@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/tips
-@node Tips, GNU Emacs Internals, Calendar, Top
-@appendix Tips and Standards
+@node Tips, GNU Emacs Internals, System Interface, Top
+@appendix Tips and Conventions
@cindex tips
@cindex standards of coding style
@cindex 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.
+ 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.
@menu
-* Style Tips:: Writing clean and robust programs.
+* 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.
@end menu
-@node Style Tips
-@section Writing Clean Lisp Programs
+@node Coding Conventions
+@section Emacs Lisp Coding Conventions
- Here are some tips for avoiding common errors in writing Lisp code
-intended for widespread use:
+ Here are conventions that you should follow when writing Emacs Lisp
+code intended for widespread use:
@itemize @bullet
@item
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 @code{cadr}.
-Believe it or not, there is more than one plausible way to define
-@code{cadr}. Play it safe; append your name prefix to produce a name
-like @code{foo-cadr} or @code{mylib-cadr} instead.
+primitives that are not primitives in Emacs Lisp---even to
+@code{copy-list}. 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@@prep.ai.mit.edu} suggesting we add
+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 may use two or three
library program, at least if there is more than one entry point to the
program.
+@item
+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 @code{require} to make sure they are loaded.
+
@item
If one file @var{foo} uses a macro defined in another file @var{bar},
-@var{foo} should contain @code{(require '@var{bar})} before the first
-use of the macro. (And @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 @var{foo} without the necessary macro loaded, and that
-would produce compiled code that won't work right. @xref{Compiling
-Macros}.
+@var{foo} should contain this expression before the first use of the
+macro:
+
+@example
+(eval-when-compile (require '@var{bar}))
+@end example
+
+@noindent
+(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
+@var{foo} 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}.
+
+@item
+When defining a major mode, please follow the major mode
+conventions. @xref{Major Mode Conventions}.
@item
-If you define a major mode, make sure to run a hook variable using
-@code{run-hooks}, just as the existing major modes do. @xref{Hooks}.
+When defining a minor mode, please follow the minor mode
+conventions. @xref{Minor Mode Conventions}.
@item
If the purpose of a function is to tell you whether a certain condition
name that ends in @samp{-flag}.
@item
+@cindex reserved keys
+@cindex keys, reserved
Please do not define @kbd{C-c @var{letter}} as a key in your major
modes. These sequences are reserved for users; they are the
-@strong{only} sequences reserved for users, so we cannot do without
-them.
+@strong{only} sequences reserved for users, so do not block them.
-Instead, define sequences consisting of @kbd{C-c} followed by a
-non-letter. These sequences are reserved for major modes.
+Instead, define sequences consisting of @kbd{C-c} followed by a control
+character, a digit, or certain punctuation characters. These sequences
+are reserved for major modes.
-Changing all the major modes in Emacs 18 so they would follow this
-convention was a lot of work. Abandoning this convention would make
-that work go to waste, and inconvenience users.
+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.
@item
Sequences consisting of @kbd{C-c} followed by @kbd{@{}, @kbd{@}},
may be shadowed from time to time by minor modes.
@item
-You should not bind @kbd{C-h} following any prefix character (including
+Function keys @key{F5} through @key{F9} without modifier keys are
+reserved for users to define.
+
+@item
+Do not bind @kbd{C-h} following any prefix character (including
@kbd{C-c}). If you don't bind @kbd{C-h}, it is automatically available
as a help character for listing the subcommands of the prefix character.
@item
-You should 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
+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
@kbd{@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.
+@item
+Anything which acts like a temporary mode or state which the user can
+enter and leave should define @kbd{@key{ESC} @key{ESC}} of
+@kbd{@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 @kbd{@key{ESC}
+@key{ESC}}, since that would preclude recognizing an escape sequence
+after @key{ESC}. In these states, you should define @kbd{@key{ESC}
+@key{ESC} @key{ESC}} as the way to escape. Otherwise, define
+@kbd{@key{ESC} @key{ESC}} instead.
+
@item
Applications should not bind mouse events based on button 1 with the
shift key held down. These events include @kbd{S-mouse-1},
users.
@item
-Modes should redefine @kbd{mouse-2} as a command to follow some sort of
-reference in the text of a buffer, if users usually would not want to
-alter the text in that buffer by hand. Modes such as Dired, Info,
-Compilation, and Occur redefine it in this way.
+Special major modes used for read-only text should usually redefine
+@kbd{mouse-2} 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.
@item
When a package provides a modification of ordinary Emacs behavior, it is
standard names instead.
@item
-Redefining an Emacs primitive is an even worse idea.
-It may do the right thing for a particular program, but
-there is no telling what other programs might break as a result.
+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.
@item
If a file does replace any of the functions or library programs of
say which functions are replaced, and how the behavior of the
replacements differs from that of the originals.
-@item
-If a file requires certain standard library programs to be loaded
-beforehand, then the comments at the beginning of the file should say
-so.
-
@item
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
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 these functions:
+In particular, don't use any of these functions:
@itemize @bullet
@item
Do not use @code{message}, @code{throw}, @code{sleep-for},
or @code{beep} to report errors.
+@item
+An error message should start with a capital letter but should not end
+with a period.
+
+@item
+Many commands that take a long time to execute display a message that
+says @samp{Operating...} when they start, and change it to
+@samp{Operating...done} when they finish. Please keep the style of
+these messages uniform: @emph{no} space around the ellipsis, and
+@emph{no} period at the end.
+
@item
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
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 program-generated buffers.) The users will find Emacs more
+only for special-purpose buffers.) The users will find Emacs more
coherent if all libraries use the same conventions.
+@item
+Try to avoid compiler warnings about undefined free variables, by adding
+@code{defvar} definitions for these variables.
+
+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.
+
@item
Indent each function with @kbd{C-M-q} (@code{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 them in one or two significant places.
+to split the sequence in one or two significant places.
@item
Please put a copyright notice on the file if you give copies to anyone.
-Use the same lines that appear at the top of the Lisp files in Emacs
-itself. If you have not signed papers to assign the copyright to the
-Foundation, then place your name in the copyright notice in place of the
-Foundation's name.
+Use a message like this one:
+
+@smallexample
+;; 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 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
+@end 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.
@end itemize
@node Compilation Tips
@cindex profiling
@cindex timing programs
@cindex @file{profile.el}
-Use the @file{profile} library to profile your program. See the file
-@file{profile.el} for instructions.
+@cindex @file{elp.el}
+Profile your program with the @file{profile} library or the @file{elp}
+library. See the files @file{profile.el} and @file{elp.el} for
+instructions.
@item
Use iteration rather than recursion whenever possible.
is calling another compiled function.
@item
-Using the primitive list-searching functions @code{memq}, @code{assq}, or
-@code{assoc} is even faster than explicit iteration. It may be worth
-rearranging a data structure so that one of these primitive search
-functions can be used.
+Using the primitive list-searching functions @code{memq}, @code{member},
+@code{assq}, 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.
@item
Certain built-in functions are handled specially in byte-compiled code,
handled specially.
For example, the following input will show you that @code{aref} is
-compiled specially (@pxref{Array Functions}) while @code{elt} is not
-(@pxref{Sequence Functions}):
+compiled specially (@pxref{Array Functions}):
@example
@group
(get 'aref 'byte-compile)
@result{} byte-compile-two-args
@end group
-
-@group
-(get 'elt 'byte-compile)
- @result{} nil
-@end group
@end example
@item
-If calling a small function accounts for a substantial part of your
+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
@node Documentation Tips
@section Tips for Documentation Strings
- Here are some tips for the writing of documentation strings.
+@tindex checkdoc-minor-mode
+@findex 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
+@kbd{M-x checkdoc-minor-mode}.
@itemize @bullet
@item
@item
For consistency, phrase the verb in the first sentence of a
-documentation string as an infinitive with ``to'' omitted. For
+function's documentation string as an infinitive with ``to'' omitted. 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
view the documentation. Remember that the indentation before the
starting double-quote is not part of the string!
+@item
+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.
+
@item
A variable's documentation string should start with @samp{*} if the
variable is one that users would often want to set interactively. If
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 normally do use
-single-quotes for those symbols.)
+t and nil without single-quotes. (In this manual, we use a different
+convention, with single-quotes for all symbols.)
@end ifinfo
+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
+@samp{variable}, @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
+
+@example
+This function sets the variable `buffer-file-name'.
+@end example
+
+@noindent
+then the hyperlink will refer only to the variable documentation of
+@code{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 @samp{symbol} before the symbol name to prevent
+making any hyperlink. For example,
+
+@example
+If the argument KIND-OF-RESULT is the symbol `list',
+this function returns a list of all the objects
+that satisfy the criterion.
+@end example
+
+@noindent
+does not make a hyperlink to the documentation, irrelevant here, of the
+function @code{list}.
+
@item
Don't write key sequences directly in documentation strings. Instead,
use the @samp{\\[@dots{}]} construct to stand for them. For example,
-instead of writing @samp{C-f}, write @samp{\\[forward-char]}. 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}.
+instead of writing @samp{C-f}, write the construct
+@samp{\\[forward-char]}. 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}.
@item
In documentation strings for a major mode, you will want to refer to the
display of the documentation string will become slow. So use this to
describe the most important commands in your major mode, and then use
@samp{\\@{@dots{}@}} to display the rest of the mode's keymap.
-
-@item
-Don't use the term ``Elisp'', since that is or was a trademark.
-Use the term ``Emacs Lisp''.
@end itemize
@node Comment Tips
@end group
@end smallexample
-Every function that has no documentation string (because it is use only
-internally within the package it belongs to), should have instead 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.
+Every function that has no documentation string (presumably one that is
+used only internally within the package it belongs to), should have
+instead 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.
@item ;;;
Comments that start with three semicolons, @samp{;;;}, should start at
@noindent
The indentation commands of the Lisp modes in Emacs, such as @kbd{M-;}
-(@code{indent-for-comment}) and @key{TAB} (@code{lisp-indent-line})
+(@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}.
@cindex header comments
@cindex library header comments
- Emacs 19 has conventions for using special comments in Lisp libraries
+ 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. First, an example:
;; Keywords: docs
;; This file is part of GNU Emacs.
-@var{copying permissions}@dots{}
+@dots{}
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
@end group
@end smallexample
@item 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.
@table @samp
@item ;;; Commentary:
This begins introductory comments that explain how the library works.
-It should come right after the copying permissions.
+It should come right after the copying permissions, terminated by a
+@samp{Change Log}, @samp{History} or @samp{Code} comment line. This
+text is used by the Finder package, so it should make sense in that
+context.
+
+@item ;;; Documentation
+This has been used in some files in place of @samp{;;; Commentary:},
+but @samp{;;; Commentary:} is preferred.
-@item ;;; Change log:
+@item ;;; Change Log:
This begins change log information stored in the library file (if you
store the change history there). For most of the 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 do
-not have a @samp{;;; Change log:} line.
+not have a @samp{;;; Change Log:} line.
@item ;;; Code:
This begins the actual code of the program.