define-minor-mode offers a convenient way of
implementing a mode in one self-contained definition.
This macro defines a new minor mode whose name is mode (a symbol). It defines a command named mode to toggle the minor mode, with doc as its documentation string.
The toggle command takes one optional (prefix) argument.
If called interactively with no argument it toggles the mode on or off.
A positive prefix argument enables the mode, any other prefix argument
disables it. From Lisp, an argument of
toggle toggles the mode,
whereas an omitted or
nil argument enables the mode.
This makes it easy to enable the minor mode in a major mode hook, for example.
If doc is
nil, the macro supplies a default documentation string
explaining the above.
By default, it also defines a variable named mode, which is set to
nil by enabling or disabling the mode. The variable
is initialized to init-value. Except in unusual circumstances
(see below), this value must be
The string lighter 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. If non-
nil, it should be a variable name (whose value is
a keymap), a keymap, or an alist of the form
(key-sequence . definition)
where each key-sequence and definition are arguments
suitable for passing to
define-key (see Changing Key Bindings). If keymap is a keymap or an alist, this also
defines the variable
The above three arguments init-value, lighter, and keymap can be (partially) omitted when keyword-args are used. The keyword-args consist of keywords followed by corresponding values. A few keywords have special meanings:
Custom group name to use in all generated
Defaults to mode without the possible trailing ‘-mode’.
Warning: don’t use this default group name unless you have
defgroup to define that group properly. See Group Definitions.
nil, this specifies that the minor mode should be global
rather than buffer-local. It defaults to
One of the effects of making a minor mode global is that the
mode variable becomes a customization variable. Toggling it
through the Customize interface turns the mode on and off, and its
value can be saved for future Emacs sessions (see Saving
Customizations in The GNU Emacs Manual. For the saved
variable to work, you should ensure that the
form is evaluated each time Emacs starts; for packages that are not
part of Emacs, the easiest way to do this is to specify a
This is equivalent to specifying init-value positionally.
This is equivalent to specifying lighter positionally.
This is equivalent to specifying keymap positionally.
This replaces the default variable mode, used to store the state
of the mode. If you specify this, the mode variable is not
defined, and any init-value argument is unused. place
can be a different named variable (which you must define yourself), or
anything that can be used with the
(see Generalized Variables).
place can also be a cons
(get . set),
where get is an expression that returns the current state,
and set is a function of one argument (a state) that sets it.
This defines a single Lisp form which is evaluated after the mode hooks have run. It should not be quoted.
Any other keyword arguments are passed directly to the
defcustom generated for the variable mode.
The command named mode first performs the standard actions such as
setting the variable named mode and then executes the body
forms, if any. It then runs the mode hook variable
mode-hook and finishes by evaluating any form in
The initial value must be
nil except in cases where (1) the
mode is preloaded in Emacs, or (2) it is painless for loading to
enable the mode even though the user did not request it. For
instance, if the mode has no effect unless something else is enabled,
and will always be loaded by that time, enabling it by default is
harmless. But these are unusual circumstances. Normally, the
initial value must be
easy-mmode-define-minor-mode is an alias
for this macro.
Here is an example of using
(define-minor-mode hungry-mode "Toggle Hungry mode. Interactively with no argument, this command toggles the mode. A positive prefix argument enables the mode, any other prefix argument disables it. From Lisp, argument omitted or nil enables the mode, `toggle' toggles the state. 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-backspace] . hungry-electric-delete)))
This defines a minor mode named “Hungry mode”, a command named
hungry-mode to toggle it, a variable named
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 a key binding for
C-DEL. There are no body forms—many minor modes
don’t need any.
Here’s an equivalent way to write it:
(define-minor-mode hungry-mode "Toggle Hungry mode. ...rest of documentation as before..." ;; The initial value. :init-value nil ;; The indicator for the mode line. :lighter " Hungry" ;; The minor mode bindings. :keymap '(([C-backspace] . hungry-electric-delete) ([C-M-backspace] . (lambda () (interactive) (hungry-electric-delete t)))))
This defines a global toggle named global-mode whose meaning is to enable or disable the buffer-local minor mode mode in all buffers. It also executes the body forms. To turn on the minor mode in a buffer, it uses the function turn-on; to turn off the minor mode, it calls mode with -1 as argument.
Globally enabling the mode also affects buffers subsequently created by visiting files, and buffers that use a major mode other than Fundamental mode; but it does not detect the creation of a new buffer in Fundamental mode.
This defines the customization option global-mode (see Customization),
which can be toggled in the Customize interface to turn the minor mode on
and off. As with
define-minor-mode, you should ensure that the
define-globalized-minor-mode form is evaluated each time Emacs
starts, for example by providing a
:group group in keyword-args to specify the
custom group for the mode variable of the global minor mode.
Generally speaking, when you define a globalized minor mode, you should also define a non-globalized version, so that people can use (or disable) it in individual buffers. This also allows them to disable a globally enabled minor mode in a specific major mode, by using that mode’s hook.