@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2002, 2003,
-@c 2004, 2005 Free Software Foundation, Inc.
+@c 2004, 2005, 2006 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/tips
@node Tips, GNU Emacs Internals, GPL, Top
@menu
* 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.
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
@code{copy-list}. Believe it or not, there is more than one plausible
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
+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,
Lisp programs.
@item
-It is often useful to put a call to @code{provide} in each separate
-library program, at least if there is more than one entry point to the
-program.
+Put a call to @code{provide} at the end of each separate Lisp file.
@item
-If a file requires certain other library programs to be loaded
+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.
to store a list of functions (i.e., the variable is a hook), please
follow the naming conventions for hooks. @xref{Hooks}.
+@item
+@cindex unloading packages
+If loading the file adds functions to hooks, define a function
+@code{@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.
+@xref{Unloading}.
+
+@item
+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.
+
+@item
+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.
+
+@example
+(defalias 'gnus-point-at-bol
+ (if (fboundp 'point-at-bol)
+ 'point-at-bol
+ 'line-beginning-position))
+@end example
+
+@item
+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
+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.
+
+@item
+Avoid using macros that define functions and variables with names that
+are constructed. It is best for maintenance when the name of the
+function or variable being defined is given explicitly in the source
+code, as the second element of the list---as it is when you use
+@code{defun}, @code{defalias}, @code{defvar} and @code{defcustom}.
+
+@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
+will be 14 characters or less, which is short enough to fit on all kinds
+of Unix systems.
+
+@item
+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.
+
+@item
+Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the
+default indentation parameters.
+
+@item
+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.
+
+@item
+Please put a copyright notice and copying permission notice on the
+file if you distribute copies. Use a notice 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., 51 Franklin Street, Fifth Floor, Boston,
+;; MA 02110-1301 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. See also @xref{Library Headers}.
+@end itemize
+
+@node Key Binding Conventions
+@section Key Binding Conventions
+
+@itemize @bullet
+@item
+@cindex mouse-2
+@cindex references, following
+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.
+
+In addition, they should mark the text as a kind of ``link'' so that
+@kbd{mouse-1} will follow it also. @xref{Links and Mouse-1}.
+
@item
@cindex reserved keys
@cindex keys, reserved
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.
+@end itemize
-@item
-@cindex mouse-2
-@cindex references, following
-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.
-
-In addition, they should mark the text as a kind of ``link'' so that
-@kbd{mouse-1} will follow it also. @xref{Links and Mouse-1}.
-
-@cindex unloading packages
-If loading the file adds functions to hooks, define a function
-@code{@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.
-@xref{Unloading}.
-
-@item
-It is a bad idea to define aliases for the Emacs primitives. Use the
-standard names instead.
-
-@item
-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.
-
-@example
-(defalias 'gnus-point-at-bol
- (if (fboundp 'point-at-bol)
- 'point-at-bol
- 'line-beginning-position))
-@end example
-
-@item
-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
-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.
-
-@item
-Avoid using macros that define functions and variables with names that
-are constructed. It is best for maintenance when the name of the
-function or variable being defined is given explicitly in the source
-code, as the second element of the list---as it is when you use
-@code{defun}, @code{defalias}, @code{defvar} and @code{defcustom}.
+@node Programming Tips
+@section Emacs Programming Tips
-@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
-will be 14 characters or less, which is short enough to fit on all kinds
-of Unix systems.
+ Following these conventions will make your program fit better
+into Emacs when it runs.
+@itemize @bullet
@item
Don't use @code{next-line} or @code{previous-line} in programs; nearly
always, @code{forward-line} is more convenient as well as more
@code{beginning-of-buffer}, @code{end-of-buffer}
@item
@code{replace-string}, @code{replace-regexp}
+@item
+@code{insert-file}, @code{insert-buffer}
@end itemize
-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.
+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.
@item
Use lists rather than vectors, except when there is a particular reason
An error message should start with a capital letter but should not end
with a period.
+@item
+A question asked in the minibuffer with @code{y-or-n-p} or
+@code{yes-or-no-p} should start with a capital letter and end with
+@samp{? }.
+
+@item
+When you mention a default value in a minibuffer prompt,
+put it and the word @samp{default} inside parentheses.
+It should look like this:
+
+@example
+Enter the answer (default 42):
+@end example
+
@item
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
to switch back to the old local keymap. Or do what the
@code{edit-options} command does: switch to another buffer and let the
user switch back at will. @xref{Recursive Editing}.
-
-@item
-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.
-
-@item
-Try to avoid compiler warnings about undefined free variables, by adding
-dummy @code{defvar} definitions for these variables, like this:
-
-@example
-(defvar foo)
-@end 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.
-
-@item
-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,
-
-@example
-(eval-when-compile
- (require 'foo))
-@end example
-
-@item
-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.
-
-@item
-Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the
-default indentation parameters.
-
-@item
-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.
-
-@item
-Please put a copyright notice on the file if you give copies to anyone.
-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., 51 Franklin Street, Fifth Floor, Boston,
-;; MA 02110-1301 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. See also @xref{Library Headers}.
@end itemize
@node Compilation Tips
the speed. @xref{Inline Functions}.
@end itemize
+@node Warning Tips
+@section Tips for Avoiding Compiler Warnings
+
+@itemize @bullet
+@item
+Try to avoid compiler warnings about undefined free variables, by adding
+dummy @code{defvar} definitions for these variables, like this:
+
+@example
+(defvar foo)
+@end 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.
+
+@item
+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,
+
+@example
+(eval-when-compile
+ (require 'foo))
+@end example
+
+@item
+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.
+
+@item
+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.
+@end itemize
+
@node Documentation Tips
@section Tips for Documentation Strings
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
-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
-@samp{*}. @xref{Defining Variables}.
+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{*}.
+@xref{Defining Variables}.
@item
The documentation string for a variable that is a yes-or-no flag should
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,
+you can write the words @samp{symbol} or @samp{program} before the
+symbol name to prevent making any hyperlink. For example,
@example
If the argument KIND-OF-RESULT is the symbol `list',
See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
@end smallexample
+Finally, to create a hyperlink to URLs, write the URL in single
+quotes, preceded by @samp{URL}. For example,
+
+@smallexample
+The home page for the GNU project has more information (see URL
+`http://www.gnu.org/').
+@end smallexample
+
@item
Don't write key sequences directly in documentation strings. Instead,
use the @samp{\\[@dots{}]} construct to stand for them. For example,