This is elisp, produced by makeinfo version 4.0f from ./elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This Info file contains edition 2.8 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 21.2. Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Copying", with the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development."  File: elisp, Node: GPL, Next: Tips, Prev: GNU Free Documentation License, Up: Top GNU General Public License ************************** Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 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. TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 0. 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. 1. 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. 2. 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: a. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change. b. 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. c. 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.) 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. 3. 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: a. 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, b. 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, c. 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.) 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. 4. 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. 5. 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. 6. 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. 7. 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. 8. 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. 9. 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. 10. 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. NO WARRANTY 11. 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. 12. 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 OF TERMS AND CONDITIONS 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. ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES. Copyright (C) YEAR 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., 59 Temple Place, Suite 330, Boston, MA 02111, 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) YEAR 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 Lesser General Public License instead of this License.  File: elisp, Node: Tips, Next: GNU Emacs Internals, Prev: GPL, Up: Top Tips and Conventions ******************** This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters, and describes conventions Emacs Lisp programmers should follow. You can automatically check some of the conventions described below by running the command `M-x checkdoc RET' when visiting a Lisp file. It cannot check all of the conventions, and not all the warnings it gives necessarily correspond to problems, but it is worth examining them all. * Menu: * Coding Conventions:: Conventions for clean and robust programs. * Compilation Tips:: Making compiled code run fast. * Documentation Tips:: Writing readable documentation strings. * Comment Tips:: Conventions for writing comments. * Library Headers:: Standard headers for library packages.  File: elisp, Node: Coding Conventions, Next: Compilation Tips, Up: Tips Emacs Lisp Coding Conventions ============================= Here are conventions that you should follow when writing Emacs Lisp code intended for widespread use: * Since all global variables share the same name space, and all functions share another name space, you should choose a short word to distinguish your program from other Lisp programs.(1) Then take care to begin the names of all global variables, constants, and functions in your program with the chosen prefix. This helps avoid name conflicts. This recommendation applies even to names for traditional Lisp primitives that are not primitives in Emacs Lisp--even to `copy-list'. Believe it or not, there is more than one plausible way to define `copy-list'. Play it safe; append your name prefix to produce a name like `foo-copy-list' or `mylib-copy-list' instead. If you write a function that you think ought to be added to Emacs under a certain name, such as `twiddle-files', don't call it by that name in your program. Call it `mylib-twiddle-files' in your program, and send mail to `bug-gnu-emacs@gnu.org' suggesting we add it to Emacs. If and when we do, we can change the name easily enough. If one prefix is insufficient, your package may use two or three alternative common prefixes, so long as they make sense. Separate the prefix from the rest of the symbol name with a hyphen, `-'. This will be consistent with Emacs itself and with most Emacs Lisp programs. * It is often useful to put a call to `provide' in each separate library program, at least if there is more than one entry point to the program. * If a file requires certain other library programs to be loaded beforehand, then the comments at the beginning of the file should say so. Also, use `require' to make sure they are loaded. * If one file FOO uses a macro defined in another file BAR, FOO should contain this expression before the first use of the macro: (eval-when-compile (require 'BAR)) (And the library BAR should contain `(provide 'BAR)', to make the `require' work.) This will cause BAR to be loaded when you byte-compile FOO. Otherwise, you risk compiling FOO without the necessary macro loaded, and that would produce compiled code that won't work right. *Note Compiling Macros::. Using `eval-when-compile' avoids loading BAR when the compiled version of FOO is _used_. * Please don't require the `cl' package of Common Lisp extensions at run time. Use of this package is optional, and it is not part of the standard Emacs namespace. If your package loads `cl' at run time, that could cause name clashes for users who don't use that package. However, there is no problem with using the `cl' package at compile time, for the sake of macros. You do that like this: (eval-when-compile (require 'cl)) * When defining a major mode, please follow the major mode conventions. *Note Major Mode Conventions::. * When defining a minor mode, please follow the minor mode conventions. *Note Minor Mode Conventions::. * If the purpose of a function is to tell you whether a certain condition is true or false, give the function a name that ends in `p'. If the name is one word, add just `p'; if the name is multiple words, add `-p'. Examples are `framep' and `frame-live-p'. * If a user option variable records a true-or-false condition, give it a name that ends in `-flag'. * Please do not define `C-c LETTER' as a key in your major modes. These sequences are reserved for users; they are the *only* sequences reserved for users, so do not block them. Instead, define sequences consisting of `C-c' followed by a control character, a digit, or certain punctuation characters. These sequences are reserved for major modes. Changing all the Emacs major modes to follow this convention was a lot of work. Abandoning this convention would make that work go to waste, and inconvenience users. * Sequences consisting of `C-c' followed by `{', `}', `<', `>', `:' or `;' are also reserved for major modes. * Sequences consisting of `C-c' followed by any other punctuation character are allocated for minor modes. Using them in a major mode is not absolutely prohibited, but if you do that, the major mode binding may be shadowed from time to time by minor modes. * Function keys through without modifier keys are reserved for users to define. * Do not bind `C-h' following any prefix character (including `C-c'). If you don't bind `C-h', it is automatically available as a help character for listing the subcommands of the prefix character. * Do not bind a key sequence ending in except following another . (That is, it is OK to bind a sequence ending in ` '.) The reason for this rule is that a non-prefix binding for in any context prevents recognition of escape sequences as function keys in that context. * Anything which acts like a temporary mode or state which the user can enter and leave should define ` ' or ` ' as a way to escape. For a state which accepts ordinary Emacs commands, or more generally any kind of state in which followed by a function key or arrow key is potentially meaningful, then you must not define ` ', since that would preclude recognizing an escape sequence after . In these states, you should define ` ' as the way to escape. Otherwise, define ` ' instead. * Applications should not bind mouse events based on button 1 with the shift key held down. These events include `S-mouse-1', `M-S-mouse-1', `C-S-mouse-1', and so on. They are reserved for users. * Special major modes used for read-only text should usually redefine `mouse-2' and to trace some sort of reference in the text. Modes such as Dired, Info, Compilation, and Occur redefine it in this way. * When a package provides a modification of ordinary Emacs behavior, it is good to include a command to enable and disable the feature, Provide a command named `WHATEVER-mode' which turns the feature on or off, and make it autoload (*note Autoload::). Design the package so that simply loading it has no visible effect--that should not enable the feature.(2) Users will request the feature by invoking the command. * It is a bad idea to define aliases for the Emacs primitives. Use the standard names instead. * If a package needs to define an alias or a new function for compatibility with some other version of Emacs, name it with the package prefix, not with the raw name with which it occurs in the other version. Here is an example from Gnus, which provides many examples of such compatibility issues. (defalias 'gnus-point-at-bol (if (fboundp 'point-at-bol) 'point-at-bol 'line-beginning-position)) * Redefining (or advising) an Emacs primitive is discouraged. It may do the right thing for a particular program, but there is no telling what other programs might break as a result. * If a file does replace any of the functions or library programs of standard Emacs, prominent comments at the beginning of the file should say which functions are replaced, and how the behavior of the replacements differs from that of the originals. * Please keep the names of your Emacs Lisp source files to 13 characters or less. This way, if the files are compiled, the compiled files' names will be 14 characters or less, which is short enough to fit on all kinds of Unix systems. * Don't use `next-line' or `previous-line' in programs; nearly always, `forward-line' is more convenient as well as more predictable and robust. *Note Text Lines::. * Don't call functions that set the mark, unless setting the mark is one of the intended features of your program. The mark is a user-level feature, so it is incorrect to change the mark except to supply a value for the user's benefit. *Note The Mark::. In particular, don't use any of these functions: * `beginning-of-buffer', `end-of-buffer' * `replace-string', `replace-regexp' If you just want to move point, or replace a certain string, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code. * Use lists rather than vectors, except when there is a particular reason to use a vector. Lisp has more facilities for manipulating lists than for vectors, and working with lists is usually more convenient. Vectors are advantageous for tables that are substantial in size and are accessed in random order (not searched front to back), provided there is no need to insert or delete elements (only lists allow that). * The recommended way to print a message in the echo area is with the `message' function, not `princ'. *Note The Echo Area::. * When you encounter an error condition, call the function `error' (or `signal'). The function `error' does not return. *Note Signaling Errors::. Do not use `message', `throw', `sleep-for', or `beep' to report errors. * An error message should start with a capital letter but should not end with a period. * In `interactive', if you use a Lisp expression to produce a list of arguments, don't try to provide the "correct" default values for region or position arguments. Instead, provide `nil' for those arguments if they were not specified, and have the function body compute the default value when the argument is `nil'. For instance, write this: (defun foo (pos) (interactive (list (if SPECIFIED SPECIFIED-POS))) (unless pos (setq pos DEFAULT-POS)) ...) rather than this: (defun foo (pos) (interactive (list (if SPECIFIED SPECIFIED-POS DEFAULT-POS))) ...) This is so that repetition of the command will recompute these defaults based on the current circumstances. You do not need to take such precautions when you use interactive specs `d', `m' and `r', because they make special arrangements to recompute the argument values on repetition of the command. * Many commands that take a long time to execute display a message that says something like `Operating...' when they start, and change it to `Operating...done' when they finish. Please keep the style of these messages uniform: _no_ space around the ellipsis, and _no_ period after `done'. * Try to avoid using recursive edits. Instead, do what the Rmail `e' command does: use a new local keymap that contains one command defined to switch back to the old local keymap. Or do what the `edit-options' command does: switch to another buffer and let the user switch back at will. *Note Recursive Editing::. * In some other systems there is a convention of choosing variable names that begin and end with `*'. We don't use that convention in Emacs Lisp, so please don't use it in your programs. (Emacs uses such names only for special-purpose buffers.) The users will find Emacs more coherent if all libraries use the same conventions. * Try to avoid compiler warnings about undefined free variables, by adding `defvar' definitions for these variables. Sometimes adding a `require' for another package is useful to avoid compilation warnings for variables and functions defined in that package. If you do this, often it is better if the `require' acts only at compile time. Here's how to do that: (eval-when-compile (require 'foo) (defvar bar-baz)) If you bind a variable in one function, and use it or set it in another function, the compiler warns about the latter function unless the variable has a definition. But often these variables have short names, and it is not clean for Lisp packages to define such variable names. Therefore, you should rename the variable to start with the name prefix used for the other functions and variables in your package. * Indent each function with `C-M-q' (`indent-sexp') using the default indentation parameters. * Don't make a habit of putting close-parentheses on lines by themselves; Lisp programmers find this disconcerting. Once in a while, when there is a sequence of many consecutive close-parentheses, it may make sense to split the sequence in one or two significant places. * Please put a copyright notice on the file if you give copies to anyone. Use a message like this one: ;; Copyright (C) YEAR NAME ;; 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., 59 Temple Place, Suite 330, Boston, ;; MA 02111-1307 USA If you have signed papers to assign the copyright to the Foundation, then use `Free Software Foundation, Inc.' as NAME. Otherwise, use your name. ---------- Footnotes ---------- (1) The benefits of a Common Lisp-style package system are considered not to outweigh the costs. (2) Consider that the package may be loaded arbitrarily by Custom for instance.  File: elisp, Node: Compilation Tips, Next: Documentation Tips, Prev: Coding Conventions, Up: Tips Tips for Making Compiled Code Fast ================================== Here are ways of improving the execution speed of byte-compiled Lisp programs. * Profile your program with the `profile' library or the `elp' library. See the files `profile.el' and `elp.el' for instructions. * Use iteration rather than recursion whenever possible. Function calls are slow in Emacs Lisp even when a compiled function is calling another compiled function. * Using the primitive list-searching functions `memq', `member', `assq', or `assoc' is even faster than explicit iteration. It can be worth rearranging a data structure so that one of these primitive search functions can be used. * Certain built-in functions are handled specially in byte-compiled code, avoiding the need for an ordinary function call. It is a good idea to use these functions rather than alternatives. To see whether a function is handled specially by the compiler, examine its `byte-compile' property. If the property is non-`nil', then the function is handled specially. For example, the following input will show you that `aref' is compiled specially (*note Array Functions::): (get 'aref 'byte-compile) => byte-compile-two-args * If calling a small function accounts for a substantial part of your program's running time, make the function inline. This eliminates the function call overhead. Since making a function inline reduces the flexibility of changing the program, don't do it unless it gives a noticeable speedup in something slow enough that users care about the speed. *Note Inline Functions::.  File: elisp, Node: Documentation Tips, Next: Comment Tips, Prev: Compilation Tips, Up: Tips Tips for Documentation Strings ============================== Here are some tips and conventions for the writing of documentation strings. You can check many of these conventions by running the command `M-x checkdoc-minor-mode'. * Every command, function, or variable intended for users to know about should have a documentation string. * An internal variable or subroutine of a Lisp program might as well have a documentation string. In earlier Emacs versions, you could save space by using a comment instead of a documentation string, but that is no longer the case--documentation strings now take up very little space in a running Emacs. * The first line of the documentation string should consist of one or two complete sentences that stand on their own as a summary. `M-x apropos' displays just the first line, and if that line's contents don't stand on their own, the result looks bad. In particular, start the first line with a capital letter and end with a period. The documentation string is not limited to one line; use as many lines as you need to explain the details of how to use the function or variable. Please use complete sentences in the additional lines. * For consistency, phrase the verb in the first sentence of a function's documentation string as an imperative-for instance, use "Return the cons of A and B." in preference to "Returns the cons of A and B." Usually it looks good to do likewise for the rest of the first paragraph. Subsequent paragraphs usually look better if each sentence has a proper subject. * Write documentation strings in the active voice, not the passive, and in the present tense, not the future. For instance, use "Return a list containing A and B." instead of "A list containing A and B will be returned." * Avoid using the word "cause" (or its equivalents) unnecessarily. Instead of, "Cause Emacs to display text in boldface," write just "Display text in boldface." * When a command is meaningful only in a certain mode or situation, do mention that in the documentation string. For example, the documentation of `dired-find-file' is: In Dired, visit the file or directory named on this line. * Do not start or end a documentation string with whitespace. * Format the documentation string so that it fits in an Emacs window on an 80-column screen. It is a good idea for most lines to be no wider than 60 characters. The first line should not be wider than 67 characters or it will look bad in the output of `apropos'. You can fill the text if that looks good. However, rather than blindly filling the entire documentation string, you can often make it much more readable by choosing certain line breaks with care. Use blank lines between topics if the documentation string is long. * *Do not* indent subsequent lines of a documentation string so that the text is lined up in the source code with the text of the first line. This looks nice in the source code, but looks bizarre when users view the documentation. Remember that the indentation before the starting double-quote is not part of the string! * When the user tries to use a disabled command, Emacs displays just the first paragraph of its documentation string--everything through the first blank line. If you wish, you can choose which information to include before the first blank line so as to make this display useful. * A variable's documentation string should start with `*' if the variable is one that users would often want to set interactively. If the value is a long list, or a function, or if the variable would be set only in init files, then don't start the documentation string with `*'. *Note Defining Variables::. * The documentation string for a variable that is a yes-or-no flag should start with words such as "Non-nil means...", to make it clear that all non-`nil' values are equivalent and indicate explicitly what `nil' and non-`nil' mean. * When a function's documentation string mentions the value of an argument of the function, use the argument name in capital letters as if it were a name for that value. Thus, the documentation string of the function `eval' refers to its second argument as `FORM', because the actual argument name is `form': Evaluate FORM and return its value. Also write metasyntactic variables in capital letters, such as when you show the decomposition of a list or vector into subunits, some of which may vary. `KEY' and `VALUE' in the following example illustrate this practice: The argument TABLE should be an alist whose elements have the form (KEY . VALUE). Here, KEY is ... * If a line in a documentation string begins with an open-parenthesis, write a backslash before the open-parenthesis, like this: The argument FOO can be either a number \(a buffer position) or a string (a file name). This prevents the open-parenthesis from being treated as the start of a defun (*note Defuns: (emacs)Defuns.). * When a documentation string refers to a Lisp symbol, write it as it would be printed (which usually means in lower case), with single-quotes around it. For example: `lambda'. There are two exceptions: write t and nil without single-quotes. (In this manual, we use a different convention, with single-quotes for all symbols.) Help mode automatically creates a hyperlink when a documentation string uses a symbol name inside single quotes, if the symbol has either a function or a variable definition. You do not need to do anything special to make use of this feature. However, when a symbol has both a function definition and a variable definition, and you want to refer to just one of them, you can specify which one by writing one of the words `variable', `option', `function', or `command', immediately before the symbol name. (Case makes no difference in recognizing these indicator words.) For example, if you write This function sets the variable `buffer-file-name'. then the hyperlink will refer only to the variable documentation of `buffer-file-name', and not to its function documentation. If a symbol has a function definition and/or a variable definition, but those are irrelevant to the use of the symbol that you are documenting, you can write the word `symbol' before the symbol name to prevent making any hyperlink. For example, If the argument KIND-OF-RESULT is the symbol `list', this function returns a list of all the objects that satisfy the criterion. does not make a hyperlink to the documentation, irrelevant here, of the function `list'. To make a hyperlink to Info documentation, write the name of the Info node in single quotes, preceded by `info node' or `Info node'. The Info file name defaults to `emacs'. For example, See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'. * Don't write key sequences directly in documentation strings. Instead, use the `\\[...]' construct to stand for them. For example, instead of writing `C-f', write the construct `\\[forward-char]'. When Emacs displays the documentation string, it substitutes whatever key is currently bound to `forward-char'. (This is normally `C-f', but it may be some other character if the user has moved key bindings.) *Note Keys in Documentation::. * In documentation strings for a major mode, you will want to refer to the key bindings of that mode's local map, rather than global ones. Therefore, use the construct `\\<...>' once in the documentation string to specify which key map to use. Do this before the first use of `\\[...]'. The text inside the `\\<...>' should be the name of the variable containing the local keymap for the major mode. It is not practical to use `\\[...]' very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use `\\{...}' to display the rest of the mode's keymap.  File: elisp, Node: Comment Tips, Next: Library Headers, Prev: Documentation Tips, Up: Tips Tips on Writing Comments ======================== We recommend these conventions for where to put comments and how to indent them: `;' Comments that start with a single semicolon, `;', should all be aligned to the same column on the right of the source code. Such comments usually explain how the code on the same line does its job. In Lisp mode and related modes, the `M-;' (`indent-for-comment') command automatically inserts such a `;' in the right place, or aligns such a comment if it is already present. This and following examples are taken from the Emacs sources. (setq base-version-list ; there was a base (assoc (substring fn 0 start-vn) ; version to which file-version-assoc-list)) ; this looks like ; a subversion `;;' Comments that start with two semicolons, `;;', should be aligned to the same level of indentation as the code. Such comments usually describe the purpose of the following lines or the state of the program at that point. For example: (prog1 (setq auto-fill-function ... ... ;; update mode line (force-mode-line-update))) We also normally use two semicolons for comments outside functions. ;; This Lisp code is run in Emacs ;; when it is to operate as a server ;; for other processes. Every function that has no documentation string (presumably one that is used only internally within the package it belongs to), should instead have a two-semicolon comment right before the function, explaining what the function does and how to call it properly. Explain precisely what each argument means and how the function interprets its possible values. `;;;' Comments that start with three semicolons, `;;;', should start at the left margin. These are used, occasionally, for comments within functions that should start at the margin. We also use them sometimes for comments that are between functions--whether to use two or three semicolons there is a matter of style. Another use for triple-semicolon comments is for commenting out lines within a function. We use three semicolons for this precisely so that they remain at the left margin. (defun foo (a) ;;; This is no longer necessary. ;;; (force-mode-line-update) (message "Finished with %s" a)) `;;;;' Comments that start with four semicolons, `;;;;', should be aligned to the left margin and are used for headings of major sections of a program. For example: ;;;; The kill ring The indentation commands of the Lisp modes in Emacs, such as `M-;' (`indent-for-comment') and (`lisp-indent-line'), automatically indent comments according to these conventions, depending on the number of semicolons. *Note Manipulating Comments: (emacs)Comments.