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This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. 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) v3.2, April, May 1997 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. File: lispref.info, Node: Backtracking, Next: Debugging Backquote, 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: lispref.info, Node: Debugging Backquote, Next: Specification Examples, Prev: Backtracking, Up: Instrumenting Macro Calls Debugging Backquote ................... Backquote (``') is a macro that results in an expression that may or may not be evaluated. It is often used to simplify the definition of a macro to return an expression that is evaluted, but Edebug does not know when this is the case. However, the forms inside unquotes (`,' and `,@') are evaluated and Edebug instruments them. Nested backquotes are supported by Edebug, but there is a limit on the support of quotes inside of backquotes. Quoted forms (with `'') are not normally evaluated, but if the quoted form appears immediately within `,' and `,@' forms, Edebug treats this as a backquoted form at the next higher level (even if there is not a next higher level - this is difficult to fix). If the backquoted forms happen to be code intended to be evaluated, you can have Edebug instrument them by using `edebug-`' instead of the regular ``'. Unquoted forms can always appear inside `edebug-`' anywhere a form is normally allowed. But `(, FORM)' may be used in two other places specially recognized by Edebug: wherever a predicate specification would match, and at the head of a list form in place of a function name or lambda expression. The FORM inside a spliced unquote, `(,@ FORM)', will be wrapped, but the unquote form itself will not be wrapped since this would interfere with the splicing. There is one other complication with using `edebug-`'. If the `edebug-`' call is in a macro and the macro may be called from code that is also instrumented, and if unquoted forms contain any macro arguments bound to instrumented forms, then you should modify the specification for the macro as follows: the specifications for those arguments must use `def-form' instead of `form'. (This is to reestablish the Edebugging context for those external forms.) For example, the `for' macro (*note Problems with Macros: ()Problems with Macros.) is shown here but with `edebug-`' substituted for regular ``'. (defmacro inc (var) (list 'setq var (list '1+ var))) (defmacro for (var from init to final do &rest body) (let ((tempvar (make-symbol "max"))) (edebug-` (let (((, var) (, init)) ((, tempvar) (, final))) (while (<= (, var) (, tempvar)) (, body) (inc (, var))))))) Here is the corresponding modified Edebug specification and some code that calls the macro: (def-edebug-spec for (symbolp "from" def-form "to" def-form "do" &rest def-form)) (let ((n 5)) (for i from n to (* n (+ n 1)) do (message "%s" i))) After instrumenting the `for' macro and the macro call, Edebug first steps to the beginning of the macro call, then into the macro body, then through each of the unquoted expressions in the backquote showing the expressions that will be embedded in the backquote form. Then when the macro expansion is evaluated, Edebug will step through the `let' form and each time it gets to an unquoted form, it will jump back to an argument of the macro call to step through that expression. Finally stepping will continue after the macro call. Even more convoluted execution paths may result when using anonymous functions. When the result of an expression is an instrumented expression, it is difficult to see the expression inside the instrumentation. So you may want to set the option `edebug-unwrap-results' to a non-`nil' value while debugging such expressions, but it would slow Edebug down to always do this. File: lispref.info, Node: Specification Examples, Prev: Debugging Backquote, Up: Instrumenting Macro Calls Specification Examples ...................... Here we provide several examples of Edebug specifications to show many of its capabilities. 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. (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 the expression argument of an interactive form specially since 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 provided 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: lispref.info, 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. See *Note Instrumenting::. - User Option: edebug-all-defs If non-`nil', normal evaluation of any defining forms (e.g. `defun' and `defmacro') will instrument them for Edebug. This applies to `eval-defun', `eval-region', and `eval-current-buffer'. Use the command `M-x edebug-all-defs' to toggle the value of this variable. You may want to make this variable local to each buffer by calling `(make-local-variable 'edebug-all-defs)' in your `emacs-lisp-mode-hook'. See *Note Instrumenting::. - User Option: edebug-all-forms If non-`nil', normal evaluation of any forms by `eval-defun', `eval-region', and `eval-current-buffer' will instrument them for Edebug. Use the command `M-x edebug-all-forms' to toggle the value of this option. See *Note Instrumenting::. - User Option: edebug-save-windows If non-`nil', save and restore window configuration on Edebug calls. It takes some time to do this, so if your program does not care what happens to data about windows, you may want to set this variable to `nil'. If the value is a list, only the listed windows are saved and restored. `M-x edebug-toggle-save-windows' may be used to change this variable. This command is bound to `W' in source code buffers. See *Note Edebug Display Update::. - User Option: edebug-save-displayed-buffer-points If non-`nil', save and restore point in all displayed buffers. This 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, the buffer's point will be changed to the window's point. This is an expensive operation since it visits each window and therefore each displayed buffer twice for each Edebug activation, so it is best to avoid it if you can. See *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'. See *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'. See *Note Tracing::. - 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. See *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. See *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'. See *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 `debug-on-error' is bound to this while Edebug is active. See *Note Trapping Errors::. - User Option: edebug-on-quit `debug-on-quit' is bound to this while Edebug is active. See *Note Trapping Errors::. - User Option: edebug-unwrap-results Non-`nil' if Edebug should unwrap results of expressions. This is useful when debugging macros where the results of expressions are instrumented expressions. But don't do this when results might be circular or an infinite loop will result. See *Note Debugging Backquote::. - 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. See *Note Global Break Condition::. File: lispref.info, 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: lispref.info, 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: 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'. 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'. 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. 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. 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. 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. * Minibuffer Misc:: Various customization hooks and variables. 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. (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'. 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: 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 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: 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-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 `t' in this example.