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[Emacs-diffs] Changes to tips.texi
|
From: |
Glenn Morris |
|
Subject: |
[Emacs-diffs] Changes to tips.texi |
|
Date: |
Thu, 06 Sep 2007 04:14:53 +0000 |
CVSROOT: /sources/emacs
Module name: emacs
Changes by: Glenn Morris <gm> 07/09/06 04:14:53
Index: tips.texi
===================================================================
RCS file: tips.texi
diff -N tips.texi
--- tips.texi 13 Aug 2007 13:41:21 -0000 1.97
+++ /dev/null 1 Jan 1970 00:00:00 -0000
@@ -1,1130 +0,0 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Emacs Lisp Reference Manual.
address@hidden Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2001,
2002,
address@hidden 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
address@hidden See the file elisp.texi for copying conditions.
address@hidden ../info/tips
address@hidden Tips, GNU Emacs Internals, GPL, Top
address@hidden Tips and Conventions
address@hidden tips for writing Lisp
address@hidden standards of coding style
address@hidden coding standards
-
- 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 @kbd{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.
-
address@hidden
-* Coding Conventions:: Conventions for clean and robust programs.
-* Key Binding Conventions:: Which keys should be bound by which programs.
-* Programming Tips:: Making Emacs code fit smoothly in Emacs.
-* Compilation Tips:: Making compiled code run fast.
-* Warning Tips:: Turning off compiler warnings.
-* Documentation Tips:: Writing readable documentation strings.
-* Comment Tips:: Conventions for writing comments.
-* Library Headers:: Standard headers for library packages.
address@hidden menu
-
address@hidden Coding Conventions
address@hidden Emacs Lisp Coding Conventions
-
address@hidden coding conventions in Emacs Lisp
- Here are conventions that you should follow when writing Emacs Lisp
-code intended for widespread use:
-
address@hidden @bullet
address@hidden
-Simply loading the package should not change Emacs's editing behavior.
-Include a command or commands to enable and disable the feature,
-or to invoke it.
-
-This convention is mandatory for any file that includes custom
-definitions. If fixing such a file to follow this convention requires
-an incompatible change, go ahead and make the incompatible change;
-don't postpone it.
-
address@hidden
-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 address@hidden
-benefits of a Common Lisp-style package system are considered not to
-outweigh the costs.}. 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.
-
-Occasionally, for a command name intended for users to use, it is more
-convenient if some words come before the package's name prefix. And
-constructs that define functions, variables, etc., work better if they
-start with @samp{defun} or @samp{defvar}, so put the name prefix later
-on in the name.
-
-This recommendation applies even to names for traditional Lisp
-primitives that are not primitives in Emacs Lisp---such as
address@hidden Believe it or not, there is more than one plausible
-way to define @code{copy-list}. Play it safe; append your name prefix
-to produce a name like @code{foo-copy-list} or @code{mylib-copy-list}
-instead.
-
-If you write a function that you think ought to be added to Emacs under
-a certain name, such as @code{twiddle-files}, don't call it by that name
-in your program. Call it @code{mylib-twiddle-files} in your program,
-and send mail to @samp{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 can 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,
address@hidden This will be consistent with Emacs itself and with most Emacs
-Lisp programs.
-
address@hidden
-Put a call to @code{provide} at the end of each separate Lisp file.
-
address@hidden
-If a file requires certain other Lisp programs to be loaded
-beforehand, then the comments at the beginning of the file should say
-so. Also, use @code{require} to make sure they are loaded.
-
address@hidden
-If one file @var{foo} uses a macro defined in another file @var{bar},
address@hidden should contain this expression before the first use of the
-macro:
-
address@hidden
-(eval-when-compile (require '@var{bar}))
address@hidden example
-
address@hidden
-(And the library @var{bar} should contain @code{(provide '@var{bar})},
-to make the @code{require} work.) This will cause @var{bar} to be
-loaded when you byte-compile @var{foo}. Otherwise, you risk compiling
address@hidden without the necessary macro loaded, and that would produce
-compiled code that won't work right. @xref{Compiling Macros}.
-
-Using @code{eval-when-compile} avoids loading @var{bar} when
-the compiled version of @var{foo} is @emph{used}.
-
address@hidden
-Please don't require the @code{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 @code{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 @code{cl} package at
-compile time, with @code{(eval-when-compile (require 'cl))}. That's
-sufficient for using the macros in the @code{cl} package, because the
-compiler expands them before generating the byte-code.
-
address@hidden
-When defining a major mode, please follow the major mode
-conventions. @xref{Major Mode Conventions}.
-
address@hidden
-When defining a minor mode, please follow the minor mode
-conventions. @xref{Minor Mode Conventions}.
-
address@hidden
-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 @samp{p}. If
-the name is one word, add just @samp{p}; if the name is multiple words,
-add @samp{-p}. Examples are @code{framep} and @code{frame-live-p}.
-
address@hidden
-If a user option variable records a true-or-false condition, give it a
-name that ends in @samp{-flag}.
-
address@hidden
-If the purpose of a variable is to store a single function, give it a
-name that ends in @samp{-function}. If the purpose of a variable is
-to store a list of functions (i.e., the variable is a hook), please
-follow the naming conventions for hooks. @xref{Hooks}.
-
address@hidden
address@hidden unloading packages, preparing for
-If loading the file adds functions to hooks, define a function
address@hidden@var{feature}-unload-hook}, where @var{feature} is the name of
-the feature the package provides, and make it undo any such changes.
-Using @code{unload-feature} to unload the file will run this function.
address@hidden
-
address@hidden
-It is a bad idea to define aliases for the Emacs primitives. Normally
-you should use the standard names instead. The case where an alias
-may be useful is where it facilitates backwards compatibility or
-portability.
-
address@hidden
-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.
-
address@hidden
-(defalias 'gnus-point-at-bol
- (if (fboundp 'point-at-bol)
- 'point-at-bol
- 'line-beginning-position))
address@hidden example
-
address@hidden
-Redefining (or advising) an Emacs primitive is a bad idea. It may do
-the right thing for a particular program, but there is no telling what
-other programs might break as a result. In any case, it is a problem
-for debugging, because the advised function doesn't do what its source
-code says it does. If the programmer investigating the problem is
-unaware that there is advice on the function, the experience can be
-very frustrating.
-
-We hope to remove all the places in Emacs that advise primitives.
-In the mean time, please don't add any more.
-
address@hidden
-It is likewise a bad idea for one Lisp package to advise a function
-in another Lisp package.
-
address@hidden
-Likewise, avoid using @code{eval-after-load} (@pxref{Hooks for
-Loading}) in libraries and packages. This feature is meant for
-personal customizations; using it in a Lisp program is unclean,
-because it modifies the behavior of another Lisp file in a way that's
-not visible in that file. This is an obstacle for debugging, much
-like advising a function in the other package.
-
address@hidden
-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.
-
address@hidden
-Constructs that define a function or variable should be macros,
-not functions, and their names should start with @samp{def}.
-
address@hidden
-A macro that defines a function or variable should have a name that
-starts with @samp{define-}. The macro should receive the name to be
-defined as the first argument. That will help various tools find the
-definition automatically. Avoid constructing the names in the macro
-itself, since that would confuse these tools.
-
address@hidden
-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.
-
address@hidden
-In some other systems there is a convention of choosing variable names
-that begin and end with @samp{*}. 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.
-
address@hidden
-If your program contains non-ASCII characters in string or character
-constants, you should make sure Emacs always decodes these characters
-the same way, regardless of the user's settings. There are two ways
-to do that:
-
address@hidden -
address@hidden
-Use coding system @code{emacs-mule}, and specify that for
address@hidden in the @samp{-*-} line or the local variables list.
-
address@hidden
-;; XXX.el -*- coding: emacs-mule; -*-
address@hidden example
-
address@hidden
-Use one of the coding systems based on ISO 2022 (such as
address@hidden and iso-2022-7bit), and specify it with @samp{!} at
-the end for @code{coding}. (The @samp{!} turns off any possible
-character translation.)
-
address@hidden
-;; XXX.el -*- coding: iso-latin-2!; -*-
address@hidden example
address@hidden itemize
-
address@hidden
-Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the
-default indentation parameters.
-
address@hidden
-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.
-
address@hidden
-Please put a copyright notice and copying permission notice on the
-file if you distribute copies. Use a notice like this one:
-
address@hidden
-;; Copyright (C) @var{year} @var{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 3 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., 51 Franklin Street, Fifth Floor,
-;; Boston, MA 02110-1301 USA
address@hidden smallexample
-
-If you have signed papers to assign the copyright to the Foundation,
-then use @samp{Free Software Foundation, Inc.} as @var{name}.
-Otherwise, use your name. See also @xref{Library Headers}.
address@hidden itemize
-
address@hidden Key Binding Conventions
address@hidden Key Binding Conventions
address@hidden key binding, conventions for
-
address@hidden @bullet
address@hidden
address@hidden mouse-2
address@hidden references, following
-Special major modes used for read-only text should usually redefine
address@hidden and @key{RET} to trace some sort of reference in the text.
-Modes such as Dired, Info, Compilation, and Occur redefine it in this
-way.
-
-In addition, they should mark the text as a kind of ``link'' so that
address@hidden will follow it also. @xref{Links and Mouse-1}.
-
address@hidden
address@hidden reserved keys
address@hidden keys, reserved
-Please do not define @kbd{C-c @var{letter}} as a key in Lisp programs.
-Sequences consisting of @kbd{C-c} and a letter (either upper or lower
-case) are reserved for users; they are the @strong{only} sequences
-reserved for users, so do not block them.
-
-Changing all the Emacs major modes to respect this convention was a
-lot of work; abandoning this convention would make that work go to
-waste, and inconvenience users. Please comply with it.
-
address@hidden
-Function keys @key{F5} through @key{F9} without modifier keys are
-also reserved for users to define.
-
address@hidden
-Applications should not bind mouse events based on button 1 with the
-shift key held down. These events include @kbd{S-mouse-1},
address@hidden, @kbd{C-S-mouse-1}, and so on. They are reserved for
-users.
-
address@hidden
-Sequences consisting of @kbd{C-c} followed by a control character or a
-digit are reserved for major modes.
-
address@hidden
-Sequences consisting of @kbd{C-c} followed by @address@hidden, @address@hidden,
address@hidden<}, @kbd{>}, @kbd{:} or @kbd{;} are also reserved for major modes.
-
address@hidden
-Sequences consisting of @kbd{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.
-
address@hidden
-Do not bind @kbd{C-h} following any prefix character (including
address@hidden). If you don't bind @kbd{C-h}, it is automatically available
-as a help character for listing the subcommands of the prefix character.
-
address@hidden
-Do not bind a key sequence ending in @key{ESC} except following
-another @key{ESC}. (That is, it is OK to bind a sequence ending in
address@hidden@key{ESC} @key{ESC}}.)
-
-The reason for this rule is that a non-prefix binding for @key{ESC} in
-any context prevents recognition of escape sequences as function keys in
-that context.
-
address@hidden
-Anything which acts like a temporary mode or state which the user can
-enter and leave should define @address@hidden @key{ESC}} or
address@hidden@key{ESC} @key{ESC} @key{ESC}} as a way to escape.
-
-For a state which accepts ordinary Emacs commands, or more generally any
-kind of state in which @key{ESC} followed by a function key or arrow key
-is potentially meaningful, then you must not define @address@hidden
address@hidden, since that would preclude recognizing an escape sequence
-after @key{ESC}. In these states, you should define @address@hidden
address@hidden @key{ESC}} as the way to escape. Otherwise, define
address@hidden@key{ESC} @key{ESC}} instead.
address@hidden itemize
-
address@hidden Programming Tips
address@hidden Emacs Programming Tips
address@hidden programming conventions
-
- Following these conventions will make your program fit better
-into Emacs when it runs.
-
address@hidden @bullet
address@hidden
-Don't use @code{next-line} or @code{previous-line} in programs; nearly
-always, @code{forward-line} is more convenient as well as more
-predictable and robust. @xref{Text Lines}.
-
address@hidden
-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. @xref{The Mark}.
-
-In particular, don't use any of these functions:
-
address@hidden @bullet
address@hidden
address@hidden, @code{end-of-buffer}
address@hidden
address@hidden, @code{replace-regexp}
address@hidden
address@hidden, @code{insert-buffer}
address@hidden itemize
-
-If you just want to move point, or replace a certain string, or insert
-a file or buffer's contents, without any of the other features
-intended for interactive users, you can replace these functions with
-one or two lines of simple Lisp code.
-
address@hidden
-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).
-
address@hidden
-The recommended way to show a message in the echo area is with
-the @code{message} function, not @code{princ}. @xref{The Echo Area}.
-
address@hidden
-When you encounter an error condition, call the function @code{error}
-(or @code{signal}). The function @code{error} does not return.
address@hidden Errors}.
-
-Do not use @code{message}, @code{throw}, @code{sleep-for},
-or @code{beep} to report errors.
-
address@hidden
-An error message should start with a capital letter but should not end
-with a period.
-
address@hidden
-A question asked in the minibuffer with @code{y-or-n-p} or
address@hidden should start with a capital letter and end with
address@hidden }.
-
address@hidden
-When you mention a default value in a minibuffer prompt,
-put it and the word @samp{default} inside parentheses.
-It should look like this:
-
address@hidden
-Enter the answer (default 42):
address@hidden example
-
address@hidden
-In @code{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 @code{nil} for those
-arguments if they were not specified, and have the function body
-compute the default value when the argument is @code{nil}. For
-instance, write this:
-
address@hidden
-(defun foo (pos)
- (interactive
- (list (if @var{specified} @var{specified-pos})))
- (unless pos (setq pos @var{default-pos}))
- ...)
address@hidden example
-
address@hidden
-rather than this:
-
address@hidden
-(defun foo (pos)
- (interactive
- (list (if @var{specified} @var{specified-pos}
- @var{default-pos})))
- ...)
address@hidden example
-
address@hidden
-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 @samp{d}, @samp{m} and @samp{r}, because they make special
-arrangements to recompute the argument values on repetition of the
-command.
-
address@hidden
-Many commands that take a long time to execute display a message that
-says something like @samp{Operating...} when they start, and change it to
address@hidden when they finish. Please keep the style of
-these messages uniform: @emph{no} space around the ellipsis, and
address@hidden period after @samp{done}.
-
address@hidden
-Try to avoid using recursive edits. Instead, do what the Rmail @kbd{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
address@hidden command does: switch to another buffer and let the
-user switch back at will. @xref{Recursive Editing}.
address@hidden itemize
-
address@hidden Compilation Tips
address@hidden Tips for Making Compiled Code Fast
address@hidden execution speed
address@hidden speedups
-
- Here are ways of improving the execution speed of byte-compiled
-Lisp programs.
-
address@hidden @bullet
address@hidden
address@hidden profiling
address@hidden timing programs
address@hidden @file{elp.el}
-Profile your program with the @file{elp} library. See the file
address@hidden for instructions.
-
address@hidden
address@hidden @file{benchmark.el}
address@hidden benchmarking
-Check the speed of individual Emacs Lisp forms using the
address@hidden library. See the functions @code{benchmark-run} and
address@hidden in @file{benchmark.el}.
-
address@hidden
-Use iteration rather than recursion whenever possible.
-Function calls are slow in Emacs Lisp even when a compiled function
-is calling another compiled function.
-
address@hidden
-Using the primitive list-searching functions @code{memq}, @code{member},
address@hidden, or @code{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.
-
address@hidden
-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 @code{byte-compile}
-property. If the property is address@hidden, then the function is
-handled specially.
-
-For example, the following input will show you that @code{aref} is
-compiled specially (@pxref{Array Functions}):
-
address@hidden
address@hidden
-(get 'aref 'byte-compile)
- @result{} byte-compile-two-args
address@hidden group
address@hidden example
-
address@hidden
-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. @xref{Inline Functions}.
address@hidden itemize
-
address@hidden Warning Tips
address@hidden Tips for Avoiding Compiler Warnings
address@hidden byte compiler warnings, how to avoid
-
address@hidden @bullet
address@hidden
-Try to avoid compiler warnings about undefined free variables, by adding
-dummy @code{defvar} definitions for these variables, like this:
-
address@hidden
-(defvar foo)
address@hidden example
-
-Such a definition has no effect except to tell the compiler
-not to warn about uses of the variable @code{foo} in this file.
-
address@hidden
-If you use many functions and variables from a certain file, you can
-add a @code{require} for that package to avoid compilation warnings
-for them. For instance,
-
address@hidden
-(eval-when-compile
- (require 'foo))
address@hidden example
-
address@hidden
-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 adding a definition would be
-unclean if the variable has a short name, since Lisp packages should
-not define short variable names. The right thing to do is to rename
-this variable to start with the name prefix used for the other
-functions and variables in your package.
-
address@hidden
-The last resort for avoiding a warning, when you want to do something
-that usually is a mistake but it's not a mistake in this one case,
-is to put a call to @code{with-no-warnings} around it.
address@hidden itemize
-
address@hidden Documentation Tips
address@hidden Tips for Documentation Strings
address@hidden documentation strings, conventions and tips
-
address@hidden checkdoc-minor-mode
- Here are some tips and conventions for the writing of documentation
-strings. You can check many of these conventions by running the command
address@hidden checkdoc-minor-mode}.
-
address@hidden @bullet
address@hidden
-Every command, function, or variable intended for users to know about
-should have a documentation string.
-
address@hidden
-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.
-
address@hidden
-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 @code{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.
-
address@hidden
-The first line of the documentation string should consist of one or two
-complete sentences that stand on their own as a summary. @kbd{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.
-
-For a function, the first line should briefly answer the question,
-``What does this function do?'' For a variable, the first line should
-briefly answer the question, ``What does this value mean?''
-
-Don't limit the documentation string 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 for the rest of the text too.
-
address@hidden
-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.
-
address@hidden
-The first line should mention all the important arguments of the
-function, and should mention them in the order that they are written
-in a function call. If the function has many arguments, then it is
-not feasible to mention them all in the first line; in that case, the
-first line should mention the first few arguments, including the most
-important arguments.
-
address@hidden
-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
address@hidden refers to its second argument as @samp{FORM}, because the
-actual argument name is @code{form}:
-
address@hidden
-Evaluate FORM and return its value.
address@hidden example
-
-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. @samp{KEY} and @samp{VALUE} in the following example
-illustrate this practice:
-
address@hidden
-The argument TABLE should be an alist whose elements
-have the form (KEY . VALUE). Here, KEY is ...
address@hidden example
-
address@hidden
-Never change the case of a Lisp symbol when you mention it in a doc
-string. If the symbol's name is @code{foo}, write ``foo,'' not
-``Foo'' (which is a different symbol).
-
-This might appear to contradict the policy of writing function
-argument values, but there is no real contradiction; the argument
address@hidden is not the same thing as the @emph{symbol} which the
-function uses to hold the value.
-
-If this puts a lower-case letter at the beginning of a sentence
-and that annoys you, rewrite the sentence so that the symbol
-is not at the start of it.
-
address@hidden
-Do not start or end a documentation string with whitespace.
-
address@hidden
address@hidden 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!
-
address@hidden hyperlinks}
address@hidden
address@hidden
-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: @samp{`lambda'}. There are two exceptions:
-write @code{t} and @code{nil} without single-quotes.
address@hidden iftex
address@hidden
-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: @samp{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.)
address@hidden ifnottex
-
address@hidden hyperlinks in documentation strings
-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
address@hidden, @samp{option}, @samp{function}, or @samp{command},
-immediately before the symbol name. (Case makes no difference in
-recognizing these indicator words.) For example, if you write
-
address@hidden
-This function sets the variable `buffer-file-name'.
address@hidden example
-
address@hidden
-then the hyperlink will refer only to the variable documentation of
address@hidden, 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 words @samp{symbol} or @samp{program} before the
-symbol name to prevent making any hyperlink. For example,
-
address@hidden
-If the argument KIND-OF-RESULT is the symbol `list',
-this function returns a list of all the objects
-that satisfy the criterion.
address@hidden example
-
address@hidden
-does not make a hyperlink to the documentation, irrelevant here, of the
-function @code{list}.
-
-Normally, no hyperlink is made for a variable without variable
-documentation. You can force a hyperlink for such variables by
-preceding them with one of the words @samp{variable} or
address@hidden
-
-Hyperlinks for faces are only made if the face name is preceded or
-followed by the word @samp{face}. In that case, only the face
-documentation will be shown, even if the symbol is also defined as a
-variable or as a function.
-
-To make a hyperlink to Info documentation, write the name of the Info
-node (or anchor) in single quotes, preceded by @samp{info node},
address@hidden node}, @samp{info anchor} or @samp{Info anchor}. The Info
-file name defaults to @samp{emacs}. For example,
-
address@hidden
-See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
address@hidden smallexample
-
-Finally, to create a hyperlink to URLs, write the URL in single
-quotes, preceded by @samp{URL}. For example,
-
address@hidden
-The home page for the GNU project has more information (see URL
-`http://www.gnu.org/').
address@hidden smallexample
-
address@hidden
-Don't write key sequences directly in documentation strings. Instead,
-use the @address@hidden construct to stand for them. For example,
-instead of writing @samp{C-f}, write the construct
address@hidden When Emacs displays the documentation string,
-it substitutes whatever key is currently bound to @code{forward-char}.
-(This is normally @samp{C-f}, but it may be some other character if the
-user has moved key bindings.) @xref{Keys in Documentation}.
-
address@hidden
-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 @samp{\\<@dots{}>} once in the
-documentation string to specify which key map to use. Do this before
-the first use of @address@hidden The text inside the
address@hidden<@dots{}>} should be the name of the variable containing the
-local keymap for the major mode.
-
-It is not practical to use @address@hidden 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
address@hidden@address@hidden@}} to display the rest of the mode's keymap.
-
address@hidden
-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
address@hidden''
-Usually it looks good to do likewise for the rest of the first
-paragraph. Subsequent paragraphs usually look better if each sentence
-is indicative and has a proper subject.
-
address@hidden
-The documentation string for a function that is a yes-or-no predicate
-should start with words such as ``Return t if,'' to indicate
-explicitly what constitutes ``truth.'' The word ``return'' avoids
-starting the sentence with lower-case ``t,'' which could be somewhat
-distracting.
-
address@hidden
-If a line in a documentation string begins with an open-parenthesis,
-write a backslash before the open-parenthesis, like this:
-
address@hidden
-The argument FOO can be either a number
-\(a buffer position) or a string (a file name).
address@hidden example
-
-This prevents the open-parenthesis from being treated as the start of a
-defun (@pxref{Defuns,, Defuns, emacs, The GNU Emacs Manual}).
-
address@hidden
-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.''
-
address@hidden
-Avoid using the word ``cause'' (or its equivalents) unnecessarily.
-Instead of, ``Cause Emacs to display text in boldface,'' write just
-``Display text in boldface.''
-
address@hidden
-Avoid using ``iff'' (a mathematics term meaning ``if and only if''),
-since many people are unfamiliar with it and mistake it for a typo. In
-most cases, the meaning is clear with just ``if''. Otherwise, try to
-find an alternate phrasing that conveys the meaning.
-
address@hidden
-When a command is meaningful only in a certain mode or situation,
-do mention that in the documentation string. For example,
-the documentation of @code{dired-find-file} is:
-
address@hidden
-In Dired, visit the file or directory named on this line.
address@hidden example
-
address@hidden
-When you define a variable that users ought to set interactively, you
-normally should use @code{defcustom}. However, if for some reason you
-use @code{defvar} instead, start the doc string with a @samp{*}.
address@hidden Variables}.
-
address@hidden
-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 address@hidden values are equivalent and indicate explicitly what
address@hidden and address@hidden mean.
address@hidden itemize
-
address@hidden Comment Tips
address@hidden Tips on Writing Comments
address@hidden comments, Lisp convention for
-
- We recommend these conventions for where to put comments and how to
-indent them:
-
address@hidden @samp
address@hidden ;
-Comments that start with a single semicolon, @samp{;}, 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 @kbd{M-;} (@code{indent-for-comment})
-command automatically inserts such a @samp{;} in the right place, or
-aligns such a comment if it is already present.
-
-This and following examples are taken from the Emacs sources.
-
address@hidden
address@hidden
-(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
address@hidden group
address@hidden smallexample
-
address@hidden ;;
-Comments that start with two semicolons, @samp{;;}, 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:
-
address@hidden
address@hidden
-(prog1 (setq auto-fill-function
- @dots{}
- @dots{}
- ;; update mode line
- (force-mode-line-update)))
address@hidden group
address@hidden smallexample
-
-We also normally use two semicolons for comments outside functions.
-
address@hidden
address@hidden
-;; This Lisp code is run in Emacs
-;; when it is to operate as a server
-;; for other processes.
address@hidden group
address@hidden smallexample
-
-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.
-
address@hidden ;;;
-Comments that start with three semicolons, @samp{;;;}, 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 depends on whether the comment should be considered a
-``heading'' by Outline minor mode. By default, comments starting with
-at least three semicolons (followed by a single space and a
-non-whitespace character) are considered headings, comments starting
-with two or less are not.
-
-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. By default, Outline minor mode does
-not consider a comment to be a heading (even if it starts with at
-least three semicolons) if the semicolons are followed by at least two
-spaces. Thus, if you add an introductory comment to the commented out
-code, make sure to indent it by at least two spaces after the three
-semicolons.
-
address@hidden
-(defun foo (a)
-;;; This is no longer necessary.
-;;; (force-mode-line-update)
- (message "Finished with %s" a))
address@hidden smallexample
-
-When commenting out entire functions, use two semicolons.
-
address@hidden ;;;;
-Comments that start with four semicolons, @samp{;;;;}, should be aligned
-to the left margin and are used for headings of major sections of a
-program. For example:
-
address@hidden
-;;;; The kill ring
address@hidden smallexample
address@hidden table
-
address@hidden
-The indentation commands of the Lisp modes in Emacs, such as @kbd{M-;}
-(@code{indent-for-comment}) and @key{TAB} (@code{lisp-indent-line}),
-automatically indent comments according to these conventions,
-depending on the number of semicolons. @xref{Comments,,
-Manipulating Comments, emacs, The GNU Emacs Manual}.
-
address@hidden Library Headers
address@hidden Conventional Headers for Emacs Libraries
address@hidden header comments
address@hidden library header comments
-
- Emacs has conventions for using special comments in Lisp libraries
-to divide them into sections and give information such as who wrote
-them. This section explains these conventions.
-
- We'll start with an example, a package that is included in the Emacs
-distribution.
-
- Parts of this example reflect its status as part of Emacs; for
-example, the copyright notice lists the Free Software Foundation as the
-copyright holder, and the copying permission says the file is part of
-Emacs. When you write a package and post it, the copyright holder would
-be you (unless your employer claims to own it instead), and you should
-get the suggested copying permission from the end of the GNU General
-Public License itself. Don't say your file is part of Emacs
-if we haven't installed it in Emacs yet!
-
- With that warning out of the way, on to the example:
-
address@hidden
address@hidden
-;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers
-
-;; Copyright (C) 1992 Free Software Foundation, Inc.
address@hidden group
-
-;; Author: Eric S. Raymond <esr@@snark.thyrsus.com>
-;; Maintainer: Eric S. Raymond <esr@@snark.thyrsus.com>
-;; Created: 14 Jul 1992
-;; Version: 1.2
address@hidden
-;; Keywords: docs
-
-;; This file is part of GNU Emacs.
address@hidden
-;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
-;; Boston, MA 02110-1301, USA.
address@hidden group
address@hidden smallexample
-
- The very first line should have this format:
-
address@hidden
-;;; @var{filename} --- @var{description}
address@hidden example
-
address@hidden
-The description should be complete in one line. If the file
-needs a @samp{-*-} specification, put it after @var{description}.
-
- After the copyright notice come several @dfn{header comment} lines,
-each beginning with @samp{;; @var{header-name}:}. Here is a table of
-the conventional possibilities for @var{header-name}:
-
address@hidden @samp
address@hidden Author
-This line states the name and net address of at least the principal
-author of the library.
-
-If there are multiple authors, you can list them on continuation lines
-led by @code{;;} and a tab character, like this:
-
address@hidden
address@hidden
-;; Author: Ashwin Ram <Ram-Ashwin@@cs.yale.edu>
-;; Dave Sill <de5@@ornl.gov>
-;; Dave Brennan <brennan@@hal.com>
-;; Eric Raymond <esr@@snark.thyrsus.com>
address@hidden group
address@hidden smallexample
-
address@hidden Maintainer
-This line should contain a single name/address as in the Author line, or
-an address only, or the string @samp{FSF}. If there is no maintainer
-line, the person(s) in the Author field are presumed to be the
-maintainers. The example above is mildly bogus because the maintainer
-line is redundant.
-
-The idea behind the @samp{Author} and @samp{Maintainer} lines is to make
-possible a Lisp function to ``send mail to the maintainer'' without
-having to mine the name out by hand.
-
-Be sure to surround the network address with @samp{<@dots{}>} if
-you include the person's full name as well as the network address.
-
address@hidden Created
-This optional line gives the original creation date of the
-file. For historical interest only.
-
address@hidden Version
-If you wish to record version numbers for the individual Lisp program, put
-them in this line.
-
address@hidden Adapted-By
-In this header line, place the name of the person who adapted the
-library for installation (to make it fit the style conventions, for
-example).
-
address@hidden Keywords
-This line lists keywords for the @code{finder-by-keyword} help command.
-Please use that command to see a list of the meaningful keywords.
-
-This field is important; it's how people will find your package when
-they're looking for things by topic area. To separate the keywords, you
-can use spaces, commas, or both.
address@hidden table
-
- Just about every Lisp library ought to have the @samp{Author} and
address@hidden header comment lines. Use the others if they are
-appropriate. You can also put in header lines with other header
-names---they have no standard meanings, so they can't do any harm.
-
- We use additional stylized comments to subdivide the contents of the
-library file. These should be separated by blank lines from anything
-else. Here is a table of them:
-
address@hidden @samp
address@hidden ;;; Commentary:
-This begins introductory comments that explain how the library works.
-It should come right after the copying permissions, terminated by a
address@hidden Log}, @samp{History} or @samp{Code} comment line. This
-text is used by the Finder package, so it should make sense in that
-context.
-
address@hidden ;;; Documentation:
-This was used in some files in place of @samp{;;; Commentary:},
-but it is deprecated.
-
address@hidden ;;; Change Log:
-This begins change log information stored in the library file (if you
-store the change history there). For Lisp files distributed with Emacs,
-the change history is kept in the file @file{ChangeLog} and not in the
-source file at all; these files generally do not have a @samp{;;; Change
-Log:} line. @samp{History} is an alternative to @samp{Change Log}.
-
address@hidden ;;; Code:
-This begins the actual code of the program.
-
address@hidden ;;; @var{filename} ends here
-This is the @dfn{footer line}; it appears at the very end of the file.
-Its purpose is to enable people to detect truncated versions of the file
-from the lack of a footer line.
address@hidden table
-
address@hidden
- arch-tag: 9ea911c2-6b1d-47dd-88b7-0a94e8b27c2e
address@hidden ignore
- [Emacs-diffs] Changes to tips.texi,
Glenn Morris <=