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This is Info file elisp, produced by Makeinfo-1.63 from the input file
elisp.texi.
This version is the edition 2.4.2 of the GNU Emacs Lisp Reference
Manual. It corresponds to Emacs Version 19.34.
Published by the Free Software Foundation 59 Temple Place, Suite 330
Boston, MA 02111-1307 USA
Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996 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.
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.
File: elisp, Node: Specification List, Next: Backtracking, Up: Instrumenting Macro Calls
Specification List
..................
A "specification list" is required for an Edebug specification if
some arguments of a macro call are evaluated while others are not. Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements. The latter, called
"specification keywords", are symbols beginning with `&' (such as
`&optional').
A specification list may contain sublists which match arguments that
are themselves lists, or it may contain vectors used for grouping.
Sublists and groups thus subdivide the specification list into a
hierarchy of levels. Specification keywords only apply to the
remainder of the sublist or group they are contained in.
When a specification list involves alternatives or repetition,
matching it against an actual macro call may require backtracking.
*Note Backtracking::, for more details.
Edebug specifications provide the power of regular expression
matching, plus some context-free grammar constructs: the matching of
sublists with balanced parentheses, recursive processing of forms, and
recursion via indirect specifications.
Here's a table of the possible elements of a specification list, with
their meanings:
`sexp'
A single Lisp object, not unevaluated.
`form'
A single evaluated expression, which is instrumented.
`place'
A place to store a value, as in the Common Lisp `setf' construct.
`body'
Short for `&rest form'. See `&rest' below.
`function-form'
A function form: either a quoted function symbol, a quoted lambda
expression, or a form (that should evaluate to a function symbol or
lambda expression). This is useful when an argument that's a
lambda expression might be quoted with `quote' rather than
`function', since it instruments the body of the lambda expression
either way.
`lambda-expr'
A lambda expression with no quoting.
`&optional'
All following elements in the specification list are optional; as
soon as one does not match, Edebug stops matching at this level.
To make just a few elements optional followed by non-optional
elements, use `[&optional SPECS...]'. To specify that several
elements must all match or none, use `&optional [SPECS...]'. See
the `defun' example below.
`&rest'
All following elements in the specification list are repeated zero
or more times. All the elements need not match in the last
repetition, however.
To repeat only a few elements, use `[&rest SPECS...]'. To specify
several elements that must all match on every repetition, use
`&rest [SPECS...]'.
`&or'
Each of the following elements in the specification list is an
alternative. One of the alternatives must match, or the `&or'
specification fails.
Each list element following `&or' is a single alternative. To
group two or more list elements as a single alternative, enclose
them in `[...]'.
`¬'
Each of the following elements is matched as alternatives as if by
using `&or', but if any of them match, the specification fails.
If none of them match, nothing is matched, but the `¬'
specification succeeds.
`&define'
Indicates that the specification is for a defining form. The
defining form itself is not instrumented (i.e. Edebug does not
stop before and after the defining form), but forms inside it
typically will be instrumented. The `&define' keyword should be
the first element in a list specification.
`nil'
This is successful when there are no more arguments to match at the
current argument list level; otherwise it fails. See sublist
specifications and the backquote example below.
`gate'
No argument is matched but backtracking through the gate is
disabled while matching the remainder of the specifications at
this level. This is primarily used to generate more specific
syntax error messages. See *Note Backtracking::, for more
details. Also see the `let' example below.
`OTHER-SYMBOL'
Any other symbol in a specification list may be a predicate or an
indirect specification.
If the symbol has an Edebug specification, this "indirect
specification" should be either a list specification that is used
in place of the symbol, or a function that is called to process the
arguments. The specification may be defined with `def-edebug-spec'
just as for macros. See the `defun' example below.
Otherwise, the symbol should be a predicate. The predicate is
called with the argument and the specification fails if the
predicate returns `nil'. In either case, that argument is not
instrumented.
Some suitable predicates include `symbolp', `integerp', `stringp',
`vectorp', and `atom'.
`[ELEMENTS...]'
A vector of elements groups the elements into a single "group
specification". Its meaning has nothing to do with vectors.
`"STRING"'
The argument should be a symbol named STRING. This specification
is equivalent to the quoted symbol, `'SYMBOL', where the name of
SYMBOL is the STRING, but the string form is preferred.
`(vector ELEMENTS...)'
The argument should be a vector whose elements must match the
ELEMENTS in the specification. See the backquote example below.
`(ELEMENTS...)'
Any other list is a "sublist specification" and the argument must
be a list whose elements match the specification ELEMENTS.
A sublist specification may be a dotted list and the corresponding
list argument may then be a dotted list. Alternatively, the last
CDR of a dotted list specification may be another sublist
specification (via a grouping or an indirect specification, e.g.
`(spec . [(more specs...)])') whose elements match the non-dotted
list arguments. This is useful in recursive specifications such
as in the backquote example below. Also see the description of a
`nil' specification above for terminating such recursion.
Note that a sublist specification written as `(specs . nil)' is
equivalent to `(specs)', and `(specs . (sublist-elements...))' is
equivalent to `(specs sublist-elements...)'.
Here is a list of additional specifications that may only appear
after `&define'. See the `defun' example below.
`name'
The argument, a symbol, is the name of the defining form.
A defining form is not required to have a name field; and it may
have multiple name fields.
`:name'
This construct does not actually match an argument. The element
following `:name' should be a symbol; it is used as an additional
name component for the definition. You can use this to add a
unique, static component to the name of the definition. It may be
used more than once.
`arg'
The argument, a symbol, is the name of an argument of the defining
form. However, lambda list keywords (symbols starting with ``&'')
are not allowed.
`lambda-list'
This matches a lambda list--the argument list of a lambda
expression.
`def-body'
The argument is the body of code in a definition. This is like
`body', described above, but a definition body must be instrumented
with a different Edebug call that looks up information associated
with the definition. Use `def-body' for the highest level list of
forms within the definition.
`def-form'
The argument is a single, highest-level form in a definition.
This is like `def-body', except use this to match a single form
rather than a list of forms. As a special case, `def-form' also
means that tracing information is not output when the form is
executed. See the `interactive' example below.
File: elisp, Node: Backtracking, Next: Specification Examples, Prev: Specification List, Up: Instrumenting Macro Calls
Backtracking
............
If a specification fails to match at some point, this does not
necessarily mean a syntax error will be signaled; instead,
"backtracking" will take place until all alternatives have been
exhausted. Eventually every element of the argument list must be
matched by some element in the specification, and every required element
in the specification must match some argument.
Backtracking is disabled for the remainder of a sublist or group when
certain conditions occur, described below. Backtracking is reenabled
when a new alternative is established by `&optional', `&rest', or
`&or'. It is also reenabled initially when processing a sublist or
group specification or an indirect specification.
You might want to disable backtracking to commit to some alternative
so that Edebug can provide a more specific syntax error message.
Normally, if no alternative matches, Edebug reports that none matched,
but if one alternative is committed to, Edebug can report how it failed
to match.
First, backtracking is disabled while matching any of the form
specifications (i.e. `form', `body', `def-form', and `def-body').
These specifications will match any form so any error must be in the
form itself rather than at a higher level.
Second, backtracking is disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct. If you have a set of alternative constructs that
all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
`["foo" &or [first case] [second case] ...]'.
Third, backtracking may be explicitly disabled by using the `gate'
specification. This is useful when you know that no higher
alternatives may apply.
File: elisp, Node: Specification Examples, Prev: Backtracking, Up: Instrumenting Macro Calls
Specification Examples
......................
It may be easier to understand Edebug specifications by studying the
examples provided here.
A `let' special form has a sequence of bindings and a body. Each of
the bindings is either a symbol or a sublist with a symbol and optional
value. In the specification below, notice the `gate' inside of the
sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let
((&rest
&or symbolp (gate symbolp &optional form))
body))
Edebug uses the following specifications for `defun' and `defmacro'
and the associated argument list and `interactive' specifications. It
is necessary to handle interactive forms specially since an expression
argument it is actually evaluated outside of the function body.
(def-edebug-spec defmacro defun) ; Indirect ref to `defun' spec.
(def-edebug-spec defun
(&define name lambda-list
[&optional stringp] ; Match the doc string, if present.
[&optional ("interactive" interactive)]
def-body))
(def-edebug-spec lambda-list
(([&rest arg]
[&optional ["&optional" arg &rest arg]]
&optional ["&rest" arg]
)))
(def-edebug-spec interactive
(&optional &or stringp def-form)) ; Notice: `def-form'
The specification for backquote below illustrates how to match
dotted lists and use `nil' to terminate recursion. It also illustrates
how components of a vector may be matched. (The actual specification
defined by Edebug does not support dotted lists because doing so causes
very deep recursion that could fail.)
(def-edebug-spec ` (backquote-form)) ; Alias just for clarity.
(def-edebug-spec backquote-form
(&or ([&or "," ",@"] &or ("quote" backquote-form) form)
(backquote-form . [&or nil backquote-form])
(vector &rest backquote-form)
sexp))
File: elisp, Node: Edebug Options, Prev: Instrumenting Macro Calls, Up: Edebug
Edebug Options
--------------
These options affect the behavior of Edebug:
- User Option: edebug-setup-hook
Functions to call before Edebug is used. Each time it is set to a
new value, Edebug will call those functions once and then
`edebug-setup-hook' is reset to `nil'. You could use this to load
up Edebug specifications associated with a package you are using
but only when you also use Edebug. *Note Instrumenting::.
- User Option: edebug-all-defs
If this is non-`nil', normal evaluation of defining forms such as
`defun' and `defmacro' instruments them for Edebug. This applies
to `eval-defun', `eval-region', `eval-buffer', and
`eval-current-buffer'.
Use the command `M-x edebug-all-defs' to toggle the value of this
option. *Note Instrumenting::.
- User Option: edebug-all-forms
If this is non-`nil', the commands `eval-defun', `eval-region',
`eval-buffer', and `eval-current-buffer' instrument all forms,
even those that don't define anything. This doesn't apply to
loading or evaluations in the minibuffer.
Use the command `M-x edebug-all-forms' to toggle the value of this
option. *Note Instrumenting::.
- User Option: edebug-save-windows
If this is non-`nil', Edebug saves and restores the window
configuration. That takes some time, so if your program does not
care what happens to the window configurations, it is better to
set this variable to `nil'.
If the value is a list, only the listed windows are saved and
restored.
You can use the `W' command in Edebug to change this variable
interactively. *Note Edebug Display Update::.
- User Option: edebug-save-displayed-buffer-points
If this is non-`nil', Edebug saves and restores point in all
displayed buffers.
Saving and restoring point in other buffers is necessary if you are
debugging code that changes the point of a buffer which is
displayed in a non-selected window. If Edebug or the user then
selects the window, point in that buffer will move to the window's
value of point.
Saving and restoring point in all buffers is expensive, since it
requires selecting each window twice, so enable this only if you
need it. *Note Edebug Display Update::.
- User Option: edebug-initial-mode
If this variable is non-`nil', it specifies the initial execution
mode for Edebug when it is first activated. Possible values are
`step', `next', `go', `Go-nonstop', `trace', `Trace-fast',
`continue', and `Continue-fast'.
The default value is `step'. *Note Edebug Execution Modes::.
- User Option: edebug-trace
Non-`nil' means display a trace of function entry and exit.
Tracing output is displayed in a buffer named `*edebug-trace*', one
function entry or exit per line, indented by the recursion level.
The default value is `nil'.
Also see `edebug-tracing', in *Note Trace Buffer::.
- User Option: edebug-test-coverage
If non-`nil', Edebug tests coverage of all expressions debugged.
This is done by comparing the result of each expression with the
previous result. Coverage is considered OK if two different
results are found. So to sufficiently test the coverage of your
code, try to execute it under conditions that evaluate all
expressions more than once, and produce different results for each
expression.
Use `M-x edebug-display-freq-count' to display the frequency count
and coverage information for a definition. *Note Coverage
Testing::.
- User Option: edebug-continue-kbd-macro
If non-`nil', continue defining or executing any keyboard macro
that is executing outside of Edebug. Use this with caution since
it is not debugged. *Note Edebug Execution Modes::.
- User Option: edebug-print-length
If non-`nil', bind `print-length' to this while printing results
in Edebug. The default value is `50'. *Note Printing in Edebug::.
- User Option: edebug-print-level
If non-`nil', bind `print-level' to this while printing results in
Edebug. The default value is `50'.
- User Option: edebug-print-circle
If non-`nil', bind `print-circle' to this while printing results
in Edebug. The default value is `nil'.
- User Option: edebug-on-error
Edebug binds `debug-on-error' to this value, if `debug-on-error'
was previously `nil'. *Note Trapping Errors::.
- User Option: edebug-on-quit
Edebug binds `debug-on-quit' to this value, if `debug-on-quit' was
previously `nil'. *Note Trapping Errors::.
If you change the values of `edebug-on-error' or `edebug-on-quit'
while Edebug is active, their values won't be used until the *next*
time Edebug is invoked via a new command.
- User Option: edebug-global-break-condition
If non-`nil', an expression to test for at every stop point. If
the result is non-nil, then break. Errors are ignored. *Note
Global Break Condition::.
File: elisp, Node: Read and Print, Next: Minibuffers, Prev: Debugging, Up: Top
Reading and Printing Lisp Objects
*********************************
"Printing" and "reading" are the operations of converting Lisp
objects to textual form and vice versa. They use the printed
representations and read syntax described in *Note Lisp Data Types::.
This chapter describes the Lisp functions for reading and printing.
It also describes "streams", which specify where to get the text (if
reading) or where to put it (if printing).
* Menu:
* Streams Intro:: Overview of streams, reading and printing.
* Input Streams:: Various data types that can be used as input streams.
* Input Functions:: Functions to read Lisp objects from text.
* Output Streams:: Various data types that can be used as output streams.
* Output Functions:: Functions to print Lisp objects as text.
* Output Variables:: Variables that control what the printing functions do.
File: elisp, Node: Streams Intro, Next: Input Streams, Up: Read and Print
Introduction to Reading and Printing
====================================
"Reading" a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
"read syntax" of the object. For example, the text `(a . 5)' is the
read syntax for a cons cell whose CAR is `a' and whose CDR is the
number 5.
"Printing" a Lisp object means producing text that represents that
object--converting the object to its printed representation. Printing
the cons cell described above produces the text `(a . 5)'.
Reading and printing are more or less inverse operations: printing
the object that results from reading a given piece of text often
produces the same text, and reading the text that results from printing
an object usually produces a similar-looking object. For example,
printing the symbol `foo' produces the text `foo', and reading that text
returns the symbol `foo'. Printing a list whose elements are `a' and
`b' produces the text `(a b)', and reading that text produces a list
(but not the same list) with elements `a' and `b'.
However, these two operations are not precisely inverses. There are
three kinds of exceptions:
* Printing can produce text that cannot be read. For example,
buffers, windows, frames, subprocesses and markers print into text
that starts with `#'; if you try to read this text, you get an
error. There is no way to read those data types.
* One object can have multiple textual representations. For example,
`1' and `01' represent the same integer, and `(a b)' and `(a .
(b))' represent the same list. Reading will accept any of the
alternatives, but printing must choose one of them.
* Comments can appear at certain points in the middle of an object's
read sequence without affecting the result of reading it.
File: elisp, 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' 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'.
- Function: get-file-char
This function is used internally as an input stream to read from
the input file opened by the function `load'. Don't use this
function yourself.
File: elisp, 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'.
File: elisp, 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.
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'.
(setq m (set-marker (make-marker) 10 (get-buffer "foo")))
=> #<marker at 10 in foo>
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
=> "This is the output"
m
=> #<marker at 32 in foo>
---------- 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
=> (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
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.
File: elisp, 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 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 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. Emacs 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.
File: elisp, 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-length
The value of this variable is the maximum number of elements of a
list, vector or bitvector that will be printed. If an object
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.
File: elisp, Node: Minibuffers, Next: Command Loop, Prev: Read and Print, Up: Top
Minibuffers
***********
A "minibuffer" is a special buffer that Emacs 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
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.
* 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.
* Minibuffer Misc:: Various customization hooks and variables.
File: elisp, Node: Intro to Minibuffers, Next: Text from Minibuffer, 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. Minibuffers are
displayed only in special windows used only for minibuffers; these
windows always appear at the bottom of a frame. (Sometime 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' or by putting properties of that name on
command symbols (*note Minibuffer Misc::.).
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.
File: elisp, 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
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.
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 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.)
- 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'. The keymap used is `minibuffer-local-map'.
This is a simplified interface to the `read-from-minibuffer'
function:
(read-string PROMPT INITIAL)
==
(read-from-minibuffer PROMPT INITIAL nil nil nil)
- Variable: minibuffer-local-map
This is the default local keymap for reading from the minibuffer.
By default, it makes the following bindings:
LFD
`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'
- Function: read-no-blanks-input PROMPT &optional 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 is a simplified interface to the `read-from-minibuffer'
function, and passes the value of the `minibuffer-local-ns-map'
keymap 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, in addition to those of
`minibuffer-local-map':
SPC
`exit-minibuffer'
TAB
`exit-minibuffer'
`?'
`self-insert-and-exit'
File: elisp, 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-minibuffer PROMPT &optional INITIAL
This function reads a Lisp object in the minibuffer and returns it,
without evaluating it. The arguments PROMPT and INITIAL are used
as in `read-from-minibuffer'.
This is a simplified interface to the `read-from-minibuffer'
function:
(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 (`"')
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.
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 `nil' in this example.