2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 2006, 2010, 2011
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 ...]
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 [args ...]
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 Whether value history is on or not. @xref{Value History}.
451 What to do when an error happens. By default, @code{debug}, meaning to
452 enter the debugger. Other values include @code{backtrace}, to show a
453 backtrace without entering the debugger, or @code{report}, to simply
454 show a short error printout.
457 Default values for REPL options may be set using
458 @code{repl-default-option-set!} from @code{(system repl common)}:
460 @deffn {Scheme Procedure} repl-set-default-option! key value
461 Set the default value of a REPL option. This function is particularly
462 useful in a user's init file. @xref{Init File}.
467 @subsection Error Handling
469 When code being evaluated from the REPL hits an error, Guile enters a
470 new prompt, allowing you to inspect the context of the error.
473 scheme@@(guile-user)> (map string-append '("a" "b") '("c" #\d))
474 ERROR: In procedure string-append:
475 ERROR: Wrong type (expecting string): #\d
476 Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
477 scheme@@(guile-user) [1]>
480 The new prompt runs inside the old one, in the dynamic context of the
481 error. It is a recursive REPL, augmented with a reified representation
482 of the stack, ready for debugging.
484 @code{,backtrace} (abbreviated @code{,bt}) displays the Scheme call
485 stack at the point where the error occurred:
488 scheme@@(guile-user) [1]> ,bt
489 1 (map #<procedure string-append _> ("a" "b") ("c" #\d))
490 0 (string-append "b" #\d)
493 In the above example, the backtrace doesn't have much source
494 information, as @code{map} and @code{string-append} are both
495 primitives. But in the general case, the space on the left of the
496 backtrace indicates the line and column in which a given procedure calls
499 You can exit a recursive REPL in the same way that you exit any REPL:
500 via @samp{(quit)}, @samp{,quit} (abbreviated @samp{,q}), or
501 @kbd{C-d}, among other options.
504 @node Interactive Debugging
505 @subsection Interactive Debugging
507 A recursive debugging REPL exposes a number of other meta-commands that
508 inspect the state of the computation at the time of the error. These
509 commands allow you to
513 display the Scheme call stack at the point where the error occurred;
516 move up and down the call stack, to see in detail the expression being
517 evaluated, or the procedure being applied, in each @dfn{frame}; and
520 examine the values of variables and expressions in the context of each
525 @xref{Debug Commands}, for documentation of the individual
526 commands. This section aims to give more of a walkthrough of a typical
529 First, we're going to need a good error. Let's try to macroexpand the
530 expression @code{(unquote foo)}, outside of a @code{quasiquote} form,
531 and see how the macroexpander reports this error.
534 scheme@@(guile-user)> (macroexpand '(unquote foo))
535 ERROR: In procedure macroexpand:
536 ERROR: unquote: expression not valid outside of quasiquote in (unquote foo)
537 Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
538 scheme@@(guile-user) [1]>
541 The @code{backtrace} command, which can also be invoked as @code{bt},
542 displays the call stack (aka backtrace) at the point where the debugger
546 scheme@@(guile-user) [1]> ,bt
547 In ice-9/psyntax.scm:
548 1130:21 3 (chi-top (unquote foo) () ((top)) e (eval) (hygiene #))
549 1071:30 2 (syntax-type (unquote foo) () ((top)) #f #f (# #) #f)
550 1368:28 1 (chi-macro #<procedure de9360 at ice-9/psyntax.scm...> ...)
552 0 (scm-error syntax-error macroexpand "~a: ~a in ~a" # #f)
555 A call stack consists of a sequence of stack @dfn{frames}, with each
556 frame describing one procedure which is waiting to do something with the
557 values returned by another. Here we see that there are four frames on
560 Note that @code{macroexpand} is not on the stack -- it must have made a
561 tail call to @code{chi-top}, as indeed we would find if we searched
562 @code{ice-9/psyntax.scm} for its definition.
564 When you enter the debugger, the innermost frame is selected, which
565 means that the commands for getting information about the ``current''
566 frame, or for evaluating expressions in the context of the current
567 frame, will do so by default with respect to the innermost frame. To
568 select a different frame, so that these operations will apply to it
569 instead, use the @code{up}, @code{down} and @code{frame} commands like
573 scheme@@(guile-user) [1]> ,up
574 In ice-9/psyntax.scm:
575 1368:28 1 (chi-macro #<procedure de9360 at ice-9/psyntax.scm...> ...)
576 scheme@@(guile-user) [1]> ,frame 3
577 In ice-9/psyntax.scm:
578 1130:21 3 (chi-top (unquote foo) () ((top)) e (eval) (hygiene #))
579 scheme@@(guile-user) [1]> ,down
580 In ice-9/psyntax.scm:
581 1071:30 2 (syntax-type (unquote foo) () ((top)) #f #f (# #) #f)
584 Perhaps we're interested in what's going on in frame 2, so we take a
585 look at its local variables:
588 scheme@@(guile-user) [1]> ,locals
590 $1 = e = (unquote foo)
595 $6 = mod = (hygiene guile-user)
599 $10 = fval = #<procedure de9360 at ice-9/psyntax.scm:2817:2 (x)>
603 $14 = fmod = (hygiene guile-user)
606 All of the values are accessible by their value-history names
610 scheme@@(guile-user) [1]> $10
611 $15 = #<procedure de9360 at ice-9/psyntax.scm:2817:2 (x)>
614 We can even invoke the procedure at the REPL directly:
617 scheme@@(guile-user) [1]> ($10 'not-going-to-work)
618 ERROR: In procedure macroexpand:
619 ERROR: source expression failed to match any pattern in not-going-to-work
620 Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
623 Well at this point we've caused an error within an error. Let's just
624 quit back to the top level:
627 scheme@@(guile-user) [2]> ,q
628 scheme@@(guile-user) [1]> ,q
629 scheme@@(guile-user)>
632 Finally, as a word to the wise: hackers close their REPL prompts with
636 @node Using Guile in Emacs
637 @section Using Guile in Emacs
640 Any text editor can edit Scheme, but some are better than others. Emacs
641 is the best, of course, and not just because it is a fine text editor.
642 Emacs has good support for Scheme out of the box, with sensible
643 indentation rules, parenthesis-matching, syntax highlighting, and even a
644 set of keybindings for structural editing, allowing navigation,
645 cut-and-paste, and transposition operations that work on balanced
648 As good as it is, though, two things will vastly improve your experience
649 with Emacs and Guile.
652 The first is Taylor Campbell's
653 @uref{http://www.emacswiki.org/emacs/ParEdit, Paredit}. You should not
654 code in any dialect of Lisp without Paredit. (They say that
655 unopinionated writing is boring---hence this tone---but it's the
656 truth, regardless.) Paredit is the bee's knees.
666 Antonio Ortega Ruiz's
667 @uref{http://www.nongnu.org/geiser/, Geiser}. Geiser complements Emacs'
668 @code{scheme-mode} with tight integration to running Guile processes via
669 a @code{comint-mode} REPL buffer.
671 Of course there are keybindings to switch to the REPL, and a good REPL
672 environment, but Geiser goes beyond that, providing:
676 Form evaluation in the context of the current file's module.
680 File/module loading and/or compilation.
682 Namespace-aware identifier completion (including local bindings, names
683 visible in the current module, and module names).
685 Autodoc: the echo area shows information about the signature of the
686 procedure/macro around point automatically.
688 Jump to definition of identifier at point.
690 Access to documentation (including docstrings when the implementation
693 Listings of identifiers exported by a given module.
695 Listings of callers/callees of procedures.
697 Rudimentary support for debugging and error navigation.
699 Support for multiple, simultaneous REPLs.
702 See Geiser's web page at @uref{http://www.nongnu.org/geiser/}, for more
706 @node Using Guile Tools
707 @section Using Guile Tools
712 Guile also comes with a growing number of command-line utilities: a
713 compiler, a disassembler, some module inspectors, and in the future, a
714 system to install Guile packages from the internet. These tools may be
715 invoked using the @code{guild} program.
718 $ guild compile -o foo.go foo.scm
722 This program used to be called @code{guile-tools} up to
723 Guile version 2.0.1, and for backward
724 compatibility it still may be called as such. However we changed the
725 name to @code{guild}, not only because it is pleasantly shorter and
726 easier to read, but also because this tool will serve to bind Guile
727 wizards together, by allowing hackers to share code with each other
728 using a CPAN-like system.
730 @xref{Compilation}, for more on @code{guild compile}.
732 A complete list of guild scripts can be had by invoking @code{guild
733 list}, or simply @code{guild}.
736 @node Installing Site Packages
737 @section Installing Site Packages
744 At some point, you will probably want to share your code with other
745 people. To do so effectively, it is important to follow a set of common
746 conventions, to make it easy for the user to install and use your
749 The first thing to do is to install your Scheme files where Guile can
750 find them. When Guile goes to find a Scheme file, it will search a
751 @dfn{load path} to find the file: first in Guile's own path, then in
752 paths for @dfn{site packages}. A site package is any Scheme code that
753 is installed and not part of Guile itself. @xref{Loading}, for more on
756 There are several site paths, for historical reasons, but the one that
757 should generally be used can be obtained by invoking the
758 @code{%site-dir} procedure. @xref{Build Config}. If Guile
759 @value{EFFECTIVE-VERSION} is installed on your system in @code{/usr/},
760 then @code{(%site-dir)} will be
761 @code{/usr/share/guile/site/@value{EFFECTIVE-VERSION}}. Scheme files
762 should be installed there.
764 If you do not install compiled @code{.go} files, Guile will compile your
765 modules and programs when they are first used, and cache them in the
766 user's home directory. @xref{Compilation}, for more on
767 auto-compilation. However, it is better to compile the files before
768 they are installed, and to just copy the files to a place that Guile can
771 As with Scheme files, Guile searches a path to find compiled @code{.go}
772 files, the @code{%load-compiled-path}. By default, this path has two
773 entries: a path for Guile's files, and a path for site packages. You
774 should install your @code{.go} files into the latter. Currently there
775 is no procedure to get at this path, which is probably a bug. As in the
776 previous example, if Guile @value{EFFECTIVE-VERSION} is installed on
777 your system in @code{/usr/}, then the place to put compiled files for
778 site packages will be
779 @code{/usr/lib/guile/@value{EFFECTIVE-VERSION}/site-ccache}.
781 Note that a @code{.go} file will only be loaded in preference to a
782 @code{.scm} file if it is newer. For that reason, you should install
783 your Scheme files first, and your compiled files second.
785 Finally, although this section is only about Scheme, sometimes you need
786 to install C extensions too. Shared libraries should be installed in
787 the @dfn{extensions dir}. This value can be had from the build config
788 (@pxref{Build Config}). Again, if Guile @value{EFFECTIVE-VERSION} is
789 installed on your system in @code{/usr/}, then the extensions dir will
790 be @code{/usr/lib/guile/@value{EFFECTIVE-VERSION}/extensions}.
794 @c TeX-master: "guile.texi"