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Version 2, June 1991
Copyright © 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.
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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.
Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.
The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.
If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.
If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.
Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.
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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.
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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 2.0.
1.1 Caveats | Flaws and a request for help. | |
1.2 Lisp History | Emacs Lisp is descended from Maclisp. | |
1.3 Conventions | How the manual is formatted. | |
1.4 Acknowledgements | The authors, editors, and sponsors of this manual. |
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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.
Please mail comments and corrections to
bug-lisp-manual@prep.ai.mit.edu
–Bil Lewis, Dan LaLiberte, Richard Stallman
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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.
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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.
1.3.1 Some Terms | Explanation of terms we use in this manual. | |
1.3.2 nil and t | How the symbols nil and t are used.
| |
1.3.3 Evaluation Notation | The format we use for examples of evaluation. | |
1.3.4 Printing Notation | The format we use for examples that print output. | |
1.3.5 Error Messages | The format we use for examples of errors. | |
1.3.6 Buffer Text Notation | The format we use for buffer contents in examples. | |
1.3.7 Format of Descriptions | Notation for describing functions, variables, etc. |
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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. @xref{Printed Representation}, 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.
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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. @xref{Accessing
Variables}.
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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)
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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
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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
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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 ----------
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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 description follows on succeeding lines, sometimes with examples.
1.3.7.1 A Sample Function Description | ||
1.3.7.2 A Sample Variable Description |
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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
:
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. (@xref{Types of Lisp Object}, 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.
@xref{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:
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.
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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.
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’.
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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.
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