2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../info/commands
6 @node Command Loop, Keymaps, Minibuffers, Top
8 @cindex editor command loop
11 When you run Emacs, it enters the @dfn{editor command loop} almost
12 immediately. This loop reads key sequences, executes their definitions,
13 and displays the results. In this chapter, we describe how these things
14 are done, and the subroutines that allow Lisp programs to do them.
17 * Command Overview:: How the command loop reads commands.
18 * Defining Commands:: Specifying how a function should read arguments.
19 * Interactive Call:: Calling a command, so that it will read arguments.
20 * Command Loop Info:: Variables set by the command loop for you to examine.
21 * Input Events:: What input looks like when you read it.
22 * Reading Input:: How to read input events from the keyboard or mouse.
23 * Special Events:: Events processed immediately and individually.
24 * Waiting:: Waiting for user input or elapsed time.
25 * Quitting:: How @kbd{C-g} works. How to catch or defer quitting.
26 * Prefix Command Arguments:: How the commands to set prefix args work.
27 * Recursive Editing:: Entering a recursive edit,
28 and why you usually shouldn't.
29 * Disabling Commands:: How the command loop handles disabled commands.
30 * Command History:: How the command history is set up, and how accessed.
31 * Keyboard Macros:: How keyboard macros are implemented.
34 @node Command Overview
35 @section Command Loop Overview
37 The first thing the command loop must do is read a key sequence, which
38 is a sequence of events that translates into a command. It does this by
39 calling the function @code{read-key-sequence}. Your Lisp code can also
40 call this function (@pxref{Key Sequence Input}). Lisp programs can also
41 do input at a lower level with @code{read-event} (@pxref{Reading One
42 Event}) or discard pending input with @code{discard-input}
43 (@pxref{Event Input Misc}).
45 The key sequence is translated into a command through the currently
46 active keymaps. @xref{Key Lookup}, for information on how this is done.
47 The result should be a keyboard macro or an interactively callable
48 function. If the key is @kbd{M-x}, then it reads the name of another
49 command, which it then calls. This is done by the command
50 @code{execute-extended-command} (@pxref{Interactive Call}).
52 To execute a command requires first reading the arguments for it.
53 This is done by calling @code{command-execute} (@pxref{Interactive
54 Call}). For commands written in Lisp, the @code{interactive}
55 specification says how to read the arguments. This may use the prefix
56 argument (@pxref{Prefix Command Arguments}) or may read with prompting
57 in the minibuffer (@pxref{Minibuffers}). For example, the command
58 @code{find-file} has an @code{interactive} specification which says to
59 read a file name using the minibuffer. The command's function body does
60 not use the minibuffer; if you call this command from Lisp code as a
61 function, you must supply the file name string as an ordinary Lisp
64 If the command is a string or vector (i.e., a keyboard macro) then
65 @code{execute-kbd-macro} is used to execute it. You can call this
66 function yourself (@pxref{Keyboard Macros}).
68 To terminate the execution of a running command, type @kbd{C-g}. This
69 character causes @dfn{quitting} (@pxref{Quitting}).
71 @defvar pre-command-hook
72 The editor command loop runs this normal hook before each command. At
73 that time, @code{this-command} contains the command that is about to
74 run, and @code{last-command} describes the previous command.
78 @defvar post-command-hook
79 The editor command loop runs this normal hook after each command
80 (including commands terminated prematurely by quitting or by errors),
81 and also when the command loop is first entered. At that time,
82 @code{this-command} describes the command that just ran, and
83 @code{last-command} describes the command before that. @xref{Hooks}.
86 Quitting is suppressed while running @code{pre-command-hook} and
87 @code{post-command-hook}. If an error happens while executing one of
88 these hooks, it terminates execution of the hook, and clears the hook
89 variable to @code{nil} so as to prevent an infinite loop of errors.
91 @node Defining Commands
92 @section Defining Commands
93 @cindex defining commands
94 @cindex commands, defining
95 @cindex functions, making them interactive
96 @cindex interactive function
98 A Lisp function becomes a command when its body contains, at top
99 level, a form that calls the special form @code{interactive}. This
100 form does nothing when actually executed, but its presence serves as a
101 flag to indicate that interactive calling is permitted. Its argument
102 controls the reading of arguments for an interactive call.
105 * Using Interactive:: General rules for @code{interactive}.
106 * Interactive Codes:: The standard letter-codes for reading arguments
108 * Interactive Examples:: Examples of how to read interactive arguments.
111 @node Using Interactive
112 @subsection Using @code{interactive}
114 This section describes how to write the @code{interactive} form that
115 makes a Lisp function an interactively-callable command.
117 @defspec interactive arg-descriptor
118 @cindex argument descriptors
119 This special form declares that the function in which it appears is a
120 command, and that it may therefore be called interactively (via
121 @kbd{M-x} or by entering a key sequence bound to it). The argument
122 @var{arg-descriptor} declares how to compute the arguments to the
123 command when the command is called interactively.
125 A command may be called from Lisp programs like any other function, but
126 then the caller supplies the arguments and @var{arg-descriptor} has no
129 The @code{interactive} form has its effect because the command loop
130 (actually, its subroutine @code{call-interactively}) scans through the
131 function definition looking for it, before calling the function. Once
132 the function is called, all its body forms including the
133 @code{interactive} form are executed, but at this time
134 @code{interactive} simply returns @code{nil} without even evaluating its
138 There are three possibilities for the argument @var{arg-descriptor}:
142 It may be omitted or @code{nil}; then the command is called with no
143 arguments. This leads quickly to an error if the command requires one
147 It may be a Lisp expression that is not a string; then it should be a
148 form that is evaluated to get a list of arguments to pass to the
150 @cindex argument evaluation form
152 If this expression reads keyboard input (this includes using the
153 minibuffer), keep in mind that the integer value of point or the mark
154 before reading input may be incorrect after reading input. This is
155 because the current buffer may be receiving subprocess output;
156 if subprocess output arrives while the command is waiting for input,
157 it could relocate point and the mark.
159 Here's an example of what @emph{not} to do:
163 (list (region-beginning) (region-end)
164 (read-string "Foo: " nil 'my-history)))
168 Here's how to avoid the problem, by examining point and the mark only
169 after reading the keyboard input:
173 (let ((string (read-string "Foo: " nil 'my-history)))
174 (list (region-beginning) (region-end) string)))
178 @cindex argument prompt
179 It may be a string; then its contents should consist of a code character
180 followed by a prompt (which some code characters use and some ignore).
181 The prompt ends either with the end of the string or with a newline.
182 Here is a simple example:
185 (interactive "bFrobnicate buffer: ")
189 The code letter @samp{b} says to read the name of an existing buffer,
190 with completion. The buffer name is the sole argument passed to the
191 command. The rest of the string is a prompt.
193 If there is a newline character in the string, it terminates the prompt.
194 If the string does not end there, then the rest of the string should
195 contain another code character and prompt, specifying another argument.
196 You can specify any number of arguments in this way.
199 The prompt string can use @samp{%} to include previous argument values
200 (starting with the first argument) in the prompt. This is done using
201 @code{format} (@pxref{Formatting Strings}). For example, here is how
202 you could read the name of an existing buffer followed by a new name to
207 (interactive "bBuffer to rename: \nsRename buffer %s to: ")
211 @cindex @samp{*} in interactive
212 @cindex read-only buffers in interactive
213 If the first character in the string is @samp{*}, then an error is
214 signaled if the buffer is read-only.
216 @cindex @samp{@@} in interactive
218 If the first character in the string is @samp{@@}, and if the key
219 sequence used to invoke the command includes any mouse events, then
220 the window associated with the first of those events is selected
221 before the command is run.
223 You can use @samp{*} and @samp{@@} together; the order does not matter.
224 Actual reading of arguments is controlled by the rest of the prompt
225 string (starting with the first character that is not @samp{*} or
229 @node Interactive Codes
230 @comment node-name, next, previous, up
231 @subsection Code Characters for @code{interactive}
232 @cindex interactive code description
233 @cindex description for interactive codes
234 @cindex codes, interactive, description of
235 @cindex characters for interactive codes
237 The code character descriptions below contain a number of key words,
238 defined here as follows:
242 @cindex interactive completion
243 Provide completion. @key{TAB}, @key{SPC}, and @key{RET} perform name
244 completion because the argument is read using @code{completing-read}
245 (@pxref{Completion}). @kbd{?} displays a list of possible completions.
248 Require the name of an existing object. An invalid name is not
249 accepted; the commands to exit the minibuffer do not exit if the current
253 @cindex default argument string
254 A default value of some sort is used if the user enters no text in the
255 minibuffer. The default depends on the code character.
258 This code letter computes an argument without reading any input.
259 Therefore, it does not use a prompt string, and any prompt string you
262 Even though the code letter doesn't use a prompt string, you must follow
263 it with a newline if it is not the last code character in the string.
266 A prompt immediately follows the code character. The prompt ends either
267 with the end of the string or with a newline.
270 This code character is meaningful only at the beginning of the
271 interactive string, and it does not look for a prompt or a newline.
272 It is a single, isolated character.
275 @cindex reading interactive arguments
276 Here are the code character descriptions for use with @code{interactive}:
280 Signal an error if the current buffer is read-only. Special.
283 Select the window mentioned in the first mouse event in the key
284 sequence that invoked this command. Special.
287 A function name (i.e., a symbol satisfying @code{fboundp}). Existing,
291 The name of an existing buffer. By default, uses the name of the
292 current buffer (@pxref{Buffers}). Existing, Completion, Default,
296 A buffer name. The buffer need not exist. By default, uses the name of
297 a recently used buffer other than the current buffer. Completion,
301 A character. The cursor does not move into the echo area. Prompt.
304 A command name (i.e., a symbol satisfying @code{commandp}). Existing,
308 @cindex position argument
309 The position of point, as an integer (@pxref{Point}). No I/O.
312 A directory name. The default is the current default directory of the
313 current buffer, @code{default-directory} (@pxref{System Environment}).
314 Existing, Completion, Default, Prompt.
317 The first or next mouse event in the key sequence that invoked the command.
318 More precisely, @samp{e} gets events that are lists, so you can look at
319 the data in the lists. @xref{Input Events}. No I/O.
321 You can use @samp{e} more than once in a single command's interactive
322 specification. If the key sequence that invoked the command has
323 @var{n} events that are lists, the @var{n}th @samp{e} provides the
324 @var{n}th such event. Events that are not lists, such as function keys
325 and @sc{ASCII} characters, do not count where @samp{e} is concerned.
328 A file name of an existing file (@pxref{File Names}). The default
329 directory is @code{default-directory}. Existing, Completion, Default,
333 A file name. The file need not exist. Completion, Default, Prompt.
336 An irrelevant argument. This code always supplies @code{nil} as
337 the argument's value. No I/O.
340 A key sequence (@pxref{Keymap Terminology}). This keeps reading events
341 until a command (or undefined command) is found in the current key
342 maps. The key sequence argument is represented as a string or vector.
343 The cursor does not move into the echo area. Prompt.
345 This kind of input is used by commands such as @code{describe-key} and
346 @code{global-set-key}.
349 A key sequence, whose definition you intend to change. This works like
350 @samp{k}, except that it suppresses, for the last input event in the key
351 sequence, the conversions that are normally used (when necessary) to
352 convert an undefined key into a defined one.
355 @cindex marker argument
356 The position of the mark, as an integer. No I/O.
359 Arbitrary text, read in the minibuffer using the current buffer's input
360 method, and returned as a string (@pxref{Input Methods,,, emacs, The GNU
361 Emacs Manual}). Prompt.
364 A number read with the minibuffer. If the input is not a number, the
365 user is asked to try again. The prefix argument, if any, is not used.
369 @cindex raw prefix argument usage
370 The numeric prefix argument; but if there is no prefix argument, read a
371 number as with @kbd{n}. Requires a number. @xref{Prefix Command
375 @cindex numeric prefix argument usage
376 The numeric prefix argument. (Note that this @samp{p} is lower case.)
380 The raw prefix argument. (Note that this @samp{P} is upper case.) No
384 @cindex region argument
385 Point and the mark, as two numeric arguments, smallest first. This is
386 the only code letter that specifies two successive arguments rather than
390 Arbitrary text, read in the minibuffer and returned as a string
391 (@pxref{Text from Minibuffer}). Terminate the input with either
392 @kbd{C-j} or @key{RET}. (@kbd{C-q} may be used to include either of
393 these characters in the input.) Prompt.
396 An interned symbol whose name is read in the minibuffer. Any whitespace
397 character terminates the input. (Use @kbd{C-q} to include whitespace in
398 the string.) Other characters that normally terminate a symbol (e.g.,
399 parentheses and brackets) do not do so here. Prompt.
402 A variable declared to be a user option (i.e., satisfying the predicate
403 @code{user-variable-p}). @xref{High-Level Completion}. Existing,
407 A Lisp object, specified with its read syntax, terminated with a
408 @kbd{C-j} or @key{RET}. The object is not evaluated. @xref{Object from
412 @cindex evaluated expression argument
413 A Lisp form is read as with @kbd{x}, but then evaluated so that its
414 value becomes the argument for the command. Prompt.
417 A coding system name (a symbol). If the user enters null input, the
418 argument value is @code{nil}. @xref{Coding Systems}. Completion,
422 A coding system name (a symbol)---but only if this command has a prefix
423 argument. With no prefix argument, @samp{Z} provides @code{nil} as the
424 argument value. Completion, Existing, Prompt.
427 @node Interactive Examples
428 @comment node-name, next, previous, up
429 @subsection Examples of Using @code{interactive}
430 @cindex examples of using @code{interactive}
431 @cindex @code{interactive}, examples of using
433 Here are some examples of @code{interactive}:
437 (defun foo1 () ; @r{@code{foo1} takes no arguments,}
438 (interactive) ; @r{just moves forward two words.}
444 (defun foo2 (n) ; @r{@code{foo2} takes one argument,}
445 (interactive "p") ; @r{which is the numeric prefix.}
446 (forward-word (* 2 n)))
451 (defun foo3 (n) ; @r{@code{foo3} takes one argument,}
452 (interactive "nCount:") ; @r{which is read with the Minibuffer.}
453 (forward-word (* 2 n)))
458 (defun three-b (b1 b2 b3)
459 "Select three existing buffers.
460 Put them into three windows, selecting the last one."
462 (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:")
463 (delete-other-windows)
464 (split-window (selected-window) 8)
465 (switch-to-buffer b1)
467 (split-window (selected-window) 8)
468 (switch-to-buffer b2)
470 (switch-to-buffer b3))
473 (three-b "*scratch*" "declarations.texi" "*mail*")
478 @node Interactive Call
479 @section Interactive Call
480 @cindex interactive call
482 After the command loop has translated a key sequence into a command it
483 invokes that command using the function @code{command-execute}. If the
484 command is a function, @code{command-execute} calls
485 @code{call-interactively}, which reads the arguments and calls the
486 command. You can also call these functions yourself.
488 @defun commandp object
489 Returns @code{t} if @var{object} is suitable for calling interactively;
490 that is, if @var{object} is a command. Otherwise, returns @code{nil}.
492 The interactively callable objects include strings and vectors (treated
493 as keyboard macros), lambda expressions that contain a top-level call to
494 @code{interactive}, byte-code function objects made from such lambda
495 expressions, autoload objects that are declared as interactive
496 (non-@code{nil} fourth argument to @code{autoload}), and some of the
499 A symbol satisfies @code{commandp} if its function definition satisfies
502 Keys and keymaps are not commands. Rather, they are used to look up
503 commands (@pxref{Keymaps}).
505 See @code{documentation} in @ref{Accessing Documentation}, for a
506 realistic example of using @code{commandp}.
509 @defun call-interactively command &optional record-flag keys
510 This function calls the interactively callable function @var{command},
511 reading arguments according to its interactive calling specifications.
512 An error is signaled if @var{command} is not a function or if it cannot
513 be called interactively (i.e., is not a command). Note that keyboard
514 macros (strings and vectors) are not accepted, even though they are
515 considered commands, because they are not functions.
517 @cindex record command history
518 If @var{record-flag} is non-@code{nil}, then this command and its
519 arguments are unconditionally added to the list @code{command-history}.
520 Otherwise, the command is added only if it uses the minibuffer to read
521 an argument. @xref{Command History}.
523 The argument @var{keys}, if given, specifies the sequence of events to
524 supply if the command inquires which events were used to invoke it.
527 @defun command-execute command &optional record-flag keys
528 @cindex keyboard macro execution
529 This function executes @var{command}. The argument @var{command} must
530 satisfy the @code{commandp} predicate; i.e., it must be an interactively
531 callable function or a keyboard macro.
533 A string or vector as @var{command} is executed with
534 @code{execute-kbd-macro}. A function is passed to
535 @code{call-interactively}, along with the optional @var{record-flag}.
537 A symbol is handled by using its function definition in its place. A
538 symbol with an @code{autoload} definition counts as a command if it was
539 declared to stand for an interactively callable function. Such a
540 definition is handled by loading the specified library and then
541 rechecking the definition of the symbol.
543 The argument @var{keys}, if given, specifies the sequence of events to
544 supply if the command inquires which events were used to invoke it.
547 @deffn Command execute-extended-command prefix-argument
548 @cindex read command name
549 This function reads a command name from the minibuffer using
550 @code{completing-read} (@pxref{Completion}). Then it uses
551 @code{command-execute} to call the specified command. Whatever that
552 command returns becomes the value of @code{execute-extended-command}.
554 @cindex execute with prefix argument
555 If the command asks for a prefix argument, it receives the value
556 @var{prefix-argument}. If @code{execute-extended-command} is called
557 interactively, the current raw prefix argument is used for
558 @var{prefix-argument}, and thus passed on to whatever command is run.
560 @c !!! Should this be @kindex?
562 @code{execute-extended-command} is the normal definition of @kbd{M-x},
563 so it uses the string @w{@samp{M-x }} as a prompt. (It would be better
564 to take the prompt from the events used to invoke
565 @code{execute-extended-command}, but that is painful to implement.) A
566 description of the value of the prefix argument, if any, also becomes
571 (execute-extended-command 1)
572 ---------- Buffer: Minibuffer ----------
573 1 M-x forward-word RET
574 ---------- Buffer: Minibuffer ----------
581 This function returns @code{t} if the containing function (the one whose
582 code includes the call to @code{interactive-p}) was called
583 interactively, with the function @code{call-interactively}. (It makes
584 no difference whether @code{call-interactively} was called from Lisp or
585 directly from the editor command loop.) If the containing function was
586 called by Lisp evaluation (or with @code{apply} or @code{funcall}), then
587 it was not called interactively.
590 The most common use of @code{interactive-p} is for deciding whether to
591 print an informative message. As a special exception,
592 @code{interactive-p} returns @code{nil} whenever a keyboard macro is
593 being run. This is to suppress the informative messages and speed
594 execution of the macro.
602 (when (interactive-p)
610 (setq foobar (list (foo) (interactive-p))))
615 ;; @r{Type @kbd{M-x foo}.}
620 ;; @r{Type @kbd{M-x bar}.}
621 ;; @r{This does not print anything.}
630 The other way to do this sort of job is to make the command take an
631 argument @code{print-message} which should be non-@code{nil} in an
632 interactive call, and use the @code{interactive} spec to make sure it is
633 non-@code{nil}. Here's how:
636 (defun foo (&optional print-message)
642 The numeric prefix argument, provided by @samp{p}, is never @code{nil}.
644 @node Command Loop Info
645 @comment node-name, next, previous, up
646 @section Information from the Command Loop
648 The editor command loop sets several Lisp variables to keep status
649 records for itself and for commands that are run.
652 This variable records the name of the previous command executed by the
653 command loop (the one before the current command). Normally the value
654 is a symbol with a function definition, but this is not guaranteed.
656 The value is copied from @code{this-command} when a command returns to
657 the command loop, except when the command has specified a prefix
658 argument for the following command.
660 This variable is always local to the current terminal and cannot be
661 buffer-local. @xref{Multiple Displays}.
664 @tindex real-last-command
665 @defvar real-last-command
666 This variable is set up by Emacs just like @code{last-command},
667 but never altered by Lisp programs.
671 @cindex current command
672 This variable records the name of the command now being executed by
673 the editor command loop. Like @code{last-command}, it is normally a symbol
674 with a function definition.
676 The command loop sets this variable just before running a command, and
677 copies its value into @code{last-command} when the command finishes
678 (unless the command specified a prefix argument for the following
681 @cindex kill command repetition
682 Some commands set this variable during their execution, as a flag for
683 whatever command runs next. In particular, the functions for killing text
684 set @code{this-command} to @code{kill-region} so that any kill commands
685 immediately following will know to append the killed text to the
689 If you do not want a particular command to be recognized as the previous
690 command in the case where it got an error, you must code that command to
691 prevent this. One way is to set @code{this-command} to @code{t} at the
692 beginning of the command, and set @code{this-command} back to its proper
693 value at the end, like this:
696 (defun foo (args@dots{})
697 (interactive @dots{})
698 (let ((old-this-command this-command))
699 (setq this-command t)
700 @r{@dots{}do the work@dots{}}
701 (setq this-command old-this-command)))
705 We do not bind @code{this-command} with @code{let} because that would
706 restore the old value in case of error---a feature of @code{let} which
707 in this case does precisely what we want to avoid.
709 @defun this-command-keys
710 This function returns a string or vector containing the key sequence
711 that invoked the present command, plus any previous commands that
712 generated the prefix argument for this command. The value is a string
713 if all those events were characters. @xref{Input Events}.
718 ;; @r{Now use @kbd{C-u C-x C-e} to evaluate that.}
724 @defun this-command-keys-vector
725 Like @code{this-command-keys}, except that it always returns
726 the events in a vector, so you do never need to deal with the complexities
727 of storing input events in a string (@pxref{Strings of Events}).
730 @defvar last-nonmenu-event
731 This variable holds the last input event read as part of a key sequence,
732 not counting events resulting from mouse menus.
734 One use of this variable is for telling @code{x-popup-menu} where to pop
735 up a menu. It is also used internally by @code{y-or-n-p}
736 (@pxref{Yes-or-No Queries}).
739 @defvar last-command-event
740 @defvarx last-command-char
741 This variable is set to the last input event that was read by the
742 command loop as part of a command. The principal use of this variable
743 is in @code{self-insert-command}, which uses it to decide which
749 ;; @r{Now use @kbd{C-u C-x C-e} to evaluate that.}
755 The value is 5 because that is the @sc{ASCII} code for @kbd{C-e}.
757 The alias @code{last-command-char} exists for compatibility with
762 @defvar last-event-frame
763 This variable records which frame the last input event was directed to.
764 Usually this is the frame that was selected when the event was
765 generated, but if that frame has redirected input focus to another
766 frame, the value is the frame to which the event was redirected.
771 @section Input Events
775 The Emacs command loop reads a sequence of @dfn{input events} that
776 represent keyboard or mouse activity. The events for keyboard activity
777 are characters or symbols; mouse events are always lists. This section
778 describes the representation and meaning of input events in detail.
781 This function returns non-@code{nil} if @var{object} is an input event
784 Note that any symbol might be used as an event or an event type.
785 @code{eventp} cannot distinguish whether a symbol is intended by Lisp
786 code to be used as an event. Instead, it distinguishes whether the
787 symbol has actually been used in an event that has been read as input in
788 the current Emacs session. If a symbol has not yet been so used,
789 @code{eventp} returns @code{nil}.
793 * Keyboard Events:: Ordinary characters--keys with symbols on them.
794 * Function Keys:: Function keys--keys with names, not symbols.
795 * Mouse Events:: Overview of mouse events.
796 * Click Events:: Pushing and releasing a mouse button.
797 * Drag Events:: Moving the mouse before releasing the button.
798 * Button-Down Events:: A button was pushed and not yet released.
799 * Repeat Events:: Double and triple click (or drag, or down).
800 * Motion Events:: Just moving the mouse, not pushing a button.
801 * Focus Events:: Moving the mouse between frames.
802 * Misc Events:: Other events window systems can generate.
803 * Event Examples:: Examples of the lists for mouse events.
804 * Classifying Events:: Finding the modifier keys in an event symbol.
806 * Accessing Events:: Functions to extract info from events.
807 * Strings of Events:: Special considerations for putting
808 keyboard character events in a string.
811 @node Keyboard Events
812 @subsection Keyboard Events
814 There are two kinds of input you can get from the keyboard: ordinary
815 keys, and function keys. Ordinary keys correspond to characters; the
816 events they generate are represented in Lisp as characters. The event
817 type of a character event is the character itself (an integer); see
818 @ref{Classifying Events}.
820 @cindex modifier bits (of input character)
821 @cindex basic code (of input character)
822 An input character event consists of a @dfn{basic code} between 0 and
823 524287, plus any or all of these @dfn{modifier bits}:
834 bit in the character code indicates a character
835 typed with the meta key held down.
845 bit in the character code indicates a non-@sc{ASCII}
848 @sc{ASCII} control characters such as @kbd{C-a} have special basic
849 codes of their own, so Emacs needs no special bit to indicate them.
850 Thus, the code for @kbd{C-a} is just 1.
852 But if you type a control combination not in @sc{ASCII}, such as
853 @kbd{%} with the control key, the numeric value you get is the code
861 (assuming the terminal supports non-@sc{ASCII}
872 bit in the character code indicates an @sc{ASCII} control
873 character typed with the shift key held down.
875 For letters, the basic code itself indicates upper versus lower case;
876 for digits and punctuation, the shift key selects an entirely different
877 character with a different basic code. In order to keep within the
878 @sc{ASCII} character set whenever possible, Emacs avoids using the
885 bit for those characters.
887 However, @sc{ASCII} provides no way to distinguish @kbd{C-A} from
888 @kbd{C-a}, so Emacs uses the
895 bit in @kbd{C-A} and not in
906 bit in the character code indicates a character
907 typed with the hyper key held down.
917 bit in the character code indicates a character
918 typed with the super key held down.
928 bit in the character code indicates a character typed with
929 the alt key held down. (On some terminals, the key labeled @key{ALT}
930 is actually the meta key.)
933 It is best to avoid mentioning specific bit numbers in your program.
934 To test the modifier bits of a character, use the function
935 @code{event-modifiers} (@pxref{Classifying Events}). When making key
936 bindings, you can use the read syntax for characters with modifier bits
937 (@samp{\C-}, @samp{\M-}, and so on). For making key bindings with
938 @code{define-key}, you can use lists such as @code{(control hyper ?x)} to
939 specify the characters (@pxref{Changing Key Bindings}). The function
940 @code{event-convert-list} converts such a list into an event type
941 (@pxref{Classifying Events}).
944 @subsection Function Keys
946 @cindex function keys
947 Most keyboards also have @dfn{function keys}---keys that have names or
948 symbols that are not characters. Function keys are represented in Emacs
949 Lisp as symbols; the symbol's name is the function key's label, in lower
950 case. For example, pressing a key labeled @key{F1} places the symbol
951 @code{f1} in the input stream.
953 The event type of a function key event is the event symbol itself.
954 @xref{Classifying Events}.
956 Here are a few special cases in the symbol-naming convention for
960 @item @code{backspace}, @code{tab}, @code{newline}, @code{return}, @code{delete}
961 These keys correspond to common @sc{ASCII} control characters that have
962 special keys on most keyboards.
964 In @sc{ASCII}, @kbd{C-i} and @key{TAB} are the same character. If the
965 terminal can distinguish between them, Emacs conveys the distinction to
966 Lisp programs by representing the former as the integer 9, and the
967 latter as the symbol @code{tab}.
969 Most of the time, it's not useful to distinguish the two. So normally
970 @code{function-key-map} (@pxref{Translating Input}) is set up to map
971 @code{tab} into 9. Thus, a key binding for character code 9 (the
972 character @kbd{C-i}) also applies to @code{tab}. Likewise for the other
973 symbols in this group. The function @code{read-char} likewise converts
974 these events into characters.
976 In @sc{ASCII}, @key{BS} is really @kbd{C-h}. But @code{backspace}
977 converts into the character code 127 (@key{DEL}), not into code 8
978 (@key{BS}). This is what most users prefer.
980 @item @code{left}, @code{up}, @code{right}, @code{down}
982 @item @code{kp-add}, @code{kp-decimal}, @code{kp-divide}, @dots{}
983 Keypad keys (to the right of the regular keyboard).
984 @item @code{kp-0}, @code{kp-1}, @dots{}
985 Keypad keys with digits.
986 @item @code{kp-f1}, @code{kp-f2}, @code{kp-f3}, @code{kp-f4}
988 @item @code{kp-home}, @code{kp-left}, @code{kp-up}, @code{kp-right}, @code{kp-down}
989 Keypad arrow keys. Emacs normally translates these into the
990 corresponding non-keypad keys @code{home}, @code{left}, @dots{}
991 @item @code{kp-prior}, @code{kp-next}, @code{kp-end}, @code{kp-begin}, @code{kp-insert}, @code{kp-delete}
992 Additional keypad duplicates of keys ordinarily found elsewhere. Emacs
993 normally translates these into the like-named non-keypad keys.
996 You can use the modifier keys @key{ALT}, @key{CTRL}, @key{HYPER},
997 @key{META}, @key{SHIFT}, and @key{SUPER} with function keys. The way to
998 represent them is with prefixes in the symbol name:
1004 The control modifier.
1015 Thus, the symbol for the key @key{F3} with @key{META} held down is
1016 @code{M-f3}. When you use more than one prefix, we recommend you
1017 write them in alphabetical order; but the order does not matter in
1018 arguments to the key-binding lookup and modification functions.
1021 @subsection Mouse Events
1023 Emacs supports four kinds of mouse events: click events, drag events,
1024 button-down events, and motion events. All mouse events are represented
1025 as lists. The @sc{car} of the list is the event type; this says which
1026 mouse button was involved, and which modifier keys were used with it.
1027 The event type can also distinguish double or triple button presses
1028 (@pxref{Repeat Events}). The rest of the list elements give position
1029 and time information.
1031 For key lookup, only the event type matters: two events of the same type
1032 necessarily run the same command. The command can access the full
1033 values of these events using the @samp{e} interactive code.
1034 @xref{Interactive Codes}.
1036 A key sequence that starts with a mouse event is read using the keymaps
1037 of the buffer in the window that the mouse was in, not the current
1038 buffer. This does not imply that clicking in a window selects that
1039 window or its buffer---that is entirely under the control of the command
1040 binding of the key sequence.
1043 @subsection Click Events
1045 @cindex mouse click event
1047 When the user presses a mouse button and releases it at the same
1048 location, that generates a @dfn{click} event. Mouse click events have
1053 (@var{window} @var{buffer-pos} (@var{x} . @var{y}) @var{timestamp})
1057 Here is what the elements normally mean:
1060 @item @var{event-type}
1061 This is a symbol that indicates which mouse button was used. It is
1062 one of the symbols @code{mouse-1}, @code{mouse-2}, @dots{}, where the
1063 buttons are numbered left to right.
1065 You can also use prefixes @samp{A-}, @samp{C-}, @samp{H-}, @samp{M-},
1066 @samp{S-} and @samp{s-} for modifiers alt, control, hyper, meta, shift
1067 and super, just as you would with function keys.
1069 This symbol also serves as the event type of the event. Key bindings
1070 describe events by their types; thus, if there is a key binding for
1071 @code{mouse-1}, that binding would apply to all events whose
1072 @var{event-type} is @code{mouse-1}.
1075 This is the window in which the click occurred.
1077 @item @var{x}, @var{y}
1078 These are the pixel-denominated coordinates of the click, relative to
1079 the top left corner of @var{window}, which is @code{(0 . 0)}.
1081 @item @var{buffer-pos}
1082 This is the buffer position of the character clicked on.
1084 @item @var{timestamp}
1085 This is the time at which the event occurred, in milliseconds. (Since
1086 this value wraps around the entire range of Emacs Lisp integers in about
1087 five hours, it is useful only for relating the times of nearby events.)
1089 @item @var{click-count}
1090 This is the number of rapid repeated presses so far of the same mouse
1091 button. @xref{Repeat Events}.
1094 The meanings of @var{buffer-pos}, @var{x} and @var{y} are somewhat
1095 different when the event location is in a special part of the screen,
1096 such as the mode line or a scroll bar.
1098 If the location is in a scroll bar, then @var{buffer-pos} is the symbol
1099 @code{vertical-scroll-bar} or @code{horizontal-scroll-bar}, and the pair
1100 @code{(@var{x} . @var{y})} is replaced with a pair @code{(@var{portion}
1101 . @var{whole})}, where @var{portion} is the distance of the click from
1102 the top or left end of the scroll bar, and @var{whole} is the length of
1103 the entire scroll bar.
1105 If the position is on a mode line or the vertical line separating
1106 @var{window} from its neighbor to the right, then @var{buffer-pos} is
1107 the symbol @code{mode-line} or @code{vertical-line}. For the mode line,
1108 @var{y} does not have meaningful data. For the vertical line, @var{x}
1109 does not have meaningful data.
1111 In one special case, @var{buffer-pos} is a list containing a symbol (one
1112 of the symbols listed above) instead of just the symbol. This happens
1113 after the imaginary prefix keys for the event are inserted into the
1114 input stream. @xref{Key Sequence Input}.
1117 @subsection Drag Events
1119 @cindex mouse drag event
1121 With Emacs, you can have a drag event without even changing your
1122 clothes. A @dfn{drag event} happens every time the user presses a mouse
1123 button and then moves the mouse to a different character position before
1124 releasing the button. Like all mouse events, drag events are
1125 represented in Lisp as lists. The lists record both the starting mouse
1126 position and the final position, like this:
1130 (@var{window1} @var{buffer-pos1} (@var{x1} . @var{y1}) @var{timestamp1})
1131 (@var{window2} @var{buffer-pos2} (@var{x2} . @var{y2}) @var{timestamp2})
1135 For a drag event, the name of the symbol @var{event-type} contains the
1136 prefix @samp{drag-}. For example, dragging the mouse with button 2 held
1137 down generates a @code{drag-mouse-2} event. The second and third
1138 elements of the event give the starting and ending position of the drag.
1139 Aside from that, the data have the same meanings as in a click event
1140 (@pxref{Click Events}). You can access the second element of any mouse
1141 event in the same way, with no need to distinguish drag events from
1144 The @samp{drag-} prefix follows the modifier key prefixes such as
1145 @samp{C-} and @samp{M-}.
1147 If @code{read-key-sequence} receives a drag event that has no key
1148 binding, and the corresponding click event does have a binding, it
1149 changes the drag event into a click event at the drag's starting
1150 position. This means that you don't have to distinguish between click
1151 and drag events unless you want to.
1153 @node Button-Down Events
1154 @subsection Button-Down Events
1155 @cindex button-down event
1157 Click and drag events happen when the user releases a mouse button.
1158 They cannot happen earlier, because there is no way to distinguish a
1159 click from a drag until the button is released.
1161 If you want to take action as soon as a button is pressed, you need to
1162 handle @dfn{button-down} events.@footnote{Button-down is the
1163 conservative antithesis of drag.} These occur as soon as a button is
1164 pressed. They are represented by lists that look exactly like click
1165 events (@pxref{Click Events}), except that the @var{event-type} symbol
1166 name contains the prefix @samp{down-}. The @samp{down-} prefix follows
1167 modifier key prefixes such as @samp{C-} and @samp{M-}.
1169 The function @code{read-key-sequence} ignores any button-down events
1170 that don't have command bindings; therefore, the Emacs command loop
1171 ignores them too. This means that you need not worry about defining
1172 button-down events unless you want them to do something. The usual
1173 reason to define a button-down event is so that you can track mouse
1174 motion (by reading motion events) until the button is released.
1175 @xref{Motion Events}.
1178 @subsection Repeat Events
1179 @cindex repeat events
1180 @cindex double-click events
1181 @cindex triple-click events
1183 If you press the same mouse button more than once in quick succession
1184 without moving the mouse, Emacs generates special @dfn{repeat} mouse
1185 events for the second and subsequent presses.
1187 The most common repeat events are @dfn{double-click} events. Emacs
1188 generates a double-click event when you click a button twice; the event
1189 happens when you release the button (as is normal for all click
1192 The event type of a double-click event contains the prefix
1193 @samp{double-}. Thus, a double click on the second mouse button with
1194 @key{meta} held down comes to the Lisp program as
1195 @code{M-double-mouse-2}. If a double-click event has no binding, the
1196 binding of the corresponding ordinary click event is used to execute
1197 it. Thus, you need not pay attention to the double click feature
1198 unless you really want to.
1200 When the user performs a double click, Emacs generates first an ordinary
1201 click event, and then a double-click event. Therefore, you must design
1202 the command binding of the double click event to assume that the
1203 single-click command has already run. It must produce the desired
1204 results of a double click, starting from the results of a single click.
1206 This is convenient, if the meaning of a double click somehow ``builds
1207 on'' the meaning of a single click---which is recommended user interface
1208 design practice for double clicks.
1210 If you click a button, then press it down again and start moving the
1211 mouse with the button held down, then you get a @dfn{double-drag} event
1212 when you ultimately release the button. Its event type contains
1213 @samp{double-drag} instead of just @samp{drag}. If a double-drag event
1214 has no binding, Emacs looks for an alternate binding as if the event
1215 were an ordinary drag.
1217 Before the double-click or double-drag event, Emacs generates a
1218 @dfn{double-down} event when the user presses the button down for the
1219 second time. Its event type contains @samp{double-down} instead of just
1220 @samp{down}. If a double-down event has no binding, Emacs looks for an
1221 alternate binding as if the event were an ordinary button-down event.
1222 If it finds no binding that way either, the double-down event is
1225 To summarize, when you click a button and then press it again right
1226 away, Emacs generates a down event and a click event for the first
1227 click, a double-down event when you press the button again, and finally
1228 either a double-click or a double-drag event.
1230 If you click a button twice and then press it again, all in quick
1231 succession, Emacs generates a @dfn{triple-down} event, followed by
1232 either a @dfn{triple-click} or a @dfn{triple-drag}. The event types of
1233 these events contain @samp{triple} instead of @samp{double}. If any
1234 triple event has no binding, Emacs uses the binding that it would use
1235 for the corresponding double event.
1237 If you click a button three or more times and then press it again, the
1238 events for the presses beyond the third are all triple events. Emacs
1239 does not have separate event types for quadruple, quintuple, etc.@:
1240 events. However, you can look at the event list to find out precisely
1241 how many times the button was pressed.
1243 @defun event-click-count event
1244 This function returns the number of consecutive button presses that led
1245 up to @var{event}. If @var{event} is a double-down, double-click or
1246 double-drag event, the value is 2. If @var{event} is a triple event,
1247 the value is 3 or greater. If @var{event} is an ordinary mouse event
1248 (not a repeat event), the value is 1.
1251 @defvar double-click-time
1252 To generate repeat events, successive mouse button presses must be at
1253 the same screen position, and the number of milliseconds between
1254 successive button presses must be less than the value of
1255 @code{double-click-time}. Setting @code{double-click-time} to
1256 @code{nil} disables multi-click detection entirely. Setting it to
1257 @code{t} removes the time limit; Emacs then detects multi-clicks by
1262 @subsection Motion Events
1263 @cindex motion event
1264 @cindex mouse motion events
1266 Emacs sometimes generates @dfn{mouse motion} events to describe motion
1267 of the mouse without any button activity. Mouse motion events are
1268 represented by lists that look like this:
1271 (mouse-movement (@var{window} @var{buffer-pos} (@var{x} . @var{y}) @var{timestamp}))
1274 The second element of the list describes the current position of the
1275 mouse, just as in a click event (@pxref{Click Events}).
1277 The special form @code{track-mouse} enables generation of motion events
1278 within its body. Outside of @code{track-mouse} forms, Emacs does not
1279 generate events for mere motion of the mouse, and these events do not
1280 appear. @xref{Mouse Tracking}.
1283 @subsection Focus Events
1286 Window systems provide general ways for the user to control which window
1287 gets keyboard input. This choice of window is called the @dfn{focus}.
1288 When the user does something to switch between Emacs frames, that
1289 generates a @dfn{focus event}. The normal definition of a focus event,
1290 in the global keymap, is to select a new frame within Emacs, as the user
1291 would expect. @xref{Input Focus}.
1293 Focus events are represented in Lisp as lists that look like this:
1296 (switch-frame @var{new-frame})
1300 where @var{new-frame} is the frame switched to.
1302 Most X window managers are set up so that just moving the mouse into a
1303 window is enough to set the focus there. Emacs appears to do this,
1304 because it changes the cursor to solid in the new frame. However, there
1305 is no need for the Lisp program to know about the focus change until
1306 some other kind of input arrives. So Emacs generates a focus event only
1307 when the user actually types a keyboard key or presses a mouse button in
1308 the new frame; just moving the mouse between frames does not generate a
1311 A focus event in the middle of a key sequence would garble the
1312 sequence. So Emacs never generates a focus event in the middle of a key
1313 sequence. If the user changes focus in the middle of a key
1314 sequence---that is, after a prefix key---then Emacs reorders the events
1315 so that the focus event comes either before or after the multi-event key
1316 sequence, and not within it.
1319 @subsection Miscellaneous Window System Events
1321 A few other event types represent occurrences within the window system.
1324 @cindex @code{delete-frame} event
1325 @item (delete-frame (@var{frame}))
1326 This kind of event indicates that the user gave the window manager
1327 a command to delete a particular window, which happens to be an Emacs frame.
1329 The standard definition of the @code{delete-frame} event is to delete @var{frame}.
1331 @cindex @code{iconify-frame} event
1332 @item (iconify-frame (@var{frame}))
1333 This kind of event indicates that the user iconified @var{frame} using
1334 the window manager. Its standard definition is @code{ignore}; since the
1335 frame has already been iconified, Emacs has no work to do. The purpose
1336 of this event type is so that you can keep track of such events if you
1339 @cindex @code{make-frame-visible} event
1340 @item (make-frame-visible (@var{frame}))
1341 This kind of event indicates that the user deiconified @var{frame} using
1342 the window manager. Its standard definition is @code{ignore}; since the
1343 frame has already been made visible, Emacs has no work to do.
1345 @cindex @code{mouse-wheel} event
1346 @item (mouse-wheel @var{position} @var{delta})
1347 This kind of event is generated by moving a wheel on a mouse (such as
1348 the MS Intellimouse). Its effect is typically a kind of scroll or zoom.
1350 The element @var{delta} describes the amount and direction of the wheel
1351 rotation. Its absolute value is the number of increments by which the
1352 wheel was rotated. A negative @var{delta} indicates that the wheel was
1353 rotated backwards, towards the user, and a positive @var{delta}
1354 indicates that the wheel was rotated forward, away from the user.
1356 The element @var{position} is a list describing the position of the
1357 event, in the same format as used in a mouse-click event.
1359 This kind of event is generated only on some kinds of systems.
1361 @cindex @code{drag-n-drop} event
1362 @item (drag-n-drop @var{position} @var{files})
1363 This kind of event is generated when a group of files is
1364 selected in an application outside of Emacs, and then dragged and
1365 dropped onto an Emacs frame.
1367 The element @var{position} is a list describing the position of the
1368 event, in the same format as used in a mouse-click event, and
1369 @var{files} is the list of file names that were dragged and dropped.
1370 The usual way to handle this event is by visiting these files.
1372 This kind of event is generated, at present, only on some kinds of
1376 If one of these events arrives in the middle of a key sequence---that
1377 is, after a prefix key---then Emacs reorders the events so that this
1378 event comes either before or after the multi-event key sequence, not
1381 @node Event Examples
1382 @subsection Event Examples
1384 If the user presses and releases the left mouse button over the same
1385 location, that generates a sequence of events like this:
1388 (down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
1389 (mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
1392 While holding the control key down, the user might hold down the
1393 second mouse button, and drag the mouse from one line to the next.
1394 That produces two events, as shown here:
1397 (C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
1398 (C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
1399 (#<window 18 on NEWS> 3510 (0 . 28) -729648))
1402 While holding down the meta and shift keys, the user might press the
1403 second mouse button on the window's mode line, and then drag the mouse
1404 into another window. That produces a pair of events like these:
1407 (M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
1408 (M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
1409 (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
1413 @node Classifying Events
1414 @subsection Classifying Events
1417 Every event has an @dfn{event type}, which classifies the event for
1418 key binding purposes. For a keyboard event, the event type equals the
1419 event value; thus, the event type for a character is the character, and
1420 the event type for a function key symbol is the symbol itself. For
1421 events that are lists, the event type is the symbol in the @sc{car} of
1422 the list. Thus, the event type is always a symbol or a character.
1424 Two events of the same type are equivalent where key bindings are
1425 concerned; thus, they always run the same command. That does not
1426 necessarily mean they do the same things, however, as some commands look
1427 at the whole event to decide what to do. For example, some commands use
1428 the location of a mouse event to decide where in the buffer to act.
1430 Sometimes broader classifications of events are useful. For example,
1431 you might want to ask whether an event involved the @key{META} key,
1432 regardless of which other key or mouse button was used.
1434 The functions @code{event-modifiers} and @code{event-basic-type} are
1435 provided to get such information conveniently.
1437 @defun event-modifiers event
1438 This function returns a list of the modifiers that @var{event} has. The
1439 modifiers are symbols; they include @code{shift}, @code{control},
1440 @code{meta}, @code{alt}, @code{hyper} and @code{super}. In addition,
1441 the modifiers list of a mouse event symbol always contains one of
1442 @code{click}, @code{drag}, and @code{down}.
1444 The argument @var{event} may be an entire event object, or just an event
1447 Here are some examples:
1450 (event-modifiers ?a)
1452 (event-modifiers ?\C-a)
1454 (event-modifiers ?\C-%)
1456 (event-modifiers ?\C-\S-a)
1457 @result{} (control shift)
1458 (event-modifiers 'f5)
1460 (event-modifiers 's-f5)
1462 (event-modifiers 'M-S-f5)
1463 @result{} (meta shift)
1464 (event-modifiers 'mouse-1)
1466 (event-modifiers 'down-mouse-1)
1470 The modifiers list for a click event explicitly contains @code{click},
1471 but the event symbol name itself does not contain @samp{click}.
1474 @defun event-basic-type event
1475 This function returns the key or mouse button that @var{event}
1476 describes, with all modifiers removed. For example:
1479 (event-basic-type ?a)
1481 (event-basic-type ?A)
1483 (event-basic-type ?\C-a)
1485 (event-basic-type ?\C-\S-a)
1487 (event-basic-type 'f5)
1489 (event-basic-type 's-f5)
1491 (event-basic-type 'M-S-f5)
1493 (event-basic-type 'down-mouse-1)
1498 @defun mouse-movement-p object
1499 This function returns non-@code{nil} if @var{object} is a mouse movement
1503 @defun event-convert-list list
1504 This function converts a list of modifier names and a basic event type
1505 to an event type which specifies all of them. For example,
1508 (event-convert-list '(control ?a))
1510 (event-convert-list '(control meta ?a))
1511 @result{} -134217727
1512 (event-convert-list '(control super f1))
1517 @node Accessing Events
1518 @subsection Accessing Events
1520 This section describes convenient functions for accessing the data in
1521 a mouse button or motion event.
1523 These two functions return the starting or ending position of a
1524 mouse-button event, as a list of this form:
1527 (@var{window} @var{buffer-position} (@var{x} . @var{y}) @var{timestamp})
1530 @defun event-start event
1531 This returns the starting position of @var{event}.
1533 If @var{event} is a click or button-down event, this returns the
1534 location of the event. If @var{event} is a drag event, this returns the
1535 drag's starting position.
1538 @defun event-end event
1539 This returns the ending position of @var{event}.
1541 If @var{event} is a drag event, this returns the position where the user
1542 released the mouse button. If @var{event} is a click or button-down
1543 event, the value is actually the starting position, which is the only
1544 position such events have.
1547 These five functions take a position list as described above, and
1548 return various parts of it.
1550 @defun posn-window position
1551 Return the window that @var{position} is in.
1554 @defun posn-point position
1555 Return the buffer position in @var{position}. This is an integer.
1558 @defun posn-x-y position
1559 Return the pixel-based x and y coordinates in @var{position}, as a cons
1560 cell @code{(@var{x} . @var{y})}.
1563 @defun posn-col-row position
1564 Return the row and column (in units of characters) of @var{position}, as
1565 a cons cell @code{(@var{col} . @var{row})}. These are computed from the
1566 @var{x} and @var{y} values actually found in @var{position}.
1569 @defun posn-timestamp position
1570 Return the timestamp in @var{position}.
1573 These functions are useful for decoding scroll bar events.
1575 @defun scroll-bar-event-ratio event
1576 This function returns the fractional vertical position of a scroll bar
1577 event within the scroll bar. The value is a cons cell
1578 @code{(@var{portion} . @var{whole})} containing two integers whose ratio
1579 is the fractional position.
1582 @defun scroll-bar-scale ratio total
1583 This function multiplies (in effect) @var{ratio} by @var{total},
1584 rounding the result to an integer. The argument @var{ratio} is not a
1585 number, but rather a pair @code{(@var{num} . @var{denom})}---typically a
1586 value returned by @code{scroll-bar-event-ratio}.
1588 This function is handy for scaling a position on a scroll bar into a
1589 buffer position. Here's how to do that:
1594 (posn-x-y (event-start event))
1595 (- (point-max) (point-min))))
1598 Recall that scroll bar events have two integers forming a ratio, in place
1599 of a pair of x and y coordinates.
1602 @node Strings of Events
1603 @subsection Putting Keyboard Events in Strings
1605 In most of the places where strings are used, we conceptualize the
1606 string as containing text characters---the same kind of characters found
1607 in buffers or files. Occasionally Lisp programs use strings that
1608 conceptually contain keyboard characters; for example, they may be key
1609 sequences or keyboard macro definitions. However, storing keyboard
1610 characters in a string is a complex matter, for reasons of historical
1611 compatibility, and it is not always possible.
1613 We recommend that new programs avoid dealing with these complexities
1614 by not storing keyboard events in strings. Here is how to do that:
1618 Use vectors instead of strings for key sequences, when you plan to use
1619 them for anything other than as arguments to @code{lookup-key} and
1620 @code{define-key}. For example, you can use
1621 @code{read-key-sequence-vector} instead of @code{read-key-sequence}, and
1622 @code{this-command-keys-vector} instead of @code{this-command-keys}.
1625 Use vectors to write key sequence constants containing meta characters,
1626 even when passing them directly to @code{define-key}.
1629 When you have to look at the contents of a key sequence that might be a
1630 string, use @code{listify-key-sequence} (@pxref{Event Input Misc})
1631 first, to convert it to a list.
1634 The complexities stem from the modifier bits that keyboard input
1635 characters can include. Aside from the Meta modifier, none of these
1636 modifier bits can be included in a string, and the Meta modifier is
1637 allowed only in special cases.
1639 The earliest GNU Emacs versions represented meta characters as codes
1640 in the range of 128 to 255. At that time, the basic character codes
1641 ranged from 0 to 127, so all keyboard character codes did fit in a
1642 string. Many Lisp programs used @samp{\M-} in string constants to stand
1643 for meta characters, especially in arguments to @code{define-key} and
1644 similar functions, and key sequences and sequences of events were always
1645 represented as strings.
1647 When we added support for larger basic character codes beyond 127, and
1648 additional modifier bits, we had to change the representation of meta
1649 characters. Now the flag that represents the Meta modifier in a
1657 and such numbers cannot be included in a string.
1659 To support programs with @samp{\M-} in string constants, there are
1660 special rules for including certain meta characters in a string.
1661 Here are the rules for interpreting a string as a sequence of input
1666 If the keyboard character value is in the range of 0 to 127, it can go
1667 in the string unchanged.
1670 The meta variants of those characters, with codes in the range of
1684 can also go in the string, but you must change their
1685 numeric values. You must set the
1699 bit, resulting in a value between 128 and 255. Only a unibyte string
1700 can include these codes.
1703 Non-@sc{ASCII} characters above 256 can be included in a multibyte string.
1706 Other keyboard character events cannot fit in a string. This includes
1707 keyboard events in the range of 128 to 255.
1710 Functions such as @code{read-key-sequence} that construct strings of
1711 keyboard input characters follow these rules: they construct vectors
1712 instead of strings, when the events won't fit in a string.
1714 When you use the read syntax @samp{\M-} in a string, it produces a
1715 code in the range of 128 to 255---the same code that you get if you
1716 modify the corresponding keyboard event to put it in the string. Thus,
1717 meta events in strings work consistently regardless of how they get into
1720 However, most programs would do well to avoid these issues by
1721 following the recommendations at the beginning of this section.
1724 @section Reading Input
1726 The editor command loop reads key sequences using the function
1727 @code{read-key-sequence}, which uses @code{read-event}. These and other
1728 functions for event input are also available for use in Lisp programs.
1729 See also @code{momentary-string-display} in @ref{Temporary Displays},
1730 and @code{sit-for} in @ref{Waiting}. @xref{Terminal Input}, for
1731 functions and variables for controlling terminal input modes and
1732 debugging terminal input. @xref{Translating Input}, for features you
1733 can use for translating or modifying input events while reading them.
1735 For higher-level input facilities, see @ref{Minibuffers}.
1738 * Key Sequence Input:: How to read one key sequence.
1739 * Reading One Event:: How to read just one event.
1740 * Quoted Character Input:: Asking the user to specify a character.
1741 * Event Input Misc:: How to reread or throw away input events.
1744 @node Key Sequence Input
1745 @subsection Key Sequence Input
1746 @cindex key sequence input
1748 The command loop reads input a key sequence at a time, by calling
1749 @code{read-key-sequence}. Lisp programs can also call this function;
1750 for example, @code{describe-key} uses it to read the key to describe.
1752 @defun read-key-sequence prompt
1753 @cindex key sequence
1754 This function reads a key sequence and returns it as a string or
1755 vector. It keeps reading events until it has accumulated a complete key
1756 sequence; that is, enough to specify a non-prefix command using the
1757 currently active keymaps.
1759 If the events are all characters and all can fit in a string, then
1760 @code{read-key-sequence} returns a string (@pxref{Strings of Events}).
1761 Otherwise, it returns a vector, since a vector can hold all kinds of
1762 events---characters, symbols, and lists. The elements of the string or
1763 vector are the events in the key sequence.
1765 The argument @var{prompt} is either a string to be displayed in the echo
1766 area as a prompt, or @code{nil}, meaning not to display a prompt.
1768 In the example below, the prompt @samp{?} is displayed in the echo area,
1769 and the user types @kbd{C-x C-f}.
1772 (read-key-sequence "?")
1775 ---------- Echo Area ----------
1777 ---------- Echo Area ----------
1783 The function @code{read-key-sequence} suppresses quitting: @kbd{C-g}
1784 typed while reading with this function works like any other character,
1785 and does not set @code{quit-flag}. @xref{Quitting}.
1788 @defun read-key-sequence-vector prompt
1789 This is like @code{read-key-sequence} except that it always
1790 returns the key sequence as a vector, never as a string.
1791 @xref{Strings of Events}.
1794 @cindex upper case key sequence
1795 @cindex downcasing in @code{lookup-key}
1796 If an input character is an upper-case letter and has no key binding,
1797 but its lower-case equivalent has one, then @code{read-key-sequence}
1798 converts the character to lower case. Note that @code{lookup-key} does
1799 not perform case conversion in this way.
1801 The function @code{read-key-sequence} also transforms some mouse events.
1802 It converts unbound drag events into click events, and discards unbound
1803 button-down events entirely. It also reshuffles focus events and
1804 miscellaneous window events so that they never appear in a key sequence
1805 with any other events.
1807 When mouse events occur in special parts of a window, such as a mode
1808 line or a scroll bar, the event type shows nothing special---it is the
1809 same symbol that would normally represent that combination of mouse
1810 button and modifier keys. The information about the window part is kept
1811 elsewhere in the event---in the coordinates. But
1812 @code{read-key-sequence} translates this information into imaginary
1813 ``prefix keys'', all of which are symbols: @code{mode-line},
1814 @code{vertical-line}, @code{horizontal-scroll-bar} and
1815 @code{vertical-scroll-bar}. You can define meanings for mouse clicks in
1816 special window parts by defining key sequences using these imaginary
1819 For example, if you call @code{read-key-sequence} and then click the
1820 mouse on the window's mode line, you get two events, like this:
1823 (read-key-sequence "Click on the mode line: ")
1824 @result{} [mode-line
1826 (#<window 6 on NEWS> mode-line
1827 (40 . 63) 5959987))]
1830 @defvar num-input-keys
1832 This variable's value is the number of key sequences processed so far in
1833 this Emacs session. This includes key sequences read from the terminal
1834 and key sequences read from keyboard macros being executed.
1837 @defvar num-nonmacro-input-events
1838 @tindex num-nonmacro-input-events
1839 This variable holds the total number of input events received so far
1840 from the terminal---not counting those generated by keyboard macros.
1843 @node Reading One Event
1844 @subsection Reading One Event
1846 The lowest level functions for command input are those that read a
1849 @defun read-event &optional prompt suppress-input-method
1850 This function reads and returns the next event of command input, waiting
1851 if necessary until an event is available. Events can come directly from
1852 the user or from a keyboard macro.
1854 If @var{prompt} is non-@code{nil}, it should be a string to display in
1855 the echo area as a prompt. Otherwise, @code{read-event} does not
1856 display any message to indicate it is waiting for input; instead, it
1857 prompts by echoing: it displays descriptions of the events that led to
1858 or were read by the current command. @xref{The Echo Area}.
1860 If @var{suppress-input-method} is non-@code{nil}, then the current input
1861 method is disabled for reading this event. If you want to read an event
1862 without input-method processing, always do it this way; don't try binding
1863 @code{input-method-function} (see below).
1865 If @code{cursor-in-echo-area} is non-@code{nil}, then @code{read-event}
1866 moves the cursor temporarily to the echo area, to the end of any message
1867 displayed there. Otherwise @code{read-event} does not move the cursor.
1869 If @code{read-event} gets an event that is defined as a help character, in
1870 some cases @code{read-event} processes the event directly without
1871 returning. @xref{Help Functions}. Certain other events, called
1872 @dfn{special events}, are also processed directly within
1873 @code{read-event} (@pxref{Special Events}).
1875 Here is what happens if you call @code{read-event} and then press the
1876 right-arrow function key:
1887 This function reads and returns a character of command input. It
1888 discards any events that are not characters, until it gets a character.
1890 In the first example, the user types the character @kbd{1} (@sc{ASCII}
1891 code 49). The second example shows a keyboard macro definition that
1892 calls @code{read-char} from the minibuffer using @code{eval-expression}.
1893 @code{read-char} reads the keyboard macro's very next character, which
1894 is @kbd{1}. Then @code{eval-expression} displays its return value in
1904 ;; @r{We assume here you use @kbd{M-:} to evaluate this.}
1905 (symbol-function 'foo)
1906 @result{} "^[:(read-char)^M1"
1909 (execute-kbd-macro 'foo)
1916 @code{read-event} also invokes the current input method, if any. If
1917 the value of @code{input-method-function} is non-@code{nil}, it should
1918 be a function; when @code{read-event} reads a printing character
1919 (including @key{SPC}) with no modifier bits, it calls that function,
1920 passing the event as an argument.
1922 @defvar input-method-function
1923 If this is non-@code{nil}, its value specifies the current input method
1926 @strong{Note:} Don't bind this variable with @code{let}. It is often
1927 buffer-local, and if you bind it around reading input (which is exactly
1928 when you @emph{would} bind it), switching buffers asynchronously while
1929 Emacs is waiting will cause the value to be restored in the wrong
1933 The input method function should return a list of events which should
1934 be used as input. (If the list is @code{nil}, that means there is no
1935 input, so @code{read-event} waits for another event.) These events are
1936 processed before the events in @code{unread-command-events}. Events
1937 returned by the input method function are not passed to the input method
1938 function again, even if they are printing characters with no modifier
1941 If the input method function calls @code{read-event} or
1942 @code{read-key-sequence}, it should bind @code{input-method-function} to
1943 @code{nil} first, to prevent recursion.
1945 The input method function is not called when reading the second and
1946 subsequent event of a key sequence. Thus, these characters are not
1947 subject to input method processing. It is usually a good idea for the
1948 input method processing to test the values of
1949 @code{overriding-local-map} and @code{overriding-terminal-local-map}; if
1950 either of these variables is non-@code{nil}, the input method should put
1951 its argument into a list and return that list with no further
1954 @node Quoted Character Input
1955 @subsection Quoted Character Input
1956 @cindex quoted character input
1958 You can use the function @code{read-quoted-char} to ask the user to
1959 specify a character, and allow the user to specify a control or meta
1960 character conveniently, either literally or as an octal character code.
1961 The command @code{quoted-insert} uses this function.
1963 @defun read-quoted-char &optional prompt
1964 @cindex octal character input
1965 @cindex control characters, reading
1966 @cindex nonprinting characters, reading
1967 This function is like @code{read-char}, except that if the first
1968 character read is an octal digit (0-7), it reads any number of octal
1969 digits (but stopping if a non-octal digit is found), and returns the
1970 character represented by that numeric character code.
1972 Quitting is suppressed when the first character is read, so that the
1973 user can enter a @kbd{C-g}. @xref{Quitting}.
1975 If @var{prompt} is supplied, it specifies a string for prompting the
1976 user. The prompt string is always displayed in the echo area, followed
1977 by a single @samp{-}.
1979 In the following example, the user types in the octal number 177 (which
1983 (read-quoted-char "What character")
1986 ---------- Echo Area ----------
1987 What character-@kbd{177}
1988 ---------- Echo Area ----------
1996 @node Event Input Misc
1997 @subsection Miscellaneous Event Input Features
1999 This section describes how to ``peek ahead'' at events without using
2000 them up, how to check for pending input, and how to discard pending
2001 input. See also the function @code{read-passwd} (@pxref{Reading a
2004 @defvar unread-command-events
2006 @cindex peeking at input
2007 This variable holds a list of events waiting to be read as command
2008 input. The events are used in the order they appear in the list, and
2009 removed one by one as they are used.
2011 The variable is needed because in some cases a function reads an event
2012 and then decides not to use it. Storing the event in this variable
2013 causes it to be processed normally, by the command loop or by the
2014 functions to read command input.
2016 @cindex prefix argument unreading
2017 For example, the function that implements numeric prefix arguments reads
2018 any number of digits. When it finds a non-digit event, it must unread
2019 the event so that it can be read normally by the command loop.
2020 Likewise, incremental search uses this feature to unread events with no
2021 special meaning in a search, because these events should exit the search
2022 and then execute normally.
2024 The reliable and easy way to extract events from a key sequence so as to
2025 put them in @code{unread-command-events} is to use
2026 @code{listify-key-sequence} (@pxref{Strings of Events}).
2028 Normally you add events to the front of this list, so that the events
2029 most recently unread will be reread first.
2032 @defun listify-key-sequence key
2033 This function converts the string or vector @var{key} to a list of
2034 individual events, which you can put in @code{unread-command-events}.
2037 @defvar unread-command-char
2038 This variable holds a character to be read as command input.
2039 A value of -1 means ``empty''.
2041 This variable is mostly obsolete now that you can use
2042 @code{unread-command-events} instead; it exists only to support programs
2043 written for Emacs versions 18 and earlier.
2046 @defun input-pending-p
2047 @cindex waiting for command key input
2048 This function determines whether any command input is currently
2049 available to be read. It returns immediately, with value @code{t} if
2050 there is available input, @code{nil} otherwise. On rare occasions it
2051 may return @code{t} when no input is available.
2054 @defvar last-input-event
2055 @defvarx last-input-char
2056 This variable records the last terminal input event read, whether
2057 as part of a command or explicitly by a Lisp program.
2059 In the example below, the Lisp program reads the character @kbd{1},
2060 @sc{ASCII} code 49. It becomes the value of @code{last-input-event},
2061 while @kbd{C-e} (we assume @kbd{C-x C-e} command is used to evaluate
2062 this expression) remains the value of @code{last-command-event}.
2066 (progn (print (read-char))
2067 (print last-command-event)
2075 The alias @code{last-input-char} exists for compatibility with
2079 @defun discard-input
2081 @cindex discard input
2082 @cindex terminate keyboard macro
2083 This function discards the contents of the terminal input buffer and
2084 cancels any keyboard macro that might be in the process of definition.
2085 It returns @code{nil}.
2087 In the following example, the user may type a number of characters right
2088 after starting the evaluation of the form. After the @code{sleep-for}
2089 finishes sleeping, @code{discard-input} discards any characters typed
2093 (progn (sleep-for 2)
2099 @node Special Events
2100 @section Special Events
2102 @cindex special events
2103 Special events are handled at a very low level---as soon as they are
2104 read. The @code{read-event} function processes these events itself, and
2107 Events that are handled in this way do not echo, they are never grouped
2108 into key sequences, and they never appear in the value of
2109 @code{last-command-event} or @code{(this-command-keys)}. They do not
2110 discard a numeric argument, they cannot be unread with
2111 @code{unread-command-events}, they may not appear in a keyboard macro,
2112 and they are not recorded in a keyboard macro while you are defining
2115 These events do, however, appear in @code{last-input-event} immediately
2116 after they are read, and this is the way for the event's definition to
2117 find the actual event.
2119 The events types @code{iconify-frame}, @code{make-frame-visible} and
2120 @code{delete-frame} are normally handled in this way. The keymap which
2121 defines how to handle special events---and which events are special---is
2122 in the variable @code{special-event-map} (@pxref{Active Keymaps}).
2125 @section Waiting for Elapsed Time or Input
2129 The wait functions are designed to wait for a certain amount of time
2130 to pass or until there is input. For example, you may wish to pause in
2131 the middle of a computation to allow the user time to view the display.
2132 @code{sit-for} pauses and updates the screen, and returns immediately if
2133 input comes in, while @code{sleep-for} pauses without updating the
2136 @defun sit-for seconds &optional millisec nodisp
2137 This function performs redisplay (provided there is no pending input
2138 from the user), then waits @var{seconds} seconds, or until input is
2139 available. The value is @code{t} if @code{sit-for} waited the full
2140 time with no input arriving (see @code{input-pending-p} in @ref{Event
2141 Input Misc}). Otherwise, the value is @code{nil}.
2143 The argument @var{seconds} need not be an integer. If it is a floating
2144 point number, @code{sit-for} waits for a fractional number of seconds.
2145 Some systems support only a whole number of seconds; on these systems,
2146 @var{seconds} is rounded down.
2148 The optional argument @var{millisec} specifies an additional waiting
2149 period measured in milliseconds. This adds to the period specified by
2150 @var{seconds}. If the system doesn't support waiting fractions of a
2151 second, you get an error if you specify nonzero @var{millisec}.
2153 @cindex forcing redisplay
2154 Redisplay is always preempted if input arrives, and does not happen at
2155 all if input is available before it starts. Thus, there is no way to
2156 force screen updating if there is pending input; however, if there is no
2157 input pending, you can force an update with no delay by using
2160 If @var{nodisp} is non-@code{nil}, then @code{sit-for} does not
2161 redisplay, but it still returns as soon as input is available (or when
2162 the timeout elapses).
2164 Iconifying or deiconifying a frame makes @code{sit-for} return, because
2165 that generates an event. @xref{Misc Events}.
2167 The usual purpose of @code{sit-for} is to give the user time to read
2168 text that you display.
2171 @defun sleep-for seconds &optional millisec
2172 This function simply pauses for @var{seconds} seconds without updating
2173 the display. It pays no attention to available input. It returns
2176 The argument @var{seconds} need not be an integer. If it is a floating
2177 point number, @code{sleep-for} waits for a fractional number of seconds.
2178 Some systems support only a whole number of seconds; on these systems,
2179 @var{seconds} is rounded down.
2181 The optional argument @var{millisec} specifies an additional waiting
2182 period measured in milliseconds. This adds to the period specified by
2183 @var{seconds}. If the system doesn't support waiting fractions of a
2184 second, you get an error if you specify nonzero @var{millisec}.
2186 Use @code{sleep-for} when you wish to guarantee a delay.
2189 @xref{Time of Day}, for functions to get the current time.
2196 Typing @kbd{C-g} while a Lisp function is running causes Emacs to
2197 @dfn{quit} whatever it is doing. This means that control returns to the
2198 innermost active command loop.
2200 Typing @kbd{C-g} while the command loop is waiting for keyboard input
2201 does not cause a quit; it acts as an ordinary input character. In the
2202 simplest case, you cannot tell the difference, because @kbd{C-g}
2203 normally runs the command @code{keyboard-quit}, whose effect is to quit.
2204 However, when @kbd{C-g} follows a prefix key, they combine to form an
2205 undefined key. The effect is to cancel the prefix key as well as any
2208 In the minibuffer, @kbd{C-g} has a different definition: it aborts out
2209 of the minibuffer. This means, in effect, that it exits the minibuffer
2210 and then quits. (Simply quitting would return to the command loop
2211 @emph{within} the minibuffer.) The reason why @kbd{C-g} does not quit
2212 directly when the command reader is reading input is so that its meaning
2213 can be redefined in the minibuffer in this way. @kbd{C-g} following a
2214 prefix key is not redefined in the minibuffer, and it has its normal
2215 effect of canceling the prefix key and prefix argument. This too
2216 would not be possible if @kbd{C-g} always quit directly.
2218 When @kbd{C-g} does directly quit, it does so by setting the variable
2219 @code{quit-flag} to @code{t}. Emacs checks this variable at appropriate
2220 times and quits if it is not @code{nil}. Setting @code{quit-flag}
2221 non-@code{nil} in any way thus causes a quit.
2223 At the level of C code, quitting cannot happen just anywhere; only at the
2224 special places that check @code{quit-flag}. The reason for this is
2225 that quitting at other places might leave an inconsistency in Emacs's
2226 internal state. Because quitting is delayed until a safe place, quitting
2227 cannot make Emacs crash.
2229 Certain functions such as @code{read-key-sequence} or
2230 @code{read-quoted-char} prevent quitting entirely even though they wait
2231 for input. Instead of quitting, @kbd{C-g} serves as the requested
2232 input. In the case of @code{read-key-sequence}, this serves to bring
2233 about the special behavior of @kbd{C-g} in the command loop. In the
2234 case of @code{read-quoted-char}, this is so that @kbd{C-q} can be used
2235 to quote a @kbd{C-g}.
2237 You can prevent quitting for a portion of a Lisp function by binding
2238 the variable @code{inhibit-quit} to a non-@code{nil} value. Then,
2239 although @kbd{C-g} still sets @code{quit-flag} to @code{t} as usual, the
2240 usual result of this---a quit---is prevented. Eventually,
2241 @code{inhibit-quit} will become @code{nil} again, such as when its
2242 binding is unwound at the end of a @code{let} form. At that time, if
2243 @code{quit-flag} is still non-@code{nil}, the requested quit happens
2244 immediately. This behavior is ideal when you wish to make sure that
2245 quitting does not happen within a ``critical section'' of the program.
2247 @cindex @code{read-quoted-char} quitting
2248 In some functions (such as @code{read-quoted-char}), @kbd{C-g} is
2249 handled in a special way that does not involve quitting. This is done
2250 by reading the input with @code{inhibit-quit} bound to @code{t}, and
2251 setting @code{quit-flag} to @code{nil} before @code{inhibit-quit}
2252 becomes @code{nil} again. This excerpt from the definition of
2253 @code{read-quoted-char} shows how this is done; it also shows that
2254 normal quitting is permitted after the first character of input.
2257 (defun read-quoted-char (&optional prompt)
2258 "@dots{}@var{documentation}@dots{}"
2259 (let ((message-log-max nil) done (first t) (code 0) char)
2261 (let ((inhibit-quit first)
2263 (and prompt (message "%s-" prompt))
2264 (setq char (read-event))
2265 (if inhibit-quit (setq quit-flag nil)))
2266 @r{@dots{}set the variable @code{code}@dots{}})
2271 If this variable is non-@code{nil}, then Emacs quits immediately, unless
2272 @code{inhibit-quit} is non-@code{nil}. Typing @kbd{C-g} ordinarily sets
2273 @code{quit-flag} non-@code{nil}, regardless of @code{inhibit-quit}.
2276 @defvar inhibit-quit
2277 This variable determines whether Emacs should quit when @code{quit-flag}
2278 is set to a value other than @code{nil}. If @code{inhibit-quit} is
2279 non-@code{nil}, then @code{quit-flag} has no special effect.
2282 @deffn Command keyboard-quit
2283 This function signals the @code{quit} condition with @code{(signal 'quit
2284 nil)}. This is the same thing that quitting does. (See @code{signal}
2288 You can specify a character other than @kbd{C-g} to use for quitting.
2289 See the function @code{set-input-mode} in @ref{Terminal Input}.
2291 @node Prefix Command Arguments
2292 @section Prefix Command Arguments
2293 @cindex prefix argument
2294 @cindex raw prefix argument
2295 @cindex numeric prefix argument
2297 Most Emacs commands can use a @dfn{prefix argument}, a number
2298 specified before the command itself. (Don't confuse prefix arguments
2299 with prefix keys.) The prefix argument is at all times represented by a
2300 value, which may be @code{nil}, meaning there is currently no prefix
2301 argument. Each command may use the prefix argument or ignore it.
2303 There are two representations of the prefix argument: @dfn{raw} and
2304 @dfn{numeric}. The editor command loop uses the raw representation
2305 internally, and so do the Lisp variables that store the information, but
2306 commands can request either representation.
2308 Here are the possible values of a raw prefix argument:
2312 @code{nil}, meaning there is no prefix argument. Its numeric value is
2313 1, but numerous commands make a distinction between @code{nil} and the
2317 An integer, which stands for itself.
2320 A list of one element, which is an integer. This form of prefix
2321 argument results from one or a succession of @kbd{C-u}'s with no
2322 digits. The numeric value is the integer in the list, but some
2323 commands make a distinction between such a list and an integer alone.
2326 The symbol @code{-}. This indicates that @kbd{M--} or @kbd{C-u -} was
2327 typed, without following digits. The equivalent numeric value is
2328 @minus{}1, but some commands make a distinction between the integer
2329 @minus{}1 and the symbol @code{-}.
2332 We illustrate these possibilities by calling the following function with
2337 (defun display-prefix (arg)
2338 "Display the value of the raw prefix arg."
2345 Here are the results of calling @code{display-prefix} with various
2346 raw prefix arguments:
2349 M-x display-prefix @print{} nil
2351 C-u M-x display-prefix @print{} (4)
2353 C-u C-u M-x display-prefix @print{} (16)
2355 C-u 3 M-x display-prefix @print{} 3
2357 M-3 M-x display-prefix @print{} 3 ; @r{(Same as @code{C-u 3}.)}
2359 C-u - M-x display-prefix @print{} -
2361 M-- M-x display-prefix @print{} - ; @r{(Same as @code{C-u -}.)}
2363 C-u - 7 M-x display-prefix @print{} -7
2365 M-- 7 M-x display-prefix @print{} -7 ; @r{(Same as @code{C-u -7}.)}
2368 Emacs uses two variables to store the prefix argument:
2369 @code{prefix-arg} and @code{current-prefix-arg}. Commands such as
2370 @code{universal-argument} that set up prefix arguments for other
2371 commands store them in @code{prefix-arg}. In contrast,
2372 @code{current-prefix-arg} conveys the prefix argument to the current
2373 command, so setting it has no effect on the prefix arguments for future
2376 Normally, commands specify which representation to use for the prefix
2377 argument, either numeric or raw, in the @code{interactive} declaration.
2378 (@xref{Using Interactive}.) Alternatively, functions may look at the
2379 value of the prefix argument directly in the variable
2380 @code{current-prefix-arg}, but this is less clean.
2382 @defun prefix-numeric-value arg
2383 This function returns the numeric meaning of a valid raw prefix argument
2384 value, @var{arg}. The argument may be a symbol, a number, or a list.
2385 If it is @code{nil}, the value 1 is returned; if it is @code{-}, the
2386 value @minus{}1 is returned; if it is a number, that number is returned;
2387 if it is a list, the @sc{car} of that list (which should be a number) is
2391 @defvar current-prefix-arg
2392 This variable holds the raw prefix argument for the @emph{current}
2393 command. Commands may examine it directly, but the usual method for
2394 accessing it is with @code{(interactive "P")}.
2398 The value of this variable is the raw prefix argument for the
2399 @emph{next} editing command. Commands such as @code{universal-argument}
2400 that specify prefix arguments for the following command work by setting
2404 @tindex last-prefix-arg
2405 @defvar last-prefix-arg
2406 The raw prefix argument value used by the previous command.
2409 The following commands exist to set up prefix arguments for the
2410 following command. Do not call them for any other reason.
2412 @deffn Command universal-argument
2413 This command reads input and specifies a prefix argument for the
2414 following command. Don't call this command yourself unless you know
2418 @deffn Command digit-argument arg
2419 This command adds to the prefix argument for the following command. The
2420 argument @var{arg} is the raw prefix argument as it was before this
2421 command; it is used to compute the updated prefix argument. Don't call
2422 this command yourself unless you know what you are doing.
2425 @deffn Command negative-argument arg
2426 This command adds to the numeric argument for the next command. The
2427 argument @var{arg} is the raw prefix argument as it was before this
2428 command; its value is negated to form the new prefix argument. Don't
2429 call this command yourself unless you know what you are doing.
2432 @node Recursive Editing
2433 @section Recursive Editing
2434 @cindex recursive command loop
2435 @cindex recursive editing level
2436 @cindex command loop, recursive
2438 The Emacs command loop is entered automatically when Emacs starts up.
2439 This top-level invocation of the command loop never exits; it keeps
2440 running as long as Emacs does. Lisp programs can also invoke the
2441 command loop. Since this makes more than one activation of the command
2442 loop, we call it @dfn{recursive editing}. A recursive editing level has
2443 the effect of suspending whatever command invoked it and permitting the
2444 user to do arbitrary editing before resuming that command.
2446 The commands available during recursive editing are the same ones
2447 available in the top-level editing loop and defined in the keymaps.
2448 Only a few special commands exit the recursive editing level; the others
2449 return to the recursive editing level when they finish. (The special
2450 commands for exiting are always available, but they do nothing when
2451 recursive editing is not in progress.)
2453 All command loops, including recursive ones, set up all-purpose error
2454 handlers so that an error in a command run from the command loop will
2457 @cindex minibuffer input
2458 Minibuffer input is a special kind of recursive editing. It has a few
2459 special wrinkles, such as enabling display of the minibuffer and the
2460 minibuffer window, but fewer than you might suppose. Certain keys
2461 behave differently in the minibuffer, but that is only because of the
2462 minibuffer's local map; if you switch windows, you get the usual Emacs
2465 @cindex @code{throw} example
2467 @cindex exit recursive editing
2469 To invoke a recursive editing level, call the function
2470 @code{recursive-edit}. This function contains the command loop; it also
2471 contains a call to @code{catch} with tag @code{exit}, which makes it
2472 possible to exit the recursive editing level by throwing to @code{exit}
2473 (@pxref{Catch and Throw}). If you throw a value other than @code{t},
2474 then @code{recursive-edit} returns normally to the function that called
2475 it. The command @kbd{C-M-c} (@code{exit-recursive-edit}) does this.
2476 Throwing a @code{t} value causes @code{recursive-edit} to quit, so that
2477 control returns to the command loop one level up. This is called
2478 @dfn{aborting}, and is done by @kbd{C-]} (@code{abort-recursive-edit}).
2480 Most applications should not use recursive editing, except as part of
2481 using the minibuffer. Usually it is more convenient for the user if you
2482 change the major mode of the current buffer temporarily to a special
2483 major mode, which should have a command to go back to the previous mode.
2484 (The @kbd{e} command in Rmail uses this technique.) Or, if you wish to
2485 give the user different text to edit ``recursively'', create and select
2486 a new buffer in a special mode. In this mode, define a command to
2487 complete the processing and go back to the previous buffer. (The
2488 @kbd{m} command in Rmail does this.)
2490 Recursive edits are useful in debugging. You can insert a call to
2491 @code{debug} into a function definition as a sort of breakpoint, so that
2492 you can look around when the function gets there. @code{debug} invokes
2493 a recursive edit but also provides the other features of the debugger.
2495 Recursive editing levels are also used when you type @kbd{C-r} in
2496 @code{query-replace} or use @kbd{C-x q} (@code{kbd-macro-query}).
2498 @defun recursive-edit
2499 @cindex suspend evaluation
2500 This function invokes the editor command loop. It is called
2501 automatically by the initialization of Emacs, to let the user begin
2502 editing. When called from a Lisp program, it enters a recursive editing
2505 In the following example, the function @code{simple-rec} first
2506 advances point one word, then enters a recursive edit, printing out a
2507 message in the echo area. The user can then do any editing desired, and
2508 then type @kbd{C-M-c} to exit and continue executing @code{simple-rec}.
2511 (defun simple-rec ()
2513 (message "Recursive edit in progress")
2516 @result{} simple-rec
2522 @deffn Command exit-recursive-edit
2523 This function exits from the innermost recursive edit (including
2524 minibuffer input). Its definition is effectively @code{(throw 'exit
2528 @deffn Command abort-recursive-edit
2529 This function aborts the command that requested the innermost recursive
2530 edit (including minibuffer input), by signaling @code{quit}
2531 after exiting the recursive edit. Its definition is effectively
2532 @code{(throw 'exit t)}. @xref{Quitting}.
2535 @deffn Command top-level
2536 This function exits all recursive editing levels; it does not return a
2537 value, as it jumps completely out of any computation directly back to
2538 the main command loop.
2541 @defun recursion-depth
2542 This function returns the current depth of recursive edits. When no
2543 recursive edit is active, it returns 0.
2546 @node Disabling Commands
2547 @section Disabling Commands
2548 @cindex disabled command
2550 @dfn{Disabling a command} marks the command as requiring user
2551 confirmation before it can be executed. Disabling is used for commands
2552 which might be confusing to beginning users, to prevent them from using
2553 the commands by accident.
2556 The low-level mechanism for disabling a command is to put a
2557 non-@code{nil} @code{disabled} property on the Lisp symbol for the
2558 command. These properties are normally set up by the user's
2559 @file{.emacs} file with Lisp expressions such as this:
2562 (put 'upcase-region 'disabled t)
2566 For a few commands, these properties are present by default and may be
2567 removed by the @file{.emacs} file.
2569 If the value of the @code{disabled} property is a string, the message
2570 saying the command is disabled includes that string. For example:
2573 (put 'delete-region 'disabled
2574 "Text deleted this way cannot be yanked back!\n")
2577 @xref{Disabling,,, emacs, The GNU Emacs Manual}, for the details on
2578 what happens when a disabled command is invoked interactively.
2579 Disabling a command has no effect on calling it as a function from Lisp
2582 @deffn Command enable-command command
2583 Allow @var{command} to be executed without special confirmation from now
2584 on, and (if the user confirms) alter the user's @file{.emacs} file so
2585 that this will apply to future sessions.
2588 @deffn Command disable-command command
2589 Require special confirmation to execute @var{command} from now on, and
2590 (if the user confirms) alter the user's @file{.emacs} file so that this
2591 will apply to future sessions.
2594 @defvar disabled-command-hook
2595 When the user invokes a disabled command interactively, this normal hook
2596 is run instead of the disabled command. The hook functions can use
2597 @code{this-command-keys} to determine what the user typed to run the
2598 command, and thus find the command itself. @xref{Hooks}.
2600 By default, @code{disabled-command-hook} contains a function that asks
2601 the user whether to proceed.
2604 @node Command History
2605 @section Command History
2606 @cindex command history
2607 @cindex complex command
2608 @cindex history of commands
2610 The command loop keeps a history of the complex commands that have
2611 been executed, to make it convenient to repeat these commands. A
2612 @dfn{complex command} is one for which the interactive argument reading
2613 uses the minibuffer. This includes any @kbd{M-x} command, any
2614 @kbd{M-:} command, and any command whose @code{interactive}
2615 specification reads an argument from the minibuffer. Explicit use of
2616 the minibuffer during the execution of the command itself does not cause
2617 the command to be considered complex.
2619 @defvar command-history
2620 This variable's value is a list of recent complex commands, each
2621 represented as a form to evaluate. It continues to accumulate all
2622 complex commands for the duration of the editing session, but when it
2623 reaches the maximum size (specified by the variable
2624 @code{history-length}), the oldest elements are deleted as new ones are
2630 @result{} ((switch-to-buffer "chistory.texi")
2631 (describe-key "^X^[")
2632 (visit-tags-table "~/emacs/src/")
2633 (find-tag "repeat-complex-command"))
2638 This history list is actually a special case of minibuffer history
2639 (@pxref{Minibuffer History}), with one special twist: the elements are
2640 expressions rather than strings.
2642 There are a number of commands devoted to the editing and recall of
2643 previous commands. The commands @code{repeat-complex-command}, and
2644 @code{list-command-history} are described in the user manual
2645 (@pxref{Repetition,,, emacs, The GNU Emacs Manual}). Within the
2646 minibuffer, the usual minibuffer history commands are available.
2648 @node Keyboard Macros
2649 @section Keyboard Macros
2650 @cindex keyboard macros
2652 A @dfn{keyboard macro} is a canned sequence of input events that can
2653 be considered a command and made the definition of a key. The Lisp
2654 representation of a keyboard macro is a string or vector containing the
2655 events. Don't confuse keyboard macros with Lisp macros
2658 @defun execute-kbd-macro kbdmacro &optional count
2659 This function executes @var{kbdmacro} as a sequence of events. If
2660 @var{kbdmacro} is a string or vector, then the events in it are executed
2661 exactly as if they had been input by the user. The sequence is
2662 @emph{not} expected to be a single key sequence; normally a keyboard
2663 macro definition consists of several key sequences concatenated.
2665 If @var{kbdmacro} is a symbol, then its function definition is used in
2666 place of @var{kbdmacro}. If that is another symbol, this process repeats.
2667 Eventually the result should be a string or vector. If the result is
2668 not a symbol, string, or vector, an error is signaled.
2670 The argument @var{count} is a repeat count; @var{kbdmacro} is executed that
2671 many times. If @var{count} is omitted or @code{nil}, @var{kbdmacro} is
2672 executed once. If it is 0, @var{kbdmacro} is executed over and over until it
2673 encounters an error or a failing search.
2675 @xref{Reading One Event}, for an example of using @code{execute-kbd-macro}.
2678 @defvar executing-macro
2679 This variable contains the string or vector that defines the keyboard
2680 macro that is currently executing. It is @code{nil} if no macro is
2681 currently executing. A command can test this variable so as to behave
2682 differently when run from an executing macro. Do not set this variable
2686 @defvar defining-kbd-macro
2687 This variable indicates whether a keyboard macro is being defined. A
2688 command can test this variable so as to behave differently while a macro
2689 is being defined. The commands @code{start-kbd-macro} and
2690 @code{end-kbd-macro} set this variable---do not set it yourself.
2692 The variable is always local to the current terminal and cannot be
2693 buffer-local. @xref{Multiple Displays}.
2696 @defvar last-kbd-macro
2697 This variable is the definition of the most recently defined keyboard
2698 macro. Its value is a string or vector, or @code{nil}.
2700 The variable is always local to the current terminal and cannot be
2701 buffer-local. @xref{Multiple Displays}.