The bindings between input events and commands are recorded in data structures called keymaps. Each binding in a keymap associates (or binds) an individual event type either with another keymap or with a command. When an event is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup.
A keymap is a table mapping event types to definitions (which can be any Lisp objects, though only certain types are meaningful for execution by the command loop). Given an event (or an event type) and a keymap, Emacs can get the event's definition. Events include ordinary ASCII characters, function keys, and mouse actions (see section Input Events).
A sequence of input events that form a unit is called a key sequence, or key for short. A sequence of one event is always a key sequence, and so are some multi-event sequences.
A keymap determines a binding or definition for any key sequence. If the key sequence is a single event, its binding is the definition of the event in the keymap. The binding of a key sequence of more than one event is found by an iterative process: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up.
If the binding of a key sequence is a keymap, we call the key sequence
a prefix key. Otherwise, we call it a complete key (because
no more events can be added to it). If the binding is nil,
we call the key undefined. Examples of prefix keys are C-c,
C-x, and C-x 4. Examples of defined complete keys are
X, RET, and C-x 4 C-f. Examples of undefined complete
keys are C-x C-g, and C-c 3. See section Prefix Keys, for more
details.
The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit--it is not really a key sequence. In other words, removing one or more events from the end of any valid key must always yield a prefix key. For example, C-f C-f is not a key; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key.
Note that the set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active---that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See section Active Keymaps, for details.
A keymap is a list whose CAR is the symbol keymap. The
remaining elements of the list define the key bindings of the keymap.
Use the function keymapp (see below) to test whether an object is
a keymap.
Each ordinary binding applies to events of a particular event type, which is always a character or a symbol. See section Classifying Events.
An ordinary element of a keymap is a cons cell of the form
(type . binding). This specifies one binding, for
events of type type.
A cons cell whose CAR is t is a default key binding;
any event not bound by other elements of the keymap is given
binding as its binding. Default bindings allow a keymap to bind
all possible event types without having to enumerate all of them. A
keymap that has a default binding completely masks any lower-precedence
keymap.
If an element of a keymap is a vector, the vector counts as bindings for all the ASCII characters; vector element n is the binding for the character with code n. This is a compact way to record lots of bindings. A keymap with such a vector is called a full keymap. Other keymaps are called sparse keymaps.
When a keymap contains a vector, it always defines a binding for every
ASCII character even if the vector element is nil. Such a
binding of nil overrides any default binding in the keymap.
However, default bindings are still meaningful for events that are not
ASCII characters. A binding of nil does not
override lower-precedence keymaps; thus, if the local map gives a
binding of nil, Emacs uses the binding from the global map.
Aside from bindings, a keymap can also have a string as an element. This is called the overall prompt string and makes it possible to use the keymap as a menu. See section Menu Keymaps.
Keymaps do not directly record bindings for the meta characters, whose
codes are from 128 to 255. Instead, meta characters are regarded for
purposes of key lookup as sequences of two characters, the first of
which is ESC (or whatever is currently the value of
meta-prefix-char). Thus, the key M-a is really represented
as ESC a, and its global binding is found at the slot for
a in esc-map (see section Prefix Keys).
Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for DEL and TAB, plus C-c C-l, M-C-q, and M-C-x.
lisp-mode-map
=>
(keymap
;; TAB
(9 . lisp-indent-line)
;; DEL
(127 . backward-delete-char-untabify)
(3 keymap
;; C-c C-l
(12 . run-lisp))
(27 keymap
;; M-C-q, treated as ESC C-q
(17 . indent-sexp)
;; M-C-x, treated as ESC C-x
(24 . lisp-send-defun)))
t if object is a keymap, nil
otherwise. More precisely, this function tests for a list whose
CAR is keymap.
(keymapp '(keymap))
=> t
(keymapp (current-global-map))
=> t
Here we describe the functions for creating keymaps.
nil, and does not bind any other kind of event.
(make-keymap)
=> (keymap [nil nil nil ... nil nil])
If you specify prompt, that becomes the overall prompt string for the keymap. The prompt string is useful for menu keymaps (see section Menu Keymaps).
make-keymap.
(make-sparse-keymap)
=> (keymap)
(setq map (copy-keymap (current-local-map)))
=> (keymap
;; (This implements meta characters.)
(27 keymap
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
(eq map (current-local-map))
=> nil
(equal map (current-local-map))
=> t
A keymap can inherit the bindings of another keymap. Do do this, make a keymap whose "tail" is another existing keymap to inherit from. Such a keymap looks like this:
(keymap bindings... . other-keymap)
The effect is that this keymap inherits all the bindings of other-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with bindings.
If you change the bindings in other-keymap using define-key
or other key-binding functions, these changes are visible in the
inheriting keymap unless shadowed by bindings. The converse is
not true: if you use define-key to change the inheriting keymap,
that affects bindings, but has no effect on other-keymap.
Here is an example showing how to make a keymap that inherits
from text-mode-map:
(setq my-mode-map (cons 'keymap text-mode-map))
A prefix key has an associated keymap that defines what to do
with key sequences that start with the prefix key. For example,
C-x is a prefix key, and it uses a keymap that is also stored in
the variable ctl-x-map. Here is a list of the standard prefix
keys of Emacs and their keymaps:
esc-map is used for events that follow ESC. Thus, the
global definitions of all meta characters are actually found here. This
map is also the function definition of ESC-prefix.
help-map is used for events that follow C-h.
mode-specific-map is for events that follow C-c. This
map is not actually mode specific; its name was chosen to be informative
for the user in C-h b (display-bindings), where it
describes the main use of the C-c prefix key.
ctl-x-map is the map used for events that follow C-x. This
map is also the function definition of Control-X-prefix.
ctl-x-4-map is used for events that follow C-x 4.
ctl-x-5-map is used for events that follow C-x 5.
The binding of a prefix key is the keymap to use for looking up the
events that follow the prefix key. (It may instead be a symbol whose
function definition is a keymap. The effect is the same, but the symbol
serves as a name for the prefix key.) Thus, the binding of C-x is
the symbol Control-X-prefix, whose function definition is the
keymap for C-x commands. (The same keymap is also the value of
ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and ESC as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See section Active Keymaps.
If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then
the binding for C-p C-f is the function find-file, just
like C-x C-f. The key sequence C-p 6 is not found in any
active keymap.
(use-local-map (make-sparse-keymap))
=> nil
(local-set-key "\C-p" ctl-x-map)
=> nil
(key-binding "\C-p\C-f")
=> find-file
(key-binding "\C-p6")
=> nil
In Emacs version 18, only the function definition of symbol was set, not the value as a variable.
Emacs normally contains many keymaps; at any given time, just a few of them are active in that they participate in the interpretation of user input. These are the global keymap, the current buffer's local keymap, and the keymaps of any enabled minor modes.
The global keymap holds the bindings of keys that are defined
regardless of the current buffer, such as C-f. The variable
global-map holds this keymap, which is always active.
Each buffer may have another keymap, its local keymap, which may
contain new or overriding definitions for keys. The current buffer's
local keymap is always active except when overriding-local-map
overrides it. Text properties can specify an alternative local map for
certain parts of the buffer; see section Properties with Special Meanings.
Each minor mode may have a keymap; if it does, the keymap is active when the minor mode is enabled.
The variable overriding-local-map, if non-nil, specifies
another local keymap that overrides the buffer's local map and all the
minor mode keymaps.
All the active keymaps are used together to determine what command to execute when a key is entered. Emacs searches these maps one by one, in order of decreasing precedence, until it finds a binding in one of the maps.
Normally, Emacs first searches for the key in the minor mode
maps (one map at a time); if they do not supply a binding for the key,
Emacs searches the local map; if that too has no binding, Emacs then
searches the global map. However, if overriding-local-map is
non-nil, Emacs searches that map first, followed by the global
map.
The procedure for searching a single keymap is called key lookup; see section Key Lookup.
Since every buffer that uses the same major mode normally uses the
same local keymap, you can think of the keymap as local to the mode. A
change to the local keymap of a buffer (using local-set-key, for
example) is seen also in the other buffers that share that keymap.
The local keymaps that are used for Lisp mode, C mode, and several
other major modes exist even if they have not yet been used. These
local maps are the values of the variables lisp-mode-map,
c-mode-map, and so on. For most other modes, which are less
frequently used, the local keymap is constructed only when the mode is
used for the first time in a session.
The minibuffer has local keymaps, too; they contain various completion and exit commands. See section Introduction to Minibuffers.
See section Standard Keymaps, for a list of standard keymaps.
self-insert-command to all of the printing characters.
It is normal practice to change the bindings in the global map, but you should not assign this variable any value other than the keymap it starts out with.
global-map unless you change one or the
other.
(current-global-map)
=> (keymap [set-mark-command beginning-of-line ...
delete-backward-char])
nil
if it has none. In the following example, the keymap for the
`*scratch*' buffer (using Lisp Interaction mode) is a sparse keymap
in which the entry for ESC, ASCII code 27, is another sparse
keymap.
(current-local-map)
=> (keymap
(10 . eval-print-last-sexp)
(9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap
(24 . eval-defun)
(17 . indent-sexp)))
nil.
It is very unusual to change the global keymap.
nil, then the buffer has no local
keymap. use-local-map returns nil. Most major mode
commands use this function.
(variable . keymap)
The keymap keymap is active whenever variable has a
non-nil value. Typically variable is the variable that
enables or disables a minor mode. See section Keymaps and Minor Modes.
Note that elements of minor-mode-map-alist do not have the same
structure as elements of minor-mode-alist. The map must be the
CDR of the element; a list with the map as the second element will
not do.
What's more, the keymap itself must appear in the CDR. It does not work to store a variable in the CDR and make the map the value of that variable.
When more than one minor mode keymap is active, their order of priority
is the order of minor-mode-map-alist. But you should design
minor modes so that they don't interfere with each other. If you do
this properly, the order will not matter.
See also minor-mode-key-binding in section Functions for Key Lookup. See section Keymaps and Minor Modes, for more information about
minor modes.
nil, this variable holds a keymap to use instead of the
buffer's local keymap and instead of all the minor mode keymaps. This
keymap, if any, overrides all other maps that would have been active,
except for the current global map.
Key lookup is the process of finding the binding of a key sequence from a given keymap. Actual execution of the binding is not part of key lookup.
Key lookup uses just the event type of each event in the key
sequence; the rest of the event is ignored. In fact, a key sequence
used for key lookup may designate mouse events with just their types
(symbols) instead of with entire mouse events (lists). See section Input Events. Such a pseudo-key-sequence is insufficient for
command-execute, but it is sufficient for looking up or rebinding
a key.
When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.
Let's use the term keymap entry to describe the value found by
looking up an event type in a keymap. (This doesn't include the item
string and other extra elements in menu key bindings because
lookup-key and other key lookup functions don't include them in
the returned value.) While any Lisp object may be stored in a keymap as
a keymap entry, not all make sense for key lookup. Here is a list of
the meaningful kinds of keymap entries:
nil
nil means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at all, and
has no default binding, that is equivalent to a binding of nil
for that event type.
keymap, then the list
is a keymap, and is treated as a keymap (see above).
lambda, then the list is a
lambda expression. This is presumed to be a command, and is treated as
such (see above).
(othermap . othertype)When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that. This feature permits you to define one key as an alias for another key. For example, an entry whose CAR is the keymap called
esc-map
and whose CDR is 32 (the code for space) means, "Use the global
binding of Meta-SPC, whatever that may be."
command-execute
(see section Interactive Call).
The symbol undefined is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and its
binding is the command undefined; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling ding) but does not signal an error.
undefined is used in local keymaps to override a global key
binding and make the key "undefined" locally. A local binding of
nil would fail to do this because it would not override the
global binding.
In short, a keymap entry may be a keymap, a command, a keyboard macro,
a symbol that leads to one of them, or an indirection or nil.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap. This map is the normal value
of emacs-lisp-mode-map. Note that 9 is the code for TAB,
127 for DEL, 27 for ESC, 17 for C-q and 24 for
C-x.
(keymap (9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap (17 . indent-sexp) (24 . eval-defun)))
Here are the functions and variables pertaining to key lookup.
If accept-defaults is non-nil, then lookup-key
considers default bindings as well as bindings for the specific events
in key. Otherwise, lookup-key reports only bindings for
the specific sequence key, ignoring default bindings except when
you explicitly ask about them. (To do this, supply t as an
element of key; see section Format of Keymaps.)
All the other functions described in this chapter that look up keys use
lookup-key.
(lookup-key (current-global-map) "\C-x\C-f")
=> find-file
(lookup-key (current-global-map) "\C-x\C-f12345")
=> 2
If key contains a meta character, that character is implicitly
replaced by a two-character sequence: the value of
meta-prefix-char, followed by the corresponding non-meta
character. Thus, the first example below is handled by conversion into
the second example.
(lookup-key (current-global-map) "\M-f")
=> forward-word
(lookup-key (current-global-map) "\ef")
=> forward-word
Unlike read-key-sequence, this function does not modify the
specified events in ways that discard information (see section Key Sequence Input). In particular, it does not convert letters to lower case and
it does not change drag events to clicks.
ding, but does
not cause an error.
nil if
key is undefined in the keymaps.
The argument accept-defaults controls checking for default
bindings, as in lookup-key (above).
An error is signaled if key is not a string or a vector.
(key-binding "\C-x\C-f")
=> find-file
nil if it is undefined there.
The argument accept-defaults controls checking for default bindings,
as in lookup-key (above).
nil if it is undefined there.
The argument accept-defaults controls checking for default bindings,
as in lookup-key (above).
(modename . binding), where modename is the
variable that enables the minor mode, and binding is key's
binding in that mode. If key has no minor-mode bindings, the
value is nil.
If the first binding is not a prefix command, all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.
The argument accept-defaults controls checking for default
bindings, as in lookup-key (above).
As long as the value of meta-prefix-char remains 27, key
lookup translates M-b into ESC b, which is normally
defined as the backward-word command. However, if you set
meta-prefix-char to 24, the code for C-x, then Emacs will
translate M-b into C-x b, whose standard binding is the
switch-to-buffer command.
meta-prefix-char ; The default value.
=> 27
(key-binding "\M-b")
=> backward-word
?\C-x ; The print representation
=> 24 ; of a character.
(setq meta-prefix-char 24)
=> 24
(key-binding "\M-b")
=> switch-to-buffer ; Now, typing M-b is
; like typing C-x b.
(setq meta-prefix-char 27) ; Avoid confusion!
=> 27 ; Restore the default value!
The way to rebind a key is to change its entry in a keymap. If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one). If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The global-set-key and local-set-key functions are
convenient interfaces for these operations (see section Commands for Binding Keys). You can also use define-key, a more general
function; then you must specify explicitly the map to change.
In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (see section String Type).
The syntax `\C-' means that the following character is a control
character and `\M-' means that the following character is a meta
character. Thus, the string "\M-x" is read as containing a
single M-x, "\C-f" is read as containing a single
C-f, and "\M-\C-x" and "\C-\M-x" are both read as
containing a single C-M-x. You can also use this escape syntax in
vectors, as well as others that aren't allowed in strings; one example
is `[?\C-\H-x home]'. See section Character Type.
For the functions below, an error is signaled if keymap is not a keymap or if key is not a string or vector representing a key sequence. You can use event types (symbols) as shorthand for events that are lists.
define-key is binding.
Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled.
If some prefix of key is undefined, then define-key defines
it as a prefix key so that the rest of key may be defined as
specified.
Here is an example that creates a sparse keymap and makes a number of bindings in it:
(setq map (make-sparse-keymap))
=> (keymap)
(define-key map "\C-f" 'forward-char)
=> forward-char
map
=> (keymap (6 . forward-char))
;; Build sparse submap for C-x and bind f in that.
(define-key map "\C-xf" 'forward-word)
=> forward-word
map
=> (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map "\C-p" ctl-x-map)
;; ctl-x-map
=> [nil ... find-file ... backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map "\C-p\C-f" 'foo)
=> 'foo
map
=> (keymap ; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for C-p C-f actually works by
changing an entry in ctl-x-map, and this has the effect of
changing the bindings of both C-p C-f and C-x C-f in the
default global map.
nil.
For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:
(substitute-key-definition 'find-file 'find-file-read-only (current-global-map))
If oldmap is non-nil, then its bindings determine which
keys to rebind. The rebindings still happen in newmap, not in
oldmap. Thus, you can change one map under the control of the
bindings in another. For example,
(substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map)
puts the special deletion command in my-map for whichever keys
are globally bound to the standard deletion command.
Here is an example showing a keymap before and after substitution:
(setq map '(keymap
(?1 . olddef-1)
(?2 . olddef-2)
(?3 . olddef-1)))
=> (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))
(substitute-key-definition 'olddef-1 'newdef map)
=> nil
map
=> (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
undefined. This makes ordinary insertion of
text impossible. suppress-keymap returns nil.
If nodigits is nil, then suppress-keymap defines
digits to run digit-argument, and - to run
negative-argument. Otherwise it makes them undefined like the
rest of the printing characters.
The suppress-keymap function does not make it impossible to
modify a buffer, as it does not suppress commands such as yank
and quoted-insert. To prevent any modification of a buffer, make
it read-only (see section Read-Only Buffers).
Since this function modifies keymap, you would normally use it
on a newly created keymap. Operating on an existing keymap
that is used for some other purpose is likely to cause trouble; for
example, suppressing global-map would make it impossible to use
most of Emacs.
Most often, suppress-keymap is used to initialize local
keymaps of modes such as Rmail and Dired where insertion of text is not
desirable and the buffer is read-only. Here is an example taken from
the file `emacs/lisp/dired.el', showing how the local keymap for
Dired mode is set up:
... (setq dired-mode-map (make-keymap)) (suppress-keymap dired-mode-map) (define-key dired-mode-map "r" 'dired-rename-file) (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted) (define-key dired-mode-map "d" 'dired-flag-file-deleted) (define-key dired-mode-map "v" 'dired-view-file) (define-key dired-mode-map "e" 'dired-find-file) (define-key dired-mode-map "f" 'dired-find-file) ...
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling define-key.
People often use global-set-key in their `.emacs' file for
simple customization. For example,
(global-set-key "\C-x\C-\\" 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
redefines C-x C-\ to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, typed with the Meta key, to set point where you click.
(global-set-key key definition) == (define-key (current-global-map) key definition)
One use of this function is in preparation for defining a longer key that uses key as a prefix--which would not be allowed if key has a non-prefix binding. For example:
(global-unset-key "\C-l")
=> nil
(global-set-key "\C-l\C-l" 'redraw-display)
=> nil
This function is implemented simply using define-key:
(global-unset-key key) == (define-key (current-global-map) key nil)
(local-set-key key definition) == (define-key (current-local-map) key definition)
(local-unset-key key) == (define-key (current-local-map) key nil)
This section describes functions used to scan all the current keymaps for the sake of printing help information.
(key . map), where
key is a prefix key whose definition in keymap is
map.
The elements of the alist are ordered so that the key increases
in length. The first element is always ("" . keymap),
because the specified keymap is accessible from itself with a prefix of
no events.
If prefix is given, it should be a prefix key sequence; then
accessible-keymaps includes only the submaps whose prefixes start
with prefix. These elements look just as they do in the value of
(accessible-keymaps); the only difference is that some elements
are omitted.
In the example below, the returned alist indicates that the key
ESC, which is displayed as `^[', is a prefix key whose
definition is the sparse keymap (keymap (83 . center-paragraph)
(115 . foo)).
(accessible-keymaps (current-local-map))
=>(("" keymap
(27 keymap ; Note this keymap for ESC is repeated below.
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
("^[" keymap
(83 . center-paragraph)
(115 . foo)))
In the following example, C-h is a prefix key that uses a sparse
keymap starting with (keymap (118 . describe-variable)...).
Another prefix, C-x 4, uses a keymap which is also the value of
the variable ctl-x-4-map. The event mode-line is one of
several dummy events used as prefixes for mouse actions in special parts
of a window.
(accessible-keymaps (current-global-map))
=> (("" keymap [set-mark-command beginning-of-line ...
delete-backward-char])
("^H" keymap (118 . describe-variable) ...
(8 . help-for-help))
("^X" keymap [x-flush-mouse-queue ...
backward-kill-sentence])
("^[" keymap [mark-sexp backward-sexp ...
backward-kill-word])
("^X4" keymap (15 . display-buffer) ...)
([mode-line] keymap
(S-mouse-2 . mouse-split-window-horizontally) ...))
These are not all the keymaps you would see in an actual case.
The argument command can be any object; it is compared with all
keymap entries using eq.
If keymap is nil, then the maps used are the current active
keymaps, disregarding overriding-local-map (that is, pretending
its value is nil). If keymap is non-nil, then the
maps searched are keymap and the global keymap.
Usually it's best to use overriding-local-map as the expression
for keymap. Then where-is-internal searches precisely the
keymaps that are active. To search only the global map, pass
(keymap) (an empty keymap) as keymap.
If firstonly is non-ascii, then the value is a single
string representing the first key sequence found, rather than a list of
all possible key sequences. If firstonly is t, then the
value is the first key sequence, except that key sequences consisting
entirely of ASCII characters (or meta variants of ASCII
characters) are preferred to all other key sequences.
If noindirect is non-nil, where-is-internal doesn't
follow indirect keymap bindings. This makes it possible to search for
an indirect definition itself.
This function is used by where-is (see section `Help' in The GNU Emacs Manual).
(where-is-internal 'describe-function)
=> ("\^hf" "\^hd")
If prefix is non-nil, it should be a prefix key; then the
listing includes only keys that start with prefix.
The listing describes meta characters as ESC followed by the corresponding non-meta character.
When several characters with consecutive ASCII codes have the
same definition, they are shown together, as
`firstchar..lastchar'. In this instance, you need to
know the ASCII codes to understand which characters this means.
For example, in the default global map, the characters `SPC
.. ~' are described by a single line. SPC is ASCII 32,
~ is ASCII 126, and the characters between them include all
the normal printing characters, (e.g., letters, digits, punctuation,
etc.); all these characters are bound to self-insert-command.
A keymap can define a menu as well as bindings for keyboard keys and mouse button. Menus are usually actuated with the mouse, but they can work with the keyboard also.
A keymap is suitable for menu use if it has an overall prompt
string, which is a string that appears as an element of the keymap.
(See section Format of Keymaps.) The string should describe the purpose of
the menu. The easiest way to construct a keymap with a prompt string is
to specify the string as an argument when you call make-keymap or
make-sparse-keymap (see section Creating Keymaps).
The individual bindings in the menu keymap should have item strings; these strings become the items displayed in the menu. A binding with an item string looks like this:
(string . real-binding)
The item string for a binding should be short--one or two words. It should describe the action of the command it corresponds to.
As far as define-key is concerned, string is part of the
event's binding. However, lookup-key returns just
real-binding, and only real-binding is used for executing
the key.
You can also supply a second string, called the help string, as follows:
(string help-string . real-binding)
Currently Emacs does not actually use help-string; it knows only how to ignore help-string in order to extract real-binding. In the future we hope to make help-string serve as extended documentation for the menu item, available on request.
If real-binding is nil, then string appears in the
menu but cannot be selected.
If real-binding is a symbol and has a non-nil
menu-enable property, that property is an expression that
controls whether the menu item is enabled. Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-nil. When a
menu item is disabled, it is displayed in a "fuzzy" fashion, and
cannot be selected with the mouse.
The order of items in the menu is the same as the order of bindings in
the keymap. Since define-key puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order. When you add an item to
an existing menu, you can specify its position in the menu using
define-key-after (see section Modifying Menus).
You've probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this:
(string [help-string] (key-binding-data) . real-binding)
Don't put these sublists in the menu item yourself; menu display calculates them automatically. Don't add keyboard equivalents to the item strings in a mouse menu, since that is redundant.
The way to make a menu keymap produce a menu is to make it the definition of a prefix key.
If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)
It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.
A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings an item string that starts with `@'. The rest of the item string becomes the name of the pane. See the file `lisp/mouse.el' for an example of this. Any ordinary bindings with `@'-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.
X toolkit menus don't have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with `@' or not. In a toolkit version of Emacs, the only thing special about `@' at the beginning of an item string is that the `@' doesn't appear in the menu item.
You can also get multiple panes from separate keymaps. The full definition of a prefix key always comes from merging the definitions supplied by the various active keymaps (minor mode, local, and global). When more than one of these keymaps is a menu, each of them makes a separate pane or panes. See section Active Keymaps.
In toolkit versions of Emacs, menus don't have panes, so submenus are used to represent the separate keymaps. Each keymap's contribution becomes one submenu.
A Lisp program can explicitly pop up a menu and receive the user's choice. You can use keymaps for this also. See section Pop-Up Menus.
When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the user can use the keyboard to choose a menu item.
Emacs displays the menu alternatives (the item strings of the bindings)
in the echo area. If they don't all fit at once, the user can type
SPC to see the next line of alternatives. Successive uses of
SPC eventually get to the end of the menu and then cycle around to
the beginning. (The variable menu-prompt-more-char specifies
which character is used for this; SPC is the default.)
When the user has found the desired alternative from the menu, he or she should type the corresponding character--the one whose binding is that alternative.
In a menu intended for keyboard use, each menu item must clearly indicate what character to type. The best convention to use is to make the character the first letter of the item string. That is something users will understand without being told.
This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.
Here is a simple example of how to set up a menu for mouse use.
(defvar my-menu-map
(make-sparse-keymap "Key Commands <==> Functions"))
(fset 'help-for-keys my-menu-map)
(define-key my-menu-map [bindings]
'("List all keystroke commands" . describe-bindings))
(define-key my-menu-map [key]
'("Describe key briefly" . describe-key-briefly))
(define-key my-menu-map [key-verbose]
'("Describe key verbose" . describe-key))
(define-key my-menu-map [function]
'("Describe Lisp function" . describe-function))
(define-key my-menu-map [where-is]
'("Where is this command" . where-is))
(define-key global-map [C-S-down-mouse-1] 'help-for-keys)
The symbols used in the key sequences bound in the menu are fictitious
"function keys"; they don't appear on the keyboard, but that doesn't
stop you from using them in the menu. Their names were chosen to be
mnemonic, because they show up in the output of where-is and
apropos to identify the corresponding menu items.
However, if you want the menu to be usable from the keyboard as well, you must bind real ASCII characters as well as fictitious function keys.
Most window systems allow each frame to have a menu bar---a
permanently displayed menu stretching horizontally across the top of the
frame. The items of the menu bar are the subcommands of the fake
"function key" menu-bar, as defined by all the active keymaps.
To add an item to the menu bar, invent a fake "function key" of your
own (let's call it key), and make a binding for the key sequence
[menu-bar key]. Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined submenu containing all the subcommands of that item--the global subcommands, the local subcommands, and the minor mode subcommands, all together.
In order for a frame to display a menu bar, its menu-bar-lines
parameter must be greater than zero. Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame. We
recommend you try 1 or 2 as the value of menu-bar-lines. See section X Window Frame Parameters.
Here's an example of setting up a menu bar item:
(modify-frame-parameters (selected-frame)
'((menu-bar-lines . 2)))
;; Make a menu keymap (with a prompt string)
;; and make it the menu bar item's definition.
(define-key global-map [menu-bar words]
(cons "Words" (make-sparse-keymap "Words")))
;; Define specific subcommands in the item's menu.
(define-key global-map
[menu-bar words forward]
'("Forward word" . forward-word))
(define-key global-map
[menu-bar words backward]
'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by
rebinding the same fake function key with undefined as the
binding. For example, this is how Dired suppresses the `Edit' menu
bar item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
edit is the fake function key used by the global map for the
`Edit' menu bar item. The main reason to suppress a global
menu bar item is to regain space for mode-specific items.
This variable holds a list of fake function keys for items to display at
the end of the menu bar rather than in normal sequence. The default
value is (help); thus, the `Help' menu item normally appears
at the end of the menu bar, following local menu items.
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use define-key to add the item, it normally goes at the front of
the menu. To put it elsewhere, use define-key-after:
define-key, but position the binding in map after
the binding for the event after. For example,
(define-key-after my-menu [drink]
'("Drink" . drink-command) 'eat)
makes a binding for the fake function key drink and puts it right after the binding for eat.
Here is how to insert an item called `Work' in the `Signals'
menu of Shell mode, after the item break:
(define-key-after
(lookup-key shell-mode-map [menu-bar signals])
[work] '("Work" . work-command) 'break)
Note that key is a sequence containing just one event type, but after is just an event type (not a sequence).