-level subroutines for completing a file name. For other completion functions, see section Completion.
Function: file-name-all-completions partial-filename directory
This function returns a list of all possible completions for a file whose name starts with partial-filename in directory directory. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information.
The argument partial-filename must be a file name containing no directory part and no slash. The current buffer's default directory is prepended to directory, if directory is not an absolute file name.
In the following example, suppose that the current default directory, `~rms/lewis', has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-all-completions "f" "")
=> ("foo" "file~" "file.c.~2~"
"file.c.~1~" "file.c")
(file-name-all-completions "fo" "")
=> ("foo")
Function: file-name-completion filename directory
This function completes the file name filename in directory directory. It returns the longest prefix common to all file names in directory directory that start with filename.
If only one match exists and filename matches it exactly, the
function returns t. The function returns nil if directory
directory contains no name starting with filename.
In the following example, suppose that the current default directory has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-completion "fi" "")
=> "file"
(file-name-completion "file.c.~1" "")
=> "file.c.~1~"
(file-name-completion "file.c.~1~" "")
=> t
(file-name-completion "file.c.~3" "")
=> nil
User Option: completion-ignored-extensions
file-name-completion usually ignores file names that end in any
string in this list. It does not ignore them when all the possible
completions end in one of these suffixes or when a buffer showing all
possible completions is displayed.
A typical value might look like this:
completion-ignored-extensions
=> (".o" ".elc" "~" ".dvi")
You can implement special handling for certain file names. This is called making those names magic. You must supply a regular expression to define the class of names (all those which match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match.
The value of file-name-handler-alist is a list of handlers,
together with regular expressions that decide when to apply each
handler. Each element has this form:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to handler is the name of the primitive; the remaining arguments are the arguments that were passed to that operation. (The first of these arguments is typically the file name itself.) For example, if you do this:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
Here are the operations that you can handle for a magic file name:
add-name-to-file,copy-file,delete-directory,delete-file,directory-file-name,directory-files,dired-compress-file,dired-uncache,expand-file-name,file-accessible-directory-p,file-attributes,file-directory-p,file-executable-p,file-exists-p,file-local-copy,file-modes,file-name-all-completions,file-name-as-directory,file-name-completion,file-name-directory,file-name-nondirectory,file-name-sans-versions,file-newer-than-file-p,file-readable-p,file-symlink-p,file-writable-p,insert-directory,insert-file-contents,load,make-directory,make-symbolic-link,rename-file,set-file-modes,set-visited-file-modtime,unhandled-file-name-directory,verify-visited-file-modtime,write-region.
The handler function must handle all of the above operations, and possibly others to be added in the future. Therefore, it should always reinvoke the ordinary Lisp primitive when it receives an operation it does not recognize. Here's one way to do this:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let (file-name-handler-alist)
(apply operation args)))))
Function: find-file-name-handler file
This function returns the handler function for file name file, or
nil if there is none.
Function: file-local-copy filename
This function copies file filename to the local site, if it isn't there already. If filename specifies a "magic" file name which programs outside Emacs cannot directly read or write, this copies the contents to an ordinary file and returns that file's name.
If filename is an ordinary file name, not magic, then this function
does nothing and returns nil.
Function: unhandled-file-name-directory filename
This function returns the name of a directory that is not magic. It uses the directory part of filename if that is not magic. Otherwise, it asks the handler what to do.
This is used for running a subprocess; any subprocess must have a non-magic directory to serve as its current directory.
Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user's own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session.
A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Normally, this means that the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists.
Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don't want them any more, or Emacs can delete them automatically.
Function: backup-buffer
This function makes a backup of the file visited by the current
buffer, if appropriate. It is called by save-buffer before
saving the buffer the first time.
Variable: buffer-backed-up
This buffer-local variable indicates whether this buffer's file has
been backed up on account of this buffer. If it is non-nil, then
the backup file has been written. Otherwise, the file should be backed
up when it is next saved (if backup files are enabled). This is a
permanent local; kill-local-variables does not alter it.
User Option: make-backup-files
This variable determines whether or not to make backup files. If it
is non-nil, then Emacs creates a backup of each file when it is
saved for the first time.
The following example shows how to change the make-backup-files
variable only in the `RMAIL' buffer and not elsewhere. Setting it
nil stops Emacs from making backups of the `RMAIL' file,
which may save disk space. (You would put this code in your
`.emacs' file.)
(add-hook 'rmail-mode-hook
(function (lambda ()
(make-local-variable
'make-backup-files)
(setq make-backup-files nil))))
Variable: backup-enable-predicate filename
This variable's value is a function to be called on certain occasions
to decide whether a there should be backup files for file name filename.
If it returns nil, backups are disabled. Otherwise, backups are
enabled (if make-backup-files is true).
There are two ways that Emacs can make a backup file:
The first method, renaming, is the default.
The variable backup-by-copying, if non-nil, says to use
the second method, which is to copy the original file and overwrite it
with the new buffer contents. The variable file-precious-flag,
if non-nil, also has this effect (as a sideline of its main
significance). See section Saving Buffers.
The following two variables, when non-nil, cause the second
method to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
Variable: backup-by-copying
This variable controls whether to make backup files by copying. If it
is non-nil, then Emacs always copies the current contents of the
file into the backup file before writing the buffer to be saved to the
file. (In many circumstances, this has the same effect as
file-precious-flag.)
Variable: backup-by-copying-when-linked
This variable controls whether to make backups by copying for files
with multiple names (hard links). If it is non-nil, then Emacs
uses copying to create backups for those files.
This variable is significant only if backup-by-copying is
nil, since copying is always used when that variable is
non-nil.
Variable: backup-by-copying-when-mismatch
This variable controls whether to make backups by copying in cases
where renaming would change either the owner or the group of the file.
If it is non-nil then Emacs creates backups by copying in such
cases.
The value has no effect when renaming would not alter the owner or group of the file; that is, for files which are owned by the user and whose group matches the default for a new file created there by the user.
This variable is significant only if backup-by-copying is
nil, since copying is always used when that variable is
non-nil.
If a file's name is `foo', the names of its numbered backup versions are `foo.~v~', for various integers v, like this: `foo.~1~', `foo.~2~', `foo.~3~', ..., `foo.~259~', and so on.
User Option: version-control
This variable controls whether to make a single non-numbered backup file or multiple numbered backups.
nil
never
The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically.
User Option: kept-new-versions
The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The newly made backup is included in the count. The default value is 2.
User Option: kept-old-versions
The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The default value is 2.
User Option: dired-kept-versions
This variable plays a role in Dired's dired-clean-directory
(.) command like that played by kept-old-versions when a
backup file is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is deleted. The function find-backup-file-name
(see section Naming Backup Files) is responsible for determining which backup
versions to delete, but does not delete them itself.
User Option: trim-versions-without-asking
If this variable is non-nil, then saving a file deletes excess
backup versions silently. Otherwise, it asks the user whether to delete
them.
The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.
Function: backup-file-name-p filename
This function returns a non-nil value if filename is a
possible name for a backup file. A file with the name filename
need not exist; the function just checks the name.
(backup-file-name-p "foo")
=> nil
(backup-file-name-p "foo~")
=> 3
The standard definition of this function is as follows:
(defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~$" file))
Thus, the function returns a non-nil value if the file name ends
with a `~'. (We use a backslash to split the documentation
string's first line into two lines in the text, but produce just one
line in the string itself.)
This simple expression is placed in a separate function to make it easy to redefine for customization.
Function: make-backup-file-name filename
This function returns a string which is the name to use for a non-numbered backup file for file filename. On Unix, this is just filename with a tilde appended.
The standard definition of this function is as follows:
(defun make-backup-file-name (file) "Create the non-numeric backup file name for FILE..." (concat file "~"))
You can change the backup file naming convention by redefining this
function. In the following example, make-backup-file-name is
redefined to prepend a `.' as well as to append a tilde.
(defun make-backup-file-name (filename)
(concat "." filename "~"))
(make-backup-file-name "backups.texi")
=> ".backups.texi~"
Function: find-backup-file-name filename
This function computes the file name for a new backup file for
filename. It may also propose certain existing backup files for
deletion. find-backup-file-name returns a list whose CAR is
the name for the new backup file and whose CDR is a list of backup
files whose deletion is proposed.
Two variables, kept-old-versions and kept-new-versions,
determine which old backup versions should be kept (by excluding them
from the list of backup files ripe for deletion). See section Making and Deleting Numbered Backup Files.
In this example, the value says that `~rms/foo.~5~' is the name to use for the new backup file, and `~rms/foo.~3~' is an "excess" version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo")
=> ("~rms/foo.~5~" "~rms/foo.~3~")
Function: file-newest-backup filename
This function returns the name of the most recent backup file for
filename, or nil that file has no backup files.
Some file comparison commands use this function in order to compare a file by default with its most recent backup.
Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See section 'Auto-Saving: Protection Against Disasters' in The GNU Emacs Manual, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them.
Variable: buffer-auto-save-file-name
This buffer-local variable is the name of the file used for
auto-saving the current buffer. It is nil if the buffer
should not be auto-saved.
buffer-auto-save-file-name => "/xcssun/users/rms/lewis/#files.texi#"
Command: auto-save-mode arg
When used interactively without an argument, this command is a toggle
switch: it turns on auto-saving of the current buffer if it is off, and
vice-versa. With an argument arg, the command turns auto-saving
on if the value of arg is t, a nonempty list, or a positive
integer. Otherwise, it turns auto-saving off.
Function: auto-save-file-name-p filename
This function returns a non-nil value if filename is a
string that could be the name of an auto-save file. It works based on
knowledge of the naming convention for auto-save files: a name that
begins and ends with hash marks (`#') is a possible auto-save file
name. The argument filename should not contain a directory part.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#files.texi#"
(auto-save-file-name-p "#files.texi#")
=> 0
(auto-save-file-name-p "files.texi")
=> nil
The standard definition of this function is as follows:
(defun auto-save-file-name-p (filename) "Return non-nil if FILENAME can be yielded by..." (string-match "^#.*#$" filename))
This function exists so that you can customize it if you wish to
change the naming convention for auto-save files. If you redefine it,
be sure to redefine the function make-auto-save-file-name
correspondingly.
Function: make-auto-save-file-name
This function returns the file name to use for auto-saving the current
buffer. This is just the file name with hash marks (`#') appended
and prepended to it. This function does not look at the variable
auto-save-visited-file-name; that should be checked before this
function is called.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#backup.texi#"
The standard definition of this function is as follows:
(defun make-auto-save-file-name ()
"Return file name to use for auto-saves \
of current buffer..."
(if buffer-file-name
(concat
(file-name-directory buffer-file-name)
"#"
(file-name-nondirectory buffer-file-name)
"#")
(expand-file-name
(concat "#%" (buffer-name) "#"))))
This exists as a separate function so that you can redefine it to
customize the naming convention for auto-save files. Be sure to
change auto-save-file-name-p in a corresponding way.
Variable: auto-save-visited-file-name
If this variable is non-nil, Emacs auto-saves buffers in
the files they are visiting. That is, the auto-save is done in the same
file which you are editing. Normally, this variable is nil, so
auto-save files have distinct names that are created by
make-auto-save-file-name.
When you change the value of this variable, the value does not take
effect until the next time auto-save mode is reenabled in any given
buffer. If auto-save mode is already enabled, auto-saves continue to go
in the same file name until auto-save-mode is called again.
Function: recent-auto-save-p
This function returns t if the current buffer has been
auto-saved since the last time it was read in or saved.
Function: set-buffer-auto-saved
This function marks the current buffer as auto-saved. The buffer will
not be auto-saved again until the buffer text is changed again. The
function returns nil.
User Option: auto-save-interval
The value of this variable is the number of characters that Emacs reads from the keyboard between auto-saves. Each time this many more characters are read, auto-saving is done for all buffers in which it is enabled.
User Option: auto-save-timeout
The value of this variable is the number of seconds of idle time that should cause auto-saving. Each time the user pauses for this long, Emacs auto-saves any buffers that need it. (Actually, the specified timeout is multiplied by a factor depending on the size of the current buffer.)
Variable: auto-save-hook
This normal hook is run whenever an auto-save is about to happen.
User Option: auto-save-default
If this variable is non-nil, buffers that are visiting files
have auto-saving enabled by default. Otherwise, they do not.
Command: do-auto-save &optional no-message
This function auto-saves all buffers that need to be auto-saved. This is all buffers for which auto-saving is enabled and that have been changed since the last time they were auto-saved.
Normally, if any buffers are auto-saved, a message that says
`Auto-saving...' is displayed in the echo area while auto-saving is
going on. However, if no-message is non-nil, the message
is inhibited.
Function: delete-auto-save-file-if-necessary
This function deletes the current buffer's auto-save file if
delete-auto-save-files is non-nil. It is called every
time a buffer is saved.
Variable: delete-auto-save-files
This variable is used by the function
delete-auto-save-file-if-necessary. If it is non-nil,
Emacs deletes auto-save files when a true save is done (in the visited
file). This saves on disk space and unclutters your directory.
Function: rename-auto-save-file
This function adjusts the current buffer's auto-save file name if the visited file name has changed. It also renames an existing auto-save file. If the visited file name has not changed, this function does nothing.
If you have made extensive changes to a file and then change your mind
about them, you can get rid of them by reading in the previous version
of the file with the revert-buffer command. See section 'Reverting a Buffer' in The GNU Emacs Manual.
Command: revert-buffer &optional check-auto-save noconfirm
This command replaces the buffer text with the text of the visited file on disk. This action undoes all changes since the file was visited or saved.
If the argument check-auto-save is non-nil, and the
latest auto-save file is more recent than the visited file,
revert-buffer asks the user whether to use that instead.
Otherwise, it always uses the text of the visited file itself.
Interactively, check-auto-save is set if there is a numeric prefix
argument.
When the value of the noconfirm argument is non-nil,
revert-buffer does not ask for confirmation for the reversion
action. This means that the buffer contents are deleted and replaced by
the text from the file on the disk, with no further opportunities for
the user to prevent it.
Since reverting works by deleting the entire text of the buffer and inserting the file contents, all the buffer's markers are relocated to point at the beginning of the buffer. This is not "correct", but then, there is no way to determine what would be correct. It is not possible to determine, from the text before and after, which characters after reversion correspond to which characters before.
If the value of the revert-buffer-function variable is
non-nil, it is called as a function with no arguments to do the
work.
Variable: revert-buffer-function
The value of this variable is the function to use to revert this
buffer; but if the value of this variable is nil, then the
revert-buffer function carries out its default action. Modes
such as Dired mode, in which the text being edited does not consist of a
file's contents but can be regenerated in some other fashion, give this
variable a buffer-local value that is a function to regenerate the
contents.
Variable: revert-buffer-insert-file-contents-function
The value of this variable, if non-nil, is the function to use
to insert contents when reverting this buffer. The function receives
two arguments, first the file name to use, and second, t if the
user has asked to read the auto-save file.
Command: recover-file filename
This function visits filename, but gets the contents from its last auto-save file. This is useful after the system has crashed, to resume editing the same file without losing all the work done in the previous session.
An error is signaled if there is no auto-save file for filename, or if filename is newer than its auto-save file. If filename does not exist, but its auto-save file does, then the auto-save file is read as usual. This last situation may occur if you visited a nonexistent file and never actually saved it.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers which are not visiting files. While several buffers may exist at one time, exactly one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
Buffers in Emacs editing are objects which have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. The contents of a buffer may be viewed as an extendable string; insertions and deletions may occur in any part of the buffer. See section Text.
A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is only accessible through special-purpose functions. For example, the width of a tab character is directly accessible through a variable, while the value of point is accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored in
buffer-local variable bindings, which are variable values that are
effective only in a particular buffer. This feature allows each buffer
to override the values of certain variables. Most major modes override
variables such as fill-column or comment-column in this
way. For more information about buffer-local variables and functions
related to them, see section Buffer-Local Variables.
For functions and variables related to visiting files in buffers, see section Visiting Files and section Saving Buffers. For functions and variables related to the display of buffers in windows, see section Buffers and Windows.
Function: bufferp object
This function returns t if object is a buffer,
nil otherwise.
Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer is required to be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, which prevents them from being listed
by the list-buffers or buffer-menu commands. (A name
starting with space also initially disables recording undo information;
see section Undo.)
Function: buffer-name &optional buffer
This function returns the name of buffer as a string. If buffer is not supplied, it defaults to the current buffer.
If buffer-name returns nil, it means that buffer
has been killed. See section Killing Buffers.
(buffer-name)
=> "buffers.texi"
(setq foo (get-buffer "temp"))
=> #<buffer temp>
(kill-buffer foo)
=> nil
(buffer-name foo)
=> nil
foo
=> #<killed buffer>
Command: rename-buffer newname &optional unique
This function renames the current buffer to newname. An error
is signaled if newname is not a string, or if there is already a
buffer with that name. The function returns nil.
Ordinarily, rename-buffer signals an error if newname is
already in use. However, if unique is non-nil, it modifies
newname to make a name that is not in use. Interactively, you can
make unique non-nil with a numeric prefix argument.
One application of this command is to rename the `*shell*' buffer to some other name, thus making it possible to create a second shell buffer under the name `*shell*'.
Function: get-buffer buffer-or-name
This function returns the buffer specified by buffer-or-name.
If buffer-or-name is a string and there is no buffer with that
name, the value is nil. If buffer-or-name is a buffer, it
is returned as given. (That is not very useful, so the argument is usually
a name.) For example:
(setq b (get-buffer "lewis"))
=> #<buffer lewis>
(get-buffer b)
=> #<buffer lewis>
(get-buffer "Frazzle-nots")
=> nil
See also the function get-buffer-create in section Creating Buffers.
Function: generate-new-buffer-name starting-name
This function returns a name that would be unique for a new buffer--but does not create the buffer. It starts with starting-name, and produces a name not currently in use for any buffer by appending a number inside of `<...>'.
See the related function generate-new-buffer in section Creating Buffers.
The buffer file name is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file name
is nil. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently.
See section Visiting Files.
Function: buffer-file-name &optional buffer
This function returns the absolute file name of the file that
buffer is visiting. If buffer is not visiting any file,
buffer-file-name returns nil. If buffer is not
supplied, it defaults to the current buffer.
(buffer-file-name (other-buffer))
=> "/usr/user/lewis/manual/files.texi"
Variable: buffer-file-name
This buffer-local variable contains the name of the file being visited
in the current buffer, or nil if it is not visiting a file. It
is a permanent local, unaffected by kill-local-variables.
buffer-file-name
=> "/usr/user/lewis/manual/buffers.texi"
It is risky to change this variable's value without doing various other
things. See the definition of set-visited-file-name in
`files.el'; some of the things done there, such as changing the
buffer name, are not strictly necessary, but others are essential to
avoid confusing Emacs.
Variable: buffer-file-truename
This buffer-local variable holds the truename of the file visited in the
current buffer, or nil if no file is visited. It is a permanent
local, unaffected by kill-local-variables. See section Truenames.
Variable: buffer-file-number
This buffer-local variable holds the file number and directory device
number of the file visited in the current buffer, or nil if no
file or a nonexistent file is visited. It is a permanent local,
unaffected by kill-local-variables. See section Truenames.
The value is normally a list of the form (filenum
devnum). This pair of numbers uniquely identifies the file among
all files accessible on the system. See the function
file-attributes, in section Other Information about Files, for more information
about them.
Function: get-file-buffer filename
This function returns the buffer visiting file filename. If
there is no such buffer, it returns nil. The argument
filename, which must be a string, is expanded (see section Functions that Expand Filenames), then compared against the visited file names of all live
buffers.
(get-file-buffer "buffers.texi")
=> #<buffer buffers.texi>
In unusual circumstances, there can be more than one buffer visiting the same file name. In such cases, this function returns the first such buffer in the buffer list.
Command: set-visited-file-name filename
If filename is a non-empty string, this function changes the name of the file visited in current buffer to filename. (If the buffer had no visited file, this gives it one.) The next time the buffer is saved it will go in the newly-specified file. This command marks the buffer as modified, since it does not (as far as Emacs knows) match the contents of filename, even if it matched the former visited file.
If filename is nil or the empty string, that stands for
"no visited file". In this case, set-visited-file-name marks
the buffer as having no visited file.
When the function set-visited-file-name is called interactively, it
prompts for filename in the minibuffer.
See also clear-visited-file-modtime and
verify-visited-file-modtime in section Buffer Modification.
Variable: list-buffers-directory
This buffer-local variable records a string to display in a buffer listing in place of the visited file name, for buffers that don't have a visited file name. Dired buffers use this variable.
Emacs keeps a flag called the modified flag for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to t whenever you alter the contents of the buffer, and
cleared to nil when you save it. Thus, the flag shows whether
there are unsaved changes. The flag value is normally shown in the mode
line (see section Variables Used in the Mode Line), and controls saving (see section Saving Buffers) and auto-saving (see section Auto-Saving).
Some Lisp programs set the flag explicitly. For example, the function
set-visited-file-name sets the flag to t, because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.
The functions that modify the contents of buffers are described in section Text.
Function: buffer-modified-p &optional buffer
This function returns t if the buffer buffer has been modified
since it was last read in from a file or saved, or nil
otherwise. If buffer is not supplied, the current buffer
is tested.
Function: set-buffer-modified-p flag
This function marks the current buffer as modified if flag is
non-nil, or as unmodified if the flag is nil.
Another effect of calling this function is to cause unconditional
redisplay of the mode line for the current buffer. In fact, the
function force-mode-line-update works by doing this:
(set-buffer-modified-p (buffer-modified-p))
Command: not-modified
This command marks the current buffer as unmodified, and not needing
to be saved. Don't use this function in programs, since it prints a
message in the echo area; use set-buffer-modified-p (above) instead.
Function: buffer-modified-tick &optional buffer
This function returns buffer`s modification-count. This is a
counter that increments every time the buffer is modified. If
buffer is nil (or omitted), the current buffer is used.
Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file's modification time using the functions described below before saving the file.
Function: verify-visited-file-modtime buffer
This function compares Emacs's record of the modification time for the file that the buffer is visiting against the actual modification time of the file as recorded by the operating system. The two should be the same unless some other process has written the file since Emacs visited or saved it.
The function returns t if the last actual modification time and
Emacs's recorded modification time are the same, nil otherwise.
Function: clear-visited-file-modtime
This function clears out the record of the last modification time of the file being visited by the current buffer. As a result, the next attempt to save this buffer will not complain of a discrepancy in file modification times.
This function is called in set-visited-file-name and other
exceptional places where the usual test to avoid overwriting a changed
file should not be done.
Function: set-visited-file-modtime &optional time
This function updates the buffer's record of the last modification time
of the visited file, to the value specified by time if time
is not nil, and otherwise to the last modification time of the
visited file.
If time is not nil, it should have the form
(high . low) or (high low), in
either case containing two integers, each of which holds 16 bits of the
time. (This is the same format that file-attributes uses to
return time values; see section Other Information about Files.)
This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason.
Function: visited-file-modtime
This function returns the buffer's recorded last file modification time,
as a list of the form (high . low). Note that this
is not identical to the last modification time of the file that is
visited (though under normal circumstances the values are equal).
Function: ask-user-about-supersession-threat fn
This function is used to ask a user how to proceed after an attempt to modify an obsolete buffer. An obsolete buffer is an unmodified buffer for which the associated file on disk is newer than the last save-time of the buffer. This means some other program has probably altered the file.
This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file `userlock.el' for the standard definition.
Depending on the user's answer, the function may return normally, in
which case the modification of the buffer proceeds, or it may signal a
file-supersession error with data (fn), in which
case the proposed buffer modification is not allowed.
See also the file locking mechanism in section File Locks.
A buffer may be designated as read-only. This means that the buffer's contents may not be modified, although you may change your view of the contents by scrolling, narrowing, or widening, etc.
Read-only buffers are used in two kinds of situations:
Here, the purpose is to show the user that editing the buffer with the
aim of saving it in the file may be futile or undesirable. The user who
wants to change the buffer text despite this can do so after clearing
the read-only flag with the function toggle-read-only.
The special commands of the mode in question bind
buffer-read-only to nil (with let) around the
places where they change the text.
Variable: buffer-read-only
This buffer-local variable specifies whether the buffer is read-only.
The buffer is read-only if this variable is non-nil.
Variable: inhibit-read-only
If this variable is non-nil, then read-only buffers and read-only
characters may be modified. The value of buffer-read-only does
not matter when inhibit-read-only is non-nil.
If inhibit-read-only is t, all read-only text
properties have no effect (see section Special Properties). If
inhibit-read-only is a list, then read-only text
properties are ignored if they are members of the list (comparison is
done with eq).
Command: toggle-read-only
This command changes whether the current buffer is read-only. It is
intended for interactive use; don't use it in programs. At any given
point in a program, you should know whether you want the read-only flag
on or off; so you can set buffer-read-only explicitly to the
proper value, t or nil.
Function: barf-if-buffer-read-only
This function signals a buffer-read-only error if the current
buffer is read-only. See section Interactive Call, for another way to
signal an error if the current buffer is read-only.
The buffer list is a list of all buffers that have not been
killed. The order of the buffers in the list is based primarily on how
recently each buffer has been displayed in the selected window. Several
functions, notably other-buffer, make use of this ordering.
Function: buffer-list
This function returns a list of all buffers, including those whose names begin with a space. The elements are actual buffers, not their names.
(buffer-list)
=> (#<buffer buffers.texi>
#<buffer *Minibuf-1*> #<buffer buffer.c>
#<buffer *Help*> #<buffer TAGS>)
;; Note that the name of the minibuffer
;; begins with a space!
(mapcar (function buffer-name) (buffer-list))
=> ("buffers.texi" " *Minibuf-1*"
"buffer.c" "*Help*" "TAGS")
Buffers appear earlier in the list if they were current more recently.
This list is a copy of a list used inside Emacs; modifying it has no effect on the buffers.
Function: other-buffer &optional buffer-or-name visible-ok
This function returns the first buffer in the buffer list other than buffer-or-name. Usually this is the buffer most recently shown in the selected window, aside from buffer-or-name. Buffers are moved to the front of the list when they are selected and to the end when they are buried. Buffers whose names start with a space are not even considered.
If buffer-or-name is not supplied (or if it is not a buffer),
then other-buffer returns the first buffer on the buffer list
that is not visible in any window in a visible frame.
Normally, other-buffer avoids returning a buffer visible in any
window on any visible frame, except as a last resort. However, if
visible-ok is non-nil, then a buffer displayed in some
window is admissible to return.
If no suitable buffer exists, the buffer `*scratch*' is returned (and created, if necessary).
Command: list-buffers &optional files-only
This function displays a listing of the names of existing buffers. It
clears the buffer `*Buffer List*', then inserts the listing into
that buffer and displays it in a window. list-buffers is
intended for interactive use, and is described fully in The GNU
Emacs Manual. It returns nil.
Command: bury-buffer &optional buffer-or-name
This function puts buffer-or-name at the end of the buffer list
without changing the order of any of the other buffers on the list.
This buffer therefore becomes the least desirable candidate for
other-buffer to return, and appears last in the list displayed by
list-buffers.
If buffer-or-name is nil or omitted, this means to bury
the current buffer. In addition, this switches to some other buffer
(obtained using other-buffer) in the selected window. If the
buffer is displayed in a window other than the selected one, it remains
there.
If you wish to remove a buffer from all the windows that display it,
you can do so with a loop that uses get-buffer-window.
See section Buffers and Windows.
This section describes the two primitives for creating buffers.
get-buffer-create creates a buffer if it finds no existing
buffer; generate-new-buffer always creates a new buffer, and
gives it a unique name.
Other functions you can use to create buffers include
with-output-to-temp-buffer (see section Temporary Displays) and
create-file-buffer (see section Visiting Files).
Function: get-buffer-create name
This function returns a buffer named name. If such a buffer already exists, it is returned. If such a buffer does not exist, one is created and returned. The buffer does not become the current buffer--this function does not change which buffer is current.
An error is signaled if name is not a string.
(get-buffer-create "foo")
=> #<buffer foo>
The major mode for the new buffer is set by the value of
default-major-mode. See section How Emacs Chooses a Major Mode.
Function: generate-new-buffer name
This function returns a newly created, empty buffer, but does not make it current. If there is no buffer named name, then that is the name of the new buffer. If that name is in use, this function adds suffixes of the form `<n>' are added to name, where n is an integer. It tries successive integers starting with 2 until it finds an available name.
An error is signaled if name is not a string.
(generate-new-buffer "bar")
=> #<buffer bar>
(generate-new-buffer "bar")
=> #<buffer bar<2>>
(generate-new-buffer "bar")
=> #<buffer bar<3>>
The major mode for the new buffer is set by the value of
default-major-mode. See section How Emacs Chooses a Major Mode.
See the related function generate-new-buffer-name in section Buffer Names.
Killing a buffer makes its name unknown to Emacs and makes its space available for other use.
The buffer object for the buffer which has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
their identity, however; two distinct buffers, when killed, remain
distinct according to eq.
If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). See section The Current Buffer.
The buffer-name of a killed buffer is nil. You can use
this feature to test whether a buffer has been killed:
(defun killed-buffer-p (buffer) "Return t if BUFFER is killed." (not (buffer-name buffer)))
Command: kill-buffer buffer-or-name
This function kills the buffer buffer-or-name, freeing all its
memory for use as space for other buffers. (Emacs version 18 and older
was unable to return the memory to the operating system.) It returns
nil.
Any processes that have this buffer as the process-buffer are
sent the SIGHUP signal, which normally causes them to terminate.
(The usual meaning of SIGHUP is that a dialup line has been
disconnected.) See section Deleting Processes.
If the buffer is visiting a file when kill-buffer is called and
the buffer has not been saved since it was last modified, the user is
asked to confirm before the buffer is killed. This is done even if
kill-buffer is not called interactively. To prevent the request
for confirmation, clear the modified flag before calling
kill-buffer. See section Buffer Modification.
Just before actually killing the buffer, after asking all questions,
kill-buffer runs the normal hook kill-buffer-hook. The
buffer to be killed is current when the hook functions run.
See section Hooks.
Killing a buffer that is already dead has no effect.
(kill-buffer "foo.unchanged")
=> nil
(kill-buffer "foo.changed")
---------- Buffer: Minibuffer ----------
Buffer foo.changed modified; kill anyway? (yes or no) yes
---------- Buffer: Minibuffer ----------
=> nil
There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the current buffer. This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (see section Text). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can designate any buffer as current temporarily in order to operate on its contents, without changing what is displayed on the screen.
The way to designate a current buffer in a Lisp program is by calling
set-buffer. The specified buffer remains current until a new one
is designated.
When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window as
current, to prevent confusion: the buffer that the cursor is in, when
Emacs reads a command, is the one to which the command will apply.
(See section Command Loop.) Therefore, set-buffer is not usable for
switching visibly to a different buffer so that the user can edit it.
For this, you must use the functions described in section Displaying Buffers in Windows.
However, Lisp functions that change to a different current buffer
should not leave it to the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
as well as from the command loop. It is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose). Therefore, you should
normally use set-buffer within a save-excursion that will
restore the current buffer when your program is done
(see section Excursions). Here is an example, the code for the command
append-to-buffer (with the documentation string abridged):
(defun append-to-buffer (buffer start end)
"Append to specified buffer the text of the region..."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-excursion
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
This function binds a local variable to the current buffer, and then
save-excursion records the values of point, the mark, and the
original buffer. Next, set-buffer makes another buffer current.
Finally, insert-buffer-substring copies the string from the
original current buffer to the new current buffer.
If the buffer appended to happens to be displayed in some window, then the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed.
Changing the current buffer between the binding and unbinding of a buffer-local variable can cause it to be bound in one buffer, and then unbound in another! You can avoid this problem by using save-excursion to make sure that the buffer from which the variable was bound is current again whenever the variable is unbound.
(let (buffer-read-only)
(save-excursion
(set-buffer ...)
...))
Function: current-buffer
This function returns the current buffer.
(current-buffer)
=> #<buffer buffers.texi>
Function: set-buffer buffer-or-name
This function makes buffer-or-name the current buffer. However, it does not display the buffer in the currently selected window or in any other window. This means that the user cannot necessarily see the buffer, but Lisp programs can in any case work on it.
This function returns the buffer identified by buffer-or-name. An error is signaled if buffer-or-name does not identify an existing buffer.
This chapter describes most of the functions and variables related to Emacs windows. See section Emacs Display, for information on how text is displayed in windows.
A window is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object which represents that screen area in Emacs Lisp. It should be clear from the context which is meant.
There is always at least one window displayed on the screen, and there
is exactly one window that we call the selected window. The
cursor is in the selected window. The selected window's buffer is
usually the current buffer (except when set-buffer has
been used.) See section The Current Buffer.
For all intents, a window only exists while it is displayed on the terminal. Once removed from the display, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See section Deleting Windows.)
Each window has the following attributes:
Applications use multiple windows for a variety of reasons, but most often to give different views of the same information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.
The term "window" in Emacs means something similar to what it means in the context of general purpose window systems such as X, but not identical. The X Window System subdivides the screen into X windows; Emacs uses one or more X windows, called frames in Emacs terminology, and subdivides each of them into (nonoverlapping) Emacs windows. When you use Emacs on an ordinary display terminal, Emacs subdivides the terminal screen into Emacs windows.
Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole of the screen or frame. Because of the way in which Emacs creates new windows and resizes them, you can't create every conceivable tiling on an Emacs screen. See section Splitting Windows. Also, see section The Size of a Window.
See section Emacs Display, for information on how the contents of the window's buffer are displayed in the window.
Function: windowp object
This function returns t if object is a window.
The functions described here are the primitives used to split a window
into two windows. Two higher level functions sometimes split a window,
but not always: pop-to-buffer and display-buffer
(see section Displaying Buffers in Windows).
The functions described here do not accept a buffer as an argument. They let the two "halves" of the split window display the same buffer previously visible in the window that was split.
Function: one-window-p &optional no-mini
This function returns non-nil if there is only one window. The
argument no-mini, if non-nil, means don't count the
minibuffer even if it is active; otherwise, the minibuffer window is
included, if active, in the total number of windows which is compared
against one.
Command: split-window &optional window size horizontal
This function splits window into two windows. The original window window remains the selected window, but occupies only part of its former screen area. The rest is occupied by a newly created window which is returned as the value of this function.
If horizontal is non-nil, then window splits side
by side, keeping the leftmost size columns and giving the rest of
the columns to the new window. Otherwise, it splits into halves one
above the other, keeping the upper size lines and giving the rest
of the lines to the new window. The original window is therefore the
right-hand or upper of the two, and the new window is the left-hand or
lower.
If window is omitted or nil, then the selected window is
split. If size is omitted or nil, then window is
divided evenly into two parts. (If there is an odd line, it is
allocated to the new window.) When split-window is called
interactively, all its arguments are nil.
The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then the window is split.
(setq w (selected-window))
=> #<window 8 on windows.texi>
(window-edges) ; Edges in order:
=> (0 0 80 50) ; left--top--right--bottom
;; Returns window created
(setq w2 (split-window w 15))
=> #<window 28 on windows.texi>
(window-edges w2)
=> (0 15 80 50) ; Bottom window;
; top is line 15
(window-edges w)
=> (0 0 80 15) ; Top window
The screen looks like this:
__________
| | line 0
| w |
|__________|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
Next, the top window is split horizontally:
(setq w3 (split-window w 35 t))
=> #<window 32 on windows.texi>
(window-edges w3)
=> (35 0 80 15) ; Left edge at column 35
(window-edges w)
=> (0 0 35 15) ; Right edge at column 35
(window-edges w2)
=> (0 15 80 50) ; Bottom window unchanged
Now, the screen looks like this:
column 35
__________
| | | line 0
| w | w3 |
|___|______|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
Command: split-window-vertically size
This function splits the selected window into two windows, one above the other, leaving the selected window with size lines.
This function is simply an interface to split-windows.
Here is the complete function definition for it:
(defun split-window-vertically (&optional arg) "Split selected window into two windows, one above the other..." (interactive "P") (split-window nil (and arg (prefix-numeric-value arg))))
Command: split-window-horizontally size
This function splits the selected window into two windows side-by-side, leaving the selected window with size columns.
This function is simply an interface to split-windows. Here is
the complete definition for split-window-horizontally (except for
part of the documentation string):
(defun split-window-horizontally (&optional arg) "Split selected window into two windows side by side..." (interactive "P") (split-window nil (and arg (prefix-numeric-value arg)) t))
A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see section Window Configurations). Restoring a window configuration also deletes any windows that aren't part of that configuration.
When you delete a window, the space it took up is given to one adjacent sibling. (In Emacs version 18, the space was divided evenly among all the siblings.)
Function: window-live-p window
This function returns nil if window is deleted, and
t otherwise.
Warning: erroneous information or fatal errors may result from using a deleted window as if it were live.
Command: delete-window &optional window
This function removes window from the display. If window
is omitted, then the selected window is deleted. An error is signaled
if there is only one window when delete-window is called.
This function returns nil.
When delete-window is called interactively, window
defaults to the selected window.
Command: delete-other-windows &optional window
This function makes window the only window on its frame, by
deleting all the other windows. If window is omitted or
nil, then the selected window is used by default.
The result is nil.
Command: delete-windows-on buffer &optional frame
This function deletes all windows showing buffer. If there are
no windows showing buffer, then this function does nothing. If
all windows in some frame are showing buffer (including the case
where there is only one window), then the frame reverts to having a
single window showing the buffer chosen by other-buffer.
See section The Buffer List.
If there are several windows showing different buffers, then those showing buffer are removed, and the others are expanded to fill the void.
If frame is a frame, then delete-windows-on considers just
the windows on frame. If frame is nil, all windows
on all frames are considered. If frame is t, that stands
for the selected frame.
This function always returns nil.
When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it.
Function: selected-window
This function returns the selected window. This is the window in which the cursor appears and to which many commands apply.
Function: select-window window
This function makes window the selected window. The cursor then appears in window (on redisplay). The buffer being displayed in window is immediately designated the current buffer.
The return value is window.
(setq w (next-window))
(select-window w)
=> #<window 65 on windows.texi>
The following functions choose one of the windows on the screen, offering various criteria for the choice.
Function: get-lru-window &optional all-frames
This function returns the window least recently "used" (that is, selected). The selected window is always the most recently used window.
The selected window can be the least recently used window if it is the only window. A newly created window becomes the least recently used window until it is selected. The minibuffer window is not considered a candidate.
The argument all-frames controls which set of windows are
considered. If it is non-nil, then all windows on all frames are
considered. Otherwise, only windows in the selected frame are
considered.
Function: get-largest-window &optional all-frames
This function returns the window with the largest area (height times width). If there are no side-by-side windows, then this is the window with the most lines. The minibuffer window is not considered a candidate.
If there are two windows of the same size, then the function returns the window which is first in the cyclic ordering of windows (see following section), starting from the selected window.
The argument all-frames controls which set of windows are
considered. If it is non-nil, then all windows on all frames are
considered. Otherwise, only windows in the selected frame are
considered.
When you use the command C-x o (other-window) to select
the next window, it moves through all the windows on the screen in a
specific cyclic order. For any given configuration of windows, this
order never varies. It is called the cyclic ordering of windows.
This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split.
If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom.
Function: next-window window &optional minibuf all-frames
This function returns the window following window in the cyclic ordering of windows. This is the window which C-x o would select if done when window is selected. If window is the only window visible, then this function returns window.
The value of the argument minibuf determines whether the
minibuffer is included in the window order. Normally, when
minibuf is nil, the minibuffer is included if it is
currently active; this is the behavior of C-x o.
If minibuf is t, then the cyclic ordering includes the
minibuffer window even if it is not active.
If minibuf is neither t nor nil, then the minibuffer
window is not included even if it is active. (The minibuffer window is
active while the minibuffer is in use. See section Minibuffers.)
When there are multiple frames, this functions normally cycles through all the windows in the selected frame, plus the minibuffer used by the selected frame even if it lies in some other frame.
If all-frames is t, then it cycles through all the windows
in all the frames that currently exist.
If all-frames is neither t nor nil, then it cycles
through precisely the windows in the selected frame, excluding the
minibuffer in use if it lies in some other frame.
This example shows two windows, which both happen to be displaying the same buffer:
(selected-window)
=> #<window 56 on windows.texi>
(next-window (selected-window))
=> #<window 52 on windows.texi>
(next-window (next-window (selected-window)))
=> #<window 56 on windows.texi>
Function: previous-window window &optional minibuf all-frames
This function returns the window preceding window in the cyclic
ordering of windows. The other arguments affect which windows are
included in the cycle, as in next-window.
Command: other-window count
This function selects the countth next window in the cyclic
order. If count is negative, then it selects the -countth
preceding window. It returns nil.
In an interactive call, count is the numeric prefix argument.
Function: walk-windows proc &optional minibuf all-frames
This function cycles through all visible windows, calling proc
once for each window with the window as its sole argument.
The optional argument minibuf says whether to include minibuffer
windows. A value of t means count the minibuffer window even if
not active. A value of nil means count it only if active. Any
other value means not to count the minibuffer even if it is active.
If the optional third argument all-frames is t, that means
include all windows in all frames. If all-frames is nil,
it means to cycle within the selected frame, but include the minibuffer
window (if minibuf says so) that that frame uses, even if it is on
another frame. If all-frames is neither nil nor t,
walk-windows sticks strictly to the selected frame.
This section describes low-level functions to examine windows or to show buffers in windows in a precisely controlled fashion. See the following section for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control.
Function: set-window-buffer window buffer-or-name
This function makes window display buffer-or-name as its
contents. It returns nil.
(set-window-buffer (selected-window) "foo")
=> nil
Function: window-buffer &optional window
This function returns the buffer that window is displaying. If window is omitted, then this function returns the buffer for the selected window.
(window-buffer)
=> #<buffer windows.texi>
Function: get-buffer-window buffer-or-name &optional all-frames
This function returns a window currently displaying
buffer-or-name, or nil if there is none. If there are
several such windows, then the function returns the first one in the
cyclic ordering of windows, starting from the selected window.
See section Cycling Ordering of Windows.
The argument all-frames controls which set of windows are considered.
nil, then windows on the selected frame are considered.
t, then windows on all visible frames are considered.
nil value, then all windows on all frames
are considered.
Command: replace-buffer-in-windows buffer
This function replaces buffer with some other buffer in all
windows displaying it. The other buffer used is chosen with
other-buffer. In the usual applications of this function, you
don't care which other buffer is used; you just want to make sure that
buffer is no longer displayed.
This function returns nil.
In this section we describe convenient functions that choose a window automatically and use it to display a specified buffer. These functions can also split an existing window in certain circumstances. We also describe variables that parameterize the heuristics used for choosing a window. See the preceding section for low-level functions that give you more precise control.
Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which is gratuitous and will surprise the user. Instead, use
set-buffer (see section The Current Buffer) and save-excursion
(see section Excursions), which designate buffers as current for programmed
access without affecting the display of buffers in windows.
Command: switch-to-buffer buffer-or-name &optional norecord
This function makes buffer-or-name the current buffer, and also
displays the buffer in the selected window. This means that a human can
see the buffer and subsequent keyboard commands will apply to it.
Contrast this with set-buffer, which makes buffer-or-name
the current buffer but does not display it in the selected window.
See section The Current Buffer.
If buffer-or-name does not identify an existing buffer, then a new buffer by that name is created.
Normally the specified buffer is put at the front of the buffer list.
This affects the operation of other-buffer. However, if
norecord is non-nil, this is not done. See section The Buffer List.
The switch-to-buffer function is often used interactively, as
the binding of C-x b. It is also used frequently in programs. It
always returns nil.
Command: switch-to-buffer-other-window buffer-or-name
This function makes buffer-or-name the current buffer and
displays it in a window not currently selected. It then selects that
window. The handling of the buffer is the same as in
switch-to-buffer.
The previously selected window is absolutely never used to display the buffer. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well.
Function: pop-to-buffer buffer-or-name &optional other-window
This function makes buffer-or-name the current buffer and switches to it in some window, preferably not the window previously selected. The "popped-to" window becomes the selected window.
If the variable pop-up-frames is non-nil,
pop-to-buffer creates a new frame to display the buffer in.
Otherwise, if the variable pop-up-windows is non-nil,
windows may be split to create a new window that is different from the
original window. For details, see section Choosing a Window.
If other-window is non-nil, pop-to-buffer finds or
creates another window even if buffer-or-name is already visible
in the selected window. Thus buffer-or-name could end up
displayed in two windows. On the other hand, if buffer-or-name is
already displayed in the selected window and other-window is
nil, then the selected window is considered sufficient display
for buffer-or-name, so that nothing needs to be done.
If buffer-or-name is a string that does not name an existing buffer, a buffer by that name is created.
An example use of this function is found at the end of section Process Filter Functions.
This section describes the basic facility which chooses a window to
display a buffer in---display-buffer. All the higher-level
functions and commands use this subroutine. Here we describe how to use
display-buffer and how to customize it.
Function: display-buffer buffer-or-name &optional not-this-window
This function makes buffer-or-name appear in some window, like
pop-to-buffer, but it does not select that window and does not
make the buffer current. The identity of the selected window is
unaltered by this function.
If not-this-window is non-nil, it means that the
specified buffer should be displayed in a window other than the selected
one, even if it is already on display in the selected window. This can
cause the buffer to appear in two windows at once. Otherwise, if
buffer-or-name is already being displayed in any window, that is
good enough, so this function does nothing.
display-buffer returns the window chosen to display
buffer-or-name.
Precisely how display-buffer finds or creates a window depends on
the variables described below.
A window can be marked as "dedicated" to its buffer. Then
display-buffer does not try to use that window.
Function: window-dedicated-p window
This function returns t if window is marked as dedicated;
otherwise nil.
Function: set-window-dedicated-p window flag
This function marks window as dedicated if flags is
non-nil, and nondedicated otherwise.
User Option: pop-up-windows
This variable controls whether display-buffer makes new windows.
If it is non-nil and there is only one window, then that window
is split. If it is nil, then display-buffer does not
split the single window, but rather replaces its buffer.
User Option: split-height-threshold
This variable determines when display-buffer may split a
window, if there are multiple windows. display-buffer splits the
largest window if it has at least this many lines.
If there is only one window, it is split regardless of this value,
provided pop-up-windows is non-nil.
User Option: pop-up-frames
This variable controls whether display-buffer makes new
frames. If it is non-nil, display-buffer makes a new
frame. If it is nil, then display-buffer either splits a
window or reuses one.
If this is non-nil, the variables pop-up-windows and
split-height-threshold do not matter.
See section Frames, for more information.
Variable: pop-up-frame-function
This variable specifies how to make a new frame if pop-up-frame
is non-nil.
Its value should be a function of no arguments. When
display-buffer makes a new frame, it does so by calling that
function, which should return a frame. The default value of the
variable is a function which creates a frame using parameters from
pop-up-frame-alist.
Variable: pop-up-frame-alist
This variable holds an alist specifying frame parameters used when
display-buffer makes a new frame. See section Frame Parameters, for
more information about frame parameters.
Variable: display-buffer-function
This variable is the most flexible way to customize the behavior of
display-buffer. If it is non-nil, it should be a function
that display-buffer calls to do the work. The function should
accept two arguments, the same two arguments that display-buffer
received. It should choose or create a window, display the specified
buffer, and then return the window.
This hook takes precedence over all the other options and hooks described above.
Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.
As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.
Function: window-point window
This function returns the current position of point in window. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected.
When window is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer.
Strictly speaking, it would be more correct to return the
"top-level" value of point, outside of any save-excursion
forms. But that value is hard to find.
Function: set-window-point window position
This function positions point in window at position position in window's buffer.
Each window contains a marker used to keep track of a buffer position which specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
Function: window-start &optional window
This function returns the display-start position of window
window. If window is nil, the selected window is
used.
(window-start)
=> 7058
For a more complicated example of use, see the description of
count-lines in section Motion by Text Lines.
Function: window-end &optional window
This function returns the position of the end of the display in window
window. If window is nil, the selected window is
used.
Function: set-window-start window position &optional noforce
This function sets the display-start position of window to position in window's buffer.
The display routines insist that the position of point be visible when
a buffer is displayed. Normally, they change the display-start position
(that is, scroll the window) whenever necessary to make point visible.
However, if you specify the start position with this function with
nil for noforce, it means you want display to start at
position even if that would put the location of point off the
screen. What the display routines do in this case is move point
instead, to the left margin on the middle line in the window.
For example, if point is 1 and you attempt to set the start of the window to 2, then the position of point would be "above" the top of the window. The display routines would automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what `foo' looks like before executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (1+ (window-start))) ;; Here is what `foo' looks like after executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- his is the contents of buffer foo. 2 3 -!-4 5 6 ---------- Buffer: foo ---------- => 2
However, when noforce is non-nil, set-window-start
does nothing if the specified start position would make point invisible.
This function returns position, regardless of whether the noforce option caused that position to be overruled.
Function: pos-visible-in-window-p &optional position window
This function returns t if position is within the range
of text currently visible on the screen in window. It returns
nil if position is scrolled vertically out of view. The
argument position defaults to the current position of point;
window, to the selected window. Here is an example:
(or
(pos-visible-in-window-p
(point) (selected-window))
(recenter 0))
The pos-visible-in-window-p function considers only vertical
scrolling. It returns t if position is out of view only
because window has been scrolled horizontally. See section Horizontal Scrolling.
Vertical scrolling means moving the text up or down in a window. It
works by changing the value of the window's display-start location. It
may also change the value of window-point to keep it on the
screen.
In the commands scroll-up and scroll-down, the directions
"up" and "down" refer to the motion of the text in the buffer at which
you are looking through the window. Imagine that the text is
written on a long roll of paper and that the scrolling commands move the
paper up and down. Thus, if you are looking at text in the middle of a
buffer and repeatedly call scroll-down, you will eventually see
the beginning of the buffer.
Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then "down" commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view.
The scrolling functions (aside from scroll-other-window) will
have unpredictable results if the current buffer is different from the
buffer that is displayed in the selected window. See section The Current Buffer.
Command: scroll-up &optional count
This function scrolls the text in the selected window upward count lines. If count is negative, scrolling is actually downward.
If count is nil (or omitted), then the length of scroll
is next-screen-context-lines lines less than the usable height of
the window (not counting its mode line).
scroll-up returns nil.
Command: scroll-down &optional count
This function scrolls the text in the selected window downward count lines. If count is negative, scrolling is actually upward.
If count is omitted or nil, then the length of the scroll
is next-screen-context-lines lines less than the usable height of
the window.
scroll-down returns nil.
Command: scroll-other-window &optional count
This function scrolls the text in another window upward count
lines. Negative values of count, or nil, are handled
as in scroll-up.
The window that is scrolled is normally the one following the selected
window in the cyclic ordering of windows--the window that
next-window would return. See section Cycling Ordering of Windows.
If the selected window is the minibuffer, the next window is normally
the one at the top left corner. However, you can specify the window to
scroll by binding the variable minibuffer-scroll-window. This
variable has no effect when any other window is selected.
See section Minibuffer Miscellany.
When the minibuffer is active, it is the next window if the selected
window is the one at the bottom right corner. In this case,
scroll-other-window attempts to scroll the minibuffer. If the
minibuffer contains just one line, it has nowhere to scroll to, so the
line reappears after the echo area momentarily displays the message
"Beginning of buffer".
Variable: other-window-scroll-buffer
If this variable is non-nil, it tells scroll-other-window
which buffer to scroll.
User Option: scroll-step
This variable controls how scrolling is done automatically when point moves off the screen. If the value is zero, then the text is scrolled so that point is centered vertically in the window. If the value is a positive integer n, then if it is possible to bring point back on screen by scrolling n lines in either direction, that is done; otherwise, point is centered vertically as usual. The default value is zero.
User Option: next-screen-context-lines
The value of this variable is the number of lines of continuity to
retain when scrolling by full screens. For example, when
scroll-up executes, this many lines that were visible at the
bottom of the window move to the top of the window. The default value
is 2.
Command: recenter &optional count
This function scrolls the selected window to put the text where point is located at a specified vertical position within the window.
If count is a nonnegative number, it puts the line containing
point count lines down from the top of the window. If count
is a negative number, then it counts upward from the bottom of the
window, so that -1 stands for the last usable line in the window.
If count is a non-nil list, then it stands for the line in
the middle of the window.
If count is nil, then it puts the line containing point
in the middle of the window, then clears and redisplays the entire
selected frame.
When recenter is called interactively, Emacs sets count
to the raw prefix argument. Thus, typing C-u as the prefix sets
the count to a non-nil list, while typing C-u 4 sets
count to 4, which positions the current line four lines from the
top.
Typing C-u 0 C-l positions the current line at the top of the window. This action is so handy that some people bind the command to a function key. For example,
(defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key "\C-cl" 'line-to-top-of-window)
Because we read English first from top to bottom and second from left
to right, horizontal scrolling is not like vertical scrolling. Vertical
scrolling involves selection of a contiguous portion of text to display.
Horizontal scrolling causes part of each line to go off screen. The
amount of horizontal scrolling is therefore specified as a number of
columns rather than as a position in the buffer. It has nothing to do
with the display-start position returned by window-start.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the screen to be revealed by it, so it is not allowed. Scrolling to the left is allowed; it causes the first columns of text to go off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.
Command: scroll-left count
This function scrolls the selected window count columns to the
left (or to the right if count is negative). The return value is
the total amount of leftward horizontal scrolling in effect after the
change--just like the value returned by window-hscroll.
Command: scroll-right count
This function scrolls the selected window count columns to the right
(or to the left if count is negative). The return value is the
total amount of leftward horizontal scrolling in effect after the
change--just like the value returned by window-hscroll.
Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther have no effect.
Function: window-hscroll &optional window
This function returns the total leftward horizontal scrolling of window---the number of columns by which the text in window is scrolled left past the left margin.
The value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).
If window is nil, the selected window is used.
(window-hscroll)
=> 0
(scroll-left 5)
=> 5
(window-hscroll)
=> 5
Function: set-window-hscroll window columns
This function sets the number of columns from the left margin that window is scrolled to the value of columns. The argument columns should be zero or positive; if not, it is taken as zero.
The value returned is columns.
(set-window-hscroll (selected-window) 10)
=> 10
Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window))))
An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. For a window that does not abut the right hand edge of the screen, the column of `|' characters that separates it from the window on the right is included in the width.
The following three functions return size information about a window:
Function: window-height &optional window
This function returns the number of lines in window, including
its mode line. If window fills its entire frame, this is one less
than the value of frame-height on that frame (since the last line
is always reserved for the minibuffer).
If window is nil, the function uses the selected window.
(window-height)
=> 23
(split-window-vertically)
=> #<window 4 on windows.texi>
(window-height)
=> 11
Function: window-width &optional window
This function returns the number of columns in window. If
window fills its entire frame, this is the same as the value of
frame-width on that frame.
If window is nil, the function uses the selected window.
(window-width)
=> 80
Function: window-edges &optional window
This function returns a list of the edge coordinates of window.
If window is nil, the selected window is used.
The order of the list is (left top right
bottom), all elements relative to 0, 0 at the top left corner of
the frame. The element right of the value is one more than the
rightmost column used by window, and bottom is one more than
the bottommost row used by window and its mode-line.
Here is the result obtained on a typical 24-line terminal with just one window:
(window-edges (selected-window))
=> (0 0 80 23)
If window is at the upper left corner of its frame, right
and bottom are the same as the values returned by
(window-width) and (window-height) respectively, and
top and bottom are zero. For example, the edges of the
following window are `0 0 5 8'. Assuming that the frame has
more than 8 columns, the last column of the window (column 7) holds a
border rather than text. The last row (row 4) holds the mode line,
shown here with `xxxxxxxxx'.
0
_______
0 | |
| |
| |
| |
xxxxxxxxx 4
7
When there are side-by-side windows, any window not at the right edge of its frame has a border in its last column. This border counts as one column in the width of the window. A window never includes a border on its left, since the border there belongs to the window to the left.
In the following example, let's imagine that the frame is 7 columns wide. Then the edges of the left window are `0 0 4 3' and the edges of the right window are `4 0 7 3'.
___ ___
| | |
| | |
xxxxxxxxx
0 34 7
The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows.
Command: enlarge-window size &optional horizontal
This function makes the selected window size lines bigger,
stealing lines from neighboring windows. It takes the lines from one
window at a time until that window is used up, then takes from another.
If a window from which lines are stolen shrinks below
window-min-height lines, then that window disappears.
If horizontal is non-nil, then this function makes
window wider by size columns, stealing columns instead of
lines. If a window from which columns are stolen shrinks below
window-min-width columns, then that window disappears.
If the window's frame is smaller than size lines (or columns), then the function makes the window occupy the entire height (or width) of the frame.
If size is negative, this function shrinks the window by
-size lines. If it becomes shorter than
window-min-height, it disappears.
enlarge-window returns nil.
Command: enlarge-window-horizontally columns
This function makes the selected window columns wider. It could be defined as follows:
(defun enlarge-window-horizontally (columns) (enlarge-window columns t))
Command: shrink-window size &optional horizontal
This function is like enlarge-window but negates the argument
size, making the selected window smaller by giving lines (or
columns) to the other windows. If the window shrinks below
window-min-height or window-min-width, then it disappears.
If size is negative, the window is enlarged by -size lines.
Command: shrink-window-horizontally columns
This function makes the selected window columns narrower. It could be defined as follows:
(defun shrink-window-horizontally (columns) (shrink-window columns t))
The following two variables constrain the window size changing functions to a minimum height and width.
User Option: window-min-height
The value of this variable determines how short a window may become
before it disappears. A window disappears when it becomes smaller than
window-min-height, and no window may be created that is smaller.
The absolute minimum height is two (allowing one line for the mode line,
and one line for the buffer display). Actions which change window sizes
reset this variable to two if it is less than two. The default value is
4.
User Option: window-min-width
The value of this variable determines how narrow a window may become
before it disappears. A window disappears when it becomes narrower than
window-min-width, and no window may be created that is narrower.
The absolute minimum width is one; any value below that is ignored. The
default value is 10.
This section describes how to compare screen coordinates with windows.
Function: window-at x y &optional frame
This function returns the window containing the specified cursor position in the frame frame. The coordinates x and y are measured in characters and count from the top left corner of the screen or frame.
If you omit frame, the selected frame is used.
Function: coordinates-in-window-p coordinates window
This function checks whether a particular frame position falls within the window window.
The argument coordinates is a cons cell of this form:
(x . y)
The coordinates x and y are measured in characters, and count from the top left corner of the screen or frame.
The value of coordinates-in-window-p is non-nil if the
coordinates are inside window. The value also indicates what part
of the window the position is in, as follows:
(relx . rely)
mode-line
vertical-split
nil
The function coordinates-in-window-p does not require a frame as
argument because it always uses the frame that window window is
on.
A window configuration records the entire layout of a frame--all windows, their sizes, which buffers they contain, what part of each buffer is displayed, and the values of point and the mark. You can bring back an entire previous layout by restoring a window configuration previously saved.
If you want to record all frames instead of just one, use a frame configuration instead of a window configuration. See section Frame Configurations.
Function: current-window-configuration
This function returns a new object representing Emacs's current window configuration, namely the number of windows, their sizes and current buffers, which window is the selected window, and for each window the displayed buffer, the display-start position, and the positions of point and the mark. An exception is made for point in the current buffer, whose value is not saved.
Function: set-window-configuration configuration
This function restores the configuration of Emacs's windows and
buffers to the state specified by configuration. The argument
configuration must be a value that was previously returned by
current-window-configuration.
Here is a way of using this function to get the same effect
as save-window-excursion:
(let ((config (current-window-configuration)))
(unwind-protect
(progn (split-window-vertically nil)
...)
(set-window-configuration config)))
Special Form: save-window-excursion forms...
This special form executes forms in sequence, preserving window
sizes and contents, including the value of point and the portion of the
buffer which is visible. It also preserves the choice of selected
window. However, it does not restore the value of point in the current
buffer; use save-excursion for that.
The return value is the value of the final form in forms. For example:
(split-window)
=> #<window 25 on control.texi>
(setq w (selected-window))
=> #<window 19 on control.texi>
(save-window-excursion
(delete-other-windows w)
(switch-to-buffer "foo")
'do-something)
=> do-something
;; The screen is now split again.
Function: window-configuration-p object
This function returns t if object is a window configuration.
Primitives to look inside of window configurations would make sense, but none are implemented. It is not clear they are useful enough to be worth implementing.
A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows.
When Emacs runs on a text-only terminal, it has just one frame, a terminal frame. There is no way to create another terminal frame after startup. If Emacs has an X display, it does not make a terminal frame; instead, it initially creates a single X window frame. You can create more; see section Creating Frames.
Function: framep object
This predicate returns t if object is a frame, and
nil otherwise.
See section Emacs Display, for related information.
To create a new frame, call the function make-frame.
Function: make-frame alist
This function creates a new frame, if the display mechanism permits creation of frames. (An X server does; an ordinary terminal does not.)
The argument is an alist specifying frame parameters. Any parameters
not mentioned in alist default according to the value of the
variable default-frame-alist; parameters not specified there
either default from the standard X defaults file and X resources.
The set of possible parameters depends in principle on what kind of window system Emacs uses to display its the frames. See section X Window Frame Parameters, for documentation of individual parameters you can specify when creating an X window frame.
Variable: default-frame-alist
An alist specifying default values of frame parameters. Each element has the form:
(parameter . value)
If you use options that specify window appearance when you invoke Emacs,
they take effect by adding elements to default-frame-alist.
A frame has many parameters that control how it displays.
These functions let you read and change the parameter values of a frame.
Function: frame-parameters frame
The function frame-parameters returns an alist of all the
parameters of frame.
Function: modify-frame-parameters frame alist
This function alters the parameters of frame frame based on the
elements of alist. Each element of alist has the form
(parm . value), where parm is a symbol naming a
parameter. If you don't mention a parameter in alist, its value
doesn't change.
You can specify the parameters for the initial startup frame
by setting initial-frame-alist in your `.emacs' file.
Variable: initial-frame-alist
This variable's value is an alist of parameter values to when creating the initial X window frame.
If these parameters specify a separate minibuffer-only frame, and you have not created one, Emacs creates one for you.
Variable: minibuffer-frame-alist
This variable's value is an alist of parameter values to when creating an initial minibuffer-only frame--if such a frame is needed, according to the parameters for the main initial frame.
Just what parameters a frame has depends on what display mechanism it uses. Here is a table of the parameters of an X window frame:
name
left
top
height
width
window-id
minibuffer
t means
yes, nil means no, only means this frame is just a
minibuffer, a minibuffer window (in some other frame) means the new
frame uses that minibuffer.
font
auto-raise
nil means yes).
auto-lower
nil means yes).
vertical-scroll-bars
nil means yes).
horizontal-scroll-bars
nil means yes). (Horizontal scroll bars are not currently
implemented.)
icon-type
nil specifies a bitmap icon, nil a text icon.
foreground-color
background-color
mouse-color
cursor-color
border-color
cursor-type
bar and box. The value bar specifies a vertical
bar between characters as the cursor. The value box specifies an
ordinary black box overlaying the character after point; that is the
default.
border-width
internal-border-width
unsplittable
nil, this frame's window is never split automatically.
visibility
nil for invisible, t for visible, and icon for
iconified. See section Visibility of Frames.
menu-bar-lines
parent-id
You can read or change the size and position of a frame using the
frame parameters left, top, height and
width. When you create a frame, you must specify either both
size parameters or neither. Likewise, you must specify either both
position parameters or neither. Whatever geometry parameters you don't
specify are chosen by the window manager in its usual fashion.
Here are some special features for working with sizes and positions:
Function: set-frame-position frame left top
This function sets the position of the top left corner of frame---to left and top. These arguments are measured in pixels, counting from the top left corner of the screen.
Function: frame-height &optional frame
Function: frame-width &optional frame
These functions return the height and width of frame, measured in characters. If you don't supply frame, they use the selected frame.
Function: frame-pixel-height &optional frame
Function: frame-pixel-width &optional frame
These functions return the height and width of frame, measured in pixels. If you don't supply frame, they use the selected frame.
Function: frame-char-height &optional frame
Function: frame-char-width &optional frame
These functions return the height and width, respectively, of a character in frame, measured in pixels. The values depend on the choice of font. If you don't supply frame, these functions use the selected frame.
Function: set-frame-size frame cols rows
This function sets the size of frame, measured in characters; cols and rows specify the new width and height.
To set the size with values measured in pixels, use
modify-frame-parameters to set the width and height
parameters. See section X Window Frame Parameters.
The old-fashioned functions set-screen-height and
set-screen-width, which were used to specify the height and width
of the screen in Emacs versions that did not support multiple frames,
are still usable. They apply to the selected frame. See section Screen Size.
Function: x-parse-geometry geom
The function x-parse-geometry converts a standard X windows
geometry string to an alist which you can use as part of the argument to
x-create-frame.
The alist describes which parameters were specified in geom, and
gives the values specified for them. Each element looks like
(parameter . value). The possible parameter
values are left, top, width, and height.
(x-geometry "35x70+0-0")
=> ((width . 35) (height . 70) (left . 0) (top . -1))
Frames remain potentially visible until you explicitly delete them. A deleted frame cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a frame aside from restoring a saved frame configuration (see section Frame Configurations); this is similar to the way windows behave.
Command: delete-frame &optional frame
This function deletes the frame frame. By default, frame is the selected frame.
Function: frame-live-p frame
The function frame-live-p returns non-nil if the frame
frame has not been deleted.
Function: frame-list
The function frame-list returns a list of all the frames that
have not been deleted. It is analogous to buffer-list for
buffers. The list that you get is newly created, so modifying the list
doesn't have any effect on the internals of Emacs.
Function: visible-frame-list
This function returns a list of just the currently visible frames.
Function: next-frame &optional frame minibuf
The function next-frame lets you cycle conveniently through all
the frames from an arbitrary starting point. It returns the "next"
frame after frame in the cycle. If frame is omitted or
nil, it defaults to the selected frame.
The second argument, minibuf, says which frames to consider:
nil
Function: previous-frame &optional frame minibuf
Like next-frame, but cycles through all frames in the opposite
direction.
All the non-minibuffer windows in a frame are arranged in a tree of
subdivisions; the root of this tree is available via the function
frame-root-window. Each window is part of one and
only one frame; you can get the frame with window-frame.
Function: frame-root-window frame
This returns the root window of frame frame.
Function: window-frame window
This function returns the frame that window is on.
At any time, exactly one window on any frame is selected within the
frame. The significance of this designation is that selecting the
frame also selects this window. You can get the frame's current
selected window with frame-selected-window.
Function: frame-selected-window frame
This function returns the window on frame which is selected within frame.
Conversely, selecting a window for Emacs with select-window also
makes that window selected within its frame. See section Selecting Windows.
Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected. If the frame has a minibuffer,
you can get it with minibuffer-window (see section Minibuffer Miscellany).
However, you can also create a frame with no minibuffer. Such a frame
must use the minibuffer window of some other frame. When you create the
frame, you can specify explicitly the frame on which to find the
minibuffer to use. If you don't, then the minibuffer is found in the
frame which is the value of the variable
default-minibuffer-frame. Its value should be a frame which does
have a minibuffer.
At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.
Function: selected-frame
This function returns the selected frame.
The X server normally directs keyboard input to the X window that the mouse is in. Some window managers use mouse clicks or keyboard events to shift the focus to various X windows, overriding the normal behavior of the server.
Lisp programs can switch frames "temporarily" by calling
the function select-frame. This does not override the window
manager; rather, it escapes from the window manager's control until
that control is somehow reasserted.
Function: select-frame frame
This function selects frame frame, temporarily disregarding the X Windows focus. The selection of frame lasts until the next time the user does something to select a different frame, or until the next time this function is called.
Emacs cooperates with the X server and the window managers by arranging
to select frames according to what the server and window manager ask
for. It does so by generating a special kind of input event, called a
focus event. The command loop handles a focus event by calling
internal-select-frame. See section Focus Events.
Function: internal-select-frame frame
This function selects frame frame, assuming that the X server focus already points to frame.
Focus events normally do their job by invoking this command. Don't call it for any other reason.
A frame may be visible, invisible, or iconified. If it is visible, you can see its contents. If it is iconified, the frame's contents do not appear on the screen, but an icon does. If the frame is invisible, it doesn't show in the screen, not even as an icon.
Command: make-frame-visible &optional frame
This function makes frame frame visible. If you omit frame, it makes the selected frame visible.
Command: make-frame-invisible &optional frame
This function makes frame frame invisible. If you omit frame, it makes the selected frame invisible.
Command: iconify-frame &optional frame
This function iconifies frame frame. If you omit frame, it iconifies the selected frame.
Function: frame-visible-p frame
This returns the visibility status of frame frame. The value is
t if frame is visible, nil if it is invisible, and
icon if it is iconified.
The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See section X Window Frame Parameters.
The X window system uses a desktop metaphor. Part of this metaphor is the idea that windows are stacked in a notional third dimension perpendicular to the screen surface, and thus ordered from "highest" to "lowest". Where two windows overlap, the one higher up covers the one underneath. Even a window at the bottom of the stack can be seen if no other window overlaps it.
A window's place in this ordering is not fixed; in fact, users tend to change the order frequently. Raising a window means moving it "up", to the top of the stack. Lowering a window means moving it to the bottom of the stack. This motion is in the notional third dimension only, and does not change the position of the window on the screen.
You can raise and lower Emacs's X windows with these functions:
Function: raise-frame frame
This function raises frame frame.
Function: lower-frame frame
This function lowers frame frame.
You can also specify auto-raise (raising automatically when a frame is selected) or auto-lower (lowering automatically when it is deselected) for any frame using frame parameters. See section X Window Frame Parameters.
Function: current-frame-configuration
This function returns a frame configuration list which describes the current arrangement of frames, all their properties, and the window configuration of each one.
Function: set-frame-configuration configuration
This function restores the state of frames described in configuration.
Sometimes it is useful to track the mouse, which means, to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves.
The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don't want to track the mouse forever--only until some other event, such as the release of a button.
Special Form: track-mouse body...
Execute body, meanwhile generating input events for mouse motion.
The code in body can read these events with read-event or
read-key-sequence. See section Motion Events, for the format of mouse
motion events.
The value of track-mouse is that of the last form in body.
The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.
The new functions mouse-position and set-mouse-position
give access to the current position of the mouse.
Function: mouse-position
This function returns a description of the position of the mouse. The
value looks like (frame x . y), where x
and y are integers giving the position in pixels relative to the
top left corner of the inside of frame.
Function: set-mouse-position frame x y
This function warps the mouse to position x, y in frame frame. The arguments x and y are integers, giving the position in pixels relative to the top left corner of the inside of frame.
Warping the mouse means changing the screen position of the mouse as if the user had moved the physical mouse--thus simulating the effect of actual mouse motion.
Function: x-popup-menu position menu
This function displays a pop-up menu and returns an indication of what selection the user makes.
The argument position specifies where on the screen to put the menu. It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:
((xoffset yoffset) window)
where xoffset and yoffset are positions measured in characters, counting from the top left corner of window's frame.
The argument menu says what to display in the menu. It can be a keymap or a list of keymaps (see section Menu Keymaps). Alternatively, it can have the following form:
(title pane1 pane2...)
where each pane is a list of form
(title (line item)...)
Each line should be a string, and each item should be the value to return if that line is chosen.
The X server records a set of selections which permit transfer of data between application programs. The various selections are distinguished by selection types, represented in Emacs by symbols. X clients including Emacs can read or set the selection for any given type.
Function: x-set-selection type data
This function sets a "selection" in the X server.
It takes two arguments: a selection type type, and the value to
assign to it, data. If data is nil, it means to
clear out the selection. Otherwise, data may be a string, a
symbol, an integer (or a cons of two integers or list of two integers),
or a cons of two markers pointing to the same buffer. In the last case,
the selection is considered to be the text between the markers. The
data may also be a vector of valid non-vector selection values.
Each possible type has its own selection value, which changes
independently. The usual values of type are PRIMARY and
SECONDARY; these are symbols with upper-case names, in accord
with X Windows conventions. The default is PRIMARY.
Function: x-get-selection type data-type
This function accesses selections set up by Emacs or by other X
clients. It takes two optional arguments, type and
data-type. The default for type, the selection type, is
PRIMARY.
The data-type argument specifies the form of data conversion to
use, to convert the raw data obtained from another X client into Lisp
data. Meaningful values include TEXT, STRING,
TARGETS, LENGTH, DELETE, FILE_NAME,
CHARACTER_POSITION, LINE_NUMBER, COLUMN_NUMBER,
OWNER_OS, HOST_NAME, USER, CLASS,
NAME, ATOM, and INTEGER. (These are symbols with
upper-case names in accord with X conventions.) The default for
data-type is STRING.
The X server also has a set of numbered cut buffers which can store text or other data being moved between applications. Cut buffers are considered obsolete, but Emacs supports them for the sake of X clients that still use them.
Function: x-get-cut-buffer n
This function returns the contents of cut buffer number n.
Function: x-set-cut-buffer string
This function stores string into the first cut buffer (cut buffer 0), moving the other values down through the series of cut buffers, kill-ring-style.
This section describes how to access and change the overall status of the X server Emacs is using.
You can close the connection with the X server with the function
x-close-current-connection, and open a new one with
x-open-connection (perhaps with a different server and display).
Function: x-close-current-connection
This function closes the connection to the X server. It deletes all frames, making Emacs effectively inaccessible to the user; therefore, a Lisp program that closes the connection should open another one.
Function: x-open-connection display &optional resource-string
This function opens a connection to an X server, for use of display display.
The optional argument resource-string is a string of resource names and values, in the same format used in the `.Xresources' file. The values you specify override the resource values recorded in the X server itself. Here's an example of what this string might look like:
"*BorderWidth: 3\n*InternalBorder: 2\n"
Function: x-color-display-p
This returns t if the connected X display has color, and
nil otherwise.
Function: x-color-defined-p color
This function reports whether a color name is meaningful and supported
on the X display Emacs is using. It returns t if the display
supports that color; otherwise, nil.
Black-and-white displays support just two colors, "black" or
"white". Color displays support many other colors.
Function: x-synchronize flag
The function x-synchronize enables or disables synchronous
communication with the X server. It enables synchronous communication
if flag is non-nil, and disables it if flag is
nil.
In synchronous mode, Emacs waits for a response to each X protocol command before doing anything else. This is useful for debugging Emacs, because protocol errors are reported right away, which helps you find the erroneous command. Synchronous mode is not the default because it is much slower.
Function: x-get-resource attribute &optional name class
The function x-get-resource retrieves a resource value from the X
Windows defaults database.
Resources are indexed by a combination of a key and a class. This function searches using a key of the form `instance.attribute', where instance is the name under which Emacs was invoked, and uses `Emacs' as the class.
The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is `instance.component.attribute', and the class is `Emacs.subclass'.
This section describes functions and a variable that you can use to get information about the capabilities and origin of the X server that Emacs is displaying its frames on.
Function: x-display-screens
This function returns the number of screens associated with the current display.
Function: x-server-version
This function returns the list of version numbers of the X server in use.
Function: x-server-vendor
This function returns the vendor supporting the X server in use.
Function: x-display-pixel-height
This function returns the height of this X screen in pixels.
Function: x-display-mm-height
This function returns the height of this X screen in millimeters.
Function: x-display-pixel-width
This function returns the width of this X screen in pixels.
Function: x-display-mm-width
This function returns the width of this X screen in millimeters.
Function: x-display-backing-store
This function returns the backing store capability of this screen.
Values can be the symbols always, when-mapped, or
not-useful.
Function: x-display-save-under
This function returns non-nil if this X screen supports the
SaveUnder feature.
Function: x-display-planes
This function returns the number of planes this display supports.
Function: x-display-visual-class
This function returns the visual class for this X screen. The value is
one of the symbols static-gray, gray-scale,
static-color, pseudo-color, true-color, and
direct-color.
Function: x-display-color-p
This function returns t if the X screen in use is a color
screen.
Function: x-display-color-cells
This function returns the number of color cells this X screen supports.
Variable: x-no-window-manager
This variable's value is is t if no X window manager is in use.
A position is the index of a character in the text of buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, the character after a position is often said to be "at" that position.
Positions are usually represented as integers starting from 1, but can also be represented as markers---special objects which relocate automatically when text is inserted or deleted so they stay with the surrounding characters. See section Markers.
Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Many terminals display the cursor over the character that immediately follows point; on such terminals, point is actually before the character on which the cursor sits.
The value of point is a number between 1 and the buffer size plus 1. If narrowing is in effect (see section Narrowing), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See section Window Point, for more details.
Function: point
This function returns the position of point in the current buffer, as an integer.
(point)
=> 175
Function: point-min
This function returns the minimum accessible value of point in the current buffer. This is 1, unless narrowing is in effect, in which case it is the position of the start of the region that you narrowed to. (See section Narrowing.)
Function: point-max
This function returns the maximum accessible value of point in the
current buffer. This is (1+ (buffer-size)), unless narrowing is
in effect, in which case it is the position of the end of the region
that you narrowed to. (See section Narrowing).
Function: buffer-end flag
This function returns (point-min) if flag is less than 1,
(point-max) otherwise. The argument flag must be a number.
Function: buffer-size
This function returns the total number of characters in the current
buffer. In the absence of any narrowing (see section Narrowing),
point-max returns a value one larger than this.
(buffer-size)
=> 35
(point-max)
=> 36
Variable: buffer-saved-size
The value of this buffer-local variable is the former length of the current buffer, as of the last time it was read in, saved or auto-saved.
Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See section Point.
These functions move point based on a count of characters.
goto-char is a fundamental primitive because it is the way to
move point to a specified position.
Command: goto-char position
This function sets point in the current buffer to the value position. If position is less than 1, then point is set to the beginning of the buffer. If it is greater than the length of the buffer, then point is set to the end of the buffer.
If narrowing is in effect, then the position is still measured from the beginning of the buffer, but point cannot be moved outside of the accessible portion. Therefore, if position is too small, point is set to the beginning of the accessible portion of the text; if position is too large, point is set to the end.
When this function is called interactively, position is the numeric prefix argument, if provided; otherwise it is read from the minibuffer.
goto-char returns position.
Command: forward-char &optional count
This function moves point forward, towards the end of the buffer,
count characters (or backward, towards the beginning of the
buffer, if count is negative). If the function attempts to move
point past the beginning or end of the buffer (or the limits of the
accessible portion, when narrowing is in effect), an error is signaled
with error code beginning-of-buffer or end-of-buffer.
In an interactive call, count is the numeric prefix argument.
Command: backward-char &optional count
This function moves point backward, towards the beginning of the buffer,
count characters (or forward, towards the end of the buffer, if
count is negative). If the function attempts to move point past
the beginning or end of the buffer (or the limits of the accessible
portion, when narrowing is in effect), an error is signaled with error
code beginning-of-buffer or end-of-buffer.
In an interactive call, count is the numeric prefix argument.
These functions for parsing words use the syntax table to decide whether a given character is part of a word. See section Syntax Tables.
Command: forward-word count
This function moves point forward count words (or backward if
count is negative). Normally it returns t. If this motion
encounters the beginning or end of the buffer, or the limits of the
accessible portion when narrowing is in effect, point stops there
and the value is nil.
In an interactive call, count is set to the numeric prefix argument.
Command: backward-word count
This function just like forward-word, except that it moves
backward until encountering the front of a word, rather than forward.
In an interactive call, count is set to the numeric prefix argument.
This function is rarely used in programs, as it is more efficient to
call forward-word with negative argument.
Variable: words-include-escapes
This variable affects the behavior of forward-word and everything
that uses it. If it is non-nil, then characters in the
"escape" and "character quote" syntax classes count as part of
words. Otherwise, they do not.
To move point to the beginning of the buffer, write:
(goto-char (point-min))
Likewise, to move to the end of the buffer, use:
(goto-char (point-max))
Here are two commands which users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area.
Command: beginning-of-buffer &optional n
This function moves point to the beginning of the buffer (or the limits
of the accessible portion, when narrowing is in effect), setting the
mark at the previous position. If n is non-nil, then it
puts point n tenths of the way from the beginning of the buffer.
In an interactive call, n is the numeric prefix argument,
if provided; otherwise n defaults to nil.
Don't use this function in Lisp programs!
Command: end-of-buffer &optional n
This function moves point to the end of the buffer (or the limits of
the accessible portion, when narrowing is in effect), setting the mark
at the previous position. If n is non-nil, then it puts
point n tenths of the way from the end.
In an interactive call, n is the numeric prefix argument,
if provided; otherwise n defaults to nil.
Don't use this function in Lisp programs!
Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, or by how tabs and control characters are displayed.
Command: goto-line line
This function moves point to the front of the lineth line, counting from line 1 at beginning of buffer. If line is less than 1, then point is set to the beginning of the buffer. If line is greater than the number of lines in the buffer, then point is set to the end of the last line of the buffer.
If narrowing is in effect, then line still counts from the beginning of the buffer, but point cannot go outside the accessible portion. So point is set at the beginning or end of the accessible portion of the text if the line number specifies a position that is inaccessible.
The return value of goto-line is the difference between
line and the line number of the line to which point actually was
able move (before taking account of any narrowing). Thus, the value is
positive if the scan encounters the end of the buffer.
In an interactive call, line is the numeric prefix argument if one has been provided. Otherwise line is read in the minibuffer.
Command: beginning-of-line &optional count
This function moves point to the beginning of the current line. With an
argument count not nil or 1, it moves forward
count-1 lines and then to the beginning of the line.
If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point at the beginning of the last line. No error is signaled.
Command: end-of-line &optional count
This function moves point to the end of the current line. With an
argument count not nil or 1, it moves forward
count-1 lines and then to the end of the line.
If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point at the end of the last line. No error is signaled.
Command: forward-line &optional count
This function moves point forward count lines, to the beginning of the line. If count is negative, it moves point -count lines backward, to the beginning of the line.
If the beginning or end of the buffer (or of the accessible portion) is encountered before that many lines are found, then point stops at the beginning or end. No error is signaled.
forward-line returns the difference between count and the
number of lines actually moved. If you attempt to move down five lines
from the beginning of a buffer that has only three lines, point will
positioned at the end of the last line, and the value will be 2.
In an interactive call, count is the numeric prefix argument.
Function: count-lines start end
This function returns the number of lines between the positions start and end in the current buffer. If start and end are equal, then it returns 0. Otherwise it returns at least 1, even if start and end are on the same line. This is because the text between them, considered in isolation, must contain at least one line unless it is empty.
Here is an example of using count-lines:
(defun current-line ()
"Return the vertical position of point
in the selected window. Top line is 0.
Counts each text line only once, even if it wraps."
(+ (count-lines (window-start) (point))
(if (= (current-column) 0) 1 0)
-1))
Also see the functions bolp and eolp in section Examining Text Near Point.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. Then vertical-motion
moves point just like forward-line. See section Truncation.
Because the width of a given string depends on the flags which control
the appearance of certain characters, vertical-motion will behave
differently on a given piece of text found in different buffers. It
will even act differently in different windows showing the same buffer,
because the width may differ and so may the truncation flag.
See section Usual Display Conventions.
Function: vertical-motion count
This function moves point to the start of the screen line count screen lines down from the screen line containing point. If count is negative, it moves up instead.
This function returns the number of lines moved. The value may be less in absolute value than count if the beginning or end of the buffer was reached.
Command: move-to-window-line count
This function moves point with respect to the text currently displayed in the selected window. Point is moved to the beginning of the screen line count screen lines from the top of the window. If count is negative, point moves either to the beginning of the line -count lines from the bottom or else to the last line of the buffer if the buffer ends above the specified screen position.
If count is nil, then point moves to the beginning of the
line in the middle of the window. If the absolute value of count
is greater than the size of the window, then point moves to the place
which would appear on that screen line if the window were tall enough.
This will probably cause the next redisplay to scroll to bring that
location onto the screen.
In an interactive call, count is the numeric prefix argument.
The value returned is the window line number, with the top line in the window numbered 0.
A goal column is useful if you want to edit text such as a table in
which you want to move point to a certain column on each line. The goal
column affects the vertical text line motion commands, next-line
and previous-line. See section 'Basic Editing Commands' in The GNU Emacs Manual.
User Option: goal-column
This variable holds an explicitly specified goal column for vertical
line motion commands. If it is an integer, it specifies a column, and
these commands try to move to that column on each line. If it is
nil, then the commands set their own goal columns. Any other
value is invalid.
Variable: temporary-goal-column
This variable holds the temporary goal column during a sequence of
consecutive vertical line motion commands. It is overridden by
goal-column if that is non-nil. It is set each time a
vertical motion command is invoked, unless the previous command was also
a vertical motion command.
User Option: track-eol
This variable controls how the vertical line motion commands operate
when starting at the end of a line. If track-eol is
non-nil, then vertical motion starting at the end of a line will
keep to the ends of lines. This means moving to the end of each line
moved onto. The value of track-eol has no effect if point is not
at the end of a line when the first vertical motion command is given.
track-eol has its effect by causing temporary-goal-column
to be set to 9999 instead of to the current column.
Command: set-goal-column unset
This command sets the variable goal-column to specify a permanent
goal column for the vertical line motion commands. If unset is
nil, then goal-column is set to the current column of
point. If unset is non-nil, then goal-column is set
to nil.
This function is intended for interactive use; and in an interactive call, unset is the raw prefix argument.
Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see section Syntax Tables. See section Parsing Balanced Expressions, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see section 'Lists and Sexps' in GNU Emacs Manual.
Command: forward-list arg
Move forward across arg balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
Command: backward-list arg
Move backward across arg balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
Command: up-list arg
Move forward out of arg levels of parentheses. A negative argument means move backward but still to a less deep spot.
Command: down-list arg
Move forward down arg levels of parentheses. A negative argument means move backward but still go down arg level.
Command: forward-sexp arg
Move forward across arg balanced expressions. Balanced expressions include both those delimited by parentheses and other kinds, such as words and string constants. For example,
---------- Buffer: foo ----------
(concat-!- "foo " (car x) y z)
---------- Buffer: foo ----------
(forward-sexp 3)
=> nil
---------- Buffer: foo ----------
(concat "foo " (car x) y-!- z)
---------- Buffer: foo ----------
Command: backward-sexp arg
Move backward across arg balanced expressions.
The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see section Motion and Syntax.
Function: skip-chars-forward character-set &optional limit
This function moves point in the current buffer forward, skipping over
a given set of characters. Emacs first examines the character following
point; if it matches character-set, then point is advanced and the
next character is examined. This continues until a character is found
that does not match. The function returns nil.
The argument character-set is like the inside of a
`[...]' in a regular expression except that `]' is never
special and `\' quotes `^', `-' or `\'. Thus,
"a-zA-Z" skips over all letters, stopping before the first
nonletter, and "^a-zA-Z" skips nonletters stopping before the
first letter. See section Regular Expressions.
If limit is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before limit.
In the following example, point is initially located directly before the `T'. After the form is evaluated, point is located at the end of that line (between the `t' of `hat' and the newline). The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(skip-chars-forward "a-zA-Z ")
=> nil
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
Function: skip-chars-backward character-set &optional limit
This function moves point backward, skipping characters that match
character-set. It just like skip-chars-forward
except for the direction of motion.
It is often useful to move point "temporarily" within a localized
portion of the program, or to switch buffers temporarily. This is
called an excursion, and it is done with the save-excursion
special form. This construct saves the current buffer and its values of
point and the mark so they can be restored after the completion of the
excursion.
The forms for saving and restoring the configuration of windows are described elsewhere (see section Window Configurations, and see section Frame Configurations).
Special Form: save-excursion forms...
The save-excursion special form saves the identity of the current
buffer and the values of point and the mark in it, evaluates forms,
and finally restores the buffer and its saved values of point and the mark.
All three saved values are restored even in case of an abnormal exit
via throw or error (see section Nonlocal Exits).
The save-excursion special form is the standard way to switch
buffers or move point within one part of a program and avoid affecting
the rest of the program. It is used more than 500 times in the Lisp
sources of Emacs.
The values of point and the mark for other buffers are not saved by
save-excursion, so any changes made to point and the mark in the
other buffers will remain in effect after save-excursion exits.
Likewise, save-excursion does not restore window-buffer
correspondences altered by functions such as switch-to-buffer.
One way to restore these correspondences, and the selected window, is to
use save-window-excursion inside save-excursion
(see section Window Configurations).
The value returned by save-excursion is the result of the last of
forms, or nil if no forms are given.
(save-excursion
forms)
==
(let ((old-buf (current-buffer))
(old-pnt (point-marker))
(old-mark (copy-marker (mark-marker))))
(unwind-protect
(progn forms)
(set-buffer old-buf)
(goto-char old-pnt)
(set-marker (mark-marker) old-mark)))
Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.
Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion.
Values such as positions or line numbers which usually count from the beginning of the buffer continue to do so, but the functions which use them will refuse to operate on text that is inaccessible.
The commands for saving buffers are unaffected by narrowing; the entire buffer is saved regardless of the any narrowing.
Command: narrow-to-region start end
This function sets the accessible portion of the current buffer to start at start and end at end. Both arguments should be character positions.
In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).
Command: narrow-to-page move-count
This function sets the accessible portion of the current buffer to
include just the current page. An optional first argument
move-count non-nil means to move forward or backward by
move-count pages and then narrow.
In an interactive call, move-count is set to the numeric prefix argument.
Command: widen
This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called widening. It is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
Special Form: save-restriction body...
This special form saves the current bounds of the accessible portion, evaluates the body forms, and finally restores the saved bounds, thus restoring the same state of narrowing (or absence thereof) formerly in effect. The state of narrowing is restored even in the event of an abnormal exit via throw or error (see section Nonlocal Exits). Therefore, this construct is a clean way to narrow a buffer temporarily.
The value returned by save-restriction is that returned by the
last form in body, or nil if no body forms were given.
Caution: it is easy to make a mistake when using the
save-restriction function. Read the entire description here
before you try it.
If body changes the current buffer, save-restriction still
restores the restrictions on the original buffer (the buffer they came
from), but it does not restore the identity of the current buffer.
Point and the mark are not restored by this special form; use
save-excursion for that. If you use both save-restriction
and save-excursion together, save-excursion should come
first (on the outside). Otherwise, the old point value would be
restored with temporary narrowing still in effect. If the old point
value were outside the limits of the temporary narrowing, this would
fail to restore it accurately.
The save-restriction special form records the values of the
beginning and end of the accessible portion as distances from the
beginning and end of the buffer. In other words, it records the amount
of inaccessible text before and after the accessible portion.
This technique yields correct results if body does further
narrowing. However, save-restriction can become confused if they
widen and then make changes outside the area of the saved narrowing.
When this is what you want to do, save-restriction is not the
right tool for the job. Here is what you must use instead:
(let ((beg (point-min-marker))
(end (point-max-marker)))
(unwind-protect
(progn body)
(save-excursion
(set-buffer (marker-buffer beg))
(narrow-to-region beg end))))
Here is a simple example of correct use of save-restriction:
---------- Buffer: foo ----------
This is the contents of foo
This is the contents of foo
This is the contents of foo-!-
---------- Buffer: foo ----------
(save-excursion
(save-restriction
(goto-char 1)
(forward-line 2)
(narrow-to-region 1 (point))
(goto-char (point-min))
(replace-string "foo" "bar")))
---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo-!-
---------- Buffer: foo ----------
A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it.
A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. See section Positions, for a complete description of positions.
A marker has two attributes: the marker position, and the marker buffer. The marker position is an integer which is equivalent (at the moment) to the marker as a position in that buffer; however, as text is inserted or deleted in the buffer, the marker is relocated, so that its integer equivalent changes. The idea is that a marker positioned between two characters in a buffer will remain between those two characters despite any changes made to the contents of the buffer; thus, a marker's offset from the beginning of a buffer may change often during the life of the marker.
If the text around a marker is deleted, the marker is repositioned
between the characters immediately before and after the deleted text. If
text is inserted at the position of a marker, the marker remains in front
of the new text unless it is inserted with insert-before-markers
(see section Insertion). When text is inserted or deleted somewhere before the
marker position (not next to the marker), the marker moves back and forth
with the two neighboring characters.
When a buffer is modified, all of its markers must be checked so that they can be relocated if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Unreferenced markers will eventually be garbage collected, but until then will continue to be updated if they do point somewhere.
Because it is quite common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including + and
-) accept markers as arguments. In such cases, the current position
of the marker is used.
Here are examples of creating markers, setting markers, and moving point to markers:
;; Make a new marker that initially does not point anywhere:
(setq m1 (make-marker))
=> #<marker in no buffer>
;; Set m1 to point between the 100th and 101st characters
;; in the current buffer:
(set-marker m1 100)
=> #<marker at 100 in markers.texi>
;; Now insert one character at the beginning of the buffer:
(goto-char (point-min))
=> 1
(insert "Q")
=> nil
;; m1 is updated appropriately.
m1
=> #<marker at 101 in markers.texi>
;; Two markers that point to the same position
;; are not eq, but they are equal.
(setq m2 (copy-marker m1))
=> #<marker at 101 in markers.texi>
(eq m1 m2)
=> nil
(equal m1 m2)
=> t
;; When you are finished using a marker, make it point nowhere.
(set-marker m1 nil)
=> #<marker in no buffer>
You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful when you are using the arithmetic functions that work with both markers and integers.
Function: markerp object
This function returns t if object is a marker,
nil otherwise. In particular, integers are not markers,
even though many functions will accept either a marker or an
integer.
Function: integer-or-marker-p object
This function returns t if object is an integer or a marker,
nil otherwise.
Function: number-or-marker-p object
This function returns t if object is a number (of any
type) or a marker, nil otherwise.
When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker.
Function: make-marker
This functions returns a newly allocated marker that does not point anywhere.
(make-marker)
=> #<marker in no buffer>
Function: point-marker
This function returns a new marker that points to the present position
of point in the current buffer. See section Point. For an example, see
copy-marker, below.
Function: point-min-marker
This function returns a new marker that points to the beginning of the accessible portion of the buffer. This will be the beginning of the buffer unless narrowing is in effect. See section Narrowing.
Function: point-max-marker
This function returns a new marker that points to the end of the accessible portion of the buffer. This will be the end of the buffer unless narrowing is in effect. See section Narrowing.
Here are examples of this function and point-min-marker, shown in
a buffer containing a version of the source file for the text of this
chapter.
(point-min-marker)
=> #<marker at 1 in markers.texi>
(point-max-marker)
=> #<marker at 15573 in markers.texi>
(narrow-to-region 100 200)
=> nil
(point-min-marker)
=> #<marker at 100 in markers.texi>
(point-max-marker)
=> #<marker at 200 in markers.texi>
Function: copy-marker marker-or-integer
If passed a marker as its argument, copy-marker returns a
new marker that points to the same place and the same buffer as does
marker-or-integer. If passed an integer as its argument,
copy-marker returns a new marker that points to position
marker-or-integer in the current buffer.
If passed an argument that is an integer whose value is less than 1,
copy-marker returns a new marker that points to the
beginning of the current buffer. If passed an argument that is an
integer whose value is greater than the length of the buffer, then
copy-marker returns a new marker that points to the end of the
buffer.
An error is signaled if marker is neither a marker nor an integer.
(setq p (point-marker))
=> #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
=> #<marker at 2139 in markers.texi>
(eq p q)
=> nil
(equal p q)
=> t
(copy-marker 0)
=> #<marker at 1 in markers.texi>
(copy-marker 20000)
=> #<marker at 7572 in markers.texi>
This section describes the functions for accessing the components of a marker object.
Function: marker-position marker
This function returns the position that marker points to, or
nil if it points nowhere.
Function: marker-buffer marker
This function returns the buffer that marker points into, or
nil if it points nowhere.
(setq m (make-marker))
=> #<marker in no buffer>
(marker-position m)
=> nil
(marker-buffer m)
=> nil
(set-marker m 3770 (current-buffer))
=> #<marker at 3770 in markers.texi>
(marker-buffer m)
=> #<buffer markers.texi>
(marker-position m)
=> 3770
Two distinct markers will be found equal (even though not
eq) to each other if they have the same position and buffer, or
if they both point nowhere.
This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it--otherwise, confusing things may happen in other parts of Emacs.
Function: set-marker marker position &optional buffer
This function moves marker to position in buffer. If buffer is not provided, it defaults to the current buffer.
If position is less than 1, set-marker moves marker to
the beginning of the buffer. If the value of position is greater
than the size of the buffer, set-marker moves marker to the end
of the buffer. If position is nil or a marker that points
nowhere, then marker is set to point nowhere.
The value returned is marker.
(setq m (point-marker))
=> #<marker at 4714 in markers.texi>
(set-marker m 55)
=> #<marker at 55 in markers.texi>
(setq b (get-buffer "foo"))
=> #<buffer foo>
(set-marker m 0 b)
=> #<marker at 1 in foo>
Function: move-marker marker position &optional buffer
This is another name for set-marker.
A special marker in each buffer is designated the mark. It
records a position for the user for the sake of commands such as
C-w and C-x TAB. Lisp programs should set the mark
only to values that have a potential use to the user, and never for
their own internal purposes. For example, the replace-regexp
command sets the mark to the value of point before doing any
replacements, because this enables the user to move back there
conveniently after the replace is finished.
Many commands are designed so that when called interactively they
operate on the text between point and the mark. If you are writing such
a command, don't examine the mark directly; instead, use
interactive with the `r' specification. This will provide
the values of point and the mark as arguments to the command in an
interactive call, but will permit other Lisp programs to specify
arguments explicitly. See section Code Characters for interactive.
Each buffer has its own value of the mark that is independent of the value of the mark in other buffers. When a buffer is created, the mark exists but does not point anywhere. We consider this state as "the absence of a mark in that buffer".
Once the mark "exists" in a buffer, it normally never ceases to
exist. However, it may become inactive, if Transient Mark mode is
enabled. The variable mark-active, which is always local in all
buffers, indicates whether the mark is active: non-nil means
yes. A command can request deactivation of the mark upon return to the
editor command loop by setting deactivate-mark to a
non-nil value (but this deactivation only follows if Transient
Mark mode is enabled).
The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. See section Emacs Display.
In addition to the mark, each buffer has a mark ring which is a
list of markers that are the previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The mark ring may contain no more than the
maximum number of entries specified by the variable mark-ring-max;
excess entries are discarded on a first-in-first-out basis.
Function: mark &optional force
This function returns the position of the current buffer's mark as an integer.
Normally, if the mark is inactive mark signals an error.
However, if force is non-nil, then it returns the mark
position anyway--or nil, if the mark is not yet set for this
buffer.
Function: mark-marker
This function returns the current buffer's mark. This is the very marker which records the mark location inside Emacs, not a copy. Therefore, changing this marker's position will directly affect the position of the mark. Don't do it unless that is the effect you want.
(setq m (mark-marker))
=> #<marker at 3420 in markers.texi>
(set-marker m 100)
=> #<marker at 100 in markers.texi>
(mark-marker)
=> #<marker at 100 in markers.texi>
Like any marker, this marker can be set to point at any buffer you like. We don't recommend that you make it point at any buffer other than the one of which it is the mark. If you do, it will yield perfectly consistent, if rather odd, results.
Function: set-mark position
This function sets the mark to position, and activates the mark. The old value of the mark is not pushed onto the mark ring.
Please note: use this function only if you want the user to
see that the mark has moved, and you want the previous mark position to
be lost. Normally, when a new mark is set, the old one should go on the
mark-ring. For this reason, most applications should use
push-mark and pop-mark, not set-mark.
Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user's convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:
(let ((beg (point))) (forward-line 1) (delete-region beg (point))).
Variable: mark-ring
The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first.
mark-ring
=> (#<marker at 11050 in markers.texi>
#<marker at 10832 in markers.texi>
...)
User Option: mark-ring-max
The value of this variable is the maximum size of mark-ring.
If more marks than this are pushed onto the mark-ring, it
discards marks on a first-in, first-out basis.
Function: push-mark &optional position nomsg activate
This function sets the current buffer's mark to position, and
pushes a copy of the previous mark onto mark-ring. If
position is nil, then the value of point is used.
push-mark returns nil.
The function push-mark normally does not activate the
mark. To do that, specify t for the argument activate.
A `Mark set' message is displayed unless nomsg is
non-nil.
Function: pop-mark
This function pops off the top element of mark-ring and makes
that mark become the buffer's actual mark. This does not change the
buffer's point, and does nothing if mark-ring is empty. It
deactivates the mark.
The return value is not useful.
User Option: transient-mark-mode
This variable enables Transient Mark mode, in which every
buffer-modifying primitive sets deactivate-mark. The consequence
of this is that commands that modify the buffer normally cause the mark
to become inactive.
Variable: deactivate-mark
If an editor command sets this variable non-nil, then the editor
command loop deactivates the mark after the command returns.
Variable: mark-active
The mark is active when this variable is non-nil. This variable
is always local in each buffer.
Variable: activate-mark-hook
Variable: deactivate-mark-hook
These normal hooks are run, respectively, when the mark becomes active
and when it becomes inactive. The hook activate-mark-hook is also
run at the end of a command if the mark is active and the region may
have changed.
The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.
Function: region-beginning
This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller.
If the mark does not point anywhere, an error is signaled.
Function: region-end
This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger.
If the mark does not point anywhere, an error is signaled.
Few programs need to use the region-beginning and
region-end functions. A command designed to operate on a region
should instead use interactive with the `r' specification,
so that the same function can be called with explicit bounds arguments
from programs. (See section Code Characters for interactive.)
This chapter describes the functions that deal with the text in a buffer. Most examine, insert or delete text in the current buffer, often in the vicinity of point. Many are interactive. All the functions that change the text provide for undoing the changes (see section Undo).
Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named start and end.
These arguments should be either markers (see section Markers) or or numeric
character positions (see section Positions). The order of these arguments
does not matter; it is all right for start to be the end of the
region and end the beginning. For example, (delete-region 1
10) and (delete-region 10 1) perform identically. An
args-out-of-range error is signaled if either start or
end is outside the accessible portion of the buffer. In an
interactive call, point and the mark are used for these arguments.
Throughout this chapter, "text" refers to the characters in the buffer.
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in section Regular Expression Searching.
Function: char-after position
This function returns the character in the current buffer at (i.e.,
immediately after) position position. If position is out of
range for this purpose, either before the beginning of the buffer, or at
or beyond the end, then the value is nil.
Remember that point is always between characters, and the terminal
cursor normally appears over the character following point. Therefore,
the character returned by char-after is the character the cursor
is over.
In the following example, assume that the first character in the buffer is `@':
(char-to-string (char-after 1))
=> "@"
Function: following-char
This function returns the character following point in the current
buffer. This is similar to (char-after (point)). However, if
point is at the end of the buffer, then the result of
following-char is 0.
In this example, point is between the `a' and the `c'.
---------- Buffer: foo ----------
Gentlemen may cry "Pea-!-ce! Peace!,"
but there is no peace.
---------- Buffer: foo ----------
(char-to-string (preceding-char))
=> "a"
(char-to-string (following-char))
=> "c"
Function: preceding-char
This function returns the character preceding point in the current
buffer. See above, under following-char, for an example. If
point is at the beginning of the buffer, then the result of
preceding-char is 0.
Function: bobp
This function returns t if point is at the beginning of the
buffer. If narrowing is in effect, this means the beginning of the
accessible portion of the text. See also point-min in
section Point.
Function: eobp
This function returns t if point is at the end of the buffer.
If narrowing is in effect, this means the end of accessible portion of
the text. See also point-max in See section Point.
Function: bolp
This function returns t if point is at the beginning of a line.
See section Motion by Text Lines.
Function: eolp
This function returns t if point is at the end of a line.
The end of the buffer is always considered the end of a line.
This section describes two functions that allow a Lisp program to convert any portion of the text in the buffer into a string.
Function: buffer-substring start end
This function returns a string containing a copy of the text of the
region defined by positions start and end in the current
buffer. If the arguments are not positions in the accessible portion of
the buffer, Emacs signals an args-out-of-range error.
It is not necessary for start to be less than end; the arguments can be given in either order. But most often the smaller argument is written first.
---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) => "This is t" (buffer-substring (point-max) 10) => "he contents of buffer foo "
Function: buffer-string
This function returns the contents of the accessible portion of the
current buffer as a string. This is the portion between
(point-min) and (point-max) (see section Narrowing).
---------- Buffer: foo ----------
This is the contents of buffer foo
---------- Buffer: foo ----------
(buffer-string)
=> "This is the contents of buffer foo
"
This function lets you compare portions of the text in a buffer, without copying them into strings first.
Function: compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
This function lets you compare two substrings of the same buffer or two
different buffers. The first three arguments specify one substring,
giving a buffer and two positions within the buffer. The last three
arguments specify the other substring in the same way. You can use
nil for buffer1, buffer2 or both to stand for the
current buffer.
The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings.
This function ignores case when comparing characters
if case-fold-search is non-nil.
Suppose the current buffer contains the text `foobarbar haha!rara!'; then in this example the two substrings are `rbar ' and `rara!'. The value is 2 because the first substring is greater at the second character.
(compare-buffer-substring nil 6 11 nil 16 21)
=> 2
This function does not exist in Emacs version 18 and earlier.
Insertion takes place at point. Markers pointing at positions after
the insertion point are relocated with the surrounding text
(see section Markers). When a marker points at the place of insertion, it
is normally not relocated, so that it points to the beginning of the
inserted text; however, when insert-before-markers is used, all
such markers are relocated to point after the inserted text.
Point may end up either before or after inserted text, depending on the function used. If point is left after the inserted text, we speak of insertion before point.
Each of these functions signals an error if the current buffer is read-only.
Function: insert &rest args
This function inserts the strings and/or characters args into the
current buffer, at point, moving point forward. An error is signaled
unless all args are either strings or characters. The value is
nil.
Function: insert-before-markers &rest args
This function inserts the strings and/or characters args into the
current buffer, at point, moving point forward. An error is signaled
unless all args are either strings or characters. The value is
nil.
This function is unlike the other insertion functions in that a marker whose position initially equals point is relocated to come after the newly inserted text.
Function: insert-char character count
This function inserts count instances of character into the
current buffer before point. count must be a number, and
character must be a character. The value is nil.
Function: insert-buffer-substring from-buffer-or-name &optional start end
This function inserts a substring of the contents of buffer
from-buffer-or-name (which must already exist) into the current
buffer before point. The text inserted consists of the characters in
the region defined by start and end (These arguments default
to the beginning and end of the accessible portion of that buffer). The
function returns nil.
In this example, the form is executed with buffer `bar' as the current buffer. We assume that buffer `bar' is initially empty.
---------- Buffer: foo ----------
We hold these truths to be self-evident, that all
---------- Buffer: foo ----------
(insert-buffer-substring "foo" 1 20)
=> nil
---------- Buffer: bar ----------
We hold these truth
---------- Buffer: bar ----------
This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.
Command: insert-buffer from-buffer-or-name
This function inserts the entire contents of from-buffer-or-name
(which must exist) into the current buffer after point. It leaves
the mark after the inserted text. The value is nil.
Command: self-insert-command count
This function inserts the last character typed count times and
returns nil. Most printing characters are bound to this
command. In routine use, self-insert-command is the most
frequently called function in Emacs, but programs rarely use it except
to install it on a keymap.
In an interactive call, count is the numeric prefix argument.
This function calls auto-fill-function if the current column number
is greater than the value of fill-column and the character
inserted is a space (see section Auto Filling).
This function performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See section Abbrevs And Abbrev Expansion, and section Table of Syntax Classes.)
This function is also responsible for calling
blink-paren-function when the inserted character has close
parenthesis syntax (see section Blinking).
Command: newline &optional number-of-newlines
This function inserts newlines into the current buffer before point. If number-of-newlines is supplied, that many newline characters are inserted.
In Auto Fill mode, newline can break the preceding line if
number-of-newlines is not supplied. When this happens, it
actually inserts two newlines at different places: one at point, and
another earlier in the line. newline does not auto-fill if
number-of-newlines is non-nil.
The value returned is nil. In an interactive call, count
is the numeric prefix argument.
Command: split-line
This function splits the current line, moving the portion of the line
after point down vertically, so that it is on the next line directly
below where it was before. Whitespace is inserted as needed at the
beginning of the lower line, using the indent-to function.
split-line returns the position of point.
Programs hardly ever use this function.
Variable: overwrite-mode
This variable controls whether overwrite mode is in effect: a
non-nil value enables the mode. It is automatically made
buffer-local when set in any fashion.
All of the deletion functions operate on the current buffer, and all
return a value of nil. In addition to these functions, you can
also delete text using the "kill" functions that save it in the kill
ring; some of these functions save text in the kill ring in some cases
but not in the usual case. See section The Kill Ring.
Function: erase-buffer
This function deletes the entire text of the current buffer, leaving it
empty. If the buffer is read-only, it signals a buffer-read-only
error. Otherwise, it deletes the text without asking for any
confirmation. The value is always nil.
Normally, deleting a large amount of text from a buffer inhibits further
auto-saving of that buffer "because it has shrunk". However,
erase-buffer does not do this, the idea being that the future
text is not really related to the former text, and its size should not
be compared with that of the former text.
Command: delete-region start end
This function deletes the text in the current buffer in the region
defined by start and end. The value is nil.
Command: delete-char count &optional killp
This function deletes count characters directly after point, or
before point if count is negative. If killp is
non-nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always nil.
Command: delete-backward-char count &optional killp
This function deletes count characters directly before point, or
after point if count is negative. If killp is
non-nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always nil.
Command: backward-delete-char-untabify count &optional killp
This function deletes count characters backward, changing tabs
into spaces. When the next character to be deleted is a tab, it is
first replaced with the proper number of spaces to preserve alignment
and then one of those spaces is deleted instead of the tab. If
killp is non-nil, then the command saves the deleted
characters in the kill ring.
If count is negative, then tabs are not changed to spaces, and the
characters are deleted by calling delete-backward-char with
count.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always nil.
This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.
Command: delete-horizontal-space
This function deletes all spaces and tabs around point. It returns
nil.
In the following examples, assume that delete-horizontal-space is
called four times, once on each line, with point between the second and
third characters on the line.
---------- Buffer: foo ----------
I -!-thought
I -!- thought
We-!- thought
Yo-!-u thought
---------- Buffer: foo ----------
(delete-horizontal-space) ; Four times.
=> nil
---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------
Command: delete-indentation &optional join-following-p
This function joins the line point is on to the previous line, deleting
any whitespace at the join and in some cases replacing it with one
space. If join-following-p is non-nil,
delete-indentation joins this line to the following line
instead. The value is nil.
If there is a fill prefix, and the second of the lines being joined
starts with the prefix, then delete-indentation deletes the
fill prefix before joining the lines.
In the example below, point is located on the line starting `events', and it makes no difference if there are trailing spaces in the preceding line.
---------- Buffer: foo ----------
When in the course of human
-!- events, it becomes necessary
---------- Buffer: foo ----------
(delete-indentation)
=> nil
---------- Buffer: foo ----------
When in the course of human-!- events, it becomes necessary
---------- Buffer: foo ----------
After the lines are joined, the function fixup-whitespace is
responsible for deciding whether to leave a space at the junction.
Function: fixup-whitespace
This function replaces white space between the objects on either side of
point with either one space or no space as appropriate. It returns
nil.
The appropriate amount of space is none at the beginning or end of the line. Otherwise, it is one space except when point is before a character with close parenthesis syntax or after a character with open parenthesis or expression-prefix syntax. See section Table of Syntax Classes.
In the example below, when fixup-whitespace is called the first
time, point is before the word `spaces' in the first line. It is
located directly after the `(' for the second invocation.
---------- Buffer: foo ----------
This has too many -!-spaces
This has too many spaces at the start of (-!- this list)
---------- Buffer: foo ----------
(fixup-whitespace)
=> nil
(fixup-whitespace)
=> nil
---------- Buffer: foo ----------
This has too many spaces
This has too many spaces at the start of (this list)
---------- Buffer: foo ----------
Command: just-one-space
This command replaces any spaces and tabs around point with a single
space. It returns nil.
Command: delete-blank-lines
This function deletes blank lines surrounding point. If point is on a blank line with one or more blank lines before or after it, then all but one of them are deleted. If point is on an isolated blank line, then it is deleted. If point is on a nonblank line, the command deletes all blank lines following it.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-lines returns nil.
Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have `kill-' in their name. By contrast, the functions whose names start with `delete-' normally do not save text for yanking (though they can still be undone); these are "deletion" functions.
Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. When deleting text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See section Deletion of Text.
Emacs saves the last several batches of killed text in a list. We
call it the kill ring because, in yanking, the elements are
considered to be in a cyclic order. The list is kept in the variable
kill-ring, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
which treat it as a ring.
Some people think use of the word "kill" in Emacs is unfortunate, since it refers to processes which specifically do not destroy the entities "killed". This is in sharp contrast to ordinary life, in which death is permanent and "killed" entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term "cut ring" makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change now.
The kill ring records killed text as strings in a list. A short kill ring, for example, might look like this:
("some text" "a different piece of text" "yet more text")
New entries in the kill ring go at the front of the list. When the
list reaches kill-ring-max entries in length, adding a new entry
automatically deletes the last entry.
When kill commands are interwoven with other commands, the killed portions of text are put into separate entries in the kill ring. But when two or more kill commands are executed in succession, the text they kill forms a single entry, because the second and subsequent consecutive kill commands append to the entry made by the first one.
The user can reinsert or yank text from any element in the kill ring. One of the entries in the ring is considered the "front", and the simplest yank command yanks that entry. Other yank commands "rotate" the ring by designating other entries as the "front".
kill-region is the usual subroutine for killing text. Any
command that calls this function is a "kill command" (and should
probably have `kill' in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element. It uses the last-command
variable to keep track of whether the previous was a kill command, and
in such cases appends the killed text to the most recent entry.
Command: kill-region start end
This function kills the text in the region defined by start and
end. The text is deleted but saved in the kill ring. The value
is always nil.
In an interactive call, start and end are point and the mark.
If the buffer is read-only, kill-region modifies the kill ring
just the same, then signals an error without modifying the buffer. This
is convenient because it lets the user use all the kill commands to copy
text into the kill ring from a read-only buffer.
Command: copy-region-as-kill start end
This function saves the region defined by start and end on
the kill ring, but does not delete the text from the buffer. It returns
nil. It also indicates the extent of the text copied by moving
the cursor momentarily, or by displaying a message in the echo area.
Don't use this command in Lisp programs; use kill-new or
kill-append instead. See section Low Level Kill Ring.
In an interactive call, start and end are point and the mark.
Command: yank &optional arg
This function inserts the text in the first entry in the kill ring directly before point. After the yank, the mark is positioned at the beginning and point is positioned after the end of the inserted text.
If arg is a list (which occurs interactively when the user
types C-u with no digits), then yank inserts the text as
described above, but puts point before the yanked text and puts the mark
after it. If arg is a number, then yank inserts the
argth most recently killed text.
yank does not alter the contents of the kill ring or rotate it.
It returns nil.
Command: yank-pop arg
This function replaces the just-yanked text with another batch of killed text--another element of the kill ring.
This command is allowed only immediately after a yank or a
yank-pop. At such a time, the region contains text that was just
inserted by the previous yank. yank-pop deletes that text
and inserts in its place a different stretch of killed text. The text
that is deleted is not inserted into the kill ring, since it is already
in the kill ring somewhere.
If arg is nil, then the existing region contents are
replaced with the previous element of the kill ring. If arg is
numeric, then the argth previous kill is the replacement. If
arg is negative, a more recent kill is the replacement.
The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest.
The value is always nil.
These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs. They take care of interaction with X Window selections. They do not exist in Emacs version 18.
Function: current-kill n &optional do-not-move
The function current-kill rotates the yanking pointer in the
kill ring by n places, and returns the text at that place in the
ring.
If the optional second argument do-not-move is non-nil,
then current-kill doesn't alter the yanking pointer; it just
returns the nth kill forward from the current yanking pointer.
If n is zero, indicating a request for the latest kill,
current-kill calls the value of
interprogram-paste-function (documented below) before consulting
the kill ring.
Function: kill-new string
This function puts the text string into the kill ring as a new
entry at the front of the ring. It also discards the oldest entry if
appropriate. It also invokes the value of interprogram-cut-function
(see below).
Function: kill-append string before-p
This function appends the text string to the first entry in the
kill ring. Normally string goes at the end of the entry, but if
before-p is non-nil, it goes at the beginning. This
function also invokes the value of interprogram-cut-function (see
below).
Variable: interprogram-paste-function
This variable provides a way of transferring killed text from other
programs, when you are using a window system. Its value should be
nil or a function of no arguments.
If the value is a function, it is called when the "most recent kill"
value is called for. If the function returns a non-nil values,
then that value is used as the "most recent kill". If it returns
nil, then the first element of the kill ring is used.
Variable: interprogram-cut-function
This variable provides a way of communicating killed text to and from
other programs, when you are using a window system. Its value should be
nil or a function of one argument.
If the value is a function, it is called whenever the "most recent kill" is changed, with the new string of killed text as an argument.
The variable kill-ring holds the kill ring contents, in the
form of a list of strings. The most recent kill is always at the front
of the list.
The kill-ring-yank-pointer variable points to a link in the
kill ring list, whose CAR is the text that yank functions
should copy. Moving kill-ring-yank-pointer to a different link
is called rotating the kill ring. We call the kill ring a
"ring" because the functions that move the yank pointer wrap around
from the end of the list to the beginning, or vice-versa. Rotating the
ring does not change the value of kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp
variables whose values are normally lists. The word "pointer" in the
name of the kill-ring-yank-pointer indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.
The value of kill-ring-yank-pointer is always eq to one
of the links in the kill ring list. The element it identifies is the
CAR of that link. Commands which change the text in the kill ring
also set this variable from kill-ring. The effect is to rotate
the ring so that the newly killed text is at front.
Here is a diagram that shows the variable kill-ring-yank-pointer
pointing to the second entry in the kill ring ("some text" "a
different piece of text" "yet more text").
kill-ring kill-ring-yank-pointer
| |
| ___ ___ ---> ___ ___ ___ ___
--> |___|___|------> |___|___|--> |___|___|--> nil
| | |
| | |
| | -->"yet more text"
| |
| --> "a different piece of text"
|
--> "some text"
This circumstance might occur after C-y (yank) immediately
followed by M-y (yank-pop).
Variable: kill-ring
List of killed text sequences, most recently killed first.
Variable: kill-ring-yank-pointer
This variable's value indicates which element of the kill ring is at
the "front" of the ring for yanking. More precisely, the value is a
sublist of the value of kill-ring, and its CAR is the kill
string that C-y should yank.
User Option: kill-ring-max
The value of this variable is the maximum length to which the kill
ring can grow, before elements are thrown away at the end. The default
value for kill-ring-max is 30.
Most buffers have an undo list which records all changes made to
the buffer's text so that they can be undone. (The buffers which don't
have one are usually special-purpose buffers for which Emacs assumes
that undoing is not useful.) All the primitives which modify the text
in the buffer automatically add elements to the front of the undo list,
which you can find in the variable buffer-undo-list.
Variable: buffer-undo-list
This variable's value is the undo list of the current buffer.
A value of t disables the recording of undo information.
Here are the kinds of elements an undo list can have:
integer
(beg . end)
(pos . deleted)
(t high . low)
primitive-undo uses those
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's modification time matches those numbers.
(nil property value beg . end)
(put-text-property beg end
property value)
nil
undo-boundary adds
these elements. The elements between two boundaries are called a
change group; normally, each change group corresponds to one
keyboard command, and undo commands normally undo an entire group as a
unit.
Function: undo-boundary
This function places a boundary element in the undo list. The undo
command stops at such a boundary, and successive undo commands undo
to earlier and earlier boundaries. This function returns nil.
The editor command loop automatically creates an undo boundary between
keystroke commands. Thus, each undo normally undoes the effects of one
command. Calling this function explicitly is useful for splitting the
effects of a command into more than one unit. For example,
query-replace calls this function after each replacement so that
the user can undo individual replacements one by one.
Function: primitive-undo count list
This is the basic function for undoing elements of an undo list. It undoes the first count elements of list, returning the rest of list. You could write this function in Lisp, but it is convenient to have it in C.
primitive-undo adds elements to the buffer's undo list. Undo
commands avoid confusion by saving the undo list value at the beginning
of a sequence of undo operations. Then the undo operations use and
update the saved value. The new elements added by undoing never get
into the saved value, so they don't cause any trouble.
This section describes how to enable and disable undo information for a given buffer. It also explains how data from the undo list is discarded automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
buffer-undo-list yourself.
Command: buffer-enable-undo &optional buffer-or-name
This function enables recording undo information for buffer
buffer-or-name, so that subsequent changes can be undone. If no
argument is supplied, then the current buffer is used. This function
does nothing if undo recording is already enabled in the buffer. It
returns nil.
In an interactive call, buffer-or-name is the current buffer. You cannot specify any other buffer.
Function: buffer-disable-undo buffer
Function: buffer-flush-undo buffer
This function discards the undo list of buffer, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of buffer is already disabled, this function has no effect.
This function returns nil. It cannot be called interactively.
The name buffer-flush-undo is not considered obsolete,
but the preferred name buffer-disable-undo was not provided
in Emacs versions 18 and earlier.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the "size"
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Two variables control the range of acceptable
sizes: undo-limit and undo-strong-limit.
Variable: undo-limit
This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept.
Variable: undo-strong-limit
The upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all subsequent changes). There is one exception: garbage collection always keeps the very last change group no matter how big it is.
Filling means adjusting the lengths of lines (by moving words
between them) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be justified, which means
that spaces are inserted between words to make the line exactly the
specified width. The width is controlled by the variable
fill-column. For ease of reading, lines should be no longer than
70 or so columns.
You can use Auto Fill mode (see section Auto Filling) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly.
Most of the functions in this section return values that are not meaningful.
Command: fill-paragraph justify-flag
This function fills the paragraph at or after point. If
justify-flag is non-nil, each line is justified as well.
It uses the ordinary paragraph motion commands to find paragraph
boundaries.
Command: fill-region start end &optional justify-flag
This function fills each of the paragraphs in the region from
start to end. It justifies as well if justify-flag is
non-nil. (In an interactive call, this is true if there is a
prefix argument.)
The variable paragraph-separate controls how to distinguish
paragraphs.
Command: fill-individual-paragraphs start end &optional justify-flag mail-flag
This function fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph are indented with spaces, the filled paragraph will continue to be indented in the same fashion.
The first two arguments, start and end, are the beginning
and end of the region that will be filled. The third and fourth
arguments, justify-flag and mail-flag, are optional. If
justify-flag is non-nil, the paragraphs are justified as
well as filled. If mail-flag is non-nil, the function is
told that it is operating on a mail message and therefore should not
fill the header lines.
Ordinarily, fill-individual-paragraphs regards each change in
indentation as starting a new paragraph. If
fill-individual-varying-indent is non-nil, then only
separator lines separate paragraphs. That mode can handle paragraphs
with extra indentation on the first line.
User Option: fill-individual-varying-indent
This variable alters the action of fill-individual-paragraphs as
described above.
Command: fill-region-as-paragraph start end &optional justify-flag
This function considers a region of text as a paragraph and fills it.
If the region was made up of many paragraphs, the blank lines between
paragraphs are removed. This function justifies as well as filling when
justify-flag is non-nil. In an interactive call, any
prefix argument requests justification.
In Adaptive Fill mode, which is enabled by default,
fill-region-as-paragraph on an indented paragraph when there is
no fill prefix uses the indentation of the second line of the paragraph
as the fill prefix.
Command: justify-current-line
This function inserts spaces between the words of the current line so
that the line ends exactly at fill-column. It returns
nil.
User Option: fill-column
This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification and centering commands are affected by this variable, including Auto Fill mode (see section Auto Filling).
As a practical matter, if you are writing text for other people to
read, you should set fill-column to no more than 70. Otherwise
the line will be too long for people to read comfortably, and this can
make the text seem clumsy.
Variable: default-fill-column
The value of this variable is the default value for fill-column in
buffers that do not override it. This is the same as
(default-value 'fill-column).
The default value for default-fill-column is 70.
Filling breaks text into lines that are no more than a specified number of columns wide. Filled lines end between words, and therefore may have to be shorter than the maximum width.
Auto Fill mode is a minor mode in which Emacs fills lines automatically as text as inserted. This section describes the hook and the two variables used by Auto Fill mode. For a description of functions that you can call manually to fill and justify text, see section Filling.
Variable: auto-fill-function
The value of this variable should be a function (of no arguments) to
be called after self-inserting a space at a column beyond
fill-column. It may be nil, in which case nothing
special is done.
The default value for auto-fill-function is do-auto-fill,
a function whose sole purpose is to implement the usual strategy
for breaking a line.
In older Emacs versions, this variable was namedauto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed toauto-fill-functionin version 19.
The sorting commands described in this section all rearrange text in a
buffer. This is in contrast to the function sort, which
rearranges the order of the elements of a list (see section Functions that Rearrange Lists).
The values returned by these commands are not meaningful.
Command: sort-regexp-fields reverse record-regexp key-regexp start end
This command sorts the region between start and end alphabetically as specified by record-regexp and key-regexp. If reverse is a negative integer, then sorting is in reverse order.
Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical values. Since Emacs uses the ASCII character set, the ordering in that set determines alphabetical order.
The value of the record-regexp argument specifies the textual units or records that should be sorted. At the end of each record, a search is done for this regular expression, and the text that matches it is the next record. For example, the regular expression `^.+$', which matches lines with at least one character besides a newline, would make each such line into a sort record. See section Regular Expressions, for a description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each record is to be compared against the other records. The key-regexp could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position.
The key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own.
If key-regexp is:
For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter `f', you should set record-regexp to `^.*$' and set key-regexp to `\<f\w*\>'. The resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
(region-beginning)
(region-end))
If you call sort-regexp-fields interactively, you are prompted
for record-regexp and key-regexp in the minibuffer.
Command: sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun
This command is the general text sorting routine that divides a buffer
into records and sorts them. The functions sort-lines,
sort-paragraphs, sort-pages, sort-fields,
sort-regexp-fields and sort-numeric-fields all use
sort-subr.
To understand how sort-subr works, consider the whole
accessible portion of the buffer as being divided into disjoint pieces
called sort records. A portion of each sort record (perhaps all
of it) is designated as the sort key. The records are rearranged in the
buffer in order by their sort keys. The records may or may not be
contiguous.
Usually, the records are rearranged in order of ascending sort key.
If the first argument to the sort-subr function, reverse,
is non-nil, the sort records are rearranged in order of
descending sort key.
The next four arguments to sort-subr are functions that are
called to move point across a sort record. They are called many times
from within sort-subr.
sort-subr is
called. (Therefore, you should usually move point to the beginning of
the buffer before calling sort-subr.)
This function can indicate there are no more sort records by leaving point at the end of the buffer.
nil value to be used as the
sort key, or return nil to indicate that the sort key is in the
buffer starting at point. In the latter case, endkeyfun is called
to find the end of the sort key.
nil and this argument is omitted (or
nil), then the sort key extends to the end of the record. There
is no need for endkeyfun if startkeyfun returns a
non-nil value.
As an example of sort-subr, here is the complete function
definition for sort-lines:
;; Note that the first two lines of doc string
;; are effectively one line when viewed by a user.
(defun sort-lines (reverse beg end)
"Sort lines in region alphabetically;\
argument means descending order.
Called from a program, there are three arguments:
REVERSE (non-nil means reverse order),
and BEG and END (the region to sort)."
(interactive "P\nr")
(save-restriction
(narrow-to-region beg end)
(goto-char (point-min))
(sort-subr reverse
'forward-line
'end-of-line)))
Here forward-line moves point to the start of the next record,
and end-of-line moves point to the end of record. We do not pass
the arguments startkeyfun and endkeyfun, because the entire
record is used as the sort key.
The sort-paragraphs function is very much the same, except that
its sort-subr call looks like this:
(sort-subr reverse
(function
(lambda ()
(skip-chars-forward "\n \t\f")))
'forward-paragraph)
Command: sort-lines reverse start end
This command sorts lines in the region between start and
end alphabetically. If reverse is non-nil, the sort
is in reverse order.
Command: sort-paragraphs reverse start end
This command sorts paragraphs in the region between start and
end alphabetically. If reverse is non-nil, the sort
is in reverse order.
Command: sort-pages reverse start end
This command sorts pages in the region between start and
end alphabetically. If reverse is non-nil, the sort
is in reverse order.
Command: sort-fields field start end
This command sorts lines in the region between start and end, comparing them alphabetically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the -fieldth field from the end of the line. This command is useful for sorting tables.
Command: sort-numeric-fields field start end
This command sorts lines in the region between start and end, comparing them numerically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. The specified field must contain a number in each line of the region. If field is negative, sorting is by the -fieldth field from the end of the line. This command is useful for sorting tables.
Command: sort-columns reverse &optional beg end
This command sorts the lines in the region between beg and end, comparing them alphabetically by a certain range of columns. The column positions of beg and end bound the range of columns to sort on.
If reverse is non-nil, the sort is in reverse order.
One unusual thing about this command is that the entire line containing position beg, and the entire line containing position end, are included in the region sorted.
Note that sort-columns uses the sort utility program,
and so cannot work properly on text containing tab characters. Use
M-x untabify to convert tabs to spaces before sorting.
The sort-columns function did not work on VMS prior to Emacs
19.
The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Indentation always counts from zero at the left margin.
This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives.
Function: current-indentation
This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line.
Command: indent-to column &optional minimum
This function indents from point with tabs and spaces until
column is reached. If minimum is specified and
non-nil, then at least that many spaces are inserted even if this
requires going beyond column. The value is the column at which
the inserted indentation ends.
User Option: indent-tabs-mode
If this variable is non-nil, indentation functions can insert
tabs as well as spaces. Otherwise, they insert only spaces. Setting
this variable automatically makes it local to the current buffer.
An important function of each major mode is to customize the TAB key to indent properly for the language being edited. This section describes the mechanism of the TAB key and how to control it. The functions in this section return unpredictable values.
Variable: indent-line-function
This variable's value is the function to be used by TAB (and
various commands) to indent the current line. The command
indent-according-to-mode does no more than call this function.
In Lisp mode, the value is the symbol lisp-indent-line; in C
mode, c-indent-line; in Fortran mode, fortran-indent-line.
In Fundamental mode, Text mode, and many other modes with no standard
for indentation, the value is indent-to-left-margin (which is the
default value).
Command: indent-according-to-mode
This command calls the function in indent-line-function to
indent the current line in a way appropriate for the current major mode.
Command: indent-for-tab-command
This command calls the function in indent-line-function to
indent the current line, except that if that function is
indent-to-left-margin, insert-tab is called instead.
(That is a trivial command which inserts a tab character.)
Variable: left-margin
This variable is the column to which the default
indent-line-function will indent. (That function is
indent-to-left-margin.) In Fundamental mode, LFD indents
to this column. This variable automatically becomes buffer-local when
set in any fashion.
Function: indent-to-left-margin
This is the default indent-line-function, used in Fundamental
mode, Text mode, etc. Its effect is to adjust the indentation at the
beginning of the current line to the value specified by the variable
left-margin. This may involve either inserting or deleting
whitespace.
Command: newline-and-indent
This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode.
Indentation is done using the current indent-line-function. In
programming language modes, this is the same thing TAB does, but
in some text modes, where TAB inserts a tab,
newline-and-indent indents to the column specified by
left-margin.
Command: reindent-then-newline-and-indent
This command reindents the current line, inserts a newline at point, and then reindents the new line (the one following the newline just inserted).
Indentation of both lines is done according to the current major mode;
this means that the current value of indent-line-function is
called. In programming language modes, this is the same thing TAB
does, but in some text modes, where TAB inserts a tab,
reindent-then-newline-and-indent indents to the column specified
by left-margin.
This section describes commands which indent all the lines in the region. They return unpredictable values.
Command: indent-region start end to-column
This command indents each nonblank line starting between start
(inclusive) and end (exclusive). If to-column is
nil, indent-region indents each nonblank line by calling
the current mode's indentation function, the value of
indent-line-function.
If to-column is non-nil, it should be an integer
specifying the number of columns of indentation; then this function
gives each line exactly that much indentation, by either adding or
deleting whitespace.
If there is a fill prefix, indent-region indents each line
by making it start with the fill prefix.
Variable: indent-region-function
The value of this variable is a function that can be used by
indent-region as a short cut. You should design the function so
that it will produce the same results as indenting the lines of the
region one by one (but presumably faster).
If the value is nil, there is no short cut, and
indent-region actually works line by line.
A short cut function is useful in modes such as C mode and Lisp mode,
where the indent-line-function must scan from the beginning of
the function: applying it to each line would be quadratic in time. The
short cut can update the scan information as it moves through the lines
indenting them; this takes linear time. If indenting a line
individually is fast, there is no need for a short cut.
indent-region with a non-nil argument has a different
definition and does not use this variable.
Command: indent-rigidly start end count
This command indents all lines starting between start
(inclusive) and end (exclusive) sideways by count columns.
This "preserves the shape" of the affected region, moving it as a
rigid unit. Consequently, this command is useful not only for indenting
regions of unindented text, but also for indenting regions of formatted
code.
For example, if count is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified.
In Mail mode, C-c C-y (mail-yank-original) uses
indent-rigidly to indent the text copied from the message being
replied to.
Function: indent-code-rigidly start end columns &optional nochange-regexp
This is like indent-rigidly, except that it doesn't alter lines
that start within strings or comments.
In addition, it doesn't alter a line if nochange-regexp matches at
the beginning of the line (if nochange-regexp is non-nil).
This section describes two commands which indent the current line based on the contents of previous lines.
Command: indent-relative &optional unindented-ok
This function inserts whitespace at point, extending to the same column as the next indent point of the previous nonblank line. An indent point is a non-whitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace.
If the previous nonblank line has no next indent point (i.e., none at
a great enough column position), this function either does nothing (if
unindented-ok is non-nil) or calls tab-to-tab-stop.
Thus, if point is underneath and to the right of the last column of a
short line of text, this function moves point to the next tab stop by
inserting whitespace.
This command returns an unpredictable value.
In the following example, point is at the beginning of the second line:
This line is indented twelve spaces.
-!-The quick brown fox jumped.
Evaluation of the expression (indent-relative nil) produces the
following:
This line is indented twelve spaces.
-!-The quick brown fox jumped.
In this example, point is between the `m' and `p' of `jumped':
This line is indented twelve spaces.
The quick brown fox jum-!-ped.
Evaluation of the expression (indent-relative nil) produces the
following:
This line is indented twelve spaces.
The quick brown fox jum -!-ped.
Command: indent-relative-maybe
This command indents the current line like the previous nonblank line.
The function consists of a call to indent-relative with a
non-nil value passed to the unindented-ok optional
argument. The value is unpredictable.
If the previous line has no indentation, the current line is given no indentation (any existing indentation is deleted); if the previous nonblank line has no indent points beyond the column at which point starts, nothing is changed.
This section explains the mechanism for user-specified "tab stops" and the mechanisms which use and set them. The name "tab stops" is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the designated position, like the other indentation functions; it does not affect the display of tab characters in the buffer (see section Usual Display Conventions). Note that the TAB character as input uses this tab stop feature only in a few major modes, such as Text mode.
Function: tab-to-tab-stop
This function inserts spaces or tabs up to the next tab stop column
defined by tab-stop-list. It searches the list for an element
greater than the current column number, and uses that element as the
column to indent to. If no such element is found, then nothing is done.
User Option: tab-stop-list
This variable is the list of tab stop columns used by
tab-to-tab-stops. The elements should be integers in increasing
order. The tab stop columns need not be evenly spaced.
Use M-x edit-tab-stops to edit the location of tab stops interactively.
These commands, primarily for interactive use, act based on the indentation in the text.
Command: back-to-indentation
This command moves point to the first non-whitespace character in the
current line (which is the line in which point is located). It returns
nil.
Command: backward-to-indentation arg
This command moves point backward arg lines and then to the
first nonblank character on that line. It returns nil.
Command: forward-to-indentation arg
This command moves point forward arg lines and then to the first
nonblank character on that line. It returns nil.
The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line).
Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0.
A character counts according to the number of columns it occupies on
the screen. This means control characters count as occupying 2 or 4
columns, depending upon the value of ctl-arrow, and tabs count as
occupying a number of columns that depends on the value of
tab-width and on the column where the tab begins. See section Usual Display Conventions.
Function: current-column
This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column count is calculated by adding together the widths of all the displayed representations of the characters between the start of the current line and point.
For a more complicated example of the use of current-column,
see the description of count-lines in section Motion by Text Lines.
Function: move-to-column column &optional force
This function moves point to column in the current line. The calculation of column takes into account the widths of all the displayed representations of the characters between the start of the line and point.
If the argument column is greater than the column position of the end of the line, point moves to the end of the line. If column is negative, point moves to the beginning of the line.
If it is impossible to move to column column because that is in
the middle of a multicolumn character such as a tab, point moves to the
end of that character. However, if force is non-nil, and
column is in the middle of a tab, then move-to-column
converts the tab into spaces so that it can move precisely to column
column.
The argument force also has an effect if the line isn't long enough to reach column column; in that case, it says to indent at the end of the line to reach that column.
If column is not an integer, an error is signaled.
The return value is the column number actually moved to.
The case change commands described here work on text in the current buffer. See section Character Case, for case conversion commands that work on strings and characters. See section The Case Table, for how to customize which characters are upper or lower case and how to convert them.
Command: capitalize-region start end
This function capitalizes all words in the region defined by
start and end. To capitalize means to convert each word's
first character to upper case and convert the rest of each word to lower
case. The function returns nil.
If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word.
When capitalize-region is called interactively, start and
end are point and the mark, with the smallest first.
---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ----------
Command: downcase-region start end
This function converts all of the letters in the region defined by
start and end to lower case. The function returns
nil.
When downcase-region is called interactively, start and
end are point and the mark, with the smallest first.
Command: upcase-region start end
This function converts all of the letters in the region defined by
start and end to upper case. The function returns
nil.
When upcase-region is called interactively, start and
end are point and the mark, with the smallest first.
Command: capitalize-word count
This function capitalizes count words after point, moving point
over as it does. To capitalize means to convert each word's first
character to upper case and convert the rest of each word to lower case.
If count is negative, the function capitalizes the
-count previous words but does not move point. The value
is nil.
If point is in the middle of a word, the part of word the before point (if moving forward) or after point (if operating backward) is ignored. The rest is treated as an entire word.
When capitalize-word is called interactively, count is
set to the numeric prefix argument.
Command: downcase-word count
This function converts the count words after point to all lower
case, moving point over as it does. If count is negative, it
converts the -count previous words but does not move point.
The value is nil.
When downcase-word is called interactively, count is set
to the numeric prefix argument.
Command: upcase-word count
This function converts the count words after point to all upper
case, moving point over as it does. If count is negative, it
converts the -count previous words but does not move point.
The value is nil.
When upcase-word is called interactively, count is set to
the numeric prefix argument.
Each character position in a buffer or a string can have a text property list, much like the property list of a symbol. The properties belong to a particular character at a particular place, such as, the letter `T' at the beginning of this sentence or the first `o' in `foo'---if the same character occurs in two different places, the two occurrences generally have different properties.
Each property has a name, which is usually a symbol, and an associated value, which can be any Lisp object--just as for properties of symbols (see section Property Lists).
If a character has a category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
substring, insert, and buffer-substring.
The simplest way to examine text properties is to ask for the value of
a particular property of a particular character. For that, use
get-text-property. Use text-properties-at to get the
entire property list of a character. See section Property Search Functions, for
functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1.
Function: get-text-property pos prop &optional object
This function returns the value of the prop property of the character after position pos in object (a buffer or string). The argument object is optional and defaults to the current buffer.
If there is no prop property strictly speaking, but the character
has a category which is a symbol, then get-text-property returns
the prop property of that symbol.
Function: text-properties-at position &optional object
This function returns the list of properties held by the character at
position in the string or buffer object. If object is
nil, it defaults to the current buffer.
Function: text-property-any start end prop value &optional object
This function returns non-nil if at least one character between
start and end has a property prop whose value is
value. More precisely, it returns the position of the first such
character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object.
Function: text-property-not-all start end prop value &optional object
This function returns non-nil if at least one character between
start and end has a property prop whose value differs
from value. More precisely, it returns the position of the
first such character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object.
The primitives for changing properties apply to a specified range of
text. The function set-text-properties (see end of section) sets
the entire property list of the text in that range; more often, it is
useful to add, change, or delete just certain properties specified by
name.
Since text properties are considered part of the buffer's contents, and can affect how the buffer looks on the screen, any change in the text properties is considered a buffer modification. Buffer text property changes are undoable.
Function: add-text-properties start end props &optional object
This function modifies the text properties for the text between
start and end in the string or buffer object. If
object is nil, it defaults to the current buffer.
The argument props specifies which properties to change. It should have the form of a property list (see section Property Lists): a list whose elements include the property names followed alternately by the corresponding values.
The return value is t if the function actually changed some
property's value; nil otherwise (if props is nil or
its values agree with those in the text).
For example, here is how to set the comment property to t
for a range of text:
(add-text-properties (region-beginning)
(region-end)
(list 'comment t))
Function: put-text-property start end prop value &optional object
This function sets the prop property to value for the text
between start and end in the string or buffer object.
If object is nil, it defaults to the current buffer.
Function: remove-text-properties start end props &optional object
This function deletes specified text properties from the text between
start and end in the string or buffer object. If
object is nil, it defaults to the current buffer.
The argument props specifies which properties to delete. It should have the form of a property list (see section Property Lists): a list whose elements include the property names followed by the corresponding values. The property names mentioned in props are the ones deleted from the text. The values associated in props with these names do not matter.
The return value is t if the function actually changed some
property's value; nil otherwise (if props is nil or
if none of the text had any of those properties).
Function: set-text-properties start end props &optional object
This function completely replaces the text property list for the text
between start and end in the string or buffer object.
If object is nil, it defaults to the current buffer.
The argument props is the new property list. It should have the form of a list whose elements include the property names followed by the corresponding values.
After set-text-properties returns, all the characters in the
specified range have identical properties.
If props is nil, the effect is to get rid of all properties
from the specified range of text. Here's an example:
(set-text-properties (region-beginning)
(region-end)
nil)
In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.
Here are functions you can use to do this. In all cases, object defaults to the current buffer.
Function: next-property-change pos &optional object
The function scans the text forward from position pos in the string or buffer object till it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose properties are not identical to those of the character just after pos.
The value is nil if the properties remain unchanged all the way
to the end of object. If the value is non-nil, it is a
position greater than pos, never equal.
Here is an example of how to scan the buffer by chunks of text within which all properties are constant:
(while (not (eobp))
(let ((plist (text-properties-at (point)))
(next-change
(or (next-property-change (point) (current-buffer))
(point-max))))
Process text from point to next-change...
(goto-char next-change)))
Function: next-single-property-change pos prop &optional object
The function scans the text forward from position pos in the string or buffer object till it finds a change in the prop property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose prop property differs from that of the character just after pos.
The value is nil if the properties remain unchanged all the way
to the end of object. If the value is non-nil, it is a
position greater than pos, never equal.
Function: previous-property-change pos &optional object
This is like next-property-change, but scans back from pos
instead of forward. If the value is non-nil, it is a position
always strictly less than pos. Remember that a position is
always between two characters; the position returned by this function
is between two characters with different properties.
Function: previous-single-property-change pos prop &optional object
This is like next-property-change, but scans back from pos
instead of forward. If the value is non-nil, it is a position
always strictly less than pos.
If a character has a category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
You can use the property face to control the font and color of
text. See section Faces, for more information. This feature is temporary;
in the future, we may replace it with other ways of specifying how to
display text.
The property mouse-face is used instead of face when the
mouse is on or near the character. For this purpose, "near" means
that all text between the character and where the mouse is have the same
mouse-face property value.
You can specify a different keymap for a portion of the text by means
of a local-map property. The property's value, for the character
after point, replaces the buffer's local map. See section Active Keymaps.
If a character has the property read-only, then modifying that
character is not allowed. Any command that would do so gets an error.
Insertion next to a read-only character is also an error if inserting
ordinary text there would inherit the read-only property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. See section Stickiness of Text Properties.
Since changing properties counts as modifying the buffer, it is not
possible to remove a read-only property unless you know the
special trick: bind inhibit-read-only to a non-nil value
and then remove the property. See section Read-Only Buffers.
A non-nil invisible property means a character does not
appear on the screen. This works much like selective display. Details
of this feature are likely to change in future versions, so check the
`etc/NEWS' file in the version you are using.
If a character has the property modification-hooks, then its
value should be a list of functions; modifying that character calls all
of those functions. Each function receives two arguments: the beginning
and end of the part of the buffer being modified. Note that if a
particular modification hook function appears on several characters
being modified by a single primitive, you can't predict how many times
the function will be called.
Insertion of text does not, strictly speaking, change any existing
character, so there is a special rule for insertion. It compares the
read-only properties of the two surrounding characters; if they
are non-nil and eq to each other, then the insertion is
not allowed. Assuming insertion is allowed, it then calls the functions
listed in the insert-in-front-hooks property of the following
character and in the insert-behind-hooks property of the
preceding character. These functions receive two arguments, the
beginning and end of the inserted text.
See also section Change Hooks, for other hooks that are called when you change text in a buffer.
The special properties point-entered and point-left
record hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
point-left property of the character after the old location,
and
point-entered property of the character after the new
location.
If these two values differ, each of them is called (if not nil)
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and new
locations. The result may be to execute two point-left functions
(which may be the same function) and/or two point-entered
functions (which may be the same function). The point-left
functions are always called before the point-entered functions.
A primitive function may examine characters at various positions without moving point to those positions. Only an actual change in the value of point runs these hook functions.
Variable: inhibit-point-motion-hooks
When this variable is non-nil, point-left and
point-entered hooks are not run.
Self-inserting characters normally take on the same properties as the preceding character. This is called inheritance of properties; the inherited properties normally come from the preceding character because properties are normally rear-sticky and not front-sticky.
You can control how properties are inherited by setting the
front-sticky and rear-nonsticky properties of characters
in the text.
If you make a character's front-sticky property t, then
insertion before the character receives its properties. If you make the
rear-nonsticky property t, then insertion after that
character does not receive its properties. You can regard
characters as being normally "rear-sticky" by default, but not
"front-sticky"; thus, by default, insertion normally receives
properties from the previous character only.
If neither side of an insertion is suitably sticky, then the inserted text gets no properties. If both sides are sticky, then the inserted text gets the properties of both sides, with the previous character's properties taking precedence when both sides have a property in common.
You can also specify stickiness for individual properties. To do so,
use a list of property names as the value of the front-sticky
property or the rear-nonsticky property. For example, if a
character has a rear-nonsticky property whose value is
(face read-only), then insertion after the character does not
receive its face property its or read-only property (if
any), but does receive any other properties it has.
The merging of properties when both sides of the insertion are sticky
takes place one property at a time. If the preceding character is
rear-sticky for the property, and the property is non-nil,
it dominates. Otherwise, the following character's property value is
used if it is front-sticky for that property.
Function: insert-and-inherit &rest strings
Insert the strings strings, just like the function insert,
but inherit any sticky properties from the adjoining text.
Function: insert-before-markers-and-inherit &rest strings
Insert the strings strings, just like the function
insert-before-markers, but inherit any sticky properties from the
adjoining text.
Some editors that support adding attributes to text in the buffer do so by letting the user specify "intervals" within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you undo the kill, you get two intervals with the same properties. Thus, the distinction can't be preserved when editing happens.
But suppose we "fix" this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But if it was two intervals, and the killed text equals one of them, then undoing the kill yields just one interval. Again, the distinction can't be preserved.
Insertion of text at the border between intervals also raises questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for questions of the form, "What are the properties of this character?" So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end.
For practical purposes, the property search functions serve in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See section Property Search Functions.
Emacs also provides explicit intervals as a presentation feature; see section Overlays.
The following functions replace characters within a specified region based on their character codes.
Function: subst-char-in-region start end old-char new-char &optional noundo
This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.
If noundo is non-nil, then subst-char-in-region
does not record the change for undo and does not mark the buffer as
modified. This feature is useful for changes which are not considered
significant, such as when Outline mode changes visible lines to
invisible lines and vice versa.
subst-char-in-region does not move point and returns
nil.
---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
(subst-char-in-region 1 20 ?i ?X)
=> nil
---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------
Function: translate-region start end table
This function applies a translation table to the characters in the buffer between positions start and end.
The translation table table is a string; (aref table
ochar) gives the translated character corresponding to
ochar. If the length of table is less than 256, any
characters with codes larger than the length of table are not
altered by the translation.
The return value of translate-region is the number of
characters which were actually changed by the translation. This does
not count characters which were mapped into themselves in the
translation table.
This function is available in Emacs versions 19 and later.
The underlining commands are somewhat obsolete. The
underline-region function actually inserts `_^H' before each
appropriate character in the region. This command provides a minimal
text formatting feature that might work on your printer; however, we
recommend instead that you use more powerful text formatting facilities,
such as Texinfo.
Command: underline-region start end
This function underlines all nonblank characters in the region defined
by start and end. That is, an underscore character and a
backspace character are inserted just before each non-whitespace
character in the region. The backspace characters are intended to cause
overstriking, but in Emacs they display as either `\010' or
`^H', depending on the setting of ctl-arrow. There is no
way to see the effect of the overstriking within Emacs. The value is
nil.
Command: ununderline-region start end
This function removes all underlining (overstruck underscores) in the
region defined by start and end. The value is nil.
A register is a sort of variable used in Emacs editing that can hold a marker, a string, a rectangle, a window configuration (of one frame), or a frame configuration (of all frames). Each register is named by a single character. All characters, including control and meta characters (but with the exception of C-g), can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by a character which is its name.
The functions in this section return unpredictable values unless otherwise stated.
Variable: register-alist
This variable is an alist of elements of the form (name .
contents). Normally, there is one element for each Emacs
register that has been used.
The object name is a character (an integer) identifying the register. The object contents is a string, marker, or list representing the register contents. A string represents text stored in the register. A marker represents a position. A list represents a rectangle; its elements are strings, one per line of the rectangle.
Command: view-register reg
This command displays what is contained in register reg.
Function: get-register reg
This function returns the contents of the register
reg, or nil if it has no contents.
Function: set-register reg value
This function sets the contents of register reg to value. A register can be set to any value, but the other register functions expect only certain data types. The return value is value.
Command: point-to-register reg
This command stores both the current location of point and the current buffer in register reg as a marker.
Command: jump-to-register reg
Command: register-to-point reg
This command restores the status recorded in register reg.
If reg contains a marker, it moves point to the position stored in
the marker. Since both the buffer and the location within the buffer
are stored by the point-to-register function, this command can
switch you to another buffer.
If reg contains a window configuration or a frame configuration.
jump-to-register restores that configuration.
Command: insert-register reg &optional beforep
This command inserts contents of register reg into the current buffer.
Normally, this command puts point before the inserted text, and the
mark after it. However, if the optional second argument beforep
is non-nil, it puts the mark before and point after.
You can pass a non-nil second argument beforep to this
function interactively by supplying any prefix argument.
If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines.
If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future.
Command: copy-to-register reg start end &optional delete-flag
This command copies the region from start to end into
register reg. If delete-flag is non-nil, it deletes
the region from the buffer after copying it into the register.
Command: prepend-to-register reg start end &optional delete-flag
This command prepends the region from start to end into
register reg. If delete-flag is non-nil, it deletes
the region from the buffer after copying it to the register.
Command: append-to-register reg start end &optional delete-flag
This command appends the region from start to end to the
text already in register reg. If delete-flag is
non-nil, it deletes the region from the buffer after copying it
to the register.
Command: copy-rectangle-to-register reg start end &optional delete-flag
This command copies a rectangular region from start to end
into register reg. If delete-flag is non-nil, it
deletes the region from the buffer after copying it to the register.
Command: window-configuration-to-register reg
This function stores the window configuration of the selected frame in register reg.
Command: frame-configuration-to-register reg
This function stores the current frame configuration in register reg.
These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also section Special Properties, for how to detect changes to specific parts of the text.
The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them.
Variable: before-change-function
If this variable is non-nil, then it should be a function; the
function is called before any buffer modification. Its arguments are
the beginning and end of the region that is going to change,
represented as integers. The buffer that's about to change is always
the current buffer.
Variable: after-change-function
If this variable is non-nil, then it should be a function; the
function is called after any buffer modification. It receives three
arguments: the beginning and end of the region just changed, and the
length of the text that existed before the change. (To get the
current length, subtract the region beginning from the region end.)
All three arguments are integers. The buffer that's about to change
is always the current buffer.
Both of these variables are temporarily bound to nil during the
time that either of these hooks is running. This means that if one of
these functions changes the buffer, that change won't run these
functions. If you do want the hook function to be run recursively,
write your hook functions to bind these variables back to their usual
values.
Variable: first-change-hook
This variable is a normal hook; its hook functions are run using
run-hooks whenever a buffer is changed that was previously in
the unmodified state.
The variables described in this section are meaningful only starting with Emacs version 19.
GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can identify the text matched by parts of the regular expression by examining the match data.
These are the primitive functions for searching through the text in a
buffer. They are meant for use in programs, but you may call them
interactively. If you do so, they prompt for the search string;
limit and noerror are set to nil, and repeat
is set to 1.
Command: search-forward string &optional limit noerror repeat
This function searches forward from point for an exact match for string. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on noerror (see below).
In the following example, point is positioned at the beginning of the
line. Then (search-forward "fox") is evaluated in the minibuffer
and point is left after the last letter of `fox':
---------- Buffer: foo ----------
-!-The quick brown fox jumped over the lazy dog.
---------- Buffer: foo ----------
(search-forward "fox")
=> t
---------- Buffer: foo ----------
The quick brown fox-!- jumped over the lazy dog.
---------- Buffer: foo ----------
The argument limit specifies the upper bound to the search. (It
must be a position in the current buffer.) No match extending after
that position is accepted. If limit is omitted or nil, it
defaults to the end of the accessible portion of the buffer.
What happens when the search fails depends on the value of
noerror. If noerror is nil, a search-failed
error is signaled. If noerror is t, search-forward
returns nil and does nothing. If noerror is neither
nil nor t, then search-forward moves point to the
upper bound and returns nil. (It would be more consistent now
to return the new position of point in that case, but some programs
may depend on a value of nil.)
If repeat is non-nil, then the search is repeated that
many times. Point is positioned at the end of the last match.
Command: search-backward string &optional limit noerror repeat
This function searches backward from point for string. It is
just like search-forward except that it searches backwards and
leaves point at the beginning of the match.
Command: word-search-forward string &optional limit noerror repeat
This function searches forward from point for a "word" match for string. If it finds a match, it sets point to the end of the match found, and returns the new value of point.
A word search differs from a simple string search in that a word search requires that the words it searches for are present as entire words (searching for the word `ball' does not match the word `balls'), and punctuation and spacing are ignored (searching for `ball boy' does match `ball. Boy!').
In this example, point is first placed at the beginning of the buffer; the search leaves it between the y and the !.
---------- Buffer: foo ----------
-!-He said "Please! Find
the ball boy!"
---------- Buffer: foo ----------
(word-search-forward "Please find the ball, boy.")
=> t
---------- Buffer: foo ----------
He said "Please! Find
the ball boy-!-!"
---------- Buffer: foo ----------
If limit is non-nil (it must be a position in the current
buffer), then it is the upper bound to the search. The match found must
not extend after that position.
If noerror is t, then word-search-forward returns
nil when a search fails, instead of signaling an error. If
noerror is neither nil nor t, then
word-search-forward moves point to limit (or the end of the
buffer) and returns nil.
If repeat is non-nil, then the search is repeated that many
times. Point is positioned at the end of the last match.
Command: word-search-backward string &optional limit noerror repeat
This function searches backward from point for a word match to
string. This function is just like word-search-forward
except that it searches backward and normally leaves point at the
beginning of the match.
A regular expression (regexp, for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them.
Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression which matches that character and nothing else. The special characters are `$', `^', `.', `*', `+', `?', `[', `]' and `\'; no new special characters will be defined in the future. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it.
For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does not match the string `ff'.) Likewise, `o' is a regular expression that matches only `o'.
Any two regular expressions a and b can be concatenated. The result is a regular expression which matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.
As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something more powerful, you need to use one of the special characters. Here is a list of them:
`*' always applies to the smallest possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'.
The matcher processes a `*' construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the `*'-modified construct in case that makes it possible to match the rest of the pattern. For example, matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully.
Character ranges can also be included in a character set, by writing two characters with a `-' between them. Thus, `[a-z]' matches any lower case letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower case letter or `$', `%' or a period.
Note that the usual special characters are not special any more inside a character set. A completely different set of special characters exists inside character sets: `]', `-' and `^'.
To include a `]' in a character set, make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first or last character in the range.
To include `^', make it other than the first character in the set.
`^' is not special in a character set unless it is the first character. The character following the `^' is treated as if it were first (thus, `-' and `]' are not special there).
Note that a complement character set can match a newline, unless newline is mentioned as one of the characters not to match.
When matching a string, `^' matches at the beginning of the string or after a newline character `\n'.
When matching a string, `$' matches at the end of the string or before a newline character `\n'.
Because `\' quotes special characters, `\$' is a regular expression which matches only `$', and `\[' is a regular expression which matches only `[', and so on.
Note that `\' also has special meaning in the read syntax of Lisp
strings (see section String Type), and must be quoted with `\'. For
example, the regular expression that matches the `\' character is
`\\'. To write a Lisp string that contains the characters
`\\', Lisp syntax requires you to quote each `\' with another
`\'. Therefore, the read syntax for a regular expression matching
`\' is "\\\\".
Please note: for historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; better to quote the special character anyway, regardless of where it appears.
For the most part, `\' followed by any character matches only that character. However, there are several exceptions: characters which, when preceded by `\', are special constructs. Such characters are always ordinary when encountered on their own. Here is a table of `\' constructs:
Thus, `foo\|bar' matches either `foo' or `bar' but no other string.
`\|' applies to the largest possible surrounding expressions. Only a surrounding `\( ... \)' grouping can limit the grouping power of `\|'.
Full backtracking capability exists to handle multiple uses of `\|'.
This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature which happens to be assigned as a second meaning to the same `\( ... \)' construct because there is no conflict in practice between the two meanings. Here is an explanation of this feature:
In other words, after the end of a `\( ... \)' construct. the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use `\' followed by digit to mean "match the same text matched the digitth time by the `\( ... \)' construct."
The strings matching the first nine `\( ... \)' constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use `\1' through `\9' to refer to the text matched by the corresponding `\( ... \)' constructs.
For example, `\(.*\)\1' matches any newline-free string that is composed of two identical halves. The `\(.*\)' matches the first half, which may be anything, but the `\1' that follows must match the same exact text.
Not every string is a valid regular expression. For example, any
string with unbalanced square brackets is invalid, and so is a string
that ends with a single `\'. If an invalid regular expression is
passed to any of the search functions, an invalid-regexp error is
signaled.
Function: regexp-quote string
This function returns a regular expression string which matches exactly string and nothing else. This allows you to request an exact string match when calling a function that wants a regular expression.
(regexp-quote "^The cat$")
=> "\\^The cat\\$"
One use of regexp-quote is to combine an exact string match with
context described as a regular expression. For example, this searches
for the string which is the value of string, surrounded by
whitespace:
(re-search-forward (concat "\\s " (regexp-quote string) "\\s "))
Here is a complicated regexp, used by Emacs to recognize the end of a
sentence together with any whitespace that follows. It is the value of
the variable sentence-end.
First, we show the regexp as a string in Lisp syntax to enable you to distinguish the spaces from the tab characters. The string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the string, `\\' for a backslash as part of the string, `\t' for a tab and `\n' for a newline.
"[.?!][]\"')}]*\\($\\|\t\\| \\)[ \t\n]*"
In contrast, if you evaluate the variable sentence-end, you
will see the following:
sentence-end => "[.?!][]\"')}]*\\($\\| \\| \\)[ ]*"
In this case, the tab and carriage return are the actual characters.
This regular expression contains four parts in succession and can be deciphered as follows:
[.?!]
[]\"')}]*
\" is Lisp syntax for a double-quote in
a string. The `*' at the end indicates that the immediately
preceding regular expression (a character set, in this case) may be
repeated zero or more times.
\\($\\|\t\\| \\)
[ \t\n]*
In GNU Emacs, you can search for the next match for a regexp either
incrementally or not. Incremental search commands are described in the
The GNU Emacs Manual. See section 'Regular Expression Search' in The GNU Emacs Manual. Here we describe only the search
functions useful in programs. The principal one is
re-search-forward.
Command: re-search-forward regexp &optional limit noerror repeat
This function searches forward in the current buffer for a string of text that is matched by the regular expression regexp. The function skips over any amount of text that is not matched by regexp, and leaves point at the end of the first string found that does match.
If the search is successful (i.e., if text matching regexp is found), then point moves to the end of that text, and the function returns the new value of point.
What happens when the search fails depends on the value of
noerror. If noerror is nil, a search-failed
error is signaled. If noerror is t,
re-search-forward does nothing and returns nil. If
noerror is neither nil nor t, then
re-search-forward moves point to limit (or the end of the
buffer) and returns nil.
If limit is non-nil (it must be a position in the current
buffer), then it is the upper bound to the search. No match extending
after that position is accepted.
If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). The call succeeds if all these searches succeeded, and point is left at the end of the match found by the last search. Otherwise the search fails.
In the following example, point is initially located directly before the `T'. After evaluating the form, point is located at the end of that line (between the `t' of `hat' and before the newline).
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(re-search-forward "[a-z]+" nil t 5)
=> t
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
Command: re-search-backward regexp &optional limit noerror repeat
This function searches backward in the current buffer for a string of text that is matched by the regular expression regexp, leaving point at the beginning of the first text found.
This function is analogous to re-search-forward, but they are
not simple mirror images. re-search-forward finds the match
whose beginning is as close as possible. If re-search-backward
were a perfect mirror image, it would find the match whose end is as
close as possible. However, in fact it finds the match whose beginning
is as close as possible. The reason is that matching a regular
expression at a given spot always works from beginning to end, and is
done at a specified beginning position. Thus, true mirror-image
behavior would require a special feature for matching regexps from end
to beginning.
Function: string-match regexp string &optional start
This function returns the index of the start of the first match for
the regular expression regexp in string, or nil if
there is no match. If start is non-nil, the search starts
at that index in string.
For example,
(string-match
"quick" "The quick brown fox jumped quickly.")
=> 4
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
The index of the first character of the string is 0, the index of the second character is 1, and so on.
After this function returns, the index of the first character beyond
the match is available as (match-end 0). See section The Match Data.
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
(match-end 0)
=> 32
The match-beginning and match-end functions are
described together; see section The Match Data.
Function: looking-at regexp
This function determines whether the text in the current buffer
directly following point matches the regular expression
regexp. "Directly following" means precisely that: the search
is "anchored" and it must succeed starting with the first character
following point. The result is t if so, nil
otherwise.
This function does not move point, but it updates the match data,
which you can access using match-beginning or match-end.
See section The Match Data.
In this example, point is located directly before the `T'. If it
were anywhere else, the result would be nil.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(looking-at "The cat in the hat$")
=> t
Function: perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map
This function is the guts of query-replace and related commands.
It searches for occurrences of from-string and replaces some or
all of them. If query-flag is nil, it replaces all
occurrences; otherwise, it asks the user what to do about each one.
If regexp-flag is non-nil, then from-string is
considered a regular expression; otherwise, it must match literally. If
delimited-flag is non-nil, then only replacements
surrounded by word boundaries are considered.
The argument replacements specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order.
If repeat-count is non-nil, it should be an integer, the
number of occurrences to consider. In this case, perform-replace
returns after considering that many occurrences.
Normally, the keymap query-replace-map defines the possible user
responses. The argument map, if non-nil, is a keymap to
use instead of query-replace-map.
Variable: query-replace-map
This variable holds a special keymap that defines the valid user
responses for query-replace and related functions, as well as
y-or-n-p and map-y-or-n-p. It is special in two ways:
Here are the meaningful "bindings" for query-replace-map.
Several of them are meaningful only for query-replace and
friends.
act
skip
exit
act-and-exit
act-and-show
automatic
backup
edit
delete-and-edit
recenter
quit
y-or-n-p functions use this
answer.
help
Emacs keeps track of the positions of the start and end of segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and extract parts of it.
Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten.
This section explains how to use the match data to find the starting point or ending point of the text that was matched by a particular search, or by a particular parenthetical subexpression of a regular expression.
Function: match-beginning count
This function returns the position of the start of text matched by the last regular expression searched for. count, a number, specifies a subexpression whose start position is the value. If count is zero, then the value is the position of the text matched by the whole regexp. If count is greater than zero, then the value is the position of the beginning of the text matched by the countth subexpression, regardless of whether it was used in the final match.
Subexpressions of a regular expression are those expressions grouped inside of parentheses, `\(...\)'. The countth subexpression is found by counting occurrences of `\(' from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on.
The value is nil for a parenthetical grouping inside of a
`\|' alternative that wasn't used in the match.
The match-end function is similar to the match-beginning
function except that it returns the position of the end of the matched
text.
Here is an example, with a comment showing the numbers of the positions in the text:
(string-match
"\\(qu\\)\\(ick\\)" "The quick fox jumped quickly.")
=> 4 ;^^^^^^^^^^
;0123456789
(match-beginning 1) ; The beginning of the match
=> 4 ; with `qu' is at index 4.
(match-beginning 2) ; The beginning of the match
=> 6 ; with `ick' is at index 6.
(match-end 1) ; The end of the match
=> 6 ; with `qu' is at index 6.
(match-end 2) ; The end of the match
=> 9 ; with `ick' is at index 9.
Here is another example. Before the form is evaluated, point is located at the beginning of the line. After evaluating the search form, point is located on the line between the space and the word `in'. The beginning of the entire match is at the 9th character of the buffer (`T'), and the beginning of the match for the first subexpression is at the 13th character (`c').
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
=> (t 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(Note that in this case, the index returned is a buffer position; the first character of the buffer counts as 1.)
Function: match-end count
This function returns the position of the end of text matched by the
last regular expression searched for. This function is otherwise
similar to match-beginning.
This function replaces the text matched by the last search with replacement.
Function: replace-match replacement &optional fixedcase literal
If fixedcase is non-nil, then the case of the replacement
text is not changed; otherwise, the replacement text is converted to a
different case depending upon the capitalization of the text to be
replaced. If the original text is all upper case, the replacement text
is converted to upper case, except when all of the words in the original
text are only one character long. In that event, the replacement text
is capitalized. If all of the words in the original text are
capitalized, then all of the words in the replacement text are
capitalized.
If literal is non-nil, then replacement is inserted
exactly as it is, the only alterations being case changes as needed.
If it is nil (the default), then the character `\' is treated
specially. If a `\' appears in replacement, then it must be
part of one of the following sequences:
replace-match leaves point at the end of the replacement text,
and returns t.
The functions match-data and store-match-data let you
read or write the entire match data, all at once.
Function: match-data
This function returns a new list containing all the information on
what text the last search matched. Element zero is the position of the
beginning of the match for the whole expression; element one is the
position of the end of the match for the expression. The next two
elements are the positions of the beginning and end of the match for the
first subexpression. In general, element
corresponds to (match-beginning n); and
element
corresponds to (match-end n).
All the elements are markers or nil if matching was done on a
buffer, and all are integers or nil if matching was done on a
string with string-match. (In Emacs 18 and earlier versions,
markers were used even for matching on a string, except in the case
of the integer 0.)
As always, there must be no possibility of intervening searches between
the call to a search function and the call to match-data that is
intended to access the match-data for that search.
(match-data)
=> (#<marker at 9 in foo>
#<marker at 17 in foo>
#<marker at 13 in foo>
#<marker at 17 in foo>)
Function: store-match-data match-list
This function sets the match data from the elements of match-list,
which should be a list that was the value of a previous call to
match-data.
If match-list refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way.
All asynchronous process functions (filters and sentinels) and
functions that use recursive-edit should save and restore the
match data if they do a search or if they let the user type arbitrary
commands. Saving the match data is useful in other cases as
well--whenever you want to access the match data resulting from an
earlier search, notwithstanding another intervening search.
This example shows the problem that can arise if you fail to attend to this requirement:
(re-search-forward "The \\(cat \\)")
=> 48
(foo) ; Perhaps foo does
; more searching.
(match-end 0)
=> 61 ; Unexpected result--not 48!
In Emacs versions 19 and later, you can save and restore the match
data with save-match-data:
Special Form: save-match-data body...
This special form executes body, saving and restoring the match data around it. This is useful if you wish to do a search without altering the match data that resulted from an earlier search.
You can use store-match-data together with match-data to
imitate the effect of the special form save-match-data. This is
useful for writing code that can run in Emacs 18. Here is how:
(let ((data (match-data)))
(unwind-protect
... ; May change the original match data.
(store-match-data data)))
Here are the regular expressions standardly used in editing:
Variable: page-delimiter
This is the regexp describing line-beginnings that separate pages. The
default value is "^\014" (i.e., "^^L" or "^\C-l").
Variable: paragraph-separate
This is the regular expression for recognizing the beginning of a line
that separates paragraphs. (If you change this, you may have to
change paragraph-start also.) The default value is "^[
\t\f]*$", which is a line that consists entirely of spaces, tabs, and
form feeds.
Variable: paragraph-start
This is the regular expression for recognizing the beginning of a line
that starts or separates paragraphs. The default value is
"^[ \t\n\f]", which matches a line starting with a space, tab,
newline, or form feed.
Variable: sentence-end
This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is:
"[.?!][]\"')}]*\\($\\|\t\\| \\)[ \t\n]*"
This means a period, question mark or exclamation mark, followed by a closing brace, followed by tabs, spaces or new lines.
For a detailed explanation of this regular expression, see section Complex Regexp Example.
By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' or `foo' is also considered a match. Regexps, and in particular character sets, are included: thus, `[aB]' would match `a' or `A' or `b' or `B'.
If you do not want this feature, set the variable
case-fold-search to nil. Then all letters must match
exactly, including case. This is a per-buffer-local variable; altering
the variable affects only the current buffer. (See section Introduction to Buffer-Local Variables.) Alternatively, you may change the value of
default-case-fold-search, which is the default value of
case-fold-search for buffers that do not override it.
User Option: case-replace
This variable determines whether query-replace should
preserve case in replacements. If the variable is nil, then case
need not be preserved.
User Option: case-fold-search
This buffer-local variable determines whether searches should ignore
case. If the variable is nil they do not ignore case; otherwise
they do ignore case.
Variable: default-case-fold-search
The value of this variable is the default value for
case-fold-search in buffers that do not override it. This is the
same as (default-value 'case-fold-search).
A syntax table provides Emacs with the information that determines the syntactic use of each character in a buffer. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see section Motion by Words) and the list motion functions (see section Moving over Balanced Expressions) as well as the functions in this chapter.
A syntax table is a vector of 256 elements; it contains one entry for each of the 256 ASCII characters of an 8-bit byte. Each element is an integer that encodes the syntax of the character in question.
Syntax tables are used only for moving across text, not for the GNU Emacs Lisp reader. GNU Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed.
Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character `;' begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer which uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. See section Major Mode Examples, for an example of how to set up a syntax table.
Function: syntax-table-p object
This function returns t if object is a vector of length
256 elements. This means that the vector may be a syntax table.
However, according to this test, any vector of length 256 is considered
to be a syntax table, no matter what its contents.
This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a syntax
descriptor, which is a Lisp string that you pass to
modify-syntax-entry to specify the desired syntax.
Emacs defines twelve syntax classes. Each syntax table puts each character into one class. There is no necessary relationship between the class of a character in one syntax table and its class in any other table.
Each class is designated by a mnemonic character which serves as the name of the class when you need to specify a class. Usually the designator character is one which is frequently put in that class; however, its meaning as a designator is unvarying and independent of how it is actually classified.
A syntax descriptor is a Lisp string which specifies a syntax class, a matching character (unused except for parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient.
Thus, the descriptor for the character `*' in C mode is `. 23' (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of an comment-ender), and the entry for `/' is `. 14' (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender).
Here is a summary of the classes, the characters that stand for them, their meanings, and examples of their use.
Syntax class: whitespace character
Whitespace characters (designated with ` ' or `-') separate symbols and words from each other. Typically, whitespace characters have no other syntactic use, and multiple whitespace characters are syntactically equivalent to a single one. Space, tab, newline and formfeed are almost always considered whitespace.
Syntax class: word constituent
Word constituents (designated with `w') are parts of normal English words and are typically used in variable and command names in programs. All upper and lower case letters and the digits are typically word constituents.
Syntax class: symbol constituent
Symbol constituents (designated with `_') are the extra characters that are used in variable and command names along with word constituents. For example, the symbol constituents class is used in Lisp mode to indicate that certain characters may be part of symbol names even though they are not part of English words. These characters are `$&*+-_<>'. In standard C, the only non-word-constituent character that is valid in symbols is underscore (`_').
Syntax class: punctuation character
Punctuation characters (`.') are those characters that are used as punctuation in English, or are used in some way in a programming language to separate symbols from one another. Most programming language modes, including Emacs Lisp mode, have no characters in this class since the few characters that are not symbol or word constituents all have other uses.
Syntax class: open parenthesis character
Syntax class: close parenthesis character
Open and close parenthesis characters are characters used in dissimilar pairs to surround sentences or expressions. Such a grouping is begun with an open parenthesis character and terminated with a close. Each open parenthesis character matches a particular close parenthesis character, and vice versa. Normally, Emacs indicates momentarily the matching open parenthesis when you insert a close parenthesis. See section Blinking.
The class of open parentheses is designated with `(', and that of close parentheses with `)'.
In English text, and in C code, the parenthesis pairs are `()', `[]', and `{}'. In Emacs Lisp, the delimiters for lists and vectors (`()' and `[]') are classified as parenthesis characters.
Syntax class: string quote
String quote characters (designated with `"') is used to delimit string constants in many languages, including Lisp and C. The same string quote character appears at the beginning and the end of a string. Such quoted strings do not nest.
The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed.
The Lisp modes have two string quote characters: double-quote (`"') and vertical bar (`|'). `|' is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and single-quote (`'') for character constants.
English text has no string quote characters because English is not a programming language. Although quotation marks are used in English, we do not want them to turn off the usual syntactic properties of other characters in the quotation.
Syntax class: escape
An escape character (designated with `\') starts an escape sequence such as is used in C string and character constants. The character `\' belongs to this class in both C and Lisp. (In C, it is used thus only inside strings, but it turns out to cause no trouble to treat it this way throughout C code.)
Characters in this class count as part of words if
words-include-escapes is non-nil. See section Motion by Words.
Syntax class: character quote
A character quote character (designated with `/') quotes the following character so that it loses its normal syntactic meaning. This differs from an escape character in that only the character immediately following is ever affected.
Characters in this class count as part of words if
words-include-escapes is non-nil. See section Motion by Words.
This class is not currently used in any standard Emacs modes.
Syntax class: paired delimiter
Paired delimiter characters (designated with `$') are like string quote characters except that the syntactic properties of the characters between the delimiters are not suppressed. Only TeX mode uses a paired identical delimiter presently--the `$' that begins and ends math mode.
Syntax class: expression prefix
An expression prefix operator (designated with `'') is used for syntactic operators that are part of an expression if they appear next to one but are not part of an adjoining symbol. These characters in Lisp include the apostrophe, `'' (used for quoting), the comma, `,' (used in macros), and `#' (used in the read syntax for certain data types).
Syntax class: comment starter
Syntax class: comment ender
The comment starter and comment ender characters are used in different languages to delimit comments. These classes are designated with `<' and `>', respectively.
English text has no comment characters. In Lisp, the semicolon (`;') starts a comment and a newline or formfeed ends one.
In addition to the classes, entries for characters in a syntax table can include flags. There are six possible flags, represented by the characters `1', `2', `3', `4', `b' and `p'.
All the flags except `p' are used to describe multi-character comment delimiters. The digit flags indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as `*' in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (`/*'), and the first character of an end-of-comment sequence (`*/').
The flags for a character c are:
Emacs can now supports two comment styles simultaneously. (This is for the sake of C++.) More specifically, it can recognize two different comment-start sequences. Both must share the same first character; only the second character may differ. Mark the second character of the "b"-style comment start sequence with the `b' flag.
The two styles of comment can have different comment-end sequences. A comment-end sequence (one or two characters) applies to the "b" style if its first character has the `b' flag set; otherwise, it applies to the "a" style.
The appropriate comment syntax settings for C++ are as follows:
Thus `/*' is a comment-start sequence for "a" style, `//' is a comment-start sequence for "b" style, `*/' is a comment-end sequence for "a" style, and newline is a comment-end sequence for "b" style.
The function backward-prefix-chars moves back over these
characters, as well as over characters whose primary syntax class is
prefix (`'').
In this section we describe functions for creating, accessing and altering syntax tables.
Function: make-syntax-table &optional table
This function constructs a copy of table and returns it. If
table is not supplied (or is nil), it returns a copy of the
current syntax table. Otherwise, an error is signaled if table is
not a syntax table.
Function: copy-syntax-table &optional table
This function is identical to make-syntax-table.
Command: modify-syntax-entry char syntax-descriptor &optional table
This function sets the syntax entry for char according to syntax-descriptor. The syntax is changed only for table, which defaults to the current buffer's syntax table, and not in any other syntax table. The argument syntax-descriptor specifies the desired syntax; this is a string beginning with a class designator character, and optionally containing a matching character and flags as well. See section Syntax Descriptors.
This function always returns nil. The old syntax information in
the table for this character is discarded.
An error is signaled if the first character of the syntax descriptor is not one of the twelve syntax class designator characters. An error is also signaled if char is not a character.
Examples:
;; Put the space character in class whitespace.
(modify-syntax-entry ?\ " ")
=> nil
;; Make `$' an open parenthesis character,
;; with `^' as its matching close.
(modify-syntax-entry ?$ "(^")
=> nil
;; Make `^' a close parenthesis character,
;; with `$' as its matching open.
(modify-syntax-entry ?^ ")$")
=> nil
;; Make `/' a punctuation character,
;; the first character of a start-comment sequence,
;; and the second character of an end-comment sequence.
;; This is used in C mode.
(modify-syntax-entry ?/ ".13")
=> nil
Function: char-syntax character
This function returns the syntax class of character, represented by its mnemonic designator character. This only returns the class, not any matching parenthesis or flags.
An error is signaled if char is not a character.
The first example shows that the syntax class of space is whitespace (represented by a space). The second example shows that the syntax of `/' is punctuation in C-mode. This does not show the fact that it is also a comment sequence character. The third example shows that open parenthesis is in the class of open parentheses. This does not show the fact that it has a matching character, `)'.
(char-to-string (char-syntax ?\ ))
=> " "
(char-to-string (char-syntax ?/))
=> "."
(char-to-string (char-syntax ?\())
=> "("
Function: set-syntax-table table
This function makes table the syntax table for the current buffer. It returns table.
Function: syntax-table
This function returns the current syntax table, which is the table for the current buffer.
This section describes functions for moving across characters in certain syntax classes. None of these functions exists in Emacs version 18 or earlier.
Function: skip-syntax-forward syntaxes &optional limit
This function moves point forward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the end of the buffer, or position lim (if specified), or a character it is not supposed to skip.
The return value is the distance traveled, which is a nonnegative integer.
Function: skip-syntax-backward syntaxes &optional limit
This function moves point backward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the beginning of the buffer, or position lim (if specified), or a character it is not supposed to skip.
The return value indicates the distance traveled. It is an integer that is zero or less.
Function: backward-prefix-chars
This function moves point backward over any number of chars with expression prefix syntax. This includes both characters in the expression prefix syntax class, and characters with the `p' flag.
Here are several functions for parsing and scanning balanced expressions. The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See section Moving over Balanced Expressions, for convenient higher-level functions for moving over balanced expressions.
Function: parse-partial-sexp start limit &optional target-depth stop-before state stop-comment
This function parses an expression in the current buffer starting at start, not scanning past limit. Parsing stops at limit or when certain criteria described below are met; point is set to the location where parsing stops. The value returned is a description of the status of the parse at the point where it stops.
Normally, start is assumed to be the top level of an expression
to be parsed, such as the beginning of a function definition.
Alternatively, you might wish to resume parsing in the middle of an
expression. To do this, you must provide a state argument that
describes the initial status of parsing. If state is omitted (or
nil), parsing assumes that start is the beginning of a new
parse at level 0.
If the third argument target-depth is non-nil, parsing
stops if the depth in parentheses becomes equal to target-depth.
The depth starts at 0, or at whatever is given in state.
If the fourth argument stop-before is non-nil, parsing
stops when it comes to any character that starts a sexp. If
stop-comment is non-nil, parsing stops when it comes to the
start of a comment.
The fifth argument state is a seven-element list of the same
form as the value of this function, described below. The return value
of one call may be used to initialize the state of the parse on another
call to parse-partial-sexp.
The result is a list of seven elements describing the final state of the parse:
nil if none.
nil if none.
nil if inside a string. (It is the character that will
terminate the string.)
t if inside a comment.
t if point is just after a quote character.
Elements 1, 4, 5, and 6 are significant in the argument state.
This function is used to determine how to indent lines in programs written in languages that have nested parentheses.
Function: scan-lists from count depth
This function scans forward count balanced parenthetical groupings from character number from. It returns the character number of the position thus found.
If depth is nonzero, parenthesis depth counting begins from that
value. The only candidates for stopping are places where the depth in
parentheses becomes zero; scan-lists counts count such
places and then stops. Thus, a positive value for depth means go
out levels of parenthesis.
Comments are ignored if parse-sexp-ignore-comments is non-nil.
If the beginning or end of the buffer (or its accessible portion) is
reached and the depth is not zero, an error is signaled. If the depth
is zero but the count is not used up, nil is returned.
Function: scan-sexps from count
Scan from character number from by count balanced expressions. It returns the character number of the position thus found.
Comments are ignored if parse-sexp-ignore-comments is non-nil.
If the beginning or end of (the accessible part of) the buffer is
reached in the middle of a parenthetical grouping, an error is
signaled. If the beginning or end is reached between groupings but
before count is used up, nil is returned.
Variable: parse-sexp-ignore-comments
If the value is non-nil, then comments are treated as
whitespace by the functions in this section and by forward-sexp.
In older Emacs versions, this feature worked only when the comment
terminator is something like `*/', and appears only to end a
comment. In languages where newlines terminate comments, it was
necessary make this variable nil, since not every newline is the
end of a comment. This limitation no longer exists.
You can use forward-comment to move forward or backward over
one comment or several comments.
Function: forward-comment count
This function moves point forward across count comments (backward, if count is negative). If it finds anything other than a comment or whitespace, it stops, leaving point at the place where it stopped. It also stops after satisfying count.
To move forward over all comments and whitespace following point, use
(forward-comment (buffer-size)). (buffer-size) is a good
argument to use, because the number of comments to skip cannot exceed
that many.
Each of the major modes in Emacs has its own syntax table. Here are several of them:
Function: standard-syntax-table
This function returns the standard syntax table, which is the syntax table used in Fundamental mode.
Variable: text-mode-syntax-table
The value of this variable is the syntax table used in Text mode.
Variable: c-mode-syntax-table
The value of this variable is the syntax table in use in C-mode buffers.
Variable: emacs-lisp-mode-syntax-table
The value of this variable is the syntax table used in Emacs Lisp mode
by editing commands. (It has no effect on the Lisp read
function.)
Each element of a syntax table is an integer that translates into the full meaning of the entry: class, possible matching character, and flags. However, it is not common for a programmer to work with the entries directly in this form since the Lisp-level syntax table functions usually work with syntax descriptors (see section Syntax Descriptors).
The low 8 bits of each element of a syntax table indicates the syntax class.
The next 8 bits are the matching opposite parenthesis (if the character has parenthesis syntax); otherwise, they are not meaningful. The next 6 bits are the flags.
An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.
The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.
An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol's name is the abbreviation. Its value is the expansion; its function definition is the hook; its property list cell contains the use count, the number of times the abbreviation has been expanded. Because these symbols are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, they will never be used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. See section Creating and Interning Symbols.
For the user-level commands for abbrevs, see section 'Abbrev Mode' in The GNU Emacs Manual.
Abbrev mode is a minor mode controlled by the value of the variable
abbrev-mode.
Variable: abbrev-mode
A non-nil value of this variable turns on the automatic expansion
of abbrevs when their abbreviations are inserted into a buffer.
If the value is nil, abbrevs may be defined, but they are not
expanded automatically.
This variable automatically becomes local when set in any fashion.
Variable: default-abbrev-mode
This is the value abbrev-mode for buffers that do not override it.
This is the same as (default-value 'abbrev-mode).
This section describes how to create and manipulate abbrev tables.
Function: make-abbrev-table
This function creates and returns a new, empty abbrev table--an obarray
containing no symbols. It is a vector filled with nils.
Function: clear-abbrev-table table
This function undefines all the abbrevs in abbrev table table,
leaving it empty. The function returns nil.
Function: define-abbrev-table tabname definitions
This function defines tabname (a symbol) as an abbrev table name,
i.e., as a variable whose value is an abbrev table. It defines abbrevs
in the table according to definitions, a list of elements of the
form (abbrevname expansion hook
usecount). The value is always nil.
Variable: abbrev-table-name-list
This is a list of symbols whose values are abbrev tables.
define-abbrev-table adds the new abbrev table name to this list.
Function: insert-abbrev-table-description name &optional human
This function inserts before point a description of the abbrev table
named name. The argument name is a symbol whose value is an
abbrev table. The value is always nil.
If human is non-nil, a human-oriented description is
inserted. Otherwise the description is a Lisp expression--a call to
define-abbrev-table which would define name exactly as it
is currently defined.
These functions define an abbrev in a specified abbrev table.
define-abbrev is the low-level basic function, while
add-abbrev is used by commands that ask for information from the
user.
Function: add-abbrev table type arg
This function adds an abbreviation to abbrev table table. The
argument type is a string describing in English the kind of abbrev
this will be (typically, "global" or "mode-specific");
this is used in prompting the user. The argument arg is the
number of words in the expansion.
The return value is the symbol which internally represents the new
abbrev, or nil if the user declines to redefine an existing
abbrev.
Function: define-abbrev table name expansion hook
This function defines an abbrev in table named name, to expand to expansion, and call hook. The return value is an uninterned symbol which represents the abbrev inside Emacs; its name is name.
The argument name should be a string. The argument
expansion should be a string, or nil, to undefine the
abbrev.
The argument hook is a function or nil. If hook is
non-nil, then it is called with no arguments after the abbrev is
replaced with expansion; point is located at the end of
expansion.
The use count of the abbrev is initialized to zero.
User Option: only-global-abbrevs
If this variable is non-nil, it means that the user plans to use
global abbrevs only. This tells the commands that define mode-specific
abbrevs to define global ones instead. This variable does not alter the
functioning of the functions in this section; it is examined by their
callers.
A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents. Therefore, you can load the file
with load (see section How Programs Do Loading). However, the
function quietly-read-abbrev-file is provided as a more
convenient interface.
User-level facilities such as save-some-buffers can save
abbrevs in a file automatically, under the control of variables
described here.
User Option: abbrev-file-name
This is the default file name for reading and saving abbrevs.
Function: quietly-read-abbrev-file filename
This function reads abbrev definitions from a file named filename,
previously written with write-abbrev-file. If filename is
nil, the file specified in abbrev-file-name is used.
save-abbrevs is set to t so that changes will be saved.
This function does not display any messages. It returns nil.
User Option: save-abbrevs
A non-nil value for save-abbrev means that Emacs should
save abbrevs when files are saved. abbrev-file-name specifies
the file to save the abbrevs in.
Variable: abbrevs-changed
This variable is set non-nil by defining or altering any
abbrevs. This serves as a flag for various Emacs commands to offer to
save your abbrevs.
Command: write-abbrev-file filename
Save all abbrev definitions, in all abbrev tables, in the file
filename, in the form of a Lisp program which when loaded will
define the same abbrevs. This function returns nil.
Abbrevs are usually expanded by commands for interactive use,
including self-insert-command. This section describes the
subroutines used in writing such functions, as well as the variables
they use for communication.
Function: abbrev-symbol abbrev &optional table
This function returns the symbol representing the abbrev named
abbrev. The value returned is nil if that abbrev is not
defined. The optional second argument table is the abbrev table
to look it up in. By default, this function tries first the current
buffer's local abbrev table, and second the global abbrev table.
User Option: abbrev-all-caps
When this is set non-nil, an abbrev entered entirely in upper
case is expanded using all upper case. Otherwise, an abbrev entered
entirely in upper case is expanded by capitalizing each word of the
expansion.
Function: abbrev-expansion abbrev &optional table
This function returns the string that abbrev would expand into (as defined by the abbrev tables used for the current buffer). The optional argument table specifies the abbrev table to use; if it is specified, the abbrev is looked up in that table only.
Variable: abbrev-start-location
This is the buffer position for expand-abbrev to use as the start
of the next abbrev to be expanded. (nil means use the word
before point instead.) abbrev-start-location is set to
nil each time expand-abbrev is called. This variable is
also set by abbrev-prefix-mark.
Variable: abbrev-start-location-buffer
The value of this variable is the buffer for which
abbrev-start-location has been set. Trying to expand an abbrev
in any other buffer clears abbrev-start-location. This variable
is set by abbrev-prefix-mark.
Variable: last-abbrev
This is the abbrev-symbol of the last abbrev expanded. This
information is left by expand-abbrev for the sake of the
unexpand-abbrev command.
Variable: last-abbrev-location
This is the location of the last abbrev expanded. This contains
information left by expand-abbrev for the sake of the
unexpand-abbrev command.
Variable: last-abbrev-text
This is the exact expansion text of the last abbrev expanded, as
results from case conversion. Its value is
nil if the abbrev has already been unexpanded. This
contains information left by expand-abbrev for the sake of the
unexpand-abbrev command.
Variable: pre-abbrev-expand-hook
This is a normal hook whose functions are executed, in sequence, just before any expansion of an abbrev. See section Hooks. Since it is a normal hook, the hook functions receive no arguments. However, they can find the abbrev to be expanded by looking in the buffer before point.
The following sample code shows a simple use of
pre-abbrev-expand-hook. If the user terminates an abbrev with a
punctuation character, the function issues a prompt. Thus, this hook allows
the user to decide whether the abbrev should be expanded, and to abort
expansion if it is not desired.
(add-hook 'pre-abbrev-expand-hook 'query-if-not-space) ;; This is the function invoked bypre-abbrev-expand-hook. ;; If the user terminated the abbrev with a space, the function does ;; nothing (that is, it returns so that the abbrev can expand). If the ;; user entered some other character, this function asks whether ;; expansion should continue. ;; If the user enters the prompt with y, the function returns ;;nil(because of thenotfunction), but that is ;; acceptable; the return value has no effect on expansion. (defun query-if-not-space () (if (/= ?\ (preceding-char)) (if (not (y-or-n-p "Do you want to expand this abbrev? ")) (error "Not expanding this abbrev"))))
Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.
Variable: global-abbrev-table
This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table.
Variable: local-abbrev-table
The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer.
Variable: fundamental-mode-abbrev-table
This is the local abbrev table used in Fundamental mode. It is the local abbrev table in all buffers in Fundamental mode.
Variable: text-mode-abbrev-table
This is the local abbrev table used in Text mode.
Variable: c-mode-abbrev-table
This is the local abbrev table used in C mode.
Variable: lisp-mode-abbrev-table
This is the local abbrev table used in Lisp mode and Emacs Lisp mode.
In the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.
A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a "process". Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.
Function: processp object
This function returns t if object is a process,
nil otherwise.
There are three functions that create a new subprocess in which to run
a program. One of them, start-process, creates an asynchronous
process and returns a process object (see section Creating an Asynchronous Process).
The other two, call-process and call-process-region,
create a synchronous process and do not return a process object
(see section Creating a Synchronous Process).
Synchronous and asynchronous processes are explained in following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.
In all cases, the function's program argument specifies the
program to be run. An error is signaled if the file is not found or
cannot be executed. The actual file containing the program is found by
following normal system rules: if the file name is absolute, then the
program must be found in the specified file; if the name is relative,
then the directories in exec-path are searched sequentially for a
suitable file. The variable exec-path is initialized when Emacs
is started, based on the value of the environment variable PATH.
The standard file name constructs, `~', `.', and `..',
are interpreted as usual in exec-path, but environment variable
substitutions (`$HOME', etc.) are not recognized; use
substitute-in-file-name to perform them (see section Functions that Expand Filenames).
Each of the subprocess-creating functions has a buffer-or-name
argument which specifies where the standard output from the program will
go. If buffer-or-name is nil, that says to discard the
output unless a filter function handles it. (See section Process Filter Functions,
and section Reading and Printing Lisp Objects.) Normally, you should avoid having multiple
processes send output to the same buffer because their output would be
intermixed randomly.
All three of the subprocess-creating functions have a &rest
argument, args. The args must all be strings, and they are
supplied to program as separate command line arguments. Wildcard
characters and other shell constructs are not allowed in these strings,
since they are passed directly to the specified program.
Please note: the argument program contains only the name of the program; it may not contain any command-line arguments. Such arguments must be provided via args.
The subprocess gets its current directory from the value of
default-directory (see section Functions that Expand Filenames).
The subprocess inherits its environment from Emacs; but you can
specify overrides for it with process-environment. See section Operating System Environment.
Variable: exec-directory
The value of this variable is the name of a directory (a string) that
contains programs that come with GNU Emacs, that are intended for Emacs
to invoke. The program wakeup is an example of such a program;
the display-time command uses it to get a reminder once per
minute.
The default value is the name of a directory whose name ends in
`arch-lib'. We call the directory `emacs/arch-lib', since its
name usually ends that way. We sometimes refer to "the directory
`emacs/arch-lib'," when strictly speaking we ought to say, "the
directory named by the variable exec-directory." Most of the
time, there is no difference.
(In earlier Emacs versions, prior to version 19, these files lived in the directory `emacs/etc' instead of in `emacs/arch-lib'.)
User Option: exec-path
The value of this variable is a list of directories to search for
programs to run in subprocesses. Each element is either the name of a
directory (i.e., a string), or nil, which stands for the default
directory (which is the value of default-directory).
The value of exec-path is used by call-process and
start-process when the program argument is not an absolute
file name.
After a synchronous process is created, Emacs waits for the
process to terminate before continuing. Starting Dired is an example of
this: it runs ls in a synchronous process, then modifies the
output slightly. Because the process is synchronous, the entire
directory listing arrives in the buffer before Emacs tries to do
anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing C-g, and the process is killed by sending
it a SIGKILL signal. See section Quitting.
The synchronous subprocess functions return nil in version 18.
In version 19, they will return an indication of how the process
terminated.
Function: call-process program &optional infile buffer-or-name display &rest args
This function calls program in a separate process and waits for it to finish.
The standard input for the process comes from file infile if
infile is not nil and from `/dev/null' otherwise. The
process output gets inserted in buffer buffer-or-name before point,
if that argument names a buffer. If buffer-or-name is t,
output is sent to the current buffer; if buffer-or-name is
nil, output is discarded.
If buffer-or-name is the integer 0, call-process returns
nil immediately and discards any output. In this case, the
process is not truly synchronous, since it can run in parallel with
Emacs; but you can think of it as synchronous in that Emacs is
essentially finished with the subprocess as soon as this function
returns.
If display is non-nil, then call-process redisplays
the buffer as output is inserted. Otherwise the function does no
redisplay, and the results become visible on the screen only when Emacs
redisplays that buffer in the normal course of events.
The remaining arguments, args, are strings that are supplied as the command line arguments for the program.
The value returned by call-process (unless you told it not to
wait) indicates the reason for process termination. A number gives the
exit status of the subprocess; 0 means success, and any other value
means failure. If the process terminated with a signal,
call-process returns a string describing the signal.
The examples below are both run with the buffer `foo' current.
(call-process "pwd" nil t)
=> nil
---------- Buffer: foo ----------
/usr/user/lewis/manual
---------- Buffer: foo ----------
(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
=> nil
---------- Buffer: bar ----------
lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
---------- Buffer: bar ----------
The dired-readin function contains a good example of the use of
call-process:
(call-process "ls" nil buffer nil dired-listing-switches dirname)
Function: call-process-region start end program &optional delete buffer-or-name display &rest args
This function sends the text between start to end as
standard input to a process running program. It deletes the text
sent if delete is non-nil, which may be useful when the
output is going to be inserted back in the current buffer.
If buffer-or-name names a buffer, the output is inserted in that
buffer at point. If buffer-or-name is t, the output is
sent to the current buffer. If buffer-or-name is nil, the
output is discarded. If buffer-or-name is the integer 0, the
output is discarded and call-process returns nil
immediately, just as call-process would.
If display is non-nil, then call-process-region
redisplays the buffer as output is inserted. Otherwise the function
does no redisplay, and the results become visible on the screen only
when Emacs redisplays that buffer in the normal course of events.
The remaining arguments, args, are strings that are supplied as the command line arguments for the program.
The return value of call-process-region is just like that of
call-process: nil if you told it to return without
waiting; otherwise, a number or string which indicates how the
subprocess terminated.
In the following example, we use call-process-region to run the
cat utility, with standard input being the first five characters
in buffer `foo' (the word `input'). cat copies its
standard input into its standard output. Since the argument
buffer-or-name is t, this output is inserted in the current
buffer.
---------- Buffer: foo ----------
input-!-
---------- Buffer: foo ----------
(call-process-region 1 6 "cat" nil t)
=> nil
---------- Buffer: foo ----------
inputinput-!-
---------- Buffer: foo ----------
The shell-command-on-region command uses
call-process-region like this:
(call-process-region
start end
shell-file-name ; Name of program.
nil ; Do not delete region.
buffer ; Send output to buffer.
nil ; No redisplay during output.
"-c" command) ; Arguments for the shell.
After an asynchronous process is created, Emacs and the Lisp
program can continue running immediately. The process may thereafter
run in parallel with Emacs, and the two may communicate with each other
using the functions described in following sections. Here we describe
how to create an asynchronous process, with start-process.
Function: start-process name buffer-or-name program &rest args
This function creates a new asynchronous subprocess and starts the program program running in it. It returns a process object that stands for the new subprocess for Emacs Lisp programs. The argument name specifies the name for the process object; if a process with this name already exists, then name is modified (by adding `<1>', etc.) to be unique. The buffer buffer-or-name is the buffer to associate with the process.
The remaining arguments, args, are strings that are supplied as the command line arguments for the program.
In the example below, the first process is started and runs (rather, sleeps) for 100 seconds. Meanwhile, the second process is started, given the name `my-process<1>' for the sake of uniqueness. It inserts the directory listing at the end of the buffer `foo', before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100")
=> #<process my-process>
(start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
=> #<process my-process<1>>
---------- Buffer: foo ----------
total 2
lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs
-rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon
Process my-process<1> finished
Process my-process finished
---------- Buffer: foo ----------
Function: start-process-shell-command name buffer-or-name command &rest command-args
This function is like start-process except that it uses a shell
to execute the specified command. The argument command is a shell
command name, and command-args are the arguments for the shell
command.
Variable: process-connection-type
This variable controls the type of device used to communicate with
asynchronous subprocesses. If it is nil, then pipes are used.
If it is t, then PTYs are used (or pipes if PTYs are
not supported).
PTYs are usually preferable for processes visible to the user, as in Shell mode, because they allow job control (C-c, C-z, etc.) to work between the process and its children whereas pipes do not. For subprocesses used for internal purposes by programs, it is often better to use a pipe, because they are more efficient. In addition, the total number of PTYs is limited on many systems and it is good not to waste them.
The value process-connection-type is used when
start-process is called, so in order to change it for just one
call of start-process, temporarily rebind it with let.
(let ((process-connection-type nil)) ; Use a pipe. (start-process ...))
Deleting a process disconnects Emacs immediately from the subprocess, and removes it from the list of active processes. It sends a signal to the subprocess to make the subprocess terminate, but this is not guaranteed to happen immediately. (The process object itself continues to exist as long as other Lisp objects point to it.)
You can delete a process explicitly at any time. Processes are deleted automatically after they terminate, but not necessarily right away. If you delete a terminated process explicitly before it is deleted automatically, no harm results.
Variable: delete-exited-processes
This variable controls automatic deletion of processes that have
terminated (due to calling exit or to a signal). If it is
nil, then they continue to exist until the user runs
list-processes. Otherwise, they are deleted immediately after
they exit.
Function: delete-process name
This function deletes the process associated with name. The
argument name may be a process, the name of a process, a buffer,
or the name of a buffer. The subprocess is killed with a SIGHUP
signal.
(delete-process "*shell*")
=> nil
Function: process-kill-without-query process
This function declares that Emacs need not query the user if
process is still running when Emacs is exited. The process will
be deleted silently. The value is t.
(process-kill-without-query (get-process "shell"))
=> t
Several functions return information about processes.
list-processes is provided for interactive use.
Command: list-processes
This command displays a listing of all living processes. (Any processes
listed as `Exited' or `Signaled' are actually eliminated after
the listing is made.) This function returns nil.
Function: process-list
This function returns a list of all processes that have not been deleted.
(process-list)
=> (#<process display-time> #<process shell>)
Function: get-process name
This function returns the process named name, or nil if
there is none. An error is signaled if name is not a string.
(get-process "shell")
=> #<process shell>
Function: process-command process
This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program.
(process-command (get-process "shell"))
=> ("/bin/csh" "-i")
Function: process-exit-status process
This function returns the exit status of process or the signal
number that killed it. (Use the result of process-status to
determine which of those it is.) If process has not yet
terminated, the value is 0.
Function: process-id process
This function returns the PID of process. This is an integer which distinguishes the process process from all other processes running on the same computer at the current time. The PID of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists.
Function: process-name process
This function returns the name of process.
Function: process-status process-name
This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, a process name (string) or a buffer name (string).
The possible values for an actual subprocess are:
run
stop
exit
signal
open
closed
nil
(process-status "shell")
=> run
(process-status (get-buffer "*shell*"))
=> run
x
=> #<process xx<1>>
(process-status x)
=> exit
For a network connection, process-status returns one of the symbols
open or closed. The latter means that the other side
closed the connection, or Emacs did delete-process.
In earlier Emacs versions (prior to version 19), the status of a network
connection was run if open, and exit if closed.
Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the "standard input" of the subprocess.
Some operating systems have limited space for buffered input in a PTY. On these systems, the subprocess will cease to read input correctly if you send an input line longer than the system can handle. You cannot avoid the problem by breaking the input into pieces and sending them separately, for the operating system will still have to put all the pieces together in the input buffer before it lets the subprocess read the line. The only solution is to put the input in a temporary file, and send the process a brief command to read that file.
Function: process-send-string process-name string
This function sends process-name the contents of string as standard input. The argument process-name must be a process or the name of a process.
The function returns nil.
(process-send-string "shell<1>" "ls\n")
=> nil
---------- Buffer: *shell* ----------
...
introduction.texi syntax-tables.texi~
introduction.texi~ text.texi
introduction.txt text.texi~
...
---------- Buffer: *shell* ----------
Command: process-send-region process-name start end
This function sends the text in the region defined by start and end as standard input to process-name, which is a process or a process name.
An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)
Function: process-send-eof &optional process-name
This function makes process-name see an end-of-file in its input. The EOF comes after any text already sent to it.
If process-name is not supplied, or if it is nil, then
this function sends the EOF to the current buffer's process. An
error is signaled if the current buffer has no process.
The function returns process-name.
(process-send-eof "shell")
=> "shell"
Sending a signal to a subprocess is a way of interrupting its
activities. There are several different signals, each with its own
meaning. For example, the signal SIGINT means that the user
has typed C-c, or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop or resume execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.
The set of signals and their names is defined by the operating system; Emacs has facilities for sending only a few of the signals that are defined. Emacs can send signals only to its own subprocesses.
You can send signals explicitly by calling the functions in this
section. Emacs also sends signals automatically at certain times:
killing a buffer sends a SIGHUP signal to all its associated
processes; killing Emacs sends a SIGHUP signal to all remaining
processes. (SIGHUP is a signal that usually indicates that the
user hung up the phone.)
Each of the signal-sending functions takes two optional arguments: process-name and current-group.
The argument process-name must be either a process, the name of
one, or nil. If it is nil, the process defaults to the
process associated with the current buffer. An error is signaled if
process-name does not identify a process.
The argument current-group is a flag that makes a difference
when you are running a job-control shell as an Emacs subprocess. If it
is non-nil, then the signal is sent to the current process-group
of the terminal which Emacs uses to communicate with the subprocess. If
the process is a job-control shell, this means the shell's current
subjob. If it is nil, the signal is sent to the process group of
the immediate subprocess of Emacs. If the subprocess is a job-control
shell, this is the shell itself.
The flag current-group has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes. For the same reason,
job-control shells won't work when a pipe is used. See
process-connection-type in section Creating an Asynchronous Process.
Function: interrupt-process &optional process-name current-group
This function interrupts the process process-name by sending the
signal SIGINT. Outside of Emacs, typing the "interrupt
character" (normally C-c on some systems, and DEL on
others) sends this signal. When the argument current-group is
non-nil, you can think of this function as "typing C-c"
on the terminal by which Emacs talks to the subprocess.
Function: kill-process &optional process-name current-group
This function kills the process process-name by sending the
signal SIGKILL. This signal kills the subprocess immediately,
and cannot be handled by the subprocess.
Function: quit-process &optional process-name current-group
This function sends the signal SIGQUIT to the process
process-name. This signal is the one sent by the "quit
character" (usually C-b or C-\) when you are not inside
Emacs.
Function: stop-process &optional process-name current-group
This function stops the process process-name by sending the
signal SIGTSTP. Use continue-process to resume its
execution.
On systems with job control, the "stop character" (usually C-z)
sends this signal (outside of Emacs). When current-group is
non-nil, you can think of this function as "typing C-z"
on the terminal Emacs uses to communicate with the subprocess.
Function: continue-process &optional process-name current-group
This function resumes execution of the process process by sending
it the signal SIGCONT. This presumes that process-name was
stopped previously.
Function: signal-process pid signal
This function sends a signal to process pid, which need not be a child of Emacs. The argument signal specifies which signal to send; it should be an integer.
There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the filter function can be called to act on the output.
A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp.
Unless the process has a filter function (see section Process Filter Functions),
its output is inserted in the associated buffer. The position to insert
the output is determined by the process-mark (see section Process Information), which is then updated to point to the end of the text
just inserted. Usually, but not always, the process-mark is at
the end of the buffer. If the process has no buffer and no filter
function, its output is discarded.
Function: process-buffer process
This function returns the associated buffer of the process process.
(process-buffer (get-process "shell"))
=> #<buffer *shell*>
Function: process-mark process
This function returns the marker which controls where additional output from the process will be inserted in the process buffer. When output is inserted, the marker is updated to point at the end of the output. This causes successive batches of output to be inserted consecutively.
If process does not insert its output into a buffer, then
process-mark returns a marker that points nowhere.
Filter functions normally should use this marker in the same fashion
as is done by direct insertion of output in the buffer. A good
example of a filter function that uses process-mark is found at
the end of the following section.
When the user is expected to enter input in the process buffer for transmission to the process, the process marker is useful for distinguishing the new input from previous output.
Function: set-process-buffer process buffer
This function sets the buffer associated with process to
buffer. If buffer is nil, the process will
not be associated with any buffer.
Function: get-buffer-process buffer-or-name
This function returns the process associated with buffer-or-name. If there are several processes associated with it, then one is chosen. (Presently, the one chosen is the one most recently created.) It is usually a bad idea to have more than one process associated with the same buffer.
(get-buffer-process "*shell*")
=> #<process shell>
If the process's buffer is killed, the actual child process is killed
with a SIGHUP signal (see section Sending Signals to Processes).
A process filter function is a function that receives the standard output from the associated process. If a process has a filter, then all output from that process, that would otherwise have been in a buffer, is passed to the filter. The process buffer is used for output from the process only when there is no filter.
A filter function must accept two arguments: the associated process and a string, which is the output. The function is then free to do whatever it chooses with the output.
A filter function runs only while Emacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output). This avoids the
timing errors that could result from running filters at random places in
the middle of other Lisp programs. You may explicitly cause Emacs to
wait, so that filter functions will run, by calling sit-for,
sleep-for or accept-process-output (see section Accepting Output from Processes). Emacs is also waiting when the command loop is reading input.
Quitting is normally inhibited within a filter function--otherwise,
the effect of typing C-g at command level or to quit a user
command would be unpredictable. If you want to permit quitting inside a
filter function, bind inhibit-quit to nil.
See section Quitting.
Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter. Such filter functions need to use set-buffer in order to
be sure to insert in that buffer. To avoid setting the current buffer
semipermanently, these filter functions must use unwind-protect
to make sure to restore the previous current buffer. They should also
update the process marker, and in some cases update the value of point.
Here is how to do these things:
(defun ordinary-insertion-filter (proc string)
(let ((old-buffer (current-buffer)))
(unwind-protect
(let (moving)
(set-buffer (process-buffer proc))
(setq moving (= (point) (process-mark proc)))
(save-excursion
;; Insert the text, moving the process-marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc))))
(set-buffer old-buffer))))
The reason to use an explicit unwind-protect rather than letting
save-excursion restore the current buffer is so as to preserve
the change in point made by goto-char.
To make the filter force the process buffer to be visible whenever new
text arrives, insert the following line just before the
unwind-protect:
(display-buffer (process-buffer proc))
To force point to move to the end of the new output no matter where
it was previously, eliminate the variable moving and call
goto-char unconditionally.
All filter functions that do regexp searching or matching should save
and restore the match data. Otherwise, a filter function that runs
during a call to sit-for might clobber the match data of the
program that called sit-for. See section The Match Data.
A filter function that writes the output into the buffer of the
process should check whether the process is still alive. If it tries to
insert into a dead buffer, it will get an error. If the buffer is dead,
(buffer-name (process-buffer process)) returns nil.
The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next.
Function: set-process-filter process filter
This function gives process the filter function filter. If
filter is nil, then the process will have no filter.
Function: process-filter process
This function returns the filter function of process, or nil
if it has none.
Here is an example of use of a filter function:
(defun keep-output (process output)
(setq kept (cons output kept)))
=> keep-output
(setq kept nil)
=> nil
(set-process-filter (get-process "shell") 'keep-output)
=> keep-output
(process-send-string "shell" "ls ~/other\n")
=> nil
kept
=> ("lewis@slug[8] % "
"FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
address.txt backup.psf kolstad.psf
backup.bib~ david.mss resume-Dec-86.mss~
backup.err david.psf resume-Dec.psf
backup.mss dland syllabus.mss
"
"#backups.mss# backup.mss~ kolstad.mss
")
Here is another, more realistic example, which demonstrates how to use the process mark to do insertion in the same fashion as is done when there is no filter function:
;; Insert input in the buffer specified by my-shell-buffer
;; and make sure that buffer is shown in some window.
(defun my-process-filter (proc str)
(let ((cur (selected-window))
(pop-up-windows t))
(pop-to-buffer my-shell-buffer)
(goto-char (point-max))
(insert str)
(set-marker (process-mark proc) (point-max))
(select-window cur)))
Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process.
Function: accept-process-output &optional process seconds millisec
This function allows Emacs to read pending output from processes. The
output is inserted in the associated buffers or given to their filter
functions. If process is non-nil then this function does
not return until some output has been received from process.
The arguments seconds and millisec let you specify timeout
periods. The former specifies a period measured in seconds and the
latter specifies one measured in milliseconds. The two time periods
thus specified are added together, and accept-process-output
returns after that much time whether or not there has been any
subprocess output.
Not all operating systems support waiting periods other than multiples of a second; on those that do not, you get an error if you specify nonzero millisec.
The function accept-process-output returns non-nil if it
did get some output, or nil if the timeout expired before output
arrived.
A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.
The string describing the event looks like one of the following:
"finished\n".
"exited abnormally with code exitcode\n".
"name-of-signal\n".
"name-of-signal (core dumped)\n".
A sentinel runs only while Emacs is waiting (e.g., for terminal input,
or for time to elapse, or for process output). This avoids the timing
errors that could result from running them at random places in the
middle of other Lisp programs. You may explicitly cause Emacs to wait,
so that sentinels will run, by calling sit-for, sleep-for
or accept-process-output (see section Accepting Output from Processes). Emacs is
also waiting when the command loop is reading input.
Quitting is normally inhibited within a sentinel--otherwise, the
effect of typing C-g at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a
sentinel, bind inhibit-quit to nil. See section Quitting.
A sentinel that writes the output into the buffer of the process
should check whether the process is still alive. If it tries to insert
into a dead buffer, it will get an error. If the buffer is dead,
(buffer-name (process-buffer process)) returns nil.
All sentinels that do regexp searching or matching should save and
restore the match data. Otherwise, a sentinel that runs during a call
to sit-for might clobber the match data of the program that
called sit-for. See section The Match Data.
Function: set-process-sentinel process sentinel
This function associates sentinel with process. If
sentinel is nil, then the process will have no sentinel.
The default behavior when there is no sentinel is to insert a message in
the process's buffer when the process status changes.
(defun msg-me (process event)
(princ
(format "Process: %s had the event `%s'" process event)))
(set-process-sentinel (get-process "shell") 'msg-me)
=> msg-me
(kill-process (get-process "shell"))
-| Process: #<process shell> had the event `killed'
=> #<process shell>
Function: process-sentinel process
This function returns the sentinel of process, or nil if it
has none.
Function: waiting-for-user-input-p
While a sentinel or filter function is running, this function returns
non-nil if Emacs was waiting for keyboard input from the user at
the time the sentinel or filter function was called, nil if it
was not.
You can use a transaction queue for more convenient communication
with subprocesses using transactions. First use tq-create to
create a transaction queue communicating with a specified process. Then
you can call tq-enqueue to send a transaction.
Function: tq-create process
This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server possibly on another machine.
Function: tq-enqueue queue question regexp closure fn
This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.
The argument question is the outgoing message which starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.
The argument regexp is a regular expression to match the entire
answer; that's how tq-enqueue tells where the answer ends.
The return value of tq-enqueue itself is not meaningful.
Function: tq-close queue
Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.
Transaction queues are implemented by means of a filter function. See section Process Filter Functions.
Emacs Lisp programs can open TCP connections to other processes on the
same machine or other machines. A network connection is handled by Lisp
much like a subprocess, and is represented by a process object.
However, the process you are communicating with is not a child of the
Emacs process, so you can't kill it or send it signals. All you can do
is send and receive data. delete-process closes the connection,
but does not kill the process at the other end; that process must decide
what to do about closure of the connection.
You can distinguish process objects representing network connections
from those representing subprocesses with the process-status
function. See section Process Information.
Function: open-network-stream name buffer-or-name host service
This function opens a TCP connection for a service to a host. It returns a process object to represent the connection.
The name argument specifies the name for the process object. It is modified as necessary to make it unique.
The buffer-or-name argument is the buffer to associate with the
connection. Output from the connection is inserted in the buffer,
unless you specify a filter function to handle the output. If
buffer-or-name is nil, it means that the connection is not
associated with any buffer.
The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer).
This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output and flow control.
See section Building Emacs, for related information. See also section Emacs Display, for additional operating system status information pertaining to the terminal and the screen.
This section describes what Emacs does when it is started, and how you can customize these actions.
The order of operations performed (in `startup.el') by Emacs when it is started up is as follows:
before-init-hook.
inhibit-default-init is
non-nil. (This is not done in `-batch' mode or if `-q'
was specified on command line.)
after-init-hook.
term-setup-hook.
window-setup-hook. See section Window Systems.
inhibit-startup-message is non-nil.
This display is also inhibited in batch mode, and if the current buffer is not `*scratch*'.
User Option: inhibit-startup-message
This variable inhibits the initial startup messages (the nonwarranty,
etc.). If it is non-nil, then the messages are not printed.
This variable exists so you can set it in your personal init file, once you are familiar with the contents of the startup message. Do not set this variable in the init file of a new user, or in a way that affects more than one user, because that would prevent new users from receiving the information they are supposed to see.
When you start Emacs, it normally attempts to load the file `.emacs' from your home directory. This file, if it exists, must contain Lisp code. It is called your init file. The command line switches `-q' and `-u' can be used to control the use of the init file; `-q' says not to load an init file, and `-u' says to load a specified user's init file instead of yours. See section 'Entering Emacs' in The GNU Emacs Manual.
Emacs may also have a default init file, which is the library
named `default.el'. Emacs finds the `default.el' file through
the standard search path for libraries (see section How Programs Do Loading). The Emacs distribution does not have any such file; you may
create one at your site for local customizations. If the default init
file exists, it is loaded whenever you start Emacs, except in batch mode
or if `-q' is specified. But your own personal init file, if any,
is loaded first; if it sets inhibit-default-init to a
non-nil value, then Emacs will not subsequently load the
`default.el' file.
If there is a great deal of code in your `.emacs' file, you
should move it into another file named `something.el',
byte-compile it (see section Byte Compilation), and make your `.emacs'
file load the other file using load (see section Loading).
See section 'Init File Examples' in The GNU Emacs Manual, for examples of how to make various commonly desired customizations in your `.emacs' file.
User Option: inhibit-default-init
This variable prevents Emacs from loading the default initialization
library file for your session of Emacs. If its value is non-nil,
then the default library is not loaded. The default value is
nil.
Variable: before-init-hook
Variable: after-init-hook
These two normal hooks are run just before, and just after, loading of the user's init file or `default.el'.
Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal. For a terminal type named termtype,
the library is called `term/termtype'. Emacs finds the file
by searching the load-path directories as it does for other
files, and trying the `.elc' and `.el' suffixes. Normally,
terminal-specific Lisp library is located in `emacs/lisp/term', a
subdirectory of the `emacs/lisp' directory in which most Emacs Lisp
libraries are kept.
The library's name is constructed by concatenating the value of the
variable term-file-prefix and the terminal type. Normally,
term-file-prefix has the value "term/"; changing this
is not recommended.
The usual function of a terminal-specific library is to enable special
keys to send sequences that Emacs can recognize. It may also need to
set or add to function-key-map if the Termcap entry does not
fully explain what should go in it. See section Terminal Input.
When the name of the terminal type contains a hyphen, only the part of
the name before the first hyphen is significant in choosing the library
name. Thus, terminal types `aaa-48' and `aaa-30-rv' both use
the `term/aaa' library. If necessary, the library can evaluate
(getenv "TERM") to find the full name of the terminal
type.
Your `.emacs' file can prevent the loading of the
terminal-specific library by setting the variable
term-file-prefix to nil. This feature is very useful when
experimenting with your own peculiar customizations.
You can also arrange to override some of the actions of the
terminal-specific library by setting the variable
term-setup-hook. This is a normal hook which Emacs runs using
run-hooks at the end of Emacs initialization, after loading both
your `.emacs' file and any terminal-specific libraries. You can
use this variable to define initializations for terminals that do not
have their own libraries. See section Hooks.
Variable: term-file-prefix
If the term-file-prefix variable is non-nil, Emacs loads
a terminal-specific initialization file as follows:
(load (concat term-file-prefix (getenv "TERM")))
You may set the term-file-prefix variable to nil in your
`.emacs' file if you do not wish to load the
terminal-initialization file. To do this, put the following in
your `.emacs' file: (setq term-file-prefix nil).
Variable: term-setup-hook
This variable is a normal hook which Emacs runs after loading your `.emacs' file, the default initialization file (if any) and after loading terminal-specific Lisp files. arguments.
You can use term-setup-hook to override the definitions made by
a terminal-specific file.
See window-setup-hook in section Window Systems, for a related
feature.
You can use command line arguments to request various actions when you start Emacs. Since you do not need to start Emacs more than once per day, and will often leave your Emacs session running longer than that, command line arguments are hardly ever used. As a practical matter, it is best to avoid making the habit of using them, since this habit would encourage you to kill and restart Emacs unnecessarily often. These options exist for two reasons: to be compatible with other editors (for invocation by other programs) and to enable shell scripts to run specific Lisp programs.
Function: command-line
This function parses the command line which Emacs was called with, processes it, loads the user's `.emacs' file and displays the initial nonwarranty information, etc.
Variable: command-line-processed
The value of this variable is t once the command line has been
processed.
If you redump Emacs by calling dump-emacs, you may wish to set
this variable to nil first in order to cause the new dumped Emacs
to process its new command line arguments.
Variable: command-switch-alist
The value of this variable is an alist of user-defined command-line options and associated handler functions. This variable exists so you can add elements to it.
A command line option is an argument on the command line of the form:
-option
The elements of the command-switch-alist look like this:
(option . handler-function)
The handler-function is called to handle option and receives the option name as its sole argument.
In some cases, the option is followed in the command line by an
argument. In these cases, the handler-function can find all the
remaining command-line arguments in the variable
command-line-args-left. (The entire list of command-line
arguments is in command-line-args.)
The command line arguments are parsed by the command-line-1
function in the `startup.el' file. See also section 'Command Line Switches and Arguments' in The GNU Emacs Manual.
Variable: command-line-args
The value of this variable is the arguments passed by the shell to Emacs, as a list of strings.
There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. As a practical matter, you seldom kill Emacs--only when you are about to log out. Suspending is much more common.
Killing Emacs means ending the execution of the Emacs process. The parent process normally resumes control.
All the information in the Emacs process, aside from files that have been saved, is lost when the Emacs is killed. Because killing Emacs inadvertently can lose a lot of work, Emacs queries for confirmation before actually terminating if you have buffers that need saving or subprocesses that are running.
Function: kill-emacs &optional no-query
This function exits the Emacs process and kills it.
Normally, if there are modified files or if there are running
processes, kill-emacs asks the user for confirmation before
exiting. However, if no-query is supplied and non-nil,
then Emacs exits without confirmation.
If no-query is an integer, then it is used as the exit status of the Emacs process. (This is useful primarily in batch operation; see section Batch Mode.)
If no-query is a string, its contents are stuffed into the terminal input buffer so that the shell (or whatever program next reads input) can read them.
Variable: kill-emacs-hook
This variable is a normal hook (a list of functions); the first thing
kill-emacs does is to run this hook with run-hooks. That
calls each of the functions in the list, with no arguments.
Suspending Emacs means stopping Emacs temporarily and returning
control to its superior process, which is usually the shell. This
allows you to resume editing later in the same Emacs process, with the
same buffers, the same kill ring, the same undo history, and so on. To
resume Emacs, use the appropriate command in the parent shell--most
likely fg.
Some operating systems do not support suspension of jobs; on these systems, "suspension" actually creates a new shell temporarily as a subprocess of Emacs. Then you would exit the shell to return to Emacs.
Suspension is not useful with window systems such as X, because the Emacs job may not have a parent that can resume it again, and in any case you can give input to some other job such as a shell merely by moving to a different window. Therefore, suspending is not allowed when Emacs is an X client.
Function: suspend-emacs string
This function stops Emacs and returns to the superior process. It
returns nil.
If string is non-nil, its characters are sent to be read
as terminal input by Emacs's superior shell. The characters in
string are not echoed by the superior shell; only the results
appear.
Before suspending, suspend-emacs runs the normal hook
suspend-hook. In Emacs version 18, suspend-hook was not a
normal hook; its value was a single function, and if its value was
non-nil, then suspend-emacs returned immediately without
actually suspending anything.
After the user resumes Emacs, it runs the normal hook
suspend-resume-hook using run-hooks. See section Hooks.
The next redisplay after resumption will redraw the entire screen,
unless the variable no-redraw-on-reenter is non-nil
(see section Refreshing the Screen).
In the following example, note that `pwd' is not echoed after Emacs is suspended. But it is read and executed by the shell.
(suspend-emacs)
=> nil
(add-hook 'suspend-hook
(function (lambda ()
(or (y-or-n-p
"Really suspend? ")
(error "Suspend cancelled")))))
=> (lambda nil
(or (y-or-n-p "Really suspend? ")
(error "Suspend cancelled")))
(add-hook 'suspend-resume-hook
(function (lambda () (message "Resumed!"))))
=> (lambda nil (message "Resumed!"))
(suspend-emacs "pwd")
=> nil
---------- Buffer: Minibuffer ----------
Really suspend? y
---------- Buffer: Minibuffer ----------
---------- Parent Shell ----------
lewis@slug[23] % /user/lewis/manual
lewis@slug[24] % fg
---------- Echo Area ----------
Resumed!
Variable: suspend-hook
This variable is a normal hook run before suspending.
Variable: suspend-resume-hook
This variable is a normal hook run after suspending.
Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's UID, and so on.
Variable: system-type
The value of this variable is a symbol indicating the type of operating system Emacs is operating on. Here is a table of the symbols for the operating systems that Emacs can run on up to version 19.1.
aix-v3
berkeley-unix
hpux
irix
rtu
unisoft-unix
usg-unix-v
vax-vms
xenix
We do not wish to add new symbols to make finer distinctions unless it is absolutely necessary! In fact, it would be nice to eliminate some of these alternatives in the future.
Function: system-name
This function returns the name of the machine you are running on.
(system-name)
=> "prep.ai.mit.edu"
Function: getenv var
This function returns the value of the environment variable var,
as a string. If the variable process-environment specifies a
value for var, that overrides the actual environment.
(getenv "USER")
=> "lewis"
lewis@slug[10] % printenv
PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
USER=lewis
TERM=ibmapa16
SHELL=/bin/csh
HOME=/user/lewis
Command: setenv variable value
This command sets the value of the environment variable named
variable to value. Both arguments should be strings. This
works by modifying process-environment; binding that variable
with let is also reasonable practice.
Variable: process-environment
This variable is a list of strings to append to the environment of
processes as they are created. Each string assigns a value to a shell
environment variable. (This applies both to asynchronous and
synchronous processes.) The function getenv also looks at this
variable.
process-environment
=> ("l=/usr/stanford/lib/gnuemacs/lisp"
"PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
"USER=lewis"
"TERM=ibmapa16"
"SHELL=/bin/csh"
"HOME=/user/lewis")
Function: load-average
This function returns the current 1 minute, 5 minute and 15 minute load averages in a list. The values are integers that are 100 times the system load averages. (The load averages indicate the number of processes trying to run.)
(load-average)
=> (169 48 36)
lewis@rocky[5] % uptime
11:55am up 1 day, 19:37, 3 users,
load average: 1.69, 0.48, 0.36
Function: setprv privilege-name &optional setp getprv
This function sets or resets a VMS privilege. (It does not exist on
Unix.) The first arg is the privilege name, as a string. The second
argument, setp, is t or nil, indicating whether the
privilege is to be turned on or off. Its default is nil. The
function returns t if success, nil if not.
If the third argument, getprv, is non-nil, setprv
does not change the privilege, but returns t or nil
indicating whether the privilege is currently enabled.
Function: user-login-name
This function returns the name under which the user is logged in. This is based on the effective UID, not the real UID.
(user-login-name)
=> "lewis"
Function: user-real-login-name
This function returns the name under which the user logged in.
This is based on the real UID, not the effective UID. This
differs from user-login-name only when running with the setuid
bit.
Function: user-full-name
This function returns the full name of the user.
(user-full-name)
=> "Bil Lewis"
Function: user-real-uid
This function returns the real UID of the user.
(user-real-uid)
=> 19
Function: user-uid
This function returns the effective UID of the user.
This section explains how to determine the current time and the time zone.
Function: current-time-string &optional time-value
This function returns the current time and date as a humanly-readable
string. The format of the string is unvarying; the number of characters
used for each part is always the same, so you can reliably use
substring to extract pieces of it. However, it would be wise to
count the characters from the beginning of the string rather than from
the end, as additional information may be added at the end.
The argument time-value, if given, specifies a time to format
instead of the current time. The argument should be a cons cell
containing two integers, or a list whose first two elements are
integers. Thus, you can use times obtained from current-time
(see below) and from file-attributes (see section Other Information about Files).
(current-time-string)
=> "Wed Oct 14 22:21:05 1987"
Function: current-time
This function returns the system's time value as a list of three
integers: (high low microsec). The integers
high and low combine to give the number of seconds since
0:00 January 1, 1970, which is high * 2**16 + low.
The third element, microsec, gives the microseconds since the start of the current second (or 0 for systems that return time only on the resolution of a second).
The first two elements can be compared with file time values such as you
get with the function file-attributes. See section Other Information about Files.
Function: current-time-zone &optional time-value
This function returns a list describing the time zone that the user is in.
The value has the form (offset name). Here
offset is an integer giving the number of seconds ahead of UTC
(east of Greenwich). A negative value means west of Greenwich. The
second element, name is a string giving the name of the time
zone. Both elements change when daylight savings time begins or ends;
if the user has specified a time zone that does not use a seasonal time
adjustment, then the value is constant through time.
If the operating system doesn't supply all the information necessary to
compute the value, both elements of the list are nil.
The argument time-value, if given, specifies a time to analyze
instead of the current time. The argument should be a cons cell
containing two integers, or a list whose first two elements are
integers. Thus, you can use times obtained from current-time
(see below) and from file-attributes (see section Other Information about Files).
You can set up a timer to call a function at a specified future time.
Function: run-at-time time repeat function &rest args
This function arranges to call function with arguments args at time time. The argument function is a function to call later, and args are the arguments to give it when it is called. The time time is specified as a string.
Absolute times may be specified in a wide variety of formats; The form
`hour:min:sec timezone
month/day/year', where all fields are numbers, works;
the format that current-time-string returns is also allowed.
To specify a relative time, use numbers followed by units. For example:
If time is an integer, that specifies a relative time measured in seconds.
The argument repeat specifies how often to repeat the call. If
repeat is nil, there are no repetitions; function is
called just once, at time. If repeat is an integer, it
specifies a repetition period measured in seconds.
Function: cancel-timer timer
Cancel the requested action for timer, which should be a value
previously returned by run-at-time. This cancels the effect of
that call to run-at-time; the arrival of the specified time will
not cause anything special to happen.
This section describes functions and variables for recording or manipulating terminal input. See section Emacs Display, for related functions.
Function: set-input-mode interrupt flow meta quit-char
This function sets the mode for reading keyboard input. If
interrupt is non-null, then Emacs uses input interrupts. If it is
nil, then it uses CBREAK mode.
If flow is non-nil, then Emacs uses XON/XOFF (C-q,
C-s) flow control for output to terminal. This has no effect except
in CBREAK mode. See section Flow Control.
The normal setting is system dependent. Some systems always use CBREAK mode regardless of what is specified.
The argument meta controls support for input character codes
above 127. If meta is t, Emacs converts characters with
the 8th bit set into Meta characters. If meta is nil,
Emacs disregards the 8th bit; this is necessary when the terminal uses
it as a parity bit. If meta is neither t nor nil,
Emacs uses all 8 bits of input unchanged. This is good for terminals
using European 8-bit character sets.
If quit-char is non-nil, it specifies the character to
use for quitting. Normally this character is C-g.
See section Quitting.
The current-input-mode function returns the input mode settings
Emacs is currently using.
Function: current-input-mode
This function returns current mode for reading keyboard input. It
returns a list, corresponding to the arguments of set-input-mode,
of the form (INTERRUPT FLOW META QUIT) in
which:
nil when Emacs is using interrupt-driven input. If
nil, Emacs is using CBREAK mode.
nil if Emacs uses XON/XOFF (C-q, C-s)
flow control for output to the terminal. This value has no effect
unless INTERRUPT is non-nil.
nil if Emacs is paying attention to the eighth bit of
input characters; if nil, Emacs clears the eighth bit of every input
character.
Variable: meta-flag
This variable used to control whether to treat the 0200 bit in
keyboard input as the Meta bit. nil meant no, and anything
else meant yes. This variable existed in Emacs versions 18 and earlier
but no longer exists in Emacs 19; use set-input-mode instead.
Variable: extra-keyboard-modifiers
This variable lets Lisp programs "press" the modifier keys on the keyboard. The value is a bit mask:
Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down.
When you use X windows, the program can "press" any of the modifier keys in this way. Otherwise, only the CTL and META keys can be virtually pressed.
Variable: keyboard-translate-table
This variable is the translate table for keyboard characters. It lets
you reshuffle the keys on the keyboard without changing any command
bindings. Its value must be a string or nil.
If keyboard-translate-table is a string, then each character read
from the keyboard is looked up in this string and the character in the
string is used instead. If the string is of length n, character codes
n and up are untranslated.
In the example below, we set keyboard-translate-table to a
string of 128 characters. Then we fill it in to swap the characters
C-s and C-\ and the characters C-q and C-^.
Subsequently, typing C-\ has all the usual effects of typing
C-s, and vice versa. (See section Flow Control for more information on
this subject.)
(defun evade-flow-control ()
"Replace C-s with C-\ and C-q with C-^."
(interactive)
(let ((the-table (make-string 128 0)))
(let ((i 0))
(while (< i 128)
(aset the-table i i)
(setq i (1+ i))))
;; Swap C-s and C-\.
(aset the-table ?\034 ?\^s)
(aset the-table ?\^s ?\034)
;; Swap C-q and C-^.
(aset the-table ?\036 ?\^q)
(aset the-table ?\^q ?\036)
(setq keyboard-translate-table the-table)))
Note that this translation is the first thing that happens to a
character after it is read from the terminal. Record-keeping features
such as recent-keys and dribble files record the characters after
translation.
Function: keyboard-translate from to
This function modifies keyboard-translate-table to translate
character code from into character code to. It creates
or enlarges the translate table if necessary.
Variable: function-key-map
This variable holds a keymap which describes the character sequences sent by function keys on an ordinary character terminal. This keymap uses the data structure as other keymaps, but is used differently: it specifies translations to make while reading events.
If function-key-map "binds" a key sequence k to a vector
v, then when k appears as a subsequence anywhere in a
key sequence, it is replaced with the events in v.
For example, VT100 terminals send ESC O P when the
keypad PF1 key is pressed. Therefore, we want Emacs to translate
that sequence of events into the single event pf1. We accomplish
this by "binding" ESC O P to [pf1] in
function-key-map, when using a VT100.
Thus, typing C-c PF1 sends the character sequence C-c
ESC O P; later the function read-key-sequence translates
this back into C-c PF1, which it returns as the vector
[?\C-c pf1].
Entries in function-key-map are ignored if they conflict with
bindings made in the minor mode, local, or global keymaps. The intent
is that the character sequences that function keys send should not have
command bindings in their own right.
The value of function-key-map is usually set up automatically
according to the terminal's Terminfo or Termcap entry, but sometimes
those need help from terminal-specific Lisp files. Emacs comes with a
number of terminal-specific files for many common terminals; their main
purpose is to make entries in function-key-map beyond those that
can be deduced from Termcap and Terminfo. See section Terminal-Specific Initialization.
Emacs versions 18 and earlier used totally different means of detecting the character sequences that represent function keys.
Variable: key-translation-map
This variable is another keymap used just like function-key-map
to translate input events into other events. It differs from
function-key-map in two ways:
key-translation-map goes to work after function-key-map is
finished; it receives the results of translation by
function-key-map.
key-translation-map overrides actual key bindings.
The intent of key-translation-map is for users to map one
character set to another, including ordinary characters normally bound
to self-insert-command.
Function: recent-keys
This function returns a vector containing the last 100 input events from the keyboard or mouse. All input events are included, whether or not they were used as parts of key sequences. Thus, you always get the last 100 inputs, not counting keyboard macros. (Events from keyboard macros are excluded because they are less interesting for debugging; it should be enough to see the events which invoked the macros.)
Command: open-dribble-file filename
This function opens a dribble file named filename. When a dribble file is open, each input event from the keyboard or mouse (but not those from keyboard macros) are written in that file. A non-character event is expressed using its printed representation surrounded by `<...>'.
You close the dribble file by calling this function with an argument
of nil. The function always returns nil.
This function is normally used to record the input necessary to trigger an Emacs bug, for the sake of a bug report.
(open-dribble-file "~/dribble")
=> nil
See also the open-termscript function (see section Terminal Output).
The terminal output functions send output to the terminal or keep
track of output sent to the terminal. The variable baud-rate
tells you what Emacs thinks is the output speed of the terminal.
Variable: baud-rate
This variable's value is the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations such as padding. It also affects decisions about whether to scroll part of the screen or repaint--even when using a window system, (We designed it this way despite the fact that a window system has no true "output speed", to give you a way to tune these decisions.)
The value is measured in baud.
If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal. Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not. If Emacs has the wrong value, it makes decisions that are less
than optimal. To fix the problem, set baud-rate.
Function: baud-rate
This function returns the value of the variable baud-rate. In
Emacs versions 18 and earlier, this was the only way to find out the
terminal speed.
Function: send-string-to-terminal string
This function sends string to the terminal without alteration. Control characters in string have terminal-dependent effects.
One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how on certain terminals to define function key 4 to move forward four characters (by transmitting the characters C-u C-f to the computer):
(send-string-to-terminal "\eF4\^U\^F")
=> nil
Command: open-termscript filename
This function is used to open a termscript file that will record
all the characters sent by Emacs to the terminal. It returns
nil. Termscript files are useful for investigating problems
where Emacs garbles the screen, problems which are due to incorrect
Termcap entries or to undesirable settings of terminal options more
often than actual Emacs bugs. Once you are certain which characters
were actually output, you can determine reliably whether they correspond
to the Termcap specifications in use.
See also open-dribble-file in section Terminal Input.
(open-termscript "../junk/termscript")
=> nil
This section attempts to answer the question "Why does Emacs choose to use flow-control characters in its command character set?" For a second view on this issue, read the comments on flow control in the `emacs/INSTALL' file from the distribution; for help with Termcap entries and DEC terminal concentrators, see `emacs/etc/TERMS'.
At one time, most terminals did not need flow control, and none used
C-s and C-q for flow control. Therefore, the choice of
C-s and C-q as command characters was unobjectionable.
Emacs, for economy of keystrokes and portability, used nearly all the
ASCII control characters, with mnemonic meanings when possible;
thus, C-s for search and C-q for quote.
Later, some terminals were introduced which required these characters for flow control. They were not very good terminals for full-screen editing, so Emacs maintainers did not pay attention. In later years, flow control with C-s and C-q became widespread among terminals, but by this time it was usually an option. And the majority of users, who can turn flow control off, were unwilling to switch to less mnemonic key bindings for the sake of flow control.
So which usage is "right", Emacs's or that of some terminal and concentrator manufacturers? This is a rhetorical (or religious) question; it has no simple answer.
One reason why we are reluctant to cater to the problems caused by C-s and C-q is that they are gratuitous. There are other techniques (albeit less common in practice) for flow control that preserve transparency of the character stream. Note also that their use for flow control is not an official standard. Interestingly, on the model 33 teletype with a paper tape punch (which is very old), C-s and C-q were sent by the computer to turn the punch on and off!
GNU Emacs version 19 provides a convenient way of enabling flow
control if you want it: call the function enable-flow-control.
Function: enable-flow-control
This function enables use of C-s and C-q for output flow
control, and provides the characters C-\ and C-^ as aliases
for them using keyboard-translate-table (see section Translating Input Events).
You can use the function enable-flow-control-on in your
`.emacs' file to enable flow control automatically on certain
terminal types.
Function: enable-flow-control-on &rest termtypes
This function enables flow control, and the aliases C-\ and C-^, if the terminal type is one of termtypes. For example:
(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
Here is how enable-flow-control does its job:
(set-input-mode nil t).
keyboard-translate-table to translate C-\ and
C-^ into C-s and C-q were typed. Except at its very
lowest level, Emacs never knows that the characters typed were anything
but C-s and C-q, so you can in effect type them as C-\
and C-^ even when they are input for other commands. For example:
(setq keyboard-translate-table (make-string 128 0))
(let ((i 0))
;; Map most characters into themselves.
(while (< i 128)
(aset keyboard-translate-table i i)
(setq i (1+ i))))
;; Map C-\ to C-s.
(aset the-table ?\034 ?\^s)
;; Map C-^ to C-q.
(aset the-table ?\036 ?\^q)))
If the terminal is the source of the flow control characters, then once
you enable kernel flow control handling, you probably can make do with
less padding than normal for that terminal. You can reduce the amount
of padding by customizing the Termcap entry. You can also reduce it by
setting baud-rate to a smaller value so that Emacs uses a smaller
speed when calculating the padding needed. See section Terminal Output.
The command line option `-batch' causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with `-l file', which loads the library named file, and `-f function', which calls function with no arguments.
Any Lisp program output that would normally go to the echo area,
either using message or using prin1, etc., with t
as the stream, goes instead to Emacs's standard output descriptor when
in batch mode. Thus, Emacs behaves much like a noninteractive
application program. (The echo area output that Emacs itself normally
generates, such as command echoing, is suppressed entirely.)
Variable: noninteractive
This variable is non-nil when Emacs is running in batch mode.
This chapter describes a number of features related to the display that Emacs presents to the user.
The function redraw-frame redisplays the entire contents of a
given frame. See section Frames.
Function: redraw-frame frame
This function clears and redisplays frame frame.
Even more powerful is redraw-display.
Command: redraw-display
This function clears and redisplays all visible frames.
Normally, suspending and resuming Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption. See section Suspending Emacs.
Variable: no-redraw-on-reenter
This variable controls whether Emacs redraws the entire screen after it
has been suspended and resumed. Non-nil means yes, nil
means no.
Processing user input takes absolute priority over redisplay. If you call these functions when input is available, they do nothing immediately, but a full redisplay does happen eventually--after all the input has been processed.
The screen size functions report or tell Emacs the height or width of the terminal. When you are using multiple frames, they apply to the selected frame (see section Frames).
Function: screen-height
This function returns the number of lines on the screen that are available for display.
(screen-height)
=> 50
Function: screen-width
This function returns the number of columns on the screen that are available for display.
(screen-width)
=> 80
Function: set-screen-height lines &optional not-actual-size
This function declares that the terminal can display lines lines. The sizes of existing windows are altered proportionally to fit.
If not-actual-size is non-nil, then Emacs displays
lines lines of output, but does not change its value for the
actual height of the screen. (Knowing the correct actual size may be
necessary for correct cursor positioning.) Using a smaller height than
the terminal actually implements may be useful to reproduce behavior
observed on a smaller screen, or if the terminal malfunctions when using
its whole screen.
If lines is different from what it was previously, then the entire screen is cleared and redisplayed using the new size.
This function returns nil.
Function: set-screen-width columns &optional not-actual-size
This function declares that the terminal can display columns
columns. The details are as in set-screen-height.
When a line of text extends beyond the right edge of a window, the line can either be truncated or continued on the next line. When a line is truncated, this is shown with a `$' in the rightmost column of the window. When a line is continued or "wrapped" onto the next line, this is shown with a `\' on the rightmost column of the window. The additional screen lines used to display a long text line are called continuation lines. (Note that wrapped lines are not filled; filling has nothing to do with continuation and truncation. See section Filling.)
User Option: truncate-lines
This buffer-local variable controls how Emacs displays lines that
extend beyond the right edge of the window. If it is non-nil,
then Emacs does not display continuation lines; rather each line of
text occupies exactly one screen line, and a dollar sign appears at the
edge of any line that extends to or beyond the edge of the window. The
default is nil.
If the variable truncate-partial-width-windows is
non-nil, then truncation is used for windows that are not the
full width of the screen, regardless of the value of
truncate-lines.
Variable: default-truncate-lines
This variable is the default value for truncate-lines in buffers
that do not have local values for it.
User Option: truncate-partial-width-windows
This variable determines how lines that are too wide to fit on the
screen are displayed in side-by-side windows (see section Splitting Windows). If it is non-nil, then wide lines are truncated (with
a `$' at the end of the line); otherwise they wrap to the next
screen line (with a `\' at the end of the line).
You can override the images that indicate continuation or truncation with the display table; see section Display Tables.
The echo area is used for displaying messages made with the
message primitive, and for echoing keystrokes. It is not the
same as the minibuffer, despite the fact that the minibuffer appears
(when active) in the same place on the screen as the echo area. The
GNU Emacs Manual specifies the rules for resolving conflicts
between the echo area and the minibuffer for use of that screen space
(see section 'The Minibuffer' in The GNU Emacs Manual).
Error messages appear in the echo area; see section Errors.
You can write output in the echo area by using the Lisp printing
functions with t as the stream (see section Output Functions), or as
follows:
Function: message string &rest arguments
This function prints a one-line message in the echo area. The
argument string is similar to a C language printf control
string. See format in section Conversion of Characters and Strings, for the details
on the conversion specifications. message returns the
constructed string.
If string is nil, message clears the echo area. If
the minibuffer is active, this brings the minibuffer contents back onto
the screen immediately.
(message "Minibuffer depth is %d." (minibuffer-depth)) => "Minibuffer depth is 0." ---------- Echo Area ---------- Minibuffer depth is 0. ---------- Echo Area ----------
Variable: cursor-in-echo-area
This variable controls where the cursor appears when a message is
displayed in the echo area. If it is non-nil, then the cursor
appears at the end of the message. Otherwise, the cursor appears at
point--not in the echo area at all.
The value is normally nil; Lisp programs bind it to t
for brief periods of time.
Selective display is a class of minor modes in which specially marked lines do not appear on the screen, or in which highly indented lines do not appear.
The first variant, explicit selective display, is designed for use in a Lisp program. The program controls which lines are hidden by altering the text. Outline mode uses this variant. In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed as a user-level feature.
The way you control explicit selective display is by replacing a newline (control-j) with a control-m. The text which was formerly a line following that newline is now invisible. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For
example, C-f (forward-char) moves point unhesitatingly into
invisible space. However, the replacement of newline characters with
carriage return characters affects some editing commands. For example,
next-line skips invisible lines, since it searches only for
newlines. Modes that use selective display can also define commands
that take account of the newlines, or which make parts of the text
visible or invisible.
When you write a selectively displayed buffer into a file, all the control-m's are replaced by their original newlines. This means that when you next read in the file, it looks OK, with nothing invisible. The selective display effect is seen only within Emacs.
Variable: selective-display
This buffer-local variable enables selective display. This means that lines, or portions of lines, may be made invisible.
selective-display is t, then any portion
of a line that follows a control-m is not displayed.
selective-display is a positive integer, then
lines that start with more than selective-display columns of
indentation are not displayed.
When some portion of a buffer is invisible, the vertical movement
commands operate as if that portion did not exist, allowing a single
next-line command to skip any number of invisible lines.
However, character movement commands (such as forward-char) do
not skip the invisible portion, and it is possible (if tricky) to insert
or delete text in an invisible portion.
In the examples below, what is shown is the display of the buffer
foo, which changes with the value of selective-display. The
contents of the buffer do not change.
(setq selective-display nil)
=> nil
---------- Buffer: foo ----------
1 on this column
2on this column
3n this column
3n this column
2on this column
1 on this column
---------- Buffer: foo ----------
(setq selective-display 2)
=> 2
---------- Buffer: foo ----------
1 on this column
2on this column
2on this column
1 on this column
---------- Buffer: foo ----------
Variable: selective-display-ellipses
If this buffer-local variable is non-nil, then Emacs displays
`...' at the end of a line that is followed by invisible text.
This example is a continuation of the previous one.
(setq selective-display-ellipses t)
=> t
---------- Buffer: foo ----------
1 on this column
2on this column ...
2on this column
1 on this column
---------- Buffer: foo ----------
You can use a display table to substitute other text for the ellipsis (`...'). See section Display Tables.
The overlay arrow is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed.
Variable: overlay-arrow-string
This variable holds the string to display as an arrow, or nil if
the arrow feature is not in use.
Variable: overlay-arrow-position
This variable holds a marker which indicates where to display the arrow. It should point at the beginning of a line. The arrow text is displayed at the beginning of that line, overlaying any text that would otherwise appear. Since the arrow is usually short, and the line usually begins with indentation, normally nothing significant is overwritten.
The overlay string is displayed only in the buffer which this marker points into. Thus, only one buffer can have an overlay arrow at any given time.
Temporary displays are used by commands to put output into a buffer and then present it to the user for perusal rather than for editing. Many of the help commands use this feature.
Special Form: with-output-to-temp-buffer buffer-name forms...
This function executes forms while arranging to insert any output they print into the buffer named buffer-name. The buffer is then shown in some window for viewing, displayed but not selected.
The string buffer-name specifies the temporary buffer, which
need not already exist. The argument must be a string, not a buffer.
The buffer is erased initially (with no questions asked), and it is
marked as unmodified after with-output-to-temp-buffer exits.
with-output-to-temp-buffer binds standard-output to the
temporary buffer, then it evaluates the forms in forms. Output
using the Lisp output functions within forms goes by default to
that buffer (but screen display and messages in the echo area, although
output in the general sense of the word, are not affected).
See section Output Functions.
The value of the last form in forms is returned.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(with-output-to-temp-buffer "foo"
(print 20)
(print standard-output))
=> #<buffer foo>
---------- Buffer: foo ----------
20
#<buffer foo>
---------- Buffer: foo ----------
Variable: temp-buffer-show-function
The value of this variable, if non-nil, is called as a function
to display a help buffer. This variable is used by
with-output-to-temp-buffer.
In Emacs versions 18 and earlier, this variable was called
temp-buffer-show-hook.
Function: momentary-string-display string position &optional char message
This function momentarily displays string in the current buffer at position (which is a character offset from the beginning of the buffer). The display remains until the next character is typed.
If the next character the user types is char, Emacs ignores it. Otherwise, that character remains buffered for subsequent use as input. Thus, typing char will simply remove the string from the display, while typing (say) C-f will remove the string from the display and later (presumably) move point forward. The argument char is a space by default.
The return value of momentary-string-display is not meaningful.
If message is non-nil, it is displayed in the echo area
while string is displayed in the buffer. If it is nil,
then instructions to type char are displayed there, e.g.,
`Type RET to continue editing'.
In this example, point is initially located at the beginning of the second line:
---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") => t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------
This function works by actually changing the text in the buffer. As a result, if you later undo in this buffer, you will see the message come and go.
You can use overlays to alter the appearance of a buffer's text on the screen. An overlay is an object which belongs to a particular buffer, and has a specified beginning and end. It also has properties which you can examine and set; these affect the display of the text within the overlay.
Overlay properties are like text properties in some respects, but the differences are more important than the similarities. Text properties are considered a part of the text; overlays are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not.
face
mouse-face
face when the mouse is within
the range of the overlay. This feature is not yet implemented, and may
be temporary. It is documented here because we are likely to implement it
this way at least for a while.
priority
priority value is larger takes priority over the
other, and its face attributes override the face attributes of the lower
priority overlay.
Currently, all overlays take priority over text properties. Please avoid using negative priority values, as we have not yet decided just what they should mean.
window
window property is non-nil, then the overlay
applies only on that window.
before-string
after-string
modification-hooks
insert-in-front-hooks
insert-behind-hooks
These are the functions for reading and writing the properties of an overlay.
Function: overlay-get overlay prop
This function returns the value of property prop recorded in
overlay. If overlay does not record any value for that
property, then the value is nil.
Function: overlay-put overlay prop value
This function sets the value of property prop recorded in overlay to value. It returns value.
Function: make-overlay start end &optional buffer
This function creates and returns an overlay which belongs to buffer and ranges from start to end. Both start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay is created in the current buffer.
The return value is the overlay itself.
Function: overlay-start overlay
This function returns the position at which overlay starts.
Function: overlay-end overlay
This function returns the position at which overlay ends.
Function: overlay-buffer overlay
This function returns the buffer that overlay belongs to.
Function: delete-overlay overlay
This function deletes overlay. The overlay continues to exist as a Lisp object, but ceases to be part of the buffer it belonged to, and ceases to have any effect on display.
Function: move-overlay overlay start end &optional buffer
This function moves overlay to buffer, and places its bounds at start and end. Both arguments start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay stays in the same buffer.
The return value is overlay.
This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be "lost".
Function: overlays-at pos
This function returns a list of all the overlays that contain position pos in the current buffer. The list is in no particular order. An overlay contains position pos if it begins at or before pos, and ends after pos.
Function: next-overlay-change pos
This function returns the buffer position of the next beginning or end of an overlay, after pos.
A face is a named collection of graphical attributes: font, foreground color, background color and optional underlining. Faces control the display of text on the screen.
Each face has its own face id number which distinguishes faces at low levels within Emacs. However, for most purposes, you can refer to faces in Lisp programs by their names.
Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish.
The face named default is used for ordinary text. The face named
modeline is used for displaying the mode line and menu bars. The
face named region is used for highlighting the region (in
Transient Mark mode only).
Here are all the ways to specify which face to use for display of text:
face property; if so,
it's displayed with that face. If the character has a mouse-face
property, that is used instead of the face property when the mouse
is "near enough" to the character. See section Special Properties.
face and mouse-face
properties too; they apply to all the text covered by the overlay.
If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. The attributes of the faces of special glyphs come first; then come attributes of faces from overlays, followed by those from text properties, and last the default face.
When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See section Overlays.
If an attribute such as the font or a color is not specified in any of the above ways, the frame's own font or color is used.
The attributes a face can specify include the font, the foreground
color, the background color, and underlining. The face can also leave
these unspecified by giving the value nil for them.
Here are the primitives for creating and changing faces.
Function: make-face name
This function defines a new face named name, initially with all
attributes nil. It does nothing if there is already a face named
name.
Function: face-list
This function returns a list of all defined face names.
Function: copy-face old-face new-name &optional frame new-frame
This function defines a new face named new-name which is a copy of the existing face named old-face. If there is already a face named new-name, then it alters the face to have the same attributes as old-face.
If the optional argument frame is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from old-face in that frame to new-face in the same frame.
If the optional argument new-frame is given, then copy-face
copies the attributes of old-face in frame to new-name
in new-frame.
You can modify the attributes of an existing face with the following functions. If you specify frame, they affect just that frame; otherwise, they affect all frames as well as the defaults that apply to new frames.
Function: set-face-foreground face color &optional frame
Function: set-face-background face color &optional frame
These functions set the foreground (respectively, background) color of face face to color. The argument color color should be a string, the name of a color.
Function: set-face-font face font &optional frame
This function sets the font of face face. The argument font should be a string.
Function: set-face-underline-p face underline-p &optional frame
This function sets the underline attribute of face face.
Function: invert-face face &optional frame
Swap the foreground and background colors of face face. If the face doesn't specify both foreground and background, then its foreground and background are set to the default background and foreground.
These functions examine the attributes of a face. If you don't specify frame, they refer to the default data for new frames.
Function: face-foreground face &optional frame
Function: face-background face &optional frame
These functions return the foreground (respectively, background) color of face face. The argument color color should be a string, the name of a color.
Function: face-font face &optional frame
This function returns the name of the font of face face.
Function: face-underline-p face &optional frame
This function returns the underline attribute of face face.
Function: face-id-number face
This function returns the id number of face face.
Function: face-equal face1 face2 &optional frame
This returns t if the faces face1 and face2 have the
same attributes for display.
Function: face-differs-from-default-p face &optional frame
This returns t if the face face displays differently from
the default face. A face is considered to be "the same" as the normal
face if each attribute is either the same as that of the default face or
nil (meaning to inherit from the default).
Variable: region-face
This variable's value specifies the face id to use to display characters in the region when it is active (in Transient Mark mode only). The face thus specified takes precedence over all faces that come from text properties and overlays, for characters in the region. See section The Mark, for more information about Transient Mark mode.
Normally, the value is the id number of the face named region.
This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.
Variable: blink-paren-function
The value of this variable should be a function (of no arguments) to
be called whenever a char with close parenthesis syntax is inserted.
The value of blink-paren-function may be nil, in which
case nothing is done.
Please note: this variable was namedblink-paren-hookin older Emacs versions, but since it is not called with the standard convention for hooks, it was renamed toblink-paren-functionin version 19.
Variable: blink-matching-paren
If this variable is nil, then blink-matching-open does
nothing.
Variable: blink-matching-paren-distance
This variable specifies the maximum distance to scan for a matching parenthesis before giving up.
Function: blink-matching-open
This function is the default value of blink-paren-function. It
assumes that point follows a character with close parenthesis syntax and
moves the cursor momentarily to the matching opening character. If that
character is not already on the screen, then its context is shown by
displaying it in the echo area. To avoid long delays, this function
does not search farther than blink-matching-paren-distance
characters.
Here is an example of calling this function explicitly.
(defun interactive-blink-matching-open ()
"Indicate momentarily the start of sexp before point."
(interactive)
(let ((blink-matching-paren-distance
(buffer-size))
(blink-matching-paren t))
(blink-matching-open)))
User Option: inverse-video
This variable controls whether Emacs uses inverse video for all text
on the screen. Non-nil means yes, nil means no. The
default is nil.
User Option: mode-line-inverse-video
This variable controls the use of inverse video for mode lines. If it
is non-nil, then mode lines are displayed in inverse video (under
X, this uses the face named modeline, which you can set as you
wish). Otherwise, mode lines are displayed normally, just like text.
The default is t.
The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see section Display Tables). Here are the usual display conventions:
tab-width.
ctl-arrow. If it is is
non-nil, these codes map to sequences of two glyphs, where the
first glyph is the ASCII code for `^'. Otherwise, these codes map
just like the codes in the range 128 to 255.
The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
nil. Thus, when you set up a display table, you need only
specify the the characters for which you want unusual behavior.
These variables affect the way certain characters are displayed on the screen. Since they change the number of columns the characters occupy, they also affect the indentation functions.
User Option: ctl-arrow
This buffer-local variable controls how control characters are
displayed. If it is non-nil, they are displayed as a caret
followed by the character: `^A'. If it is nil, they are
displayed as a backslash followed by three octal digits: `\001'.
Variable: default-ctl-arrow
The value of this variable is the default value for ctl-arrow in
buffers that do not override it. This is the same as executing the
following expression:
(default-value 'ctl-arrow)
See section The Default Value of a Buffer-Local Variable.
User Option: tab-width
The value of this variable is the spacing between tab stops used for
displaying tab characters in Emacs buffers. The default is 8. Note
that this feature is completely independent from the user-settable tab
stops used by the command tab-to-tab-stop. See section Adjustable "Tab Stops".
You can use the display table feature to control how all 256 possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ASCII character set.
The display table maps each character code into a sequence of glyphs, each glyph being an image that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table.
A display table is actually an array of 261 elements.
Function: make-display-table
This creates and returns a display table. The table initially has
nil in all elements.
The first 256 elements correspond to character codes; the nth
element says how to display the character code n. The value
should be nil or a vector of glyph values (see section Glyphs). If
an element is nil, it says to display that character according to
the usual display conventions (see section Usual Display Conventions).
The remaining five elements of a display table serve special purposes,
and nil means use the default stated below.
For example, here is how to construct a display table that mimics the
effect of setting ctl-arrow to a non-nil value:
(setq disptab (make-display-table))
(let ((i 0))
(while (< i 32)
(or (= i ?\t) (= i ?\n)
(aset disptab i (vector ?^ (+ i 64))))
(setq i (1+ i)))
(aset disptab 127 (vector ?^ ??)))
Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table.
Function: window-display-table window
This function returns window's display table, or nil
if window does not have an assigned display table.
Function: set-window-display-table window table
This function sets the display table of window to table.
The argument table should be either a display table or
nil.
Variable: buffer-display-table
This variable is automatically local in all buffers; its value in a
particular buffer is the display table for that buffer, or nil if
the buffer does not have any assigned display table.
Variable: standard-display-table
This variable's value is the default display table, used when neither
the current buffer nor the window displaying it has an assigned display
table. This variable is nil by default.
If neither the selected window nor the current buffer has a display
table, and if the variable standard-display-table is nil,
then Emacs uses the usual display conventions. See section Usual Display Conventions.
A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Glyphs are represented in Lisp as integers, just as characters are.
The meaning of each integer, as a glyph, is defined by the glyph
table, which is the value of the variable glyph-table.
Variable: glyph-table
The value of this variable is the current glyph table. It should be a
vector; the gth element defines glyph code g. If the value
is nil instead of a vector, then all glyphs are simple (see
below).
Here are the possible types of elements in the glyph table:
nil
If a glyph code is greater than or equal to the length of the glyph table, that code is automatically simple.
If you have a terminal that can handle the entire ISO Latin 1 character set, you can arrange to use that character set as follows:
(require 'disp-table) ;; Set char codes 160--255 to display as themselves. ;; (Codes 128--159 are the additional control characters.) (standard-display-8bit 160 255)
If you are editing buffers written in the ISO Latin 1 character set and your terminal doesn't handle anything but ASCII, you can load the file `iso-ascii' to set up a display table which makes the other ISO characters display as sequences of ASCII characters. For example, the character "o with umlaut" displays as `{"o}'.
Some European countries have terminals that don't support ISO Latin 1 but do support the special characters for that country's language. You can define a display table to work one language using such terminals. For an example, see `lisp/iso-swed.el', which handles certain Swedish terminals.
You can load the appropriate display table for your terminal automatically by writing a terminal-specific Lisp file for the terminal type.
You can make Emacs ring a bell (or blink the screen) to attract the user's attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use beeping alone when signaling an error is appropriate. (See section Errors.)
Function: ding &optional dont-terminate
This function beeps, or flashes the screen (see visible-bell below).
It also terminates any keyboard macro currently executing unless
dont-terminate is non-nil.
Function: beep &optional dont-terminate
This is a synonym for ding.
Variable: visible-bell
This variable determines whether Emacs should flash the screen to
represent a bell. Non-nil means yes, nil means no. This
is effective only if the Termcap entry for the terminal in use has the
visible bell flag (`vb') set.
Emacs works with several window systems, most notably the X Window Syste,. Note that both Emacs and X use the term "window", but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.
Variable: window-system
This variable tells Lisp programs what window system Emacs is running
under. Its value should be a symbol such as x (if Emacs is
running under X) or nil (if Emacs is running on an ordinary
terminal).
Variable: window-system-version
This variable distinguishes between different versions of the X Window
System. Its value is 10 or 11 when using X; nil otherwise.
Variable: window-setup-hook
This variable is a normal hook which Emacs runs after loading your
`.emacs' file and the default initialization file (if any), after
loading terminal-specific Lisp code, and after running the hook
term-setup-hook.
This hook is used for internal purposes: setting up communication with the window system, and creating the initial window. Users should not interfere with it.
There are many customizations that you can use to make the calendar and diary suit your personal tastes.
If you set the variable view-diary-entries-initially to
t, calling up the calendar automatically displays the diary
entries for the current date as well. The diary dates appear only if
the current date is visible. If you add both of the following lines to
your `.emacs' file:
(setq view-diary-entries-initially t) (calendar)
they display both the calendar and diary windows whenever you start Emacs.
Similarly, if you set the variable
view-calendar-holidays-initially to t, entering the
calendar automatically displays a list of holidays for the current three
month period. The holiday list appears in a separate window.
You can set the variable mark-diary-entries-in-calendar to t
in order to place a plus sign (`+') beside any dates with diary entries.
Whenever the calendar window is displayed or redisplayed, the diary entries
are automatically marked for holidays.
Similarly, setting the variable mark-holidays-in-calendar to
t places an asterisk (`*') after all holiday dates visible
in the calendar window.
There are many customizations that you can make with the hooks
provided. For example, the variable calendar-load-hook, whose
default value is nil, is a normal hook run when the calendar
package is first loaded (before actually starting to display the
calendar).
The variable initial-calendar-window-hook, whose default value
is nil, is a normal hook run the first time the calendar window
is displayed. The function is invoked only when you first enter
Calendar mode, not when you redisplay an existing Calendar window. But
if you leave the calendar with the q command and reenter it, the
hook runs again.
The variable today-visible-calendar-hook, whose default value
is nil, is a normal hook run after the calendar buffer has been
prepared with the calendar when the current date is visible in the
window. One use of this hook is to replace today's date with asterisks;
a function calendar-star-date is included for this purpose. In
your `.emacs' file, put:
(setq today-visible-calendar-hook 'calendar-star-date)
Another standard hook function adds asterisks around the current date. Here's how to use it:
(setq today-visible-calendar-hook 'calendar-mark-today)
A corresponding variable, today-invisible-calendar-hook, whose
default value is nil, is a normal hook run after the calendar
buffer text has been prepared, if the current date is not visible
in the window.
Emacs knows about holidays defined by entries on one of several lists.
You can customize theses lists of holidays to your own needs, adding
holidays or deleting lists of holidays. The lists of holidays that
Emacs uses are for general holidays (general-holidays), local
holidays (local-holidays), Christian holidays
(christian-holidays), Hebrew (Jewish) holidays
(hebrew-holidays), Islamic (Moslem) holidays
(islamic-holidays), and other holidays (other-holidays).
The general holidays are, by default, holidays common throughout the
United States. To eliminate these holidays, set general-holidays
to nil.
There are no default local holidays (but sites may supply some). You
can set the variable local-holidays to any list of holidays, as
described below.
By default, Emacs does not consider all the holidays of these
religions, only those commonly found in secular calendars. For a more
extensive collection of religious holidays, you can set any (or all) of
the variables all-christian-calendar-holidays,
all-hebrew-calendar-holidays, or
all-islamic-calendar-holidays to t. If you want to
eliminate the religious holidays, set any or all of the corresponding
variables christian-holidays, hebrew-holidays, and
islamic-holidays to nil.
You can set the variable other-holidays to any list of
holidays. This list, normally empty, is intended for your use.
Each of the lists (general-holidays, local-holidays,
christian-holidays, hebrew-holidays,
islamic-holidays, and other-holidays) is a list of
holiday forms, each holiday form describing a holiday (or
sometimes a list of holidays). Holiday forms may have the following
formats:
(holiday-fixed month day string)
(holiday-float month dayname k string)
(holiday-hebrew month day string)
(holiday-islamic month day string)
(holiday-julian month day string)
(holiday-sexp sexp string)
year
to compute the date of a holiday, or nil if the holiday doesn't
happen this year. The value represents the date as a list of the form
(month day year). string is the name of
the holiday.
(if boolean holiday-form &optional holiday-form)
(function &optional args)
calendar-holiday-function-function.
For example, suppose you want to add Bastille Day, celebrated in France on July 14. You can do this by adding the following line to your `.emacs' file:
(setq other-holidays '((holiday-fixed 7 14 "Bastille Day")))
The holiday form (holiday-fixed 7 14 "Bastille Day") specifies the
fourteenth day of the seventh month (July).
Many holidays occur on a specific day of the week, at a specific time of month. Here is a holiday form describing Hurricane Supplication Day, celebrated in the Virgin Islands on the fourth Monday in August:
(holiday-float 8 1 4 "Hurricane Supplication Day")
Here the 8 specifies August, the 1 specifies Monday (Sunday is 0, Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in the month (1 specifies the first occurrence, 2 the second occurrence, -1 the last occurrence, -2 the second-to-last occurrence, and so on).
You can specify holidays that occur on fixed days of the Hebrew, Islamic, and Julian calendars too. For example,
(setq other-holidays
'((holiday-hebrew 10 2 "Last day of Hanukkah")
(holiday-islamic 3 12 "Mohammed's Birthday")
(holiday-julian 4 2 "Jefferson's Birthday")))
adds the last day of Hanukkah (since the Hebrew months are numbered with 1 starting from Nisan), the Islamic feast celebrating Mohammed's birthday (since the Islamic months are numbered from 1 starting with Muharram), and Thomas Jefferson's birthday, which is 2 April 1743 on the Julian calendar.
To include a holiday conditionally, use either the `if' or the `sexp' form. For example, American presidential elections occur on the first Tuesday after the first Monday in November of years divisible by 4:
(holiday-sexp (if (= 0 (% year 4))
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 year))))))
"US Presidential Election"))
or
(if (= 0 (% displayed-year 4))
(fixed 11
(extract-calendar-day
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 displayed-year)))))))
"US Presidential Election"))
Some holidays just don't fit into any of these forms because special
calculations are involved in their determination. In such cases you
must write a Lisp function to do the calculation. To include
eclipses of the sun, for example, add (eclipses) to
other-holidays and write an Emacs Lisp function
eclipses that returns a (possibly
empty) list of the relevant Gregorian dates among the
range visible in the calendar window, with descriptive strings, like
this:
(((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )
You can customize the manner of displaying dates in the diary,
in mode lines, and in messages by setting
calendar-date-display-form. This variable is a list of
expressions that can involve the variables month, day, and
year, all numbers in string form, and monthname and
dayname, both alphabetic strings. In the American style, the
default value of this list is as follows:
((if dayname (concat dayname ", ")) monthname " " day ", " year)
while in the European style this value is the default:
((if dayname (concat dayname ", ")) day " " monthname " " year)
The ISO standard date representation is this:
(year "-" month "-" day)
This specifies a typical American format:
(month "/" day "/" (substring year -2))
In the calendar, diary, and related buffers, Emacs displays times of
day in the conventional American style with the hours from 1 through 12,
minutes, and either `am' or `pm'. If you prefer the
"military" (European) style of writing times--in which the hours go
from 00 to 23--you can alter the variable
calendar-time-display-form. This variable is a list of
expressions that can involve the variables 12-hours,
24-hours, and minutes, all numbers in string form, and
am-pm and time-zone, both alphabetic strings. The default
definition of calendar-time-display-form is as follows:
(12-hours ":" minutes am-pm
(if time-zone " (") time-zone (if time-zone ")"))
Setting calendar-time-display-form to
(24-hours ":" minutes
(if time-zone " (") time-zone (if time-zone ")"))
gives military-style times like `21:07 (UT)' if time zone names are defined, and times like `21:07' if they are not.
Emacs understands the difference between standard time and daylight savings time--the times given for sunrise, sunset, solstices, equinoxes, and the phases of the moon take that into account. The rules for daylight savings time vary from place to place and have also varied historically from year to year. To do the job properly, Emacs needs to know which rules to use.
Some operating systems keep track of the rules that apply to the place where you are; on these systems, Emacs gets the information it needs from the system automatically. If some or all of this information is missing, Emacs fills in the gaps with the rules currently used in Cambridge, Massachusetts. If the default choice of rules is not appropriate for your location, you can tell Emacs the rules to use by setting certain variables.
These variables are calendar-daylight-savings-starts and
calendar-daylight-savings-ends. Their values should be Lisp
expressions that refer to the variable year, and evaluate to the
Gregorian date on which daylight savings time starts or (respectively)
ends, in the form of a list (month day year).
The values should be nil if your area does not use daylight
savings time.
Emacs uses these expressions to determine the starting date of daylight savings time for the holiday list and for correcting times of day in the solar and lunar calculations.
The values for Cambridge, Massachusetts are as follows:
(calendar-nth-named-day 1 0 4 year) (calendar-nth-named-day -1 0 10 year)
i.e. the first 0th day (Sunday) of the fourth month (April) in
the year specified by year, and the last Sunday of the tenth month
(October) of that year. If daylight savings time were
changed to start on October 1, you would set
calendar-daylight-savings-starts to this:
(list 10 1 year)
For a more complex example, suppose daylight savings time begins on
the first of Nisan on the Hebrew calendar. You would set
calendar-daylight-savings-starts as follows:
(calendar-gregorian-from-absolute
(calendar-absolute-from-hebrew
(list 1 1 (+ year 3760))))
because Nisan is the first month in the Hebrew calendar and the Hebrew year differs from the Gregorian year by 3760 at Nisan.
If there is no daylight savings time at your location, or if you want
all times in standard time, set calendar-daylight-savings-starts
and calendar-daylight-savings-ends to nil.
This variable specifies the difference between daylight savings time and standard time, measured in minutes. The value for Cambridge is 60.
These variables specify is the number of minutes after midnight local time when the transition to and from daylight savings time should occur. For Cambridge, both variables' values are 120.
Ordinarily, the mode line of the diary buffer window indicates any
holidays that fall on the date of the diary entries. The process of
checking for holidays can take several seconds, so including holiday
information delays the display of the diary buffer noticeably. If you'd
prefer to have a faster display of the diary buffer but without the
holiday information, set the variable holidays-in-diary-buffer to
nil.
The variable number-of-diary-entries controls the number of
days of diary entries to be displayed at one time. It affects the
initial display when view-diary-entries-initially is t, as
well as the command M-x diary. For example, the default value is
1, which says to display only the current day's diary entries. If the
value is 2, both the current day's and the next day's entries are
displayed. The value can also be a vector of seven elements: if the
value is [0 2 2 2 2 4 1] then no diary entries appear on Sunday,
the current date's and the next day's diary entries appear Monday
through Thursday, Friday through Monday's entries appear on Friday,
while on Saturday only that day's entries appear.
The variable print-diary-entries-hook is a normal hook run
after preparation of a temporary buffer containing just the diary
entries currently visible in the diary buffer. (The other, irrelevant
diary entries are really absent from the temporary buffer; in the diary
buffer, they are merely hidden.) The default value of this hook does
the printing with the command lpr-buffer. If you want to use a
different command to do the printing, just change the value of this
hook. Other uses might include, for example, rearranging the lines into
order by day and time.
You can customize the form of dates in your diary file, if neither the
standard American nor European styles suits your needs, by setting the
variable diary-date-forms. This variable is a list of forms of
dates recognized in the diary file. Each form is a list of regular
expressions (see section Regular Expressions) and the variables
month, day, year, monthname, and
dayname. The variable monthname matches the name of the
month, capitalized or not, or its three-letter abbreviation, followed by
a period or not; it matches `*'. Similarly, dayname matches
the name of the day, capitalized or not, or its three-letter
abbreviation, followed by a period or not. The variables month,
day, and year match those numerical values, preceded by
arbitrarily many zeros; they also match `*'. The default value of
diary-date-forms in the American style is
((month "/" day "[^/0-9]") (month "/" day "/" year "[^0-9]") (monthname " *" day "[^,0-9]") (monthname " *" day ", *" year "[^0-9]") (dayname "\\W"))
Emacs matches of the diary entries with the date forms is done with the standard syntax table from Fundamental mode (see section Syntax Tables), but with the `*' changed so that it is a word constituent.
The forms on the list must be mutually exclusive and must not
match any portion of the diary entry itself, just the date. If, to be
mutually exclusive, the pattern must match a portion of the diary entry
itself, the first element of the form must be backup.
This causes the date recognizer to back up to the beginning of the
current word of the diary entry. Even if you use backup, the
form must absolutely not match more than a portion of the first word of
the diary entry. The default value of diary-date-forms in the
European style is this list:
((day "/" month "[^/0-9]") (day "/" month "/" year "[^0-9]") (backup day " *" monthname "\\W+\\<[^*0-9]") (day " *" monthname " *" year "[^0-9]") (dayname "\\W"))
Notice the use of backup in the middle form because part of the
diary entry must be matched to distinguish this form from the following one.
Your diary file can have entries based on Hebrew or Islamic dates, as well as entries based on our usual Gregorian calendar. However, because the processing of such entries is time-consuming and most people don't need them, you must customize the processing of your diary file to specify that you want such entries recognized. If you want Hebrew-date diary entries, for example, you must include these lines in your `.emacs' file:
(setq nongregorian-diary-listing-hook 'list-hebrew-diary-entries) (setq nongregorian-diary-marking-hook 'mark-hebrew-diary-entries)
If you want Islamic-date entries, include these lines in your `.emacs' file:
(setq nongregorian-diary-listing-hook 'list-islamic-diary-entries) (setq nongregorian-diary-marking-hook 'mark-islamic-diary-entries)
If you want both Hebrew- and Islamic-date entries, include these lines:
(setq nongregorian-diary-listing-hook
'(list-hebrew-diary-entries list-islamic-diary-entries))
(setq nongregorian-diary-marking-hook
'(mark-hebrew-diary-entries mark-islamic-diary-entries))
Hebrew- and Islamic-date diary entries have the same formats as Gregorian-date diary entries, except that the date must be preceded with an `H' for Hebrew dates and an `I' for Islamic dates. Moreover, because the Hebrew and Islamic month names are not uniquely specified by the first three letters, you may not abbreviate them. For example, a diary entry for the Hebrew date Heshvan 25 could look like
HHeshvan 25 Happy Hebrew birthday!
and would appear in the diary for any date that corresponds to Heshvan 25 on the Hebrew calendar. Similarly, an Islamic-date diary entry might be
IDhu al-Qada 25 Happy Islamic birthday!
and would appear in the diary for any date that corresponds to Dhu al-Qada 25 on the Islamic calendar.
As with Gregorian-date diary entries, Hebrew- and Islamic-date entries are nonmarking if they are preceded with an ampersand (`&').
There are commands to help you in making Hebrew- and Islamic-date entries to your diary:
insert-hebrew-diary-entry).
insert-monthly-hebrew-diary-entry).
insert-yearly-hebrew-diary-entry).
insert-islamic-diary-entry).
insert-monthly-islamic-diary-entry).
insert-yearly-islamic-diary-entry).
These commands work exactly like the corresponding commands for ordinary diary entries: Move point to a date in the calendar window and the above commands insert the Hebrew or Islamic date (corresponding to the date indicated by point) at the end of your diary file and you can then type the diary entry. If you want the diary entry to be nonmarking, give a numeric argument to the command.
Diary display works by preparing the diary buffer and then running the
hook diary-display-hook. The default value of this hook hides
the irrelevant diary entries and then displays the buffer
(simple-diary-display). However, if you specify the hook as
follows,
(add-hook 'diary-display-hook 'fancy-diary-display)
then fancy mode displays diary entries and holidays by copying them into a special buffer that exists only for display. Copying provides an opportunity to change the displayed text to make it prettier--for example, to sort the entries by the dates they apply to.
As with simple diary display, you can print a hard copy of the buffer
with print-diary-entries. To print a hard copy of a day-by-day
diary for a week by positioning point on Sunday of that week, type
7 d and then do M-x print-diary-entries. As usual, the
inclusion of the holidays slows down the display slightly; you can speed
things up by setting the variable holidays-in-diary-buffer to
nil.
Ordinarily, the fancy diary buffer does not show days for which there are
no diary entries, even if that day is a holiday. If you want such days to be
shown in the fancy diary buffer, set the variable
diary-list-include-blanks to t.
If you use the fancy diary display, you can use the normal hook
list-diary-entries-hook to sort each day's diary entries by their
time of day. Add this line to your `.emacs' file:
(add-hook 'list-diary-entries-hook 'sort-diary-entries)
For each day, this sorts diary entries that begin with a recognizable time of day according to their times. Diary entries without times come first within each day.
If you use the fancy diary display, you can have diary entries from other files included with your own by an "include" mechanism. This facility makes possible the sharing of common diary files among groups of users. Lines in the diary file of this form:
#include "filename"
includes the diary entries from the file filename in the fancy diary buffer (because the ordinary diary buffer is just the buffer associated with your diary file, you cannot use the include mechanism unless you use the fancy diary buffer). The include mechanism is recursive, by the way, so that included files can include other files, and so on; you must be careful not to have a cycle of inclusions, of course. To enable the include facility, add lines as follows to your `.emacs' file:
(add-hook 'list-diary-entries-hook 'include-other-diary-files) (add-hook 'mark-diary-entries-hook 'mark-included-diary-files)
Sexp diary entries allow you to do more than just have complicated conditions under which a diary entry applies. If you use the fancy diary display, sexp entries can generate the text of the entry depending on the date itself. For example, an anniversary diary entry can insert the number of years since the anniversary date into the text of the diary entry. Thus the `%d' in this dairy entry:
%%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)
gets replaced by the age, so on October 31, 1990 the entry appears in the fancy diary buffer like this:
Arthur's birthday (42 years old)
If the diary file instead contains this entry:
%%(diary-anniversary 10 31 1948) Arthur's %d%s birthday
the entry in the fancy diary buffer for October 31, 1990 appears like this:
Arthur's 42nd birthday
Similarly, cyclic diary entries can interpolate the number of repetitions that have occurred:
%%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)
looks like this:
Renew medication (5th time)
in the fancy diary display on September 8, 1990.
The generality of sexp diary entries lets you specify any diary entry that you can describe algorithmically. Suppose you get paid on the 21st of the month if it is a weekday, and to the Friday before if the 21st is on a weekend. The diary entry
&%%(let ((dayname (calendar-day-of-week date))
(day (car (cdr date))))
(or (and (= day 21) (memq dayname '(1 2 3 4 5)))
(and (memq day '(19 20)) (= dayname 5)))
) Pay check deposited
applies to just those dates. This example illustrates how the sexp can
depend on the variable date; this variable is a list (month
day year) that gives the Gregorian date for which the diary
entries are being found. If the value of the expression is t,
the entry applies to that date. If the expression evaluates to
nil, the entry does not apply to that date.
The following sexp diary entries take advantage of the ability (in the fancy diary display) to concoct diary entries based on the date:
%%(diary-sunrise-sunset)
%%(diary-phases-of-moon)
%%(diary-day-of-year)
%%(diary-iso-date)
%%(diary-julian-date)
%%(diary-astro-day-number)
%%(diary-hebrew-date)
%%(diary-islamic-date)
%%(diary-french-date)
%%(diary-mayan-date)
Thus including the diary entry
&%%(diary-hebrew-date)
causes every day's diary display to contain the equivalent date on the Hebrew calendar, if you are using the fancy diary display. (With simple diary display, the line `&%%(diary-hebrew-date)' appears in the diary for any date, but does nothing particularly useful.)
There are a number of other available sexp diary entries that are important to those who follow the Hebrew calendar:
%%(diary-rosh-hodesh)
%%(diary-parasha)
%%(diary-sabbath-candles)
%%(diary-omer)
%%(diary-yahrzeit month day year) name
You can specify exactly how Emacs reminds you of an appointment and how far in advance it begins doing so. Here are the variables that you can set:
appt-message-warning-time
appt-audible
t (the default), Emacs rings the terminal bell for
appointment reminders.
appt-visible
t (the default), Emacs displays the appointment
message in echo area.
appt-display-mode-line
t (the default), Emacs displays the number of minutes
to the appointment on the mode line.
appt-msg-window
t (the default), Emacs displays the appointment
message in another window.
appt-display-duration
This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters.
Here are some tips for avoiding common errors in writing Lisp code intended for widespread use:
This recommendation applies even to names for traditional Lisp
primitives that are not primitives in Emacs Lisp--even to cadr.
Believe it or not, there is more than one plausible way to define
cadr. Play it safe; append your name prefix to produce a name
like foo-cadr or mylib-cadr instead.
If one prefix is insufficient, your package may use two or three alternative common prefixes, so long as they make sense.
Separate the prefix from the rest of the symbol name with a hyphen, `-'. This will be consistent with Emacs itself and with most Emacs Lisp programs.
provide in each separate
library program, at least if there is more than one entry point to the
program.
(require 'bar) before the first
use of the macro. (And bar should contain (provide
'bar), to make the require work.) This will cause
bar to be loaded when you byte-compile foo. Otherwise, you
risk compiling foo without the necessary macro loaded, and that
would produce compiled code that won't work right. See section Macros and Byte Compilation.
run-hooks, just as the existing major modes do. See section Hooks.
Instead, define sequences consisting of C-c followed by a non-letter. These sequences are reserved for major modes.
Changing all the major modes in Emacs 18 so they would follow this convention was a lot of work. Abandoning this convention would waste that work and inconvenience the users.
next-line or previous-line in programs; nearly
always, forward-line is more convenient as well as more
predictable and robust. See section Motion by Text Lines.
In particular, don't use these functions:
beginning-of-buffer, end-of-buffer
replace-string, replace-regexp
If you just want to move point, or replace a certain string, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code.
message function, not princ. See section The Echo Area.
error
(or signal). The function error does not return.
See section How to Signal an Error.
Do not use message, throw, sleep-for,
or beep to report errors.
edit-options
command does: switch to another buffer and let the user switch back at
will. See section Recursive Editing.
indent-sexp) using the
default indentation parameters.
Here are ways of improving the execution speed of byte-compiled lisp programs.
memq, assq or
assoc is even faster than explicit iteration. It may be worth
rearranging a data structure so that one of these primitive search
functions can be used.
byte-compile
property. If the property is non-nil, then the function is
handled specially.
For example, the following input will show you that aref is
compiled specially (see section Functions that Operate on Arrays) while elt is not
(see section Sequences):
(get 'aref 'byte-compile)
=> byte-compile-two-args
(get 'elt 'byte-compile)
=> nil
Here are some tips for the writing of documentation strings.
The documentation string can have additional lines which expand on the details of how to use the function or variable. The additional lines should be made up of complete sentences also, but they may be filled if that looks good.
However, rather than simply filling the entire documentation string, you can make it much more readable by choosing line breaks with care. Use blank lines between topics if the documentation string is long.
/ refers to its second argument as `DIVISOR'.
Also use all caps for meta-syntactic variables, such as when you show the decomposition of a list or vector into subunits, some of which may be variable.
t and nil without single-quotes.
forward-char. This will usually be
`C-f', but if the user has moved key bindings, it will be the
correct key for that user. See section Substituting Key Bindings in Documentation.
It is not practical to use `\\[...]' very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use `\\{...}' to display the rest of the mode's keymap.
We recommend these conventions for where to put comments and how to indent them:
indent-for-comment)
command automatically inserts such a `;' in the right place, or
aligns such a comment if it is already inserted.
(The following examples are taken from the Emacs sources.)
(setq base-version-list ; there was a base
(assoc (substring fn 0 start-vn) ; version to which
file-version-assoc-list)) ; this looks like
; a subversion
(prog1 (setq auto-fill-function
...
...
;; update mode-line
(force-mode-line-update)))
These comments are also written before a function definition to explain what the function does and how to call it properly.
;;; This Lisp code is run in Emacs ;;; when it is to operate as a server ;;; for other processes.
;;;; The kill ring
The indentation commands of the Lisp modes in Emacs, such as M-;
(indent-for-comment) and TAB (lisp-indent-line)
automatically indent comments according to these conventions,
depending on the the number of semicolons. See section 'Manipulating Comments' in The GNU Emacs Manual.
If you wish to "comment out" a number of lines of code, use triple semicolons at the beginnings of the lines.
Any character may be included in a comment, but it is advisable to precede a character with syntactic significance in Lisp (such as `\' or unpaired `(' or `)') with a `\', to prevent it from confusing the Emacs commands for editing Lisp.
Emacs 19 has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions. First, an example:
;;; lisp-mnt.el -- minor mode for Emacs Lisp maintainers ;; Copyright (C) 1992 Free Software Foundation, Inc. ;; Author: Eric S. Raymond <esr@snark.thyrsus.com> ;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com> ;; Created: 14 Jul 1992 ;; Version: 1.2 ;; Keywords: docs ;; This file is part of GNU Emacs. copying conditions...
The very first line should have this format:
;;; filename -- description
The description should be complete in one line.
After the copyright notice come several header comment lines, each beginning with `;;; header-name:'. Here is a table of the conventional possibilities for header-name:
If there are multiple authors, you can list them on continuation lines
led by ;;<TAB>, like this:
;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu> ;; Dave Sill <de5@ornl.gov> ;; Dave Brennan <brennan@hal.com> ;; Eric Raymond <esr@snark.thyrsus.com>
The idea behind the `Author' and `Maintainer' lines is to make possible a Lisp function to "send mail to the maintainer" without having to mine the name out by hand.
Be sure to surround the network address with `<...>' if you include the person's full name as well as the network address.
finder-by-keyword help command.
This field is important; it's how people will find your package when
they're looking for things by topic area.
Just about every Lisp library ought to have the `Author' and `Keywords' header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names--they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the library file. Here is a table of them:
This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers.
The first step in building Emacs is to compile the C sources. This produces a program called `temacs', also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.
Then, to create a working Emacs editor, issue the `temacs -l loadup' command. This directs `temacs' to evaluate the Lisp files specified in the file `loadup.el'. These files set up the normal Emacs editing environment, resulting in an Emacs which is still impure but no longer bare.
It takes a long time to load the standard Lisp files. Luckily, you don't have to do this each time you run Emacs; `temacs' can dump out an executable program called `emacs' which has these files preloaded. `emacs' starts more quickly because it does not need to load the files. This is the program that is normally installed.
To create `emacs', use the command `temacs -batch -l loadup dump'. The purpose of `-batch' here is to prevent `temacs' from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped Emacs.
When the `emacs' executable is started, it automatically loads the user's `.emacs' file, or the default initialization file `default.el' if the user has none. (See section Starting Up Emacs.) With the `.emacs' file, you can produce a version of Emacs that suits you and is not the same as the version other people use. With `default.el', you can customize Emacs for all the users at your site who don't choose to customize it for themselves. (For further reflection: why is this different from the case of the barber who shaves every man who doesn't shave himself?)
On some systems, dumping does not work. Then, you must start Emacs with the `temacs -l loadup' command each time you use it. This takes a long time, but since you need to start Emacs once a day at most--and once a week or less frequently if you never log out--the extra time is not too severe a problem.
Before `emacs' is dumped, the documentation strings for primitive
and preloaded functions (and variables) need to be found in the file
where they are stored. This is done by calling
Snarf-documentation (see section Access to Documentation Strings). These
strings were moved out of `emacs' to make it smaller.
See section Documentation Basics.
Function: dump-emacs to-file from-file
This function dumps the current state of Emacs into an executable file to-file. It takes symbols from from-file (this is normally the executable file `temacs').
If you use this function in an Emacs that was already dumped, you must
set command-line-processed to nil first for good results.
See section Command Line Arguments.
Command: emacs-version
This function returns a string describing the version of Emacs that is running. It is useful to include this string in bug reports.
(emacs-version)
=> "GNU Emacs 18.36.1 of Fri Feb 27 1987 on slug
(berkeley-unix)"
Called interactively, the function prints the same information in the echo area.
Variable: emacs-build-time
The value of this variable is the time at which Emacs was built at the local site.
emacs-build-time
=> "Fri Feb 27 14:55:57 1987"
Variable: emacs-version
The value of this variable is the version of Emacs being run. It is a
string, e.g. "18.36.1".
There are two types of storage in GNU Emacs Lisp for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data which is created during an Emacs session is kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files: data that should never change during actual use of Emacs.
Pure storage is allocated only while `temacs' is loading the
standard preloaded Lisp libraries. In the file `emacs', it is
marked as read-only (on operating systems which permit this), so that
the memory space can be shared by all the Emacs jobs running on the
machine at once. Pure storage is not expandable; a fixed amount is
allocated when Emacs is compiled, and if that is not sufficient for the
preloaded libraries, `temacs' crashes. If that happens, you will
have to increase the compilation parameter PURESIZE in the file
`config.h'. This normally won't happen unless you try to preload
additional libraries or add features to the standard ones.
Function: purecopy object
This function makes a copy of object in pure storage and returns it. It copies strings by simply making a new string with the same characters in pure storage. It recursively copies the contents of vectors and cons cells. It does not make copies of symbols, or any other objects, but just returns them unchanged. It signals an error if asked to copy markers.
This function is used only while Emacs is being built and dumped; it is called only in the file `emacs/lisp/loaddefs.el'.
Variable: pure-bytes-used
The value of this variable is the number of bytes of pure storage allocated so far. Typically, in a dumped Emacs, this number is very close to the total amount of pure storage available--if it were not, we would preallocate less.
Variable: purify-flag
This variable determines whether defun should make a copy of the
function definition in pure storage. If it is non-nil, then the
function definition is copied into pure storage.
This flag is t while loading all of the basic functions for
building Emacs initially (allowing those functions to be sharable and
non-collectible). It is set to nil when Emacs is saved out
as `emacs'. The flag is set and reset in the C sources.
You should not change this flag in a running Emacs.
When a program creates a list or the user defines a new function (such as by loading a library), then that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc. are segregated in distinct blocks in memory. (Vectors, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while strings are packed into blocks of 8k bytes.)
It is quite common to use some storage for a while, then release it by, for example, killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. (This name is traditional, but "garbage recycler" might be a more intuitive metaphor for this facility.)
The garbage collector operates by scanning all the objects that have been allocated and marking those that are still accessible to Lisp programs. To begin with, all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects which can be reached indirectly through other accessible objects are also accessible.
When this is finished, all inaccessible objects are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will notice. That is what the garbage collector arranges to do.
Unused cons cells are chained together onto a free list for
future allocation; likewise for symbols and markers. The accessible
strings are compacted so they are contiguous in memory; then the rest of
the space formerly occupied by strings is made available to the string
creation functions. Vectors, buffers, windows and other large objects
are individually allocated and freed using malloc.
Common Lisp note: unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues untilgc-cons-thresholdbytes have been used.This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection).
Command: garbage-collect
This command runs a garbage collection, and returns information on
the amount of space in use. (Garbage collection can also occur
spontaneously if you use more than gc-cons-threshold bytes of
Lisp data since the previous garbage collection.)
garbage-collect returns a list containing the following
information:
((used-conses . free-conses)
(used-syms . free-syms)
(used-markers . free-markers)
used-string-chars
used-vector-slots
(used-floats . free-floats))
(garbage-collect)
=> ((3435 . 2332) (1688 . 0)
(57 . 417) 24510 3839 (4 . 1))
Here is a table explaining each element:
User Option: gc-cons-threshold
The value of this variable is the number of bytes of storage that must be allocated for Lisp objects after one garbage collection in order to request another garbage collection. A cons cell counts as eight bytes, a string as one byte per character plus a few bytes of overhead, and so on. (Space allocated to the contents of buffers does not count.) Note that the new garbage collection does not happen immediately when the threshold is exhausted, but only the next time the Lisp evaluator is called.
The initial threshold value is 100,000. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program which creates lots of Lisp data.
You can make collections more frequent by specifying a smaller value,
down to 10,000. A value less than 10,000 will remain in effect only
until the subsequent garbage collection, at which time
garbage-collect will set the threshold back to 10,000.
Function: memory-limit
This function returns the address of the last byte Emacs has allocated, divided by 1024. We divide the value by 1024 to make sure it fits in a Lisp integer.
You can use this to get a general idea of how your actions affect the memory usage.
Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here.
An example of a special form is the definition of or, from
`eval.c'. (An ordinary function would have the same general
appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
"Eval args until one of them yields non-NIL, then return that value.\n\
The remaining args are not evalled at all.\n\
If all args return NIL, return NIL.")
(args)
Lisp_Object args;
{
register Lisp_Object val;
Lisp_Object args_left;
struct gcpro gcpro1;
if (NULL(args))
return Qnil;
args_left = args;
GCPRO1 (args_left);
do
{
val = Feval (Fcar (args_left));
if (!NULL (val))
break;
args_left = Fcdr (args_left);
}
while (!NULL(args_left));
UNGCPRO;
return val;
}
Let's start with a precise explanation of the arguments to the
DEFUN macro. Here are the general names for them:
DEFUN (lname, fname, sname, min, max, interactive, doc)
or.
For. Remember that the arguments must
be of type Lisp_Object; various macros and functions for creating
values of type Lisp_Object are declared in the file
`lisp.h'.
or, no arguments are required.
UNEVALLED, indicating a special form
that receives unevaluated arguments. A function with the equivalent of
an &rest argument would have MANY in this position. Both
UNEVALLED and MANY are macros. This argument must be one
of these macros or a number at least as large as min. It may not
be greater than six.
interactive in a Lisp function. In the case of
or, it is 0 (a null pointer), indicating that or cannot be
called interactively. A value of "" indicates an interactive
function taking no arguments.
After the call to the DEFUN macro, you must write the list
of argument names that every C function must have, followed by
ordinary C declarations for them. Normally, all the arguments must
be declared as Lisp_Object. If the function has no upper limit
on the number of arguments in Lisp, then in C it receives two arguments:
the number of Lisp arguments, and the address of a block containing their
values. These have types int and Lisp_Object *.
Within the function For itself, note the use of the macros
GCPRO1 and UNGCPRO. GCPRO1 is used to "protect"
a variable from garbage collection--to inform the garbage collector that
it must look in that variable and regard its contents as an accessible
object. This is necessary whenever you call Feval or anything
that can directly or indirectly call Feval. At such a time, any
Lisp object that you intend to refer to again must be protected somehow.
UNGCPRO cancels the protection of the variables that are
protected in the current function. It is necessary to do this explicitly.
For most data types, it suffices to know that one pointer to the object is protected; as long as the object is not recycled, all pointers to it remain valid. This is not so for strings, because the garbage collector can move them. When a string is moved, any pointers to it that the garbage collector does not know about will not be properly relocated. Therefore, all pointers to strings must be protected across any point where garbage collection may be possible.
The macro GCPRO1 protects just one local variable. If you
want to protect two, use GCPRO2 instead; repeating GCPRO1
will not work. There are also GCPRO3 and GCPRO4.
In addition to using these macros, you must declare the local
variables such as gcpro1 which they implicitly use. If you
protect two variables, with GCPRO2, you must declare
gcpro1 and gcpro2, as it uses them both. Alas, we can't
explain all the tricky details here.
Defining the C function is not enough; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. This is done by adding code to an initialization routine. The code looks like this:
defsubr (&subr-structure-name);
subr-structure-name is the name you used as the third argument to
DEFUN.
If you are adding a primitive to a file that already has Lisp
primitives defined in it, find the function (near the end of the file)
named syms_of_something, and add that function call to it.
If the file doesn't have this function, or if you create a new file, add
to it a syms_of_filename (e.g., syms_of_myfile).
Then find the spot in `emacs.c' where all of these functions are
called, and add a call to syms_of_filename there.
This function syms_of_filename is also the place to
define any C variables which are to be visible as Lisp variables.
DEFVAR_LISP is used to make a C variable of type
Lisp_Object visible in Lisp. DEFVAR_INT is used to make a
C variable of type int visible in Lisp with a value that is an
integer.
Here is another function, with more complicated arguments. This comes from the code for the X Window System, and it demonstrates the use of macros and functions to manipulate Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2,
"xSpecify coordinate pair: \nXExpression which evals to window: ",
"Return non-nil if POSITIONS is in WINDOW.\n\
\(POSITIONS is a list, (SCREEN-X SCREEN-Y)\)\n\
Returned value is list of positions expressed\n\
relative to window upper left corner.")
(coordinate, window)
register Lisp_Object coordinate, window;
{
register Lisp_Object xcoord, ycoord;
if (!CONSP (coordinate)) wrong_type_argument (Qlistp, coordinate);
CHECK_WINDOW (window, 2);
xcoord = Fcar (coordinate);
ycoord = Fcar (Fcdr (coordinate));
CHECK_NUMBER (xcoord, 0);
CHECK_NUMBER (ycoord, 1);
if ((XINT (xcoord) < XINT (XWINDOW (window)->left))
|| (XINT (xcoord) >= (XINT (XWINDOW (window)->left)
+ XINT (XWINDOW (window)->width))))
{
return Qnil;
}
XFASTINT (xcoord) -= XFASTINT (XWINDOW (window)->left);
if (XINT (ycoord) == (screen_height - 1))
return Qnil;
if ((XINT (ycoord) < XINT (XWINDOW (window)->top))
|| (XINT (ycoord) >= (XINT (XWINDOW (window)->top)
+ XINT (XWINDOW (window)->height)) - 1))
{
return Qnil;
}
XFASTINT (ycoord) -= XFASTINT (XWINDOW (window)->top);
return (Fcons (xcoord, Fcons (ycoord, Qnil)));
}
Note that you cannot directly call functions defined in Lisp as, for
example, the primitive function Fcons is called above. You must
create the appropriate Lisp form, protect everything from garbage
collection, and Feval the form, as was done in For above.
`eval.c' is a very good file to look through for examples; `lisp.h' contains the definitions for some important macros and functions.
GNU Emacs Lisp manipulates many different types of data. The actual data are stored in a heap and the only access that programs have to it is through pointers. Pointers are thirty-two bits wide in most implementations. Depending on the operating system and type of machine for which you compile Emacs, twenty-four to twenty-six bits are used to address the object, and the remaining six to eight bits are used for a tag that identifies the object's type.
Because all access to data is through tagged pointers, it is always possible to determine the type of any object. This allows variables to be untyped, and the values assigned to them to be changed without regard to type. Function arguments also can be of any type; if you want a function to accept only a certain type of argument, you must check the type explicitly using a suitable predicate (see section Type Predicates).
Buffers contain fields not directly accessible by the Lisp programmer. We describe them here, naming them by the names used in the C code. Many are accessible indirectly in Lisp programs via Lisp primitives.
name
save_modified
modtime
auto_save_modified
last_window_start
window-start position in the buffer as of
the last time the buffer was displayed in a window.
undodata
syntax_table_v
downcase_table
upcase_table
case_canon_table
case_eqv_table
display_table
nil if it doesn't
have one. See section Display Tables.
markers
backed_up
mark
markers. See section The Mark.
local_var_alist
buffer-local-variables returns a copy of this list.
See section Buffer-Local Variables.
mode_line_format
Windows have the following accessible fields:
frame
mini_p
nil if this window is a minibuffer window.
height
width
buffer
dedicated
nil if this window is dedicated to its buffer.
start
pointm
left
top
next
prev
force_start
nil, says that the window has been
scrolled explicitly by the Lisp program. At the next redisplay, if
point is off the screen, instead of scrolling the window to show the
text around point, point will be moved to a location that is on the
screen.
hscroll
use_time
get-lru-window uses this field.
display_table
nil if none is specified for it.
The fields of a process are:
name
command
filter
nil.
sentinel
nil.
buffer
pid
childp
nil if this is really a child process.
It is nil for a network connection.
flags
run, stop, closed, etc.
reason
mark
kill_without_query
nil meaning this process should not cause
confirmation to be needed if Emacs is killed.
Here is the complete list of the error symbols in standard Emacs,
grouped by concept. The list includes each symbol's message (on the
error-message property of the symbol), and a cross reference to a
description of how the error can occur.
Each error symbol has an error-conditions property which is a
list of symbols. Normally, this list includes the error symbol itself,
and the symbol error. Occasionally it includes additional
symbols, which are intermediate classifications, narrower than error
but broader than a single error symbol. For example, all the errors
in accessing files have the condition file-error.
As a special exception, the error symbol quit does not have the
condition error, because quitting is not considered an error.
See section Errors, for an explanation of how errors are generated and handled.
symbol
error
"error"
quit
"Quit"
args-out-of-range
"Args out of range"
arith-error
"Arithmetic error"/ and % in section Numbers.
beginning-of-buffer
"Beginning of buffer"
buffer-read-only
"Buffer is read-only"
end-of-buffer
"End of buffer"
end-of-file
"End of file during parsing"file-error.
file-error
file-error is present.
file-locked
file-error.
file-already-exists
file-error.
file-supersession
file-error.
invalid-function
"Invalid function"
invalid-read-syntax
"Invalid read syntax"
invalid-regexp
"Invalid regexp"
no-catch
"No catch for tag"catch and throw.
search-failed
"Search failed"
setting-constant
"Attempt to set a constant symbol"nil and t
may not be changed.
void-function
"Symbol's function definition is void"
void-variable
"Symbol's value as variable is void"
wrong-number-of-arguments
"Wrong number of arguments"
wrong-type-argument
"Wrong type argument"The table below shows all of the variables that are automatically local (when set) in each buffer in Emacs Version 18 with the common packages loaded.
abbrev-mode
auto-fill-function
buffer-auto-save-file-name
buffer-backed-up
buffer-display-table
buffer-file-name
buffer-file-number
buffer-file-truename
buffer-offer-save
buffer-read-only
buffer-saved-size
buffer-undo-list
case-fold-search
ctl-arrow
default-directory
fill-column
left-margin
local-abbrev-table
local-write-file-hooks
major-mode
mark-active
mark-ring
minor-modes
mode-line-format
mode-name
overwrite-mode
paragraph-separate
paragraph-start
require-final-newline
selective-display
selective-display-ellipses
tab-width
truncate-lines
The following symbols are used as the names for various keymaps. Some of these exist when Emacs is first started, others are only loaded when their respective mode is used. This is not an exhaustive list.
Almost all of these maps are used as local maps. Indeed, of the modes that presently exist, only Vip mode and Terminal mode ever change the global keymap.
Buffer-menu-mode-map
c-mode-map
command-history-map
ctl-x-4-map
ctl-x-map
debugger-mode-map
dired-mode-map
dired-mode buffers.
doctor-mode-map
edit-abbrevs-map
edit-abbrevs.
edit-tab-stops-map
edit-tab-stops.
electric-buffer-menu-mode-map
electric-history-map
emacs-lisp-mode-map
function-keymap
fundamental-mode-map
Helper-help-map
Info-edit-map
Info-mode-map
isearch-mode-map
lisp-interaction-mode-map
lisp-mode-map
mode-specific-map
display-bindings),
where it describes the main use of the C-c prefix key.
occur-mode-map
query-replace-map
query-replace and related
commands; also for y-or-n-p and map-y-or-n-p. The functions
that use this map do not support prefix keys; they look up one event at a
time.
text-mode-map
view-mode-map
The following is a list of hook variables which let you provide functions to be called from within Emacs on suitable occasions.
Most of these variables have names ending with `-hook' are
normal hooks, that are run with run-hooks. The value of
such a hook is a list of functions. The recommended way to put a new
function on such a hook is to call add-hook. See section Hooks, for
more information about using hooks.
The variables whose names end in `-function' have single functions as their values. Usually there is a specific reason why the variable is not a normal hook, such as, the need to pass an argument to the function. (In older Emacs versions, some of these variables had names ending in `-hook' even though they were not normal hooks.)
The variables whose names end in `-hooks' have lists of functions as their values, but these functions are called in a special way (they are passed arguments, or else their values are used).
activate-mark-hook
after-change-function
after-init-hook
auto-fill-function
auto-save-hook
before-change-function
before-init-hook
blink-paren-function
c-mode-hook
calendar-load-hook
command-history-hook
comment-indent-function
deactivate-mark-hook
diary-display-hook
diary-hook
dired-mode-hook
disabled-command-hook
edit-picture-hook
electric-buffer-menu-mode-hook
electric-command-history-hook
electric-help-mode-hook
emacs-lisp-mode-hook
find-file-hooks
find-file-not-found-hooks
first-change-hook
fortran-comment-hook
fortran-mode-hook
ftp-setup-write-file-hooks
ftp-write-file-hook
indent-mim-hook
initial-calendar-window-hook
LaTeX-mode-hook
ledit-mode-hook
lisp-indent-function
lisp-interaction-mode-hook
lisp-mode-hook
list-diary-entries-hook
m2-mode-hook
mail-mode-hook
mail-setup-hook
mark-diary-entries-hook
medit-mode-hook
mh-compose-letter-hook
mh-folder-mode-hook
mh-letter-mode-hook
mim-mode-hook
minibuffer-setup-hook
news-mode-hook
news-reply-mode-hook
news-setup-hook
nongregorian-diary-listing-hook
nongregorian-diary-marking-hook
nroff-mode-hook
outline-mode-hook
plain-TeX-mode-hook
post-command-hook
pre-abbrev-expand-hook
pre-command-hook
print-diary-entries-hook
prolog-mode-hook
protect-innocence-hook
rmail-edit-mode-hook
rmail-mode-hook
rmail-summary-mode-hook
scheme-indent-hook
scheme-mode-hook
scribe-mode-hook
shell-mode-hook
shell-set-directory-error-hook
suspend-hook
suspend-resume-hook
temp-buffer-show-function
term-setup-hook
terminal-mode-hook
terminal-mode-break-hook
TeX-mode-hook
text-mode-hook
today-visible-calendar-hook
today-invisible-calendar-hook
vi-mode-hook
view-hook
window-setup-hook
write-contents-hooks
write-file-hooks
For those users who live backwards in time, here is information about downgrading to Emacs version 18. We hope you will enjoy the greater simplicity that results from the absence of many Emacs 19 features.
The following functions are missing or different in Emacs version 18.
delete, member, indirect-function,
map-y-or-n-p, and invocation-name have been removed.
read now skips a terminator character that
terminates a symbol when reading from a buffer. Thus, if you use
read on a buffer containing `foo(bar)' following point, it
returns foo and leaves point after the open-parenthesis. This
means there's no way you can properly read the list `(bar)', but
that's the way the cookie crumbles.
Because of this simplification, it's no longer necessary for an input stream function to accept an optional argument. In Emacs 18, an input stream is always called with no arguments, and should always return the next character of input.
documentation takes just one argument;
documentation-property takes just two.
random no longer has the optional argument n.
after-load-alist and the function
eval-after-load have been removed.
autoload no longer supports autoloading a keymap.
format function, and the
optional argument noescap from prin1-to-string. We removed
the print-level variable.
eval-when-compile and
eval-and-compile, as well as the compile-defun command.
bytecode. That function runs the byte code
interpreter.
Emacs 18 doesn't have or need floating point arithmetic built in. It has a handy Lisp program that allows you to emulate floating point. You'll have to write programs specially to use it, though.
As a result, certain macros, functions, and predicates no longer handle specifications for floating point numbers.
The function string-to-number, the predicate floatp, and
the variable float-output-format have all been eliminated.
The functions float, truncate, floor, ceil,
round, and logb do not exist; neither do the functions
abs, cos, sin, tan, acos,
asin, atan, exp, expt, log10,
log, or sqrt.
The format function no longer handles the specifications
`%e', `%f' and `%g' for printing floating point numbers;
likewise for message.
kill-new and kill-append, the primitives for putting text
in the kill ring, have been eliminated.
interprogram-paste-function and
interprogram-cut-function have been removed in Emacs 18.
In addition, there's no need for mark-active and
deactivate-mark because there is no Transient Mark mode. We also
removed the hooks activate-mark-hook and
deactivate-mark-hook.
kill-region function can no longer be used in read-only
buffers. The compare-buffer-substrings and current-kill
functions have been removed.
overwrite-mode-binary has been removed.
move-to-column allows just one argument,
column.
t when successful. This
affects the functions search-forward, search-backward,
word-search-forward, word-search-backward,
re-search-forward, and re-search-backward.
match-beginning and match-end. Moreover,
save-match-data does not exist; you must use an explicit
unwind-protect to save the match data.
translate-region is gone.
before-change-function,
after-change-function, and first-change-hook have been
eliminated.
insert-abbrev-table-description is no
longer optional.
We eliminated text properties.
The functions file-accessible-directory-p, file-truename,
make-directory, delete-directory,
set-visited-file-modtime, directory-abbrev-alist,
abbreviate-file-name, write-region,
write-contents-hooks, after-save-hook,
set-default-file-modes, default-file-modes, and
unix-sync have been eliminated.
We got rid of the "initial file name" argument to
read-file-name.
Additionally, we removed the 12th element from the list returned by
file-attributes.
directory-files always sorts the list of files. It's not user
friendly to process the files in any haphazard order.
We eliminated the variables write-contents-hooks and
local-write-file-hooks.
There are no more magic filenames. Sorry, but all the mana has been used up.
There is only one frame in Emacs 18, so all of the frame functions have been eliminated.
We have simplified the way Emacs and X interact by removing a great deal of creeping featurism.
mouse-position and set-mouse-position, and
the special form track-mouse have been eliminated.
x-set-selection, x-set-cut-buffer,
x-close-current-connection, and x-open-connection have all
been removed from Emacs Lisp 18.
x-display-screens, x-server-version,
x-server-vendor, x-display-pixel-height,
x-display-mm-height, x-display-pixel-width,
x-display-mm-width, x-display-backing-store,
x-display-save-under, x-display-planes,
x-display-visual-class, x-display-color-p, and
x-display-color-cells.
Additionally, we removed the variable x-no-window-manager and the
functions x-synchronize and x-get-resource.
We didn't abolish x-display-color-p, but we renamed it to
x-color-display-p. We did abolish x-color-defined-p.
x-popup-menu no longer accepts a keymap for its first argument.
x-rebind-key and the related
function x-rebind-keys.
x-parse-geometry.
Various behaviors of windows in Emacs 19 were obsolete by the time Emacs 18 was due to come out. We have removed them. These changes are listed below.
window-at, window-minibuffer-p,
set-window-dedicated-p, coordinates-in-window-p,
walk-windows, window-dedicated-p, and window-end.
pop-up-frames,
pop-up-frame-function, display-buffer-function, and
other-window-scroll-buffer.
minibuffer-window no longer accepts a frame as
argument, since frames as objects do not exist in Emacs version 18. It
returns the window used for minibuffers.
next-window and previous-window no longer
accept the all-frames argument since there is just one frame.
get-lru-window, get-largest-window,
get-buffer-window, and get-buffer-window also no longer
take the optional argument all-frames because there is just one
frame to search.
line-number-mode and line-number-display-limit.
baud-rate is now a function rather than a variable.
message with nil as the only
argument; therefore, you can not reliably make the contents of the
minibuffer visible.
temp-buffer-show-function has been renamed
temp-buffer-show-hook.
force-mode-line-update. Use
the following idiom instead:
(set-buffer-modified-p (buffer-modified-p))
The big news about input events is that we got rid of function key and mouse events. Now the only input events are characters. What's more, these characters now have to be in the range of 0 to 127, optionally with a meta bit. This makes for big simplifications.
define-key, global-set-key,
read-key-sequence, and local-set-key used to accept
strings or vectors in Emacs 19; now they only accept strings.
single-key-description,
key-description, etc.) also no longer accept vectors, but they do
accept strings.
read-event, event-start,
posn-window, posn-point, posn-col-row,
posn-timestamp, scroll-bar-scale, and event-end
functions, since they were only useful for non-character events.
unread-command-events and last-event-frame
variables.
this-command-keys and recent-keys now always
return a string. Likewise, a keyboard macro's definition can only be a
string, not a vector.
You can no longer define menus as keymaps; good system design requires crafting a special-purpose interface for each facility, so it can precisely fit the requirements of that facility. We decided that unifying keymaps and menus was simply too much of a strain.
In Emacs 18, you can only activate menus with the mouse. Using them with a keyboard was too confusing for too many users.
Emacs 18 has no menu bars. All functions and variables related to the menu bar have been eliminated.
The minibuffer history feature has been eliminated. Thus, we removed
the optional argument hist from the minibuffer input functions
read-from-minibuffer and completing-read.
The initial argument to read-from-minibuffer and other
minibuffer input functions can no longer be a cons cell
(string . position).
In the function read-no-blanks-input, the initial argument
is no longer optional.
enable-recursive-minibuffers no longer has any
special meaning.
We removed the third argument (meta) from the function
set-input-mode. Consequently, we added the variable
meta-flag; set it to t to enable use of a Meta key, and
to nil to disable it. (Those are the only two alternatives.)
We also removed the variable extra-keyboard-modifiers.
We removed the function keyboard-translate and the variables
num-input-keys and function-key-map.
skip-syntax-forward,
skip-syntax-backward, forward-comment.
words-include-escapes.
Case tables do not exist in Emacs 18. Due to this change, we have
removed the associated functions set-standard-case-table,
standard-case-table, current-case-table,
set-case-table, and set-case-syntax-pair.
buffer-modified-tick and generate-new-buffer-name.
buffer-disable-undo to buffer-flush-undo---a
more picturesque name, you will agree.
other-buffer takes just one argument in Emacs 18.
rename-buffer now requires you to specify precisely
the new name you want.
list-buffers-directory.
kill-buffer-hook.
kill-all-local-variables always eliminates all
buffer-local variables of the current buffer. No more exceptions.
nil.
default-boundp, because it is no
longer possible for the default binding of a variable to be void.
defconst and defvar now set the
variable's local value rather than its default value when the variable
is local in the current buffer.
call-process and call-process-region no longer indicate
the termination status of the subprocess. We call on users to have faith
that the subprocess executed properly.
signal-process has been removed.
tq-create, tq-enqueue, and tq-close.
current-time, current-time-zone,
run-at-time, and cancel-timer.
current-time-string no longer accepts any optional
arguments.
sit-for and sleep-for no longer allow an
optional argument to let you specify the time period in milliseconds;
just in seconds. Additionally, we took out the optional third argument
nodisp from sit-for.
accept-process-output function. It accepts just one argument,
the process.
nil value for
the variable debug-on-error says to invoke the debugger for any
error whatever.
command-debug-status and the function
backtrace-frame.
We removed the function memory-limit.
The list returned by garbage-collect no longer contains an
element to describe floating point numbers, since there aren't any
floating point numbers in Emacs 18.
pre-abbrev-expand-hook,
pre-command-hook, post-command-hook, and
auto-save-hook.
revert-buffer-insert-file-contents-function.
add-hook; you will have to set
your hooks by hand. If you want to get really into the swing of things,
set your hook variables the archaic way: store just one function rather
than a list of functions. But that is optional.
lisp-indent-hook has been renamed to
lisp-indent-function.
auto-fill-function has been renamed to
auto-fill-hook.
blink-paren-function has been renamed to
blink-paren-hook.
temp-buffer-show-function has been renamed to
temp-buffer-show-hook.