| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.
This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see 22. Keymaps, and 35. Syntax Tables.
23.1 Major Modes Defining major modes. 23.2 Minor Modes Defining minor modes. 23.3 Mode Line Format Customizing the text that appears in the mode line. 23.4 Imenu How a mode can provide a menu of definitions in the buffer. 23.5 Font Lock Mode How modes can highlight text according to syntax. 23.6 Hooks How to use hooks; how to write code that provides hooks.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time.
The least specialized major mode is called Fundamental mode.
This mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
C-j (eval-print-last-sexp), TAB
(lisp-indent-line), and other keys.
When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter the copy--or define a derived mode (see section 23.1.5 Defining Derived Modes). For example, Rmail Edit mode, which is in `emacs/lisp/mail/rmailedit.el', is a major mode that is very similar to Text mode except that it provides two additional commands. Its definition is distinct from that of Text mode, but uses that of Text mode.
Even if the new mode is not an obvious derivative of any other mode,
it can be convenient to define it as a derivative of
fundamental-mode, so that define-derived-mode can
automatically enforce the most important coding conventions for you.
Rmail Edit mode offers an example of changing the major mode temporarily for a buffer, so it can be edited in a different way (with ordinary Emacs commands rather than Rmail commands). In such cases, the temporary major mode usually provides a command to switch back to the buffer's usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user's options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using an alternative major mode avoids this limitation. See section 21.12 Recursive Editing.
The standard GNU Emacs Lisp library directory tree contains the code for several major modes, in files such as `text-mode.el', `texinfo.el', `lisp-mode.el', `c-mode.el', and `rmail.el'. They are found in various subdirectories of the `lisp' directory. You can study these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode.
23.1.1 Major Mode Conventions Coding conventions for keymaps, etc. 23.1.2 Major Mode Examples Text mode and Lisp modes. 23.1.3 How Emacs Chooses a Major Mode How Emacs chooses the major mode automatically. 23.1.4 Getting Help about a Major Mode Finding out how to use a mode. 23.1.5 Defining Derived Modes Defining a new major mode based on another major mode.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode.
This list of conventions is only partial, because each major mode should aim for consistency in general with other Emacs major modes. This makes Emacs as a whole more coherent. It is impossible to list here all the possible points where this issue might come up; if the Emacs developers point out an area where your major mode deviates from the usual conventions, please make it compatible.
describe-mode) in your mode will display this string.
The documentation string may include the special documentation substrings, `\[command]', `\{keymap}', and `\<keymap>', which enable the documentation to adapt automatically to the user's own key bindings. See section 24.3 Substituting Key Bindings in Documentation.
kill-all-local-variables. This is what gets rid of the
buffer-local variables of the major mode previously in effect.
major-mode to the
major mode command symbol. This is how describe-mode discovers
which documentation to print.
mode-name to the
"pretty" name of the mode, as a string. This string appears in the
mode line.
indent-line-function
to a suitable function, and probably customize other variables
for indentation.
use-local-map to install this local map. See section 22.6 Active Keymaps, for more information.
This keymap should be stored permanently in a global variable named
modename-mode-map. Normally the library that defines the
mode sets this variable.
See section 11.6 Tips for Defining Variables Robustly, for advice about how to write the code to set up the mode's keymap variable.
It is reasonable for a major mode to rebind a key sequence with a standard meaning, if it implements a command that does "the same job" in a way that fits the major mode better. For example, a major mode for editing a programming language might redefine C-M-a to "move to the beginning of a function" in a way that works better for that language.
Major modes such as Dired or Rmail that do not allow self-insertion of text can reasonably redefine letters and other printing characters as editing commands. Dired and Rmail both do this.
modename-mode-syntax-table. See section 35. Syntax Tables.
modename-mode-abbrev-table. See section 36.2 Abbrev Tables.
font-lock-defaults (see section 23.5 Font Lock Mode).
imenu-generic-expression or
imenu-create-index-function (see section 23.4 Imenu).
defvar or defcustom to set mode-related variables, so
that they are not reinitialized if they already have a value. (Such
reinitialization could discard customizations made by the user.)
make-local-variable in the major mode command, not
make-variable-buffer-local. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See section 11.10 Buffer-Local Variables.
With rare exceptions, the only reasonable way to use
make-variable-buffer-local in a Lisp package is for a variable
which is used only within that package. Using it on a variable used by
other packages would interfere with them.
modename-mode-hook. The major mode command should run that
hook, with run-hooks, as the very last thing it
does. See section 23.6 Hooks.
indented-text-mode runs text-mode-hook as
well as indented-text-mode-hook. It may run these other hooks
immediately before the mode's own hook (that is, after everything else),
or it may run them earlier.
change-major-mode-hook (see section 11.10.2 Creating and Deleting Buffer-Local Bindings).
mode-class
with value special, put on as follows:
(put 'funny-mode 'mode-class 'special) |
This tells Emacs that new buffers created while the current buffer is in Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature.
auto-mode-alist to select
the mode for those file names. If you define the mode command to
autoload, you should add this element in the same file that calls
autoload. Otherwise, it is sufficient to add the element in the
file that contains the mode definition. See section 23.1.3 How Emacs Chooses a Major Mode.
autoload form
and an example of how to add to auto-mode-alist, that users can
include in their init files (see section 40.1.2 The Init File, `.emacs').
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from `text-mode.el' that illustrate many of the conventions listed above:
;; Create mode-specific tables.
(defvar text-mode-syntax-table nil
"Syntax table used while in text mode.")
(if text-mode-syntax-table
() ; Do not change the table if it is already set up.
(setq text-mode-syntax-table (make-syntax-table))
(modify-syntax-entry ?\" ". " text-mode-syntax-table)
(modify-syntax-entry ?\\ ". " text-mode-syntax-table)
(modify-syntax-entry ?' "w " text-mode-syntax-table))
(defvar text-mode-abbrev-table nil
"Abbrev table used while in text mode.")
(define-abbrev-table 'text-mode-abbrev-table ())
(defvar text-mode-map nil ; Create a mode-specific keymap.
"Keymap for Text mode.
Many other modes, such as Mail mode, Outline mode and Indented Text mode,
inherit all the commands defined in this map.")
(if text-mode-map
() ; Do not change the keymap if it is already set up.
(setq text-mode-map (make-sparse-keymap))
(define-key text-mode-map "\e\t" 'ispell-complete-word)
(define-key text-mode-map "\t" 'indent-relative)
(define-key text-mode-map "\es" 'center-line)
(define-key text-mode-map "\eS" 'center-paragraph))
|
Here is the complete major mode function definition for Text mode:
(defun text-mode ()
"Major mode for editing text intended for humans to read...
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map)
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(make-local-variable 'paragraph-start)
(setq paragraph-start (concat "[ \t]*$\\|" page-delimiter))
(make-local-variable 'paragraph-separate)
(setq paragraph-separate paragraph-start)
(make-local-variable 'indent-line-function)
(setq indent-line-function 'indent-relative-maybe)
(setq mode-name "Text")
(setq major-mode 'text-mode)
(run-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
|
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from `lisp-mode.el' that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table
; if it is already set.
(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))
;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is |
Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:
(defun lisp-mode-variables (lisp-syntax) (cond (lisp-syntax (set-syntax-table lisp-mode-syntax-table))) (setq local-abbrev-table lisp-mode-abbrev-table) ... |
Functions such as forward-paragraph use the value of the
paragraph-start variable. Since Lisp code is different from
ordinary text, the paragraph-start variable needs to be set
specially to handle Lisp. Also, comments are indented in a special
fashion in Lisp and the Lisp modes need their own mode-specific
comment-indent-function. The code to set these variables is the
rest of lisp-mode-variables.
(make-local-variable 'paragraph-start) (setq paragraph-start (concat page-delimiter "\\|$" )) (make-local-variable 'paragraph-separate) (setq paragraph-separate paragraph-start) ... (make-local-variable 'comment-indent-function) (setq comment-indent-function 'lisp-comment-indent)) ... |
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-z to run-lisp, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following code sets up the common commands:
(defvar shared-lisp-mode-map ()
"Keymap for commands shared by all sorts of Lisp modes.")
(if shared-lisp-mode-map
()
(setq shared-lisp-mode-map (make-sparse-keymap))
(define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
(define-key shared-lisp-mode-map "\177"
'backward-delete-char-untabify))
|
And here is the code to set up the keymap for Lisp mode:
(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))
|
Finally, here is the complete major mode function definition for Lisp mode.
(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.
Entry to this mode calls the value of `lisp-mode-hook'
if that value is non-nil."
(interactive)
(kill-all-local-variables)
(use-local-map lisp-mode-map) ; Select the mode's keymap.
(setq major-mode 'lisp-mode) ; This is how |
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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.
fundamental-mode function does not
run any hooks; you're not supposed to customize it. (If you want Emacs
to behave differently in Fundamental mode, change the global
state of Emacs.)
set-auto-mode,
then it runs hack-local-variables to parse, and bind or
evaluate as appropriate, the file's local variables.
If the find-file argument to normal-mode is non-nil,
normal-mode assumes that the 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 `-*-' line. The variable
enable-local-variables controls whether to do so. See section `Local Variables in Files' in The GNU Emacs Manual, for
the syntax of the local variables section of a file.
If you run normal-mode interactively, the argument
find-file is normally nil. In this case,
normal-mode unconditionally processes any local variables list.
normal-mode uses condition-case around the call to the
major mode function, so errors are caught and reported as a `File
mode specification error', followed by the original error message.
auto-mode-alist), on the
`#!' line (using interpreter-mode-alist), or on the
file's local variables list. However, this function does not look for
the `mode:' local variable near the end of a file; the
hack-local-variables function does that. See section `How Major Modes are Chosen' in The GNU Emacs Manual.
fundamental-mode.
If the value of default-major-mode is 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 mode-class
property with value 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.
default-major-mode. If that variable is 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 switch-to-buffer and
find-file-noselect use it whenever they create buffers.
lisp-interaction-mode.
(regexp .
mode-function).
For example,
(("\\`/tmp/fol/" . text-mode)
("\\.texinfo\\'" . texinfo-mode)
("\\.texi\\'" . texinfo-mode)
("\\.el\\'" . emacs-lisp-mode)
("\\.c\\'" . c-mode)
("\\.h\\'" . c-mode)
...)
|
When you visit a file whose expanded file name (see section 25.8.4 Functions that Expand Filenames) matches a regexp, set-auto-mode calls the
corresponding mode-function. This feature enables Emacs to select
the proper major mode for most files.
If an element of auto-mode-alist has the form (regexp
function t), then after calling function, Emacs searches
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 ("\\.gz\\'"
function t) can uncompress the file and then put the uncompressed
file in the proper mode according to the name sans `.gz'.
Here is an example of how to prepend several pattern pairs to
auto-mode-alist. (You might use this sort of expression in your
init file.)
(setq auto-mode-alist
(append
;; File name (within directory) starts with a dot.
'(("/\\.[^/]*\\'" . fundamental-mode)
;; File name has no dot.
("[^\\./]*\\'" . fundamental-mode)
;; File name ends in `.C'.
("\\.C\\'" . c++-mode))
auto-mode-alist))
|
(interpreter . mode); for
example, ("perl" . perl-mode) is one element present by default.
The element says to use mode mode if the file specifies
an interpreter which matches interpreter. The value of
interpreter is actually a regular expression.
This variable is applicable only when the auto-mode-alist does
not indicate which major mode to use.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
The describe-mode function is used to provide information
about major modes. It is normally called with C-h m. The
describe-mode function uses the value of major-mode,
which is why every major mode function needs to set the
major-mode variable.
The describe-mode function calls the documentation
function using the value of major-mode as an argument. Thus, it
displays the documentation string of the major mode function.
(See section 24.2 Access to Documentation Strings.)
describe-mode function uses the
documentation string of the function as the documentation of the major
mode.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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 define-derived-mode.
The new command variant is defined to call the function parent, then override certain aspects of that parent mode:
variant-map.
define-derived-mode initializes this map to inherit from
parent-map, if it is not already set.
variant-syntax-table.
define-derived-mode initializes this variable by copying
parent-syntax-table, if it is not already set.
variant-abbrev-table.
define-derived-mode initializes this variable by copying
parent-abbrev-table, if it is not already set.
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 parent as part
of calling parent.)
In addition, you can specify how to override other aspects of
parent with body. The command variant
evaluates the forms in body after setting up all its usual
overrides, just before running variant-hook.
The argument docstring specifies the documentation string for the
new mode. If you omit docstring, define-derived-mode
generates a documentation string.
Here is a hypothetical 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)
|
Do not write an interactive spec in the definition;
define-derived-mode does that automatically.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
A 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.
23.2.1 Conventions for Writing Minor Modes Tips for writing a minor mode. 23.2.2 Keymaps and Minor Modes How a minor mode can have its own keymap. 23.2.3 Defining Minor Modes A convenient facility for defining minor modes.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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.
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 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.
The command should accept one optional argument. If the argument is
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 nil or -, or a
list whose CAR is such an integer or symbol; it should turn the
mode off otherwise.
Here is an example taken from the definition of transient-mark-mode.
It shows the use of 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.
(setq transient-mark-mode
(if (null arg) (not transient-mark-mode)
(> (prefix-numeric-value arg) 0)))
|
minor-mode-alist for each minor mode
(see section 23.3.2 Variables Used in the Mode Line), if you want to indicate the minor mode in
the mode line. This element should be a list of the following form:
(mode-variable string) |
Here mode-variable is the variable that controls enabling of the minor mode, and 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 minor-mode-alist, use assq to
check for an existing element, to avoid duplication. For example:
(unless (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
|
or like this, using add-to-list (see section 11.8 How to Alter a Variable Value):
(add-to-list 'minor-mode-alist '(leif-mode " Leif")) |
Global minor modes distributed with Emacs should if possible support
enabling and disabling via Custom (see section 14. Writing Customization Definitions). To do this,
the first step is to define the mode variable with defcustom, and
specify :type boolean.
If just setting the variable is not sufficient to enable the mode, you
should also specify a :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 (see section 15.4 Autoload),
and specify a :require so that customizing the variable will load
the library that defines the mode. This will copy suitable definitions
into `loaddefs.el' so that users can use customize-option to
enable the mode. For example:
;;;###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) |
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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 minor-mode-map-alist. See section 22.6 Active Keymaps.
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 self-insert-command are limited to
special cases (designed for abbrevs and Auto Fill mode). (Do not try
substituting your own definition of 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 C-c followed by a punctuation character other than {, }, <, >, :, and ;. (Those few punctuation characters are reserved for major modes.)
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
The macro 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.
t or nil by
enabling or disabling the mode. The variable is initialized to
init-value.
The command named mode finishes by executing the body forms, if any, after it has performed the standard actions such as setting the variable named mode.
The string mode-indicator says what to display in the mode line
when the mode is enabled; if it is nil, the mode is not displayed
in the mode line.
The optional argument 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:
(key-sequence . definition) |
Here is an example of using define-minor-mode:
(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)))))
|
This defines a minor mode named "Hungry mode", a command named
hungry-mode to toggle it, a variable named hungry-mode
which indicates whether the mode is enabled, and a variable named
hungry-mode-map which holds the keymap that is active when the
mode is enabled. It initializes the keymap with key bindings for
C-DEL and C-M-DEL.
The name easy-mmode-define-minor-mode is an alias
for this macro.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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 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.
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 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. 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 nil to t or vice-versa. If
you modify any of the variables referenced by mode-line-format
(see section 23.3.2 Variables Used in the Mode Line), or any other variables and data
structures that affect how text is displayed (see section 38. Emacs 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.
The mode line is usually displayed in inverse video; see
mode-line-inverse-video in 38.15 Inverse Video.
23.3.1 The Data Structure of the Mode Line The data structure that controls the mode line. 23.3.2 Variables Used in the Mode Line Variables used in that data structure. 23.3.3 %-Constructs in the Mode LinePutting information into a mode line. 23.3.4 Properties in the Mode Line Using text properties in the mode line. 23.3.5 Window Header Lines Like a mode line, but at the top.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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 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 (see section 29.4 Frame Titles) and header lines (see section 23.3.5 Window Header Lines).
If you set this variable to nil in a buffer, that buffer does not
have a mode line. (This feature was added in Emacs 21.)
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 mode-line-format incorporates the values
of variables such as mode-name and minor-mode-alist.
Because of this, very few modes need to alter mode-line-format
itself. For most purposes, it is sufficient to alter some of the
variables that 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 face property. See section 23.3.4 Properties in the Mode Line. In
addition, the face mode-line is used as a default for the whole
mode line (see section 38.11.1 Standard Faces).
string
%-constructs. Decimal digits after the `%'
specify the field width for space filling on the right (i.e., the data
is left justified). See section 23.3.3 %-Constructs in the Mode Line.
symbol
t and nil are ignored, as is any
symbol whose value is void.
There is one exception: if the value of symbol is a string, it is
displayed verbatim: the %-constructs are not recognized.
(string rest...) or (list rest...)
(:eval form)
:eval says to evaluate
form, and use the result as a string to display.
(This feature is new as of Emacs 21.)
(symbol then else)
nil, the second element, then, is processed
recursively as a mode line element. But if the value of symbol is
nil, the third element, else, is processed recursively.
You may omit else; then the mode line element displays nothing if
the value of symbol is nil.
(width rest...)
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: (-3 "%p").
If you do alter mode-line-format itself, the new value should
use the same variables that appear in the default value (see section 23.3.2 Variables Used in the Mode Line), 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 display-time and major
modes) via changes to those variables remain effective.
Here is an example of a mode-line-format that might be
useful for shell-mode, since it contains the host name and default
directory.
(setq mode-line-format
(list "-"
'mode-line-mule-info
'mode-line-modified
'mode-line-frame-identification
"%b--"
;; Note that this is evaluated while making the list.
;; It makes a mode line construct which is just a string.
(getenv "HOST")
":"
'default-directory
" "
'global-mode-string
" %[("
'(:eval (mode-line-mode-name))
'mode-line-process
'minor-mode-alist
"%n"
")%]--"
'(which-func-mode ("" which-func-format "--"))
'(line-number-mode "L%l--")
'(column-number-mode "C%c--")
'(-3 . "%p")
"-%-"))
|
(The variables line-number-mode, column-number-mode
and which-func-mode enable particular minor modes; as usual,
these variable names are also the minor mode command names.)
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
This section describes variables incorporated by the
standard value of 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
mode-line-format were changed to use them.
The default value of mode-line-modified is ("%1*%1+").
This means that the mode line displays `**' if the buffer is
modified, `--' if the buffer is not modified, `%%' if the
buffer is read only, and `%*' if the buffer is read only and
modified.
Changing this variable does not force an update of the mode line.
" " if you are using a window system which can show multiple
frames, or "-%F " on an ordinary terminal which shows only one
frame at a time.
("%12b"), which displays the buffer name, padded
with spaces to at least 12 columns.
display-time
sets global-mode-string to refer to the variable
display-time-string, which holds a string containing the time and
load information.
The `%M' construct substitutes the value of
global-mode-string, but that is obsolete, since the variable is
included in the mode line from mode-line-format.
minor-mode-alist should be a two-element list:
(minor-mode-variable mode-line-string) |
More generally, mode-line-string can be any mode line spec. It
appears in the mode line when the value of minor-mode-variable is
non-nil, and not otherwise. These strings should begin with
spaces so that they don't run together. Conventionally, the
minor-mode-variable for a specific mode is set to a non-nil
value when that minor mode is activated.
The default value of minor-mode-alist is:
minor-mode-alist
=> ((vc-mode vc-mode)
(abbrev-mode " Abbrev")
(overwrite-mode overwrite-mode)
(auto-fill-function " Fill")
(defining-kbd-macro " Def")
(isearch-mode isearch-mode))
|
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.
(":%s"), which allows the shell to display its status along
with the major mode as: `(Shell:run)'. Normally this variable
is nil.
Some variables are used by minor-mode-alist to display
a string for various minor modes when enabled. This is a typical
example:
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 nil for no version control.
The variable default-mode-line-format is where
mode-line-format usually gets its value:
mode-line-format for buffers
that do not override it. This is the same as (default-value
'mode-line-format).
The default value of default-mode-line-format is this list:
("-"
mode-line-mule-info
mode-line-modified
mode-line-frame-identification
mode-line-buffer-identification
" "
global-mode-string
" %[("
;; |
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
%-Constructs in the Mode Line
The following table lists the recognized %-constructs and what
they mean. In any construct except `%%', you can add a decimal
integer after the `%' to specify how many characters to display.
%b
buffer-name function.
See section 27.3 Buffer Names.
%c
%f
buffer-file-name
function. See section 27.4 Buffer File Name.
%F
%l
%n
narrow-to-region in 30.4 Narrowing).
%p
%P
%s
process-status. See section 37.6 Process Information.
%t
%*
buffer-read-only); buffer-modified-p);
%+
buffer-modified-p); buffer-read-only);
%&
%[
%]
%-
%%
%-constructs are allowed.
The following two %-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
mode-name and global-mode-string.
%m
mode-name.
%M
global-mode-string. Currently, only
display-time modifies the value of global-mode-string.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Starting in Emacs 21, certain text properties are meaningful in the
mode line. The face property affects the appearance of text; the
help-echo property associate help strings with the text, and
local-map can make the text mouse-sensitive.
There are three ways to specify text properties for text in the mode line:
local-map property directly into the
mode-line data structure.
local-map property on a mode-line %-construct
such as `%12b'; then the expansion of the %-construct
will have that same text property.
:eval form in the mode-line data
structure, and make form evaluate to a string that has a
local-map property.
You use the 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.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Starting in Emacs 21, a window can have a 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.
mode-line-format (see section 23.3.1 The Data Structure of the Mode Line).
header-line-format for buffers
that do not override it. This is the same as (default-value
'header-line-format).
It is normally nil, so that ordinary buffers have no header line.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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
imenu-generic-expression:
nil, specifies regular expressions for
finding definitions for Imenu. In the simplest case, elements should
look like this:
(menu-title regexp subexp) |
Here, if menu-title is non-nil, it says that the matches
for this element should go in a submenu of the buffer index;
menu-title itself specifies the name for the submenu. If
menu-title is nil, the matches for this element go directly
in the top level of the buffer index.
The second item in the list, regexp, is a regular expression (see section 34.2 Regular Expressions); anything in the buffer that it matches is considered a definition, something to mention in the buffer index. The third item, subexp, indicates which subexpression in regexp matches the definition's name.
An element can also look like this:
(menu-title regexp index function arguments...) |
Each match for this element creates a special index item which, if selected by the user, calls function with arguments consisting of the item name, the buffer position, and arguments.
For Emacs Lisp mode, pattern could look like this:
((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
("*Vars*" "^\\s-*(def\\(var\\|const\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
("*Types*"
"^\\s-*\
(def\\(type\\|struct\\|class\\|ine-condition\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2))
|
Setting this variable makes it buffer-local in the current buffer.
t, the default,
means matching should ignore case.
Setting this variable makes it buffer-local in the current buffer.
imenu-generic-expression, to override the syntax table
of the current buffer. Each element should have this form:
(characters . syntax-description) |
The CAR, characters, can be either a character or a string.
The element says to give that character or characters the syntax
specified by syntax-description, which is passed to
modify-syntax-entry (see section 35.3 Syntax Table Functions).
This feature is typically used to give word syntax to characters which
normally have symbol syntax, and thus to simplify
imenu-generic-expression and speed up matching.
For example, Fortran mode uses it this way:
(setq imenu-syntax-alist '(("_$" . "w")))
|
The imenu-generic-expression patterns can then use `\\sw+'
instead of `\\(\\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.
Another way to customize Imenu for a major mode is to set the
variables imenu-prev-index-position-function and
imenu-extract-index-name-function:
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 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-nil value.
Setting this variable makes it buffer-local in the current buffer.
nil, its value should be a function to
return the name for a definition, assuming point is in that definition
as the imenu-prev-index-position-function function would leave
it.
Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the
variable imenu-create-index-function:
save-excursion, so where it
leaves point makes no difference.
The default value is a function that uses
imenu-generic-expression to produce the index alist. If you
specify a different function, then imenu-generic-expression is
not used.
Setting this variable makes it buffer-local in the current buffer.
Simple elements in the alist look like (index-name
. index-position). Selecting a simple element has the effect of
moving to position index-position in the buffer.
Special elements look like (index-name position
function arguments...). Selecting a special element
performs
(funcall function index-name position arguments...) |
A nested sub-alist element looks like (index-name
sub-alist).
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
Font Lock mode is a feature that automatically attaches
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
font-lock-comment-face and font-lock-string-face
(see section 23.5.5 Faces for Font Lock). Search-based fontification follows.
23.5.1 Font Lock Basics 23.5.2 Search-based Fontification 23.5.3 Other Font Lock Variables 23.5.4 Levels of Font Lock 23.5.5 Faces for Font Lock 23.5.6 Syntactic Font Lock
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
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 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.
(keywords keywords-only case-fold syntax-alist syntax-begin other-vars...) |
The first element, keywords, indirectly specifies the value of
font-lock-keywords. It can be a symbol, a variable whose value
is the list to use for 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, keywords-only, specifies the value of the
variable font-lock-keywords-only. If this is non-nil,
syntactic fontification (of strings and comments) is not performed.
The third element, case-fold, specifies the value of
font-lock-case-fold-search. If it is non-nil, Font Lock
mode ignores case when searching as directed by
font-lock-keywords.
If the fourth element, syntax-alist, is non-nil, it should be
a list of cons cells of the form (char-or-string
. string). These are used to set up a syntax table for
fontification (see section 35.3 Syntax Table Functions). The resulting syntax
table is stored in font-lock-syntax-table.
The fifth element, syntax-begin, specifies the value of
font-lock-beginning-of-syntax-function (see below).
All the remaining elements (if any) are collectively called
other-vars. Each of these elements should have the form
(variable . value)---which means, make variable
buffer-local and then set it to value. You can use these
other-vars to set other variables that affect fontification,
aside from those you can control with the first five elements.
| [ < ] | [ > ] | [ << ] | [ Up ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |
The most important variable for customizing Font Lock mode is
font-lock-keywords. It specifies the search criteria for
search-based fontification.
Each element of font-lock-keywords specifies how to find
certain cases of text, and how to highlight those cases. Font Lock mode
processes the elements of 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 override element of a highlighter.
Each element of font-lock-keywords should have one of these
forms:
regexp
font-lock-keyword-face. For example,