User:FellowIndy/sandbox

@c -*-texinfo-*- @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 and why you usually shouldn't. @end 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.
 * Keyboard Input::     How your program can read characters from the keyboard.
 * 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,
 * 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.

@node Command Overview, Defining Commands, Command Loop, Command Loop @section Command Loop Overview

The first thing the command loop must do is read a key sequence, which is a sequence of characters 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{Keyboard Input}). Lisp programs can also do input at a lower level with @code{read-char} or discard pending input with @code{discard-input}.

The key sequence is translated into a command through the keymaps of the current buffer. @xref{Keymaps}, 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 is used instead. This is done by the command @code{execute-extended-command} (@pxref{Interactive Call}).

Once the command is read, it must be executed, which includes reading arguments to be given to 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 (i.e., a keyboard macro) then the function @code{execute-kbd-macro} is used to execute it. You can call this function yourself (@pxref{Keyboard Macros}).

If a command runs away, typing @kbd{C-g} will terminate its execution immediately. This is called @dfn{quitting} (@pxref{Quitting}).

@node Defining Commands, Interactive Call, Command Overview, Command Loop @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 which 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 in various ways. @end menu
 * Using Interactive::    General rules for @code{interactive}.
 * Interactive Codes::    The standard letter-codes for reading arguments
 * Interactive Examples:: Examples of how to read interactive arguments.

@node Using Interactive, Interactive Codes, Defining Commands, Defining Commands @subsection Using @code{interactive}

This section describes how to write the @code{interactive} form that makes a Lisp function an interactively-callable command.

@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 the way the arguments to the command are to be computed when the command is called interactively.

A command may be called from Lisp programs like any other function, but then the arguments are supplied by the caller 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

@item @cindex argument prompt It may be a string; then its contents should consist of a code character followed by a prompt (if required for that code character). The prompt ends either with the end of the string or with a newline. Here is a simple example:

@example (interactive "bFrobnicate buffer: ") @end example

@noindent The code letter @samp{b} says to read the name of an existing buffer, with completion. The buffer name will be 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. Any number of arguments may be specified in this way.

@cindex @samp{*} in interactive @kindex buffer-read-only If the first character in the string is @samp{*}, then an error is signaled if the buffer is read-only. Otherwise, the following character is the first code character. @end itemize

@node Interactive Codes, Interactive Examples, Using Interactive, Defining Commands @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 Prompt A prompt immediately follows the code character. The prompt ends either with the end of the string or with a newline.

@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. @end table

@cindex reading interactive arguments Here are the code character descriptions for use with @code{interactive}:

@table @samp @item a A function name (i.e., a symbol which is @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, 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 a number (@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{System Environment}). Existing, Completion, Default, Prompt.

@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 k A key sequence (@pxref{Keymap Terms}). This keeps reading characters until a command (or undefined command) is found in the current key maps. The key sequence argument is represented as a string. 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 m @cindex marker argument The position of the mark as a number. No I/O.

@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 raw prefix argument. If the prefix argument is @code{nil}, then a number is read as with @kbd{n}. Requires a number. Prompt.

@item p @cindex numeric prefix argument usage The numeric prefix argument. (Note that this @samp{p} is lower case.) No I/O.@refill

@item P The raw prefix argument. (Note that this @samp{P} is upper case.) @xref{Prefix Command Arguments}. No I/O.@refill

@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 @key{LFD} 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 @code{user-variable-p}). @xref{High-Level Completion}. Existing, Completion, Prompt.

@item x A Lisp object specified in printed representation, terminated with a @key{LFD} 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. @end table

@node Interactive Examples,, Interactive Codes, Defining Commands @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 (defun foo1                ; @r{@code{foo1} takes no arguments,}    (interactive)             ; @r{just moves forward two words.}    (forward-word 2)) @result{} foo1

(defun foo2 (n)              ; @r{@code{foo2} takes one argument,}    (interactive "p")         ; @r{which is the numeric prefix.}    (forward-word (* 2 n))) @result{} foo2

(defun foo3 (n)              ; @r{@code{foo3} takes one argument,}    (interactive "nCount:")   ; @r{which is read with the Minibuffer.}    (forward-word (* 2 n))) @result{} foo3

(defun three-b (b1 b2 b3) "Select three existing buffers (prompting for them in the Minibuffer).  Put them into three windows, selecting the last one."    (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 (three-b "*scratch*" "declarations.texi" "*mail*") @result{} nil @end example

@node Interactive Call, Command Loop Info, Defining Commands, Command Loop @section Interactive Call @cindex interactive call

After the command loop has translated a key sequence into a definition, it invokes that definition using the function @code{command-execute}. If the definition is a function that is a command, @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 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 (treated as keyboard macros), lambda expressions that contain a top-level call to @code{interactive}, autoload objects that are declared as interactive (non-@code{nil} fourth argument to @code{autoload}), and some of the primitive functions.

A symbol is @code{commandp} if its function definition is @code{commandp}.

Keys and keymaps are not commands. Rather, they are used to look up commands (@pxref{Keymaps}).

See @code{documentation} in @ref{Accessing Documentation}, for a realistic example of using @code{commandp}. @end defun

@defun call-interactively command &optional record-flag This function calls the interactively callable function @var{command}, reading arguments according to its interactive calling specifications. An error is signaled if @var{command} cannot be called interactively (i.e., it is not a command). Note that strings are not accepted, even though they are considered commands.

@cindex record command history If @var{record-flag} is non-@code{nil}, then this command and its arguments are unconditionally added to the list @code{command-history}. Otherwise, the command is added only if it uses the minibuffer to read an argument. @xref{Command History}. @end defun

@defun command-execute command &optional record-flag @cindex keyboard macro execution This function executes @var{command} as an editing command. The argument @var{command} must satisfy the @code{commandp} predicate; i.e., it must be an interactively callable function or a string.

A string 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}.

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. @end defun

@deffn Command execute-extended-command prefix-argument @cindex read command name This primitive 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, the value @var{prefix-argument} is supplied. If @code{execute-extended-command} is called interactively, the current raw prefix argument is used for @var{prefix-argument}, and thus passed on to whatever command is run.

@c !!! Should this be @kindex? @cindex @kbd{M-x} @code{execute-extended-command} is the normal definition of @kbd{M-x}, so it uses the string @w{@samp{M-x }} as a prompt. (It would be better to take the prompt from the characters 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 (execute-extended-command 1) -- Buffer: Minibuffer -- M-x forward-word RET -- Buffer: Minibuffer -- @result{} t @end example @end deffn

@defun interactive-p This function returns @code{t} if the containing function (the one that called @code{interactive-p}) was called interactively, with @code{call-interactively}. (It makes no difference whether @code{call-interactively} was called from Lisp or directly from the editor command loop.) Note that if the containing function was called by Lisp evaluation (or with @code{apply} or @code{funcall}), then it was not called interactively.

The usual application 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 (defun foo  (interactive)  (and (interactive-p) (message "foo"))) @result{} foo

@group (defun bar  (interactive)  (setq foobar (list (foo) (interactive-p)))) @result{} bar @end group

@print{} foo
 * @r{Type @kbd{M-x foo}.}


 * @r{Type @kbd{M-x bar}.}
 * @r{This does not print anything.}

foobar @result{} (nil t) @end example @end defun

@node Command Loop Info, Keyboard Input, Interactive Call, Command Loop @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 set by copying the value of @code{this-command} when a command returns to the command loop, except when the command specifies a prefix argument for the following command. @end defvar

@defvar this-command @cindex current command This variable records the name of the command now being executed by editor command loop. Like @code{last-command}, it is normally a symbol with a function definition.

This variable is set by the command loop just before the command is run, and its value is copied into @code{last-command} when the command finishes (unless the command specifies a prefix argument for the following command).

@cindex kill command repetition Some commands change the value of this variable during their execution, simply as a flag for whatever command runs next. In particular, the functions that kill 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

@defun this-command-keys This function returns a string containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command.

@example (this-command-keys) ;; @r{Now type @kbd{C-u C-x C-e}.} @result{} "^U^X^E" @end example @end defun

@defvar last-command-char This variable is set to the last character that was typed on the terminal and was 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 last-command-char ;; @r{Now type @kbd{C-u C-x C-e}.} @result{} 5 @end example

@noindent The value is 5 because that is the @sc{ASCII} code for @kbd{C-e}. @end defvar

@defvar echo-keystrokes This variable determines how much time should elapse before command characters are echoed. Its value must be an integer, which specifies the number of seconds to wait before echoing. If the user types a prefix key (say @kbd{C-x}) and then delays this many seconds before continuing, the key @kbd{C-x} is echoed in the echo area. Any subsequent characters in the same command will be echoed as well.

If the value is zero, then command input is not echoed. @end defvar

@node Keyboard Input, Quitting, Command Loop Info, Command Loop @section Keyboard Input

The editor command loop reads keyboard input using @code{read-key-sequence}, which uses @code{read-char}. These and other functions for keyboard 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.

@defun read-char This function reads a character from the command input (either from direct keyboard input or from an executing keyboard macro), and returns it.

No message is displayed to indicate that keyboard input is expected. If you want to display a message, call @code{message} first. If @code{cursor-in-echo-area} is non-@code{nil}, then the cursor moves to the echo area, to the end of any message displayed there. Otherwise the cursor does not move. @xref{The Echo Area}.

In the first example, the user types @kbd{1} (which is @sc{ASCII} code 49). The second example shows a keyboard macro definition that calls @code{read-char} from the minibuffer. @code{read-char} reads the keyboard macro's very next character, which is @kbd{1}. The value of this function is displayed in the echo area by the command @code{eval-expression}.

@example (read-char) @result{} 49

(symbol-function 'foo) @result{} "^[^[(read-char)^M1" (execute-kbd-macro foo) @print{} 49 @result{} nil @end example @end defun

@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 up to two more octal digits (but stopping if a non-octal digit is found) and returns the character represented by those digits as an octal number.

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 printed in the echo area and 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")

-- Echo Area -- What character-@kbd{177} -- Echo Area --

@result{} 127 @end example @end defun

@defun read-key-sequence prompt @cindex key sequence This function reads a key sequence and returns it as a string. It keeps reading characters until it has accumulated a full key sequence; that is, enough characters to specify a non-prefix command using the current local and global keymaps. @code{read-key-sequence} is used by the command loop to read command input.

@cindex upper case key sequence @cindex downcasing in @code{lookup-key} If an input character is an upper case letter and has no definition, but the lower case equivalent is defined, then the character is converted to lower case. Note that @code{lookup-key} does not perform case conversion in this way.

Quitting is suppressed inside @code{read-key-sequence}. In other words, a @kbd{C-g} typed while reading with this function is treated like any other character, and @code{quit-flag} is not set. @xref{Quitting}.

The argument @var{prompt} is either a string to be displayed in the echo area as a prompt, or @code{nil}, meaning that no prompt is displayed.

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 "?")

-- Echo Area -- ?@kbd{C-x C-f} -- Echo Area --

@result{} "^X^F" @end example @end defun

@defvar unread-command-char @cindex next input @cindex peeking at input This variable holds a character waiting to be read as the next input from the command input stream, or to the integer @minus{}1 if no character is waiting. The variable is used because in some cases an input function reads a character and then decides not to use it. Storing the character in this variable causes it to be processed normally by the command loop or when @code{read-char} is next called.

@cindex prefix argument unreading For example, the function that governs prefix arguments reads any number of digits. When it finds a non-digit character, it must unread the character so that it becomes input for the next command. Likewise, incremental search uses this feature to unread a control character used to terminate the search. @end defvar

@defun input-pending-p @cindex waiting for command key input This function determines whether command input is currently available. It returns immediately, with value @code{t} if there is input, @code{nil} otherwise. On rare occasions it may return @code{t} when no input is available. @end defun

@defvar last-input-char This variable records the last terminal input character read, whether as part of a command or explicitly by a Lisp program.

In the example below, a character is read (the character @kbd{1}, @sc{ASCII} code 49). It becomes the value of @code{last-input-char}, while @kbd{C-e} (from the @kbd{C-x C-e} command used to evaluate this expression) remains the value of @code{last-command-char}.

@example (progn (print (read-char))      (print last-command-char)       last-input-char) @print{} 49 @print{} 5 @result{} 49 @end example @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, any characters that have been typed are discarded.

@example (progn (sleep-for 2) (discard-input)) @result{} nil @end example @end defun

@node Quitting, Prefix Command Arguments, Keyboard Input, Command Loop @section Quitting @cindex @kbd{C-g} @cindex quitting

Typing @kbd{C-g} while the command loop has run a Lisp function 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, the result is 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} quit directly.

@kbd{C-g} causes a quit by setting the variable @code{quit-flag} to a non-@code{nil} value. Emacs checks this variable at appropriate times and quits if it is not @code{nil}. Setting @code{quit-flag} non-@code{nil} in any way thus causes a quit.

At the level of C code, quits cannot happen just anywhere; only at the special places which 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}.

You can prevent quitting for a portion of a Lisp function by binding the variable @code{inhibit-quit} to a non-@code{nil} value. Then, although @kbd{C-g} still sets @code{quit-flag} to @code{t} as usual, the usual result of this---a quit---is prevented. Eventually, @code{inhibit-quit} will become @code{nil} again, such as when its binding is unwound at the end of a @code{let} form. At that time, if @code{quit-flag} is still non-@code{nil}, the requested quit happens immediately. This behavior is ideal for a ``critical section'', where you wish to make sure that quitting does not happen within that part of the program.

@cindex @code{isearch-forward} quitting In some functions (such as @code{read-quoted-char}), @kbd{C-g} is handled in a special way which does not involve quitting. This is done by reading the input with @code{inhibit-quit} bound to @code{t} and setting @code{quit-flag} to @code{nil} before @code{inhibit-quit} becomes @code{nil} again. This excerpt from the definition of @code{read-quoted-char} shows how this is done; it also shows that normal quitting is permitted after the first character of input.

@example (defun read-quoted-char (&optional prompt) "@dots{}@var{documentation}@dots{}"  (let ((count 0) (code 0) char) (while (< count 3)     (let ((inhibit-quit (zerop count))            (help-form nil)) (and prompt (message "%s-" prompt)) (setq char (read-char)) (if inhibit-quit (setq quit-flag nil)))     @dots{}) (logand 255 code))) @end example

@defvar quit-flag If this variable is non-@code{nil}, then Emacs quits immediately, unless @code{inhibit-quit} is non-@code{nil}. Typing @kbd{C-g} sets @code{quit-flag} non-@code{nil}, regardless of @code{inhibit-quit}. @end defvar

@defvar inhibit-quit This variable determines whether Emacs should quit when @code{quit-flag} is set to a value other than @code{nil}. If @code{inhibit-quit} is non-@code{nil}, then @code{quit-flag} has no special effect. @end defvar

@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, Recursive Editing, Quitting, Command Loop @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 represented by a value that is always available (though it may be @code{nil}, meaning there is 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

The various possibilities may be illustrated by calling the following function with various prefixes:

@group @example (defun print-prefix (arg) "Print the value of the raw prefix arg at point."  (interactive "P")  (message "%s" arg)) @end example @end group

@noindent Here are the results of calling @code{print-prefix} with various raw prefix arguments:

@example M-x print-prefix @print{} nil

C-u    M-x print-prefix  @print{} (4)

C-u C-u M-x print-prefix @print{} (16)

C-u 3  M-x print-prefix  @print{} 3

M-3    M-x print-prefix  @print{} 3      ; @r{(Same as @code{C-u 3}.)}

C-u -  M-x print-prefix  @print{} -

M- -   M-x print-prefix  @print{} -      ; @r{(Same as @code{C-u -}.)}

C-u -7 M-x print-prefix  @print{} -7

M- -7  M-x print-prefix  @print{} -7     ; @r{(Same as @code{C-u -7}.)} @end example

There are two variables used 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{Interactive Call}.) Alternatively, functions may look at the value of the prefix argument directly in the variable @code{current-prefix-arg}, but this is less clean.

Don't call @code{universal-argument}, @code{digit-argument}, or @code{negative-argument} unless you intend to let the user enter the prefix argument for the @emph{next} command.

@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

@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 any other symbol, 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 is the value of the raw prefix argument for the @emph{current} command. Commands may examine it directly, but the usual way to access 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 that specify prefix arguments for the following command work by setting this variable. @end defvar

@node Recursive Editing, Disabling Commands, Prefix Command Arguments, Command Loop @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 is never exited until the Emacs is killed. 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 finished. (The special commands for exiting are always available, but 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 has a command to go back to the previous mode. (This technique is used by the @kbd{w} command in Rmail.) 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, Command History, Recursive Editing, Command Loop @section Disabling Commands @cindex disabled command

@dfn{Disabling a command} marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.

@kindex disabled The low-level mechanism for disabling a command is to put a non-@code{nil} @code{disabled} property on the Lisp symbol for the command. These properties are normally set up by the user's @file{.emacs} 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 and may be removed by the @file{.emacs} file.

If the value of the @code{disabled} property is a string, that string is included in the message printed when the command is used:

@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} to be executed without special confirmation from now on. The user's @file{.emacs} file is optionally altered 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. The user's @file{.emacs} file is optionally altered so that this will apply to future sessions. @end deffn

@defvar disabled-command-hook The value of this variable is a function to be called instead of any command that is disabled (i.e., that has a non-@code{nil} disabled property). By default, the value of @code{disabled-command-hook} is a function defined to ask the user whether to proceed. @end defvar

@node Command History, Keyboard Macros, Disabling Commands, Command Loop @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-ESC} 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 all but the first (most recent) thirty elements are deleted when a garbage collection takes place (@pxref{Garbage Collection}).

@example command-history @result{} ((switch-to-buffer "chistory.texi")   (describe-key "^X^[")    (visit-tags-table "~/emacs/src/")    (find-tag "repeat-complex-command")) @end example @end defvar

There are a number of commands and even two entire modes devoted to facilitating 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}).

@defvar repeat-complex-command-map The value of this variable is a sparse keymap used by the minibuffer inside of @code{read-complex-command}. @end defvar

@node Keyboard Macros,, Command History, Command Loop @section Keyboard Macros @cindex keyboard macros

A @dfn{keyboard macro} is a canned sequence of keystrokes that can be considered a command and made the definition of a key. Don't confuse keyboard macros with Lisp macros (@pxref{Macros}).

@defun execute-kbd-macro macro &optional count This function executes @var{macro} as a string of editor commands. If @var{macro} is a string, then the characters in that string are executed exactly as if they had been typed as command input.

If @var{macro} is a symbol, then its function definition is used in place of @var{macro}. If that is another symbol, this process repeats. Eventually the result should be a string. If the result is neither a symbol nor a string, an error is signaled.

The argument @var{count} is a repeat count; @var{macro} is executed that many times. If @var{count} is omitted or @code{nil}, @var{macro} is executed once. If it is 0, @var{macro} is executed over and over until it encounters an error or a failing search. @end defun

@defvar last-kbd-macro This variable is the definition of the most recently defined keyboard macro. Its value is a string or @code{nil}. @end defvar

@defvar executing-macro This variable contains the string that defines the keyboard macro that is currently executing. It is @code{nil} if no macro is currently executing. @end defvar

@defvar defining-kbd-macro This variable indicates whether a keyboard macro is being defined. It is set to @code{t} by @code{start-kbd-macro}, and @code{nil} by @code{end-kbd-macro}. It is not hard to use this variable to make a command behave differently when run from a keyboard macro (perhaps indirectly by calling @code{interactive-p}). However, do not set this variable yourself. @end defvar

The user-level commands for defining, running and editing keyboard macros include @code{call-last-kbd-macro}, @code{insert-kbd-macro}, @code{start-kbd-macro}, @code{end-kbd-macro}, @code{kbd-macro-query}, and @code{name-last-kbd-macro}. They are described in the user's manual (@pxref{Keyboard Macros,,, emacs, The GNU Emacs Manual}).