@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 2002, 2003, 2004,
+@c 2005, 2006 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/intro
-@node Copying, Introduction, Top, Top
+@node Introduction, Lisp Data Types, Top, Top
@comment node-name, next, previous, up
-@unnumbered GNU GENERAL PUBLIC LICENSE
-@center Version 2, June 1991
-
-@display
-Copyright @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.
-@end display
-
-@unnumberedsec Preamble
-
- 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.
-
-@iftex
-@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-@end iftex
-@ifinfo
-@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-@end ifinfo
-
-@enumerate 0
-@item
-This License applies to any program or other work which contains
-a notice placed by the copyright holder saying it may be distributed
-under the terms of this General Public License. The ``Program'', below,
-refers to any such program or work, and a ``work based on the Program''
-means either the Program or any derivative work under copyright law:
-that is to say, a work containing the Program or a portion of it,
-either verbatim or with modifications and/or translated into another
-language. (Hereinafter, translation is included without limitation in
-the term ``modification''.) Each licensee is addressed as ``you''.
-
-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.
-
-@item
-You may copy and distribute verbatim copies of the Program's
-source code as you receive it, in any medium, provided that you
-conspicuously and appropriately publish on each copy an appropriate
-copyright notice and disclaimer of warranty; keep intact all the
-notices that refer to this License and to the absence of any warranty;
-and give any other recipients of the Program a copy of this License
-along with the Program.
-
-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.
-
-@item
-You may modify your copy or copies of the Program or any portion
-of it, thus forming a work based on the Program, and copy and
-distribute such modifications or work under the terms of Section 1
-above, provided that you also meet all of these conditions:
-
-@enumerate a
-@item
-You must cause the modified files to carry prominent notices
-stating that you changed the files and the date of any change.
-
-@item
-You must cause any work that you distribute or publish, that in
-whole or in part contains or is derived from the Program or any
-part thereof, to be licensed as a whole at no charge to all third
-parties under the terms of this License.
-
-@item
-If the modified program normally reads commands interactively
-when run, you must cause it, when started running for such
-interactive use in the most ordinary way, to print or display an
-announcement including an appropriate copyright notice and a
-notice that there is no warranty (or else, saying that you provide
-a warranty) and that users may redistribute the program under
-these conditions, and telling the user how to view a copy of this
-License. (Exception: if the Program itself is interactive but
-does not normally print such an announcement, your work based on
-the Program is not required to print an announcement.)
-@end enumerate
-
-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.
-
-@item
-You may copy and distribute the Program (or a work based on it,
-under Section 2) in object code or executable form under the terms of
-Sections 1 and 2 above provided that you also do one of the following:
-
-@enumerate a
-@item
-Accompany it with the complete corresponding machine-readable
-source code, which must be distributed under the terms of Sections
-1 and 2 above on a medium customarily used for software interchange; or,
-
-@item
-Accompany it with a written offer, valid for at least three
-years, to give any third party, for a charge no more than your
-cost of physically performing source distribution, a complete
-machine-readable copy of the corresponding source code, to be
-distributed under the terms of Sections 1 and 2 above on a medium
-customarily used for software interchange; or,
-
-@item
-Accompany it with the information you received as to the offer
-to distribute corresponding source code. (This alternative is
-allowed only for noncommercial distribution and only if you
-received the program in object code or executable form with such
-an offer, in accord with Subsection b above.)
-@end enumerate
-
-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.
-
-@item
-You may not copy, modify, sublicense, or distribute the Program
-except as expressly provided under this License. Any attempt
-otherwise to copy, modify, sublicense or distribute the Program is
-void, and will automatically terminate your rights under this License.
-However, parties who have received copies, or rights, from you under
-this License will not have their licenses terminated so long as such
-parties remain in full compliance.
-
-@item
-You are not required to accept this License, since you have not
-signed it. However, nothing else grants you permission to modify or
-distribute the Program or its derivative works. These actions are
-prohibited by law if you do not accept this License. Therefore, by
-modifying or distributing the Program (or any work based on the
-Program), you indicate your acceptance of this License to do so, and
-all its terms and conditions for copying, distributing or modifying
-the Program or works based on it.
-
-@item
-Each time you redistribute the Program (or any work based on the
-Program), the recipient automatically receives a license from the
-original licensor to copy, distribute or modify the Program subject to
-these terms and conditions. You may not impose any further
-restrictions on the recipients' exercise of the rights granted herein.
-You are not responsible for enforcing compliance by third parties to
-this License.
-
-@item
-If, as a consequence of a court judgment or allegation of patent
-infringement or for any other reason (not limited to patent issues),
-conditions are imposed on you (whether by court order, agreement or
-otherwise) that contradict the conditions of this License, they do not
-excuse you from the conditions of this License. If you cannot
-distribute so as to satisfy simultaneously your obligations under this
-License and any other pertinent obligations, then as a consequence you
-may not distribute the Program at all. For example, if a patent
-license would not permit royalty-free redistribution of the Program by
-all those who receive copies directly or indirectly through you, then
-the only way you could satisfy both it and this License would be to
-refrain entirely from distribution of the Program.
-
-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.
-
-@item
-If the distribution and/or use of the Program is restricted in
-certain countries either by patents or by copyrighted interfaces, the
-original copyright holder who places the Program under this License
-may add an explicit geographical distribution limitation excluding
-those countries, so that distribution is permitted only in or among
-countries not thus excluded. In such case, this License incorporates
-the limitation as if written in the body of this License.
-
-@item
-The Free Software Foundation may publish revised and/or new versions
-of the General Public License from time to time. Such new versions will
-be similar in spirit to the present version, but may differ in detail to
-address new problems or concerns.
-
-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.
-
-@item
-If you wish to incorporate parts of the Program into other free
-programs whose distribution conditions are different, write to the author
-to ask for permission. For software which is copyrighted by the Free
-Software Foundation, write to the Free Software Foundation; we sometimes
-make exceptions for this. Our decision will be guided by the two goals
-of preserving the free status of all derivatives of our free software and
-of promoting the sharing and reuse of software generally.
-
-@iftex
-@heading NO WARRANTY
-@end iftex
-@ifinfo
-@center NO WARRANTY
-@end ifinfo
-
-@item
-BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
-FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW@. EXCEPT WHEN
-OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
-PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
-OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
-MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE@. THE ENTIRE RISK AS
-TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU@. SHOULD THE
-PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
-REPAIR OR CORRECTION.
-
-@item
-IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
-WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
-REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
-INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
-OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
-TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
-YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
-PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
-POSSIBILITY OF SUCH DAMAGES.
-@end enumerate
-
-@iftex
-@heading END OF TERMS AND CONDITIONS
-@end iftex
-@ifinfo
-@center END OF TERMS AND CONDITIONS
-@end ifinfo
-
-@page
-@unnumberedsec How to Apply These Terms to Your New Programs
-
- 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.
-
-@smallexample
-@var{one line to give the program's name and an idea of what it does.}
-Copyright (C) 19@var{yy} @var{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.
-@end smallexample
-
-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:
-
-@smallexample
-Gnomovision version 69, Copyright (C) 19@var{yy} @var{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.
-@end smallexample
-
-The hypothetical commands @samp{show w} and @samp{show c} should show
-the appropriate parts of the General Public License. Of course, the
-commands you use may be called something other than @samp{show w} and
-@samp{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:
-
-@smallexample
-@group
-Yoyodyne, Inc., hereby disclaims all copyright
-interest in the program `Gnomovision'
-(which makes passes at compilers) written
-by James Hacker.
-
-@var{signature of Ty Coon}, 1 April 1989
-Ty Coon, President of Vice
-@end group
-@end smallexample
-
-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.
-
-@node Introduction, Types of Lisp Object, Copying, Top
@chapter Introduction
Most of the GNU Emacs text editor is written in the programming
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 @cite{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 manual attempts to be a full description of Emacs Lisp. For a
+beginner's introduction to Emacs Lisp, see @cite{An Introduction to
+Emacs Lisp Programming}, by Bob Chassell, also published by the Free
+Software Foundation. This manual presumes considerable familiarity with
+the use of Emacs for editing; see @cite{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 2.3.
+ This is edition @value{VERSION} of the GNU Emacs Lisp Reference
+Manual, corresponding to Emacs version @value{EMACSVER}.
@menu
* Caveats:: Flaws and a request for help.
* Lisp History:: Emacs Lisp is descended from Maclisp.
* Conventions:: How the manual is formatted.
+* Version Info:: Which Emacs version is running?
* Acknowledgements:: The authors, editors, and sponsors of this manual.
@end menu
@node Caveats
@section Caveats
+@cindex bugs in this manual
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 information about usage
-on VMS.
+but not flawless. There are a few topics that are not covered, 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 information about usage on VMS.
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
the manual should be fixed. Please let us know.
@iftex
- 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
+ As you use this manual, we ask that you mark pages with corrections so
+you can later look them up and send them to us. 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.
+page numbers and chapter and section numbers will change and we may have
+trouble finding the text you are talking about. Also state the number
+of the edition you are criticizing.
@end iftex
-@ifinfo
+@ifnottex
As you use this manual, we ask that you send corrections as soon as you
find them. 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 node name and function or
variable name, as appropriate. Also state the number of the edition
-which you are criticizing.
-@end ifinfo
+you are criticizing.
+@end ifnottex
+@cindex bugs
+@cindex suggestions
Please mail comments and corrections to
@example
-bug-lisp-manual@@prep.ai.mit.edu
+bug-lisp-manual@@gnu.org
@end example
@noindent
updates. So please attach no significance to the lack of a reply---your
mail @emph{will} be acted on in due time. If you want to contact the
Emacs maintainers more quickly, send mail to
-@code{bug-gnu-emacs@@prep.ai.mit.edu}.
-
-@display
- --Bil Lewis, Dan LaLiberte, Richard Stallman
-@end display
+@code{bug-gnu-emacs@@gnu.org}.
@node Lisp History
@section Lisp History
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
+intelligence. The great power of the Lisp language makes it ideal
for other purposes as well, such as writing editing commands.
@cindex Maclisp
@cindex Common Lisp
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.
+which was written in the 1960s at MIT's Project MAC. Eventually the
+implementors of the descendants of Maclisp came together and developed a
+standard for Lisp systems, called Common Lisp. In the meantime, Gerry
+Sussman and Guy Steele at MIT developed a simplified but very powerful
+dialect of Lisp, called Scheme.
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
+However, many 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.
+@pindex cl
+ A certain amount of Common Lisp emulation is available via the
+@file{cl} library. @inforef{Top, Overview, cl}.
+
+ Emacs Lisp is not at all influenced by Scheme; but the GNU project has
+an implementation of Scheme, called Guile. We use Guile in all new GNU
+software that calls for extensibility.
+
@node Conventions
@section Conventions
* Some Terms:: Explanation of terms we use in this manual.
* nil and t:: How the symbols @code{nil} and @code{t} are used.
* Evaluation Notation:: The format we use for examples of evaluation.
-* Printing Notation:: The format we use for examples that print output.
+* Printing Notation:: The format we use when examples print text.
* Error Messages:: The format we use for examples of errors.
* Buffer Text Notation:: The format we use for buffer contents in examples.
* Format of Descriptions:: Notation for describing functions, variables, etc.
@subsection Some Terms
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
+printer'' refer to those routines in Lisp that convert textual
+representations of Lisp objects into actual Lisp 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.
+addressed as ``you''. ``The user'' is the person who uses Lisp
+programs, including those you write.
-@cindex fonts
- Examples of Lisp code appear in this font or form: @code{(list 1 2
-3)}. Names that represent arguments or metasyntactic variables appear
-in this font or form: @var{first-number}.
+@cindex fonts in this manual
+ Examples of Lisp code are formatted like this: @code{(list 1 2 3)}.
+Names that represent metasyntactic variables, or arguments to a function
+being described, are formatted like this: @var{first-number}.
@node nil and t
@subsection @code{nil} and @code{t}
@cindex boolean
@cindex false
- In Lisp, the symbol @code{nil} is overloaded with three meanings: it
+ In Lisp, the symbol @code{nil} has three separate meanings: it
is a symbol with the name @samp{nil}; it is the logical truth value
@var{false}; and it is the empty list---the list of zero elements.
When used as a variable, @code{nil} always has the value @code{nil}.
there is no way to determine which representation was actually written
by the programmer.
- In this manual, we use @code{()} when we wish to emphasize that it
-means the empty list, and we use @code{nil} when we wish to emphasize
+ In this manual, we write @code{()} when we wish to emphasize that it
+means the empty list, and we write @code{nil} when we wish to emphasize
that it means the truth value @var{false}. That is a good convention to use
in Lisp programs also.
@example
(cons 'foo ()) ; @r{Emphasize the empty list}
-(not nil) ; @r{Emphasize the truth value @var{false}}
+(setq foo-flag nil) ; @r{Emphasize the truth value @var{false}}
@end example
-@cindex @code{t} and truth
+@cindex @code{t}, uses of
@cindex true
In contexts where a truth value is expected, any non-@code{nil} value
is considered to be @var{true}. However, @code{t} is the preferred way
to represent the truth value @var{true}. When you need to choose a
value which represents @var{true}, and there is no other basis for
-choosing, use @code{t}. The symbol @code{t} always has value @code{t}.
+choosing, use @code{t}. The symbol @code{t} always has the value
+@code{t}.
In Emacs Lisp, @code{nil} and @code{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 @code{setting-constant} error. @xref{Accessing
+values results in a @code{setting-constant} error. @xref{Constant
Variables}.
+@defun booleanp object
+Return non-nil iff @var{object} is one of the two canonical boolean
+values: @code{t} or @code{nil}.
+@end defun
+
@node Evaluation Notation
@subsection Evaluation Notation
@cindex evaluation notation
@cindex documentation notation
+@cindex notation
A Lisp expression that you can evaluate is called a @dfn{form}.
Evaluating a form always produces a result, which is a Lisp object. In
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
-@samp{@expansion{}}. We may or may not show the actual result of the
+@samp{@expansion{}}. We may or may not show the result of the
evaluation of the expanded form.
@example
@result{} c
@end example
- Sometimes to help describe one form we show another form which
+ Sometimes to help describe one form we show another form that
produces identical results. The exact equivalence of two forms is
indicated with @samp{@equiv{}}.
@cindex printing notation
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 @samp{*scratch*}), the printed
-text is inserted into the buffer. If you execute the example by other
-means (such as by evaluating the function @code{eval-region}), it prints
-text by displaying it in the echo area. You should be aware that text
-displayed in the echo area is truncated to a single line.
+evaluated. If you execute example code in a Lisp Interaction buffer
+(such as the buffer @samp{*scratch*}), the printed text is inserted into
+the buffer. If you execute the example by other means (such as by
+evaluating the function @code{eval-region}), the printed text is
+displayed in the echo area.
Examples in this manual indicate printed text with @samp{@print{}},
-irrespective of where that text goes. The value returned by evaluating
-the form (here @code{bar}) follows on a separate line.
+irrespective of where that text goes. The value returned by
+evaluating the form (here @code{bar}) follows on a separate line with
+@samp{@result{}}.
@example
@group
-(progn (print 'foo) (print 'bar))
+(progn (prin1 'foo) (princ "\n") (prin1 'bar))
@print{} foo
@print{} bar
@result{} bar
@example
(+ 23 'x)
-@error{} Wrong type argument: integer-or-marker-p, x
+@error{} Wrong type argument: number-or-marker-p, x
@end example
@node Buffer Text Notation
@subsection Buffer Text Notation
@cindex buffer text notation
- Some examples show modifications to text in a buffer, with ``before''
-and ``after'' versions of the text. These examples show the contents of
-the buffer in question between two lines of dashes containing the buffer
-name. In addition, @samp{@point{}} indicates the location of point.
-(The symbol for point, of course, is not part of the text in the buffer;
-it indicates the place @emph{between} two characters where point is
-located.)
+ Some examples describe modifications to the contents of a buffer, by
+showing the ``before'' and ``after'' versions of the text. These
+examples show the contents of the buffer in question between two lines
+of dashes containing the buffer name. In addition, @samp{@point{}}
+indicates the location of point. (The symbol for point, of course, is
+not part of the text in the buffer; it indicates the place
+@emph{between} two characters where point is currently located.)
@example
---------- Buffer: foo ----------
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.
-@ifinfo
+@ifnottex
The category---function, variable, or whatever---appears at the
beginning of the line.
-@end ifinfo
+@end ifnottex
@iftex
The category---function, variable, or whatever---is printed next to the
right margin.
function, @code{foo}.
* A Sample Variable Description:: A description of an imaginary
variable,
- @code{electric-future-map}.
+ @code{electric-future-map}.
@end menu
@node A Sample Function Description
@cindex special form descriptions
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 @code{&optional} in the parameter list
-indicates that the arguments for subsequent parameters may be omitted
-(omitted parameters default to @code{nil}). Do not write
-@code{&optional} when you call the function.
-
- The keyword @code{&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.
+appears first. It is followed on the same line by a list of argument
+names. These names are also used in the body of the description, to
+stand for the values of the arguments.
+
+ The appearance of the keyword @code{&optional} in the argument list
+indicates that the subsequent arguments may be omitted (omitted
+arguments default to @code{nil}). Do not write @code{&optional} when
+you call the function.
+
+ The keyword @code{&rest} (which must be followed by a single
+argument name) indicates that any number of arguments can follow. The
+single argument name following @code{&rest} will receive, as its
+value, a list of all the remaining arguments passed to the function.
Do not write @code{&rest} when you call the function.
Here is a description of an imaginary function @code{foo}:
@result{} 14
@end example
+@need 1500
More generally,
@example
@end example
@end defun
- Any parameter whose name contains the name of a type (e.g.,
+ Any argument whose name contains the name of a type (e.g.,
@var{integer}, @var{integer1} or @var{buffer}) is expected to be of that
type. A plural of a type (such as @var{buffers}) often means a list of
-objects of that type. Parameters named @var{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., @var{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.
+objects of that type. Arguments named @var{object} may be of any type.
+(@xref{Lisp Data Types}, for a list of Emacs object types.) Arguments
+with other sorts of names (e.g., @var{new-file}) are discussed
+specifically in the description of the function. In some sections,
+features common to the arguments of several functions are described at
+the beginning.
@xref{Lambda Expressions}, for a more complete description of optional
and rest arguments.
(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
+optional and repeated arguments because they can break the argument
list down into separate arguments in more complicated ways.
-@samp{@code{@r{[}@var{optional-arg}@r{]}}} means that @var{optional-arg} is
+@samp{@r{[}@var{optional-arg}@r{]}} means that @var{optional-arg} is
optional and @samp{@var{repeated-args}@dots{}} 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
@var{body} forms and then increments the variable @var{var} on each
iteration. On the first iteration, the variable has the value
-@var{from}; on subsequent iterations, it is incremented by 1 (or by
+@var{from}; on subsequent iterations, it is incremented by one (or by
@var{inc} if that is given). The loop exits before executing @var{body}
if @var{var} equals @var{to}. Here is an example:
@example
(count-loop (i 0 10)
(prin1 i) (princ " ")
- (prin1 (aref vector i)) (terpri))
+ (prin1 (aref vector i))
+ (terpri))
@end example
-If @var{from} and @var{to} are omitted, then @var{var} is bound to
+If @var{from} and @var{to} are omitted, @var{var} is bound to
@code{nil} before the loop begins, and the loop exits if @var{var} is
non-@code{nil} at the beginning of an iteration. Here is an example:
@cindex variable descriptions
@cindex option descriptions
- A @dfn{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 @dfn{user
+ A @dfn{variable} is a name that can hold a value. Although nearly
+all variables can be set by the user, certain variables exist
+specifically so that users can change them; these are called @dfn{user
options}. Ordinary variables and user options are described using a
format like that for functions except that there are no arguments.
User option descriptions have the same format, but `Variable' is
replaced by `User Option'.
+@node Version Info
+@section Version Information
+
+ These facilities provide information about which version of Emacs is
+in use.
+
+@deffn Command emacs-version &optional here
+This function returns a string describing the version of Emacs that is
+running. It is useful to include this string in bug reports.
+
+@smallexample
+@group
+(emacs-version)
+ @result{} "GNU Emacs 20.3.5 (i486-pc-linux-gnulibc1, X toolkit)
+ of Sat Feb 14 1998 on psilocin.gnu.org"
+@end group
+@end smallexample
+
+If @var{here} is non-@code{nil}, it inserts the text in the buffer
+before point, and returns @code{nil}. Called interactively, the
+function prints the same information in the echo area, but giving a
+prefix argument makes @var{here} non-@code{nil}.
+@end deffn
+
+@defvar emacs-build-time
+The value of this variable indicates the time at which Emacs was built
+at the local site. It is a list of three integers, like the value
+of @code{current-time} (@pxref{Time of Day}).
+
+@example
+@group
+emacs-build-time
+ @result{} (13623 62065 344633)
+@end group
+@end example
+@end defvar
+
+@defvar emacs-version
+The value of this variable is the version of Emacs being run. It is a
+string such as @code{"20.3.1"}. The last number in this string is not
+really part of the Emacs release version number; it is incremented each
+time you build Emacs in any given directory. A value with four numeric
+components, such as @code{"20.3.9.1"}, indicates an unreleased test
+version.
+@end defvar
+
+ The following two variables have existed since Emacs version 19.23:
+
+@defvar emacs-major-version
+The major version number of Emacs, as an integer. For Emacs version
+20.3, the value is 20.
+@end defvar
+
+@defvar emacs-minor-version
+The minor version number of Emacs, as an integer. For Emacs version
+20.3, the value is 3.
+@end defvar
+
@node Acknowledgements
@section Acknowledgements
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.
+A. Hunt, Jr.@: of Computational Logic, Inc.
Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom,
Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence
Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland
McGrath, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson,
Francesco Potorti, Friedrich Pukelsheim, Arnold D. Robbins, Raul
-Rockwell, Per Starback, Shinichirou Sugou, Kimmo Suominen, Edward Tharp,
+Rockwell, Per Starb@"ack, Shinichirou Sugou, Kimmo Suominen, Edward Tharp,
Bill Trost, Rickard Westman, Jean White, Matthew Wilding, Carl Witty,
Dale Worley, Rusty Wright, and David D. Zuhn.
+
+@ignore
+ arch-tag: d156593f-82f8-4708-a844-204e48f7f2aa
+@end ignore