OS/2 Professional/OS2PRO194.ISO/os2/prgramer/unix/info/elisp.i10

GNU Info File | 1993-06-14 | 50.9 KB | 1,244 lines

This is Info file elisp, produced by Makeinfo-1.47 from the input file
elisp.texi.

   This file documents GNU Emacs Lisp.

   This is edition 1.03 of the GNU Emacs Lisp Reference Manual, for
Emacs Version 18.

   Published by the Free Software Foundation, 675 Massachusetts Avenue,
Cambridge, MA 02139 USA

   Copyright (C) 1990 Free Software Foundation, Inc.

   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.


File: elisp,  Node: Output Functions,  Prev: Output Streams,  Up: Streams

Output Functions
----------------

   This section describes the Lisp functions and variables that pertain
to printing.

   Some of the Emacs printing functions add quoting characters to the
output when necessary so that it can be read properly.  The quoting
characters used are `\' and `"'; they are used to distinguish strings
from symbols, and to prevent punctuation characters in strings and
symbols from being taken as delimiters.  *Note Printed
Representation::, for full details.  You specify quoting or no quoting
by the choice of printing function.

   If the text is to be read back into Lisp, then it is best to print
with quoting characters to avoid ambiguity.  Likewise, if the purpose is
to describe a Lisp object clearly for a Lisp programmer.  However, if
the purpose of the output is to look nice for humans, then it is better
to print without quoting.

   In the functions below, STREAM stands for an output stream. (See the
previous section for a description of output streams.)  If STREAM is
`nil' or omitted, it defaults to the value of `standard-output'.

 -- Function: print OBJECT &optional STREAM
     The `print' is a convenient way of printing.  It outputs the
     printed representation of OBJECT to STREAM, printing in addition
     one newline before OBJECT and another after it.  Quoting
     characters are used.  `print' returns OBJECT.  For example:

          (progn (print 'The\ cat\ in)
                 (print "the hat")
                 (print " came back"))
               -|
               -| The\ cat\ in
               -|
               -| "the hat"
               -|
               -| " came back"
               -|
               => " came back"

 -- Function: prin1 OBJECT &optional STREAM
     This function outputs the printed representation of OBJECT to
     STREAM.  It does not print any spaces or newlines to separate
     output as `print' does, but it does use quoting characters just
     like `print'.  It returns OBJECT.

          (progn (prin1 'The\ cat\ in)
                 (prin1 "the hat")
                 (prin1 " came back"))
               -| The\ cat\ in"the hat"" came back"
               => " came back"

 -- Function: prin1-to-string OBJECT
     This function returns a string containing the text that `prin1'
     would have printed for the same argument.

          (prin1-to-string 'foo)
               => "foo"
          (prin1-to-string (mark-marker))
               => "#<marker at 2773 in strings.texi>"

     See `format', in *Note String Conversion::, for other ways to
     obtain the printed representation of a Lisp object as a string.

 -- Function: princ OBJECT &optional STREAM
     This function outputs the printed representation of OBJECT to
     STREAM.  It returns OBJECT.

     This function is intended to produce output that is readable by
     people, not by `read', so quoting characters are not used and
     double-quotes are not printed around the contents of strings.  It
     does not add any spacing between calls.

          (progn
            (princ 'The\ cat)
            (princ " in the \"hat\""))
               -| The cat in the "hat"
               => " in the \"hat\""

 -- Function: terpri &optional STREAM
     This function outputs a newline to STREAM.  The name stands for
     "terminate print".

 -- Variable: standard-output
     The value of this variable is the default output stream, used when
     the STREAM argument is omitted or `nil'.

 -- Variable: print-escape-newlines
     If this variable is non-`nil', then newline characters in strings
     are printed as `\n'.  Normally they are printed as actual newlines.

     This variable affects the print functions `prin1' and `print'; it
     does not affect `princ' in Emacs 18, but this may be changed. Here
     is an example using `prin1':

          (prin1 "a\nb")
               -| "a
               -| b"
               => "a
               => b"

          (let ((print-escape-newlines t))
            (prin1 "a\nb"))
               -| "a\nb"
               => "a
               => b"

     In the second expression, the local binding of
     `print-escape-newlines' is in effect during the call to `prin1',
     but not during the printing of the result.

 -- Variable: print-length
     The value of this variable is the maximum number of elements of a
     list that will be printed.  If the list being printed has more
     than this many elements, then it is abbreviated with an ellipsis.

     If the value is `nil' (the default), then there is no limit.

          (setq print-length 2)
               => 2
          (print '(1 2 3 4 5))
               -| (1 2 ...)
               => (1 2 ...)

 -- Function: write-char CHARACTER &optional STREAM
     This function outputs CHARACTER to STREAM.  It returns CHARACTER.


File: elisp,  Node: Minibuffers,  Next: Command Loop,  Prev: Streams,  Up: Top

Minibuffers
***********

   A "minibuffer" is a special buffer used by Emacs commands to read
arguments more complicated than the single numeric prefix argument.
These arguments include file names, buffer names, and command names (as
in `M-x').  The minibuffer is displayed on the bottom line of the
screen, in the same place as the echo area, but only while it is in use
for reading an argument.

* Menu:

* Intro to Minibuffers::      Basic information about minibuffers.
* Text from Minibuffer::      How to read a straight text string.
* Object from Minibuffer::    How to read a Lisp object or expression.
* Completion::                How to invoke and customize completion.
* Yes-or-No Queries::         Asking a question with a simple answer.
* Minibuffer Misc::           Various customization hooks and variables.


File: elisp,  Node: Intro to Minibuffers,  Next: Text from Minibuffer,  Prev: Minibuffers,  Up: Minibuffers

Introduction to Minibuffers
===========================

   In most ways, a minibuffer is a normal Emacs buffer.  Most operations
*within* a buffer, such as editing commands, work normally in a
minibuffer.  However, many operations for managing buffers do not apply
to minibuffers.  The name of a minibuffer always has the form
` *Minibuf-NUMBER', and it cannot be changed.  There is a special
window used only for minibuffers, and minibuffers cannot be displayed in
any other window.  This window is normally the single line at the bottom
of the screen; it can be resized temporarily with the window sizing
commands, but reverts to its normal size when the minibuffer is exited.

   A "recursive minibuffer" may be created when there is an active
minibuffer and a command is invoked that requires input from a
minibuffer.  The first minibuffer is named ` *Minibuf-0*'. Recursive
minibuffers are named by incrementing the number at the end of the
name.  (The names begin with a space so that they won't show up in
normal buffer lists.)  Of several recursive minibuffers, the innermost
(or most recently entered) is the active minibuffer, and is the only one
that is displayed in a window.  We usually call this "the" minibuffer.
Recursive minibuffers may be allowed or disallowed by setting the
variable `enable-recursive-minibuffers'.

   Like other buffers, a minibuffer may use any of several local keymaps
(*note Keymaps::.); these contain various exit commands and in some
cases completion commands.  *Note Completion::.

   * `minibuffer-local-map' is for ordinary input (no completion).

   * `minibuffer-local-ns-map' is similar, except that SPC exits just
     like RET.  This is used mainly for Mocklisp compatibility.

   * `minibuffer-local-completion-map' is for permissive completion.

   * `minibuffer-local-must-match-map' is for strict completion and for
     cautious completion.

   * `repeat-complex-command-map' is for use in `C-x ESC'.


File: elisp,  Node: Text from Minibuffer,  Next: Object from Minibuffer,  Prev: Intro to Minibuffers,  Up: Minibuffers

Reading Text Strings with the Minibuffer
========================================

   The minibuffer is usually used to read text which is returned as a
string, but can also be used to read a Lisp object in textual form.  The
most basic primitive for minibuffer input is `read-from-minibuffer'.

 -- Function: read-from-minibuffer PROMPT-STRING &optional INITIAL
          KEYMAP READ
     This function is the most general way to get input through the
     minibuffer.  By default, it accepts arbitrary text and returns it
     as a string; however, if READ is non-`nil', then it uses `read' to
     convert the text into a Lisp object (*note Input Functions::.).

     The first thing this function does is to activate a minibuffer and
     display it with  PROMPT-STRING as the prompt.  This value must be a
     string.

     Then, if INITIAL is non-`nil', it must be a string; its contents
     are inserted into the minibuffer as initial contents.  The text
     thus inserted is treated as if the user had inserted it; the user
     can alter it with Emacs editing commands.

     If KEYMAP is non-`nil', that keymap is the local keymap to use
     while reading.  If KEYMAP is omitted or `nil', the value of
     `minibuffer-local-map' is used as the keymap.  Specifying a keymap
     is the most important way to customize minibuffer input for
     various applications including completion.

     When the user types a command to exit the minibuffer, the current
     minibuffer contents are usually made into a string which is the
     value of `read-from-minibuffer'.  However, if READ is non-`nil',
     Emacs converts the result to a Lisp object and
     `read-from-minibuffer' returns that object, unevaluated.

     Suppose, for example, you are writing a search command and want to
     record the last search string and provide it as a default for the
     next search.  Suppose that the previous search string is stored in
     the variable `last-search-string'.  Here is how you can read a
     search string while providing the previous string as initial input
     to be edited:

          (read-from-minibuffer "Find string: " last-search-string)

     Assuming the value of `last-search-string' is `No', and the user
     wants to search for `Nope', the interaction looks like this:

          (setq last-search-string "No")

          (read-from-minibuffer "Find string: " last-search-string)
          ---------- Buffer: Minibuffer ----------
          Find string: No-!-
          ---------- Buffer: Minibuffer ----------
          ;; The user now types `pe RET':
               => "Nope"

 -- Function: read-string PROMPT &optional INITIAL
     This function reads a string from the minibuffer and returns it.
     The arguments PROMPT and INITIAL are used as in
     `read-from-minibuffer'.

     This function is a simplified interface to `read-from-minibuffer':

          (read-string PROMPT INITIAL)
          ==
          (read-from-minibuffer PROMPT INITIAL nil nil)

 -- Variable: minibuffer-local-map
     This is the default local keymap for reading from the minibuffer.
     It is the keymap used by the minibuffer for local bindings in the
     function `read-string'.  By default, it makes the following
     bindings:

    LFD
          `exit-minibuffer'

    RET
          `exit-minibuffer'

    `C-g'
          `abort-recursive-edit'

 -- Function: read-no-blanks-input PROMPT INITIAL
     This function reads a string from the minibuffer, but does not
     allow whitespace characters as part of the input: instead, those
     characters terminate the input.  The arguments PROMPT and INITIAL
     are used as in `read-from-minibuffer'.

     This function is a simplified interface to `read-from-minibuffer',
     and passes the value of `minibuffer-local-ns-map' as the KEYMAP
     argument for that function.  Since the keymap
     `minibuffer-local-ns-map' does not rebind `C-q', it *is* possible
     to put a space into the string, by quoting it.

          (read-no-blanks-input PROMPT INITIAL)
          ==
          (read-from-minibuffer PROMPT INITIAL minibuffer-local-ns-map)

 -- Variable: minibuffer-local-ns-map
     This built-in variable is the keymap used as the minibuffer local
     keymap in the function `read-no-blanks-input'.  By default, it
     makes the following bindings:

    `LFD'
          `exit-minibuffer'

    `SPC'
          `exit-minibuffer'

    `TAB'
          `exit-minibuffer'

    `RET'
          `exit-minibuffer'

    `C-g'
          `abort-recursive-edit'

    `?'
          `self-insert-and-exit'


File: elisp,  Node: Object from Minibuffer,  Next: Completion,  Prev: Text from Minibuffer,  Up: Minibuffers

Reading Lisp Objects with the Minibuffer
========================================

   This section describes functions for reading Lisp objects with the
minibuffer.

 -- Function: read-minibuffer PROMPT &optional INITIAL
     This function reads a Lisp object in the minibuffer and returns it,
     unevaluated.  The arguments PROMPT and INITIAL are used as in
     `read-from-minibuffer'; in particular, INITIAL must be a string or
     `nil'.

     This function is a simplified interface to `read-from-minibuffer':

          (read-minibuffer PROMPT INITIAL)
          ==
          (read-from-minibuffer PROMPT INITIAL nil t)

     Here is an example in which we supply the string `"(testing)"' as
     initial input:

          (read-minibuffer "Enter an expression: " (format "%s" '(testing)))

          ;;  Here is how the minibuffer is displayed:

          ---------- Buffer: Minibuffer ----------
          Enter an expression: (testing)-!-
          ---------- Buffer: Minibuffer ----------

     The user can type RET immediately to use the initial input as a
     default, or can edit the input.

 -- Function: eval-minibuffer PROMPT &optional INITIAL
     This function reads a Lisp expression in the minibuffer, evaluates
     it, then returns the result.  The arguments PROMPT and INITIAL are
     used as in `read-from-minibuffer'.

     This function simply evaluates the result of a call to
     `read-minibuffer':

          (eval-minibuffer PROMPT INITIAL)
          ==
          (eval (read-minibuffer PROMPT INITIAL))

 -- Function: edit-and-eval-command PROMPT FORM
     This function reads a Lisp expression in the minibuffer, and then
     evaluates it.  The difference between this command and
     `eval-minibuffer' is that here the initial FORM is not optional
     and it is treated as a Lisp object to be converted to printed
     representation rather than as a string of text.  It is printed with
     `prin1', so if it is a string, double-quote characters (`"') will
     appear in the initial text.  *Note Output Functions::.

     The first thing `edit-and-eval-command' does is to activate the
     minibuffer with PROMPT as the prompt.  The printed representation
     of FORM is then inserted in the minibuffer, and the user is
     allowed to edit.  When the user exits the minibuffer, the edited
     text is read with `read' and then evaluated.  The resulting value
     becomes the value of `edit-and-eval-command'.

     In the following example, we offer the user an expression with
     initial text which is a valid form already:

          (edit-and-eval-command "Please edit: " '(forward-word 1))

          ;; After evaluating the preceding expression,
          ;; the following appears in the minibuffer:

          ---------- Buffer: Minibuffer ----------
          Please edit: (forward-word 1)-!-
          ---------- Buffer: Minibuffer ----------

     Typing RET right away would exit the minibuffer and evaluate the
     expression, thus moving point forward one word.
     `edit-and-eval-command' returns `nil' in this example.


File: elisp,  Node: Completion,  Next: Yes-or-No Queries,  Prev: Object from Minibuffer,  Up: Minibuffers

Completion
==========

   "Completion" is a feature that fills in the rest of a name starting
from an abbreviation for it.  Completion works by comparing the user's
input against a list of valid names and determining how much of the
name is determined uniquely by what the user has typed.

   For example, when you type `C-x b' (`switch-to-buffer') and then
type the first few letters of the name of the buffer to which you wish
to switch, and then type TAB (`minibuffer-complete'), Emacs extends the
name as far as it can.  Standard Emacs commands offer completion for
names of symbols, files, buffers, and processes; with the functions in
this section, you can implement completion for other kinds of names.

   The `try-completion' function is the basic primitive for completion:
it returns the longest determined completion of a given initial string,
with a given set of strings to match against.

   The function `completing-read' provides a higher-level interface for
completion.  A call to `completing-read' specifies how to determine the
list of valid names.  The function then activates the minibuffer with a
local keymap that binds a few keys to commands useful for completion.
Other functions provide convenient simple interfaces for reading
certain kinds of names with completion.

* Menu:

* Basic Completion::       Low-level functions for completing strings.
                             (These are too low level to use the minibuffer.)
* Programmed Completion::  Finding the completions for a given file name.
* Minibuffer Completion::  Invoking the minibuffer with completion.
* Completion Commands::    Minibuffer commands that do completion.
* High-Level Completion::  Convenient special cases of completion
                             (reading buffer name, file name, etc.)
* Reading File Names::     Using completion to read file names.
* Lisp Symbol Completion:: Completing the name of a symbol.


File: elisp,  Node: Basic Completion,  Next: Programmed Completion,  Prev: Completion,  Up: Completion

Basic Completion Functions
--------------------------

 -- Function: try-completion STRING ALIST-OR-OBARRAY &optional PREDICATE
     This function returns the longest common substring of all possible
     completions of STRING in ALIST-OR-OBARRAY.

     If ALIST-OR-OBARRAY is an association list (*note Association
     Lists::.), the CAR of each cons cell in it is compared against
     STRING; if the beginning of the CAR equals STRING, the cons cell
     matches.  If no cons cells match, `try-completion' returns `nil'.
     If only one cons cell matches, and the match is exact, then
     `try-completion' returns `t'.  Otherwise, all matching strings are
     compared, and the longest initial sequence common to them is
     returned as a string.

     If ALIST-OR-OBARRAY is an obarray (*note Creating Symbols::.), the
     names of all symbols in the obarray form the space of possible
     names.  They are tested and used just like the CARs of the elements
     of an association list.  (The global variable `obarray' holds an
     obarray containing the names of all interned Lisp symbols.)

     If the argument PREDICATE is non-`nil', then it must be a function
     of one argument.  It is used to test each possible match, and the
     match is accepted only if PREDICATE returns non-`nil'. The
     argument given to PREDICATE is either a cons cell from the alist
     (the CAR of which is a string) or else it is a symbol (*not* a
     symbol name) from the obarray.

     It is also possible to use a function as ALIST-OR-OBARRAY.  Then
     the function is solely responsible for performing completion;
     `try-completion' returns whatever this function returns.  The
     function is called with three arguments: STRING, PREDICATE and
     `nil'.  (The reason for the third argument is so that the same
     function can be used in `all-completions' and do the appropriate
     thing in either case.)  *Note Programmed Completion::.

     In the first of the following examples, the string `foo' is
     matched by three of the alist CARs.  All of the matches begin with
     the characters `fooba', so that is the result.  In the second
     example, there is only one possible match, and it is exact, so the
     value is `t'.

          (try-completion "foo"
               '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))
               => "fooba"

          (try-completion "foo" '(("barfoo" 2) ("foo" 3)))
               => t

     In the following example, numerous symbols begin with the
     characters `forw', and all of them begin with the word `forward'.
     In most of the symbols, this is followed with a `-', but not in
     all, so no more than `forward' can be completed.

          (try-completion "forw" obarray)
               => "forward"

     Finally, in the following example, only two of the three possible
     matches pass the predicate `test' (the string `foobaz' is too
     short).  Both of those begin with the string `foobar'.

          (defun test (s)
            (> (length (car s)) 6))
               => test
          (try-completion "foo"
               '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
               'test)
               => "foobar"

 -- Function: all-completions STRING ALIST-OR-OBARRAY &optional
          PREDICATE
     This function returns a list of all possible completions, instead
     of the longest substring they share.  The parameters to this
     function are the same as to `try-completion'.

     If ALIST-OR-OBARRAY is a function, it is called with three
     arguments: STRING, PREDICATE and `t', and `all-completions'
     returns whatever the function returns. *Note Programmed
     Completion::.

     Here is an example, using the same function `test' used in the
     example for `try-completion':

          (defun test (s)
            (> (length (car s)) 6))
               => test

          (all-completions  "foo"
               '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
               (function test))
               => ("foobar1" "foobar2")

 -- Variable: completion-ignore-case
     If the value of this variable is non-`nil', Emacs does not
     consider case significant in completion.

   The two functions `try-completion' and `all-completions' have
nothing in themselves to do with minibuffers.  However, completion is
most often used there, which is why it is described in this chapter.


File: elisp,  Node: Programmed Completion,  Next: Minibuffer Completion,  Prev: Basic Completion,  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 the function as the ALIST-OR-OBARRAY
argument to `completing-read'.  This command will arrange to pass the
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 predicale 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 an exact match already, or `nil' if the string matches no
     possibility.

   * `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.

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


File: elisp,  Node: Minibuffer Completion,  Next: Completion Commands,  Prev: Programmed Completion,  Up: Completion

Completion and the Minibuffer
-----------------------------

   This section describes the basic interface for reading from the
minibuffer with completion.

 -- Function: completing-read PROMPT ALIST-OR-OBARRAY &optional
          PREDICATE REQUIRE-MATCH INITIAL
     This function reads a string in the minibuffer, assisting the user
     by providing completion.  It activates the minibuffer with prompt
     PROMPT, which must be a string.  If INITIAL is non-`nil',
     `completing-read' inserts it into the minibuffer as part of the
     input.  Then it allows the user to edit the input, providing
     several commands to attempt completion.

     The actual completion is done by passing ALIST-OR-OBARRAY and
     PREDICATE to the function `try-completion'.  This happens in
     certain commands bound in the local keymaps used for completion.

     If REQUIRE-MATCH is `t', the user will not be allowed to exit
     unless the input completes to an element of ALIST-OR-OBARRAY. If
     REQUIRE-MATCH is neither `nil' nor `t', then `completing-read'
     does not exit unless the input typed is itself an element of
     ALIST-OR-OBARRAY.  To accomplish this, `completing-read' calls
     `read-minibuffer' with the keymap
     `minibuffer-local-completion-map' if REQUIRE-MATCH is `nil', or
     else with the keymap `minibuffer-local-must-match-map', if
     REQUIRE-MATCH is non-`nil'.

     Case is ignored when comparing the input against the possible
     matches if the built-in variable `completion-ignore-case' is
     non-`nil'.  *Note Basic Completion::.

     For example:

          (completing-read "Complete a foo: "
               '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
               nil t "fo")

          ;; After evaluating the preceding expression,
          ;; the following appears in the minibuffer:

          ---------- Buffer: Minibuffer ----------
          Complete a foo: fo-!-
          ---------- Buffer: Minibuffer ----------

     If the user then types `DEL DEL b RET', `completing-read' returns
     `barfoo'.

     The `completing-read' function binds three variables to pass
     information to the commands which actually do completion.  Here
     they are:

    `minibuffer-completion-table'
          This variable is bound to ALIST-OR-OBARRAY argument.  It is
          passed to the `try-completion' function.

    `minibuffer-completion-predicate'
          This variable is bound to the PREDICATE argument.  It is
          passed to the `try-completion' function.

    `minibuffer-completion-confirm'
          This variable is bound to the REQUIRE-MATCH argument.  It is
          used in the `minibuffer-complete-and-exit' function.


File: elisp,  Node: Completion Commands,  Next: High-Level Completion,  Prev: Minibuffer Completion,  Up: Completion

Minibuffer Commands That Do Completion
--------------------------------------

   This section describes the keymaps, commands and user options used in
the minibuffer to do completion.

 -- Variable: minibuffer-local-completion-map
     `completing-read' uses this value as the local keymap when an
     exact match of one of the completions is not required.  By
     default, this keymap makes the following bindings:

    `?'
          `minibuffer-completion-help'

    `SPC'
          `minibuffer-complete-word'

    `TAB'
          `minibuffer-complete'

    `LFD'
          `exit-minibuffer'

    `RET'
          `exit-minibuffer'

    `C-g'
          `abort-recursive-edit'


 -- Variable: minibuffer-local-must-match-map
     `completing-read' uses this value as the local keymap when an
     exact match of one of the completions is required.  Therefore, no
     keys are bound to `exit-minibuffer', the command which exits the
     minibuffer unconditionally.  By default, this keymap makes the
     following bindings:

    `?'
          `minibuffer-completion-help'

    `SPC'
          `minibuffer-complete-word'

    `TAB'
          `minibuffer-complete'

    `LFD'
          `minibuffer-complete-and-exit'

    `RET'
          `minibuffer-complete-and-exit'

    `C-g'
          `abort-recursive-edit'

 -- Variable: minibuffer-completion-table
     The value of this variable is the alist or obarray used for
     completion in the minibuffer.  This is the global variable that
     contains what `completing-read' passes to `try-completion'.  It is
     used by all the minibuffer completion functions, such as
     `minibuffer-complete-word'.

 -- Variable: minibuffer-completion-predicate
     The value of this variable is the predicate that `completing-read'
     passes to `try-completion'.  The variable is also used by the
     other minibuffer completion functions.

 -- Command: minibuffer-complete-word
     This function completes the minibuffer contents by at most a single
     word.  Even if the minibuffer contents has only one completion,
     `minibuffer-complete-word' will not add any characters beyond the
     first character that is not a word constituent.  *Note Syntax
     Tables::.

 -- Command: minibuffer-complete
     This function completes the minibuffer contents as far as possible.

 -- Command: minibuffer-complete-and-exit
     This function completes the minibuffer contents, and exits if
     confirmation is not required, i.e., if
     `minibuffer-completion-confirm' is non-`nil'.  If confirmation
     *is* required, it is given by repeating this command immediately.

 -- Variable: minibuffer-completion-confirm
     When the value of this variable is non-`nil', Emacs asks for
     confirmation of a completion before exiting the minibuffer.  The
     function `minibuffer-complete-and-exit' checks the value of this
     variable before it exits.

 -- Command: minibuffer-completion-help
     This function creates a list of the possible completions of the
     current minibuffer contents.  It works by calling
     `all-completions'; the values of `minibuffer-completion-table' and
     `minibuffer-completion-predicate' are used as arguments.  The list
     of completions is displayed as text in a buffer named
     `*Completions*'.

 -- Function: display-completion-list COMPLETIONS
     This function displays COMPLETIONS to the stream `standard-output'
     (usually a buffer).  (*Note Streams::, for more information about
     streams.)  The argument COMPLETIONS is normally a list of
     completions just returned by `all-completions', but it does not
     have to be.  Each element may be a symbol or a string, either of
     which is simply printed, or a list of two strings, which is printed
     as if the strings were concatenated.

     This function is called by `minibuffer-completion-help'.

 -- User Option: completion-auto-help
     If this variable is non-`nil', the completion commands
     automatically display a list of possible completions whenever
     nothing can be completed because the next character is not
     uniquely determined.


File: elisp,  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.

 -- 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.  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
     will not exit if the text is not valid, and RET will do completion
     to attempt to find a valid name.  (However, DEFAULT is not checked
     for this; 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 evaluating 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 evaluating the preceding expression,
          ;; the following appears in the 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
     `completing-read'.  It uses the `commandp' predicate to allow only
     commands to be entered, and it uses the variable `obarray' so as
     to be able to complete all extant Lisp symbols:

          (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 evaluating 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' will return
     `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))


File: elisp,  Node: Reading File Names,  Next: Lisp Symbol 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
     This function reads a file name in the minibuffer, prompting with
     PROMPT and providing completion.  If DEFAULT is non-`nil', then
     the value of DEFAULT will be returned by the function if the user
     just types RET.

     If EXISTING is non-`nil', then the name must refer to an existing
     file; then 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.

     The argument DIRECTORY specifies the directory to use for
     completion of relative file names.  Usually it is inserted in the
     minibuffer as initial input as well.  It defaults to the current
     buffer's default directory.

     Here is an example:

          (read-file-name "The file is ")

          ;; After evaluating 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
     `"/gp/gnu/elisp/manual.texi"'.

 -- User Option: insert-default-directory
     This variable is used by `read-file-name'.  The value of this
     variable controls whether `read-file-name' starts by placing the
     name of the default directory in the minibuffer.  If the value of
     this variable is `nil', then `read-file-name' does not place any
     initial input in the minibuffer.  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 containing 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 ----------


File: elisp,  Node: Lisp Symbol Completion,  Prev: Reading File Names,  Up: Completion

Lisp Symbol Completion
----------------------

   If you type a part of a symbol, and then type `M-TAB'
(`lisp-complete-symbol'), it will attempt to fill in as much more of
the symbol name as it can.  Not only does this save typing, but it can
help you with the name of a symbol that you have partially forgotten.

 -- Command: lisp-complete-symbol
     This function performs completion on the symbol name preceding
     point. The name is completed against the symbols in the global
     variable `obarray', and characters from the completion are
     inserted into the buffer, making the name longer.  If there is
     more than one completion, a list of all possible completions is
     placed in the `*Help*' buffer. The bell rings if there is no
     possible completion in `obarray'.

     If an open parenthesis immediately precedes the name, only symbols
     with function definitions are considered.  (By reducing the number
     of alternatives, this may succeed in completing more characters.)
     Otherwise, symbols with either a function definition, a value, or
     at least one property are considered.

     `lisp-complete-symbol' returns `t' if the symbol had an exact, and
     unique, match; otherwise, it returns `nil'.

     In the following example, the user has already inserted `(forwa'
     into the buffer `foo.el'.  The command `lisp-complete-symbol' then
     completes the name to `(forward-'.

          ---------- Buffer: foo.el ----------
          (forwa-!-
          ---------- Buffer: foo.el ----------

          (lisp-complete-symbol)
               => nil

          ---------- Buffer: foo.el ----------
          (forward--!-
          ---------- Buffer: foo.el ----------


File: elisp,  Node: Yes-or-No Queries,  Next: Minibuffer Misc,  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.

   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.  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', or `DEL'), 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.

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

          (y-or-n-p "Do you need a lift? ")

          ;; After evaluating 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 ----------

     Note that we show successive lines of echo area messages here.
     Only one will appear on the screen at a time.

 -- Function: yes-or-no-p PROMPT
     This function asks the user a question, expecting input in
     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 your entire directory? ")

          ;; After evaluating the preceding expression,
          ;; the following prompt appears with an empty minibuffer:

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


File: elisp,  Node: Minibuffer Misc,  Prev: Yes-or-No Queries,  Up: Minibuffers

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

   Some basic minibuffer functions and variables are described in this
section.

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

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

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

 -- Function: minibuffer-window
     This function returns the window that is used for the minibuffer.
     There is one and only one minibuffer window in Emacs 18; this
     window always exists and cannot be deleted.

 -- 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 will scroll the `minibuffer-scroll-window' 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') which use minibuffers even while in the minibuffer
     window.  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.


File: elisp,  Node: Command Loop,  Next: Keymaps,  Prev: Minibuffers,  Up: Top

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

   When you run Emacs, it enters the "editor command loop" almost
immediately.  This loop reads key sequences, executes their definitions,
and displays the results.  In this chapter, we describe how these things
are done, and the subroutines that allow Lisp programs to do them.

* Menu:

* Command Overview::    How the command loop reads commands.
* Defining Commands::   Specifying how a function should read arguments.
* Interactive Call::    Calling a command, so that it will read arguments.
* Command Loop Info::   Variables set by the command loop for you to examine.
* Keyboard Input::      How your program can read characters from the keyboard.
* 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.


File: elisp,  Node: Command Overview,  Next: Defining Commands,  Prev: Command Loop,  Up: Command Loop

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 `read-key-sequence'.  Your Lisp code
can also call this function (*note Keyboard Input::.).  Lisp programs
can also do input at a lower level with `read-char' or discard pending
input with `discard-input'.

   The key sequence is translated into a command through the keymaps of
the current buffer.  *Note Keymaps::, for information on how this is
done.  The result 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 is used instead.  This is done by the command
`execute-extended-command' (*note 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 `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 (i.e., a keyboard macro) then the function
`execute-kbd-macro' is used to execute it.  You can call this function
yourself (*note Keyboard Macros::.).

   If a command runs away, typing `C-g' will terminate its execution
immediately.  This is called "quitting" (*note Quitting::.).


File: elisp,  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 which 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.