@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990--1995, 1998--1999, 2001--2021 Free Software @c Foundation, Inc. @c See the file elisp.texi for copying conditions. @node Command Loop @chapter Command Loop @cindex editor command loop @cindex command loop When you run Emacs, it enters the @dfn{editor command loop} almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them. @menu * Command Overview:: How the command loop reads commands. * Defining Commands:: Specifying how a function should read arguments. * Interactive Call:: Calling a command, so that it will read arguments. * Distinguish Interactive:: Making a command distinguish interactive calls. * Command Loop Info:: Variables set by the command loop for you to examine. * Adjusting Point:: Adjustment of point after a command. * Input Events:: What input looks like when you read it. * Reading Input:: How to read input events from the keyboard or mouse. * Special Events:: Events processed immediately and individually. * Waiting:: Waiting for user input or elapsed time. * Quitting:: How @kbd{C-g} works. How to catch or defer quitting. * Prefix Command Arguments:: How the commands to set prefix args work. * Recursive Editing:: Entering a recursive edit, and why you usually shouldn't. * Disabling Commands:: How the command loop handles disabled commands. * Command History:: How the command history is set up, and how accessed. * Keyboard Macros:: How keyboard macros are implemented. @end menu @node Command Overview @section Command Loop Overview The first thing the command loop must do is read a key sequence, which is a sequence of input events that translates into a command. It does this by calling the function @code{read-key-sequence}. Lisp programs can also call this function (@pxref{Key Sequence Input}). They can also read input at a lower level with @code{read-key} or @code{read-event} (@pxref{Reading One Event}), or discard pending input with @code{discard-input} (@pxref{Event Input Misc}). The key sequence is translated into a command through the currently active keymaps. @xref{Key Lookup}, for information on how this is done. The result should be a keyboard macro or an interactively callable function. If the key is @kbd{M-x}, then it reads the name of another command, which it then calls. This is done by the command @code{execute-extended-command} (@pxref{Interactive Call}). Prior to executing the command, Emacs runs @code{undo-boundary} to create an undo boundary. @xref{Maintaining Undo}. To execute a command, Emacs first reads its arguments by calling @code{command-execute} (@pxref{Interactive Call}). For commands written in Lisp, the @code{interactive} specification says how to read the arguments. This may use the prefix argument (@pxref{Prefix Command Arguments}) or may read with prompting in the minibuffer (@pxref{Minibuffers}). For example, the command @code{find-file} has an @code{interactive} specification which says to read a file name using the minibuffer. The function body of @code{find-file} does not use the minibuffer, so if you call @code{find-file} as a function from Lisp code, you must supply the file name string as an ordinary Lisp function argument. If the command is a keyboard macro (i.e., a string or vector), Emacs executes it using @code{execute-kbd-macro} (@pxref{Keyboard Macros}). @defvar pre-command-hook This normal hook is run by the editor command loop before it executes each command. At that time, @code{this-command} contains the command that is about to run, and @code{last-command} describes the previous command. @xref{Command Loop Info}. @end defvar @defvar post-command-hook This normal hook is run by the editor command loop after it executes each command (including commands terminated prematurely by quitting or by errors). At that time, @code{this-command} refers to the command that just ran, and @code{last-command} refers to the command before that. This hook is also run when Emacs first enters the command loop (at which point @code{this-command} and @code{last-command} are both @code{nil}). @end defvar Quitting is suppressed while running @code{pre-command-hook} and @code{post-command-hook}. If an error happens while executing one of these hooks, it does not terminate execution of the hook; instead the error is silenced and the function in which the error occurred is removed from the hook. A request coming into the Emacs server (@pxref{Emacs Server,,, emacs, The GNU Emacs Manual}) runs these two hooks just as a keyboard command does. @node Defining Commands @section Defining Commands @cindex defining commands @cindex commands, defining @cindex functions, making them interactive @cindex interactive function The special form @code{interactive} turns a Lisp function into a command. The @code{interactive} form must be located at top-level in the function body, usually as the first form in the body; this applies to both lambda expressions (@pxref{Lambda Expressions}) and @code{defun} forms (@pxref{Defining Functions}). This form does nothing during the actual execution of the function; its presence serves as a flag, telling the Emacs command loop that the function can be called interactively. The argument of the @code{interactive} form specifies how the arguments for an interactive call should be read. @cindex @code{interactive-form} property Alternatively, an @code{interactive} form may be specified in a function symbol's @code{interactive-form} property. A non-@code{nil} value for this property takes precedence over any @code{interactive} form in the function body itself. This feature is seldom used. @anchor{The interactive-only property} @cindex @code{interactive-only} property Sometimes, a function is only intended to be called interactively, never directly from Lisp. In that case, give the function a non-@code{nil} @code{interactive-only} property, either directly or via @code{declare} (@pxref{Declare Form}). This causes the byte compiler to warn if the command is called from Lisp. The output of @code{describe-function} will include similar information. The value of the property can be: a string, which the byte-compiler will use directly in its warning (it should end with a period, and not start with a capital, e.g., @code{"use (system-name) instead."}); @code{t}; any other symbol, which should be an alternative function to use in Lisp code. Generic functions (@pxref{Generic Functions}) cannot be turned into commands by adding the @code{interactive} form to them. @menu * Using Interactive:: General rules for @code{interactive}. * Interactive Codes:: The standard letter-codes for reading arguments in various ways. * Interactive Examples:: Examples of how to read interactive arguments. * Command Modes:: Specifying that commands are for a specific mode. * Generic Commands:: Select among command alternatives. @end menu @node Using Interactive @subsection Using @code{interactive} @cindex arguments, interactive entry @cindex interactive spec, using This section describes how to write the @code{interactive} form that makes a Lisp function an interactively-callable command, and how to examine a command's @code{interactive} form. @defspec interactive &optional arg-descriptor &rest modes This special form declares that a function is a command, and that it may therefore be called interactively (via @kbd{M-x} or by entering a key sequence bound to it). The argument @var{arg-descriptor} declares how to compute the arguments to the command when the command is called interactively. A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and @var{arg-descriptor} has no effect. @cindex @code{interactive-form}, symbol property The @code{interactive} form must be located at top-level in the function body, or in the function symbol's @code{interactive-form} property (@pxref{Symbol Properties}). It has its effect because the command loop looks for it before calling the function (@pxref{Interactive Call}). Once the function is called, all its body forms are executed; at this time, if the @code{interactive} form occurs within the body, the form simply returns @code{nil} without even evaluating its argument. The @var{modes} list allows specifying which modes the command is meant to be used in. See @ref{Command Modes} for more details about the effect of specifying @var{modes}, and when to use it. By convention, you should put the @code{interactive} form in the function body, as the first top-level form. If there is an @code{interactive} form in both the @code{interactive-form} symbol property and the function body, the former takes precedence. The @code{interactive-form} symbol property can be used to add an interactive form to an existing function, or change how its arguments are processed interactively, without redefining the function. @end defspec There are three possibilities for the argument @var{arg-descriptor}: @itemize @bullet @item It may be omitted or @code{nil}; then the command is called with no arguments. This leads quickly to an error if the command requires one or more arguments. @item It may be a string; its contents are a sequence of elements separated by newlines, one for each argument@footnote{Some elements actually supply two arguments.}. Each element consists of a code character (@pxref{Interactive Codes}) optionally followed by a prompt (which some code characters use and some ignore). Here is an example: @smallexample (interactive "P\nbFrobnicate buffer: ") @end smallexample @noindent The code letter @samp{P} sets the command's first argument to the raw command prefix (@pxref{Prefix Command Arguments}). @samp{bFrobnicate buffer: } prompts the user with @samp{Frobnicate buffer: } to enter the name of an existing buffer, which becomes the second and final argument. The prompt string can use @samp{%} to include previous argument values (starting with the first argument) in the prompt. This is done using @code{format-message} (@pxref{Formatting Strings}). For example, here is how you could read the name of an existing buffer followed by a new name to give to that buffer: @smallexample @group (interactive "bBuffer to rename: \nsRename buffer %s to: ") @end group @end smallexample @cindex @samp{*} in @code{interactive} @cindex read-only buffers in interactive If @samp{*} appears at the beginning of the string, then an error is signaled if the buffer is read-only. @cindex @samp{@@} in @code{interactive} If @samp{@@} appears at the beginning of the string, and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run. @cindex @samp{^} in @code{interactive} @cindex shift-selection, and @code{interactive} spec If @samp{^} appears at the beginning of the string, and if the command was invoked through @dfn{shift-translation}, set the mark and activate the region temporarily, or extend an already active region, before the command is run. If the command was invoked without shift-translation, and the region is temporarily active, deactivate the region before the command is run. Shift-translation is controlled on the user level by @code{shift-select-mode}; see @ref{Shift Selection,,, emacs, The GNU Emacs Manual}. You can use @samp{*}, @samp{@@}, and @code{^} together; the order does not matter. Actual reading of arguments is controlled by the rest of the prompt string (starting with the first character that is not @samp{*}, @samp{@@}, or @samp{^}). @item It may be a Lisp expression that is not a string; then it should be a form that is evaluated to get a list of arguments to pass to the command. Usually this form will call various functions to read input from the user, most often through the minibuffer (@pxref{Minibuffers}) or directly from the keyboard (@pxref{Reading Input}). Providing point or the mark as an argument value is also common, but if you do this @emph{and} read input (whether using the minibuffer or not), be sure to get the integer values of point or the mark after reading. The current buffer may be receiving subprocess output; if subprocess output arrives while the command is waiting for input, it could relocate point and the mark. Here's an example of what @emph{not} to do: @smallexample (interactive (list (region-beginning) (region-end) (read-string "Foo: " nil 'my-history))) @end smallexample @noindent Here's how to avoid the problem, by examining point and the mark after reading the keyboard input: @smallexample (interactive (let ((string (read-string "Foo: " nil 'my-history))) (list (region-beginning) (region-end) string))) @end smallexample @strong{Warning:} the argument values should not include any data types that can't be printed and then read. Some facilities save @code{command-history} in a file to be read in the subsequent sessions; if a command's arguments contain a data type that prints using @samp{#<@dots{}>} syntax, those facilities won't work. There are, however, a few exceptions: it is ok to use a limited set of expressions such as @code{(point)}, @code{(mark)}, @code{(region-beginning)}, and @code{(region-end)}, because Emacs recognizes them specially and puts the expression (rather than its value) into the command history. To see whether the expression you wrote is one of these exceptions, run the command, then examine @code{(car command-history)}. @end itemize @cindex examining the @code{interactive} form @defun interactive-form function This function returns the @code{interactive} form of @var{function}. If @var{function} is an interactively callable function (@pxref{Interactive Call}), the value is the command's @code{interactive} form @code{(interactive @var{spec})}, which specifies how to compute its arguments. Otherwise, the value is @code{nil}. If @var{function} is a symbol, its function definition is used. @end defun @node Interactive Codes @subsection Code Characters for @code{interactive} @cindex interactive code description @cindex description for interactive codes @cindex codes, interactive, description of @cindex characters for interactive codes The code character descriptions below contain a number of key words, defined here as follows: @table @b @item Completion @cindex interactive completion Provide completion. @key{TAB}, @key{SPC}, and @key{RET} perform name completion because the argument is read using @code{completing-read} (@pxref{Completion}). @kbd{?} displays a list of possible completions. @item Existing Require the name of an existing object. An invalid name is not accepted; the commands to exit the minibuffer do not exit if the current input is not valid. @item Default @cindex default argument string A default value of some sort is used if the user enters no text in the minibuffer. The default depends on the code character. @item No I/O This code letter computes an argument without reading any input. Therefore, it does not use a prompt string, and any prompt string you supply is ignored. Even though the code letter doesn't use a prompt string, you must follow it with a newline if it is not the last code character in the string. @item Prompt A prompt immediately follows the code character. The prompt ends either with the end of the string or with a newline. @item Special This code character is meaningful only at the beginning of the interactive string, and it does not look for a prompt or a newline. It is a single, isolated character. @end table @cindex reading interactive arguments Here are the code character descriptions for use with @code{interactive}: @table @samp @item * Signal an error if the current buffer is read-only. Special. @item @@ Select the window mentioned in the first mouse event in the key sequence that invoked this command. Special. @item ^ If the command was invoked through shift-translation, set the mark and activate the region temporarily, or extend an already active region, before the command is run. If the command was invoked without shift-translation, and the region is temporarily active, deactivate the region before the command is run. Special. @item a A function name (i.e., a symbol satisfying @code{fboundp}). Existing, Completion, Prompt. @item b The name of an existing buffer. By default, uses the name of the current buffer (@pxref{Buffers}). Existing, Completion, Default, Prompt. @item B A buffer name. The buffer need not exist. By default, uses the name of a recently used buffer other than the current buffer. Completion, Default, Prompt. @item c A character. The cursor does not move into the echo area. Prompt. @item C A command name (i.e., a symbol satisfying @code{commandp}). Existing, Completion, Prompt. @item d @cindex position argument The position of point, as an integer (@pxref{Point}). No I/O. @item D A directory. The default is the current default directory of the current buffer, @code{default-directory} (@pxref{File Name Expansion}). Existing, Completion, Default, Prompt. @item e The first or next non-keyboard event in the key sequence that invoked the command. More precisely, @samp{e} gets events that are lists, so you can look at the data in the lists. @xref{Input Events}. No I/O. You use @samp{e} for mouse events and for special system events (@pxref{Misc Events}). The event list that the command receives depends on the event. @xref{Input Events}, which describes the forms of the list for each event in the corresponding subsections. You can use @samp{e} more than once in a single command's interactive specification. If the key sequence that invoked the command has @var{n} events that are lists, the @var{n}th @samp{e} provides the @var{n}th such event. Events that are not lists, such as function keys and @acronym{ASCII} characters, do not count where @samp{e} is concerned. @item f A file name of an existing file (@pxref{File Names}). The default directory is @code{default-directory}. Existing, Completion, Default, Prompt. @item F A file name. The file need not exist. Completion, Default, Prompt. @item G A file name. The file need not exist. If the user enters just a directory name, then the value is just that directory name, with no file name within the directory added. Completion, Default, Prompt. @item i An irrelevant argument. This code always supplies @code{nil} as the argument's value. No I/O. @item k A key sequence (@pxref{Key Sequences}). This keeps reading events until a command (or undefined command) is found in the current key maps. The key sequence argument is represented as a string or vector. The cursor does not move into the echo area. Prompt. If @samp{k} reads a key sequence that ends with a down-event, it also reads and discards the following up-event. You can get access to that up-event with the @samp{U} code character. This kind of input is used by commands such as @code{describe-key} and @code{global-set-key}. @item K A key sequence, whose definition you intend to change. This works like @samp{k}, except that it suppresses, for the last input event in the key sequence, the conversions that are normally used (when necessary) to convert an undefined key into a defined one. @item m @cindex marker argument The position of the mark, as an integer. No I/O. @item M Arbitrary text, read in the minibuffer using the current buffer's input method, and returned as a string (@pxref{Input Methods,,, emacs, The GNU Emacs Manual}). Prompt. @item n A number, read with the minibuffer. If the input is not a number, the user has to try again. @samp{n} never uses the prefix argument. Prompt. @item N The numeric prefix argument; but if there is no prefix argument, read a number as with @kbd{n}. The value is always a number. @xref{Prefix Command Arguments}. Prompt. @item p @cindex numeric prefix argument usage The numeric prefix argument. (Note that this @samp{p} is lower case.) No I/O. @item P @cindex raw prefix argument usage The raw prefix argument. (Note that this @samp{P} is upper case.) No I/O. @item r @cindex region argument Point and the mark, as two numeric arguments, smallest first. This is the only code letter that specifies two successive arguments rather than one. This will signal an error if the mark is not set in the buffer which is current when the command is invoked. No I/O. @item s Arbitrary text, read in the minibuffer and returned as a string (@pxref{Text from Minibuffer}). Terminate the input with either @kbd{C-j} or @key{RET}. (@kbd{C-q} may be used to include either of these characters in the input.) Prompt. @item S An interned symbol whose name is read in the minibuffer. Terminate the input with either @kbd{C-j} or @key{RET}. Other characters that normally terminate a symbol (e.g., whitespace, parentheses and brackets) do not do so here. Prompt. @item U A key sequence or @code{nil}. Can be used after a @samp{k} or @samp{K} argument to get the up-event that was discarded (if any) after @samp{k} or @samp{K} read a down-event. If no up-event has been discarded, @samp{U} provides @code{nil} as the argument. No I/O. @item v A variable declared to be a user option (i.e., satisfying the predicate @code{custom-variable-p}). This reads the variable using @code{read-variable}. @xref{Definition of read-variable}. Existing, Completion, Prompt. @item x A Lisp object, specified with its read syntax, terminated with a @kbd{C-j} or @key{RET}. The object is not evaluated. @xref{Object from Minibuffer}. Prompt. @item X @cindex evaluated expression argument A Lisp form's value. @samp{X} reads as @samp{x} does, then evaluates the form so that its value becomes the argument for the command. Prompt. @item z A coding system name (a symbol). If the user enters null input, the argument value is @code{nil}. @xref{Coding Systems}. Completion, Existing, Prompt. @item Z A coding system name (a symbol)---but only if this command has a prefix argument. With no prefix argument, @samp{Z} provides @code{nil} as the argument value. Completion, Existing, Prompt. @end table @node Interactive Examples @subsection Examples of Using @code{interactive} @cindex examples of using @code{interactive} @cindex @code{interactive}, examples of using Here are some examples of @code{interactive}: @example @group (defun foo1 () ; @r{@code{foo1} takes no arguments,} (interactive) ; @r{just moves forward two words.} (forward-word 2)) @result{} foo1 @end group @group (defun foo2 (n) ; @r{@code{foo2} takes one argument,} (interactive "^p") ; @r{which is the numeric prefix.} ; @r{under @code{shift-select-mode},} ; @r{will activate or extend region.} (forward-word (* 2 n))) @result{} foo2 @end group @group (defun foo3 (n) ; @r{@code{foo3} takes one argument,} (interactive "nCount:") ; @r{which is read with the Minibuffer.} (forward-word (* 2 n))) @result{} foo3 @end group @group (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." @end group (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) @result{} three-b @group (three-b "*scratch*" "declarations.texi" "*mail*") @result{} nil @end group @end example @node Command Modes @subsection Specifying Modes For Commands Many commands in Emacs are general, and not tied to any specific mode. For instance, @kbd{M-x kill-region} can be used pretty in pretty much any mode that has editable text, and commands that display information (like @kbd{M-x list-buffers}) can be used in pretty much any context. Many other commands, however, are specifically tied to a mode, and make no sense outside of that context. For instance, @code{M-x dired-diff} will just signal an error used outside of a dired buffer. Emacs therefore has a mechanism for specifying what mode (or modes) a command ``belong'' to: @lisp (defun dired-diff (...) ... (interactive "p" dired-mode) ...) @end lisp This will mark the command as applicable to @code{dired-mode} only (or any modes that are derived from @code{dired-mode}). Any number of modes can be added to the @code{interactive} form. @vindex read-extended-command-predicate Specifying modes may affect completion in @kbd{M-x}, depending on the value of @code{read-extended-command-predicate}. For instance, when using the @code{command-completion-default-include-p} predicate, @kbd{M-x} won't list commands that have been marked as being applicable to a specific mode (unless you are in a buffer that uses that mode, of course). This goes for both major and minor modes. Marking commands this way will also make @kbd{C-h m} list these commands (if they aren't bound to any keys). If using this extended @code{interactive} form isn't convenient (because the code is supposed to work in older versions of Emacs that doesn't support the extended @code{interactive} form), the following can be used instead: @lisp (declare (modes dired-mode)) @end lisp Which commands to tag with modes is to some degree a matter of taste, but commands that clearly do not work outside of the mode should be tagged. This includes commands that will signal an error if called from somewhere else, but also commands that are destructive when called from an unexpected mode. (This usually includes most of the commands that are written for special (i.e., non-editing) modes.) Some commands may be harmless, and ``work'' when called from other modes, but should still be tagged with a mode if they don't actually make much sense to use elsewhere. For instance, many special modes have commands to exit the buffer bound to @kbd{q}, and may not do anything but issue a message like "Goodbye from this mode" and then call @code{kill-buffer}. This command will ``work'' from any mode, but it is highly unlikely that anybody would actually want to use the command outside the context of this special mode. Many modes have a set of different commands that start that start the mode in different ways, (e.g., @code{eww-open-in-new-buffer} and @code{eww-open-file}). Commands like that should never be tagged as mode-specific, as then can be issued by the user from pretty much any context. @node Generic Commands @subsection Select among Command Alternatives @cindex generic commands @cindex alternatives, defining The macro @code{define-alternatives} can be used to define @dfn{generic commands}. These are interactive functions whose implementation can be selected from several alternatives, as a matter of user preference. @defmac define-alternatives command &rest customizations Define the new command @var{command}, a symbol. When a user runs @kbd{M-x @var{command} @key{RET}} for the first time, Emacs prompts for which real form of the command to use, and records the selection by way of a custom variable. Using a prefix argument repeats this process of choosing an alternative. The variable @code{@var{command}-alternatives} should contain an alist with alternative implementations of @var{command}. Until this variable is set, @code{define-alternatives} has no effect. If @var{customizations} is non-@code{nil}, it should consist of alternating @code{defcustom} keywords (typically @code{:group} and @code{:version}) and values to add to the declaration of @code{@var{command}-alternatives}. @end defmac @node Interactive Call @section Interactive Call @cindex interactive call After the command loop has translated a key sequence into a command, it invokes that command using the function @code{command-execute}. If the command is a function, @code{command-execute} calls @code{call-interactively}, which reads the arguments and calls the command. You can also call these functions yourself. Note that the term ``command'', in this context, refers to an interactively callable function (or function-like object), or a keyboard macro. It does not refer to the key sequence used to invoke a command (@pxref{Keymaps}). @defun commandp object &optional for-call-interactively This function returns @code{t} if @var{object} is a command. Otherwise, it returns @code{nil}. Commands include strings and vectors (which are treated as keyboard macros), lambda expressions that contain a top-level @code{interactive} form (@pxref{Using Interactive}), byte-code function objects made from such lambda expressions, autoload objects that are declared as interactive (non-@code{nil} fourth argument to @code{autoload}), and some primitive functions. Also, a symbol is considered a command if it has a non-@code{nil} @code{interactive-form} property, or if its function definition satisfies @code{commandp}. If @var{for-call-interactively} is non-@code{nil}, then @code{commandp} returns @code{t} only for objects that @code{call-interactively} could call---thus, not for keyboard macros. See @code{documentation} in @ref{Accessing Documentation}, for a realistic example of using @code{commandp}. @end defun @defun call-interactively command &optional record-flag keys This function calls the interactively callable function @var{command}, providing arguments according to its interactive calling specifications. It returns whatever @var{command} returns. If, for instance, you have a function with the following signature: @example (defun foo (begin end) (interactive "r") ...) @end example then saying @example (call-interactively 'foo) @end example will call @code{foo} with the region (@code{point} and @code{mark}) as the arguments. An error is signaled if @var{command} is not a function or if it cannot be called interactively (i.e., is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands, because they are not functions. If @var{command} is a symbol, then @code{call-interactively} uses its function definition. @cindex record command history If @var{record-flag} is non-@code{nil}, then this command and its arguments are unconditionally added to the list @code{command-history}. Otherwise, the command is added only if it uses the minibuffer to read an argument. @xref{Command History}. The argument @var{keys}, if given, should be a vector which specifies the sequence of events to supply if the command inquires which events were used to invoke it. If @var{keys} is omitted or @code{nil}, the default is the return value of @code{this-command-keys-vector}. @xref{Definition of this-command-keys-vector}. @end defun @defun funcall-interactively function &rest arguments This function works like @code{funcall} (@pxref{Calling Functions}), but it makes the call look like an interactive invocation: a call to @code{called-interactively-p} inside @var{function} will return @code{t}. If @var{function} is not a command, it is called without signaling an error. @end defun @defun command-execute command &optional record-flag keys special @cindex keyboard macro execution This function executes @var{command}. The argument @var{command} must satisfy the @code{commandp} predicate; i.e., it must be an interactively callable function or a keyboard macro. A string or vector as @var{command} is executed with @code{execute-kbd-macro}. A function is passed to @code{call-interactively} (see above), along with the @var{record-flag} and @var{keys} arguments. If @var{command} is a symbol, its function definition is used in its place. A symbol with an @code{autoload} definition counts as a command if it was declared to stand for an interactively callable function. Such a definition is handled by loading the specified library and then rechecking the definition of the symbol. The argument @var{special}, if given, means to ignore the prefix argument and not clear it. This is used for executing special events (@pxref{Special Events}). @end defun @deffn Command execute-extended-command prefix-argument @cindex read command name This function reads a command name from the minibuffer using @code{completing-read} (@pxref{Completion}). Then it uses @code{command-execute} to call the specified command. Whatever that command returns becomes the value of @code{execute-extended-command}. @cindex execute with prefix argument If the command asks for a prefix argument, it receives the value @var{prefix-argument}. If @code{execute-extended-command} is called interactively, the current raw prefix argument is used for @var{prefix-argument}, and thus passed on to whatever command is run. @c !!! Should this be @kindex? @cindex @kbd{M-x} @code{execute-extended-command} is the normal definition of @kbd{M-x}, so it uses the string @w{@samp{M-x }} as a prompt. (It would be better to take the prompt from the events used to invoke @code{execute-extended-command}, but that is painful to implement.) A description of the value of the prefix argument, if any, also becomes part of the prompt. @example @group (execute-extended-command 3) ---------- Buffer: Minibuffer ---------- 3 M-x forward-word @key{RET} ---------- Buffer: Minibuffer ---------- @result{} t @end group @end example @vindex read-extended-command-predicate @findex command-completion-default-include-p This command heeds the @code{read-extended-command-predicate} variable, which can filter out commands that are not applicable to the current major mode (or enabled minor modes). By default, the value of this variable is @code{nil}, and no commands are filtered out. However, customizing it to invoke the function @code{command-completion-default-include-p} will perform mode-dependent filtering. @code{read-extended-command-predicate} can be any predicate function; it will be called with two parameters: the command's symbol and the current buffer. If should return non-@code{nil} if the command is to be included when completing in that buffer. @end deffn @node Distinguish Interactive @section Distinguish Interactive Calls @cindex distinguish interactive calls @cindex is this call interactive Sometimes a command should display additional visual feedback (such as an informative message in the echo area) for interactive calls only. There are three ways to do this. The recommended way to test whether the function was called using @code{call-interactively} is to give it an optional argument @code{print-message} and use the @code{interactive} spec to make it non-@code{nil} in interactive calls. Here's an example: @example (defun foo (&optional print-message) (interactive "p") (when print-message (message "foo"))) @end example @noindent We use @code{"p"} because the numeric prefix argument is never @code{nil}. Defined in this way, the function does display the message when called from a keyboard macro. The above method with the additional argument is usually best, because it allows callers to say ``treat this call as interactive''. But you can also do the job by testing @code{called-interactively-p}. @defun called-interactively-p kind This function returns @code{t} when the calling function was called using @code{call-interactively}. The argument @var{kind} should be either the symbol @code{interactive} or the symbol @code{any}. If it is @code{interactive}, then @code{called-interactively-p} returns @code{t} only if the call was made directly by the user---e.g., if the user typed a key sequence bound to the calling function, but @emph{not} if the user ran a keyboard macro that called the function (@pxref{Keyboard Macros}). If @var{kind} is @code{any}, @code{called-interactively-p} returns @code{t} for any kind of interactive call, including keyboard macros. If in doubt, use @code{any}; the only known proper use of @code{interactive} is if you need to decide whether to display a helpful message while a function is running. A function is never considered to be called interactively if it was called via Lisp evaluation (or with @code{apply} or @code{funcall}). @end defun @noindent Here is an example of using @code{called-interactively-p}: @example @group (defun foo () (interactive) (when (called-interactively-p 'any) (message "Interactive!") 'foo-called-interactively)) @end group @group ;; @r{Type @kbd{M-x foo}.} @print{} Interactive! @end group @group (foo) @result{} nil @end group @end example @noindent Here is another example that contrasts direct and indirect calls to @code{called-interactively-p}. @example @group (defun bar () (interactive) (message "%s" (list (foo) (called-interactively-p 'any)))) @end group @group ;; @r{Type @kbd{M-x bar}.} @print{} (nil t) @end group @end example @node Command Loop Info @section Information from the Command Loop @cindex command loop variables The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run. With the exception of @code{this-command} and @code{last-command} it's generally a bad idea to change any of these variables in a Lisp program. @defvar last-command This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed. The value is copied from @code{this-command} when a command returns to the command loop, except when the command has specified a prefix argument for the following command. This variable is always local to the current terminal and cannot be buffer-local. @xref{Multiple Terminals}. @end defvar @defvar real-last-command This variable is set up by Emacs just like @code{last-command}, but never altered by Lisp programs. @end defvar @defvar last-repeatable-command This variable stores the most recently executed command that was not part of an input event. This is the command @code{repeat} will try to repeat, @xref{Repeating,,, emacs, The GNU Emacs Manual}. @end defvar @defvar this-command @cindex current command This variable records the name of the command now being executed by the editor command loop. Like @code{last-command}, it is normally a symbol with a function definition. The command loop sets this variable just before running a command, and copies its value into @code{last-command} when the command finishes (unless the command specified a prefix argument for the following command). @cindex kill command repetition Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set @code{this-command} to @code{kill-region} so that any kill commands immediately following will know to append the killed text to the previous kill. @end defvar If you do not want a particular command to be recognized as the previous command in the case where it got an error, you must code that command to prevent this. One way is to set @code{this-command} to @code{t} at the beginning of the command, and set @code{this-command} back to its proper value at the end, like this: @example (defun foo (args@dots{}) (interactive @dots{}) (let ((old-this-command this-command)) (setq this-command t) @r{@dots{}do the work@dots{}} (setq this-command old-this-command))) @end example @noindent We do not bind @code{this-command} with @code{let} because that would restore the old value in case of error---a feature of @code{let} which in this case does precisely what we want to avoid. @defvar this-original-command This has the same value as @code{this-command} except when command remapping occurs (@pxref{Remapping Commands}). In that case, @code{this-command} gives the command actually run (the result of remapping), and @code{this-original-command} gives the command that was specified to run but remapped into another command. @end defvar @defvar current-minibuffer-command This has the same value as @code{this-command}, but is bound recursively when entering a minibuffer. This variable can be used from minibuffer hooks and the like to determine what command opened the current minibuffer session. @end defvar @defun this-command-keys This function returns a string or vector containing the key sequence that invoked the present command. Any events read by the command using @code{read-event} without a timeout get tacked on to the end. However, if the command has called @code{read-key-sequence}, it returns the last read key sequence. @xref{Key Sequence Input}. The value is a string if all events in the sequence were characters that fit in a string. @xref{Input Events}. @example @group (this-command-keys) ;; @r{Now use @kbd{C-u C-x C-e} to evaluate that.} @result{} "^X^E" @end group @end example @end defun @defun this-command-keys-vector @anchor{Definition of this-command-keys-vector} Like @code{this-command-keys}, except that it always returns the events in a vector, so you don't need to deal with the complexities of storing input events in a string (@pxref{Strings of Events}). @end defun @defun clear-this-command-keys &optional keep-record This function empties out the table of events for @code{this-command-keys} to return. Unless @var{keep-record} is non-@code{nil}, it also empties the records that the function @code{recent-keys} (@pxref{Recording Input}) will subsequently return. This is useful after reading a password, to prevent the password from echoing inadvertently as part of the next command in certain cases. @end defun @defvar last-nonmenu-event This variable holds the last input event read as part of a key sequence, not counting events resulting from mouse menus. One use of this variable is for telling @code{x-popup-menu} where to pop up a menu. It is also used internally by @code{y-or-n-p} (@pxref{Yes-or-No Queries}). @end defvar @defvar last-command-event This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in @code{self-insert-command}, which uses it to decide which character to insert. @example @group last-command-event ;; @r{Now use @kbd{C-u C-x C-e} to evaluate that.} @result{} 5 @end group @end example @noindent The value is 5 because that is the @acronym{ASCII} code for @kbd{C-e}. @end defvar @defvar last-event-frame This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. @xref{Input Focus}. If the last event came from a keyboard macro, the value is @code{macro}. @end defvar @node Adjusting Point @section Adjusting Point After Commands @cindex adjusting point @cindex invisible/intangible text, and point @cindex @code{display} property, and point display @cindex @code{composition} property, and point display Emacs cannot display the cursor when point is in the middle of a sequence of text that has the @code{display} or @code{composition} property, or is invisible. Therefore, after a command finishes and returns to the command loop, if point is within such a sequence, the command loop normally moves point to the edge of the sequence, making this sequence effectively intangible. A command can inhibit this feature by setting the variable @code{disable-point-adjustment}: @defvar disable-point-adjustment If this variable is non-@code{nil} when a command returns to the command loop, then the command loop does not check for those text properties, and does not move point out of sequences that have them. The command loop sets this variable to @code{nil} before each command, so if a command sets it, the effect applies only to that command. @end defvar @defvar global-disable-point-adjustment If you set this variable to a non-@code{nil} value, the feature of moving point out of these sequences is completely turned off. @end defvar @node Input Events @section Input Events @cindex events @cindex input events The Emacs command loop reads a sequence of @dfn{input events} that represent keyboard or mouse activity, or system events sent to Emacs. The events for keyboard activity are characters or symbols; other events are always lists. This section describes the representation and meaning of input events in detail. @defun eventp object This function returns non-@code{nil} if @var{object} is an input event or event type. Note that any non-@code{nil} symbol might be used as an event or an event type; @code{eventp} cannot distinguish whether a symbol is intended by Lisp code to be used as an event. @end defun @menu * Keyboard Events:: Ordinary characters -- keys with symbols on them. * Function Keys:: Function keys -- keys with names, not symbols. * Mouse Events:: Overview of mouse events. * Click Events:: Pushing and releasing a mouse button. * Drag Events:: Moving the mouse before releasing the button. * Button-Down Events:: A button was pushed and not yet released. * Repeat Events:: Double and triple click (or drag, or down). * Motion Events:: Just moving the mouse, not pushing a button. * Focus Events:: Moving the mouse between frames. * Misc Events:: Other events the system can generate. * Event Examples:: Examples of the lists for mouse events. * Classifying Events:: Finding the modifier keys in an event symbol. Event types. * Accessing Mouse:: Functions to extract info from mouse events. * Accessing Scroll:: Functions to get info from scroll bar events. * Strings of Events:: Special considerations for putting keyboard character events in a string. @end menu @node Keyboard Events @subsection Keyboard Events @cindex keyboard events @cindex character event There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to (possibly modified) characters; the events they generate are represented in Lisp as characters. The event type of a @dfn{character event} is the character itself (an integer), which might have some modifier bits set; see @ref{Classifying Events}. @cindex modifier bits (of input character) @cindex basic code (of input character) An input character event consists of a @dfn{basic code} between 0 and 524287, plus any or all of these @dfn{modifier bits}: @table @asis @item meta The @tex @math{2^{27}} @end tex @ifnottex 2**27 @end ifnottex bit in the character code indicates a character typed with the meta key held down. @item control The @tex @math{2^{26}} @end tex @ifnottex 2**26 @end ifnottex bit in the character code indicates a non-@acronym{ASCII} control character. @sc{ascii} control characters such as @kbd{C-a} have special basic codes of their own, so Emacs needs no special bit to indicate them. Thus, the code for @kbd{C-a} is just 1. But if you type a control combination not in @acronym{ASCII}, such as @kbd{%} with the control key, the numeric value you get is the code for @kbd{%} plus @tex @math{2^{26}} @end tex @ifnottex 2**26 @end ifnottex (assuming the terminal supports non-@acronym{ASCII} control characters), i.e.@: with the 27th bit set. @item shift The @tex @math{2^{25}} @end tex @ifnottex 2**25 @end ifnottex bit (the 26th bit) in the character event code indicates an @acronym{ASCII} control character typed with the shift key held down. For letters, the basic code itself indicates upper versus lower case; for digits and punctuation, the shift key selects an entirely different character with a different basic code. In order to keep within the @acronym{ASCII} character set whenever possible, Emacs avoids using the @tex @math{2^{25}} @end tex @ifnottex 2**25 @end ifnottex bit for those character events. However, @acronym{ASCII} provides no way to distinguish @kbd{C-A} from @kbd{C-a}, so Emacs uses the @tex @math{2^{25}} @end tex @ifnottex 2**25 @end ifnottex bit in @kbd{C-A} and not in @kbd{C-a}. @item hyper The @tex @math{2^{24}} @end tex @ifnottex 2**24 @end ifnottex bit in the character event code indicates a character typed with the hyper key held down. @item super The @tex @math{2^{23}} @end tex @ifnottex 2**23 @end ifnottex bit in the character event code indicates a character typed with the super key held down. @item alt The @tex @math{2^{22}} @end tex @ifnottex 2**22 @end ifnottex bit in the character event code indicates a character typed with the alt key held down. (The key labeled @key{Alt} on most keyboards is actually treated as the meta key, not this.) @end table It is best to avoid mentioning specific bit numbers in your program. To test the modifier bits of a character, use the function @code{event-modifiers} (@pxref{Classifying Events}). When making key bindings, you can use the read syntax for characters with modifier bits (@samp{\C-}, @samp{\M-}, and so on). For making key bindings with @code{define-key}, you can use lists such as @code{(control hyper ?x)} to specify the characters (@pxref{Changing Key Bindings}). The function @code{event-convert-list} converts such a list into an event type (@pxref{Classifying Events}). @node Function Keys @subsection Function Keys @cindex function keys Most keyboards also have @dfn{function keys}---keys that have names or symbols that are not characters. Function keys are represented in Emacs Lisp as symbols; the symbol's name is the function key's label, in lower case. For example, pressing a key labeled @key{F1} generates an input event represented by the symbol @code{f1}. The event type of a function key event is the event symbol itself. @xref{Classifying Events}. Here are a few special cases in the symbol-naming convention for function keys: @table @asis @item @code{backspace}, @code{tab}, @code{newline}, @code{return}, @code{delete} These keys correspond to common @acronym{ASCII} control characters that have special keys on most keyboards. In @acronym{ASCII}, @kbd{C-i} and @key{TAB} are the same character. If the terminal can distinguish between them, Emacs conveys the distinction to Lisp programs by representing the former as the integer 9, and the latter as the symbol @code{tab}. Most of the time, it's not useful to distinguish the two. So normally @code{local-function-key-map} (@pxref{Translation Keymaps}) is set up to map @code{tab} into 9. Thus, a key binding for character code 9 (the character @kbd{C-i}) also applies to @code{tab}. Likewise for the other symbols in this group. The function @code{read-char} likewise converts these events into characters. In @acronym{ASCII}, @key{BS} is really @kbd{C-h}. But @code{backspace} converts into the character code 127 (@key{DEL}), not into code 8 (@key{BS}). This is what most users prefer. @item @code{left}, @code{up}, @code{right}, @code{down} Cursor arrow keys @item @code{kp-add}, @code{kp-decimal}, @code{kp-divide}, @dots{} Keypad keys (to the right of the regular keyboard). @item @code{kp-0}, @code{kp-1}, @dots{} Keypad keys with digits. @item @code{kp-f1}, @code{kp-f2}, @code{kp-f3}, @code{kp-f4} Keypad PF keys. @item @code{kp-home}, @code{kp-left}, @code{kp-up}, @code{kp-right}, @code{kp-down} Keypad arrow keys. Emacs normally translates these into the corresponding non-keypad keys @code{home}, @code{left}, @dots{} @item @code{kp-prior}, @code{kp-next}, @code{kp-end}, @code{kp-begin}, @code{kp-insert}, @code{kp-delete} Additional keypad duplicates of keys ordinarily found elsewhere. Emacs normally translates these into the like-named non-keypad keys. @end table You can use the modifier keys @key{ALT}, @key{CTRL}, @key{HYPER}, @key{META}, @key{SHIFT}, and @key{SUPER} with function keys. The way to represent them is with prefixes in the symbol name: @table @samp @item A- The alt modifier. @item C- The control modifier. @item H- The hyper modifier. @item M- The meta modifier. @item S- The shift modifier. @item s- The super modifier. @end table Thus, the symbol for the key @key{F3} with @key{META} held down is @code{M-f3}. When you use more than one prefix, we recommend you write them in alphabetical order; but the order does not matter in arguments to the key-binding lookup and modification functions. @node Mouse Events @subsection Mouse Events Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The @sc{car} of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (@pxref{Repeat Events}). The rest of the list elements give position and time information. For key lookup, only the event type matters: two events of the same type necessarily run the same command. The command can access the full values of these events using the @samp{e} interactive code. @xref{Interactive Codes}. A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer---that is entirely under the control of the command binding of the key sequence. @node Click Events @subsection Click Events @cindex click event @cindex mouse click event When the user presses a mouse button and releases it at the same location, that generates a @dfn{click} event. All mouse click event share the same format: @example (@var{event-type} @var{position} @var{click-count}) @end example @table @asis @item @var{event-type} This is a symbol that indicates which mouse button was used. It is one of the symbols @code{mouse-1}, @code{mouse-2}, @dots{}, where the buttons are numbered left to right. You can also use prefixes @samp{A-}, @samp{C-}, @samp{H-}, @samp{M-}, @samp{S-} and @samp{s-} for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys. This symbol also serves as the event type of the event. Key bindings describe events by their types; thus, if there is a key binding for @code{mouse-1}, that binding would apply to all events whose @var{event-type} is @code{mouse-1}. @item @var{position} @cindex mouse position list This is a @dfn{mouse position list} specifying where the mouse click occurred; see below for details. @item @var{click-count} This is the number of rapid repeated presses so far of the same mouse button. @xref{Repeat Events}. @end table To access the contents of a mouse position list in the @var{position} slot of a click event, you should typically use the functions documented in @ref{Accessing Mouse}. The explicit format of the list depends on where the click occurred. For clicks in the text area, mode line, header line, tab line, or in the fringe or marginal areas, the mouse position list has the form @example (@var{window} @var{pos-or-area} (@var{x} . @var{y}) @var{timestamp} @var{object} @var{text-pos} (@var{col} . @var{row}) @var{image} (@var{dx} . @var{dy}) (@var{width} . @var{height})) @end example @noindent The meanings of these list elements are as follows: @table @asis @item @var{window} The window in which the click occurred. @item @var{pos-or-area} The buffer position of the character clicked on in the text area; or, if the click was outside the text area, the window area where it occurred. It is one of the symbols @code{mode-line}, @code{header-line}, @code{tab-line}, @code{vertical-line}, @code{left-margin}, @code{right-margin}, @code{left-fringe}, or @code{right-fringe}. In one special case, @var{pos-or-area} is a list containing a symbol (one of the symbols listed above) instead of just the symbol. This happens after the imaginary prefix keys for the event are registered by Emacs. @xref{Key Sequence Input}. @item @var{x}, @var{y} The relative pixel coordinates of the click. For clicks in the text area of a window, the coordinate origin @code{(0 . 0)} is taken to be the top left corner of the text area. @xref{Window Sizes}. For clicks in a mode line, header line or tab line, the coordinate origin is the top left corner of the window itself. For fringes, margins, and the vertical border, @var{x} does not have meaningful data. For fringes and margins, @var{y} is relative to the bottom edge of the header line. In all cases, the @var{x} and @var{y} coordinates increase rightward and downward respectively. @item @var{timestamp} The time at which the event occurred, as an integer number of milliseconds since a system-dependent initial time. @item @var{object} Either @code{nil}, which means the click occurred on buffer text, or a cons cell of the form @w{(@var{string} . @var{string-pos})} if there is a string from a text property or an overlay at the click position. @table @asis @item @var{string} The string which was clicked on, including any properties. @item @var{string-pos} The position in the string where the click occurred. @end table @item @var{text-pos} For clicks on a marginal area or on a fringe, this is the buffer position of the first visible character in the corresponding line in the window. For clicks on the mode line, the header line or the tab line, this is @code{nil}. For other events, it is the buffer position closest to the click. @item @var{col}, @var{row} These are the actual column and row coordinate numbers of the glyph under the @var{x}, @var{y} position. If @var{x} lies beyond the last column of actual text on its line, @var{col} is reported by adding fictional extra columns that have the default character width. Row 0 is taken to be the header line if the window has one, or Row 1 if the window also has the tab line, or the topmost row of the text area otherwise. Column 0 is taken to be the leftmost column of the text area for clicks on a window text area, or the leftmost mode line or header line column for clicks there. For clicks on fringes or vertical borders, these have no meaningful data. For clicks on margins, @var{col} is measured from the left edge of the margin area and @var{row} is measured from the top of the margin area. @item @var{image} If there is an image at the click location, this is the image object as returned by @code{find-image} (@pxref{Defining Images}); otherwise this is @code{nil}. @item @var{dx}, @var{dy} These are the pixel coordinates of the click, relative to the top left corner of @var{object}, which is @code{(0 . 0)}. If @var{object} is @code{nil}, which stands for a buffer, the coordinates are relative to the top left corner of the character glyph clicked on. @item @var{width}, @var{height} These are the pixel width and height of @var{object} or, if this is @code{nil}, those of the character glyph clicked on. @end table For clicks on a scroll bar, @var{position} has this form: @example (@var{window} @var{area} (@var{portion} . @var{whole}) @var{timestamp} @var{part}) @end example @table @asis @item @var{window} The window whose scroll bar was clicked on. @item @var{area} This is the symbol @code{vertical-scroll-bar}. @item @var{portion} The number of pixels from the top of the scroll bar to the click position. On some toolkits, including GTK+, Emacs cannot extract this data, so the value is always @code{0}. @item @var{whole} The total length, in pixels, of the scroll bar. On some toolkits, including GTK+, Emacs cannot extract this data, so the value is always @code{0}. @item @var{timestamp} The time at which the event occurred, in milliseconds. On some toolkits, including GTK+, Emacs cannot extract this data, so the value is always @code{0}. @item @var{part} The part of the scroll bar on which the click occurred. It is one of the symbols @code{handle} (the scroll bar handle), @code{above-handle} (the area above the handle), @code{below-handle} (the area below the handle), @code{up} (the up arrow at one end of the scroll bar), or @code{down} (the down arrow at one end of the scroll bar). @c The 'top', 'bottom', and 'end-scroll' codes don't seem to be used. @end table For clicks on the frame's internal border (@pxref{Frame Layout}), @var{position} has this form: @example (@var{frame} @var{part} (@var{X} . @var{Y}) @var{timestamp}) @end example @table @asis @item @var{frame} The frame whose internal border was clicked on. @item @var{part} The part of the internal border which was clicked on. This can be one of the following: @table @code @item nil The frame does not have an internal border. This usually happens on text-mode frames. This can also happen on GUI frames with internal border if the frame doesn't have its @code{drag-internal-border} parameter (@pxref{Mouse Dragging Parameters}) set to a non-@code{nil} value. @item left-edge @itemx top-edge @itemx right-edge @itemx bottom-edge The click was on the corresponding border at an offset of at least one canonical character from the border's nearest corner. @item top-left-corner @itemx top-right-corner @itemx bottom-right-corner @itemx bottom-left-corner The click was on the corresponding corner of the internal border. @end table @end table @node Drag Events @subsection Drag Events @cindex drag event @cindex mouse drag event With Emacs, you can have a drag event without even changing your clothes. A @dfn{drag event} happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this: @example (@var{event-type} (@var{window1} START-POSITION) (@var{window2} END-POSITION)) @end example For a drag event, the name of the symbol @var{event-type} contains the prefix @samp{drag-}. For example, dragging the mouse with button 2 held down generates a @code{drag-mouse-2} event. The second and third elements of the event give the starting and ending position of the drag, as mouse position lists (@pxref{Click Events}). You can access the second element of any mouse event in the same way. However, the drag event may end outside the boundaries of the frame that was initially selected. In that case, the third element's position list contains that frame in place of a window. The @samp{drag-} prefix follows the modifier key prefixes such as @samp{C-} and @samp{M-}. If @code{read-key-sequence} receives a drag event that has no key binding, and the corresponding click event does have a binding, it changes the drag event into a click event at the drag's starting position. This means that you don't have to distinguish between click and drag events unless you want to. @node Button-Down Events @subsection Button-Down Events @cindex button-down event Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released. If you want to take action as soon as a button is pressed, you need to handle @dfn{button-down} events.@footnote{Button-down is the conservative antithesis of drag.} These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (@pxref{Click Events}), except that the @var{event-type} symbol name contains the prefix @samp{down-}. The @samp{down-} prefix follows modifier key prefixes such as @samp{C-} and @samp{M-}. The function @code{read-key-sequence} ignores any button-down events that don't have command bindings; therefore, the Emacs command loop ignores them too. This means that you need not worry about defining button-down events unless you want them to do something. The usual reason to define a button-down event is so that you can track mouse motion (by reading motion events) until the button is released. @xref{Motion Events}. @node Repeat Events @subsection Repeat Events @cindex repeat events @cindex double-click events @cindex triple-click events @cindex mouse events, repeated If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special @dfn{repeat} mouse events for the second and subsequent presses. The most common repeat events are @dfn{double-click} events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events). The event type of a double-click event contains the prefix @samp{double-}. Thus, a double click on the second mouse button with @key{meta} held down comes to the Lisp program as @code{M-double-mouse-2}. If a double-click event has no binding, the binding of the corresponding ordinary click event is used to execute it. Thus, you need not pay attention to the double click feature unless you really want to. When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click. This is convenient, if the meaning of a double click somehow builds on the meaning of a single click---which is recommended user interface design practice for double clicks. If you click a button, then press it down again and start moving the mouse with the button held down, then you get a @dfn{double-drag} event when you ultimately release the button. Its event type contains @samp{double-drag} instead of just @samp{drag}. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag. Before the double-click or double-drag event, Emacs generates a @dfn{double-down} event when the user presses the button down for the second time. Its event type contains @samp{double-down} instead of just @samp{down}. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored. To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event. If you click a button twice and then press it again, all in quick succession, Emacs generates a @dfn{triple-down} event, followed by either a @dfn{triple-click} or a @dfn{triple-drag}. The event types of these events contain @samp{triple} instead of @samp{double}. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event. If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc.@: events. However, you can look at the event list to find out precisely how many times the button was pressed. @defun event-click-count event This function returns the number of consecutive button presses that led up to @var{event}. If @var{event} is a double-down, double-click or double-drag event, the value is 2. If @var{event} is a triple event, the value is 3 or greater. If @var{event} is an ordinary mouse event (not a repeat event), the value is 1. @end defun @defopt double-click-fuzz To generate repeat events, successive mouse button presses must be at approximately the same screen position. The value of @code{double-click-fuzz} specifies the maximum number of pixels the mouse may be moved (horizontally or vertically) between two successive clicks to make a double-click. This variable is also the threshold for motion of the mouse to count as a drag. @end defopt @defopt double-click-time To generate repeat events, the number of milliseconds between successive button presses must be less than the value of @code{double-click-time}. Setting @code{double-click-time} to @code{nil} disables multi-click detection entirely. Setting it to @code{t} removes the time limit; Emacs then detects multi-clicks by position only. @end defopt @node Motion Events @subsection Motion Events @cindex motion event @cindex mouse motion events Emacs sometimes generates @dfn{mouse motion} events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this: @example (mouse-movement POSITION) @end example @noindent @var{position} is a mouse position list (@pxref{Click Events}), specifying the current position of the mouse cursor. As with the end-position of a drag event, this position list may represent a location outside the boundaries of the initially selected frame, in which case the list contains that frame in place of a window. The special form @code{track-mouse} enables generation of motion events within its body. Outside of @code{track-mouse} forms, Emacs does not generate events for mere motion of the mouse, and these events do not appear. @xref{Mouse Tracking}. @defvar mouse-fine-grained-tracking When non-@code{nil}, mouse motion events are generated even for very small movements. Otherwise, motion events are not generated as long as the mouse cursor remains pointing to the same glyph in the text. @end defvar @node Focus Events @subsection Focus Events @cindex focus event Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the @dfn{focus}. When the user does something to switch between Emacs frames, that generates a @dfn{focus event}. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. @xref{Input Focus}, which also describes hooks related to focus events. Focus events are represented in Lisp as lists that look like this: @example (switch-frame @var{new-frame}) @end example @noindent where @var{new-frame} is the frame switched to. Some X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Usually, there is no need for a Lisp program to know about the focus change until some other kind of input arrives. Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event. A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence---that is, after a prefix key---then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it. @node Misc Events @subsection Miscellaneous System Events A few other event types represent occurrences within the system. @table @code @cindex @code{delete-frame} event @item (delete-frame (@var{frame})) This kind of event indicates that the user gave the window manager a command to delete a particular window, which happens to be an Emacs frame. The standard definition of the @code{delete-frame} event is to delete @var{frame}. @cindex @code{iconify-frame} event @item (iconify-frame (@var{frame})) This kind of event indicates that the user iconified @var{frame} using the window manager. Its standard definition is @code{ignore}; since the frame has already been iconified, Emacs has no work to do. The purpose of this event type is so that you can keep track of such events if you want to. @cindex @code{make-frame-visible} event @item (make-frame-visible (@var{frame})) This kind of event indicates that the user deiconified @var{frame} using the window manager. Its standard definition is @code{ignore}; since the frame has already been made visible, Emacs has no work to do. @cindex @code{wheel-up} event @cindex @code{wheel-down} event @item (wheel-up @var{position}) @itemx (wheel-down @var{position}) These kinds of event are generated by moving a mouse wheel. The @var{position} element is a mouse position list (@pxref{Click Events}), specifying the position of the mouse cursor when the event occurred. @vindex mouse-wheel-up-event @vindex mouse-wheel-down-event This kind of event is generated only on some kinds of systems. On some systems, @code{mouse-4} and @code{mouse-5} are used instead. For portable code, use the variables @code{mouse-wheel-up-event} and @code{mouse-wheel-down-event} defined in @file{mwheel.el} to determine what event types to expect for the mouse wheel. @cindex @code{drag-n-drop} event @item (drag-n-drop @var{position} @var{files}) This kind of event is generated when a group of files is selected in an application outside of Emacs, and then dragged and dropped onto an Emacs frame. The element @var{position} is a list describing the position of the event, in the same format as used in a mouse-click event (@pxref{Click Events}), and @var{files} is the list of file names that were dragged and dropped. The usual way to handle this event is by visiting these files. This kind of event is generated, at present, only on some kinds of systems. @cindex @code{help-echo} event @item help-echo This kind of event is generated when a mouse pointer moves onto a portion of buffer text which has a @code{help-echo} text property. The generated event has this form: @example (help-echo @var{frame} @var{help} @var{window} @var{object} @var{pos}) @end example @noindent The precise meaning of the event parameters and the way these parameters are used to display the help-echo text are described in @ref{Text help-echo}. @cindex @code{sigusr1} event @cindex @code{sigusr2} event @cindex user signals @item sigusr1 @itemx sigusr2 These events are generated when the Emacs process receives the signals @code{SIGUSR1} and @code{SIGUSR2}. They contain no additional data because signals do not carry additional information. They can be useful for debugging (@pxref{Error Debugging}). To catch a user signal, bind the corresponding event to an interactive command in the @code{special-event-map} (@pxref{Controlling Active Maps}). The command is called with no arguments, and the specific signal event is available in @code{last-input-event} (@pxref{Event Input Misc}. For example: @smallexample (defun sigusr-handler () (interactive) (message "Caught signal %S" last-input-event)) (define-key special-event-map [sigusr1] 'sigusr-handler) @end smallexample To test the signal handler, you can make Emacs send a signal to itself: @smallexample (signal-process (emacs-pid) 'sigusr1) @end smallexample @cindex @code{language-change} event @item language-change This kind of event is generated on MS-Windows when the input language has changed. This typically means that the keyboard keys will send to Emacs characters from a different language. The generated event has this form: @smallexample (language-change @var{frame} @var{codepage} @var{language-id}) @end smallexample @noindent Here @var{frame} is the frame which was current when the input language changed; @var{codepage} is the new codepage number; and @var{language-id} is the numerical ID of the new input language. The coding-system (@pxref{Coding Systems}) that corresponds to @var{codepage} is @code{cp@var{codepage}} or @code{windows-@var{codepage}}. To convert @var{language-id} to a string (e.g., to use it for various language-dependent features, such as @code{set-language-environment}), use the @code{w32-get-locale-info} function, like this: @smallexample ;; Get the abbreviated language name, such as "ENU" for English (w32-get-locale-info language-id) ;; Get the full English name of the language, ;; such as "English (United States)" (w32-get-locale-info language-id 4097) ;; Get the full localized name of the language (w32-get-locale-info language-id t) @end smallexample @end table If one of these events arrives in the middle of a key sequence---that is, after a prefix key---then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it. Some of these special events, such as @code{delete-frame}, invoke Emacs commands by default; others are not bound. If you want to arrange for a special event to invoke a command, you can do that via @code{special-event-map}. The command you bind to a function key in that map can then examine the full event which invoked it in @code{last-input-event}. @xref{Special Events}. @node Event Examples @subsection Event Examples If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this: @smallexample (down-mouse-1 (# 2613 (0 . 38) -864320)) (mouse-1 (# 2613 (0 . 38) -864180)) @end smallexample While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here: @smallexample (C-down-mouse-2 (# 3440 (0 . 27) -731219)) (C-drag-mouse-2 (# 3440 (0 . 27) -731219) (# 3510 (0 . 28) -729648)) @end smallexample While holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces a pair of events like these: @smallexample (M-S-down-mouse-2 (# mode-line (33 . 31) -457844)) (M-S-drag-mouse-2 (# mode-line (33 . 31) -457844) (# 161 (33 . 3) -453816)) @end smallexample The frame with input focus might not take up the entire screen, and the user might move the mouse outside the scope of the frame. Inside the @code{track-mouse} special form, that produces an event like this: @smallexample (mouse-movement (# nil (563 . 205) 532301936)) @end smallexample To handle a SIGUSR1 signal, define an interactive function, and bind it to the @code{signal usr1} event sequence: @smallexample (defun usr1-handler () (interactive) (message "Got USR1 signal")) (global-set-key [signal usr1] 'usr1-handler) @end smallexample @node Classifying Events @subsection Classifying Events @cindex event type @cindex classifying events Every event has an @dfn{event type}, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the @sc{car} of the list. Thus, the event type is always a symbol or a character. Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act. Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the @key{META} key, regardless of which other key or mouse button was used. The functions @code{event-modifiers} and @code{event-basic-type} are provided to get such information conveniently. @defun event-modifiers event This function returns a list of the modifiers that @var{event} has. The modifiers are symbols; they include @code{shift}, @code{control}, @code{meta}, @code{alt}, @code{hyper} and @code{super}. In addition, the modifiers list of a mouse event symbol always contains one of @code{click}, @code{drag}, and @code{down}. For double or triple events, it also contains @code{double} or @code{triple}. The argument @var{event} may be an entire event object, or just an event type. If @var{event} is a symbol that has never been used in an event that has been read as input in the current Emacs session, then @code{event-modifiers} can return @code{nil}, even when @var{event} actually has modifiers. Here are some examples: @example (event-modifiers ?a) @result{} nil (event-modifiers ?A) @result{} (shift) (event-modifiers ?\C-a) @result{} (control) (event-modifiers ?\C-%) @result{} (control) (event-modifiers ?\C-\S-a) @result{} (control shift) (event-modifiers 'f5) @result{} nil (event-modifiers 's-f5) @result{} (super) (event-modifiers 'M-S-f5) @result{} (meta shift) (event-modifiers 'mouse-1) @result{} (click) (event-modifiers 'down-mouse-1) @result{} (down) @end example The modifiers list for a click event explicitly contains @code{click}, but the event symbol name itself does not contain @samp{click}. Similarly, the modifiers list for an @acronym{ASCII} control character, such as @samp{C-a}, contains @code{control}, even though reading such an event via @code{read-char} will return the value 1 with the control modifier bit removed. @end defun @defun event-basic-type event This function returns the key or mouse button that @var{event} describes, with all modifiers removed. The @var{event} argument is as in @code{event-modifiers}. For example: @example (event-basic-type ?a) @result{} 97 (event-basic-type ?A) @result{} 97 (event-basic-type ?\C-a) @result{} 97 (event-basic-type ?\C-\S-a) @result{} 97 (event-basic-type 'f5) @result{} f5 (event-basic-type 's-f5) @result{} f5 (event-basic-type 'M-S-f5) @result{} f5 (event-basic-type 'down-mouse-1) @result{} mouse-1 @end example @end defun @defun mouse-movement-p object This function returns non-@code{nil} if @var{object} is a mouse movement event. @xref{Motion Events}. @end defun @defun event-convert-list list This function converts a list of modifier names and a basic event type to an event type which specifies all of them. The basic event type must be the last element of the list. For example, @example (event-convert-list '(control ?a)) @result{} 1 (event-convert-list '(control meta ?a)) @result{} -134217727 (event-convert-list '(control super f1)) @result{} C-s-f1 @end example @end defun @node Accessing Mouse @subsection Accessing Mouse Events @cindex mouse events, data in @cindex keyboard events, data in This section describes convenient functions for accessing the data in a mouse button or motion event. Keyboard event data can be accessed using the same functions, but data elements that aren't applicable to keyboard events are zero or @code{nil}. The following two functions return a mouse position list (@pxref{Click Events}), specifying the position of a mouse event. @defun event-start event This returns the starting position of @var{event}. If @var{event} is a click or button-down event, this returns the location of the event. If @var{event} is a drag event, this returns the drag's starting position. @end defun @defun event-end event This returns the ending position of @var{event}. If @var{event} is a drag event, this returns the position where the user released the mouse button. If @var{event} is a click or button-down event, the value is actually the starting position, which is the only position such events have. @end defun @defun posnp object This function returns non-@code{nil} if @var{object} is a mouse position list, in the format documented in @ref{Click Events}); and @code{nil} otherwise. @end defun @cindex mouse position list, accessing These functions take a mouse position list as argument, and return various parts of it: @defun posn-window position Return the window that @var{position} is in. If @var{position} represents a location outside the frame where the event was initiated, return that frame instead. @end defun @defun posn-area position Return the window area recorded in @var{position}. It returns @code{nil} when the event occurred in the text area of the window; otherwise, it is a symbol identifying the area in which the event occurred. @end defun @defun posn-point position Return the buffer position in @var{position}. When the event occurred in the text area of the window, in a marginal area, or on a fringe, this is an integer specifying a buffer position. Otherwise, the value is undefined. @end defun @defun posn-x-y position Return the pixel-based x and y coordinates in @var{position}, as a cons cell @w{@code{(@var{x} . @var{y})}}. These coordinates are relative to the window given by @code{posn-window}. This example shows how to convert the window-relative coordinates in the text area of a window into frame-relative coordinates: @example (defun frame-relative-coordinates (position) "Return frame-relative coordinates from POSITION. POSITION is assumed to lie in a window text area." (let* ((x-y (posn-x-y position)) (window (posn-window position)) (edges (window-inside-pixel-edges window))) (cons (+ (car x-y) (car edges)) (+ (cdr x-y) (cadr edges))))) @end example @end defun @defun posn-col-row position This function returns a cons cell @w{@code{(@var{col} . @var{row})}}, containing the estimated column and row corresponding to buffer position described by @var{position}. The return value is given in units of the frame's default character width and default line height (including spacing), as computed from the @var{x} and @var{y} values corresponding to @var{position}. (So, if the actual characters have non-default sizes, the actual row and column may differ from these computed values.) Note that @var{row} is counted from the top of the text area. If the window given by @var{position} possesses a header line (@pxref{Header Lines}) or a tab line, they are @emph{not} included in the @var{row} count. @end defun @defun posn-actual-col-row position Return the actual row and column in @var{position}, as a cons cell @w{@code{(@var{col} . @var{row})}}. The values are the actual row and column numbers in the window given by @var{position}. @xref{Click Events}, for details. The function returns @code{nil} if @var{position} does not include actual position values; in that case @code{posn-col-row} can be used to get approximate values. Note that this function doesn't account for the visual width of characters on display, like the number of visual columns taken by a tab character or an image. If you need the coordinates in canonical character units, use @code{posn-col-row} instead. @end defun @defun posn-string position Return the string object described by @var{position}, either @code{nil} (which means @var{position} describes buffer text), or a cons cell @w{@code{(@var{string} . @var{string-pos})}}. @end defun @defun posn-image position Return the image object in @var{position}, either @code{nil} (if there's no image at @var{position}), or an image spec @w{@code{(image @dots{})}}. @end defun @defun posn-object position Return the image or string object described by @var{position}, either @code{nil} (which means @var{position} describes buffer text), an image @w{@code{(image @dots{})}}, or a cons cell @w{@code{(@var{string} . @var{string-pos})}}. @end defun @defun posn-object-x-y position Return the pixel-based x and y coordinates relative to the upper left corner of the object described by @var{position}, as a cons cell @w{@code{(@var{dx} . @var{dy})}}. If the @var{position} describes buffer text, return the relative coordinates of the buffer-text character closest to that position. @end defun @defun posn-object-width-height position Return the pixel width and height of the object described by @var{position}, as a cons cell @code{(@var{width} . @var{height})}. If the @var{position} describes a buffer position, return the size of the character at that position. @end defun @cindex timestamp of a mouse event @defun posn-timestamp position Return the timestamp in @var{position}. This is the time at which the event occurred, in milliseconds. @end defun These functions compute a position list given particular buffer position or screen position. You can access the data in this position list with the functions described above. @defun posn-at-point &optional pos window This function returns a position list for position @var{pos} in @var{window}. @var{pos} defaults to point in @var{window}; @var{window} defaults to the selected window. @code{posn-at-point} returns @code{nil} if @var{pos} is not visible in @var{window}. @end defun @defun posn-at-x-y x y &optional frame-or-window whole This function returns position information corresponding to pixel coordinates @var{x} and @var{y} in a specified frame or window, @var{frame-or-window}, which defaults to the selected window. The coordinates @var{x} and @var{y} are relative to the frame or window used. If @var{whole} is @code{nil}, the coordinates are relative to the window text area, otherwise they are relative to the entire window area including scroll bars, margins and fringes. @end defun @node Accessing Scroll @subsection Accessing Scroll Bar Events @cindex scroll bar events, data in These functions are useful for decoding scroll bar events. @defun scroll-bar-event-ratio event This function returns the fractional vertical position of a scroll bar event within the scroll bar. The value is a cons cell @code{(@var{portion} . @var{whole})} containing two integers whose ratio is the fractional position. @end defun @defun scroll-bar-scale ratio total This function multiplies (in effect) @var{ratio} by @var{total}, rounding the result to an integer. The argument @var{ratio} is not a number, but rather a pair @code{(@var{num} . @var{denom})}---typically a value returned by @code{scroll-bar-event-ratio}. This function is handy for scaling a position on a scroll bar into a buffer position. Here's how to do that: @example (+ (point-min) (scroll-bar-scale (posn-x-y (event-start event)) (- (point-max) (point-min)))) @end example Recall that scroll bar events have two integers forming a ratio, in place of a pair of x and y coordinates. @end defun @node Strings of Events @subsection Putting Keyboard Events in Strings @cindex keyboard events in strings @cindex strings with keyboard events In most of the places where strings are used, we conceptualize the string as containing text characters---the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. However, storing keyboard characters in a string is a complex matter, for reasons of historical compatibility, and it is not always possible. We recommend that new programs avoid dealing with these complexities by not storing keyboard events in strings. Here is how to do that: @itemize @bullet @item Use vectors instead of strings for key sequences, when you plan to use them for anything other than as arguments to @code{lookup-key} and @code{define-key}. For example, you can use @code{read-key-sequence-vector} instead of @code{read-key-sequence}, and @code{this-command-keys-vector} instead of @code{this-command-keys}. @item Use vectors to write key sequence constants containing meta characters, even when passing them directly to @code{define-key}. @item When you have to look at the contents of a key sequence that might be a string, use @code{listify-key-sequence} (@pxref{Event Input Misc}) first, to convert it to a list. @end itemize The complexities stem from the modifier bits that keyboard input characters can include. Aside from the Meta modifier, none of these modifier bits can be included in a string, and the Meta modifier is allowed only in special cases. The earliest GNU Emacs versions represented meta characters as codes in the range of 128 to 255. At that time, the basic character codes ranged from 0 to 127, so all keyboard character codes did fit in a string. Many Lisp programs used @samp{\M-} in string constants to stand for meta characters, especially in arguments to @code{define-key} and similar functions, and key sequences and sequences of events were always represented as strings. When we added support for larger basic character codes beyond 127, and additional modifier bits, we had to change the representation of meta characters. Now the flag that represents the Meta modifier in a character is @tex @math{2^{27}} @end tex @ifnottex 2**27 @end ifnottex and such numbers cannot be included in a string. To support programs with @samp{\M-} in string constants, there are special rules for including certain meta characters in a string. Here are the rules for interpreting a string as a sequence of input characters: @itemize @bullet @item If the keyboard character value is in the range of 0 to 127, it can go in the string unchanged. @item The meta variants of those characters, with codes in the range of @tex @math{2^{27}} @end tex @ifnottex 2**27 @end ifnottex to @tex @math{2^{27} + 127}, @end tex @ifnottex 2**27+127, @end ifnottex can also go in the string, but you must change their numeric values. You must set the @tex @math{2^{7}} @end tex @ifnottex 2**7 @end ifnottex bit instead of the @tex @math{2^{27}} @end tex @ifnottex 2**27 @end ifnottex bit, resulting in a value between 128 and 255. Only a unibyte string can include these codes. @item Non-@acronym{ASCII} characters above 256 can be included in a multibyte string. @item Other keyboard character events cannot fit in a string. This includes keyboard events in the range of 128 to 255. @end itemize Functions such as @code{read-key-sequence} that construct strings of keyboard input characters follow these rules: they construct vectors instead of strings, when the events won't fit in a string. When you use the read syntax @samp{\M-} in a string, it produces a code in the range of 128 to 255---the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings. However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section. @node Reading Input @section Reading Input @cindex read input @cindex keyboard input The editor command loop reads key sequences using the function @code{read-key-sequence}, which uses @code{read-event}. These and other functions for event input are also available for use in Lisp programs. See also @code{momentary-string-display} in @ref{Temporary Displays}, and @code{sit-for} in @ref{Waiting}. @xref{Terminal Input}, for functions and variables for controlling terminal input modes and debugging terminal input. For higher-level input facilities, see @ref{Minibuffers}. @menu * Key Sequence Input:: How to read one key sequence. * Reading One Event:: How to read just one event. * Event Mod:: How Emacs modifies events as they are read. * Invoking the Input Method:: How reading an event uses the input method. * Quoted Character Input:: Asking the user to specify a character. * Event Input Misc:: How to reread or throw away input events. @end menu @node Key Sequence Input @subsection Key Sequence Input @cindex key sequence input The command loop reads input a key sequence at a time, by calling @code{read-key-sequence}. Lisp programs can also call this function; for example, @code{describe-key} uses it to read the key to describe. @defun read-key-sequence prompt &optional continue-echo dont-downcase-last switch-frame-ok command-loop This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a complete key sequence; that is, enough to specify a non-prefix command using the currently active keymaps. (Remember that a key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer.) If the events are all characters and all can fit in a string, then @code{read-key-sequence} returns a string (@pxref{Strings of Events}). Otherwise, it returns a vector, since a vector can hold all kinds of events---characters, symbols, and lists. The elements of the string or vector are the events in the key sequence. Reading a key sequence includes translating the events in various ways. @xref{Translation Keymaps}. The argument @var{prompt} is either a string to be displayed in the echo area as a prompt, or @code{nil}, meaning not to display a prompt. The argument @var{continue-echo}, if non-@code{nil}, means to echo this key as a continuation of the previous key. Normally any upper case event is converted to lower case if the original event is undefined and the lower case equivalent is defined. The argument @var{dont-downcase-last}, if non-@code{nil}, means do not convert the last event to lower case. This is appropriate for reading a key sequence to be defined. The argument @var{switch-frame-ok}, if non-@code{nil}, means that this function should process a @code{switch-frame} event if the user switches frames before typing anything. If the user switches frames in the middle of a key sequence, or at the start of the sequence but @var{switch-frame-ok} is @code{nil}, then the event will be put off until after the current key sequence. The argument @var{command-loop}, if non-@code{nil}, means that this key sequence is being read by something that will read commands one after another. It should be @code{nil} if the caller will read just one key sequence. In the following example, Emacs displays the prompt @samp{?} in the echo area, and then the user types @kbd{C-x C-f}. @example (read-key-sequence "?") @group ---------- Echo Area ---------- ?@kbd{C-x C-f} ---------- Echo Area ---------- @result{} "^X^F" @end group @end example The function @code{read-key-sequence} suppresses quitting: @kbd{C-g} typed while reading with this function works like any other character, and does not set @code{quit-flag}. @xref{Quitting}. @end defun @defun read-key-sequence-vector prompt &optional continue-echo dont-downcase-last switch-frame-ok command-loop This is like @code{read-key-sequence} except that it always returns the key sequence as a vector, never as a string. @xref{Strings of Events}. @end defun @cindex upper case key sequence @cindex downcasing in @code{lookup-key} @cindex shift-translation If an input character is upper-case (or has the shift modifier) and has no key binding, but its lower-case equivalent has one, then @code{read-key-sequence} converts the character to lower case. Note that @code{lookup-key} does not perform case conversion in this way. @vindex this-command-keys-shift-translated When reading input results in such a @dfn{shift-translation}, Emacs sets the variable @code{this-command-keys-shift-translated} to a non-@code{nil} value. Lisp programs can examine this variable if they need to modify their behavior when invoked by shift-translated keys. For example, the function @code{handle-shift-selection} examines the value of this variable to determine how to activate or deactivate the region (@pxref{The Mark, handle-shift-selection}). The function @code{read-key-sequence} also transforms some mouse events. It converts unbound drag events into click events, and discards unbound button-down events entirely. It also reshuffles focus events and miscellaneous window events so that they never appear in a key sequence with any other events. @cindex @code{tab-line}, prefix key @cindex @code{header-line}, prefix key @cindex @code{mode-line}, prefix key @cindex @code{vertical-line}, prefix key @cindex @code{horizontal-scroll-bar}, prefix key @cindex @code{vertical-scroll-bar}, prefix key @cindex @code{menu-bar}, prefix key @cindex @code{tab-bar}, prefix key @cindex @code{left-margin}, prefix key @cindex @code{right-margin}, prefix key @cindex @code{left-fringe}, prefix key @cindex @code{right-fringe}, prefix key @cindex @code{right-divider}, prefix key @cindex @code{bottom-divider}, prefix key @cindex mouse events, in special parts of window or frame When mouse events occur in special parts of a window or frame, such as a mode line or a scroll bar, the event type shows nothing special---it is the same symbol that would normally represent that combination of mouse button and modifier keys. The information about the window part is kept elsewhere in the event---in the coordinates. But @code{read-key-sequence} translates this information into imaginary prefix keys, all of which are symbols: @code{tab-line}, @code{header-line}, @code{horizontal-scroll-bar}, @code{menu-bar}, @code{tab-bar}, @code{mode-line}, @code{vertical-line}, @code{vertical-scroll-bar}, @code{left-margin}, @code{right-margin}, @code{left-fringe}, @code{right-fringe}, @code{right-divider}, and @code{bottom-divider}. You can define meanings for mouse clicks in special window parts by defining key sequences using these imaginary prefix keys. For example, if you call @code{read-key-sequence} and then click the mouse on the window's mode line, you get two events, like this: @example (read-key-sequence "Click on the mode line: ") @result{} [mode-line (mouse-1 (# mode-line (40 . 63) 5959987))] @end example @defvar num-input-keys This variable's value is the number of key sequences processed so far in this Emacs session. This includes key sequences read from the terminal and key sequences read from keyboard macros being executed. @end defvar @node Reading One Event @subsection Reading One Event @cindex reading a single event @cindex event, reading only one The lowest level functions for command input are @code{read-event}, @code{read-char}, and @code{read-char-exclusive}. If you need a function to read a character using the minibuffer, use @code{read-char-from-minibuffer} (@pxref{Multiple Queries}). @defun read-event &optional prompt inherit-input-method seconds This function reads and returns the next event of command input, waiting if necessary until an event is available. The returned event may come directly from the user, or from a keyboard macro. It is not decoded by the keyboard's input coding system (@pxref{Terminal I/O Encoding}). If the optional argument @var{prompt} is non-@code{nil}, it should be a string to display in the echo area as a prompt. If @var{prompt} is @code{nil} or the string @samp{""}, @code{read-event} does not display any message to indicate it is waiting for input; instead, it prompts by echoing: it displays descriptions of the events that led to or were read by the current command. @xref{The Echo Area}. If @var{inherit-input-method} is non-@code{nil}, then the current input method (if any) is employed to make it possible to enter a non-@acronym{ASCII} character. Otherwise, input method handling is disabled for reading this event. If @code{cursor-in-echo-area} is non-@code{nil}, then @code{read-event} moves the cursor temporarily to the echo area, to the end of any message displayed there. Otherwise @code{read-event} does not move the cursor. If @var{seconds} is non-@code{nil}, it should be a number specifying the maximum time to wait for input, in seconds. If no input arrives within that time, @code{read-event} stops waiting and returns @code{nil}. A floating point @var{seconds} means to wait for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, @var{seconds} is rounded down. If @var{seconds} is @code{nil}, @code{read-event} waits as long as necessary for input to arrive. If @var{seconds} is @code{nil}, Emacs is considered idle while waiting for user input to arrive. Idle timers---those created with @code{run-with-idle-timer} (@pxref{Idle Timers})---can run during this period. However, if @var{seconds} is non-@code{nil}, the state of idleness remains unchanged. If Emacs is non-idle when @code{read-event} is called, it remains non-idle throughout the operation of @code{read-event}; if Emacs is idle (which can happen if the call happens inside an idle timer), it remains idle. If @code{read-event} gets an event that is defined as a help character, then in some cases @code{read-event} processes the event directly without returning. @xref{Help Functions}. Certain other events, called @dfn{special events}, are also processed directly within @code{read-event} (@pxref{Special Events}). Here is what happens if you call @code{read-event} and then press the right-arrow function key: @example @group (read-event) @result{} right @end group @end example @end defun @defun read-char &optional prompt inherit-input-method seconds This function reads and returns a character input event. If the user generates an event which is not a character (i.e., a mouse click or function key event), @code{read-char} signals an error. The arguments work as in @code{read-event}. If the event has modifiers, Emacs attempts to resolve them and return the code of the corresponding character. For example, if the user types @kbd{C-a}, the function returns 1, which is the @acronym{ASCII} code of the @samp{C-a} character. If some of the modifiers cannot be reflected in the character code, @code{read-char} leaves the unresolved modifier bits set in the returned event. For example, if the user types @kbd{C-M-a}, the function returns 134217729, 8000001 in hex, i.e.@: @samp{C-a} with the Meta modifier bit set. This value is not a valid character code: it fails the @code{characterp} test (@pxref{Character Codes}). Use @code{event-basic-type} (@pxref{Classifying Events}) to recover the character code with the modifier bits removed; use @code{event-modifiers} to test for modifiers in the character event returned by @code{read-char}. In the first example below, the user types the character @kbd{1} (@acronym{ASCII} code 49). The second example shows a keyboard macro definition that calls @code{read-char} from the minibuffer using @code{eval-expression}. @code{read-char} reads the keyboard macro's very next character, which is @kbd{1}. Then @code{eval-expression} displays its return value in the echo area. @example @group (read-char) @result{} 49 @end group @group ;; @r{We assume here you use @kbd{M-:} to evaluate this.} (symbol-function 'foo) @result{} "^[:(read-char)^M1" @end group @group (execute-kbd-macro 'foo) @print{} 49 @result{} nil @end group @end example @end defun @defun read-char-exclusive &optional prompt inherit-input-method seconds This function reads and returns a character input event. If the user generates an event which is not a character event, @code{read-char-exclusive} ignores it and reads another event, until it gets a character. The arguments work as in @code{read-event}. The returned value may include modifier bits, as with @code{read-char}. @end defun None of the above functions suppress quitting. @defvar num-nonmacro-input-events This variable holds the total number of input events received so far from the terminal---not counting those generated by keyboard macros. @end defvar We emphasize that, unlike @code{read-key-sequence}, the functions @code{read-event}, @code{read-char}, and @code{read-char-exclusive} do not perform the translations described in @ref{Translation Keymaps}. If you wish to read a single key taking these translations into account (for example, to read @ref{Function Keys} in a terminal or @ref{Mouse Events} from @code{xterm-mouse-mode}), use the function @code{read-key}: @defun read-key &optional prompt disable-fallbacks This function reads a single key. It is intermediate between @code{read-key-sequence} and @code{read-event}. Unlike the former, it reads a single key, not a key sequence. Unlike the latter, it does not return a raw event, but decodes and translates the user input according to @code{input-decode-map}, @code{local-function-key-map}, and @code{key-translation-map} (@pxref{Translation Keymaps}). The argument @var{prompt} is either a string to be displayed in the echo area as a prompt, or @code{nil}, meaning not to display a prompt. If argument @var{disable-fallbacks} is non-@code{nil} then the usual fallback logic for unbound keys in @code{read-key-sequence} is not applied. This means that mouse button-down and multi-click events will not be discarded and @code{local-function-key-map} and @code{key-translation-map} will not get applied. If @code{nil} or unspecified, the only fallback disabled is downcasing of the last event. @end defun @defun read-char-choice prompt chars &optional inhibit-quit This function uses @code{read-key} to read and return a single character. It ignores any input that is not a member of @var{chars}, a list of accepted characters. Optionally, it will also ignore keyboard-quit events while it is waiting for valid input. If you bind @code{help-form} (@pxref{Help Functions}) to a non-@code{nil} value while calling @code{read-char-choice}, then pressing @code{help-char} causes it to evaluate @code{help-form} and display the result. It then continues to wait for a valid input character, or keyboard-quit. @end defun @defun read-multiple-choice prompt choices Ask user a multiple choice question. @var{prompt} should be a string that will be displayed as the prompt. @var{choices} is an alist where the first element in each entry is a character to be entered, the second element is a short name for the entry to be displayed while prompting (if there's room, it might be shortened), and the third, optional entry is a longer explanation that will be displayed in a help buffer if the user requests more help. The return value is the matching value from @var{choices}. @lisp (read-multiple-choice "Continue connecting?" '((?a "always" "Accept certificate for this and future sessions.") (?s "session only" "Accept certificate this session only.") (?n "no" "Refuse to use certificate, close connection."))) @end lisp The @code{read-multiple-choice-face} face is used to highlight the matching characters in the name string on graphical terminals. @end defun @node Event Mod @subsection Modifying and Translating Input Events @cindex modifiers of events @cindex translating input events @cindex event translation Emacs modifies every event it reads according to @code{extra-keyboard-modifiers}, then translates it through @code{keyboard-translate-table} (if applicable), before returning it from @code{read-event}. @defvar extra-keyboard-modifiers This variable lets Lisp programs ``press'' the modifier keys on the keyboard. The value is a character. Only the modifiers of the character matter. Each time the user types a keyboard key, it is altered as if those modifier keys were held down. For instance, if you bind @code{extra-keyboard-modifiers} to @code{?\C-\M-a}, then all keyboard input characters typed during the scope of the binding will have the control and meta modifiers applied to them. The character @code{?\C-@@}, equivalent to the integer 0, does not count as a control character for this purpose, but as a character with no modifiers. Thus, setting @code{extra-keyboard-modifiers} to zero cancels any modification. When using a window system, the program can press any of the modifier keys in this way. Otherwise, only the @key{CTL} and @key{META} keys can be virtually pressed. Note that this variable applies only to events that really come from the keyboard, and has no effect on mouse events or any other events. @end defvar @defvar keyboard-translate-table This terminal-local variable is the translate table for keyboard characters. It lets you reshuffle the keys on the keyboard without changing any command bindings. Its value is normally a char-table, or else @code{nil}. (It can also be a string or vector, but this is considered obsolete.) If @code{keyboard-translate-table} is a char-table (@pxref{Char-Tables}), then each character read from the keyboard is looked up in this char-table. If the value found there is non-@code{nil}, then it is used instead of the actual input character. Note that this translation is the first thing that happens to a character after it is read from the terminal. Record-keeping features such as @code{recent-keys} and dribble files record the characters after translation. Note also that this translation is done before the characters are supplied to input methods (@pxref{Input Methods}). Use @code{translation-table-for-input} (@pxref{Translation of Characters}), if you want to translate characters after input methods operate. @end defvar @defun keyboard-translate from to This function modifies @code{keyboard-translate-table} to translate character code @var{from} into character code @var{to}. It creates the keyboard translate table if necessary. @end defun Here's an example of using the @code{keyboard-translate-table} to make @kbd{C-x}, @kbd{C-c} and @kbd{C-v} perform the cut, copy and paste operations: @example (keyboard-translate ?\C-x 'control-x) (keyboard-translate ?\C-c 'control-c) (keyboard-translate ?\C-v 'control-v) (global-set-key [control-x] 'kill-region) (global-set-key [control-c] 'kill-ring-save) (global-set-key [control-v] 'yank) @end example @noindent On a graphical terminal that supports extended @acronym{ASCII} input, you can still get the standard Emacs meanings of one of those characters by typing it with the shift key. That makes it a different character as far as keyboard translation is concerned, but it has the same usual meaning. @xref{Translation Keymaps}, for mechanisms that translate event sequences at the level of @code{read-key-sequence}. @node Invoking the Input Method @subsection Invoking the Input Method @cindex invoking input method The event-reading functions invoke the current input method, if any (@pxref{Input Methods}). If the value of @code{input-method-function} is non-@code{nil}, it should be a function; when @code{read-event} reads a printing character (including @key{SPC}) with no modifier bits, it calls that function, passing the character as an argument. @defvar input-method-function If this is non-@code{nil}, its value specifies the current input method function. @strong{Warning:} don't bind this variable with @code{let}. It is often buffer-local, and if you bind it around reading input (which is exactly when you @emph{would} bind it), switching buffers asynchronously while Emacs is waiting will cause the value to be restored in the wrong buffer. @end defvar The input method function should return a list of events which should be used as input. (If the list is @code{nil}, that means there is no input, so @code{read-event} waits for another event.) These events are processed before the events in @code{unread-command-events} (@pxref{Event Input Misc}). Events returned by the input method function are not passed to the input method function again, even if they are printing characters with no modifier bits. If the input method function calls @code{read-event} or @code{read-key-sequence}, it should bind @code{input-method-function} to @code{nil} first, to prevent recursion. The input method function is not called when reading the second and subsequent events of a key sequence. Thus, these characters are not subject to input method processing. The input method function should test the values of @code{overriding-local-map} and @code{overriding-terminal-local-map}; if either of these variables is non-@code{nil}, the input method should put its argument into a list and return that list with no further processing. @node Quoted Character Input @subsection Quoted Character Input @cindex quoted character input You can use the function @code{read-quoted-char} to ask the user to specify a character, and allow the user to specify a control or meta character conveniently, either literally or as an octal character code. The command @code{quoted-insert} uses this function. @defun read-quoted-char &optional prompt @cindex octal character input @cindex control characters, reading @cindex nonprinting characters, reading This function is like @code{read-char}, except that if the first character read is an octal digit (0--7), it reads any number of octal digits (but stopping if a non-octal digit is found), and returns the character represented by that numeric character code. If the character that terminates the sequence of octal digits is @key{RET}, it is discarded. Any other terminating character is used as input after this function returns. Quitting is suppressed when the first character is read, so that the user can enter a @kbd{C-g}. @xref{Quitting}. If @var{prompt} is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single @samp{-}. In the following example, the user types in the octal number 177 (which is 127 in decimal). @example (read-quoted-char "What character") @group ---------- Echo Area ---------- What character @kbd{1 7 7}- ---------- Echo Area ---------- @result{} 127 @end group @end example @end defun @need 2000 @node Event Input Misc @subsection Miscellaneous Event Input Features This section describes how to peek ahead at events without using them up, how to check for pending input, and how to discard pending input. See also the function @code{read-passwd} (@pxref{Reading a Password}). @defvar unread-command-events @cindex next input @cindex peeking at input This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list, and removed one by one as they are used. The variable is needed because in some cases a function reads an event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input. @cindex prefix argument unreading For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally. The reliable and easy way to extract events from a key sequence so as to put them in @code{unread-command-events} is to use @code{listify-key-sequence} (see below). Normally you add events to the front of this list, so that the events most recently unread will be reread first. Events read from this list are not normally added to the current command's key sequence (as returned by, e.g., @code{this-command-keys}), as the events will already have been added once as they were read for the first time. An element of the form @w{@code{(t . @var{event})}} forces @var{event} to be added to the current command's key sequence. @cindex not recording input events @cindex input events, prevent recording Elements read from this list are normally recorded by the record-keeping features (@pxref{Recording Input}) and while defining a keyboard macro (@pxref{Keyboard Macros}). However, an element of the form @w{@code{(no-record . @var{event})}} causes @var{event} to be processed normally without recording it. @end defvar @defun listify-key-sequence key This function converts the string or vector @var{key} to a list of individual events, which you can put in @code{unread-command-events}. @end defun @defun input-pending-p &optional check-timers @cindex waiting for command key input This function determines whether any command input is currently available to be read. It returns immediately, with value @code{t} if there is available input, @code{nil} otherwise. On rare occasions it may return @code{t} when no input is available. If the optional argument @var{check-timers} is non-@code{nil}, then if no input is available, Emacs runs any timers which are ready. @xref{Timers}. @end defun @defvar last-input-event This variable records the last terminal input event read, whether as part of a command or explicitly by a Lisp program. In the example below, the Lisp program reads the character @kbd{1}, @acronym{ASCII} code 49. It becomes the value of @code{last-input-event}, while @kbd{C-e} (we assume @kbd{C-x C-e} command is used to evaluate this expression) remains the value of @code{last-command-event}. @example @group (progn (print (read-char)) (print last-command-event) last-input-event) @print{} 49 @print{} 5 @result{} 49 @end group @end example @end defvar @defmac while-no-input body@dots{} This construct runs the @var{body} forms and returns the value of the last one---but only if no input arrives. If any input arrives during the execution of the @var{body} forms, it aborts them (working much like a quit). The @code{while-no-input} form returns @code{nil} if aborted by a real quit, and returns @code{t} if aborted by arrival of other input. If a part of @var{body} binds @code{inhibit-quit} to non-@code{nil}, arrival of input during those parts won't cause an abort until the end of that part. If you want to be able to distinguish all possible values computed by @var{body} from both kinds of abort conditions, write the code like this: @example (while-no-input (list (progn . @var{body}))) @end example @end defmac @defvar while-no-input-ignore-events This variable allow setting which special events @code{while-no-input} should ignore. It is a list of event symbols (@pxref{Event Examples}). @end defvar @defun discard-input @cindex flushing input @cindex discarding input @cindex keyboard macro, terminating This function discards the contents of the terminal input buffer and cancels any keyboard macro that might be in the process of definition. It returns @code{nil}. In the following example, the user may type a number of characters right after starting the evaluation of the form. After the @code{sleep-for} finishes sleeping, @code{discard-input} discards any characters typed during the sleep. @example (progn (sleep-for 2) (discard-input)) @result{} nil @end example @end defun @node Special Events @section Special Events @cindex special events Certain @dfn{special events} are handled at a very low level---as soon as they are read. The @code{read-event} function processes these events itself, and never returns them. Instead, it keeps waiting for the first event that is not special and returns that one. Special events do not echo, they are never grouped into key sequences, and they never appear in the value of @code{last-command-event} or @code{(this-command-keys)}. They do not discard a numeric argument, they cannot be unread with @code{unread-command-events}, they may not appear in a keyboard macro, and they are not recorded in a keyboard macro while you are defining one. Special events do, however, appear in @code{last-input-event} immediately after they are read, and this is the way for the event's definition to find the actual event. The events types @code{iconify-frame}, @code{make-frame-visible}, @code{delete-frame}, @code{drag-n-drop}, @code{language-change}, and user signals like @code{sigusr1} are normally handled in this way. The keymap which defines how to handle special events---and which events are special---is in the variable @code{special-event-map} (@pxref{Controlling Active Maps}). @node Waiting @section Waiting for Elapsed Time or Input @cindex waiting The wait functions are designed to wait for a certain amount of time to pass or until there is input. For example, you may wish to pause in the middle of a computation to allow the user time to view the display. @code{sit-for} pauses and updates the screen, and returns immediately if input comes in, while @code{sleep-for} pauses without updating the screen. @defun sit-for seconds &optional nodisp This function performs redisplay (provided there is no pending input from the user), then waits @var{seconds} seconds, or until input is available. The usual purpose of @code{sit-for} is to give the user time to read text that you display. The value is @code{t} if @code{sit-for} waited the full time with no input arriving (@pxref{Event Input Misc}). Otherwise, the value is @code{nil}. The argument @var{seconds} need not be an integer. If it is floating point, @code{sit-for} waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, @var{seconds} is rounded down. The expression @code{(sit-for 0)} is equivalent to @code{(redisplay)}, i.e., it requests a redisplay, without any delay, if there is no pending input. @xref{Forcing Redisplay}. If @var{nodisp} is non-@code{nil}, then @code{sit-for} does not redisplay, but it still returns as soon as input is available (or when the timeout elapses). In batch mode (@pxref{Batch Mode}), @code{sit-for} cannot be interrupted, even by input from the standard input descriptor. It is thus equivalent to @code{sleep-for}, which is described below. It is also possible to call @code{sit-for} with three arguments, as @code{(sit-for @var{seconds} @var{millisec} @var{nodisp})}, but that is considered obsolete. @end defun @defun sleep-for seconds &optional millisec This function simply pauses for @var{seconds} seconds without updating the display. It pays no attention to available input. It returns @code{nil}. The argument @var{seconds} need not be an integer. If it is floating point, @code{sleep-for} waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, @var{seconds} is rounded down. The optional argument @var{millisec} specifies an additional waiting period measured in milliseconds. This adds to the period specified by @var{seconds}. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero @var{millisec}. Use @code{sleep-for} when you wish to guarantee a delay. @end defun @xref{Time of Day}, for functions to get the current time. @node Quitting @section Quitting @cindex @kbd{C-g} @cindex quitting @cindex interrupt Lisp functions Typing @kbd{C-g} while a Lisp function is running causes Emacs to @dfn{quit} whatever it is doing. This means that control returns to the innermost active command loop. Typing @kbd{C-g} while the command loop is waiting for keyboard input does not cause a quit; it acts as an ordinary input character. In the simplest case, you cannot tell the difference, because @kbd{C-g} normally runs the command @code{keyboard-quit}, whose effect is to quit. However, when @kbd{C-g} follows a prefix key, they combine to form an undefined key. The effect is to cancel the prefix key as well as any prefix argument. In the minibuffer, @kbd{C-g} has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop @emph{within} the minibuffer.) The reason why @kbd{C-g} does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. @kbd{C-g} following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if @kbd{C-g} always quit directly. When @kbd{C-g} does directly quit, it does so by setting the variable @code{quit-flag} to @code{t}. Emacs checks this variable at appropriate times and quits if it is not @code{nil}. Setting @code{quit-flag} non-@code{nil} in any way thus causes a quit. At the level of C code, quitting cannot happen just anywhere; only at the special places that check @code{quit-flag}. The reason for this is that quitting at other places might leave an inconsistency in Emacs's internal state. Because quitting is delayed until a safe place, quitting cannot make Emacs crash. Certain functions such as @code{read-key-sequence} or @code{read-quoted-char} prevent quitting entirely even though they wait for input. Instead of quitting, @kbd{C-g} serves as the requested input. In the case of @code{read-key-sequence}, this serves to bring about the special behavior of @kbd{C-g} in the command loop. In the case of @code{read-quoted-char}, this is so that @kbd{C-q} can be used to quote a @kbd{C-g}. @cindex preventing quitting You can prevent quitting for a portion of a Lisp function by binding the variable @code{inhibit-quit} to a non-@code{nil} value. Then, although @kbd{C-g} still sets @code{quit-flag} to @code{t} as usual, the usual result of this---a quit---is prevented. Eventually, @code{inhibit-quit} will become @code{nil} again, such as when its binding is unwound at the end of a @code{let} form. At that time, if @code{quit-flag} is still non-@code{nil}, the requested quit happens immediately. This behavior is ideal when you wish to make sure that quitting does not happen within a critical section of the program. @cindex @code{read-quoted-char} quitting In some functions (such as @code{read-quoted-char}), @kbd{C-g} is handled in a special way that does not involve quitting. This is done by reading the input with @code{inhibit-quit} bound to @code{t}, and setting @code{quit-flag} to @code{nil} before @code{inhibit-quit} becomes @code{nil} again. This excerpt from the definition of @code{read-quoted-char} shows how this is done; it also shows that normal quitting is permitted after the first character of input. @example (defun read-quoted-char (&optional prompt) "@dots{}@var{documentation}@dots{}" (let ((message-log-max nil) done (first t) (code 0) char) (while (not done) (let ((inhibit-quit first) @dots{}) (and prompt (message "%s-" prompt)) (setq char (read-event)) (if inhibit-quit (setq quit-flag nil))) @r{@dots{}set the variable @code{code}@dots{}}) code)) @end example @defvar quit-flag If this variable is non-@code{nil}, then Emacs quits immediately, unless @code{inhibit-quit} is non-@code{nil}. Typing @kbd{C-g} ordinarily sets @code{quit-flag} non-@code{nil}, regardless of @code{inhibit-quit}. @end defvar @defvar inhibit-quit This variable determines whether Emacs should quit when @code{quit-flag} is set to a value other than @code{nil}. If @code{inhibit-quit} is non-@code{nil}, then @code{quit-flag} has no special effect. @end defvar @defmac with-local-quit body@dots{} This macro executes @var{body} forms in sequence, but allows quitting, at least locally, within @var{body} even if @code{inhibit-quit} was non-@code{nil} outside this construct. It returns the value of the last form in @var{body}, unless exited by quitting, in which case it returns @code{nil}. If @code{inhibit-quit} is @code{nil} on entry to @code{with-local-quit}, it only executes the @var{body}, and setting @code{quit-flag} causes a normal quit. However, if @code{inhibit-quit} is non-@code{nil} so that ordinary quitting is delayed, a non-@code{nil} @code{quit-flag} triggers a special kind of local quit. This ends the execution of @var{body} and exits the @code{with-local-quit} body with @code{quit-flag} still non-@code{nil}, so that another (ordinary) quit will happen as soon as that is allowed. If @code{quit-flag} is already non-@code{nil} at the beginning of @var{body}, the local quit happens immediately and the body doesn't execute at all. This macro is mainly useful in functions that can be called from timers, process filters, process sentinels, @code{pre-command-hook}, @code{post-command-hook}, and other places where @code{inhibit-quit} is normally bound to @code{t}. @end defmac @deffn Command keyboard-quit This function signals the @code{quit} condition with @code{(signal 'quit nil)}. This is the same thing that quitting does. (See @code{signal} in @ref{Errors}.) @end deffn You can specify a character other than @kbd{C-g} to use for quitting. See the function @code{set-input-mode} in @ref{Input Modes}. @node Prefix Command Arguments @section Prefix Command Arguments @cindex prefix argument @cindex raw prefix argument @cindex numeric prefix argument Most Emacs commands can use a @dfn{prefix argument}, a number specified before the command itself. (Don't confuse prefix arguments with prefix keys.) The prefix argument is at all times represented by a value, which may be @code{nil}, meaning there is currently no prefix argument. Each command may use the prefix argument or ignore it. There are two representations of the prefix argument: @dfn{raw} and @dfn{numeric}. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation. Here are the possible values of a raw prefix argument: @itemize @bullet @item @code{nil}, meaning there is no prefix argument. Its numeric value is 1, but numerous commands make a distinction between @code{nil} and the integer 1. @item An integer, which stands for itself. @item A list of one element, which is an integer. This form of prefix argument results from one or a succession of @kbd{C-u}s with no digits. The numeric value is the integer in the list, but some commands make a distinction between such a list and an integer alone. @item The symbol @code{-}. This indicates that @kbd{M--} or @kbd{C-u -} was typed, without following digits. The equivalent numeric value is @minus{}1, but some commands make a distinction between the integer @minus{}1 and the symbol @code{-}. @end itemize We illustrate these possibilities by calling the following function with various prefixes: @example @group (defun display-prefix (arg) "Display the value of the raw prefix arg." (interactive "P") (message "%s" arg)) @end group @end example @noindent Here are the results of calling @code{display-prefix} with various raw prefix arguments: @example M-x display-prefix @print{} nil C-u M-x display-prefix @print{} (4) C-u C-u M-x display-prefix @print{} (16) C-u 3 M-x display-prefix @print{} 3 M-3 M-x display-prefix @print{} 3 ; @r{(Same as @code{C-u 3}.)} C-u - M-x display-prefix @print{} - M-- M-x display-prefix @print{} - ; @r{(Same as @code{C-u -}.)} C-u - 7 M-x display-prefix @print{} -7 M-- 7 M-x display-prefix @print{} -7 ; @r{(Same as @code{C-u -7}.)} @end example Emacs uses two variables to store the prefix argument: @code{prefix-arg} and @code{current-prefix-arg}. Commands such as @code{universal-argument} that set up prefix arguments for other commands store them in @code{prefix-arg}. In contrast, @code{current-prefix-arg} conveys the prefix argument to the current command, so setting it has no effect on the prefix arguments for future commands. Normally, commands specify which representation to use for the prefix argument, either numeric or raw, in the @code{interactive} specification. (@xref{Using Interactive}.) Alternatively, functions may look at the value of the prefix argument directly in the variable @code{current-prefix-arg}, but this is less clean. @defun prefix-numeric-value arg This function returns the numeric meaning of a valid raw prefix argument value, @var{arg}. The argument may be a symbol, a number, or a list. If it is @code{nil}, the value 1 is returned; if it is @code{-}, the value @minus{}1 is returned; if it is a number, that number is returned; if it is a list, the @sc{car} of that list (which should be a number) is returned. @end defun @defvar current-prefix-arg This variable holds the raw prefix argument for the @emph{current} command. Commands may examine it directly, but the usual method for accessing it is with @code{(interactive "P")}. @end defvar @defvar prefix-arg The value of this variable is the raw prefix argument for the @emph{next} editing command. Commands such as @code{universal-argument} that specify prefix arguments for the following command work by setting this variable. @end defvar @defvar last-prefix-arg The raw prefix argument value used by the previous command. @end defvar The following commands exist to set up prefix arguments for the following command. Do not call them for any other reason. @deffn Command universal-argument This command reads input and specifies a prefix argument for the following command. Don't call this command yourself unless you know what you are doing. @end deffn @deffn Command digit-argument arg This command adds to the prefix argument for the following command. The argument @var{arg} is the raw prefix argument as it was before this command; it is used to compute the updated prefix argument. Don't call this command yourself unless you know what you are doing. @end deffn @deffn Command negative-argument arg This command adds to the numeric argument for the next command. The argument @var{arg} is the raw prefix argument as it was before this command; its value is negated to form the new prefix argument. Don't call this command yourself unless you know what you are doing. @end deffn @node Recursive Editing @section Recursive Editing @cindex recursive command loop @cindex recursive editing level @cindex command loop, recursive The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it @dfn{recursive editing}. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command. The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.) All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop. @cindex minibuffer input Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands. @cindex @code{throw} example @kindex exit @cindex exit recursive editing @cindex aborting To invoke a recursive editing level, call the function @code{recursive-edit}. This function contains the command loop; it also contains a call to @code{catch} with tag @code{exit}, which makes it possible to exit the recursive editing level by throwing to @code{exit} (@pxref{Catch and Throw}). If you throw a value other than @code{t}, then @code{recursive-edit} returns normally to the function that called it. The command @kbd{C-M-c} (@code{exit-recursive-edit}) does this. Throwing a @code{t} value causes @code{recursive-edit} to quit, so that control returns to the command loop one level up. This is called @dfn{aborting}, and is done by @kbd{C-]} (@code{abort-recursive-edit}). Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The @kbd{e} command in Rmail uses this technique.) Or, if you wish to give the user different text to edit recursively, create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The @kbd{m} command in Rmail does this.) Recursive edits are useful in debugging. You can insert a call to @code{debug} into a function definition as a sort of breakpoint, so that you can look around when the function gets there. @code{debug} invokes a recursive edit but also provides the other features of the debugger. Recursive editing levels are also used when you type @kbd{C-r} in @code{query-replace} or use @kbd{C-x q} (@code{kbd-macro-query}). @deffn Command recursive-edit @cindex suspend evaluation This function invokes the editor command loop. It is called automatically by the initialization of Emacs, to let the user begin editing. When called from a Lisp program, it enters a recursive editing level. If the current buffer is not the same as the selected window's buffer, @code{recursive-edit} saves and restores the current buffer. Otherwise, if you switch buffers, the buffer you switched to is current after @code{recursive-edit} returns. In the following example, the function @code{simple-rec} first advances point one word, then enters a recursive edit, printing out a message in the echo area. The user can then do any editing desired, and then type @kbd{C-M-c} to exit and continue executing @code{simple-rec}. @example (defun simple-rec () (forward-word 1) (message "Recursive edit in progress") (recursive-edit) (forward-word 1)) @result{} simple-rec (simple-rec) @result{} nil @end example @end deffn @deffn Command exit-recursive-edit This function exits from the innermost recursive edit (including minibuffer input). Its definition is effectively @code{(throw 'exit nil)}. @end deffn @deffn Command abort-recursive-edit This function aborts the command that requested the innermost recursive edit (including minibuffer input), by signaling @code{quit} after exiting the recursive edit. Its definition is effectively @code{(throw 'exit t)}. @xref{Quitting}. @end deffn @deffn Command top-level This function exits all recursive editing levels; it does not return a value, as it jumps completely out of any computation directly back to the main command loop. @end deffn @defun recursion-depth This function returns the current depth of recursive edits. When no recursive edit is active, it returns 0. @end defun @node Disabling Commands @section Disabling Commands @cindex disabled command @dfn{Disabling a command} marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident. @kindex disabled The low-level mechanism for disabling a command is to put a non-@code{nil} @code{disabled} property on the Lisp symbol for the command. These properties are normally set up by the user's init file (@pxref{Init File}) with Lisp expressions such as this: @example (put 'upcase-region 'disabled t) @end example @noindent For a few commands, these properties are present by default (you can remove them in your init file if you wish). If the value of the @code{disabled} property is a string, the message saying the command is disabled includes that string. For example: @example (put 'delete-region 'disabled "Text deleted this way cannot be yanked back!\n") @end example @xref{Disabling,,, emacs, The GNU Emacs Manual}, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs. @deffn Command enable-command command Allow @var{command} (a symbol) to be executed without special confirmation from now on, and alter the user's init file (@pxref{Init File}) so that this will apply to future sessions. @end deffn @deffn Command disable-command command Require special confirmation to execute @var{command} from now on, and alter the user's init file so that this will apply to future sessions. @end deffn @defvar disabled-command-function The value of this variable should be a function. When the user invokes a disabled command interactively, this function is called instead of the disabled command. It can use @code{this-command-keys} to determine what the user typed to run the command, and thus find the command itself. The value may also be @code{nil}. Then all commands work normally, even disabled ones. By default, the value is a function that asks the user whether to proceed. @end defvar @node Command History @section Command History @cindex command history @cindex complex command @cindex history of commands The command loop keeps a history of the complex commands that have been executed, to make it convenient to repeat these commands. A @dfn{complex command} is one for which the interactive argument reading uses the minibuffer. This includes any @kbd{M-x} command, any @kbd{M-:} command, and any command whose @code{interactive} specification reads an argument from the minibuffer. Explicit use of the minibuffer during the execution of the command itself does not cause the command to be considered complex. @defvar command-history This variable's value is a list of recent complex commands, each represented as a form to evaluate. It continues to accumulate all complex commands for the duration of the editing session, but when it reaches the maximum size (@pxref{Minibuffer History}), the oldest elements are deleted as new ones are added. @example @group command-history @result{} ((switch-to-buffer "chistory.texi") (describe-key "^X^[") (visit-tags-table "~/emacs/src/") (find-tag "repeat-complex-command")) @end group @end example @end defvar This history list is actually a special case of minibuffer history (@pxref{Minibuffer History}), with one special twist: the elements are expressions rather than strings. There are a number of commands devoted to the editing and recall of previous commands. The commands @code{repeat-complex-command}, and @code{list-command-history} are described in the user manual (@pxref{Repetition,,, emacs, The GNU Emacs Manual}). Within the minibuffer, the usual minibuffer history commands are available. @node Keyboard Macros @section Keyboard Macros @cindex keyboard macros A @dfn{keyboard macro} is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don't confuse keyboard macros with Lisp macros (@pxref{Macros}). @defun execute-kbd-macro kbdmacro &optional count loopfunc This function executes @var{kbdmacro} as a sequence of events. If @var{kbdmacro} is a string or vector, then the events in it are executed exactly as if they had been input by the user. The sequence is @emph{not} expected to be a single key sequence; normally a keyboard macro definition consists of several key sequences concatenated. If @var{kbdmacro} is a symbol, then its function definition is used in place of @var{kbdmacro}. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled. The argument @var{count} is a repeat count; @var{kbdmacro} is executed that many times. If @var{count} is omitted or @code{nil}, @var{kbdmacro} is executed once. If it is 0, @var{kbdmacro} is executed over and over until it encounters an error or a failing search. If @var{loopfunc} is non-@code{nil}, it is a function that is called, without arguments, prior to each iteration of the macro. If @var{loopfunc} returns @code{nil}, then this stops execution of the macro. @xref{Reading One Event}, for an example of using @code{execute-kbd-macro}. @end defun @defvar executing-kbd-macro This variable contains the string or vector that defines the keyboard macro that is currently executing. It is @code{nil} if no macro is currently executing. A command can test this variable so as to behave differently when run from an executing macro. Do not set this variable yourself. @end defvar @defvar defining-kbd-macro This variable is non-@code{nil} if and only if a keyboard macro is being defined. A command can test this variable so as to behave differently while a macro is being defined. The value is @code{append} while appending to the definition of an existing macro. The commands @code{start-kbd-macro}, @code{kmacro-start-macro} and @code{end-kbd-macro} set this variable---do not set it yourself. The variable is always local to the current terminal and cannot be buffer-local. @xref{Multiple Terminals}. @end defvar @defvar last-kbd-macro This variable is the definition of the most recently defined keyboard macro. Its value is a string or vector, or @code{nil}. The variable is always local to the current terminal and cannot be buffer-local. @xref{Multiple Terminals}. @end defvar @defvar kbd-macro-termination-hook This normal hook is run when a keyboard macro terminates, regardless of what caused it to terminate (reaching the macro end or an error which ended the macro prematurely). @end defvar