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author | Richard M. Stallman <rms@gnu.org> | 1994-03-21 17:36:52 +0000 |
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committer | Richard M. Stallman <rms@gnu.org> | 1994-03-21 17:36:52 +0000 |
commit | 6b9136cd2d4ee7353467921216f9e2cc074ddaaa (patch) | |
tree | 29cbe7ffdebbeb41dbdec58cb32b81a01dc485d3 /lispref/intro.texi | |
parent | 7816ba3d3079845b5a5414068a37ca0391fa8a4c (diff) | |
download | emacs-6b9136cd2d4ee7353467921216f9e2cc074ddaaa.tar.gz |
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diff --git a/lispref/intro.texi b/lispref/intro.texi new file mode 100644 index 00000000000..2a2b02f1ad9 --- /dev/null +++ b/lispref/intro.texi @@ -0,0 +1,867 @@ +@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 See the file elisp.texi for copying conditions. +@setfilename ../info/intro + +@node Copying, Introduction, 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 +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 @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. + +@menu +* Caveats:: Flaws and a request for help. +* Lisp History:: Emacs Lisp is descended from Maclisp. +* Conventions:: How the manual is formatted. +* Acknowledgements:: The authors, editors, and sponsors of this manual. +@end menu + +@node Caveats +@section Caveats + + 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. + + 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. + +@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 +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. +@end iftex +@ifinfo + +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 + +Please mail comments and corrections to + +@example +bug-lisp-manual@@prep.ai.mit.edu +@end example + +@noindent +We let mail to this list accumulate unread until someone decides to +apply the corrections. Months, and sometimes years, go by between +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 + +@node Lisp History +@section Lisp History +@cindex 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 +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. + + 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. + +@node Conventions +@section Conventions + +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. + +@menu +* 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. +* 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. +@end menu + +@node Some Terms +@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 +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. + +@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}. + +@node nil and t +@subsection @code{nil} and @code{t} +@cindex @code{nil}, uses of +@cindex truth value +@cindex boolean +@cindex false + + In Lisp, the symbol @code{nil} is overloaded with three 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}. + + As far as the Lisp reader is concerned, @samp{()} and @samp{nil} are +identical: they stand for the same object, the symbol @code{nil}. The +different ways of writing the symbol are intended entirely for human +readers. After the Lisp reader has read either @samp{()} or @samp{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 +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}} +@end example + +@cindex @code{t} and truth +@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}. + + 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 +Variables}. + +@node Evaluation Notation +@subsection Evaluation Notation +@cindex evaluation notation +@cindex documentation 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 +the examples in this manual, this is indicated with @samp{@result{}}: + +@example +(car '(1 2)) + @result{} 1 +@end example + +@noindent +You can read this as ``@code{(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 +@samp{@expansion{}}. We may or may not show the actual result of the +evaluation of the expanded form. + +@example +(third '(a b c)) + @expansion{} (car (cdr (cdr '(a b c)))) + @result{} c +@end example + + Sometimes to help describe one form we show another form which +produces identical results. The exact equivalence of two forms is +indicated with @samp{@equiv{}}. + +@example +(make-sparse-keymap) @equiv{} (list 'keymap) +@end example + +@node Printing Notation +@subsection Printing Notation +@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. + + 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. + +@example +@group +(progn (print 'foo) (print 'bar)) + @print{} foo + @print{} bar + @result{} bar +@end group +@end example + +@node Error Messages +@subsection Error Messages +@cindex error message notation + + Some examples signal errors. This normally displays an error message +in the echo area. We show the error message on a line starting with +@samp{@error{}}. Note that @samp{@error{}} itself does not appear in +the echo area. + +@example +(+ 23 'x) +@error{} Wrong type argument: integer-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.) + +@example +---------- Buffer: foo ---------- +This is the @point{}contents of foo. +---------- Buffer: foo ---------- + +(insert "changed ") + @result{} nil +---------- Buffer: foo ---------- +This is the changed @point{}contents of foo. +---------- Buffer: foo ---------- +@end example + +@node Format of Descriptions +@subsection Format of Descriptions +@cindex description format + + 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. +@ifinfo +The category---function, variable, or whatever---appears at the +beginning of the line. +@end ifinfo +@iftex +The category---function, variable, or whatever---is printed next to the +right margin. +@end iftex +The description follows on succeeding lines, sometimes with examples. + +@menu +* A Sample Function Description:: A description of an imaginary + function, @code{foo}. +* A Sample Variable Description:: A description of an imaginary + variable, + @code{electric-future-map}. +@end menu + +@node A Sample Function Description +@subsubsection A Sample Function Description +@cindex function descriptions +@cindex command descriptions +@cindex macro descriptions +@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. +Do not write @code{&rest} when you call the function. + + Here is a description of an imaginary function @code{foo}: + +@defun foo integer1 &optional integer2 &rest integers +The function @code{foo} subtracts @var{integer1} from @var{integer2}, +then adds all the rest of the arguments to the result. If @var{integer2} +is not supplied, then the number 19 is used by default. + +@example +(foo 1 5 3 9) + @result{} 16 +(foo 5) + @result{} 14 +@end example + +More generally, + +@example +(foo @var{w} @var{x} @var{y}@dots{}) +@equiv{} +(+ (- @var{x} @var{w}) @var{y}@dots{}) +@end example +@end defun + + Any parameter 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. + + @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. +@samp{@code{@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: + +@defspec count-loop (@var{var} [@var{from} @var{to} [@var{inc}]]) @var{body}@dots{} +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{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)) +@end example + +If @var{from} and @var{to} are omitted, then @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: + +@example +(count-loop (done) + (if (pending) + (fixit) + (setq done t))) +@end example + +In this special form, the arguments @var{from} and @var{to} are +optional, but must both be present or both absent. If they are present, +@var{inc} may optionally be specified as well. These arguments are +grouped with the argument @var{var} into a list, to distinguish them +from @var{body}, which includes all remaining elements of the form. +@end defspec + +@node A Sample Variable Description +@subsubsection A Sample Variable Description +@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 +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 @code{electric-future-map} +variable.@refill + +@defvar electric-future-map +The value of this variable is a full keymap used by Electric Command +Future mode. The functions in this map allow you to edit commands you +have not yet thought about executing. +@end defvar + + User option descriptions have the same format, but `Variable' is +replaced by `User Option'. + +@node Acknowledgements +@section Acknowledgements + + 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, +Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence +R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly +Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, +Bob Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki +Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe +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, +Bill Trost, Rickard Westman, Jean White, Matthew Wilding, Carl Witty, +Dale Worley, Rusty Wright, and David D. Zuhn. |