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[Emacs-diffs] Changes to emacs/lispref/commands.texi [gnus-5_10-branch]
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From: |
Miles Bader |
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Subject: |
[Emacs-diffs] Changes to emacs/lispref/commands.texi [gnus-5_10-branch] |
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Date: |
Sat, 04 Sep 2004 08:31:25 -0400 |
Index: emacs/lispref/commands.texi
diff -c /dev/null emacs/lispref/commands.texi:1.52.2.1
*** /dev/null Sat Sep 4 12:02:39 2004
--- emacs/lispref/commands.texi Sat Sep 4 12:01:14 2004
***************
*** 0 ****
--- 1,3034 ----
+ @c -*-texinfo-*-
+ @c This is part of the GNU Emacs Lisp Reference Manual.
+ @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2004
+ @c Free Software Foundation, Inc.
+ @c See the file elisp.texi for copying conditions.
+ @setfilename ../info/commands
+ @node Command Loop, Keymaps, Minibuffers, Top
+ @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.
+ * 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 events that translates into a command. It does this by
+ calling the function @code{read-key-sequence}. Your Lisp code can also
+ call this function (@pxref{Key Sequence Input}). Lisp programs can also
+ do input at a lower level with @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}).
+
+ To execute a command requires first reading the arguments for it.
+ This is done 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 command's function body does
+ not use the minibuffer; if you call this command from Lisp code as a
+ function, you must supply the file name string as an ordinary Lisp
+ function argument.
+
+ If the command is a string or vector (i.e., a keyboard macro) then
+ @code{execute-kbd-macro} is used to execute it. You can call this
+ function yourself (@pxref{Keyboard Macros}).
+
+ To terminate the execution of a running command, type @kbd{C-g}. This
+ character causes @dfn{quitting} (@pxref{Quitting}).
+
+ @defvar pre-command-hook
+ The editor command loop runs this normal hook before 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{Hooks}.
+ @end defvar
+
+ @defvar post-command-hook
+ The editor command loop runs this normal hook after each command
+ (including commands terminated prematurely by quitting or by errors),
+ and also when the command loop is first entered. At that time,
+ @code{this-command} describes the command that just ran, and
+ @code{last-command} describes the command before that. @xref{Hooks}.
+ @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 terminates execution of the hook, and clears the hook
+ variable to @code{nil} so as to prevent an infinite loop of errors.
+
+ 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
+
+ A Lisp function becomes a command when its body contains, at top
+ level, a form that calls the special form @code{interactive}. This
+ form does nothing when actually executed, but its presence serves as a
+ flag to indicate that interactive calling is permitted. Its argument
+ controls the reading of arguments for an interactive call.
+
+ @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.
+ @end menu
+
+ @node Using Interactive
+ @subsection Using @code{interactive}
+
+ 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 arg-descriptor
+ @cindex argument descriptors
+ This special form declares that the function in which it appears 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.
+
+ The @code{interactive} form has its effect because the command loop
+ (actually, its subroutine @code{call-interactively}) scans through the
+ function definition looking for it, before calling the function. Once
+ the function is called, all its body forms including the
+ @code{interactive} form are executed, but at this time
+ @code{interactive} simply returns @code{nil} without even evaluating its
+ argument.
+ @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 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.
+ @cindex argument evaluation form
+
+ If this expression reads keyboard input (this includes using the
+ minibuffer), keep in mind that the integer value of point or the mark
+ before reading input may be incorrect after reading input. This is
+ because 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 only
+ after reading the keyboard input:
+
+ @smallexample
+ (interactive
+ (let ((string (read-string "Foo: " nil 'my-history)))
+ (list (region-beginning) (region-end) string)))
+ @end smallexample
+
+ @item
+ @cindex argument prompt
+ It may be a string; then its contents should consist of a code character
+ followed by a prompt (which some code characters use and some ignore).
+ The prompt ends either with the end of the string or with a newline.
+ Here is a simple example:
+
+ @smallexample
+ (interactive "bFrobnicate buffer: ")
+ @end smallexample
+
+ @noindent
+ The code letter @samp{b} says to read the name of an existing buffer,
+ with completion. The buffer name is the sole argument passed to the
+ command. The rest of the string is a prompt.
+
+ If there is a newline character in the string, it terminates the prompt.
+ If the string does not end there, then the rest of the string should
+ contain another code character and prompt, specifying another argument.
+ You can specify any number of arguments in this way.
+
+ @c Emacs 19 feature
+ 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} (@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 the first character in the string is @samp{*}, then an error is
+ signaled if the buffer is read-only.
+
+ @cindex @samp{@@} in @code{interactive}
+ @c Emacs 19 feature
+ If the first character in the string is @samp{@@}, 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.
+
+ You can use @samp{*} and @samp{@@} 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{*} or
+ @samp{@@}).
+ @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
+ @comment node-name, next, previous, up
+ @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 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 name. 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 mouse 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 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 i
+ An irrelevant argument. This code always supplies @code{nil} as
+ the argument's value. No I/O.
+
+ @item k
+ A key sequence (@pxref{Keymap Terminology}). 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.
+
+ 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 is asked to try again. The prefix argument, if any, is not used.
+ Prompt.
+
+ @item N
+ @cindex raw prefix argument usage
+ The numeric prefix argument; but if there is no prefix argument, read a
+ number as with @kbd{n}. Requires 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
+ 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. 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. Any whitespace
+ character terminates the input. (Use @kbd{C-q} to include whitespace in
+ the string.) Other characters that normally terminate a symbol (e.g.,
+ parentheses and brackets) do not do so here. Prompt.
+
+ @item v
+ A variable declared to be a user option (i.e., satisfying the
+ predicate @code{user-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 is read as with @kbd{x}, but then evaluated 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
+ @comment node-name, next, previous, up
+ @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 () ; @address@hidden takes no arguments,}
+ (interactive) ; @r{just moves forward two words.}
+ (forward-word 2))
+ @result{} foo1
+ @end group
+
+ @group
+ (defun foo2 (n) ; @address@hidden takes one argument,}
+ (interactive "p") ; @r{which is the numeric prefix.}
+ (forward-word (* 2 n)))
+ @result{} foo2
+ @end group
+
+ @group
+ (defun foo3 (n) ; @address@hidden 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 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.
+
+ @defun commandp object &optional for-call-interactively
+ Returns @code{t} if @var{object} is suitable for calling interactively;
+ that is, if @var{object} is a command. Otherwise, returns @code{nil}.
+
+ The interactively callable objects include strings and vectors (treated
+ as keyboard macros), lambda expressions that contain a top-level call to
+ @code{interactive}, byte-code function objects made from such lambda
+ expressions, autoload objects that are declared as interactive
+ (address@hidden fourth argument to @code{autoload}), and some of the
+ primitive functions.
+
+ A symbol satisfies @code{commandp} if its function definition
+ satisfies @code{commandp}. Keys and keymaps are not commands.
+ Rather, they are used to look up commands (@pxref{Keymaps}).
+
+ If @var{for-call-interactively} is address@hidden, 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},
+ reading arguments according to its interactive calling specifications.
+ It returns whatever @var{command} returns. 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 address@hidden, 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, 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 return value of
+ @code{this-command-keys} is used. @xref{Definition of this-command-keys}.
+ @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}, along with the optional @var{record-flag}
+ and @var{keys}.
+
+ A symbol is handled by using its function definition 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 @address@hidden }} 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 1)
+ ---------- Buffer: Minibuffer ----------
+ 1 M-x forward-word RET
+ ---------- Buffer: Minibuffer ----------
+ @result{} t
+ @end group
+ @end example
+ @end deffn
+
+ @defun interactive-p
+ This function returns @code{t} if the containing function (the one whose
+ code includes the call to @code{interactive-p}) was called
+ interactively, with the function @code{call-interactively}. (It makes
+ no difference whether @code{call-interactively} was called from Lisp or
+ directly from the editor command loop.) If the containing function was
+ called by Lisp evaluation (or with @code{apply} or @code{funcall}), then
+ it was not called interactively.
+ @end defun
+
+ The most common use of @code{interactive-p} is for deciding whether to
+ print an informative message. As a special exception,
+ @code{interactive-p} returns @code{nil} whenever a keyboard macro is
+ being run. This is to suppress the informative messages and speed
+ execution of the macro.
+
+ For example:
+
+ @example
+ @group
+ (defun foo ()
+ (interactive)
+ (when (interactive-p)
+ (message "foo")))
+ @result{} foo
+ @end group
+
+ @group
+ (defun bar ()
+ (interactive)
+ (setq foobar (list (foo) (interactive-p))))
+ @result{} bar
+ @end group
+
+ @group
+ ;; @r{Type @kbd{M-x foo}.}
+ @print{} foo
+ @end group
+
+ @group
+ ;; @r{Type @kbd{M-x bar}.}
+ ;; @r{This does not print anything.}
+ @end group
+
+ @group
+ foobar
+ @result{} (nil t)
+ @end group
+ @end example
+
+ The other way to do this sort of job is to make the command take an
+ argument @code{print-message} which should be address@hidden in an
+ interactive call, and use the @code{interactive} spec to make sure it is
+ address@hidden Here's how:
+
+ @example
+ (defun foo (&optional print-message)
+ (interactive "p")
+ (when print-message
+ (message "foo")))
+ @end example
+
+ @noindent
+ Defined in this way, the function does display the message when
+ called from a keyboard macro.
+
+ The numeric prefix argument, provided by @samp{p}, is never @code{nil}.
+
+ @node Command Loop Info
+ @comment node-name, next, previous, up
+ @section Information from the Command Loop
+
+ The editor command loop sets several Lisp variables to keep status
+ records for itself and for commands that are run.
+
+ @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 Displays}.
+ @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 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 (address@hidden)
+ (interactive @dots{})
+ (let ((old-this-command this-command))
+ (setq this-command t)
+ @address@hidden the address@hidden
+ (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
+
+ @defun this-command-keys
+ @anchor{Definition of this-command-keys}
+ This function returns a string or vector containing the key sequence
+ that invoked the present command, plus any previous commands that
+ generated the prefix argument for this command. 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{} "^U^X^E"
+ @end group
+ @end example
+ @end defun
+
+ @defun 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
+
+ @tindex clear-this-command-keys
+ @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
+ address@hidden, 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
+ @defvarx last-command-char
+ 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}.
+
+ The alias @code{last-command-char} exists for compatibility with
+ Emacs version 18.
+ @end defvar
+
+ @c Emacs 19 feature
+ @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
+
+ It is not easy to display a value of point in the middle of a sequence
+ of text that has the @code{display} or @code{composition} property. So
+ 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.
+
+ A command can inhibit this feature by setting the variable
+ @code{disable-point-adjustment}:
+
+ @defvar disable-point-adjustment
+ @tindex disable-point-adjustment
+ If this variable is address@hidden when a command returns to the command
+ loop, then the command loop does not check for text properties such as
+ @code{display} and @code{composition}, and does not move point out of
+ sequences that have these properties.
+
+ 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
+ @tindex global-disable-point-adjustment
+ If you set this variable to a address@hidden 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. The events for keyboard activity
+ are characters or symbols; mouse events are always lists. This section
+ describes the representation and meaning of input events in detail.
+
+ @defun eventp object
+ This function returns address@hidden if @var{object} is an input event
+ or event type.
+
+ Note that any 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. Instead, it distinguishes whether the
+ symbol has actually been used in an event that has been read as input in
+ the current Emacs session. If a symbol has not yet been so used,
+ @code{eventp} returns @code{nil}.
+ @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 Events:: Functions to extract info from events.
+ * Strings of Events:: Special considerations for putting
+ keyboard character events in a string.
+ @end menu
+
+ @node Keyboard Events
+ @subsection Keyboard Events
+
+ There are two kinds of input you can get from the keyboard: ordinary
+ keys, and function keys. Ordinary keys correspond to characters; the
+ events they generate are represented in Lisp as characters. The event
+ type of a character event is the character itself (an integer); 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 address@hidden
+ 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 address@hidden
+ control characters).
+
+ @item shift
+ The
+ @tex
+ @math{2^{25}}
+ @end tex
+ @ifnottex
+ 2**25
+ @end ifnottex
+ bit in the character 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 characters.
+
+ 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 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 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 code indicates a character typed with
+ the alt key held down. (On some terminals, the key labeled @key{ALT}
+ is actually the meta key.)
+ @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} places the symbol
+ @code{f1} in the input stream.
+
+ 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{function-key-map} (@pxref{Translating Input}) 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}
+ This is the position where the mouse click occurred. The actual
+ format of @var{position} depends on what part of a window was clicked
+ on. The various formats are described below.
+
+ @item @var{click-count}
+ This is the number of rapid repeated presses so far of the same mouse
+ button. @xref{Repeat Events}.
+ @end table
+
+ For mouse click events in the text area, mode line, header line, or in
+ the marginal areas, @var{position} has this 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
+
+ @table @asis
+ @item @var{window}
+ This is the window in which the click occurred.
+
+ @item @var{pos-or-area}
+ This is the buffer position of the character clicked on in the text
+ area, or if clicked outside the text area, it is the window area in
+ which the click occurred. It is one of the symbols @code{mode-line},
+ @code{header-line}, @code{vertical-line}, @code{left-margin},
+ @code{right-margin}, @code{left-fringe}, or @code{right-fringe}.
+
+ @item @var{x}, @var{y}
+ These are the pixel-denominated coordinates of the click, relative to
+ the top left corner of @var{window}, which is @code{(0 . 0)}.
+ For the mode or header line, @var{y} does not have meaningful data.
+ For the vertical line, @var{x} does not have meaningful data.
+
+ @item @var{timestamp}
+ This is the time at which the event occurred, in milliseconds.
+
+ @item @var{object}
+ This is the object on which the click occurred. It is either
+ @code{nil} if there is no string property, or it has the form
+ (@var{string} . @var{string-pos}) when there is a string-type text
+ property at the click position.
+
+ @item @var{string}
+ This is the string on which the click occurred, including any
+ properties.
+
+ @item @var{string-pos}
+ This is the position in the string on which the click occurred,
+ relevant if properties at the click need to be looked up.
+
+ @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 other events, it is the current buffer position in
+ the window.
+
+ @item @var{col}, @var{row}
+ These are the actual coordinates of the glyph under the @var{x},
+ @var{y} position, possibly padded with default character width
+ glyphs if @var{x} is beyond the last glyph on the line.
+
+ @item @var{image}
+ This is the image object on which the click occurred. It is either
+ @code{nil} if there is no image at the position clicked on, or it is
+ an image object as returned by @code{find-image} if click was in an image.
+
+ @item @var{dx}, @var{dy}
+ These are the pixel-denominated coordinates of the click, relative to
+ the top left corner of @var{object}, which is @code{(0 . 0)}. If
+ @var{object} is @code{nil}, the coordinates are relative to the top
+ left corner of the character glyph clicked on.
+ @end table
+
+ For mouse 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}
+ This is the window whose scroll-bar was clicked on.
+
+ @item @var{area}
+ This is the scroll bar where the click occurred. It is one of the
+ symbols @code{vertical-scroll-bar} or @code{horizontal-scroll-bar}.
+
+ @item @var{portion}
+ This is the distance of the click from the top or left end of
+ the scroll bar.
+
+ @item @var{whole}
+ This is the length of the entire scroll bar.
+
+ @item @var{timestamp}
+ This is the time at which the event occurred, in milliseconds.
+
+ @item @var{part}
+ This is the part of the scroll-bar which was clicked on. It is one
+ of the symbols @code{above-handle}, @code{handle}, @code{below-handle},
+ @code{up}, @code{down}, @code{top}, @code{bottom}, and @code{end-scroll}.
+ @end table
+
+ In one special case, @var{buffer-pos} 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 inserted into the
+ input stream. @xref{Key Sequence Input}.
+
+ @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} @var{buffer-pos1} (@var{x1} . @var{y1}) @var{timestamp1})
+ (@var{window2} @var{buffer-pos2} (@var{x2} . @var{y2}) @var{timestamp2})
+ @var{click-count})
+ @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.
+ Aside from that, the data have the same meanings as in a click event
+ (@pxref{Click Events}). You can access the second element of any mouse
+ event in the same way, with no need to distinguish drag events from
+ others.
+
+ 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} address@hidden 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 (@var{window} @var{buffer-pos} (@var{x} . @var{y})
@var{timestamp}))
+ @end example
+
+ The second element of the list describes the current position of the
+ mouse, just as in a click event (@pxref{Click Events}).
+
+ 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}.
+
+ @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}.
+
+ 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.
+
+ Most X window managers are set up so that just moving the mouse into a
+ window is enough to set the focus there. Emacs appears to do this,
+ because it changes the cursor to solid in the new frame. However, there
+ is no need for the Lisp program to know about the focus change until
+ some other kind of input arrives. So 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{mouse-wheel} event
+ @item (mouse-wheel @var{position} @var{delta})
+ This kind of event is generated by moving a wheel on a mouse (such as
+ the MS Intellimouse). Its effect is typically a kind of scroll or zoom.
+
+ The element @var{delta} describes the amount and direction of the wheel
+ rotation. Its absolute value is the number of increments by which the
+ wheel was rotated. A negative @var{delta} indicates that the wheel was
+ rotated backwards, towards the user, and a positive @var{delta}
+ indicates that the wheel was rotated forward, away from the user.
+
+ The element @var{position} is a list describing the position of the
+ event, in the same format as used in a mouse-click event.
+
+ This kind of event is generated only on some kinds of systems.
+
+ @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, 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{usr1-signal} event
+ @cindex @code{usr2-signal} event
+ @item usr1-signal
+ @itemx usr2-signal
+ 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.
+ @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.
+
+ @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 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
+ (mouse-1 (#<window 18 on NEWS> 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 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
+ (C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
+ (#<window 18 on NEWS> 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 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
+ (M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
+ (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
+ -453816))
+ @end smallexample
+
+ @node Classifying Events
+ @subsection Classifying Events
+ @cindex event type
+
+ 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}.
+ @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 address@hidden if @var{object} is a mouse movement
+ event.
+ @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 Events
+ @subsection Accessing Events
+ @cindex mouse events, accessing the data
+ @cindex accessing data of mouse events
+
+ This section describes convenient functions for accessing the data in
+ a mouse button or motion event.
+
+ These two functions return the starting or ending position of a
+ mouse-button event, as a list of this 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
+
+ @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
+
+ @cindex mouse position list, accessing
+ These functions take a position list as described above, and
+ return various parts of it.
+
+ @defun posn-window position
+ Return the window that @var{position} is in.
+ @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 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 @code{(@var{x} . @var{y})}. These coordinates are relative
+ to the window given by @code{posn-window}.
+
+ This example shows how to convert these window-relative coordinates
+ into frame-relative coordinates:
+
+ @example
+ (defun frame-relative-coordinates (position)
+ "Return frame-relative coordinates from POSITION."
+ (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
+ Return the row and column (in units of the frame's default character
+ height and width) of @var{position}, as a cons cell @code{(@var{col} .
+ @var{row})}. These are computed from the @var{x} and @var{y} values
+ actually found in @var{position}.
+ @end defun
+
+ @defun posn-actual-col-row position
+ Return the actual row and column in @var{position}, as a cons cell
+ @code{(@var{col} . @var{row})}. The values are the actual row number
+ in the window, and the actual character number in that row. It returns
+ @code{nil} if @var{position} does not include actual positions values.
+ You can use @code{posn-col-row} to get approximate values.
+ @end defun
+
+ @defun posn-string position
+ Return the string object in @var{position}, either @code{nil}, or a
+ cons cell @code{(@var{string} . @var{string-pos})}.
+ @end defun
+
+ @defun posn-image position
+ Return the image object in @var{position}, either @code{nil}, or an
+ image @code{(image ...)}.
+ @end defun
+
+ @defun posn-object position
+ Return the image or string object in @var{position}, either
+ @code{nil}, an image @code{(image ...)}, or a cons cell
+ @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 in @var{position} as a cons cell @code{(@var{dx}
+ . @var{dy})}. If the @var{position} is a buffer position, return the
+ relative position in the character at that position.
+ @end defun
+
+ @defun posn-object-width-height position
+ Return the pixel width and height of the object in @var{position} as a
+ cons cell @code{(@var{width} . @var{height})}. If the @var{position}
+ is a buffer position, return the size of the character at that position.
+ @end defun
+
+ @cindex mouse event, timestamp
+ @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
+ 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.
+ @end defun
+
+ 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
+ address@hidden 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
+
+ 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. @xref{Translating Input}, for features you
+ can use for translating or modifying input events while reading them.
+
+ 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.
+ * 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
+ @cindex key sequence
+ 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.
+
+ 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.
+
+ In the example below, the prompt @samp{?} is displayed in the echo area,
+ and the user types @kbd{C-x C-f}.
+
+ @example
+ (read-key-sequence "?")
+
+ @group
+ ---------- Echo Area ----------
+ address@hidden 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
+ 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}
+ If an input character is an upper-case letter 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.
+
+ 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{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 mouse events, in special parts of frame
+ When mouse events occur in special parts of a window, 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{header-line},
+ @code{horizontal-scroll-bar}, @code{menu-bar}, @code{mode-line},
+ @code{vertical-line}, and @code{vertical-scroll-bar}. 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
+ (#<window 6 on NEWS> mode-line
+ (40 . 63) 5959987))]
+ @end example
+
+ @defvar num-input-keys
+ @c Emacs 19 feature
+ 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
+
+ @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
+
+ @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 those that read a
+ single event.
+
+ None of the three functions below suppresses quitting.
+
+ @defun read-event &optional prompt inherit-input-method
+ This function reads and returns the next event of command input, waiting
+ if necessary until an event is available. Events can come directly from
+ the user or from a keyboard macro.
+
+ If the optional argument @var{prompt} is address@hidden, it should be a
+ string to display in the echo area as a prompt. Otherwise,
+ @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 address@hidden, then the current input
+ method (if any) is employed to make it possible to enter a
+ address@hidden character. Otherwise, input method handling is disabled
+ for reading this event.
+
+ If @code{cursor-in-echo-area} is address@hidden, 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 @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
+ This function reads and returns a character of command input. 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}.
+
+ In the first example, 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
+ This function reads and returns a character of command input. If the
+ user generates an event which is not a character,
+ @code{read-char-exclusive} ignores it and reads another event, until it
+ gets a character. The arguments work as in @code{read-event}.
+ @end defun
+
+ @node Invoking the Input Method
+ @subsection Invoking the 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 address@hidden, 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 address@hidden, 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
+ address@hidden, 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} (@pxref{Strings of Events}).
+
+ Normally you add events to the front of this list, so that the events
+ most recently unread will be reread first.
+ @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
+
+ @defvar unread-command-char
+ This variable holds a character to be read as command input.
+ A value of -1 means ``empty''.
+
+ This variable is mostly obsolete now that you can use
+ @code{unread-command-events} instead; it exists only to support programs
+ written for Emacs versions 18 and earlier.
+ @end defvar
+
+ @defun input-pending-p
+ @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.
+ @end defun
+
+ @defvar last-input-event
+ @defvarx last-input-char
+ 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
+
+ The alias @code{last-input-char} exists for compatibility with
+ Emacs version 18.
+ @end defvar
+
+ @defun discard-input
+ @cindex flush input
+ @cindex discard input
+ @cindex terminate keyboard macro
+ 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
+ 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.
+
+ Events that are handled in this way 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.
+
+ These 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} and
+ @code{delete-frame} 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{Active Keymaps}).
+
+ @node Waiting
+ @section Waiting for Elapsed Time or Input
+ @cindex pausing
+ @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 value is @code{t} if @code{sit-for} waited the full
+ time with no input arriving (see @code{input-pending-p} in @ref{Event
+ Input Misc}). Otherwise, the value is @code{nil}.
+
+ The argument @var{seconds} need not be an integer. If it is a floating
+ point number, @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 a convenient way to request a
+ redisplay, without any delay. @xref{Forcing Redisplay}.
+
+ If @var{nodisp} is address@hidden, then @code{sit-for} does not
+ redisplay, but it still returns as soon as input is available (or when
+ the timeout elapses).
+
+ Iconifying or deiconifying a frame makes @code{sit-for} return, because
+ that generates an event. @xref{Misc Events}.
+
+ The usual purpose of @code{sit-for} is to give the user time to read
+ text that you display.
+
+ 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 a floating
+ point number, @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}
+ address@hidden 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 prevent quitting
+ You can prevent quitting for a portion of a Lisp function by binding
+ the variable @code{inhibit-quit} to a address@hidden 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 address@hidden, 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)
+ "@address@hidden@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)))
+ @address@hidden the variable @address@hidden)
+ code))
+ @end example
+
+ @defvar quit-flag
+ If this variable is address@hidden, then Emacs quits immediately, unless
+ @code{inhibit-quit} is address@hidden Typing @kbd{C-g} ordinarily sets
+ @code{quit-flag} address@hidden, 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
+ address@hidden, then @code{quit-flag} has no special effect.
+ @end defvar
+
+ @defmac with-local-quit address@hidden
+ This macro executes @var{forms} in sequence, but allows quitting, at
+ least locally, within @var{body} even if @code{inhibit-quit} was
+ address@hidden outside this construct. It returns the value of the
+ last form in @var{forms}.
+
+ If @code{inhibit-quit} is @code{nil} on entry to @code{with-local-quit},
+ it only executes the @var{forms}, and setting @code{quit-flag} causes
+ a normal quit. However, if @code{inhibit-quit} is address@hidden so
+ that ordinary quitting is delayed, a address@hidden @code{quit-flag}
+ triggers a special kind of local quit. This ends the execution of
+ @var{forms} and exits the @code{with-local-quit} form with
+ @code{quit-flag} still address@hidden, so that another (ordinary) quit
+ will happen as soon as that is allowed. If @code{quit-flag} is
+ already address@hidden at the beginning of @var{forms}, the local quit
+ happens immediately and they don't execute at all.
+
+ This macro is mainly useful in functions that can be called from
+ timers, @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{Terminal Input}.
+
+ @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} declaration.
+ (@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}).
+
+ @defun 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.
+
+ 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 defun
+
+ @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
+ address@hidden @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 address@hidden, 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 address@hidden 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 commands
+ @code{start-kbd-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 Displays}.
+ @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 Displays}.
+ @end defvar
+
+ @defvar kbd-macro-termination-hook
+ This normal hook (@pxref{Standard Hooks}) 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
+
+ @ignore
+ arch-tag: e34944ad-7d5c-4980-be00-36a5fe54d4b1
+ @end ignore
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