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2275 lines
86 KiB
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2275 lines
86 KiB
Plaintext
@c -*-texinfo-*-
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@c This is part of the GNU Emacs Lisp Reference Manual.
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@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
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@c Free Software Foundation, Inc.
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@c See the file elisp.texi for copying conditions.
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@setfilename ../info/modes
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@node Modes, Documentation, Keymaps, Top
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@chapter Major and Minor Modes
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@cindex mode
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A @dfn{mode} is a set of definitions that customize Emacs and can be
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turned on and off while you edit. There are two varieties of modes:
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@dfn{major modes}, which are mutually exclusive and used for editing
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particular kinds of text, and @dfn{minor modes}, which provide features
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that users can enable individually.
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This chapter describes how to write both major and minor modes, how to
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indicate them in the mode line, and how they run hooks supplied by the
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user. For related topics such as keymaps and syntax tables, see
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@ref{Keymaps}, and @ref{Syntax Tables}.
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@menu
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* Major Modes:: Defining major modes.
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* Minor Modes:: Defining minor modes.
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* Mode Line Format:: Customizing the text that appears in the mode line.
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* Imenu:: How a mode can provide a menu
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of definitions in the buffer.
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* Font Lock Mode:: How modes can highlight text according to syntax.
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* Hooks:: How to use hooks; how to write code that provides hooks.
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@end menu
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@node Major Modes
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@section Major Modes
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@cindex major mode
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@cindex Fundamental mode
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Major modes specialize Emacs for editing particular kinds of text.
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Each buffer has only one major mode at a time.
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The least specialized major mode is called @dfn{Fundamental mode}.
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This mode has no mode-specific definitions or variable settings, so each
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Emacs command behaves in its default manner, and each option is in its
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default state. All other major modes redefine various keys and options.
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For example, Lisp Interaction mode provides special key bindings for
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@kbd{C-j} (@code{eval-print-last-sexp}), @key{TAB}
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(@code{lisp-indent-line}), and other keys.
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When you need to write several editing commands to help you perform a
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specialized editing task, creating a new major mode is usually a good
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idea. In practice, writing a major mode is easy (in contrast to
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writing a minor mode, which is often difficult).
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If the new mode is similar to an old one, it is often unwise to modify
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the old one to serve two purposes, since it may become harder to use and
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maintain. Instead, copy and rename an existing major mode definition
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and alter the copy---or define a @dfn{derived mode} (@pxref{Derived
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Modes}). For example, Rmail Edit mode, which is in
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@file{emacs/lisp/mail/rmailedit.el}, is a major mode that is very similar to
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Text mode except that it provides two additional commands. Its
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definition is distinct from that of Text mode, but uses that of Text mode.
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Even if the new mode is not an obvious derivative of any other mode,
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it can be convenient to define it as a derivative of
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@code{fundamental-mode}, so that @code{define-derived-mode} can
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automatically enforce the most important coding conventions for you.
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Rmail Edit mode offers an example of changing the major mode
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temporarily for a buffer, so it can be edited in a different way (with
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ordinary Emacs commands rather than Rmail commands). In such cases, the
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temporary major mode usually provides a command to switch back to the
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buffer's usual mode (Rmail mode, in this case). You might be tempted to
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present the temporary redefinitions inside a recursive edit and restore
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the usual ones when the user exits; but this is a bad idea because it
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constrains the user's options when it is done in more than one buffer:
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recursive edits must be exited most-recently-entered first. Using an
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alternative major mode avoids this limitation. @xref{Recursive
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Editing}.
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The standard GNU Emacs Lisp library directory tree contains the code
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for several major modes, in files such as @file{text-mode.el},
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@file{texinfo.el}, @file{lisp-mode.el}, @file{c-mode.el}, and
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@file{rmail.el}. They are found in various subdirectories of the
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@file{lisp} directory. You can study these libraries to see how modes
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are written. Text mode is perhaps the simplest major mode aside from
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Fundamental mode. Rmail mode is a complicated and specialized mode.
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@menu
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* Major Mode Conventions:: Coding conventions for keymaps, etc.
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* Example Major Modes:: Text mode and Lisp modes.
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* Auto Major Mode:: How Emacs chooses the major mode automatically.
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* Mode Help:: Finding out how to use a mode.
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* Derived Modes:: Defining a new major mode based on another major
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mode.
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@end menu
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@node Major Mode Conventions
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@subsection Major Mode Conventions
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The code for existing major modes follows various coding conventions,
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including conventions for local keymap and syntax table initialization,
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global names, and hooks. Please follow these conventions when you
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define a new major mode:
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@itemize @bullet
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@item
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Define a command whose name ends in @samp{-mode}, with no arguments,
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that switches to the new mode in the current buffer. This command
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should set up the keymap, syntax table, and buffer-local variables in an
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existing buffer, without changing the buffer's contents.
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@item
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Write a documentation string for this command that describes the
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special commands available in this mode. @kbd{C-h m}
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(@code{describe-mode}) in your mode will display this string.
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The documentation string may include the special documentation
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substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and
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@samp{\<@var{keymap}>}, which enable the documentation to adapt
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automatically to the user's own key bindings. @xref{Keys in
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Documentation}.
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@item
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The major mode command should start by calling
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@code{kill-all-local-variables}. This is what gets rid of the
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buffer-local variables of the major mode previously in effect.
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@item
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The major mode command should set the variable @code{major-mode} to the
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major mode command symbol. This is how @code{describe-mode} discovers
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which documentation to print.
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@item
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The major mode command should set the variable @code{mode-name} to the
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``pretty'' name of the mode, as a string. This string appears in the
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mode line.
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@item
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@cindex functions in modes
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Since all global names are in the same name space, all the global
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variables, constants, and functions that are part of the mode should
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have names that start with the major mode name (or with an abbreviation
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of it if the name is long). @xref{Coding Conventions}.
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@item
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@cindex keymaps in modes
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The major mode should usually have its own keymap, which is used as the
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local keymap in all buffers in that mode. The major mode command should
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call @code{use-local-map} to install this local map. @xref{Active
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Keymaps}, for more information.
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This keymap should be stored permanently in a global variable named
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@code{@var{modename}-mode-map}. Normally the library that defines the
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mode sets this variable.
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@xref{Tips for Defining}, for advice about how to write the code to set
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up the mode's keymap variable.
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@item
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The key sequences bound in a major mode keymap should usually start with
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@kbd{C-c}, followed by a control character, a digit, or @kbd{@{},
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@kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation
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characters are reserved for minor modes, and ordinary letters are
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reserved for users.
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It is reasonable for a major mode to rebind a key sequence with a
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standard meaning, if it implements a command that does ``the same job''
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in a way that fits the major mode better. For example, a major mode for
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editing a programming language might redefine @kbd{C-M-a} to ``move to
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the beginning of a function'' in a way that works better for that
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language.
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Major modes such as Dired or Rmail that do not allow self-insertion of
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text can reasonably redefine letters and other printing characters as
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editing commands. Dired and Rmail both do this.
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@item
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@cindex syntax tables in modes
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The mode may have its own syntax table or may share one with other
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related modes. If it has its own syntax table, it should store this in
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a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax
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Tables}.
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@item
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If the mode handles a language that has a syntax for comments, it should
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set the variables that define the comment syntax. @xref{Options for
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Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}.
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@item
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@cindex abbrev tables in modes
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The mode may have its own abbrev table or may share one with other
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related modes. If it has its own abbrev table, it should store this in
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a variable named @code{@var{modename}-mode-abbrev-table}. @xref{Abbrev
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Tables}.
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@item
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The mode should specify how to do highlighting for Font Lock mode, by
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setting up a buffer-local value for the variable
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@code{font-lock-defaults} (@pxref{Font Lock Mode}).
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@item
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The mode should specify how Imenu should find the definitions or
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sections of a buffer, by setting up a buffer-local value for the
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variable @code{imenu-generic-expression} or
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@code{imenu-create-index-function} (@pxref{Imenu}).
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@item
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Use @code{defvar} or @code{defcustom} to set mode-related variables, so
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that they are not reinitialized if they already have a value. (Such
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reinitialization could discard customizations made by the user.)
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@item
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@cindex buffer-local variables in modes
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To make a buffer-local binding for an Emacs customization variable, use
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@code{make-local-variable} in the major mode command, not
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@code{make-variable-buffer-local}. The latter function would make the
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variable local to every buffer in which it is subsequently set, which
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would affect buffers that do not use this mode. It is undesirable for a
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mode to have such global effects. @xref{Buffer-Local Variables}.
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With rare exceptions, the only reasonable way to use use
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@code{make-variable-buffer-local} in a Lisp package is for a variable
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which is used only within that package. Using it on a variable used by
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other packages would interfere with them.
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@item
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@cindex mode hook
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@cindex major mode hook
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Each major mode should have a @dfn{mode hook} named
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@code{@var{modename}-mode-hook}. The major mode command should run that
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hook, with @code{run-hooks}, as the very last thing it
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does. @xref{Hooks}.
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@item
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The major mode command may also run the hooks of some more basic modes.
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For example, @code{indented-text-mode} runs @code{text-mode-hook} as
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well as @code{indented-text-mode-hook}. It may run these other hooks
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immediately before the mode's own hook (that is, after everything else),
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or it may run them earlier.
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@item
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If something special should be done if the user switches a buffer from
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this mode to any other major mode, this mode can set up a buffer-local
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value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}).
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@item
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If this mode is appropriate only for specially-prepared text, then the
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major mode command symbol should have a property named @code{mode-class}
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with value @code{special}, put on as follows:
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@cindex @code{mode-class} property
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@cindex @code{special}
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@example
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(put 'funny-mode 'mode-class 'special)
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@end example
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@noindent
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This tells Emacs that new buffers created while the current buffer is in
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Funny mode should not inherit Funny mode. Modes such as Dired, Rmail,
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and Buffer List use this feature.
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@item
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If you want to make the new mode the default for files with certain
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recognizable names, add an element to @code{auto-mode-alist} to select
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the mode for those file names. If you define the mode command to
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autoload, you should add this element in the same file that calls
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@code{autoload}. Otherwise, it is sufficient to add the element in the
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file that contains the mode definition. @xref{Auto Major Mode}.
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@item
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In the documentation, you should provide a sample @code{autoload} form
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and an example of how to add to @code{auto-mode-alist}, that users can
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include in their init files (@pxref{Init File}).
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@item
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@cindex mode loading
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The top-level forms in the file defining the mode should be written so
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that they may be evaluated more than once without adverse consequences.
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Even if you never load the file more than once, someone else will.
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@end itemize
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@node Example Major Modes
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@subsection Major Mode Examples
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Text mode is perhaps the simplest mode besides Fundamental mode.
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Here are excerpts from @file{text-mode.el} that illustrate many of
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the conventions listed above:
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@smallexample
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@group
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;; @r{Create mode-specific tables.}
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(defvar text-mode-syntax-table nil
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"Syntax table used while in text mode.")
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@end group
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@group
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(if text-mode-syntax-table
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() ; @r{Do not change the table if it is already set up.}
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(setq text-mode-syntax-table (make-syntax-table))
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(modify-syntax-entry ?\" ". " text-mode-syntax-table)
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(modify-syntax-entry ?\\ ". " text-mode-syntax-table)
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(modify-syntax-entry ?' "w " text-mode-syntax-table))
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@end group
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@group
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(defvar text-mode-abbrev-table nil
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"Abbrev table used while in text mode.")
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(define-abbrev-table 'text-mode-abbrev-table ())
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@end group
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@group
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(defvar text-mode-map nil ; @r{Create a mode-specific keymap.}
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"Keymap for Text mode.
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Many other modes, such as Mail mode, Outline mode and Indented Text mode,
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inherit all the commands defined in this map.")
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(if text-mode-map
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() ; @r{Do not change the keymap if it is already set up.}
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(setq text-mode-map (make-sparse-keymap))
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(define-key text-mode-map "\e\t" 'ispell-complete-word)
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(define-key text-mode-map "\t" 'indent-relative)
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(define-key text-mode-map "\es" 'center-line)
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(define-key text-mode-map "\eS" 'center-paragraph))
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@end group
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@end smallexample
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Here is the complete major mode function definition for Text mode:
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@smallexample
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@group
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(defun text-mode ()
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"Major mode for editing text intended for humans to read...
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Special commands: \\@{text-mode-map@}
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@end group
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@group
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Turning on text-mode runs the hook `text-mode-hook'."
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(interactive)
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(kill-all-local-variables)
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(use-local-map text-mode-map)
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@end group
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@group
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(setq local-abbrev-table text-mode-abbrev-table)
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(set-syntax-table text-mode-syntax-table)
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@end group
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@group
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(make-local-variable 'paragraph-start)
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(setq paragraph-start (concat "[ \t]*$\\|" page-delimiter))
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(make-local-variable 'paragraph-separate)
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(setq paragraph-separate paragraph-start)
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(make-local-variable 'indent-line-function)
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(setq indent-line-function 'indent-relative-maybe)
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@end group
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@group
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(setq mode-name "Text")
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(setq major-mode 'text-mode)
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(run-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to}
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; @r{customize the mode with a hook.}
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@end group
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@end smallexample
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@cindex @file{lisp-mode.el}
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The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp
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Interaction mode) have more features than Text mode and the code is
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correspondingly more complicated. Here are excerpts from
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@file{lisp-mode.el} that illustrate how these modes are written.
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@cindex syntax table example
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@smallexample
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@group
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;; @r{Create mode-specific table variables.}
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(defvar lisp-mode-syntax-table nil "")
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(defvar emacs-lisp-mode-syntax-table nil "")
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(defvar lisp-mode-abbrev-table nil "")
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@end group
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@group
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(if (not emacs-lisp-mode-syntax-table) ; @r{Do not change the table}
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; @r{if it is already set.}
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(let ((i 0))
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(setq emacs-lisp-mode-syntax-table (make-syntax-table))
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@end group
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@group
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;; @r{Set syntax of chars up to 0 to class of chars that are}
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;; @r{part of symbol names but not words.}
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;; @r{(The number 0 is @code{48} in the @sc{ascii} character set.)}
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(while (< i ?0)
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(modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
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(setq i (1+ i)))
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@dots{}
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@end group
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@group
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;; @r{Set the syntax for other characters.}
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(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
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(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
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@dots{}
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@end group
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@group
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(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
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(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
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@dots{}))
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;; @r{Create an abbrev table for lisp-mode.}
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(define-abbrev-table 'lisp-mode-abbrev-table ())
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@end group
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@end smallexample
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Much code is shared among the three Lisp modes. The following
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function sets various variables; it is called by each of the major Lisp
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mode functions:
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@smallexample
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@group
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(defun lisp-mode-variables (lisp-syntax)
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(cond (lisp-syntax
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(set-syntax-table lisp-mode-syntax-table)))
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(setq local-abbrev-table lisp-mode-abbrev-table)
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@dots{}
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@end group
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@end smallexample
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Functions such as @code{forward-paragraph} use the value of the
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@code{paragraph-start} variable. Since Lisp code is different from
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ordinary text, the @code{paragraph-start} variable needs to be set
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specially to handle Lisp. Also, comments are indented in a special
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fashion in Lisp and the Lisp modes need their own mode-specific
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@code{comment-indent-function}. The code to set these variables is the
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rest of @code{lisp-mode-variables}.
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@smallexample
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@group
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(make-local-variable 'paragraph-start)
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(setq paragraph-start (concat page-delimiter "\\|$" ))
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(make-local-variable 'paragraph-separate)
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(setq paragraph-separate paragraph-start)
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@dots{}
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@end group
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@group
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(make-local-variable 'comment-indent-function)
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(setq comment-indent-function 'lisp-comment-indent))
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@dots{}
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@end group
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@end smallexample
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Each of the different Lisp modes has a slightly different keymap. For
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example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other
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Lisp modes do not. However, all Lisp modes have some commands in
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common. The following code sets up the common commands:
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@smallexample
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@group
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(defvar shared-lisp-mode-map ()
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"Keymap for commands shared by all sorts of Lisp modes.")
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(if shared-lisp-mode-map
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()
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(setq shared-lisp-mode-map (make-sparse-keymap))
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(define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
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(define-key shared-lisp-mode-map "\177"
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'backward-delete-char-untabify))
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@end group
|
|
@end smallexample
|
|
|
|
@noindent
|
|
And here is the code to set up the keymap for Lisp mode:
|
|
|
|
@smallexample
|
|
@group
|
|
(defvar lisp-mode-map ()
|
|
"Keymap for ordinary Lisp mode...")
|
|
|
|
(if lisp-mode-map
|
|
()
|
|
(setq lisp-mode-map (make-sparse-keymap))
|
|
(set-keymap-parent lisp-mode-map shared-lisp-mode-map)
|
|
(define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun)
|
|
(define-key lisp-mode-map "\C-c\C-z" 'run-lisp))
|
|
@end group
|
|
@end smallexample
|
|
|
|
Finally, here is the complete major mode function definition for
|
|
Lisp mode.
|
|
|
|
@smallexample
|
|
@group
|
|
(defun lisp-mode ()
|
|
"Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
|
|
Commands:
|
|
Delete converts tabs to spaces as it moves back.
|
|
Blank lines separate paragraphs. Semicolons start comments.
|
|
\\@{lisp-mode-map@}
|
|
Note that `run-lisp' may be used either to start an inferior Lisp job
|
|
or to switch back to an existing one.
|
|
@end group
|
|
|
|
@group
|
|
Entry to this mode calls the value of `lisp-mode-hook'
|
|
if that value is non-nil."
|
|
(interactive)
|
|
(kill-all-local-variables)
|
|
@end group
|
|
@group
|
|
(use-local-map lisp-mode-map) ; @r{Select the mode's keymap.}
|
|
(setq major-mode 'lisp-mode) ; @r{This is how @code{describe-mode}}
|
|
; @r{finds out what to describe.}
|
|
(setq mode-name "Lisp") ; @r{This goes into the mode line.}
|
|
(lisp-mode-variables t) ; @r{This defines various variables.}
|
|
@end group
|
|
@group
|
|
(setq imenu-case-fold-search t)
|
|
(set-syntax-table lisp-mode-syntax-table)
|
|
(run-hooks 'lisp-mode-hook)) ; @r{This permits the user to use a}
|
|
; @r{hook to customize the mode.}
|
|
@end group
|
|
@end smallexample
|
|
|
|
@node Auto Major Mode
|
|
@subsection How Emacs Chooses a Major Mode
|
|
|
|
Based on information in the file name or in the file itself, Emacs
|
|
automatically selects a major mode for the new buffer when a file is
|
|
visited. It also processes local variables specified in the file text.
|
|
|
|
@deffn Command fundamental-mode
|
|
Fundamental mode is a major mode that is not specialized for anything
|
|
in particular. Other major modes are defined in effect by comparison
|
|
with this one---their definitions say what to change, starting from
|
|
Fundamental mode. The @code{fundamental-mode} function does @emph{not}
|
|
run any hooks; you're not supposed to customize it. (If you want Emacs
|
|
to behave differently in Fundamental mode, change the @emph{global}
|
|
state of Emacs.)
|
|
@end deffn
|
|
|
|
@deffn Command normal-mode &optional find-file
|
|
This function establishes the proper major mode and buffer-local variable
|
|
bindings for the current buffer. First it calls @code{set-auto-mode},
|
|
then it runs @code{hack-local-variables} to parse, and bind or
|
|
evaluate as appropriate, the file's local variables.
|
|
|
|
If the @var{find-file} argument to @code{normal-mode} is non-@code{nil},
|
|
@code{normal-mode} assumes that the @code{find-file} function is calling
|
|
it. In this case, it may process a local variables list at the end of
|
|
the file and in the @samp{-*-} line. The variable
|
|
@code{enable-local-variables} controls whether to do so. @xref{File
|
|
variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, for
|
|
the syntax of the local variables section of a file.
|
|
|
|
If you run @code{normal-mode} interactively, the argument
|
|
@var{find-file} is normally @code{nil}. In this case,
|
|
@code{normal-mode} unconditionally processes any local variables list.
|
|
|
|
@cindex file mode specification error
|
|
@code{normal-mode} uses @code{condition-case} around the call to the
|
|
major mode function, so errors are caught and reported as a @samp{File
|
|
mode specification error}, followed by the original error message.
|
|
@end deffn
|
|
|
|
@defun set-auto-mode
|
|
@cindex visited file mode
|
|
This function selects the major mode that is appropriate for the
|
|
current buffer. It may base its decision on the value of the @w{@samp{-*-}}
|
|
line, on the visited file name (using @code{auto-mode-alist}), on the
|
|
@w{@samp{#!}} line (using @code{interpreter-mode-alist}), or on the
|
|
file's local variables list. However, this function does not look for
|
|
the @samp{mode:} local variable near the end of a file; the
|
|
@code{hack-local-variables} function does that. @xref{Choosing Modes, ,
|
|
How Major Modes are Chosen, emacs, The GNU Emacs Manual}.
|
|
@end defun
|
|
|
|
@defopt default-major-mode
|
|
This variable holds the default major mode for new buffers. The
|
|
standard value is @code{fundamental-mode}.
|
|
|
|
If the value of @code{default-major-mode} is @code{nil}, Emacs uses
|
|
the (previously) current buffer's major mode for the major mode of a new
|
|
buffer. However, if that major mode symbol has a @code{mode-class}
|
|
property with value @code{special}, then it is not used for new buffers;
|
|
Fundamental mode is used instead. The modes that have this property are
|
|
those such as Dired and Rmail that are useful only with text that has
|
|
been specially prepared.
|
|
@end defopt
|
|
|
|
@defun set-buffer-major-mode buffer
|
|
This function sets the major mode of @var{buffer} to the value of
|
|
@code{default-major-mode}. If that variable is @code{nil}, it uses
|
|
the current buffer's major mode (if that is suitable).
|
|
|
|
The low-level primitives for creating buffers do not use this function,
|
|
but medium-level commands such as @code{switch-to-buffer} and
|
|
@code{find-file-noselect} use it whenever they create buffers.
|
|
@end defun
|
|
|
|
@defvar initial-major-mode
|
|
@cindex @samp{*scratch*}
|
|
The value of this variable determines the major mode of the initial
|
|
@samp{*scratch*} buffer. The value should be a symbol that is a major
|
|
mode command. The default value is @code{lisp-interaction-mode}.
|
|
@end defvar
|
|
|
|
@defvar auto-mode-alist
|
|
This variable contains an association list of file name patterns
|
|
(regular expressions; @pxref{Regular Expressions}) and corresponding
|
|
major mode commands. Usually, the file name patterns test for suffixes,
|
|
such as @samp{.el} and @samp{.c}, but this need not be the case. An
|
|
ordinary element of the alist looks like @code{(@var{regexp} .
|
|
@var{mode-function})}.
|
|
|
|
For example,
|
|
|
|
@smallexample
|
|
@group
|
|
(("\\`/tmp/fol/" . text-mode)
|
|
("\\.texinfo\\'" . texinfo-mode)
|
|
("\\.texi\\'" . texinfo-mode)
|
|
@end group
|
|
@group
|
|
("\\.el\\'" . emacs-lisp-mode)
|
|
("\\.c\\'" . c-mode)
|
|
("\\.h\\'" . c-mode)
|
|
@dots{})
|
|
@end group
|
|
@end smallexample
|
|
|
|
When you visit a file whose expanded file name (@pxref{File Name
|
|
Expansion}) matches a @var{regexp}, @code{set-auto-mode} calls the
|
|
corresponding @var{mode-function}. This feature enables Emacs to select
|
|
the proper major mode for most files.
|
|
|
|
If an element of @code{auto-mode-alist} has the form @code{(@var{regexp}
|
|
@var{function} t)}, then after calling @var{function}, Emacs searches
|
|
@code{auto-mode-alist} again for a match against the portion of the file
|
|
name that did not match before. This feature is useful for
|
|
uncompression packages: an entry of the form @code{("\\.gz\\'"
|
|
@var{function} t)} can uncompress the file and then put the uncompressed
|
|
file in the proper mode according to the name sans @samp{.gz}.
|
|
|
|
Here is an example of how to prepend several pattern pairs to
|
|
@code{auto-mode-alist}. (You might use this sort of expression in your
|
|
init file.)
|
|
|
|
@smallexample
|
|
@group
|
|
(setq auto-mode-alist
|
|
(append
|
|
;; @r{File name (within directory) starts with a dot.}
|
|
'(("/\\.[^/]*\\'" . fundamental-mode)
|
|
;; @r{File name has no dot.}
|
|
("[^\\./]*\\'" . fundamental-mode)
|
|
;; @r{File name ends in @samp{.C}.}
|
|
("\\.C\\'" . c++-mode))
|
|
auto-mode-alist))
|
|
@end group
|
|
@end smallexample
|
|
@end defvar
|
|
|
|
@defvar interpreter-mode-alist
|
|
This variable specifies major modes to use for scripts that specify a
|
|
command interpreter in a @samp{#!} line. Its value is a list of
|
|
elements of the form @code{(@var{interpreter} . @var{mode})}; for
|
|
example, @code{("perl" . perl-mode)} is one element present by default.
|
|
The element says to use mode @var{mode} if the file specifies
|
|
an interpreter which matches @var{interpreter}. The value of
|
|
@var{interpreter} is actually a regular expression.
|
|
|
|
This variable is applicable only when the @code{auto-mode-alist} does
|
|
not indicate which major mode to use.
|
|
@end defvar
|
|
|
|
@node Mode Help
|
|
@subsection Getting Help about a Major Mode
|
|
@cindex mode help
|
|
@cindex help for major mode
|
|
@cindex documentation for major mode
|
|
|
|
The @code{describe-mode} function is used to provide information
|
|
about major modes. It is normally called with @kbd{C-h m}. The
|
|
@code{describe-mode} function uses the value of @code{major-mode},
|
|
which is why every major mode function needs to set the
|
|
@code{major-mode} variable.
|
|
|
|
@deffn Command describe-mode
|
|
This function displays the documentation of the current major mode.
|
|
|
|
The @code{describe-mode} function calls the @code{documentation}
|
|
function using the value of @code{major-mode} as an argument. Thus, it
|
|
displays the documentation string of the major mode function.
|
|
(@xref{Accessing Documentation}.)
|
|
@end deffn
|
|
|
|
@defvar major-mode
|
|
This variable holds the symbol for the current buffer's major mode.
|
|
This symbol should have a function definition that is the command to
|
|
switch to that major mode. The @code{describe-mode} function uses the
|
|
documentation string of the function as the documentation of the major
|
|
mode.
|
|
@end defvar
|
|
|
|
@node Derived Modes
|
|
@subsection Defining Derived Modes
|
|
|
|
It's often useful to define a new major mode in terms of an existing
|
|
one. An easy way to do this is to use @code{define-derived-mode}.
|
|
|
|
@defmac define-derived-mode variant parent name docstring body@dots{}
|
|
This construct defines @var{variant} as a major mode command, using
|
|
@var{name} as the string form of the mode name.
|
|
|
|
The new command @var{variant} is defined to call the function
|
|
@var{parent}, then override certain aspects of that parent mode:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
The new mode has its own keymap, named @code{@var{variant}-map}.
|
|
@code{define-derived-mode} initializes this map to inherit from
|
|
@code{@var{parent}-map}, if it is not already set.
|
|
|
|
@item
|
|
The new mode has its own syntax table, kept in the variable
|
|
@code{@var{variant}-syntax-table}.
|
|
@code{define-derived-mode} initializes this variable by copying
|
|
@code{@var{parent}-syntax-table}, if it is not already set.
|
|
|
|
@item
|
|
The new mode has its own abbrev table, kept in the variable
|
|
@code{@var{variant}-abbrev-table}.
|
|
@code{define-derived-mode} initializes this variable by copying
|
|
@code{@var{parent}-abbrev-table}, if it is not already set.
|
|
|
|
@item
|
|
The new mode has its own mode hook, @code{@var{variant}-hook},
|
|
which it runs in standard fashion as the very last thing that it does.
|
|
(The new mode also runs the mode hook of @var{parent} as part
|
|
of calling @var{parent}.)
|
|
@end itemize
|
|
|
|
In addition, you can specify how to override other aspects of
|
|
@var{parent} with @var{body}. The command @var{variant}
|
|
evaluates the forms in @var{body} after setting up all its usual
|
|
overrides, just before running @code{@var{variant}-hook}.
|
|
|
|
The argument @var{docstring} specifies the documentation string for the
|
|
new mode. If you omit @var{docstring}, @code{define-derived-mode}
|
|
generates a documentation string.
|
|
|
|
Here is a hypothetical example:
|
|
|
|
@example
|
|
(define-derived-mode hypertext-mode
|
|
text-mode "Hypertext"
|
|
"Major mode for hypertext.
|
|
\\@{hypertext-mode-map@}"
|
|
(setq case-fold-search nil))
|
|
|
|
(define-key hypertext-mode-map
|
|
[down-mouse-3] 'do-hyper-link)
|
|
@end example
|
|
@end defmac
|
|
|
|
@node Minor Modes
|
|
@section Minor Modes
|
|
@cindex minor mode
|
|
|
|
A @dfn{minor mode} provides features that users may enable or disable
|
|
independently of the choice of major mode. Minor modes can be enabled
|
|
individually or in combination. Minor modes would be better named
|
|
``generally available, optional feature modes,'' except that such a name
|
|
would be unwieldy.
|
|
|
|
A minor mode is not usually meant as a variation of a single major mode.
|
|
Usually they are general and can apply to many major modes. For
|
|
example, Auto Fill mode works with any major mode that permits text
|
|
insertion. To be general, a minor mode must be effectively independent
|
|
of the things major modes do.
|
|
|
|
A minor mode is often much more difficult to implement than a major
|
|
mode. One reason is that you should be able to activate and deactivate
|
|
minor modes in any order. A minor mode should be able to have its
|
|
desired effect regardless of the major mode and regardless of the other
|
|
minor modes in effect.
|
|
|
|
Often the biggest problem in implementing a minor mode is finding a
|
|
way to insert the necessary hook into the rest of Emacs. Minor mode
|
|
keymaps make this easier than it used to be.
|
|
|
|
@menu
|
|
* Minor Mode Conventions:: Tips for writing a minor mode.
|
|
* Keymaps and Minor Modes:: How a minor mode can have its own keymap.
|
|
* Defining Minor Modes:: A convenient facility for defining minor modes.
|
|
@end menu
|
|
|
|
@node Minor Mode Conventions
|
|
@subsection Conventions for Writing Minor Modes
|
|
@cindex minor mode conventions
|
|
@cindex conventions for writing minor modes
|
|
|
|
There are conventions for writing minor modes just as there are for
|
|
major modes. Several of the major mode conventions apply to minor
|
|
modes as well: those regarding the name of the mode initialization
|
|
function, the names of global symbols, and the use of keymaps and
|
|
other tables.
|
|
|
|
In addition, there are several conventions that are specific to
|
|
minor modes.
|
|
|
|
@itemize @bullet
|
|
@item
|
|
@cindex mode variable
|
|
Make a variable whose name ends in @samp{-mode} to control the minor
|
|
mode. We call this the @dfn{mode variable}. The minor mode command
|
|
should set this variable (@code{nil} to disable; anything else to
|
|
enable).
|
|
|
|
If possible, implement the mode so that setting the variable
|
|
automatically enables or disables the mode. Then the minor mode command
|
|
does not need to do anything except set the variable.
|
|
|
|
This variable is used in conjunction with the @code{minor-mode-alist} to
|
|
display the minor mode name in the mode line. It can also enable
|
|
or disable a minor mode keymap. Individual commands or hooks can also
|
|
check the variable's value.
|
|
|
|
If you want the minor mode to be enabled separately in each buffer,
|
|
make the variable buffer-local.
|
|
|
|
@item
|
|
Define a command whose name is the same as the mode variable.
|
|
Its job is to enable and disable the mode by setting the variable.
|
|
|
|
The command should accept one optional argument. If the argument is
|
|
@code{nil}, it should toggle the mode (turn it on if it is off, and off
|
|
if it is on). Otherwise, it should turn the mode on if the argument is
|
|
a positive integer, a symbol other than @code{nil} or @code{-}, or a
|
|
list whose @sc{car} is such an integer or symbol; it should turn the
|
|
mode off otherwise.
|
|
|
|
Here is an example taken from the definition of @code{transient-mark-mode}.
|
|
It shows the use of @code{transient-mark-mode} as a variable that enables or
|
|
disables the mode's behavior, and also shows the proper way to toggle,
|
|
enable or disable the minor mode based on the raw prefix argument value.
|
|
|
|
@smallexample
|
|
@group
|
|
(setq transient-mark-mode
|
|
(if (null arg) (not transient-mark-mode)
|
|
(> (prefix-numeric-value arg) 0)))
|
|
@end group
|
|
@end smallexample
|
|
|
|
@item
|
|
Add an element to @code{minor-mode-alist} for each minor mode
|
|
(@pxref{Mode Line Variables}), if you want to indicate the minor mode in
|
|
the mode line. This element should be a list of the following form:
|
|
|
|
@smallexample
|
|
(@var{mode-variable} @var{string})
|
|
@end smallexample
|
|
|
|
Here @var{mode-variable} is the variable that controls enabling of the
|
|
minor mode, and @var{string} is a short string, starting with a space,
|
|
to represent the mode in the mode line. These strings must be short so
|
|
that there is room for several of them at once.
|
|
|
|
When you add an element to @code{minor-mode-alist}, use @code{assq} to
|
|
check for an existing element, to avoid duplication. For example:
|
|
|
|
@smallexample
|
|
@group
|
|
(unless (assq 'leif-mode minor-mode-alist)
|
|
(setq minor-mode-alist
|
|
(cons '(leif-mode " Leif") minor-mode-alist)))
|
|
@end group
|
|
@end smallexample
|
|
|
|
@noindent
|
|
or like this, using @code{add-to-list} (@pxref{Setting Variables}):
|
|
|
|
@smallexample
|
|
@group
|
|
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
|
|
@end group
|
|
@end smallexample
|
|
@end itemize
|
|
|
|
Global minor modes distributed with Emacs should if possible support
|
|
enabling and disabling via Custom (@pxref{Customization}). To do this,
|
|
the first step is to define the mode variable with @code{defcustom}, and
|
|
specify @code{:type boolean}.
|
|
|
|
If just setting the variable is not sufficient to enable the mode, you
|
|
should also specify a @code{:set} method which enables the mode by
|
|
invoke the mode command. Note in the variable's documentation string that
|
|
setting the variable other than via Custom may not take effect.
|
|
|
|
Also mark the definition with an autoload cookie (@pxref{Autoload}),
|
|
and specify a @code{:require} so that customizing the variable will load
|
|
the library that defines the mode. This will copy suitable definitions
|
|
into @file{loaddefs.el} so that users can use @code{customize-option} to
|
|
enable the mode. For example:
|
|
|
|
@smallexample
|
|
@group
|
|
|
|
;;;###autoload
|
|
(defcustom msb-mode nil
|
|
"Toggle msb-mode.
|
|
Setting this variable directly does not take effect;
|
|
use either \\[customize] or the function `msb-mode'."
|
|
:set (lambda (symbol value)
|
|
(msb-mode (or value 0)))
|
|
:initialize 'custom-initialize-default
|
|
:version "20.4"
|
|
:type 'boolean
|
|
:group 'msb
|
|
:require 'msb)
|
|
@end group
|
|
@end smallexample
|
|
|
|
@node Keymaps and Minor Modes
|
|
@subsection Keymaps and Minor Modes
|
|
|
|
Each minor mode can have its own keymap, which is active when the mode
|
|
is enabled. To set up a keymap for a minor mode, add an element to the
|
|
alist @code{minor-mode-map-alist}. @xref{Active Keymaps}.
|
|
|
|
@cindex @code{self-insert-command}, minor modes
|
|
One use of minor mode keymaps is to modify the behavior of certain
|
|
self-inserting characters so that they do something else as well as
|
|
self-insert. In general, this is the only way to do that, since the
|
|
facilities for customizing @code{self-insert-command} are limited to
|
|
special cases (designed for abbrevs and Auto Fill mode). (Do not try
|
|
substituting your own definition of @code{self-insert-command} for the
|
|
standard one. The editor command loop handles this function specially.)
|
|
|
|
The key sequences bound in a minor mode should consist of @kbd{C-c}
|
|
followed by a punctuation character @emph{other than} @kbd{@{},
|
|
@kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:}, and @kbd{;}. (Those few punctuation
|
|
characters are reserved for major modes.)
|
|
|
|
@node Defining Minor Modes
|
|
@subsection Defining Minor Modes
|
|
|
|
The macro @code{define-minor-mode} offers a convenient way of
|
|
implementing a mode in one self-contained definition. It supports only
|
|
buffer-local minor modes, not global ones.
|
|
|
|
@defmac define-minor-mode mode doc &optional init-value mode-indicator keymap body...
|
|
@tindex define-minor-mode
|
|
This macro defines a new minor mode whose name is @var{mode} (a symbol).
|
|
It defines a command named @var{mode} to toggle the minor
|
|
mode, with @var{doc} as its documentation string. It also defines a
|
|
variable named @var{mode}, which is set to @code{t} or @code{nil} by
|
|
enabling or disabling the mode. The variable is initialized to
|
|
@var{init-value}.
|
|
|
|
The command named @var{mode} finishes by executing the @var{body} forms,
|
|
if any, after it has performed the standard actions such as setting
|
|
the variable named @var{mode}.
|
|
|
|
The string @var{mode-indicator} says what to display in the mode line
|
|
when the mode is enabled; if it is @code{nil}, the mode is not displayed
|
|
in the mode line.
|
|
|
|
The optional argument @var{keymap} specifies the keymap for the minor mode.
|
|
It can be a variable name, whose value is the keymap, or it can be an alist
|
|
specifying bindings in this form:
|
|
|
|
@example
|
|
(@var{key-sequence} . @var{definition})
|
|
@end example
|
|
@end defmac
|
|
|
|
Here is an example of using @code{define-minor-mode}:
|
|
|
|
@smallexample
|
|
(define-minor-mode hungry-mode
|
|
"Toggle Hungry mode.
|
|
With no argument, this command toggles the mode.
|
|
Non-null prefix argument turns on the mode.
|
|
Null prefix argument turns off the mode.
|
|
|
|
When Hungry mode is enabled, the control delete key
|
|
gobbles all preceding whitespace except the last.
|
|
See the command \\[hungry-electric-delete]."
|
|
;; The initial value.
|
|
nil
|
|
;; The indicator for the mode line.
|
|
" Hungry"
|
|
;; The minor mode bindings.
|
|
'(("\C-\^?" . hungry-electric-delete)
|
|
("\C-\M-\^?"
|
|
. (lambda ()
|
|
(interactive)
|
|
(hungry-electric-delete t)))))
|
|
@end smallexample
|
|
|
|
@noindent
|
|
This defines a minor mode named ``Hungry mode'', a command named
|
|
@code{hungry-mode} to toggle it, a variable named @code{hungry-mode}
|
|
which indicates whether the mode is enabled, and a variable named
|
|
@code{hungry-mode-map} which holds the keymap that is active when the
|
|
mode is enabled. It initializes the keymap with key bindings for
|
|
@kbd{C-@key{DEL}} and @kbd{C-M-@key{DEL}}.
|
|
|
|
|
|
@findex easy-mmode-define-minor-mode
|
|
The name @code{easy-mmode-define-minor-mode} is an alias
|
|
for this macro.
|
|
|
|
@node Mode Line Format
|
|
@section Mode Line Format
|
|
@cindex mode line
|
|
|
|
Each Emacs window (aside from minibuffer windows) typically has a mode
|
|
line at the bottom, which displays status information about the buffer
|
|
displayed in the window. The mode line contains information about the
|
|
buffer, such as its name, associated file, depth of recursive editing,
|
|
and major and minor modes. A window can also have a @dfn{header
|
|
line}, which is much like the mode line but appears at the top of the
|
|
window (starting in Emacs 21).
|
|
|
|
This section describes how to control the contents of the mode line
|
|
and header line. We include it in this chapter because much of the
|
|
information displayed in the mode line relates to the enabled major and
|
|
minor modes.
|
|
|
|
@code{mode-line-format} is a buffer-local variable that holds a
|
|
template used to display the mode line of the current buffer. All
|
|
windows for the same buffer use the same @code{mode-line-format}, so
|
|
their mode lines appear the same---except for scrolling percentages, and
|
|
line and column numbers, since those depend on point and on how the
|
|
window is scrolled. @code{header-line-format} is used likewise for
|
|
header lines.
|
|
|
|
The mode line and header line of a window are normally updated
|
|
whenever a different buffer is shown in the window, or when the buffer's
|
|
modified-status changes from @code{nil} to @code{t} or vice-versa. If
|
|
you modify any of the variables referenced by @code{mode-line-format}
|
|
(@pxref{Mode Line Variables}), or any other variables and data
|
|
structures that affect how text is displayed (@pxref{Display}), you may
|
|
want to force an update of the mode line so as to display the new
|
|
information or display it in the new way.
|
|
|
|
@c Emacs 19 feature
|
|
@defun force-mode-line-update
|
|
Force redisplay of the current buffer's mode line and header line.
|
|
@end defun
|
|
|
|
The mode line is usually displayed in inverse video; see
|
|
@code{mode-line-inverse-video} in @ref{Inverse Video}.
|
|
|
|
@menu
|
|
* Mode Line Data:: The data structure that controls the mode line.
|
|
* Mode Line Variables:: Variables used in that data structure.
|
|
* %-Constructs:: Putting information into a mode line.
|
|
* Properties in Mode:: Using text properties in the mode line.
|
|
* Header Lines:: Like a mode line, but at the top.
|
|
@end menu
|
|
|
|
@node Mode Line Data
|
|
@subsection The Data Structure of the Mode Line
|
|
@cindex mode line construct
|
|
|
|
The mode line contents are controlled by a data structure of lists,
|
|
strings, symbols, and numbers kept in buffer-local variables. The data
|
|
structure is called a @dfn{mode line construct}, and it is built in
|
|
recursive fashion out of simpler mode line constructs. The same data
|
|
structure is used for constructing frame titles (@pxref{Frame Titles})
|
|
and header lines (@pxref{Header Lines}).
|
|
|
|
@defvar mode-line-format
|
|
The value of this variable is a mode line construct with overall
|
|
responsibility for the mode line format. The value of this variable
|
|
controls which other variables are used to form the mode line text, and
|
|
where they appear.
|
|
|
|
If you set this variable to @code{nil} in a buffer, that buffer does not
|
|
have a mode line. (This feature was added in Emacs 21.)
|
|
@end defvar
|
|
|
|
A mode line construct may be as simple as a fixed string of text, but
|
|
it usually specifies how to use other variables to construct the text.
|
|
Many of these variables are themselves defined to have mode line
|
|
constructs as their values.
|
|
|
|
The default value of @code{mode-line-format} incorporates the values
|
|
of variables such as @code{mode-name} and @code{minor-mode-alist}.
|
|
Because of this, very few modes need to alter @code{mode-line-format}
|
|
itself. For most purposes, it is sufficient to alter some of the
|
|
variables that @code{mode-line-format} refers to.
|
|
|
|
A mode line construct may be a list, a symbol, or a string. If the
|
|
value is a list, each element may be a list, a symbol, or a string.
|
|
|
|
The mode line can display various faces, if the strings that control
|
|
it have the @code{face} property. @xref{Properties in Mode}. In
|
|
addition, the face @code{mode-line} is used as a default for the whole
|
|
mode line (@pxref{Standard Faces}).
|
|
|
|
@table @code
|
|
@cindex percent symbol in mode line
|
|
@item @var{string}
|
|
A string as a mode line construct is displayed verbatim in the mode line
|
|
except for @dfn{@code{%}-constructs}. Decimal digits after the @samp{%}
|
|
specify the field width for space filling on the right (i.e., the data
|
|
is left justified). @xref{%-Constructs}.
|
|
|
|
@item @var{symbol}
|
|
A symbol as a mode line construct stands for its value. The value of
|
|
@var{symbol} is used as a mode line construct, in place of @var{symbol}.
|
|
However, the symbols @code{t} and @code{nil} are ignored, as is any
|
|
symbol whose value is void.
|
|
|
|
There is one exception: if the value of @var{symbol} is a string, it is
|
|
displayed verbatim: the @code{%}-constructs are not recognized.
|
|
|
|
@item (@var{string} @var{rest}@dots{}) @r{or} (@var{list} @var{rest}@dots{})
|
|
A list whose first element is a string or list means to process all the
|
|
elements recursively and concatenate the results. This is the most
|
|
common form of mode line construct.
|
|
|
|
@item (:eval @var{form})
|
|
A list whose first element is the symbol @code{:eval} says to evaluate
|
|
@var{form}, and use the result as a string to display.
|
|
(This feature is new as of Emacs 21.)
|
|
|
|
@item (@var{symbol} @var{then} @var{else})
|
|
A list whose first element is a symbol that is not a keyword specifies a
|
|
conditional. Its meaning depends on the value of @var{symbol}. If the
|
|
value is non-@code{nil}, the second element, @var{then}, is processed
|
|
recursively as a mode line element. But if the value of @var{symbol} is
|
|
@code{nil}, the third element, @var{else}, is processed recursively.
|
|
You may omit @var{else}; then the mode line element displays nothing if
|
|
the value of @var{symbol} is @code{nil}.
|
|
|
|
@item (@var{width} @var{rest}@dots{})
|
|
A list whose first element is an integer specifies truncation or
|
|
padding of the results of @var{rest}. The remaining elements
|
|
@var{rest} are processed recursively as mode line constructs and
|
|
concatenated together. Then the result is space filled (if
|
|
@var{width} is positive) or truncated (to @minus{}@var{width} columns,
|
|
if @var{width} is negative) on the right.
|
|
|
|
For example, the usual way to show what percentage of a buffer is above
|
|
the top of the window is to use a list like this: @code{(-3 "%p")}.
|
|
@end table
|
|
|
|
If you do alter @code{mode-line-format} itself, the new value should
|
|
use the same variables that appear in the default value (@pxref{Mode
|
|
Line Variables}), rather than duplicating their contents or displaying
|
|
the information in another fashion. This way, customizations made by
|
|
the user or by Lisp programs (such as @code{display-time} and major
|
|
modes) via changes to those variables remain effective.
|
|
|
|
@cindex Shell mode @code{mode-line-format}
|
|
Here is an example of a @code{mode-line-format} that might be
|
|
useful for @code{shell-mode}, since it contains the host name and default
|
|
directory.
|
|
|
|
@example
|
|
@group
|
|
(setq mode-line-format
|
|
(list "-"
|
|
'mode-line-mule-info
|
|
'mode-line-modified
|
|
'mode-line-frame-identification
|
|
"%b--"
|
|
@end group
|
|
@group
|
|
;; @r{Note that this is evaluated while making the list.}
|
|
;; @r{It makes a mode line construct which is just a string.}
|
|
(getenv "HOST")
|
|
@end group
|
|
":"
|
|
'default-directory
|
|
" "
|
|
'global-mode-string
|
|
" %[("
|
|
'(:eval (mode-line-mode-name))
|
|
'mode-line-process
|
|
'minor-mode-alist
|
|
"%n"
|
|
")%]--"
|
|
@group
|
|
'(which-func-mode ("" which-func-format "--"))
|
|
'(line-number-mode "L%l--")
|
|
'(column-number-mode "C%c--")
|
|
'(-3 . "%p")
|
|
"-%-"))
|
|
@end group
|
|
@end example
|
|
|
|
@noindent
|
|
(The variables @code{line-number-mode}, @code{column-number-mode}
|
|
and @code{which-func-mode} enable particular minor modes; as usual,
|
|
these variable names are also the minor mode command names.)
|
|
|
|
@node Mode Line Variables
|
|
@subsection Variables Used in the Mode Line
|
|
|
|
This section describes variables incorporated by the
|
|
standard value of @code{mode-line-format} into the text of the mode
|
|
line. There is nothing inherently special about these variables; any
|
|
other variables could have the same effects on the mode line if
|
|
@code{mode-line-format} were changed to use them.
|
|
|
|
@defvar mode-line-mule-info
|
|
This variable holds the value of the mode-line construct that displays
|
|
information about the language environment, buffer coding system, and
|
|
current input method. @xref{Non-ASCII Characters}.
|
|
@end defvar
|
|
|
|
@defvar mode-line-modified
|
|
This variable holds the value of the mode-line construct that displays
|
|
whether the current buffer is modified.
|
|
|
|
The default value of @code{mode-line-modified} is @code{("%1*%1+")}.
|
|
This means that the mode line displays @samp{**} if the buffer is
|
|
modified, @samp{--} if the buffer is not modified, @samp{%%} if the
|
|
buffer is read only, and @samp{%*} if the buffer is read only and
|
|
modified.
|
|
|
|
Changing this variable does not force an update of the mode line.
|
|
@end defvar
|
|
|
|
@defvar mode-line-frame-identification
|
|
This variable identifies the current frame. The default value is
|
|
@code{" "} if you are using a window system which can show multiple
|
|
frames, or @code{"-%F "} on an ordinary terminal which shows only one
|
|
frame at a time.
|
|
@end defvar
|
|
|
|
@defvar mode-line-buffer-identification
|
|
This variable identifies the buffer being displayed in the window. Its
|
|
default value is @code{("%12b")}, which displays the buffer name, padded
|
|
with spaces to at least 12 columns.
|
|
@end defvar
|
|
|
|
@defvar global-mode-string
|
|
This variable holds a mode line spec that appears in the mode line by
|
|
default, just after the buffer name. The command @code{display-time}
|
|
sets @code{global-mode-string} to refer to the variable
|
|
@code{display-time-string}, which holds a string containing the time and
|
|
load information.
|
|
|
|
The @samp{%M} construct substitutes the value of
|
|
@code{global-mode-string}, but that is obsolete, since the variable is
|
|
included in the mode line from @code{mode-line-format}.
|
|
@end defvar
|
|
|
|
@defvar mode-name
|
|
This buffer-local variable holds the ``pretty'' name of the current
|
|
buffer's major mode. Each major mode should set this variable so that the
|
|
mode name will appear in the mode line.
|
|
@end defvar
|
|
|
|
@defvar minor-mode-alist
|
|
This variable holds an association list whose elements specify how the
|
|
mode line should indicate that a minor mode is active. Each element of
|
|
the @code{minor-mode-alist} should be a two-element list:
|
|
|
|
@example
|
|
(@var{minor-mode-variable} @var{mode-line-string})
|
|
@end example
|
|
|
|
More generally, @var{mode-line-string} can be any mode line spec. It
|
|
appears in the mode line when the value of @var{minor-mode-variable} is
|
|
non-@code{nil}, and not otherwise. These strings should begin with
|
|
spaces so that they don't run together. Conventionally, the
|
|
@var{minor-mode-variable} for a specific mode is set to a non-@code{nil}
|
|
value when that minor mode is activated.
|
|
|
|
The default value of @code{minor-mode-alist} is:
|
|
|
|
@example
|
|
@group
|
|
minor-mode-alist
|
|
@result{} ((vc-mode vc-mode)
|
|
(abbrev-mode " Abbrev")
|
|
(overwrite-mode overwrite-mode)
|
|
(auto-fill-function " Fill")
|
|
(defining-kbd-macro " Def")
|
|
(isearch-mode isearch-mode))
|
|
@end group
|
|
@end example
|
|
|
|
@code{minor-mode-alist} itself is not buffer-local. Each variable
|
|
mentioned in the alist should be buffer-local if its minor mode can be
|
|
enabled separately in each buffer.
|
|
@end defvar
|
|
|
|
@defvar mode-line-process
|
|
This buffer-local variable contains the mode line information on process
|
|
status in modes used for communicating with subprocesses. It is
|
|
displayed immediately following the major mode name, with no intervening
|
|
space. For example, its value in the @samp{*shell*} buffer is
|
|
@code{(":%s")}, which allows the shell to display its status along
|
|
with the major mode as: @samp{(Shell:run)}. Normally this variable
|
|
is @code{nil}.
|
|
@end defvar
|
|
|
|
Some variables are used by @code{minor-mode-alist} to display
|
|
a string for various minor modes when enabled. This is a typical
|
|
example:
|
|
|
|
@defvar vc-mode
|
|
The variable @code{vc-mode}, buffer-local in each buffer, records
|
|
whether the buffer's visited file is maintained with version control,
|
|
and, if so, which kind. Its value is a string that appears in the mode
|
|
line, or @code{nil} for no version control.
|
|
@end defvar
|
|
|
|
The variable @code{default-mode-line-format} is where
|
|
@code{mode-line-format} usually gets its value:
|
|
|
|
@defvar default-mode-line-format
|
|
This variable holds the default @code{mode-line-format} for buffers
|
|
that do not override it. This is the same as @code{(default-value
|
|
'mode-line-format)}.
|
|
|
|
The default value of @code{default-mode-line-format} is this list:
|
|
|
|
@example
|
|
@group
|
|
("-"
|
|
mode-line-mule-info
|
|
mode-line-modified
|
|
mode-line-frame-identification
|
|
mode-line-buffer-identification
|
|
@end group
|
|
" "
|
|
global-mode-string
|
|
@group
|
|
" %[("
|
|
;; @r{@code{mode-line-mode-name} is a function}
|
|
;; @r{that copies the mode name and adds text}
|
|
;; @r{properties to make it mouse-sensitive.}
|
|
(:eval (mode-line-mode-name))
|
|
mode-line-process
|
|
minor-mode-alist
|
|
"%n"
|
|
")%]--"
|
|
@end group
|
|
@group
|
|
(which-func-mode ("" which-func-format "--"))
|
|
(line-number-mode "L%l--")
|
|
(column-number-mode "C%c--")
|
|
(-3 . "%p")
|
|
"-%-")
|
|
@end group
|
|
@end example
|
|
@end defvar
|
|
|
|
@node %-Constructs
|
|
@subsection @code{%}-Constructs in the Mode Line
|
|
|
|
The following table lists the recognized @code{%}-constructs and what
|
|
they mean. In any construct except @samp{%%}, you can add a decimal
|
|
integer after the @samp{%} to specify how many characters to display.
|
|
|
|
@table @code
|
|
@item %b
|
|
The current buffer name, obtained with the @code{buffer-name} function.
|
|
@xref{Buffer Names}.
|
|
|
|
@item %c
|
|
The current column number of point.
|
|
|
|
@item %f
|
|
The visited file name, obtained with the @code{buffer-file-name}
|
|
function. @xref{Buffer File Name}.
|
|
|
|
@item %F
|
|
The title (only on a window system) or the name of the selected frame.
|
|
@xref{Window Frame Parameters}.
|
|
|
|
@item %l
|
|
The current line number of point, counting within the accessible portion
|
|
of the buffer.
|
|
|
|
@item %n
|
|
@samp{Narrow} when narrowing is in effect; nothing otherwise (see
|
|
@code{narrow-to-region} in @ref{Narrowing}).
|
|
|
|
@item %p
|
|
The percentage of the buffer text above the @strong{top} of window, or
|
|
@samp{Top}, @samp{Bottom} or @samp{All}. Note that the default
|
|
mode-line specification truncates this to three characters.
|
|
|
|
@item %P
|
|
The percentage of the buffer text that is above the @strong{bottom} of
|
|
the window (which includes the text visible in the window, as well as
|
|
the text above the top), plus @samp{Top} if the top of the buffer is
|
|
visible on screen; or @samp{Bottom} or @samp{All}.
|
|
|
|
@item %s
|
|
The status of the subprocess belonging to the current buffer, obtained with
|
|
@code{process-status}. @xref{Process Information}.
|
|
|
|
@item %t
|
|
Whether the visited file is a text file or a binary file. This is a
|
|
meaningful distinction only on certain operating systems (@pxref{MS-DOS
|
|
File Types}).
|
|
|
|
@item %*
|
|
@samp{%} if the buffer is read only (see @code{buffer-read-only}); @*
|
|
@samp{*} if the buffer is modified (see @code{buffer-modified-p}); @*
|
|
@samp{-} otherwise. @xref{Buffer Modification}.
|
|
|
|
@item %+
|
|
@samp{*} if the buffer is modified (see @code{buffer-modified-p}); @*
|
|
@samp{%} if the buffer is read only (see @code{buffer-read-only}); @*
|
|
@samp{-} otherwise. This differs from @samp{%*} only for a modified
|
|
read-only buffer. @xref{Buffer Modification}.
|
|
|
|
@item %&
|
|
@samp{*} if the buffer is modified, and @samp{-} otherwise.
|
|
|
|
@item %[
|
|
An indication of the depth of recursive editing levels (not counting
|
|
minibuffer levels): one @samp{[} for each editing level.
|
|
@xref{Recursive Editing}.
|
|
|
|
@item %]
|
|
One @samp{]} for each recursive editing level (not counting minibuffer
|
|
levels).
|
|
|
|
@item %-
|
|
Dashes sufficient to fill the remainder of the mode line.
|
|
|
|
@item %%
|
|
The character @samp{%}---this is how to include a literal @samp{%} in a
|
|
string in which @code{%}-constructs are allowed.
|
|
@end table
|
|
|
|
The following two @code{%}-constructs are still supported, but they are
|
|
obsolete, since you can get the same results with the variables
|
|
@code{mode-name} and @code{global-mode-string}.
|
|
|
|
@table @code
|
|
@item %m
|
|
The value of @code{mode-name}.
|
|
|
|
@item %M
|
|
The value of @code{global-mode-string}. Currently, only
|
|
@code{display-time} modifies the value of @code{global-mode-string}.
|
|
@end table
|
|
|
|
@node Properties in Mode
|
|
@subsection Properties in the Mode Line
|
|
|
|
Starting in Emacs 21, certain text properties are meaningful in the
|
|
mode line. The @code{face} property affects the appearance of text; the
|
|
@code{help-echo} property associate help strings with the text, and
|
|
@code{local-map} can make the text mouse-sensitive.
|
|
|
|
There are three ways to specify text properties for text in the mode
|
|
line:
|
|
|
|
@enumerate
|
|
@item
|
|
Put a string with the @code{local-map} property directly into the
|
|
mode-line data structure.
|
|
|
|
@item
|
|
Put a @code{local-map} property on a mode-line %-construct
|
|
such as @samp{%12b}; then the expansion of the %-construct
|
|
will have that same text property.
|
|
|
|
@item
|
|
Use a list containing @code{:eval @var{form}} in the mode-line data
|
|
structure, and make @var{form} evaluate to a string that has a
|
|
@code{local-map} property.
|
|
@end enumerate
|
|
|
|
You use the @code{local-map} property to specify a keymap. Like any
|
|
keymap, it can bind character keys and function keys; but that has no
|
|
effect, since it is impossible to move point into the mode line. This
|
|
keymap can only take real effect for mouse clicks.
|
|
|
|
@node Header Lines
|
|
@subsection Window Header Lines
|
|
@cindex header line (of a window)
|
|
@cindex window header line
|
|
|
|
Starting in Emacs 21, a window can have a @dfn{header line} at the
|
|
top, just as it can have a mode line at the bottom. The header line
|
|
feature works just like the mode line feature, except that it's
|
|
controlled by different variables.
|
|
|
|
@tindex header-line-format
|
|
@defvar header-line-format
|
|
This variable, local in every buffer, specifies how to display the
|
|
header line, for windows displaying the buffer. The format of the value
|
|
is the same as for @code{mode-line-format} (@pxref{Mode Line Data}).
|
|
@end defvar
|
|
|
|
@tindex default-header-line-format
|
|
@defvar default-header-line-format
|
|
This variable holds the default @code{header-line-format} for buffers
|
|
that do not override it. This is the same as @code{(default-value
|
|
'header-line-format)}.
|
|
|
|
It is normally @code{nil}, so that ordinary buffers have no header line.
|
|
@end defvar
|
|
|
|
@node Imenu
|
|
@section Imenu
|
|
|
|
@cindex Imenu
|
|
@dfn{Imenu} is a feature that lets users select a definition or
|
|
section in the buffer, from a menu which lists all of them, to go
|
|
directly to that location in the buffer. Imenu works by constructing a
|
|
buffer index which lists the names and buffer positions of the
|
|
definitions, or other named portions of the buffer; then the user can
|
|
choose one of them and move point to it. This section explains how to
|
|
customize how Imenu finds the definitions or buffer portions for a
|
|
particular major mode.
|
|
|
|
The usual and simplest way is to set the variable
|
|
@code{imenu-generic-expression}:
|
|
|
|
@defvar imenu-generic-expression
|
|
This variable, if non-@code{nil}, specifies regular expressions for
|
|
finding definitions for Imenu. In the simplest case, elements should
|
|
look like this:
|
|
|
|
@example
|
|
(@var{menu-title} @var{regexp} @var{subexp})
|
|
@end example
|
|
|
|
Here, if @var{menu-title} is non-@code{nil}, it says that the matches
|
|
for this element should go in a submenu of the buffer index;
|
|
@var{menu-title} itself specifies the name for the submenu. If
|
|
@var{menu-title} is @code{nil}, the matches for this element go directly
|
|
in the top level of the buffer index.
|
|
|
|
The second item in the list, @var{regexp}, is a regular expression
|
|
(@pxref{Regular Expressions}); anything in the buffer that it matches is
|
|
considered a definition, something to mention in the buffer index. The
|
|
third item, @var{subexp}, indicates which subexpression in @var{regexp}
|
|
matches the definition's name.
|
|
|
|
An element can also look like this:
|
|
|
|
@example
|
|
(@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{})
|
|
@end example
|
|
|
|
Each match for this element creates a special index item which, if
|
|
selected by the user, calls @var{function} with arguments consisting of
|
|
the item name, the buffer position, and @var{arguments}.
|
|
|
|
For Emacs Lisp mode, @var{pattern} could look like this:
|
|
|
|
@c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+]
|
|
@example
|
|
@group
|
|
((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\
|
|
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
|
|
@end group
|
|
@group
|
|
("*Vars*" "^\\s-*(def\\(var\\|const\\)\
|
|
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
|
|
@end group
|
|
@group
|
|
("*Types*"
|
|
"^\\s-*\
|
|
(def\\(type\\|struct\\|class\\|ine-condition\\)\
|
|
\\s-+\\([-A-Za-z0-9+]+\\)" 2))
|
|
@end group
|
|
@end example
|
|
|
|
Setting this variable makes it buffer-local in the current buffer.
|
|
@end defvar
|
|
|
|
@defvar imenu-case-fold-search
|
|
This variable controls whether matching against
|
|
@var{imenu-generic-expression} is case-sensitive: @code{t}, the default,
|
|
means matching should ignore case.
|
|
|
|
Setting this variable makes it buffer-local in the current buffer.
|
|
@end defvar
|
|
|
|
@defvar imenu-syntax-alist
|
|
This variable is an alist of syntax table modifiers to use while
|
|
processing @code{imenu-generic-expression}, to override the syntax table
|
|
of the current buffer. Each element should have this form:
|
|
|
|
@example
|
|
(@var{characters} . @var{syntax-description})
|
|
@end example
|
|
|
|
The @sc{car}, @var{characters}, can be either a character or a string.
|
|
The element says to give that character or characters the syntax
|
|
specified by @var{syntax-description}, which is passed to
|
|
@code{modify-syntax-entry} (@pxref{Syntax Table Functions}).
|
|
|
|
This feature is typically used to give word syntax to characters which
|
|
normally have symbol syntax, and thus to simplify
|
|
@code{imenu-generic-expression} and speed up matching.
|
|
For example, Fortran mode uses it this way:
|
|
|
|
@example
|
|
(setq imenu-syntax-alist '(("_$" . "w")))
|
|
@end example
|
|
|
|
The @code{imenu-generic-expression} patterns can then use @samp{\\sw+}
|
|
instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this technique may be
|
|
inconvenient when the mode needs to limit the initial character
|
|
of a name to a smaller set of characters than are allowed in the rest
|
|
of a name.
|
|
|
|
Setting this variable makes it buffer-local in the current buffer.
|
|
@end defvar
|
|
|
|
Another way to customize Imenu for a major mode is to set the
|
|
variables @code{imenu-prev-index-position-function} and
|
|
@code{imenu-extract-index-name-function}:
|
|
|
|
@defvar imenu-prev-index-position-function
|
|
If this variable is non-@code{nil}, its value should be a function that
|
|
finds the next ``definition'' to put in the buffer index, scanning
|
|
backward in the buffer from point. It should return @code{nil} if it
|
|
doesn't find another ``definition'' before point. Otherwise it shuould
|
|
leave point at the place it finds a ``definition,'' and return any
|
|
non-@code{nil} value.
|
|
|
|
Setting this variable makes it buffer-local in the current buffer.
|
|
@end defvar
|
|
|
|
@defvar imenu-extract-index-name-function
|
|
If this variable is non-@code{nil}, its value should be a function to
|
|
return the name for a definition, assuming point is in that definition
|
|
as the @code{imenu-prev-index-position-function} function would leave
|
|
it.
|
|
|
|
Setting this variable makes it buffer-local in the current buffer.
|
|
@end defvar
|
|
|
|
The last way to customize Imenu for a major mode is to set the
|
|
variable @code{imenu-create-index-function}:
|
|
|
|
@defvar imenu-create-index-function
|
|
This variable specifies the function to use for creating a buffer index.
|
|
The function should take no arguments, and return an index for the
|
|
current buffer. It is called within @code{save-excursion}, so where it
|
|
leaves point makes no difference.
|
|
|
|
The default value is a function that uses
|
|
@code{imenu-generic-expression} to produce the index alist. If you
|
|
specify a different function, then @code{imenu-generic-expression} is
|
|
not used.
|
|
|
|
Setting this variable makes it buffer-local in the current buffer.
|
|
@end defvar
|
|
|
|
@defvar imenu-index-alist
|
|
This variable holds the index alist for the current buffer.
|
|
Setting it makes it buffer-local in the current buffer.
|
|
|
|
Simple elements in the alist look like @code{(@var{index-name}
|
|
. @var{index-position})}. Selecting a simple element has the effect of
|
|
moving to position @var{index-position} in the buffer.
|
|
|
|
Special elements look like @code{(@var{index-name} @var{position}
|
|
@var{function} @var{arguments}@dots{})}. Selecting a special element
|
|
performs
|
|
|
|
@example
|
|
(funcall @var{function} @var{index-name} @var{position} @var{arguments}@dots{})
|
|
@end example
|
|
|
|
A nested sub-alist element looks like @code{(@var{index-name}
|
|
@var{sub-alist})}.
|
|
@end defvar
|
|
|
|
@node Font Lock Mode
|
|
@section Font Lock Mode
|
|
@cindex Font Lock Mode
|
|
|
|
@dfn{Font Lock mode} is a feature that automatically attaches
|
|
@code{face} properties to certain parts of the buffer based on their
|
|
syntactic role. How it parses the buffer depends on the major mode;
|
|
most major modes define syntactic criteria for which faces to use in
|
|
which contexts. This section explains how to customize Font Lock for a
|
|
particular major mode.
|
|
|
|
Font Lock mode finds text to highlight in two ways: through syntactic
|
|
parsing based on the syntax table, and through searching (usually for
|
|
regular expressions). Syntactic fontification happens first; it finds
|
|
comments and string constants, and highlights them using
|
|
@code{font-lock-comment-face} and @code{font-lock-string-face}
|
|
(@pxref{Faces for Font Lock}). Search-based fontification follows.
|
|
|
|
@menu
|
|
* Font Lock Basics::
|
|
* Search-based Fontification::
|
|
* Other Font Lock Variables::
|
|
* Levels of Font Lock::
|
|
* Faces for Font Lock::
|
|
* Syntactic Font Lock::
|
|
@end menu
|
|
|
|
@node Font Lock Basics
|
|
@subsection Font Lock Basics
|
|
|
|
There are several variables that control how Font Lock mode highlights
|
|
text. But major modes should not set any of these variables directly.
|
|
Instead, they should set @code{font-lock-defaults} as a buffer-local
|
|
variable. The value assigned to this variable is used, if and when Font
|
|
Lock mode is enabled, to set all the other variables.
|
|
|
|
@defvar font-lock-defaults
|
|
This variable is set by major modes, as a buffer-local variable, to
|
|
specify how to fontify text in that mode. The value should look like
|
|
this:
|
|
|
|
@example
|
|
(@var{keywords} @var{keywords-only} @var{case-fold}
|
|
@var{syntax-alist} @var{syntax-begin} @var{other-vars}@dots{})
|
|
@end example
|
|
|
|
The first element, @var{keywords}, indirectly specifies the value of
|
|
@code{font-lock-keywords}. It can be a symbol, a variable whose value
|
|
is the list to use for @code{font-lock-keywords}. It can also be a list of
|
|
several such symbols, one for each possible level of fontification. The
|
|
first symbol specifies how to do level 1 fontification, the second
|
|
symbol how to do level 2, and so on.
|
|
|
|
The second element, @var{keywords-only}, specifies the value of the
|
|
variable @code{font-lock-keywords-only}. If this is non-@code{nil},
|
|
syntactic fontification (of strings and comments) is not performed.
|
|
|
|
The third element, @var{case-fold}, specifies the value of
|
|
@code{font-lock-case-fold-search}. If it is non-@code{nil}, Font Lock
|
|
mode ignores case when searching as directed by
|
|
@code{font-lock-keywords}.
|
|
|
|
If the fourth element, @var{syntax-alist}, is non-@code{nil}, it should be
|
|
a list of cons cells of the form @code{(@var{char-or-string}
|
|
. @var{string})}. These are used to set up a syntax table for
|
|
fontification (@pxref{Syntax Table Functions}). The resulting syntax
|
|
table is stored in @code{font-lock-syntax-table}.
|
|
|
|
The fifth element, @var{syntax-begin}, specifies the value of
|
|
@code{font-lock-beginning-of-syntax-function} (see below).
|
|
|
|
All the remaining elements (if any) are collectively called
|
|
@var{other-vars}. Each of these elements should have the form
|
|
@code{(@var{variable} . @var{value})}---which means, make @var{variable}
|
|
buffer-local and then set it to @var{value}. You can use these
|
|
@var{other-vars} to set other variables that affect fontification,
|
|
aside from those you can control with the first five elements.
|
|
@end defvar
|
|
|
|
@node Search-based Fontification
|
|
@subsection Search-based Fontification
|
|
|
|
The most important variable for customizing Font Lock mode is
|
|
@code{font-lock-keywords}. It specifies the search criteria for
|
|
search-based fontification.
|
|
|
|
@defvar font-lock-keywords
|
|
This variable's value is a list of the keywords to highlight. Be
|
|
careful when composing regular expressions for this list; a poorly
|
|
written pattern can dramatically slow things down!
|
|
@end defvar
|
|
|
|
Each element of @code{font-lock-keywords} specifies how to find
|
|
certain cases of text, and how to highlight those cases. Font Lock mode
|
|
processes the elements of @code{font-lock-keywords} one by one, and for
|
|
each element, it finds and handles all matches. Ordinarily, once
|
|
part of the text has been fontified already, this cannot be overridden
|
|
by a subsequent match in the same text; but you can specify different
|
|
behavior using the @var{override} element of a @var{highlighter}.
|
|
|
|
Each element of @code{font-lock-keywords} should have one of these
|
|
forms:
|
|
|
|
@table @code
|
|
@item @var{regexp}
|
|
Highlight all matches for @var{regexp} using
|
|
@code{font-lock-keyword-face}. For example,
|
|
|
|
@example
|
|
;; @r{Highlight discrete occurrences of @samp{foo}}
|
|
;; @r{using @code{font-lock-keyword-face}.}
|
|
"\\<foo\\>"
|
|
@end example
|
|
|
|
The function @code{regexp-opt} (@pxref{Syntax of Regexps}) is useful for
|
|
calculating optimal regular expressions to match a number of different
|
|
keywords.
|
|
|
|
@item @var{function}
|
|
Find text by calling @var{function}, and highlight the matches
|
|
it finds using @code{font-lock-keyword-face}.
|
|
|
|
When @var{function} is called, it receives one argument, the limit of
|
|
the search. It should return non-@code{nil} if it succeeds, and set the
|
|
match data to describe the match that was found.
|
|
|
|
@item (@var{matcher} . @var{match})
|
|
In this kind of element, @var{matcher} is either a regular
|
|
expression or a function, as described above. The @sc{cdr},
|
|
@var{match}, specifies which subexpression of @var{matcher} should be
|
|
highlighted (instead of the entire text that @var{matcher} matched).
|
|
|
|
@example
|
|
;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},}
|
|
;; @r{using @code{font-lock-keyword-face}.}
|
|
("fu\\(bar\\)" . 1)
|
|
@end example
|
|
|
|
If you use @code{regexp-opt} to produce the regular expression
|
|
@var{matcher}, then you can use @code{regexp-opt-depth} (@pxref{Syntax
|
|
of Regexps}) to calculate the value for @var{match}.
|
|
|
|
@item (@var{matcher} . @var{facename})
|
|
In this kind of element, @var{facename} is an expression whose value
|
|
specifies the face name to use for highlighting.
|
|
|
|
@example
|
|
;; @r{Highlight occurrences of @samp{fubar},}
|
|
;; @r{using the face which is the value of @code{fubar-face}.}
|
|
("fubar" . fubar-face)
|
|
@end example
|
|
|
|
@item (@var{matcher} . @var{highlighter})
|
|
In this kind of element, @var{highlighter} is a list
|
|
which specifies how to highlight matches found by @var{matcher}.
|
|
It has the form
|
|
|
|
@example
|
|
(@var{subexp} @var{facename} @var{override} @var{laxmatch})
|
|
@end example
|
|
|
|
The @sc{car}, @var{subexp}, is an integer specifying which subexpression
|
|
of the match to fontify (0 means the entire matching text). The second
|
|
subelement, @var{facename}, specifies the face, as described above.
|
|
|
|
The last two values in @var{highlighter}, @var{override} and
|
|
@var{laxmatch}, are flags. If @var{override} is @code{t}, this element
|
|
can override existing fontification made by previous elements of
|
|
@code{font-lock-keywords}. If it is @code{keep}, then each character is
|
|
fontified if it has not been fontified already by some other element.
|
|
If it is @code{prepend}, the face @var{facename} is added to the
|
|
beginning of the @code{face} property. If it is @code{append}, the face
|
|
@var{facename} is added to the end of the @code{face} property.
|
|
|
|
If @var{laxmatch} is non-@code{nil}, it means there should be no error
|
|
if there is no subexpression numbered @var{subexp} in @var{matcher}.
|
|
Obviously, fontification of the subexpression numbered @var{subexp} will
|
|
not occur. However, fontification of other subexpressions (and other
|
|
regexps) will continue. If @var{laxmatch} is @code{nil}, and the
|
|
specified subexpression is missing, then an error is signalled which
|
|
terminates search-based fontification.
|
|
|
|
Here are some examples of elements of this kind, and what they do:
|
|
|
|
@smallexample
|
|
;; @r{Highlight occurrences of either @samp{foo} or @samp{bar},}
|
|
;; @r{using @code{foo-bar-face}, even if they have already been highlighted.}
|
|
;; @r{@code{foo-bar-face} should be a variable whose value is a face.}
|
|
("foo\\|bar" 0 foo-bar-face t)
|
|
|
|
;; @r{Highlight the first subexpression within each occurrence}
|
|
;; @r{that the function @code{fubar-match} finds,}
|
|
;; @r{using the face which is the value of @code{fubar-face}.}
|
|
(fubar-match 1 fubar-face)
|
|
@end smallexample
|
|
|
|
@item (@var{matcher} @var{highlighters}@dots{})
|
|
This sort of element specifies several @var{highlighter} lists for a
|
|
single @var{matcher}. In order for this to be useful, each
|
|
@var{highlighter} should have a different value of @var{subexp}; that is,
|
|
each one should apply to a different subexpression of @var{matcher}.
|
|
|
|
@ignore
|
|
@item (@var{matcher} . @var{anchored})
|
|
In this kind of element, @var{anchored} acts much like a
|
|
@var{highlighter}, but it is more complex and can specify multiple
|
|
successive searches.
|
|
|
|
For highlighting single items, typically only @var{highlighter} is
|
|
required. However, if an item or (typically) items are to be
|
|
highlighted following the instance of another item (the anchor) then
|
|
@var{anchored} may be required.
|
|
|
|
It has this format:
|
|
|
|
@example
|
|
(@var{submatcher} @var{pre-match-form} @var{post-match-form} @var{highlighters}@dots{})
|
|
@end example
|
|
|
|
@c I can't parse this text -- rms
|
|
where @var{submatcher} is much like @var{matcher}, with one
|
|
exception---see below. @var{pre-match-form} and @var{post-match-form}
|
|
are evaluated before the first, and after the last, instance
|
|
@var{anchored}'s @var{submatcher} is used. Therefore they can be used
|
|
to initialize before, and cleanup after, @var{submatcher} is used.
|
|
Typically, @var{pre-match-form} is used to move to some position
|
|
relative to the original @var{submatcher}, before starting with
|
|
@var{anchored}'s @var{submatcher}. @var{post-match-form} might be used
|
|
to move, before resuming with @var{anchored}'s parent's @var{matcher}.
|
|
|
|
For example, an element of the form highlights (if not already highlighted):
|
|
|
|
@example
|
|
("\\<anchor\\>" (0 anchor-face) ("\\<item\\>" nil nil (0 item-face)))
|
|
@end example
|
|
|
|
Discrete occurrences of @samp{anchor} in the value of
|
|
@code{anchor-face}, and subsequent discrete occurrences of @samp{item}
|
|
(on the same line) in the value of @code{item-face}. (Here
|
|
@var{pre-match-form} and @var{post-match-form} are @code{nil}.
|
|
Therefore @samp{item} is initially searched for starting from the end of
|
|
the match of @samp{anchor}, and searching for subsequent instance of
|
|
@samp{anchor} resumes from where searching for @samp{item} concluded.)
|
|
|
|
The above-mentioned exception is as follows. The limit of the
|
|
@var{submatcher} search defaults to the end of the line after
|
|
@var{pre-match-form} is evaluated. However, if @var{pre-match-form}
|
|
returns a position greater than the position after @var{pre-match-form}
|
|
is evaluated, that position is used as the limit of the search. It is
|
|
generally a bad idea to return a position greater than the end of the
|
|
line; in other words, the @var{submatcher} search should not span lines.
|
|
|
|
@item (@var{matcher} @var{highlighters-or-anchoreds} ...)
|
|
@end ignore
|
|
|
|
@item (eval . @var{form})
|
|
Here @var{form} is an expression to be evaluated the first time
|
|
this value of @code{font-lock-keywords} is used in a buffer.
|
|
Its value should have one of the forms described in this table.
|
|
@end table
|
|
|
|
@strong{Warning:} Do not design an element of @code{font-lock-keywords}
|
|
to match text which spans lines; this does not work reliably. While
|
|
@code{font-lock-fontify-buffer} handles multi-line patterns correctly,
|
|
updating when you edit the buffer does not, since it considers text one
|
|
line at a time.
|
|
|
|
@node Other Font Lock Variables
|
|
@subsection Other Font Lock Variables
|
|
|
|
This section describes additional variables that a major mode
|
|
can set by means of @code{font-lock-defaults}.
|
|
|
|
@defvar font-lock-keywords-only
|
|
Non-@code{nil} means Font Lock should not fontify comments or strings
|
|
syntactically; it should only fontify based on
|
|
@code{font-lock-keywords}.
|
|
@end defvar
|
|
|
|
@ignore
|
|
Other variables include those for buffer-specialized fontification functions,
|
|
`font-lock-fontify-buffer-function', `font-lock-unfontify-buffer-function',
|
|
`font-lock-fontify-region-function', `font-lock-unfontify-region-function',
|
|
`font-lock-inhibit-thing-lock' and `font-lock-maximum-size'.
|
|
@end ignore
|
|
|
|
@defvar font-lock-keywords-case-fold-search
|
|
Non-@code{nil} means that regular expression matching for the sake of
|
|
@code{font-lock-keywords} should be case-insensitive.
|
|
@end defvar
|
|
|
|
@defvar font-lock-syntax-table
|
|
This variable specifies the syntax table to use for fontification of
|
|
comments and strings.
|
|
@end defvar
|
|
|
|
@defvar font-lock-beginning-of-syntax-function
|
|
If this variable is non-@code{nil}, it should be a function to move
|
|
point back to a position that is syntactically at ``top level'' and
|
|
outside of strings or comments. Font Lock uses this when necessary
|
|
to get the right results for syntactic fontification.
|
|
|
|
This function is called with no arguments. It should leave point at the
|
|
beginning of any enclosing syntactic block. Typical values are
|
|
@code{beginning-of-line} (i.e., the start of the line is known to be
|
|
outside a syntactic block), or @code{beginning-of-defun} for programming
|
|
modes or @code{backward-paragraph} for textual modes (i.e., the
|
|
mode-dependent function is known to move outside a syntactic block).
|
|
|
|
If the value is @code{nil}, the beginning of the buffer is used as a
|
|
position outside of a syntactic block. This cannot be wrong, but it can
|
|
be slow.
|
|
@end defvar
|
|
|
|
@defvar font-lock-mark-block-function
|
|
If this variable is non-@code{nil}, it should be a function that is
|
|
called with no arguments, to choose an enclosing range of text for
|
|
refontification for the command @kbd{M-g M-g}
|
|
(@code{font-lock-fontify-block}).
|
|
|
|
The function should report its choice by placing the region around it.
|
|
A good choice is a range of text large enough to give proper results,
|
|
but not too large so that refontification becomes slow. Typical values
|
|
are @code{mark-defun} for programming modes or @code{mark-paragraph} for
|
|
textual modes.
|
|
@end defvar
|
|
|
|
@node Levels of Font Lock
|
|
@subsection Levels of Font Lock
|
|
|
|
Many major modes offer three different levels of fontification. You
|
|
can define multiple levels by using a list of symbols for @var{keywords}
|
|
in @code{font-lock-defaults}. Each symbol specifies one level of
|
|
fontification; it is up to the user to choose one of these levels. The
|
|
chosen level's symbol value is used to initialize
|
|
@code{font-lock-keywords}.
|
|
|
|
Here are the conventions for how to define the levels of
|
|
fontification:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Level 1: highlight function declarations, file directives (such as include or
|
|
import directives), strings and comments. The idea is speed, so only
|
|
the most important and top-level components are fontified.
|
|
|
|
@item
|
|
Level 2: in addition to level 1, highlight all language keywords,
|
|
including type names that act like keywords, as well as named constant
|
|
values. The idea is that all keywords (either syntactic or semantic)
|
|
should be fontified appropriately.
|
|
|
|
@item
|
|
Level 3: in addition to level 2, highlight the symbols being defined in
|
|
function and variable declarations, and all builtin function names,
|
|
wherever they appear.
|
|
@end itemize
|
|
|
|
@node Faces for Font Lock
|
|
@subsection Faces for Font Lock
|
|
|
|
You can make Font Lock mode use any face, but several faces are
|
|
defined specifically for Font Lock mode. Each of these symbols is both
|
|
a face name, and a variable whose default value is the symbol itself.
|
|
Thus, the default value of @code{font-lock-comment-face} is
|
|
@code{font-lock-comment-face}. This means you can write
|
|
@code{font-lock-comment-face} in a context such as
|
|
@code{font-lock-keywords} where a face-name-valued expression is used.
|
|
|
|
@table @code
|
|
@item font-lock-comment-face
|
|
@vindex font-lock-comment-face
|
|
Used (typically) for comments.
|
|
|
|
@item font-lock-string-face
|
|
@vindex font-lock-string-face
|
|
Used (typically) for string constants.
|
|
|
|
@item font-lock-keyword-face
|
|
@vindex font-lock-keyword-face
|
|
Used (typically) for keywords---names that have special syntactic
|
|
significance, like @code{for} and @code{if} in C.
|
|
|
|
@item font-lock-builtin-face
|
|
@vindex font-lock-builtin-face
|
|
Used (typically) for built-in function names.
|
|
|
|
@item font-lock-function-name-face
|
|
@vindex font-lock-function-name-face
|
|
Used (typically) for the name of a function being defined or declared,
|
|
in a function definition or declaration.
|
|
|
|
@item font-lock-variable-name-face
|
|
@vindex font-lock-variable-name-face
|
|
Used (typically) for the name of a variable being defined or declared,
|
|
in a variable definition or declaration.
|
|
|
|
@item font-lock-type-face
|
|
@vindex font-lock-type-face
|
|
Used (typically) for names of user-defined data types,
|
|
where they are defined and where they are used.
|
|
|
|
@item font-lock-constant-face
|
|
@vindex font-lock-constant-face
|
|
Used (typically) for constant names.
|
|
|
|
@item font-lock-warning-face
|
|
@vindex font-lock-warning-face
|
|
Used (typically) for constructs that are peculiar, or that greatly
|
|
change the meaning of other text. For example, this is used for
|
|
@samp{;;;###autoload} cookies in Emacs Lisp, and for @code{#error}
|
|
directives in C.
|
|
@end table
|
|
|
|
@node Syntactic Font Lock
|
|
@subsection Syntactic Font Lock
|
|
|
|
Font Lock mode can be used to update @code{syntax-table} properties
|
|
automatically. This is useful in languages for which a single syntax
|
|
table by itself is not sufficient.
|
|
|
|
@defvar font-lock-syntactic-keywords
|
|
This variable enables and controls syntactic Font Lock. Its value
|
|
should be a list of elements of this form:
|
|
|
|
@example
|
|
(@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch})
|
|
@end example
|
|
|
|
The parts of this element have the same meanings as in the corresponding
|
|
sort of element of @code{font-lock-keywords},
|
|
|
|
@example
|
|
(@var{matcher} @var{subexp} @var{facename} @var{override} @var{laxmatch})
|
|
@end example
|
|
|
|
However, instead of specifying the value @var{facename} to use for the
|
|
@code{face} property, it specifies the value @var{syntax} to use for the
|
|
@code{syntax-table} property. Here, @var{syntax} can be a variable
|
|
whose value is a syntax table, a syntax entry of the form
|
|
@code{(@var{syntax-code} . @var{matching-char})}, or an expression whose
|
|
value is one of those two types.
|
|
@end defvar
|
|
|
|
@node Hooks
|
|
@section Hooks
|
|
@cindex hooks
|
|
|
|
A @dfn{hook} is a variable where you can store a function or functions
|
|
to be called on a particular occasion by an existing program. Emacs
|
|
provides hooks for the sake of customization. Most often, hooks are set
|
|
up in the init file (@pxref{Init File}), but Lisp programs can set them also.
|
|
@xref{Standard Hooks}, for a list of standard hook variables.
|
|
|
|
@cindex normal hook
|
|
Most of the hooks in Emacs are @dfn{normal hooks}. These variables
|
|
contain lists of functions to be called with no arguments. When the
|
|
hook name ends in @samp{-hook}, that tells you it is normal. We try to
|
|
make all hooks normal, as much as possible, so that you can use them in
|
|
a uniform way.
|
|
|
|
Every major mode function is supposed to run a normal hook called the
|
|
@dfn{mode hook} as the last step of initialization. This makes it easy
|
|
for a user to customize the behavior of the mode, by overriding the
|
|
buffer-local variable assignments already made by the mode. But hooks
|
|
are used in other contexts too. For example, the hook
|
|
@code{suspend-hook} runs just before Emacs suspends itself
|
|
(@pxref{Suspending Emacs}).
|
|
|
|
The recommended way to add a hook function to a normal hook is by
|
|
calling @code{add-hook} (see below). The hook functions may be any of
|
|
the valid kinds of functions that @code{funcall} accepts (@pxref{What Is
|
|
a Function}). Most normal hook variables are initially void;
|
|
@code{add-hook} knows how to deal with this.
|
|
|
|
@cindex abnormal hook
|
|
If the hook variable's name does not end with @samp{-hook}, that
|
|
indicates it is probably an @dfn{abnormal hook}. Then you should look at its
|
|
documentation to see how to use the hook properly.
|
|
|
|
If the variable's name ends in @samp{-functions} or @samp{-hooks},
|
|
then the value is a list of functions, but it is abnormal in that either
|
|
these functions are called with arguments or their values are used in
|
|
some way. You can use @code{add-hook} to add a function to the list,
|
|
but you must take care in writing the function. (A few of these
|
|
variables are actually normal hooks which were named before we
|
|
established the convention of using @samp{-hook} for them.)
|
|
|
|
If the variable's name ends in @samp{-function}, then its value
|
|
is just a single function, not a list of functions.
|
|
|
|
Here's an example that uses a mode hook to turn on Auto Fill mode when
|
|
in Lisp Interaction mode:
|
|
|
|
@example
|
|
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
|
|
@end example
|
|
|
|
At the appropriate time, Emacs uses the @code{run-hooks} function to
|
|
run particular hooks. This function calls the hook functions that have
|
|
been added with @code{add-hook}.
|
|
|
|
@defun run-hooks &rest hookvars
|
|
This function takes one or more hook variable names as arguments, and
|
|
runs each hook in turn. Each argument should be a symbol that is a hook
|
|
variable. These arguments are processed in the order specified.
|
|
|
|
If a hook variable has a non-@code{nil} value, that value may be a
|
|
function or a list of functions. If the value is a function (either a
|
|
lambda expression or a symbol with a function definition), it is called.
|
|
If it is a list, the elements are called, in order. The hook functions
|
|
are called with no arguments. Nowadays, storing a single function in
|
|
the hook variable is semi-obsolete; you should always use a list of
|
|
functions.
|
|
|
|
For example, here's how @code{emacs-lisp-mode} runs its mode hook:
|
|
|
|
@example
|
|
(run-hooks 'emacs-lisp-mode-hook)
|
|
@end example
|
|
@end defun
|
|
|
|
@defun run-hook-with-args hook &rest args
|
|
This function is the way to run an abnormal hook which passes arguments
|
|
to the hook functions. It calls each of the hook functions, passing
|
|
each of them the arguments @var{args}.
|
|
@end defun
|
|
|
|
@defun run-hook-with-args-until-failure hook &rest args
|
|
This function is the way to run an abnormal hook which passes arguments
|
|
to the hook functions, and stops as soon as any hook function fails. It
|
|
calls each of the hook functions, passing each of them the arguments
|
|
@var{args}, until some hook function returns @code{nil}. Then it stops,
|
|
and returns @code{nil} if some hook function returned @code{nil}.
|
|
Otherwise it returns a non-@code{nil} value.
|
|
@end defun
|
|
|
|
@defun run-hook-with-args-until-success hook &rest args
|
|
This function is the way to run an abnormal hook which passes arguments
|
|
to the hook functions, and stops as soon as any hook function succeeds.
|
|
It calls each of the hook functions, passing each of them the arguments
|
|
@var{args}, until some hook function returns non-@code{nil}. Then it
|
|
stops, and returns whatever was returned by the last hook function
|
|
that was called.
|
|
@end defun
|
|
|
|
@defun add-hook hook function &optional append local
|
|
This function is the handy way to add function @var{function} to hook
|
|
variable @var{hook}. The argument @var{function} may be any valid Lisp
|
|
function with the proper number of arguments. For example,
|
|
|
|
@example
|
|
(add-hook 'text-mode-hook 'my-text-hook-function)
|
|
@end example
|
|
|
|
@noindent
|
|
adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}.
|
|
|
|
You can use @code{add-hook} for abnormal hooks as well as for normal
|
|
hooks.
|
|
|
|
It is best to design your hook functions so that the order in which they
|
|
are executed does not matter. Any dependence on the order is ``asking
|
|
for trouble.'' However, the order is predictable: normally,
|
|
@var{function} goes at the front of the hook list, so it will be
|
|
executed first (barring another @code{add-hook} call). If the optional
|
|
argument @var{append} is non-@code{nil}, the new hook function goes at
|
|
the end of the hook list and will be executed last.
|
|
|
|
If @var{local} is non-@code{nil}, that says to make the new hook
|
|
function buffer-local in the current buffer and automatically calls
|
|
@code{make-local-hook} to make the hook itself buffer-local.
|
|
@end defun
|
|
|
|
@defun remove-hook hook function &optional local
|
|
This function removes @var{function} from the hook variable @var{hook}.
|
|
|
|
If @var{local} is non-@code{nil}, that says to remove @var{function}
|
|
from the buffer-local hook list instead of from the global hook list.
|
|
If the hook variable itself is not buffer-local, then the value of
|
|
@var{local} makes no difference.
|
|
@end defun
|
|
|
|
@defun make-local-hook hook
|
|
This function makes the hook variable @code{hook} buffer-local in the
|
|
current buffer. When a hook variable is buffer-local, it can have
|
|
buffer-local and global hook functions, and @code{run-hooks} runs all of
|
|
them.
|
|
|
|
This function works by adding @code{t} as an element of the buffer-local
|
|
value. That serves as a flag to use the hook functions listed in the default
|
|
value of the hook variable, as well as those listed in the buffer-local value.
|
|
Since @code{run-hooks} understands this flag, @code{make-local-hook}
|
|
works with all normal hooks. It works for only some non-normal
|
|
hooks---those whose callers have been updated to understand this meaning
|
|
of @code{t}.
|
|
|
|
Do not use @code{make-local-variable} directly for hook variables; it is
|
|
not sufficient.
|
|
@end defun
|