Reformatted.

[chise/xemacs-chise.git] / info / lispref.info-15

This is ../info/lispref.info, produced by makeinfo version 4.0 from
lispref/lispref.texi.

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: Input Streams,  Next: Input Functions,  Prev: Streams Intro,  Up: Read and Print

Input Streams
=============

   Most of the Lisp functions for reading text take an "input stream"
as an argument.  The input stream specifies where or how to get the
characters of the text to be read.  Here are the possible types of input
stream:

BUFFER
     The input characters are read from BUFFER, starting with the
     character directly after point.  Point advances as characters are
     read.

MARKER
     The input characters are read from the buffer that MARKER is in,
     starting with the character directly after the marker.  The marker
     position advances as characters are read.  The value of point in
     the buffer has no effect when the stream is a marker.

STRING
     The input characters are taken from STRING, starting at the first
     character in the string and using as many characters as required.

FUNCTION
     The input characters are generated by FUNCTION, one character per
     call.  Normally FUNCTION is called with no arguments, and should
     return a character.

     Occasionally FUNCTION is called with one argument (always a
     character).  When that happens, FUNCTION should save the argument
     and arrange to return it on the next call.  This is called
     "unreading" the character; it happens when the Lisp reader reads
     one character too many and wants to "put it back where it came
     from".

`t'
     `t' used as a stream means that the input is read from the
     minibuffer.  In fact, the minibuffer is invoked once and the text
     given by the user is made into a string that is then used as the
     input stream.

`nil'
     `nil' supplied as an input stream means to use the value of
     `standard-input' instead; that value is the "default input
     stream", and must be a non-`nil' input stream.

SYMBOL
     A symbol as input stream is equivalent to the symbol's function
     definition (if any).

   Here is an example of reading from a stream that is a buffer, showing
where point is located before and after:

     ---------- Buffer: foo ----------
     This-!- is the contents of foo.
     ---------- Buffer: foo ----------
     
     (read (get-buffer "foo"))
          => is
     (read (get-buffer "foo"))
          => the
     
     ---------- Buffer: foo ----------
     This is the-!- contents of foo.
     ---------- Buffer: foo ----------

Note that the first read skips a space.  Reading skips any amount of
whitespace preceding the significant text.

   In Emacs 18, reading a symbol discarded the delimiter terminating the
symbol.  Thus, point would end up at the beginning of `contents' rather
than after `the'.  The Emacs 19 behavior is superior because it
correctly handles input such as `bar(foo)', where the open-parenthesis
that ends one object is needed as the beginning of another object.

   Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown.  The value
read is the symbol `This'.


     ---------- Buffer: foo ----------
     This is the contents of foo.
     ---------- Buffer: foo ----------
     
     (setq m (set-marker (make-marker) 1 (get-buffer "foo")))
          => #<marker at 1 in foo>
     (read m)
          => This
     m
          => #<marker at 5 in foo>   ;; Before the first space.

   Here we read from the contents of a string:

     (read "(When in) the course")
          => (When in)

   The following example reads from the minibuffer.  The prompt is:
`Lisp expression: '.  (That is always the prompt used when you read
from the stream `t'.)  The user's input is shown following the prompt.

     (read t)
          => 23
     ---------- Buffer: Minibuffer ----------
     Lisp expression: 23 <RET>
     ---------- Buffer: Minibuffer ----------

   Finally, here is an example of a stream that is a function, named
`useless-stream'.  Before we use the stream, we initialize the variable
`useless-list' to a list of characters.  Then each call to the function
`useless-stream' obtains the next character in the list or unreads a
character by adding it to the front of the list.

     (setq useless-list (append "XY()" nil))
          => (88 89 40 41)
     
     (defun useless-stream (&optional unread)
       (if unread
           (setq useless-list (cons unread useless-list))
         (prog1 (car useless-list)
                (setq useless-list (cdr useless-list)))))
          => useless-stream

Now we read using the stream thus constructed:

     (read 'useless-stream)
          => XY
     
     useless-list
          => (40 41)

Note that the open and close parentheses remains in the list.  The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it.  Another attempt to read from the stream at this
point would read `()' and return `nil'.

\1f
File: lispref.info,  Node: Input Functions,  Next: Output Streams,  Prev: Input Streams,  Up: Read and Print

Input Functions
===============

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

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

   An `end-of-file' error is signaled if reading encounters an
unterminated list, vector, or string.

 - Function: read &optional stream
     This function reads one textual Lisp expression from STREAM,
     returning it as a Lisp object.  This is the basic Lisp input
     function.

 - Function: read-from-string string &optional start end
     This function reads the first textual Lisp expression from the
     text in STRING.  It returns a cons cell whose CAR is that
     expression, and whose CDR is an integer giving the position of the
     next remaining character in the string (i.e., the first one not
     read).

     If START is supplied, then reading begins at index START in the
     string (where the first character is at index 0).  If END is also
     supplied, then reading stops just before that index, as if the rest
     of the string were not there.

     For example:

          (read-from-string "(setq x 55) (setq y 5)")
               => ((setq x 55) . 11)
          (read-from-string "\"A short string\"")
               => ("A short string" . 16)
          
          ;; Read starting at the first character.
          (read-from-string "(list 112)" 0)
               => ((list 112) . 10)
          ;; Read starting at the second character.
          (read-from-string "(list 112)" 1)
               => (list . 5)
          ;; Read starting at the seventh character,
          ;;   and stopping at the ninth.
          (read-from-string "(list 112)" 6 8)
               => (11 . 8)

 - Variable: standard-input
     This variable holds the default input stream--the stream that
     `read' uses when the STREAM argument is `nil'.

\1f
File: lispref.info,  Node: Output Streams,  Next: Output Functions,  Prev: Input Functions,  Up: Read and Print

Output Streams
==============

   An output stream specifies what to do with the characters produced
by printing.  Most print functions accept an output stream as an
optional argument.  Here are the possible types of output stream:

BUFFER
     The output characters are inserted into BUFFER at point.  Point
     advances as characters are inserted.

MARKER
     The output characters are inserted into the buffer that MARKER
     points into, at the marker position.  The marker position advances
     as characters are inserted.  The value of point in the buffer has
     no effect on printing when the stream is a marker.

FUNCTION
     The output characters are passed to FUNCTION, which is responsible
     for storing them away.  It is called with a single character as
     argument, as many times as there are characters to be output, and
     is free to do anything at all with the characters it receives.

`t'
     The output characters are displayed in the echo area.

`nil'
     `nil' specified as an output stream means to the value of
     `standard-output' instead; that value is the "default output
     stream", and must be a non-`nil' output stream.

SYMBOL
     A symbol as output stream is equivalent to the symbol's function
     definition (if any).

   Many of the valid output streams are also valid as input streams.
The difference between input and output streams is therefore mostly one
of how you use a Lisp object, not a distinction of types of object.

   Here is an example of a buffer used as an output stream.  Point is
initially located as shown immediately before the `h' in `the'.  At the
end, point is located directly before that same `h'.

     ---------- Buffer: foo ----------
     This is t-!-he contents of foo.
     ---------- Buffer: foo ----------
     
     (print "This is the output" (get-buffer "foo"))
          => "This is the output"
     
     ---------- Buffer: foo ----------
     This is t
     "This is the output"
     -!-he contents of foo.
     ---------- Buffer: foo ----------

   Now we show a use of a marker as an output stream.  Initially, the
marker is in buffer `foo', between the `t' and the `h' in the word
`the'.  At the end, the marker has advanced over the inserted text so
that it remains positioned before the same `h'.  Note that the location
of point, shown in the usual fashion, has no effect.

     ---------- Buffer: foo ----------
     "This is the -!-output"
     ---------- Buffer: foo ----------
     
     m
          => #<marker at 11 in foo>
     
     (print "More output for foo." m)
          => "More output for foo."
     
     ---------- Buffer: foo ----------
     "This is t
     "More output for foo."
     he -!-output"
     ---------- Buffer: foo ----------
     
     m
          => #<marker at 35 in foo>

   The following example shows output to the echo area:

     (print "Echo Area output" t)
          => "Echo Area output"
     ---------- Echo Area ----------
     "Echo Area output"
     ---------- Echo Area ----------

   Finally, we show the use of a function as an output stream.  The
function `eat-output' takes each character that it is given and conses
it onto the front of the list `last-output' (*note Building Lists::).
At the end, the list contains all the characters output, but in reverse
order.

     (setq last-output nil)
          => nil
     
     (defun eat-output (c)
       (setq last-output (cons c last-output)))
          => eat-output
     
     (print "This is the output" 'eat-output)
          => "This is the output"
     
     last-output
          => (?\n ?\" ?t ?u ?p ?t ?u ?o ?\  ?e ?h ?t
                     ?\  ?s ?i ?\  ?s ?i ?h ?T ?\" ?\n)

Now we can put the output in the proper order by reversing the list:

     (concat (nreverse last-output))
          => "
     \"This is the output\"
     "

Calling `concat' converts the list to a string so you can see its
contents more clearly.

\1f
File: lispref.info,  Node: Output Functions,  Next: Output Variables,  Prev: Output Streams,  Up: Read and Print

Output Functions
================

   This section describes the Lisp functions for printing Lisp objects.

   Some of the XEmacs printing functions add quoting characters to the
output when necessary so that it can be read properly.  The quoting
characters used are `"' and `\'; they distinguish strings from symbols,
and prevent punctuation characters in strings and symbols from being
taken as delimiters when reading.  *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.

   Printing a self-referent Lisp object requires an infinite amount of
text.  In certain cases, trying to produce this text leads to a stack
overflow.  XEmacs detects such recursion and prints `#LEVEL' instead of
recursively printing an object already being printed.  For example,
here `#0' indicates a recursive reference to the object at level 0 of
the current print operation:

     (setq foo (list nil))
          => (nil)
     (setcar foo foo)
          => (#0)

   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' function 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 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: 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 it doesn't insert quoting characters and
     doesn't put double-quotes 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".

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

 - Function: prin1-to-string object &optional noescape
     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>"

     If NOESCAPE is non-`nil', that inhibits use of quoting characters
     in the output.  (This argument is supported in Emacs versions 19
     and later.)

          (prin1-to-string "foo")
               => "\"foo\""
          (prin1-to-string "foo" t)
               => "foo"

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

\1f
File: lispref.info,  Node: Output Variables,  Prev: Output Functions,  Up: Read and Print

Variables Affecting Output
==========================

 - Variable: standard-output
     The value of this variable is the default output stream--the stream
     that print functions use when the STREAM argument is `nil'.

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

     This variable affects the print functions `prin1' and `print', as
     well as everything that uses them.  It does not affect `princ'.
     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-readably
     If non-`nil', then all objects will be printed in a readable form.
     If an object has no readable representation, then an error is
     signalled.  When `print-readably' is true, compiled-function
     objects will be written in `#[...]' form instead of in
     `#<compiled-function [...]>' form, and two-element lists of the
     form `(quote object)' will be written as the equivalent `'object'.
     Do not _set_ this variable; bind it instead.

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

 - Variable: print-level
     The value of this variable is the maximum depth of nesting of
     parentheses and brackets when printed.  Any list or vector at a
     depth exceeding this limit is abbreviated with an ellipsis.  A
     value of `nil' (which is the default) means no limit.

     This variable exists in version 19 and later versions.

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

 - Variable: print-gensym
     If non-`nil', then uninterned symbols will be printed specially.
     Uninterned symbols are those which are not present in `obarray',
     that is, those which were made with `make-symbol' or by calling
     `intern' with a second argument.

     When `print-gensym' is true, such symbols will be preceded by
     `#:', which causes the reader to create a new symbol instead of
     interning and returning an existing one.  Beware: The `#:' syntax
     creates a new symbol each time it is seen, so if you print an
     object which contains two pointers to the same uninterned symbol,
     `read' will not duplicate that structure.

     Also, since XEmacs has no real notion of packages, there is no way
     for the printer to distinguish between symbols interned in no
     obarray, and symbols interned in an alternate obarray.

 - Variable: float-output-format
     This variable holds the format descriptor string that Lisp uses to
     print floats.  This is a `%'-spec like those accepted by `printf'
     in C, but with some restrictions.  It must start with the two
     characters `%.'.  After that comes an integer precision
     specification, and then a letter which controls the format.  The
     letters allowed are `e', `f' and `g'.

        * Use `e' for exponential notation `DIG.DIGITSeEXPT'.

        * Use `f' for decimal point notation `DIGITS.DIGITS'.

        * Use `g' to choose the shorter of those two formats for the
          number at hand.

     The precision in any of these cases is the number of digits
     following the decimal point.  With `f', a precision of 0 means to
     omit the decimal point.  0 is not allowed with `f' or `g'.

     A value of nil means to use `%.16g'.

     Regardless of the value of `float-output-format', a floating point
     number will never be printed in such a way that it is ambiguous
     with an integer; that is, a floating-point number will always be
     printed with a decimal point and/or an exponent, even if the
     digits following the decimal point are all zero.  This is to
     preserve read-equivalence.

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

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

   A "minibuffer" is a special buffer that XEmacs commands use 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
frame, 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.
* Minibuffer History::        Recording previous minibuffer inputs
                                so the user can reuse them.
* Completion::                How to invoke and customize completion.
* Yes-or-No Queries::         Asking a question with a simple answer.
* Multiple Queries::          Asking a series of similar questions.
* Reading a Password::        Reading a password from the terminal.
* Minibuffer Misc::           Various customization hooks and variables.

\1f
File: lispref.info,  Node: Intro to Minibuffers,  Next: Text from Minibuffer,  Up: Minibuffers

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

   In most ways, a minibuffer is a normal XEmacs 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.  Minibuffers are
displayed only in special windows used only for minibuffers; these
windows always appear at the bottom of a frame.  (Sometimes frames have
no minibuffer window, and sometimes a special kind of frame contains
nothing but a minibuffer window; see *Note Minibuffers and Frames::.)

   The minibuffer's window is normally a single line.  You can resize it
temporarily with the window sizing commands; it reverts to its normal
size when the minibuffer is exited.  You can resize it permanently by
using the window sizing commands in the frame's other window, when the
minibuffer is not active.  If the frame contains just a minibuffer, you
can change the minibuffer's size by changing the frame's size.

   If a command uses a minibuffer while there is an active minibuffer,
this is called a "recursive 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.  We usually call this "the" minibuffer.  You can permit or
forbid recursive minibuffers 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-completion-map' is for permissive completion.

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

\1f
File: lispref.info,  Node: Text from Minibuffer,  Next: Object from Minibuffer,  Prev: Intro to Minibuffers,  Up: Minibuffers

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

   Most often, the minibuffer is used to read text as a string.  It can
also be used to read a Lisp object in textual form.  The most basic
primitive for minibuffer input is `read-from-minibuffer'; it can do
either one.

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

 - Function: read-from-minibuffer prompt-string &optional
          initial-contents keymap read hist abbrev-table default
     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-CONTENTS is a string, `read-from-minibuffer'
     inserts it into the minibuffer, leaving point at the end.  The
     minibuffer appears with this text as its contents.

     The value of INITIAL-CONTENTS may also be a cons cell of the form
     `(STRING . POSITION)'.  This means to insert STRING in the
     minibuffer but put point POSITION characters from the beginning,
     rather than at the end.

     When the user types a command to exit the minibuffer,
     `read-from-minibuffer' constructs the return value from the text in
     the minibuffer.  Normally it returns a string containing that text.
     However, if READ is non-`nil', `read-from-minibuffer' reads the
     text and returns the resulting Lisp object, unevaluated.  (*Note
     Input Functions::, for information about reading.)

     The argument DEFAULT specifies a default value to make available
     through the history commands.  It should be a string, or `nil'.

     If KEYMAP is non-`nil', that keymap is the local keymap to use in
     the minibuffer.  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 the minibuffer for various
     applications such as completion.

     The argument ABBREV-TABLE specifies `local-abbrev-table' in the
     minibuffer (*note Standard Abbrev Tables::).

     The argument HIST specifies which history list variable to use for
     saving the input and for history commands used in the minibuffer.
     It defaults to `minibuffer-history'.  *Note Minibuffer History::.

     When the user types a command to exit the minibuffer,
     `read-from-minibuffer' uses the text in the minibuffer to produce
     its return value.  Normally it simply makes a string containing
     that text.  However, if READ is non-`nil', `read-from-minibuffer'
     reads the text and returns the resulting Lisp object, unevaluated.
     (*Note Input Functions::, for information about reading.)

     *Usage note:* The INITIAL-CONTENTS argument and the DEFAULT
     argument are two alternative features for more or less the same
     job.  It does not make sense to use both features in a single call
     to `read-from-minibuffer'.  In general, we recommend using
     DEFAULT, since this permits the user to insert the default value
     when it is wanted, but does not burden the user with deleting it
     from the minibuffer on other occasions.  However, if user is
     supposed to edit default value, INITIAL-CONTENTS may be preferred.

 - Function: read-string prompt &optional initial history default-value
     This function reads a string from the minibuffer and returns it.
     The arguments PROMPT and INITIAL are used as in
     `read-from-minibuffer'.  The keymap used is `minibuffer-local-map'.

     The optional argument HISTORY, if non-nil, specifies a history
     list and optionally the initial position in the list.  The optional
     argument DEFAULT specifies a default value to return if the user
     enters null input; it should be a string.

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

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

 - Variable: minibuffer-local-map
     This is the default local keymap for reading from the minibuffer.
     By default, it makes the following bindings:

    `C-j'
          `exit-minibuffer'

    <RET>
          `exit-minibuffer'

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

    `M-n'
          `next-history-element'

    `M-p'
          `previous-history-element'

    `M-r'
          `next-matching-history-element'

    `M-s'
          `previous-matching-history-element'

\1f
File: lispref.info,  Node: Object from Minibuffer,  Next: Minibuffer History,  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-expression prompt &optional initial history
          default-value
     This function reads a Lisp object using the minibuffer, and
     returns it without evaluating it.  The arguments PROMPT and
     INITIAL are used as in `read-from-minibuffer'.

     The optional argument HISTORY, if non-nil, specifies a history
     list and optionally the initial position in the list.  The optional
     argument DEFAULT-VALUE specifies a default value to return if the
     user enters null input; it should be a string.

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

          (read-expression PROMPT INITIAL HISTORY DEFAULT-VALUE)
          ==
          (read-from-minibuffer PROMPT INITIAL nil t
                                HISTORY nil DEFAULT-VALUE)

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

          (read-expression
           "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: read-minibuffer prompt &optional initial history
          default-value
     This is a FSF Emacs compatible function.  Use `read-expression'
     instead.

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

     The optional argument HISTORY, if non-nil, specifies a history
     list and optionally the initial position in the list.  The optional
     argument DEFAULT-VALUE specifies a default value to return if the
     user enters null input; it should be a string.

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

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

 - Function: edit-and-eval-command prompt command &optional history
     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 COMMAND 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 (`"')
     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.  Then it inserts the printed
     representation of FORM in the minibuffer, and lets the user edit
     it.  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 evaluation of 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 `t' in this example.

\1f
File: lispref.info,  Node: Minibuffer History,  Next: Completion,  Prev: Object from Minibuffer,  Up: Minibuffers

Minibuffer History
==================

   A "minibuffer history list" records previous minibuffer inputs so
the user can reuse them conveniently.  A history list is actually a
symbol, not a list; it is a variable whose value is a list of strings
(previous inputs), most recent first.

   There are many separate history lists, used for different kinds of
inputs.  It's the Lisp programmer's job to specify the right history
list for each use of the minibuffer.

   The basic minibuffer input functions `read-from-minibuffer' and
`completing-read' both accept an optional argument named HIST which is
how you specify the history list.  Here are the possible values:

VARIABLE
     Use VARIABLE (a symbol) as the history list.

(VARIABLE . STARTPOS)
     Use VARIABLE (a symbol) as the history list, and assume that the
     initial history position is STARTPOS (an integer, counting from
     zero which specifies the most recent element of the history).

     If you specify STARTPOS, then you should also specify that element
     of the history as the initial minibuffer contents, for consistency.

   If you don't specify HIST, then the default history list
`minibuffer-history' is used.  For other standard history lists, see
below.  You can also create your own history list variable; just
initialize it to `nil' before the first use.

   Both `read-from-minibuffer' and `completing-read' add new elements
to the history list automatically, and provide commands to allow the
user to reuse items on the list.  The only thing your program needs to
do to use a history list is to initialize it and to pass its name to
the input functions when you wish.  But it is safe to modify the list
by hand when the minibuffer input functions are not using it.

   Here are some of the standard minibuffer history list variables:

 - Variable: minibuffer-history
     The default history list for minibuffer history input.

 - Variable: query-replace-history
     A history list for arguments to `query-replace' (and similar
     arguments to other commands).

 - Variable: file-name-history
     A history list for file name arguments.

 - Variable: regexp-history
     A history list for regular expression arguments.

 - Variable: extended-command-history
     A history list for arguments that are names of extended commands.

 - Variable: shell-command-history
     A history list for arguments that are shell commands.

 - Variable: read-expression-history
     A history list for arguments that are Lisp expressions to evaluate.

 - Variable: Info-minibuffer-history
     A history list for Info mode's minibuffer.

 - Variable: Manual-page-minibuffer-history
     A history list for `manual-entry'.

   There are many other minibuffer history lists, defined by various
libraries.  An `M-x apropos' search for `history' should prove fruitful
in discovering them.

\1f
File: lispref.info,  Node: Completion,  Next: Yes-or-No Queries,  Prev: Minibuffer History,  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 XEmacs 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.)
* 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.
* Programmed Completion::  Finding the completions for a given file name.

\1f
File: lispref.info,  Node: Basic Completion,  Next: Minibuffer Completion,  Up: Completion

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

   The two functions `try-completion' and `all-completions' have
nothing in themselves to do with minibuffers.  We describe them in this
chapter so as to keep them near the higher-level completion features
that do use the minibuffer.

 - Function: try-completion string collection &optional predicate
     This function returns the longest common substring of all possible
     completions of STRING in COLLECTION.  The value of COLLECTION must
     be an alist, an obarray, or a function that implements a virtual
     set of strings (see below).

     Completion compares STRING against each of the permissible
     completions specified by COLLECTION; if the beginning of the
     permissible completion equals STRING, it matches.  If no
     permissible completions match, `try-completion' returns `nil'.  If
     only one permissible completion matches, and the match is exact,
     then `try-completion' returns `t'.  Otherwise, the value is the
     longest initial sequence common to all the permissible completions
     that match.

     If COLLECTION is an alist (*note Association Lists::), the CARs of
     the alist elements form the set of permissible completions.

     If COLLECTION is an obarray (*note Creating Symbols::), the names
     of all symbols in the obarray form the set of permissible
     completions.  The global variable `obarray' holds an obarray
     containing the names of all interned Lisp symbols.

     Note that the only valid way to make a new obarray is to create it
     empty and then add symbols to it one by one using `intern'.  Also,
     you cannot intern a given symbol in more than one obarray.

     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.

     You can also use a symbol that is a function as COLLECTION.  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 collection &optional predicate
          nospace
     This function returns a list of all possible completions of
     STRING.  The arguments to this function are the same as those of
     `try-completion'.

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

     If NOSPACE is non-`nil', completions that start with a space are
     ignored unless STRING also starts with a space.

     Here is an example, using the function `test' shown 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))
           'test)
               => ("foobar1" "foobar2")

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

\1f
File: lispref.info,  Node: Minibuffer Completion,  Next: Completion Commands,  Prev: Basic Completion,  Up: Completion

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

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

 - Function: completing-read prompt collection &optional predicate
          require-match initial hist default
     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 COLLECTION 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 usual minibuffer exit commands won't
     exit unless the input completes to an element of COLLECTION.  If
     REQUIRE-MATCH is neither `nil' nor `t', then the exit commands
     won't exit unless the input typed is itself an element of
     COLLECTION.  If REQUIRE-MATCH is `nil', the exit commands work
     regardless of the input in the minibuffer.

     However, empty input is always permitted, regardless of the value
     of REQUIRE-MATCH; in that case, `completing-read' returns DEFAULT.
     The value of DEFAULT (if non-`nil') is also available to the user
     through the history commands.

     The user can exit with null input by typing <RET> with an empty
     minibuffer.  Then `completing-read' returns `""'.  This is how the
     user requests whatever default the command uses for the value being
     read.  The user can return using <RET> in this way regardless of
     the value of REQUIRE-MATCH, and regardless of whether the empty
     string is included in COLLECTION.

     The function `completing-read' works by calling `read-expression'.
     It uses `minibuffer-local-completion-map' as the keymap if
     REQUIRE-MATCH is `nil', and uses `minibuffer-local-must-match-map'
     if REQUIRE-MATCH is non-`nil'.  *Note Completion Commands::.

     The argument HIST specifies which history list variable to use for
     saving the input and for minibuffer history commands.  It defaults
     to `minibuffer-history'.  *Note Minibuffer History::.

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

     Here's an example of using `completing-read':

          (completing-read
           "Complete a foo: "
           '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
           nil t "fo")
          
          ;; After evaluation of 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 that actually do completion.  These
     variables are `minibuffer-completion-table',
     `minibuffer-completion-predicate' and
     `minibuffer-completion-confirm'.  For more information about them,
     see *Note Completion Commands::.