merge from master to elisp
[bpt/guile.git] / doc / ref / api-options.texi
1 @c -*-texinfo-*-
2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2008, 2009
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
6
7 @page
8 @node Options and Config
9 @section Configuration, Features and Runtime Options
10
11 Why is my Guile different from your Guile? There are three kinds of
12 possible variation:
13
14 @itemize @bullet
15 @item
16 build differences --- different versions of the Guile source code,
17 installation directories, configuration flags that control pieces of
18 functionality being included or left out, etc.
19
20 @item
21 differences in dynamically loaded code --- behaviour and features
22 provided by modules that can be dynamically loaded into a running Guile
23
24 @item
25 different runtime options --- some of the options that are provided for
26 controlling Guile's behaviour may be set differently.
27 @end itemize
28
29 Guile provides ``introspective'' variables and procedures to query all
30 of these possible variations at runtime. For runtime options, it also
31 provides procedures to change the settings of options and to obtain
32 documentation on what the options mean.
33
34 @menu
35 * Build Config:: Build and installation configuration.
36 * Feature Tracking:: Available features in the Guile process.
37 * Runtime Options:: Controlling Guile's runtime behaviour.
38 @end menu
39
40
41 @node Build Config
42 @subsection Configuration, Build and Installation
43
44 The following procedures and variables provide information about how
45 Guile was configured, built and installed on your system.
46
47 @deffn {Scheme Procedure} version
48 @deffnx {Scheme Procedure} effective-version
49 @deffnx {Scheme Procedure} major-version
50 @deffnx {Scheme Procedure} minor-version
51 @deffnx {Scheme Procedure} micro-version
52 @deffnx {C Function} scm_version ()
53 @deffnx {C Function} scm_effective_version ()
54 @deffnx {C Function} scm_major_version ()
55 @deffnx {C Function} scm_minor_version ()
56 @deffnx {C Function} scm_micro_version ()
57 Return a string describing Guile's full version number, effective
58 version number, major, minor or micro version number, respectively.
59 The @code{effective-version} function returns the version name that
60 should remain unchanged during a stable series. Currently that means
61 that it omits the micro version. The effective version should be used
62 for items like the versioned share directory name
63 i.e. @file{/usr/share/guile/1.6/}
64
65 @lisp
66 (version) @result{} "1.6.0"
67 (effective-version) @result{} "1.6"
68 (major-version) @result{} "1"
69 (minor-version) @result{} "6"
70 (micro-version) @result{} "0"
71 @end lisp
72 @end deffn
73
74 @deffn {Scheme Procedure} %package-data-dir
75 @deffnx {C Function} scm_sys_package_data_dir ()
76 Return the name of the directory under which Guile Scheme files in
77 general are stored. On Unix-like systems, this is usually
78 @file{/usr/local/share/guile} or @file{/usr/share/guile}.
79 @end deffn
80
81 @deffn {Scheme Procedure} %library-dir
82 @deffnx {C Function} scm_sys_library_dir ()
83 Return the name of the directory where the Guile Scheme files that
84 belong to the core Guile installation (as opposed to files from a 3rd
85 party package) are installed. On Unix-like systems this is usually
86 @file{/usr/local/share/guile/<GUILE_EFFECTIVE_VERSION>} or
87 @file{/usr/share/guile/<GUILE_EFFECTIVE_VERSION>};
88
89 @noindent for example @file{/usr/local/share/guile/1.6}.
90 @end deffn
91
92 @deffn {Scheme Procedure} %site-dir
93 @deffnx {C Function} scm_sys_site_dir ()
94 Return the name of the directory where Guile Scheme files specific to
95 your site should be installed. On Unix-like systems, this is usually
96 @file{/usr/local/share/guile/site} or @file{/usr/share/guile/site}.
97 @end deffn
98
99 @cindex GUILE_LOAD_PATH
100 @defvar %load-path
101 List of directories which should be searched for Scheme modules and
102 libraries. @code{%load-path} is initialized when Guile starts up to
103 @code{(list (%site-dir) (%library-dir) (%package-data-dir))},
104 prepended with the contents of the GUILE_LOAD_PATH environment variable,
105 if it is set.
106 @end defvar
107
108 @deffn {Scheme Procedure} parse-path path [tail]
109 @deffnx {C Function} scm_parse_path (path, tail)
110 Parse @var{path}, which is expected to be a colon-separated
111 string, into a list and return the resulting list with
112 @var{tail} appended. If @var{path} is @code{#f}, @var{tail}
113 is returned.
114 @end deffn
115
116 @deffn {Scheme Procedure} search-path path filename [extensions [require-exts?]]
117 @deffnx {C Function} scm_search_path (path, filename, rest)
118 Search @var{path} for a directory containing a file named
119 @var{filename}. The file must be readable, and not a directory.
120 If we find one, return its full filename; otherwise, return
121 @code{#f}. If @var{filename} is absolute, return it unchanged.
122 If given, @var{extensions} is a list of strings; for each
123 directory in @var{path}, we search for @var{filename}
124 concatenated with each @var{extension}. If @var{require-exts?}
125 is true, require that the returned file name have one of the
126 given extensions; if @var{require-exts?} is not given, it
127 defaults to @code{#f}.
128
129 For compatibility with Guile 1.8 and earlier, the C function takes only
130 three arguments
131 @end deffn
132
133 @defvar %guile-build-info
134 Alist of information collected during the building of a particular
135 Guile. Entries can be grouped into one of several categories:
136 directories, env vars, and versioning info.
137
138 Briefly, here are the keys in @code{%guile-build-info}, by group:
139
140 @cindex @code{srcdir}
141 @cindex @code{top_srcdir}
142 @cindex @code{prefix}
143 @cindex @code{exec_prefix}
144 @cindex @code{bindir}
145 @cindex @code{sbindir}
146 @cindex @code{libexecdir}
147 @cindex @code{datadir}
148 @cindex @code{sysconfdir}
149 @cindex @code{sharedstatedir}
150 @cindex @code{localstatedir}
151 @cindex @code{libdir}
152 @cindex @code{infodir}
153 @cindex @code{mandir}
154 @cindex @code{includedir}
155 @cindex @code{pkgdatadir}
156 @cindex @code{pkglibdir}
157 @cindex @code{pkgincludedir}
158 @table @asis
159 @item directories
160 srcdir, top_srcdir, prefix, exec_prefix, bindir, sbindir, libexecdir,
161 datadir, sysconfdir, sharedstatedir, localstatedir, libdir, infodir,
162 mandir, includedir, pkgdatadir, pkglibdir, pkgincludedir
163 @cindex @code{LIBS}
164 @item env vars
165 LIBS
166 @cindex @code{guileversion}
167 @cindex @code{libguileinterface}
168 @cindex @code{buildstamp}
169 @item versioning info
170 guileversion, libguileinterface, buildstamp
171 @end table
172
173 Values are all strings. The value for @code{LIBS} is typically found
174 also as a part of "guile-config link" output. The value for
175 @code{guileversion} has form X.Y.Z, and should be the same as returned
176 by @code{(version)}. The value for @code{libguileinterface} is
177 libtool compatible and has form CURRENT:REVISION:AGE
178 (@pxref{Versioning,, Library interface versions, libtool, GNU
179 Libtool}). The value for @code{buildstamp} is the output of the
180 date(1) command.
181
182 In the source, @code{%guile-build-info} is initialized from
183 libguile/libpath.h, which is completely generated, so deleting this file
184 before a build guarantees up-to-date values for that build.
185 @end defvar
186
187 @cindex GNU triplet
188 @cindex canonical host type
189
190 @defvar %host-type
191 The canonical host type (GNU triplet) of the host Guile was configured
192 for, e.g., @code{"x86_64-unknown-linux-gnu"} (@pxref{Canonicalizing,,,
193 autoconf, The GNU Autoconf Manual}).
194 @end defvar
195
196 @node Feature Tracking
197 @subsection Feature Tracking
198
199 Guile has a Scheme level variable @code{*features*} that keeps track to
200 some extent of the features that are available in a running Guile.
201 @code{*features*} is a list of symbols, for example @code{threads}, each
202 of which describes a feature of the running Guile process.
203
204 @defvar *features*
205 A list of symbols describing available features of the Guile process.
206 @end defvar
207
208 You shouldn't modify the @code{*features*} variable directly using
209 @code{set!}. Instead, see the procedures that are provided for this
210 purpose in the following subsection.
211
212 @menu
213 * Feature Manipulation:: Checking for and advertising features.
214 * Common Feature Symbols:: Commonly available features.
215 @end menu
216
217
218 @node Feature Manipulation
219 @subsubsection Feature Manipulation
220
221 To check whether a particular feature is available, use the
222 @code{provided?} procedure:
223
224 @deffn {Scheme Procedure} provided? feature
225 @deffnx {Deprecated Scheme Procedure} feature? feature
226 Return @code{#t} if the specified @var{feature} is available, otherwise
227 @code{#f}.
228 @end deffn
229
230 To advertise a feature from your own Scheme code, you can use the
231 @code{provide} procedure:
232
233 @deffn {Scheme Procedure} provide feature
234 Add @var{feature} to the list of available features in this Guile
235 process.
236 @end deffn
237
238 For C code, the equivalent function takes its feature name as a
239 @code{char *} argument for convenience:
240
241 @deftypefn {C Function} void scm_add_feature (const char *str)
242 Add a symbol with name @var{str} to the list of available features in
243 this Guile process.
244 @end deftypefn
245
246
247 @node Common Feature Symbols
248 @subsubsection Common Feature Symbols
249
250 In general, a particular feature may be available for one of two
251 reasons. Either because the Guile library was configured and compiled
252 with that feature enabled --- i.e. the feature is built into the library
253 on your system. Or because some C or Scheme code that was dynamically
254 loaded by Guile has added that feature to the list.
255
256 In the first category, here are the features that the current version of
257 Guile may define (depending on how it is built), and what they mean.
258
259 @table @code
260 @item array
261 Indicates support for arrays (@pxref{Arrays}).
262
263 @item array-for-each
264 Indicates availability of @code{array-for-each} and other array mapping
265 procedures (@pxref{Arrays}).
266
267 @item char-ready?
268 Indicates that the @code{char-ready?} function is available
269 (@pxref{Reading}).
270
271 @item complex
272 Indicates support for complex numbers.
273
274 @item current-time
275 Indicates availability of time-related functions: @code{times},
276 @code{get-internal-run-time} and so on (@pxref{Time}).
277
278 @item debug-extensions
279 Indicates that the debugging evaluator is available, together with the
280 options for controlling it.
281
282 @item delay
283 Indicates support for promises (@pxref{Delayed Evaluation}).
284
285 @item EIDs
286 Indicates that the @code{geteuid} and @code{getegid} really return
287 effective user and group IDs (@pxref{Processes}).
288
289 @item inexact
290 Indicates support for inexact numbers.
291
292 @item i/o-extensions
293 Indicates availability of the following extended I/O procedures:
294 @code{ftell}, @code{redirect-port}, @code{dup->fdes}, @code{dup2},
295 @code{fileno}, @code{isatty?}, @code{fdopen},
296 @code{primitive-move->fdes} and @code{fdes->ports} (@pxref{Ports and
297 File Descriptors}).
298
299 @item net-db
300 Indicates availability of network database functions:
301 @code{scm_gethost}, @code{scm_getnet}, @code{scm_getproto},
302 @code{scm_getserv}, @code{scm_sethost}, @code{scm_setnet}, @code{scm_setproto},
303 @code{scm_setserv}, and their `byXXX' variants (@pxref{Network
304 Databases}).
305
306 @item posix
307 Indicates support for POSIX functions: @code{pipe}, @code{getgroups},
308 @code{kill}, @code{execl} and so on (@pxref{POSIX}).
309
310 @item random
311 Indicates availability of random number generation functions:
312 @code{random}, @code{copy-random-state}, @code{random-uniform} and so on
313 (@pxref{Random}).
314
315 @item reckless
316 Indicates that Guile was built with important checks omitted --- you
317 should never see this!
318
319 @item regex
320 Indicates support for POSIX regular expressions using
321 @code{make-regexp}, @code{regexp-exec} and friends (@pxref{Regexp
322 Functions}).
323
324 @item socket
325 Indicates availability of socket-related functions: @code{socket},
326 @code{bind}, @code{connect} and so on (@pxref{Network Sockets and
327 Communication}).
328
329 @item sort
330 Indicates availability of sorting and merging functions
331 (@pxref{Sorting}).
332
333 @item system
334 Indicates that the @code{system} function is available
335 (@pxref{Processes}).
336
337 @item threads
338 Indicates support for multithreading (@pxref{Threads}).
339
340 @item values
341 Indicates support for multiple return values using @code{values} and
342 @code{call-with-values} (@pxref{Multiple Values}).
343 @end table
344
345 Available features in the second category depend, by definition, on what
346 additional code your Guile process has loaded in. The following table
347 lists features that you might encounter for this reason.
348
349 @table @code
350 @item defmacro
351 Indicates that the @code{defmacro} macro is available (@pxref{Macros}).
352
353 @item describe
354 Indicates that the @code{(oop goops describe)} module has been loaded,
355 which provides a procedure for describing the contents of GOOPS
356 instances.
357
358 @item readline
359 Indicates that Guile has loaded in Readline support, for command line
360 editing (@pxref{Readline Support}).
361
362 @item record
363 Indicates support for record definition using @code{make-record-type}
364 and friends (@pxref{Records}).
365 @end table
366
367 Although these tables may seem exhaustive, it is probably unwise in
368 practice to rely on them, as the correspondences between feature symbols
369 and available procedures/behaviour are not strictly defined. If you are
370 writing code that needs to check for the existence of some procedure, it
371 is probably safer to do so directly using the @code{defined?} procedure
372 than to test for the corresponding feature using @code{provided?}.
373
374
375 @node Runtime Options
376 @subsection Runtime Options
377
378 Guile's runtime behaviour can be modified by setting options. For
379 example, is the language that Guile accepts case sensitive, or should
380 the debugger automatically show a backtrace on error?
381
382 Guile has two levels of interface for managing options: a low-level
383 control interface, and a user-level interface which allows the enabling
384 or disabling of options.
385
386 Moreover, the options are classified in groups according to whether they
387 configure @emph{reading}, @emph{printing}, @emph{debugging} or
388 @emph{evaluating}.
389
390 @menu
391 * Low level options interfaces::
392 * User level options interfaces::
393 * Reader options::
394 * Printing options::
395 * Debugger options::
396 * Evaluator options::
397 * Evaluator trap options::
398 * Examples of option use::
399 @end menu
400
401
402 @node Low level options interfaces
403 @subsubsection Low Level Options Interfaces
404
405 @deffn {Scheme Procedure} read-options-interface [setting]
406 @deffnx {Scheme Procedure} eval-options-interface [setting]
407 @deffnx {Scheme Procedure} print-options-interface [setting]
408 @deffnx {Scheme Procedure} debug-options-interface [setting]
409 @deffnx {Scheme Procedure} evaluator-traps-interface [setting]
410 @deffnx {C Function} scm_read_options (setting)
411 @deffnx {C Function} scm_eval_options_interface (setting)
412 @deffnx {C Function} scm_print_options (setting)
413 @deffnx {C Function} scm_debug_options (setting)
414 @deffnx {C Function} scm_evaluator_traps (setting)
415 If one of these procedures is called with no arguments (or with
416 @code{setting == SCM_UNDEFINED} in C code), it returns a list describing
417 the current setting of the read, eval, print, debug or evaluator traps
418 options respectively. The setting of a boolean option is indicated
419 simply by the presence or absence of the option symbol in the list. The
420 setting of a non-boolean option is indicated by the presence of the
421 option symbol immediately followed by the option's current value.
422
423 If called with a list argument, these procedures interpret the list as
424 an option setting and modify the relevant options accordingly. [FIXME
425 --- this glosses over a lot of details!]
426
427 If called with any other argument, such as @code{'help}, these
428 procedures return a list of entries like @code{(@var{OPTION-SYMBOL}
429 @var{DEFAULT-VALUE} @var{DOC-STRING})}, with each entry giving the
430 default value and documentation for each option symbol in the relevant
431 set of options.
432 @end deffn
433
434
435 @node User level options interfaces
436 @subsubsection User Level Options Interfaces
437
438 @c @deftp {Data type} scm_option
439 @c @code{scm_option} is used to represent run time options. It can be a
440 @c @emph{boolean} type, in which case the option will be set by the strings
441 @c @code{"yes"} and @code{"no"}. It can be a
442 @c @end deftp
443
444 @c NJFIXME
445 @deffn {Scheme Procedure} <group>-options [arg]
446 @deffnx {Scheme Procedure} read-options [arg]
447 @deffnx {Scheme Procedure} print-options [arg]
448 @deffnx {Scheme Procedure} debug-options [arg]
449 @deffnx {Scheme Procedure} traps [arg]
450 These functions list the options in their group. The optional argument
451 @var{arg} is a symbol which modifies the form in which the options are
452 presented.
453
454 With no arguments, @code{<group>-options} returns the values of the
455 options in that particular group. If @var{arg} is @code{'help}, a
456 description of each option is given. If @var{arg} is @code{'full},
457 programmers' options are also shown.
458
459 @var{arg} can also be a list representing the state of all options. In
460 this case, the list contains single symbols (for enabled boolean
461 options) and symbols followed by values.
462 @end deffn
463 [FIXME: I don't think 'full is ever any different from 'help. What's
464 up?]
465
466 @c NJFIXME
467 @deffn {Scheme Procedure} <group>-enable option-symbol
468 @deffnx {Scheme Procedure} read-enable option-symbol
469 @deffnx {Scheme Procedure} print-enable option-symbol
470 @deffnx {Scheme Procedure} debug-enable option-symbol
471 @deffnx {Scheme Procedure} trap-enable option-symbol
472 These functions set the specified @var{option-symbol} in their options
473 group. They only work if the option is boolean, and throw an error
474 otherwise.
475 @end deffn
476
477 @c NJFIXME
478 @deffn {Scheme Procedure} <group>-disable option-symbol
479 @deffnx {Scheme Procedure} read-disable option-symbol
480 @deffnx {Scheme Procedure} print-disable option-symbol
481 @deffnx {Scheme Procedure} debug-disable option-symbol
482 @deffnx {Scheme Procedure} trap-disable option-symbol
483 These functions turn off the specified @var{option-symbol} in their
484 options group. They only work if the option is boolean, and throw an
485 error otherwise.
486 @end deffn
487
488 @c NJFIXME
489 @deffn syntax <group>-set! option-symbol value
490 @deffnx syntax read-set! option-symbol value
491 @deffnx syntax print-set! option-symbol value
492 @deffnx syntax debug-set! option-symbol value
493 @deffnx syntax trap-set! option-symbol value
494 These functions set a non-boolean @var{option-symbol} to the specified
495 @var{value}.
496 @end deffn
497
498
499 @node Reader options
500 @subsubsection Reader options
501 @cindex options - read
502 @cindex read options
503
504 Here is the list of reader options generated by typing
505 @code{(read-options 'full)} in Guile. You can also see the default
506 values.
507
508 @smalllisp
509 keywords #f Style of keyword recognition: #f, 'prefix or 'postfix
510 case-insensitive no Convert symbols to lower case.
511 positions yes Record positions of source code expressions.
512 copy no Copy source code expressions.
513 @end smalllisp
514
515 Notice that while Standard Scheme is case insensitive, to ease
516 translation of other Lisp dialects, notably Emacs Lisp, into Guile,
517 Guile is case-sensitive by default.
518
519 To make Guile case insensitive, you can type
520
521 @lisp
522 (read-enable 'case-insensitive)
523 @end lisp
524
525 @node Printing options
526 @subsubsection Printing options
527
528 Here is the list of print options generated by typing
529 @code{(print-options 'full)} in Guile. You can also see the default
530 values.
531
532 @smallexample
533 quote-keywordish-symbols reader How to print symbols that have a colon
534 as their first or last character. The
535 value '#f' does not quote the colons;
536 '#t' quotes them; 'reader' quotes
537 them when the reader option
538 'keywords' is not '#f'.
539
540 highlight-prefix @{ The string to print before highlighted values.
541 highlight-suffix @} The string to print after highlighted values.
542
543 source no Print closures with source.
544 closure-hook #f Hook for printing closures.
545 @end smallexample
546
547
548 @node Evaluator options
549 @subsubsection Evaluator options
550
551 These are the evaluator options with their default values, as they are
552 printed by typing @code{(eval-options 'full)} in Guile.
553
554 @smallexample
555 stack 22000 Size of thread stacks (in machine words).
556 @end smallexample
557
558
559 @node Evaluator trap options
560 @subsubsection Evaluator trap options
561 [FIXME: These flags, together with their corresponding handlers, are not
562 user level options. Probably this entire section should be moved to the
563 documentation about the low-level programmer debugging interface.]
564
565 Here is the list of evaluator trap options generated by typing
566 @code{(traps 'full)} in Guile. You can also see the default values.
567
568 @smallexample
569 exit-frame no Trap when exiting eval or apply.
570 apply-frame no Trap when entering apply.
571 enter-frame no Trap when eval enters new frame.
572 memoize-symbol no Trap when eval memoizes a symbol's value
573 traps yes Enable evaluator traps.
574 @end smallexample
575
576 @deffn apply-frame-handler key cont tailp
577 Called when a procedure is being applied.
578
579 Called if:
580
581 @itemize @bullet
582 @item
583 evaluator traps are enabled [traps interface], and
584 @item
585 either
586 @itemize @minus
587 @item
588 @code{apply-frame} is enabled [traps interface], or
589 @item
590 trace mode is on [debug-options interface], and the procedure being
591 called has the trace property enabled.
592 @end itemize
593 @end itemize
594
595 @var{cont} is a ``debug object'', which means that it can be passed to
596 @code{make-stack} to discover the stack at the point of the trap. The
597 apply frame handler's code can capture a restartable continuation if it
598 wants to by using @code{call-with-current-continuation} in the usual way.
599
600 @var{tailp} is true if this is a tail call
601 @end deffn
602
603 @deffn exit-frame-handler key cont retval
604 Called when a value is returned from a procedure.
605
606 Called if:
607
608 @itemize @bullet
609 @item
610 evaluator traps are enabled [traps interface], and
611 @item
612 either
613 @itemize @minus
614 @item
615 @code{exit-frame} is enabled [traps interface], or
616 @item
617 trace mode is on [debug-options interface], and the procedure being
618 called has the trace property enabled.
619 @end itemize
620 @end itemize
621
622 @var{cont} is a ``debug object'', which means that it can be passed to
623 @code{make-stack} to discover the stack at the point of the trap. The
624 exit frame handler's code can capture a restartable continuation if it
625 wants to by using @code{call-with-current-continuation} in the usual
626 way.
627
628 @var{retval} is the return value.
629 @end deffn
630
631 @deffn memoize-symbol-handler key cont expression env
632 Called when the evaluator memoizes the value of a procedure symbol
633
634 @var{cont} is a ``debug object'', which means that it can be passed to
635 @code{make-stack} to discover the stack at the point of the trap. The
636 exit frame handler's code can capture a restartable continuation if it
637 wants to by using @code{call-with-current-continuation} in the usual
638 way.
639
640 @var{retval} is the return value.
641 @end deffn
642
643 @deffn {Scheme Procedure} with-traps thunk
644 @deffnx {C Function} scm_with_traps (thunk)
645 Call @var{thunk} with traps enabled.
646 @end deffn
647
648 @deffn {Scheme Procedure} debug-object? obj
649 @deffnx {C Function} scm_debug_object_p (obj)
650 Return @code{#t} if @var{obj} is a debug object.
651 @end deffn
652
653
654 @node Debugger options
655 @subsubsection Debugger options
656
657 Here is the list of print options generated by typing
658 @code{(debug-options 'full)} in Guile. You can also see the default
659 values.
660
661 @smallexample
662 stack 20000 Stack size limit (0 = no check).
663 debug yes Use the debugging evaluator.
664 backtrace no Show backtrace on error.
665 depth 20 Maximal length of printed backtrace.
666 maxdepth 1000 Maximal number of stored backtrace frames.
667 frames 3 Maximum number of tail-recursive frames in backtrace.
668 indent 10 Maximal indentation in backtrace.
669 backwards no Display backtrace in anti-chronological order.
670 procnames yes Record procedure names at definition.
671 trace no *Trace mode.
672 breakpoints no *Check for breakpoints.
673 cheap yes *This option is now obsolete. Setting it has no effect.
674 @end smallexample
675
676 @subsubheading Stack overflow
677
678 @cindex overflow, stack
679 @cindex stack overflow
680 Stack overflow errors are caused by a computation trying to use more
681 stack space than has been enabled by the @code{stack} option. They are
682 reported like this:
683
684 @lisp
685 (non-tail-recursive-factorial 500)
686 @print{}
687 ERROR: Stack overflow
688 ABORT: (stack-overflow)
689 @end lisp
690
691 If you get an error like this, you can either try rewriting your code to
692 use less stack space, or increase the maximum stack size. To increase
693 the maximum stack size, use @code{debug-set!}, for example:
694
695 @lisp
696 (debug-set! stack 200000)
697 @result{}
698 (show-file-name #t stack 200000 debug backtrace depth 20
699 maxdepth 1000 frames 3 indent 10 width 79 procnames cheap)
700
701 (non-tail-recursive-factorial 500)
702 @result{}
703 122013682599111006870123878542304692625357434@dots{}
704 @end lisp
705
706 If you prefer to try rewriting your code, you may be able to save stack
707 space by making some of your procedures @dfn{tail recursive}
708 (@pxref{Tail Calls}).
709
710
711 @node Examples of option use
712 @subsubsection Examples of option use
713
714 Here is an example of a session in which some read and debug option
715 handling procedures are used. In this example, the user
716
717 @enumerate
718 @item
719 Notices that the symbols @code{abc} and @code{aBc} are not the same
720 @item
721 Examines the @code{read-options}, and sees that @code{case-insensitive}
722 is set to ``no''.
723 @item
724 Enables @code{case-insensitive}
725 @item
726 Verifies that now @code{aBc} and @code{abc} are the same
727 @item
728 Disables @code{case-insensitive} and enables debugging @code{backtrace}
729 @item
730 Reproduces the error of displaying @code{aBc} with backtracing enabled
731 [FIXME: this last example is lame because there is no depth in the
732 backtrace. Need to give a better example, possibly putting debugging
733 option examples in a separate session.]
734 @end enumerate
735
736 @smalllisp
737 guile> (define abc "hello")
738 guile> abc
739 "hello"
740 guile> aBc
741 ERROR: In expression aBc:
742 ERROR: Unbound variable: aBc
743 ABORT: (misc-error)
744
745 Type "(backtrace)" to get more information.
746 guile> (read-options 'help)
747 keywords #f Style of keyword recognition: #f, 'prefix or 'postfix
748 case-insensitive no Convert symbols to lower case.
749 positions yes Record positions of source code expressions.
750 copy no Copy source code expressions.
751 guile> (debug-options 'help)
752 stack 20000 Stack size limit (0 = no check).
753 debug yes Use the debugging evaluator.
754 backtrace no Show backtrace on error.
755 depth 20 Maximal length of printed backtrace.
756 maxdepth 1000 Maximal number of stored backtrace frames.
757 frames 3 Maximum number of tail-recursive frames in backtrace.
758 indent 10 Maximal indentation in backtrace.
759 backwards no Display backtrace in anti-chronological order.
760 procnames yes Record procedure names at definition.
761 trace no *Trace mode.
762 breakpoints no *Check for breakpoints.
763 cheap yes *This option is now obsolete. Setting it has no effect.
764 guile> (read-enable 'case-insensitive)
765 (keywords #f case-insensitive positions)
766 guile> aBc
767 "hello"
768 guile> (read-disable 'case-insensitive)
769 (keywords #f positions)
770 guile> (debug-enable 'backtrace)
771 (stack 20000 debug backtrace depth 20 maxdepth 1000 frames 3 indent 10 procnames cheap)
772 guile> aBc
773
774 Backtrace:
775 0* aBc
776
777 ERROR: In expression aBc:
778 ERROR: Unbound variable: aBc
779 ABORT: (misc-error)
780 guile>
781 @end smalllisp
782
783
784 @c Local Variables:
785 @c TeX-master: "guile.texi"
786 @c End: