2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 2006, 2010, 2011, 2012
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
7 @node Using Guile Interactively
8 @section Using Guile Interactively
10 When you start up Guile by typing just @code{guile}, without a
11 @code{-c} argument or the name of a script to execute, you get an
12 interactive interpreter where you can enter Scheme expressions, and
13 Guile will evaluate them and print the results for you. Here are some
17 scheme@@(guile-user)> (+ 3 4 5)
19 scheme@@(guile-user)> (display "Hello world!\n")
21 scheme@@(guile-user)> (values 'a 'b)
27 This mode of use is called a @dfn{REPL}, which is short for
28 ``Read-Eval-Print Loop'', because the Guile interpreter first reads the
29 expression that you have typed, then evaluates it, and then prints the
32 The prompt shows you what language and module you are in. In this case, the
33 current language is @code{scheme}, and the current module is
34 @code{(guile-user)}. @xref{Other Languages}, for more information on Guile's
35 support for languages other than Scheme.
43 * Interactive Debugging::
48 @subsection The Init File, @file{~/.guile}
51 When run interactively, Guile will load a local initialization file from
52 @file{~/.guile}. This file should contain Scheme expressions for
55 This facility lets the user customize their interactive Guile
56 environment, pulling in extra modules or parameterizing the REPL
59 To run Guile without loading the init file, use the @code{-q}
66 To make it easier for you to repeat and vary previously entered
67 expressions, or to edit the expression that you're typing in, Guile
68 can use the GNU Readline library. This is not enabled by default
69 because of licensing reasons, but all you need to activate Readline is
70 the following pair of lines.
73 scheme@@(guile-user)> (use-modules (ice-9 readline))
74 scheme@@(guile-user)> (activate-readline)
77 It's a good idea to put these two lines (without the
78 @code{scheme@@(guile-user)>} prompts) in your @file{.guile} file.
79 @xref{Init File}, for more on @file{.guile}.
83 @subsection Value History
85 Just as Readline helps you to reuse a previous input line, @dfn{value
86 history} allows you to use the @emph{result} of a previous evaluation in
87 a new expression. When value history is enabled, each evaluation result
88 is automatically assigned to the next in the sequence of variables
89 @code{$1}, @code{$2}, @dots{}. You can then use these variables in
90 subsequent expressions.
93 scheme@@(guile-user)> (iota 10)
94 $1 = (0 1 2 3 4 5 6 7 8 9)
95 scheme@@(guile-user)> (apply * (cdr $1))
97 scheme@@(guile-user)> (sqrt $2)
98 $3 = 602.3952191045344
99 scheme@@(guile-user)> (cons $2 $1)
100 $4 = (362880 0 1 2 3 4 5 6 7 8 9)
103 Value history is enabled by default, because Guile's REPL imports the
104 @code{(ice-9 history)} module. Value history may be turned off or on within the
105 repl, using the options interface:
108 scheme@@(guile-user)> ,option value-history #f
109 scheme@@(guile-user)> 'foo
111 scheme@@(guile-user)> ,option value-history #t
112 scheme@@(guile-user)> 'bar
116 Note that previously recorded values are still accessible, even if value history
117 is off. In rare cases, these references to past computations can cause Guile to
118 use too much memory. One may clear these values, possibly enabling garbage
119 collection, via the @code{clear-value-history!} procedure, described below.
121 The programmatic interface to value history is in a module:
124 (use-modules (ice-9 history))
127 @deffn {Scheme Procedure} value-history-enabled?
128 Return true iff value history is enabled.
131 @deffn {Scheme Procedure} enable-value-history!
132 Turn on value history, if it was off.
135 @deffn {Scheme Procedure} disable-value-history!
136 Turn off value history, if it was on.
139 @deffn {Scheme Procedure} clear-value-history!
140 Clear the value history. If the stored values are not captured by some other
141 data structure or closure, they may then be reclaimed by the garbage collector.
146 @subsection REPL Commands
149 The REPL exists to read expressions, evaluate them, and then print their
150 results. But sometimes one wants to tell the REPL to evaluate an
151 expression in a different way, or to do something else altogether. A
152 user can affect the way the REPL works with a @dfn{REPL command}.
154 The previous section had an example of a command, in the form of
158 scheme@@(guile-user)> ,option value-history #t
162 Commands are distinguished from expressions by their initial comma
163 (@samp{,}). Since a comma cannot begin an expression in most languages,
164 it is an effective indicator to the REPL that the following text forms a
165 command, not an expression.
167 REPL commands are convenient because they are always there. Even if the
168 current module doesn't have a binding for @code{pretty-print}, one can
169 always @code{,pretty-print}.
171 The following sections document the various commands, grouped together
172 by functionality. Many of the commands have abbreviations; see the
173 online help (@code{,help}) for more information.
178 * Language Commands::
187 @subsubsection Help Commands
189 When Guile starts interactively, it notifies the user that help can be
190 had by typing @samp{,help}. Indeed, @code{help} is a command, and a
191 particularly useful one, as it allows the user to discover the rest of
194 @deffn {REPL Command} help [@code{all} | group | @code{[-c]} command]
197 With one argument, tries to look up the argument as a group name, giving
198 help on that group if successful. Otherwise tries to look up the
199 argument as a command, giving help on the command.
201 If there is a command whose name is also a group name, use the @samp{-c
202 @var{command}} form to give help on the command instead of the group.
204 Without any argument, a list of help commands and command groups
208 @deffn {REPL Command} show [topic]
209 Gives information about Guile.
211 With one argument, tries to show a particular piece of information;
212 currently supported topics are `warranty' (or `w'), `copying' (or `c'),
213 and `version' (or `v').
215 Without any argument, a list of topics is displayed.
218 @deffn {REPL Command} apropos regexp
219 Find bindings/modules/packages.
222 @deffn {REPL Command} describe obj
223 Show description/documentation.
226 @node Module Commands
227 @subsubsection Module Commands
229 @deffn {REPL Command} module [module]
230 Change modules / Show current module.
233 @deffn {REPL Command} import module @dots{}
234 Import modules / List those imported.
237 @deffn {REPL Command} load file
238 Load a file in the current module.
241 @deffn {REPL Command} reload [module]
242 Reload the given module, or the current module if none was given.
245 @deffn {REPL Command} binding
246 List current bindings.
249 @deffn {REPL Command} in module expression
250 @deffnx {REPL Command} in module command arg @dots{}
251 Evaluate an expression, or alternatively, execute another meta-command
252 in the context of a module. For example, @samp{,in (foo bar) ,binding}
253 will show the bindings in the module @code{(foo bar)}.
256 @node Language Commands
257 @subsubsection Language Commands
259 @deffn {REPL Command} language language
263 @node Compile Commands
264 @subsubsection Compile Commands
266 @deffn {REPL Command} compile exp
267 Generate compiled code.
270 @deffn {REPL Command} compile-file file
274 @deffn {REPL Command} expand exp
275 Expand any macros in a form.
278 @deffn {REPL Command} optimize exp
279 Run the optimizer on a piece of code and print the result.
282 @deffn {REPL Command} disassemble exp
283 Disassemble a compiled procedure.
286 @deffn {REPL Command} disassemble-file file
290 @node Profile Commands
291 @subsubsection Profile Commands
293 @deffn {REPL Command} time exp
297 @deffn {REPL Command} profile exp
301 @deffn {REPL Command} trace exp
306 @subsubsection Debug Commands
308 These debugging commands are only available within a recursive REPL;
309 they do not work at the top level.
311 @deffn {REPL Command} backtrace [count] [#:width w] [#:full? f]
314 Print a backtrace of all stack frames, or innermost @var{count} frames.
315 If @var{count} is negative, the last @var{count} frames will be shown.
318 @deffn {REPL Command} up [count]
319 Select a calling stack frame.
321 Select and print stack frames that called this one.
322 An argument says how many frames up to go.
325 @deffn {REPL Command} down [count]
326 Select a called stack frame.
328 Select and print stack frames called by this one.
329 An argument says how many frames down to go.
332 @deffn {REPL Command} frame [idx]
335 Show the selected frame. With an argument, select a frame by index,
339 @deffn {REPL Command} procedure
340 Print the procedure for the selected frame.
343 @deffn {REPL Command} locals
344 Show local variables.
346 Show locally-bound variables in the selected frame.
349 @deffn {REPL Command} error-message
350 @deffnx {REPL Command} error
353 Display the message associated with the error that started the current
357 @deffn {REPL Command} registers
358 Show the VM registers associated with the current frame.
360 @xref{Stack Layout}, for more information on VM stack frames.
363 @deffn {REPL Command} width [cols]
364 Sets the number of display columns in the output of @code{,backtrace}
365 and @code{,locals} to @var{cols}. If @var{cols} is not given, the width
366 of the terminal is used.
369 The next 3 commands work at any REPL.
371 @deffn {REPL Command} break proc
372 Set a breakpoint at @var{proc}.
375 @deffn {REPL Command} break-at-source file line
376 Set a breakpoint at the given source location.
379 @deffn {REPL Command} tracepoint proc
380 Set a tracepoint on the given procedure. This will cause all calls to
381 the procedure to print out a tracing message. @xref{Tracing Traps}, for
385 The rest of the commands in this subsection all apply only when the
386 stack is @dfn{continuable} --- in other words when it makes sense for
387 the program that the stack comes from to continue running. Usually this
388 means that the program stopped because of a trap or a breakpoint.
390 @deffn {REPL Command} step
391 Tell the debugged program to step to the next source location.
394 @deffn {REPL Command} next
395 Tell the debugged program to step to the next source location in the
396 same frame. (See @ref{Traps} for the details of how this works.)
399 @deffn {REPL Command} finish
400 Tell the program being debugged to continue running until the completion
401 of the current stack frame, and at that time to print the result and
406 @node Inspect Commands
407 @subsubsection Inspect Commands
409 @deffn {REPL Command} inspect exp
410 Inspect the result(s) of evaluating @var{exp}.
413 @deffn {REPL Command} pretty-print exp
414 Pretty-print the result(s) of evaluating @var{exp}.
417 @node System Commands
418 @subsubsection System Commands
420 @deffn {REPL Command} gc
424 @deffn {REPL Command} statistics
428 @deffn {REPL Command} option [key value]
429 List/show/set options.
432 @deffn {REPL Command} quit
436 Current REPL options include:
439 @item compile-options
440 The options used when compiling expressions entered at the REPL.
441 @xref{Compilation}, for more on compilation options.
443 Whether to interpret or compile expressions given at the REPL, if such a
444 choice is available. Off by default (indicating compilation).
446 A customized REPL prompt. @code{#f} by default, indicating the default
449 A procedure of two arguments used to print the result of evaluating each
450 expression. The arguments are the current REPL and the value to print.
451 By default, @code{#f}, to use the default procedure.
453 Whether value history is on or not. @xref{Value History}.
455 What to do when an error happens. By default, @code{debug}, meaning to
456 enter the debugger. Other values include @code{backtrace}, to show a
457 backtrace without entering the debugger, or @code{report}, to simply
458 show a short error printout.
461 Default values for REPL options may be set using
462 @code{repl-default-option-set!} from @code{(system repl common)}:
464 @deffn {Scheme Procedure} repl-default-option-set! key value
465 Set the default value of a REPL option. This function is particularly
466 useful in a user's init file. @xref{Init File}.
471 @subsection Error Handling
473 When code being evaluated from the REPL hits an error, Guile enters a
474 new prompt, allowing you to inspect the context of the error.
477 scheme@@(guile-user)> (map string-append '("a" "b") '("c" #\d))
478 ERROR: In procedure string-append:
479 ERROR: Wrong type (expecting string): #\d
480 Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
481 scheme@@(guile-user) [1]>
484 The new prompt runs inside the old one, in the dynamic context of the
485 error. It is a recursive REPL, augmented with a reified representation
486 of the stack, ready for debugging.
488 @code{,backtrace} (abbreviated @code{,bt}) displays the Scheme call
489 stack at the point where the error occurred:
492 scheme@@(guile-user) [1]> ,bt
493 1 (map #<procedure string-append _> ("a" "b") ("c" #\d))
494 0 (string-append "b" #\d)
497 In the above example, the backtrace doesn't have much source
498 information, as @code{map} and @code{string-append} are both
499 primitives. But in the general case, the space on the left of the
500 backtrace indicates the line and column in which a given procedure calls
503 You can exit a recursive REPL in the same way that you exit any REPL:
504 via @samp{(quit)}, @samp{,quit} (abbreviated @samp{,q}), or
505 @kbd{C-d}, among other options.
508 @node Interactive Debugging
509 @subsection Interactive Debugging
511 A recursive debugging REPL exposes a number of other meta-commands that
512 inspect the state of the computation at the time of the error. These
513 commands allow you to
517 display the Scheme call stack at the point where the error occurred;
520 move up and down the call stack, to see in detail the expression being
521 evaluated, or the procedure being applied, in each @dfn{frame}; and
524 examine the values of variables and expressions in the context of each
529 @xref{Debug Commands}, for documentation of the individual
530 commands. This section aims to give more of a walkthrough of a typical
533 First, we're going to need a good error. Let's try to macroexpand the
534 expression @code{(unquote foo)}, outside of a @code{quasiquote} form,
535 and see how the macroexpander reports this error.
538 scheme@@(guile-user)> (macroexpand '(unquote foo))
539 ERROR: In procedure macroexpand:
540 ERROR: unquote: expression not valid outside of quasiquote in (unquote foo)
541 Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
542 scheme@@(guile-user) [1]>
545 The @code{backtrace} command, which can also be invoked as @code{bt},
546 displays the call stack (aka backtrace) at the point where the debugger
550 scheme@@(guile-user) [1]> ,bt
551 In ice-9/psyntax.scm:
552 1130:21 3 (chi-top (unquote foo) () ((top)) e (eval) (hygiene #))
553 1071:30 2 (syntax-type (unquote foo) () ((top)) #f #f (# #) #f)
554 1368:28 1 (chi-macro #<procedure de9360 at ice-9/psyntax.scm...> ...)
556 0 (scm-error syntax-error macroexpand "~a: ~a in ~a" # #f)
559 A call stack consists of a sequence of stack @dfn{frames}, with each
560 frame describing one procedure which is waiting to do something with the
561 values returned by another. Here we see that there are four frames on
564 Note that @code{macroexpand} is not on the stack -- it must have made a
565 tail call to @code{chi-top}, as indeed we would find if we searched
566 @code{ice-9/psyntax.scm} for its definition.
568 When you enter the debugger, the innermost frame is selected, which
569 means that the commands for getting information about the ``current''
570 frame, or for evaluating expressions in the context of the current
571 frame, will do so by default with respect to the innermost frame. To
572 select a different frame, so that these operations will apply to it
573 instead, use the @code{up}, @code{down} and @code{frame} commands like
577 scheme@@(guile-user) [1]> ,up
578 In ice-9/psyntax.scm:
579 1368:28 1 (chi-macro #<procedure de9360 at ice-9/psyntax.scm...> ...)
580 scheme@@(guile-user) [1]> ,frame 3
581 In ice-9/psyntax.scm:
582 1130:21 3 (chi-top (unquote foo) () ((top)) e (eval) (hygiene #))
583 scheme@@(guile-user) [1]> ,down
584 In ice-9/psyntax.scm:
585 1071:30 2 (syntax-type (unquote foo) () ((top)) #f #f (# #) #f)
588 Perhaps we're interested in what's going on in frame 2, so we take a
589 look at its local variables:
592 scheme@@(guile-user) [1]> ,locals
594 $1 = e = (unquote foo)
599 $6 = mod = (hygiene guile-user)
603 $10 = fval = #<procedure de9360 at ice-9/psyntax.scm:2817:2 (x)>
607 $14 = fmod = (hygiene guile-user)
610 All of the values are accessible by their value-history names
614 scheme@@(guile-user) [1]> $10
615 $15 = #<procedure de9360 at ice-9/psyntax.scm:2817:2 (x)>
618 We can even invoke the procedure at the REPL directly:
621 scheme@@(guile-user) [1]> ($10 'not-going-to-work)
622 ERROR: In procedure macroexpand:
623 ERROR: source expression failed to match any pattern in not-going-to-work
624 Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
627 Well at this point we've caused an error within an error. Let's just
628 quit back to the top level:
631 scheme@@(guile-user) [2]> ,q
632 scheme@@(guile-user) [1]> ,q
633 scheme@@(guile-user)>
636 Finally, as a word to the wise: hackers close their REPL prompts with
640 @node Using Guile in Emacs
641 @section Using Guile in Emacs
644 Any text editor can edit Scheme, but some are better than others. Emacs
645 is the best, of course, and not just because it is a fine text editor.
646 Emacs has good support for Scheme out of the box, with sensible
647 indentation rules, parenthesis-matching, syntax highlighting, and even a
648 set of keybindings for structural editing, allowing navigation,
649 cut-and-paste, and transposition operations that work on balanced
652 As good as it is, though, two things will vastly improve your experience
653 with Emacs and Guile.
656 The first is Taylor Campbell's
657 @uref{http://www.emacswiki.org/emacs/ParEdit, Paredit}. You should not
658 code in any dialect of Lisp without Paredit. (They say that
659 unopinionated writing is boring---hence this tone---but it's the
660 truth, regardless.) Paredit is the bee's knees.
670 Antonio Ortega Ruiz's
671 @uref{http://www.nongnu.org/geiser/, Geiser}. Geiser complements Emacs'
672 @code{scheme-mode} with tight integration to running Guile processes via
673 a @code{comint-mode} REPL buffer.
675 Of course there are keybindings to switch to the REPL, and a good REPL
676 environment, but Geiser goes beyond that, providing:
680 Form evaluation in the context of the current file's module.
684 File/module loading and/or compilation.
686 Namespace-aware identifier completion (including local bindings, names
687 visible in the current module, and module names).
689 Autodoc: the echo area shows information about the signature of the
690 procedure/macro around point automatically.
692 Jump to definition of identifier at point.
694 Access to documentation (including docstrings when the implementation
697 Listings of identifiers exported by a given module.
699 Listings of callers/callees of procedures.
701 Rudimentary support for debugging and error navigation.
703 Support for multiple, simultaneous REPLs.
706 See Geiser's web page at @uref{http://www.nongnu.org/geiser/}, for more
710 @node Using Guile Tools
711 @section Using Guile Tools
716 Guile also comes with a growing number of command-line utilities: a
717 compiler, a disassembler, some module inspectors, and in the future, a
718 system to install Guile packages from the internet. These tools may be
719 invoked using the @code{guild} program.
722 $ guild compile -o foo.go foo.scm
726 This program used to be called @code{guile-tools} up to
727 Guile version 2.0.1, and for backward
728 compatibility it still may be called as such. However we changed the
729 name to @code{guild}, not only because it is pleasantly shorter and
730 easier to read, but also because this tool will serve to bind Guile
731 wizards together, by allowing hackers to share code with each other
732 using a CPAN-like system.
734 @xref{Compilation}, for more on @code{guild compile}.
736 A complete list of guild scripts can be had by invoking @code{guild
737 list}, or simply @code{guild}.
740 @node Installing Site Packages
741 @section Installing Site Packages
748 At some point, you will probably want to share your code with other
749 people. To do so effectively, it is important to follow a set of common
750 conventions, to make it easy for the user to install and use your
753 The first thing to do is to install your Scheme files where Guile can
754 find them. When Guile goes to find a Scheme file, it will search a
755 @dfn{load path} to find the file: first in Guile's own path, then in
756 paths for @dfn{site packages}. A site package is any Scheme code that
757 is installed and not part of Guile itself. @xref{Load Paths}, for more
760 There are several site paths, for historical reasons, but the one that
761 should generally be used can be obtained by invoking the
762 @code{%site-dir} procedure. @xref{Build Config}. If Guile
763 @value{EFFECTIVE-VERSION} is installed on your system in @code{/usr/},
764 then @code{(%site-dir)} will be
765 @code{/usr/share/guile/site/@value{EFFECTIVE-VERSION}}. Scheme files
766 should be installed there.
768 If you do not install compiled @code{.go} files, Guile will compile your
769 modules and programs when they are first used, and cache them in the
770 user's home directory. @xref{Compilation}, for more on
771 auto-compilation. However, it is better to compile the files before
772 they are installed, and to just copy the files to a place that Guile can
775 As with Scheme files, Guile searches a path to find compiled @code{.go}
776 files, the @code{%load-compiled-path}. By default, this path has two
777 entries: a path for Guile's files, and a path for site packages. You
778 should install your @code{.go} files into the latter. Currently there
779 is no procedure to get at this path, which is probably a bug. As in the
780 previous example, if Guile @value{EFFECTIVE-VERSION} is installed on
781 your system in @code{/usr/}, then the place to put compiled files for
782 site packages will be
783 @code{/usr/lib/guile/@value{EFFECTIVE-VERSION}/site-ccache}.
785 Note that a @code{.go} file will only be loaded in preference to a
786 @code{.scm} file if it is newer. For that reason, you should install
787 your Scheme files first, and your compiled files second. @code{Load
788 Paths}, for more on the loading process.
790 Finally, although this section is only about Scheme, sometimes you need
791 to install C extensions too. Shared libraries should be installed in
792 the @dfn{extensions dir}. This value can be had from the build config
793 (@pxref{Build Config}). Again, if Guile @value{EFFECTIVE-VERSION} is
794 installed on your system in @code{/usr/}, then the extensions dir will
795 be @code{/usr/lib/guile/@value{EFFECTIVE-VERSION}/extensions}.
799 @c TeX-master: "guile.texi"