[chise/xemacs-chise.git] / info / lispref.info-16

This is Info file ../info/lispref.info, produced by Makeinfo version
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INFO-DIR-SECTION XEmacs Editor
START-INFO-DIR-ENTRY
* Lispref: (lispref).           XEmacs Lisp Reference Manual.
END-INFO-DIR-ENTRY

   Edition History:

   GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU
Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid
Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994
XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995
GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp
Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp
Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp
Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May,
November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998

   Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software
Foundation, Inc.  Copyright (C) 1994, 1995 Sun Microsystems, Inc.
Copyright (C) 1995, 1996 Ben Wing.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the section entitled "GNU General Public License" is included
exactly as in the original, and provided that the entire resulting
derived work is distributed under the terms of a permission notice
identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the section entitled "GNU General Public License"
may be included in a translation approved by the Free Software
Foundation instead of in the original English.

\1f
File: lispref.info,  Node: High-Level Completion,  Next: Reading File Names,  Prev: Completion Commands,  Up: Completion

High-Level Completion  Functions
--------------------------------

   This section describes the higher-level convenient functions for
reading certain sorts of names with completion.

   In most cases, you should not call these functions in the middle of a
Lisp function.  When possible, do all minibuffer input as part of
reading the arguments for a command, in the `interactive' spec.  *Note
Defining Commands::.

 - Function: read-buffer PROMPT &optional DEFAULT EXISTING
     This function reads the name of a buffer and returns it as a
     string.  The argument DEFAULT is the default name to use, the
     value to return if the user exits with an empty minibuffer.  If
     non-`nil', it should be a string or a buffer.  It is mentioned in
     the prompt, but is not inserted in the minibuffer as initial input.

     If EXISTING is non-`nil', then the name specified must be that of
     an existing buffer.  The usual commands to exit the minibuffer do
     not exit if the text is not valid, and <RET> does completion to
     attempt to find a valid name.  (However, DEFAULT is not checked
     for validity; it is returned, whatever it is, if the user exits
     with the minibuffer empty.)

     In the following example, the user enters `minibuffer.t', and then
     types <RET>.  The argument EXISTING is `t', and the only buffer
     name starting with the given input is `minibuffer.texi', so that
     name is the value.

          (read-buffer "Buffer name? " "foo" t)
          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears,
          ;;   with an empty minibuffer:
          
          ---------- Buffer: Minibuffer ----------
          Buffer name? (default foo) -!-
          ---------- Buffer: Minibuffer ----------
          
          ;; The user types `minibuffer.t <RET>'.
               => "minibuffer.texi"

 - Function: read-command PROMPT
     This function reads the name of a command and returns it as a Lisp
     symbol.  The argument PROMPT is used as in `read-from-minibuffer'.
     Recall that a command is anything for which `commandp' returns
     `t', and a command name is a symbol for which `commandp' returns
     `t'.  *Note Interactive Call::.

          (read-command "Command name? ")
          
          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears with an empty minibuffer:
          
          ---------- Buffer: Minibuffer ----------
          Command name?
          ---------- Buffer: Minibuffer ----------

     If the user types `forward-c <RET>', then this function returns
     `forward-char'.

     The `read-command' function is a simplified interface to the
     function `completing-read'.  It uses the variable `obarray' so as
     to complete in the set of extant Lisp symbols, and it uses the
     `commandp' predicate so as to accept only command names:

          (read-command PROMPT)
          ==
          (intern (completing-read PROMPT obarray
                                   'commandp t nil))

 - Function: read-variable PROMPT
     This function reads the name of a user variable and returns it as a
     symbol.

          (read-variable "Variable name? ")
          
          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears,
          ;;   with an empty minibuffer:
          
          ---------- Buffer: Minibuffer ----------
          Variable name? -!-
          ---------- Buffer: Minibuffer ----------

     If the user then types `fill-p <RET>', `read-variable' returns
     `fill-prefix'.

     This function is similar to `read-command', but uses the predicate
     `user-variable-p' instead of `commandp':

          (read-variable PROMPT)
          ==
          (intern
           (completing-read PROMPT obarray
                            'user-variable-p t nil))

\1f
File: lispref.info,  Node: Reading File Names,  Next: Programmed Completion,  Prev: High-Level Completion,  Up: Completion

Reading File Names
------------------

   Here is another high-level completion function, designed for reading
a file name.  It provides special features including automatic insertion
of the default directory.

 - Function: read-file-name PROMPT &optional DIRECTORY DEFAULT EXISTING
          INITIAL
     This function reads a file name in the minibuffer, prompting with
     PROMPT and providing completion.  If DEFAULT is non-`nil', then
     the function returns DEFAULT if the user just types <RET>.
     DEFAULT is not checked for validity; it is returned, whatever it
     is, if the user exits with the minibuffer empty.

     If EXISTING is non-`nil', then the user must specify the name of
     an existing file; <RET> performs completion to make the name valid
     if possible, and then refuses to exit if it is not valid.  If the
     value of EXISTING is neither `nil' nor `t', then <RET> also
     requires confirmation after completion.  If EXISTING is `nil',
     then the name of a nonexistent file is acceptable.

     The argument DIRECTORY specifies the directory to use for
     completion of relative file names.  If `insert-default-directory'
     is non-`nil', DIRECTORY is also inserted in the minibuffer as
     initial input.  It defaults to the current buffer's value of
     `default-directory'.

     If you specify INITIAL, that is an initial file name to insert in
     the buffer (after DIRECTORY, if that is inserted).  In this case,
     point goes at the beginning of INITIAL.  The default for INITIAL
     is `nil'--don't insert any file name.  To see what INITIAL does,
     try the command `C-x C-v'.

     Here is an example:

          (read-file-name "The file is ")
          
          ;; After evaluation of the preceding expression,
          ;;   the following appears in the minibuffer:
          
          ---------- Buffer: Minibuffer ----------
          The file is /gp/gnu/elisp/-!-
          ---------- Buffer: Minibuffer ----------

     Typing `manual <TAB>' results in the following:

          ---------- Buffer: Minibuffer ----------
          The file is /gp/gnu/elisp/manual.texi-!-
          ---------- Buffer: Minibuffer ----------

     If the user types <RET>, `read-file-name' returns the file name as
     the string `"/gp/gnu/elisp/manual.texi"'.

 - User Option: insert-default-directory
     This variable is used by `read-file-name'.  Its value controls
     whether `read-file-name' starts by placing the name of the default
     directory in the minibuffer, plus the initial file name if any.
     If the value of this variable is `nil', then `read-file-name' does
     not place any initial input in the minibuffer (unless you specify
     initial input with the INITIAL argument).  In that case, the
     default directory is still used for completion of relative file
     names, but is not displayed.

     For example:

          ;; Here the minibuffer starts out with the default directory.
          (let ((insert-default-directory t))
            (read-file-name "The file is "))
          
          ---------- Buffer: Minibuffer ----------
          The file is ~lewis/manual/-!-
          ---------- Buffer: Minibuffer ----------
          
          ;; Here the minibuffer is empty and only the prompt
          ;;   appears on its line.
          (let ((insert-default-directory nil))
            (read-file-name "The file is "))
          
          ---------- Buffer: Minibuffer ----------
          The file is -!-
          ---------- Buffer: Minibuffer ----------

\1f
File: lispref.info,  Node: Programmed Completion,  Prev: Reading File Names,  Up: Completion

Programmed Completion
---------------------

   Sometimes it is not possible to create an alist or an obarray
containing all the intended possible completions.  In such a case, you
can supply your own function to compute the completion of a given
string.  This is called "programmed completion".

   To use this feature, pass a symbol with a function definition as the
COLLECTION argument to `completing-read'.  The function
`completing-read' arranges to pass your completion function along to
`try-completion' and `all-completions', which will then let your
function do all the work.

   The completion function should accept three arguments:

   * The string to be completed.

   * The predicate function to filter possible matches, or `nil' if
     none.  Your function should call the predicate for each possible
     match, and ignore the possible match if the predicate returns
     `nil'.

   * A flag specifying the type of operation.

   There are three flag values for three operations:

   * `nil' specifies `try-completion'.  The completion function should
     return the completion of the specified string, or `t' if the
     string is a unique and exact match already, or `nil' if the string
     matches no possibility.

     If the string is an exact match for one possibility, but also
     matches other longer possibilities, the function should return the
     string, not `t'.

   * `t' specifies `all-completions'.  The completion function should
     return a list of all possible completions of the specified string.

   * `lambda' specifies a test for an exact match.  The completion
     function should return `t' if the specified string is an exact
     match for some possibility; `nil' otherwise.

   It would be consistent and clean for completion functions to allow
lambda expressions (lists that are functions) as well as function
symbols as COLLECTION, but this is impossible.  Lists as completion
tables are already assigned another meaning--as alists.  It would be
unreliable to fail to handle an alist normally because it is also a
possible function.  So you must arrange for any function you wish to
use for completion to be encapsulated in a symbol.

   Emacs uses programmed completion when completing file names.  *Note
File Name Completion::.

\1f
File: lispref.info,  Node: Yes-or-No Queries,  Next: Multiple Queries,  Prev: Completion,  Up: Minibuffers

Yes-or-No Queries
=================

   This section describes functions used to ask the user a yes-or-no
question.  The function `y-or-n-p' can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences.  `yes-or-no-p' is suitable for more
momentous questions, since it requires three or four characters to
answer.  Variations of these functions can be used to ask a yes-or-no
question using a dialog box, or optionally using one.

   If either of these functions is called in a command that was invoked
using the mouse, then it uses a dialog box or pop-up menu to ask the
question.  Otherwise, it uses keyboard input.

   Strictly speaking, `yes-or-no-p' uses the minibuffer and `y-or-n-p'
does not; but it seems best to describe them together.

 - Function: y-or-n-p PROMPT
     This function asks the user a question, expecting input in the echo
     area.  It returns `t' if the user types `y', `nil' if the user
     types `n'.  This function also accepts <SPC> to mean yes and <DEL>
     to mean no.  It accepts `C-]' to mean "quit", like `C-g', because
     the question might look like a minibuffer and for that reason the
     user might try to use `C-]' to get out.  The answer is a single
     character, with no <RET> needed to terminate it.  Upper and lower
     case are equivalent.

     "Asking the question" means printing PROMPT in the echo area,
     followed by the string `(y or n) '.  If the input is not one of
     the expected answers (`y', `n', `<SPC>', `<DEL>', or something
     that quits), the function responds `Please answer y or n.', and
     repeats the request.

     This function does not actually use the minibuffer, since it does
     not allow editing of the answer.  It actually uses the echo area
     (*note The Echo Area::.), which uses the same screen space as the
     minibuffer.  The cursor moves to the echo area while the question
     is being asked.

     The answers and their meanings, even `y' and `n', are not
     hardwired.  The keymap `query-replace-map' specifies them.  *Note
     Search and Replace::.

     In the following example, the user first types `q', which is
     invalid.  At the next prompt the user types `y'.

          (y-or-n-p "Do you need a lift? ")
          
          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears in the echo area:

          ---------- Echo area ----------
          Do you need a lift? (y or n)
          ---------- Echo area ----------
          
          ;; If the user then types `q', the following appears:
          ---------- Echo area ----------
          Please answer y or n.  Do you need a lift? (y or n)
          ---------- Echo area ----------
          
          ;; When the user types a valid answer,
          ;;   it is displayed after the question:
          ---------- Echo area ----------
          Do you need a lift? (y or n) y
          ---------- Echo area ----------

     We show successive lines of echo area messages, but only one
     actually appears on the screen at a time.

 - Function: yes-or-no-p PROMPT
     This function asks the user a question, expecting input in the
     minibuffer.  It returns `t' if the user enters `yes', `nil' if the
     user types `no'.  The user must type <RET> to finalize the
     response.  Upper and lower case are equivalent.

     `yes-or-no-p' starts by displaying PROMPT in the echo area,
     followed by `(yes or no) '.  The user must type one of the
     expected responses; otherwise, the function responds `Please answer
     yes or no.', waits about two seconds and repeats the request.

     `yes-or-no-p' requires more work from the user than `y-or-n-p' and
     is appropriate for more crucial decisions.

     Here is an example:

          (yes-or-no-p "Do you really want to remove everything? ")
          
          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears,
          ;;   with an empty minibuffer:

          ---------- Buffer: minibuffer ----------
          Do you really want to remove everything? (yes or no)
          ---------- Buffer: minibuffer ----------

     If the user first types `y <RET>', which is invalid because this
     function demands the entire word `yes', it responds by displaying
     these prompts, with a brief pause between them:

          ---------- Buffer: minibuffer ----------
          Please answer yes or no.
          Do you really want to remove everything? (yes or no)
          ---------- Buffer: minibuffer ----------

 - Function: yes-or-no-p-dialog-box PROMPT
     This function asks the user a "y or n" question with a popup dialog
     box.  It returns `t' if the answer is "yes".  PROMPT is the string
     to display to ask the question.

   The following functions ask a question either in the minibuffer or a
dialog box, depending on whether the last user event (which presumably
invoked this command) was a keyboard or mouse event.  When XEmacs is
running on a window system, the functions `y-or-n-p' and `yes-or-no-p'
are replaced with the following functions, so that menu items bring up
dialog boxes instead of minibuffer questions.

 - Function: y-or-n-p-maybe-dialog-box PROMPT
     This function asks user a "y or n" question, using either a dialog
     box or the minibuffer, as appropriate.

 - Function: yes-or-no-p-maybe-dialog-box PROMPT
     This function asks user a "yes or no" question, using either a
     dialog box or the minibuffer, as appropriate.

\1f
File: lispref.info,  Node: Multiple Queries,  Next: Reading a Password,  Prev: Yes-or-No Queries,  Up: Minibuffers

Asking Multiple Y-or-N Questions
================================

   When you have a series of similar questions to ask, such as "Do you
want to save this buffer" for each buffer in turn, you should use
`map-y-or-n-p' to ask the collection of questions, rather than asking
each question individually.  This gives the user certain convenient
facilities such as the ability to answer the whole series at once.

 - Function: map-y-or-n-p PROMPTER ACTOR LIST &optional HELP
          ACTION-ALIST
     This function, new in Emacs 19, asks the user a series of
     questions, reading a single-character answer in the echo area for
     each one.

     The value of LIST specifies the objects to ask questions about.
     It should be either a list of objects or a generator function.  If
     it is a function, it should expect no arguments, and should return
     either the next object to ask about, or `nil' meaning stop asking
     questions.

     The argument PROMPTER specifies how to ask each question.  If
     PROMPTER is a string, the question text is computed like this:

          (format PROMPTER OBJECT)

     where OBJECT is the next object to ask about (as obtained from
     LIST).

     If not a string, PROMPTER should be a function of one argument
     (the next object to ask about) and should return the question
     text.  If the value is a string, that is the question to ask the
     user.  The function can also return `t' meaning do act on this
     object (and don't ask the user), or `nil' meaning ignore this
     object (and don't ask the user).

     The argument ACTOR says how to act on the answers that the user
     gives.  It should be a function of one argument, and it is called
     with each object that the user says yes for.  Its argument is
     always an object obtained from LIST.

     If the argument HELP is given, it should be a list of this form:

          (SINGULAR PLURAL ACTION)

     where SINGULAR is a string containing a singular noun that
     describes the objects conceptually being acted on, PLURAL is the
     corresponding plural noun, and ACTION is a transitive verb
     describing what ACTOR does.

     If you don't specify HELP, the default is `("object" "objects"
     "act on")'.

     Each time a question is asked, the user may enter `y', `Y', or
     <SPC> to act on that object; `n', `N', or <DEL> to skip that
     object; `!' to act on all following objects; <ESC> or `q' to exit
     (skip all following objects); `.' (period) to act on the current
     object and then exit; or `C-h' to get help.  These are the same
     answers that `query-replace' accepts.  The keymap
     `query-replace-map' defines their meaning for `map-y-or-n-p' as
     well as for `query-replace'; see *Note Search and Replace::.

     You can use ACTION-ALIST to specify additional possible answers
     and what they mean.  It is an alist of elements of the form `(CHAR
     FUNCTION HELP)', each of which defines one additional answer.  In
     this element, CHAR is a character (the answer); FUNCTION is a
     function of one argument (an object from LIST); HELP is a string.

     When the user responds with CHAR, `map-y-or-n-p' calls FUNCTION.
     If it returns non-`nil', the object is considered "acted upon",
     and `map-y-or-n-p' advances to the next object in LIST.  If it
     returns `nil', the prompt is repeated for the same object.

     If `map-y-or-n-p' is called in a command that was invoked using the
     mouse--more precisely, if `last-nonmenu-event' (*note Command Loop
     Info::.) is either `nil' or a list--then it uses a dialog box or
     pop-up menu to ask the question.  In this case, it does not use
     keyboard input or the echo area.  You can force use of the mouse
     or use of keyboard input by binding `last-nonmenu-event' to a
     suitable value around the call.

     The return value of `map-y-or-n-p' is the number of objects acted
     on.

\1f
File: lispref.info,  Node: Reading a Password,  Next: Minibuffer Misc,  Prev: Multiple Queries,  Up: Minibuffers

Reading a Password
==================

   To read a password to pass to another program, you can use the
function `read-passwd'.

 - Function: read-passwd PROMPT &optional CONFIRM DEFAULT
     This function reads a password, prompting with PROMPT.  It does
     not echo the password as the user types it; instead, it echoes `.'
     for each character in the password.

     The optional argument CONFIRM, if non-`nil', says to read the
     password twice and insist it must be the same both times.  If it
     isn't the same, the user has to type it over and over until the
     last two times match.

     The optional argument DEFAULT specifies the default password to
     return if the user enters empty input.  It is translated to `.'
     and inserted in the minibuffer. If DEFAULT is `nil', then
     `read-passwd' returns the null string in that case.

 - User Option: passwd-invert-frame-when-keyboard-grabbed
     If non-nil swap the foreground and background colors of all faces
     while reading a password.  Default values is `t' unless feature
     `infodock' is provided.

 - User Option: passwd-echo
     This specifies the character echoed when typing a password.  When
     nil, nothing is echoed.

\1f
File: lispref.info,  Node: Minibuffer Misc,  Prev: Reading a Password,  Up: Minibuffers

Minibuffer Miscellany
=====================

   This section describes some basic functions and variables related to
minibuffers.

 - Command: exit-minibuffer
     This command exits the active minibuffer.  It is normally bound to
     keys in minibuffer local keymaps.

 - Command: self-insert-and-exit
     This command exits the active minibuffer after inserting the last
     character typed on the keyboard (found in `last-command-char';
     *note Command Loop Info::.).

 - Command: previous-history-element N
     This command replaces the minibuffer contents with the value of the
     Nth previous (older) history element.

 - Command: next-history-element N
     This command replaces the minibuffer contents with the value of the
     Nth more recent history element.

 - Command: previous-matching-history-element PATTERN
     This command replaces the minibuffer contents with the value of the
     previous (older) history element that matches PATTERN (a regular
     expression).

 - Command: next-matching-history-element PATTERN
     This command replaces the minibuffer contents with the value of
     the next (newer) history element that matches PATTERN (a regular
     expression).

 - Function: minibuffer-prompt
     This function returns the prompt string of the currently active
     minibuffer.  If no minibuffer is active, it returns `nil'.

 - Function: minibuffer-prompt-width
     This function returns the display width of the prompt string of the
     currently active minibuffer.  If no minibuffer is active, it
     returns 0.

 - Variable: minibuffer-setup-hook
     This is a normal hook that is run whenever the minibuffer is
     entered.  *Note Hooks::.

 - Variable: minibuffer-exit-hook
     This is a normal hook that is run whenever the minibuffer is
     exited.  *Note Hooks::.

 - Variable: minibuffer-help-form
     The current value of this variable is used to rebind `help-form'
     locally inside the minibuffer (*note Help Functions::.).

 - Function: active-minibuffer-window
     This function returns the currently active minibuffer window, or
     `nil' if none is currently active.

 - Function: minibuffer-window &optional FRAME
     This function returns the minibuffer window used for frame FRAME.
     If FRAME is `nil', that stands for the current frame.  Note that
     the minibuffer window used by a frame need not be part of that
     frame--a frame that has no minibuffer of its own necessarily uses
     some other frame's minibuffer window.

 - Function: window-minibuffer-p WINDOW
     This function returns non-`nil' if WINDOW is a minibuffer window.

   It is not correct to determine whether a given window is a
minibuffer by comparing it with the result of `(minibuffer-window)',
because there can be more than one minibuffer window if there is more
than one frame.

 - Function: minibuffer-window-active-p WINDOW
     This function returns non-`nil' if WINDOW, assumed to be a
     minibuffer window, is currently active.

 - Variable: minibuffer-scroll-window
     If the value of this variable is non-`nil', it should be a window
     object.  When the function `scroll-other-window' is called in the
     minibuffer, it scrolls this window.

   Finally, some functions and variables deal with recursive minibuffers
(*note Recursive Editing::.):

 - Function: minibuffer-depth
     This function returns the current depth of activations of the
     minibuffer, a nonnegative integer.  If no minibuffers are active,
     it returns zero.

 - User Option: enable-recursive-minibuffers
     If this variable is non-`nil', you can invoke commands (such as
     `find-file') that use minibuffers even while the minibuffer window
     is active.  Such invocation produces a recursive editing level for
     a new minibuffer.  The outer-level minibuffer is invisible while
     you are editing the inner one.

     This variable only affects invoking the minibuffer while the
     minibuffer window is selected.   If you switch windows while in the
     minibuffer, you can always invoke minibuffer commands while some
     other window is selected.

   In FSF Emacs 19, if a command name has a property
`enable-recursive-minibuffers' that is non-`nil', then the command can
use the minibuffer to read arguments even if it is invoked from the
minibuffer.  The minibuffer command `next-matching-history-element'
(normally `M-s' in the minibuffer) uses this feature.

   This is not implemented in XEmacs because it is a kludge.  If you
want to explicitly set the value of `enable-recursive-minibuffers' in
this fashion, just use an evaluated interactive spec and bind
`enable-recursive-minibuffers' while reading from the minibuffer.  See
the definition of `next-matching-history-element' in `lisp/minibuf.el'.

\1f
File: lispref.info,  Node: Command Loop,  Next: Keymaps,  Prev: Minibuffers,  Up: Top

Command Loop
************

   When you run XEmacs, it enters the "editor command loop" almost
immediately.  This loop reads events, 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.
* Events::              What input looks like when you read it.
* Reading Input::       How to read input events from the keyboard or mouse.
* Waiting::             Waiting for user input or elapsed time.
* Quitting::            How `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.

\1f
File: lispref.info,  Node: Command Overview,  Next: Defining Commands,  Up: Command Loop

Command Loop Overview
=====================

   The command loop in XEmacs is a standard event loop, reading events
one at a time with `next-event' and handling them with
`dispatch-event'.  An event is typically a single user action, such as
a keypress, mouse movement, or menu selection; but they can also be
notifications from the window system, informing XEmacs that (for
example) part of its window was just uncovered and needs to be redrawn.
*Note Events::.  Pending events are held in a first-in, first-out list
called the "event queue": events are read from the head of the list,
and newly arriving events are added to the tail.  In this way, events
are always processed in the order in which they arrive.

   `dispatch-event' does most of the work of handling user actions.
The first thing it must do is put the events together into a key
sequence, which is a sequence of events that translates into a command.
It does this by consulting the active keymaps, which specify what the
valid key sequences are and how to translate them into commands.  *Note
Key Lookup::, for information on how this is done.  The result of the
translation should be a keyboard macro or an interactively callable
function.  If the key is `M-x', then it reads the name of another
command, which it then calls.  This is done by the command
`execute-extended-command' (*note Interactive Call::.).

   To execute a command requires first reading the arguments for it.
This is done by calling `command-execute' (*note Interactive Call::.).
For commands written in Lisp, the `interactive' specification says how
to read the arguments.  This may use the prefix argument (*note Prefix
Command Arguments::.) or may read with prompting in the minibuffer
(*note Minibuffers::.).  For example, the command `find-file' has an
`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
`execute-kbd-macro' is used to execute it.  You can call this function
yourself (*note Keyboard Macros::.).

   To terminate the execution of a running command, type `C-g'.  This
character causes "quitting" (*note Quitting::.).

 - Variable: pre-command-hook
     The editor command loop runs this normal hook before each command.
     At that time, `this-command' contains the command that is about to
     run, and `last-command' describes the previous command.  *Note
     Hooks::.

 - Variable: post-command-hook
     The editor command loop runs this normal hook after each command.
     (In FSF Emacs, it is also run when the command loop is entered, or
     reentered after an error or quit.)  At that time, `this-command'
     describes the command that just ran, and `last-command' describes
     the command before that.  *Note Hooks::.

   Quitting is suppressed while running `pre-command-hook' and
`post-command-hook'.  If an error happens while executing one of these
hooks, it terminates execution of the hook, but that is all it does.

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File: lispref.info,  Node: Defining Commands,  Next: Interactive Call,  Prev: Command Overview,  Up: Command Loop

Defining Commands
=================

   A Lisp function becomes a command when its body contains, at top
level, a form that calls the special form `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 `interactive'.
* Interactive Codes::     The standard letter-codes for reading arguments
                             in various ways.
* Interactive Examples::  Examples of how to read interactive arguments.

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File: lispref.info,  Node: Using Interactive,  Next: Interactive Codes,  Up: Defining Commands

Using `interactive'
-------------------

   This section describes how to write the `interactive' form that
makes a Lisp function an interactively-callable command.

 - Special Form: interactive ARG-DESCRIPTOR
     This special form declares that the function in which it appears
     is a command, and that it may therefore be called interactively
     (via `M-x' or by entering a key sequence bound to it).  The
     argument 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
     ARG-DESCRIPTOR has no effect.

     The `interactive' form has its effect because the command loop
     (actually, its subroutine `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
     `interactive' form are executed, but at this time `interactive'
     simply returns `nil' without even evaluating its argument.

   There are three possibilities for the argument ARG-DESCRIPTOR:

   * It may be omitted or `nil'; then the command is called with no
     arguments.  This leads quickly to an error if the command requires
     one or more arguments.

   * 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.

     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 *not* to do:

          (interactive
           (list (region-beginning) (region-end)
                 (read-string "Foo: " nil 'my-history)))

     Here's how to avoid the problem, by examining point and the mark
     only after reading the keyboard input:

          (interactive
           (let ((string (read-string "Foo: " nil 'my-history)))
             (list (region-beginning) (region-end) string)))

   * 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:

          (interactive "bFrobnicate buffer: ")

     The code letter `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.

     The prompt string can use `%' to include previous argument values
     (starting with the first argument) in the prompt.  This is done
     using `format' (*note 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:

          (interactive "bBuffer to rename: \nsRename buffer %s to: ")

     If the first character in the string is `*', then an error is
     signaled if the buffer is read-only.

     If the first character in the string is `@', 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.

     If the first character in the string is `_', then this command will
     not cause the region to be deactivated when it completes; that is,
     `zmacs-region-stays' will be set to `t' when the command exits
     successfully.

     You can use `*', `@', and `_' 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 `*',
     `@', or `_').

 - Function: function-interactive FUNCTION
     This function retrieves the interactive specification of FUNCTION,
     which may be any funcallable object.  The specification will be
     returned as the list of the symbol `interactive' and the specs.  If
     FUNCTION is not interactive, `nil' will be returned.

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File: lispref.info,  Node: Interactive Codes,  Next: Interactive Examples,  Prev: Using Interactive,  Up: Defining Commands

Code Characters for `interactive'
---------------------------------

   The code character descriptions below contain a number of key words,
defined here as follows:

Completion
     Provide completion.  <TAB>, <SPC>, and <RET> perform name
     completion because the argument is read using `completing-read'
     (*note Completion::.).  `?' displays a list of possible
     completions.

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.

Default
     A default value of some sort is used if the user enters no text in
     the minibuffer.  The default depends on the code character.

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.

Prompt
     A prompt immediately follows the code character.  The prompt ends
     either with the end of the string or with a newline.

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.

   Here are the code character descriptions for use with `interactive':

`*'
     Signal an error if the current buffer is read-only.  Special.

`@'
     Select the window mentioned in the first mouse event in the key
     sequence that invoked this command.  Special.

`_'
     Do not cause the region to be deactivated when this command
     completes.  Special.

`a'
     A function name (i.e., a symbol satisfying `fboundp').  Existing,
     Completion, Prompt.

`b'
     The name of an existing buffer.  By default, uses the name of the
     current buffer (*note Buffers::.).  Existing, Completion, Default,
     Prompt.

`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.

`c'
     A character.  The cursor does not move into the echo area.  Prompt.

`C'
     A command name (i.e., a symbol satisfying `commandp').  Existing,
     Completion, Prompt.

`d'
     The position of point, as an integer (*note Point::.).  No I/O.

`D'
     A directory name.  The default is the current default directory of
     the current buffer, `default-directory' (*note System
     Environment::.).  Existing, Completion, Default, Prompt.

`e'
     The last mouse-button or misc-user event in the key sequence that
     invoked the command.  No I/O.

     You can use `e' more than once in a single command's interactive
     specification.  If the key sequence that invoked the command has N
     mouse-button or misc-user events, the Nth `e' provides the Nth
     such event.

`f'
     A file name of an existing file (*note File Names::.).  The default
     directory is `default-directory'.  Existing, Completion, Default,
     Prompt.

`F'
     A file name.  The file need not exist.  Completion, Default,
     Prompt.

`k'
     A key sequence (*note 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
     vector of events.  The cursor does not move into the echo area.
     Prompt.

     This kind of input is used by commands such as `describe-key' and
     `global-set-key'.

`K'
     A key sequence, whose definition you intend to change.  This works
     like `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.

`m'
     The position of the mark, as an integer.  No I/O.

`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.

`N'
     The raw prefix argument.  If the prefix argument is `nil', then
     read a number as with `n'.  Requires a number.  *Note Prefix
     Command Arguments::.  Prompt.

`p'
     The numeric prefix argument.  (Note that this `p' is lower case.)
     No I/O.

`P'
     The raw prefix argument.  (Note that this `P' is upper case.)  No
     I/O.

`r'
     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.

`s'
     Arbitrary text, read in the minibuffer and returned as a string
     (*note Text from Minibuffer::.).  Terminate the input with either
     <LFD> or <RET>.  (`C-q' may be used to include either of these
     characters in the input.)  Prompt.

`S'
     An interned symbol whose name is read in the minibuffer.  Any
     whitespace character terminates the input.  (Use `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.

`v'
     A variable declared to be a user option (i.e., satisfying the
     predicate `user-variable-p').  *Note High-Level Completion::.
     Existing, Completion, Prompt.

`x'
     A Lisp object, specified with its read syntax, terminated with a
     <LFD> or <RET>.  The object is not evaluated.  *Note Object from
     Minibuffer::.  Prompt.

`X'
     A Lisp form is read as with `x', but then evaluated so that its
     value becomes the argument for the command.  Prompt.

\1f
File: lispref.info,  Node: Interactive Examples,  Prev: Interactive Codes,  Up: Defining Commands

Examples of Using `interactive'
-------------------------------

   Here are some examples of `interactive':

     (defun foo1 ()              ; `foo1' takes no arguments,
         (interactive)           ;   just moves forward two words.
         (forward-word 2))
          => foo1
     
     (defun foo2 (n)             ; `foo2' takes one argument,
         (interactive "p")       ;   which is the numeric prefix.
         (forward-word (* 2 n)))
          => foo2
     
     (defun foo3 (n)             ; `foo3' takes one argument,
         (interactive "nCount:") ;   which is read with the Minibuffer.
         (forward-word (* 2 n)))
          => foo3
     
     (defun three-b (b1 b2 b3)
       "Select three existing buffers.
     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))
          => three-b
     (three-b "*scratch*" "declarations.texi" "*mail*")
          => nil

\1f
File: lispref.info,  Node: Interactive Call,  Next: Command Loop Info,  Prev: Defining Commands,  Up: Command Loop

Interactive Call
================

   After the command loop has translated a key sequence into a
definition, it invokes that definition using the function
`command-execute'.  If the definition is a function that is a command,
`command-execute' calls `call-interactively', which reads the arguments
and calls the command.  You can also call these functions yourself.

 - Function: commandp OBJECT
     Returns `t' if OBJECT is suitable for calling interactively; that
     is, if OBJECT is a command.  Otherwise, returns `nil'.

     The interactively callable objects include strings and vectors
     (treated as keyboard macros), lambda expressions that contain a
     top-level call to `interactive', compiled-function objects made
     from such lambda expressions, autoload objects that are declared
     as interactive (non-`nil' fourth argument to `autoload'), and some
     of the primitive functions.

     A symbol is `commandp' if its function definition is `commandp'.

     Keys and keymaps are not commands.  Rather, they are used to look
     up commands (*note Keymaps::.).

     See `documentation' in *Note Accessing Documentation::, for a
     realistic example of using `commandp'.

 - Function: call-interactively COMMAND &optional RECORD-FLAG
     This function calls the interactively callable function COMMAND,
     reading arguments according to its interactive calling
     specifications.  An error is signaled if 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 RECORD-FLAG is the symbol `lambda', the interactive calling
     arguments for `command' are read and returned as a list, but the
     function is not called on them.

     If RECORD-FLAG is `t', then this command and its arguments are
     unconditionally added to the list `command-history'.  Otherwise,
     the command is added only if it uses the minibuffer to read an
     argument.  *Note Command History::.

 - Function: command-execute COMMAND &optional RECORD-FLAG
     This function executes COMMAND as an editing command.  The
     argument COMMAND must satisfy the `commandp' predicate; i.e., it
     must be an interactively callable function or a keyboard macro.

     A string or vector as COMMAND is executed with
     `execute-kbd-macro'.  A function is passed to
     `call-interactively', along with the optional RECORD-FLAG.

     A symbol is handled by using its function definition in its place.
     A symbol with an `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.

 - Command: execute-extended-command PREFIX-ARGUMENT
     This function reads a command name from the minibuffer using
     `completing-read' (*note Completion::.).  Then it uses
     `command-execute' to call the specified command.  Whatever that
     command returns becomes the value of `execute-extended-command'.

     If the command asks for a prefix argument, it receives the value
     PREFIX-ARGUMENT.  If `execute-extended-command' is called
     interactively, the current raw prefix argument is used for
     PREFIX-ARGUMENT, and thus passed on to whatever command is run.

     `execute-extended-command' is the normal definition of `M-x', so
     it uses the string `M-x ' as a prompt.  (It would be better to
     take the prompt from the events used to invoke
     `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.

          (execute-extended-command 1)
          ---------- Buffer: Minibuffer ----------
          1 M-x forward-word RET
          ---------- Buffer: Minibuffer ----------
               => t

 - Function: interactive-p
     This function returns `t' if the containing function (the one that
     called `interactive-p') was called interactively, with the function
     `call-interactively'.  (It makes no difference whether
     `call-interactively' was called from Lisp or directly from the
     editor command loop.)  If the containing function was called by
     Lisp evaluation (or with `apply' or `funcall'), then it was not
     called interactively.

     The most common use of `interactive-p' is for deciding whether to
     print an informative message.  As a special exception,
     `interactive-p' returns `nil' whenever a keyboard macro is being
     run.  This is to suppress the informative messages and speed
     execution of the macro.

     For example:

          (defun foo ()
            (interactive)
            (and (interactive-p)
                 (message "foo")))
               => foo
          
          (defun bar ()
            (interactive)
            (setq foobar (list (foo) (interactive-p))))
               => bar
          
          ;; Type `M-x foo'.
               -| foo
          
          ;; Type `M-x bar'.
          ;; This does not print anything.
          
          foobar
               => (nil t)