2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
9 @section SRFI Support Modules
12 SRFI is an acronym for Scheme Request For Implementation. The SRFI
13 documents define a lot of syntactic and procedure extensions to standard
14 Scheme as defined in R5RS.
16 Guile has support for a number of SRFIs. This chapter gives an overview
17 over the available SRFIs and some usage hints. For complete
18 documentation, design rationales and further examples, we advise you to
19 get the relevant SRFI documents from the SRFI home page
20 @url{http://srfi.schemers.org}.
23 * About SRFI Usage:: What to know about Guile's SRFI support.
24 * SRFI-0:: cond-expand
25 * SRFI-1:: List library.
27 * SRFI-4:: Homogeneous numeric vector datatypes.
28 * SRFI-6:: Basic String Ports.
30 * SRFI-9:: define-record-type.
31 * SRFI-10:: Hash-Comma Reader Extension.
32 * SRFI-11:: let-values and let*-values.
33 * SRFI-13:: String library.
34 * SRFI-14:: Character-set library.
35 * SRFI-16:: case-lambda
36 * SRFI-17:: Generalized set!
37 * SRFI-18:: Multithreading support
38 * SRFI-19:: Time/Date library.
39 * SRFI-26:: Specializing parameters
40 * SRFI-31:: A special form `rec' for recursive evaluation
41 * SRFI-34:: Exception handling.
42 * SRFI-35:: Conditions.
43 * SRFI-37:: args-fold program argument processor
44 * SRFI-39:: Parameter objects
45 * SRFI-55:: Requiring Features.
46 * SRFI-60:: Integers as bits.
47 * SRFI-61:: A more general `cond' clause
48 * SRFI-69:: Basic hash tables.
49 * SRFI-88:: Keyword objects.
50 * SRFI-98:: Accessing environment variables.
54 @node About SRFI Usage
55 @subsection About SRFI Usage
57 @c FIXME::martin: Review me!
59 SRFI support in Guile is currently implemented partly in the core
60 library, and partly as add-on modules. That means that some SRFIs are
61 automatically available when the interpreter is started, whereas the
62 other SRFIs require you to use the appropriate support module
65 There are several reasons for this inconsistency. First, the feature
66 checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be
67 available immediately, because it must be there when the user wants to
68 check for the Scheme implementation, that is, before she can know that
69 it is safe to use @code{use-modules} to load SRFI support modules. The
70 second reason is that some features defined in SRFIs had been
71 implemented in Guile before the developers started to add SRFI
72 implementations as modules (for example SRFI-6 (@pxref{SRFI-6})). In
73 the future, it is possible that SRFIs in the core library might be
74 factored out into separate modules, requiring explicit module loading
75 when they are needed. So you should be prepared to have to use
76 @code{use-modules} someday in the future to access SRFI-6 bindings. If
77 you want, you can do that already. We have included the module
78 @code{(srfi srfi-6)} in the distribution, which currently does nothing,
79 but ensures that you can write future-safe code.
81 Generally, support for a specific SRFI is made available by using
82 modules named @code{(srfi srfi-@var{number})}, where @var{number} is the
83 number of the SRFI needed. Another possibility is to use the command
84 line option @code{--use-srfi}, which will load the necessary modules
85 automatically (@pxref{Invoking Guile}).
89 @subsection SRFI-0 - cond-expand
92 This SRFI lets a portable Scheme program test for the presence of
93 certain features, and adapt itself by using different blocks of code,
94 or fail if the necessary features are not available. There's no
95 module to load, this is in the Guile core.
97 A program designed only for Guile will generally not need this
98 mechanism, such a program can of course directly use the various
99 documented parts of Guile.
101 @deffn syntax cond-expand (feature body@dots{}) @dots{}
102 Expand to the @var{body} of the first clause whose @var{feature}
103 specification is satisfied. It is an error if no @var{feature} is
106 Features are symbols such as @code{srfi-1}, and a feature
107 specification can use @code{and}, @code{or} and @code{not} forms to
108 test combinations. The last clause can be an @code{else}, to be used
111 For example, define a private version of @code{alist-cons} if SRFI-1
118 (define (alist-cons key val alist)
119 (cons (cons key val) alist))))
122 Or demand a certain set of SRFIs (list operations, string ports,
123 @code{receive} and string operations), failing if they're not
127 (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13)
133 The Guile core has the following features,
145 Other SRFI feature symbols are defined once their code has been loaded
146 with @code{use-modules}, since only then are their bindings available.
148 The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is
149 a good way to load SRFIs to satisfy @code{cond-expand} when running a
152 Testing the @code{guile} feature allows a program to adapt itself to
153 the Guile module system, but still run on other Scheme systems. For
154 example the following demands SRFI-8 (@code{receive}), but also knows
155 how to load it with the Guile mechanism.
161 (use-modules (srfi srfi-8))))
164 It should be noted that @code{cond-expand} is separate from the
165 @code{*features*} mechanism (@pxref{Feature Tracking}), feature
166 symbols in one are unrelated to those in the other.
170 @subsection SRFI-1 - List library
174 @c FIXME::martin: Review me!
176 The list library defined in SRFI-1 contains a lot of useful list
177 processing procedures for construction, examining, destructuring and
178 manipulating lists and pairs.
180 Since SRFI-1 also defines some procedures which are already contained
181 in R5RS and thus are supported by the Guile core library, some list
182 and pair procedures which appear in the SRFI-1 document may not appear
183 in this section. So when looking for a particular list/pair
184 processing procedure, you should also have a look at the sections
185 @ref{Lists} and @ref{Pairs}.
188 * SRFI-1 Constructors:: Constructing new lists.
189 * SRFI-1 Predicates:: Testing list for specific properties.
190 * SRFI-1 Selectors:: Selecting elements from lists.
191 * SRFI-1 Length Append etc:: Length calculation and list appending.
192 * SRFI-1 Fold and Map:: Higher-order list processing.
193 * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates.
194 * SRFI-1 Searching:: Search for elements.
195 * SRFI-1 Deleting:: Delete elements from lists.
196 * SRFI-1 Association Lists:: Handle association lists.
197 * SRFI-1 Set Operations:: Use lists for representing sets.
200 @node SRFI-1 Constructors
201 @subsubsection Constructors
202 @cindex list constructor
204 @c FIXME::martin: Review me!
206 New lists can be constructed by calling one of the following
209 @deffn {Scheme Procedure} xcons d a
210 Like @code{cons}, but with interchanged arguments. Useful mostly when
211 passed to higher-order procedures.
214 @deffn {Scheme Procedure} list-tabulate n init-proc
215 Return an @var{n}-element list, where each list element is produced by
216 applying the procedure @var{init-proc} to the corresponding list
217 index. The order in which @var{init-proc} is applied to the indices
221 @deffn {Scheme Procedure} list-copy lst
222 Return a new list containing the elements of the list @var{lst}.
224 This function differs from the core @code{list-copy} (@pxref{List
225 Constructors}) in accepting improper lists too. And if @var{lst} is
226 not a pair at all then it's treated as the final tail of an improper
227 list and simply returned.
230 @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{}
231 Return a circular list containing the given arguments @var{elt1}
235 @deffn {Scheme Procedure} iota count [start step]
236 Return a list containing @var{count} numbers, starting from
237 @var{start} and adding @var{step} each time. The default @var{start}
238 is 0, the default @var{step} is 1. For example,
241 (iota 6) @result{} (0 1 2 3 4 5)
242 (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5)
245 This function takes its name from the corresponding primitive in the
250 @node SRFI-1 Predicates
251 @subsubsection Predicates
252 @cindex list predicate
254 @c FIXME::martin: Review me!
256 The procedures in this section test specific properties of lists.
258 @deffn {Scheme Procedure} proper-list? obj
259 Return @code{#t} if @var{obj} is a proper list, or @code{#f}
260 otherwise. This is the same as the core @code{list?} (@pxref{List
263 A proper list is a list which ends with the empty list @code{()} in
264 the usual way. The empty list @code{()} itself is a proper list too.
267 (proper-list? '(1 2 3)) @result{} #t
268 (proper-list? '()) @result{} #t
272 @deffn {Scheme Procedure} circular-list? obj
273 Return @code{#t} if @var{obj} is a circular list, or @code{#f}
276 A circular list is a list where at some point the @code{cdr} refers
277 back to a previous pair in the list (either the start or some later
278 point), so that following the @code{cdr}s takes you around in a
282 (define x (list 1 2 3 4))
283 (set-cdr! (last-pair x) (cddr x))
284 x @result{} (1 2 3 4 3 4 3 4 ...)
285 (circular-list? x) @result{} #t
289 @deffn {Scheme Procedure} dotted-list? obj
290 Return @code{#t} if @var{obj} is a dotted list, or @code{#f}
293 A dotted list is a list where the @code{cdr} of the last pair is not
294 the empty list @code{()}. Any non-pair @var{obj} is also considered a
295 dotted list, with length zero.
298 (dotted-list? '(1 2 . 3)) @result{} #t
299 (dotted-list? 99) @result{} #t
303 It will be noted that any Scheme object passes exactly one of the
304 above three tests @code{proper-list?}, @code{circular-list?} and
305 @code{dotted-list?}. Non-lists are @code{dotted-list?}, finite lists
306 are either @code{proper-list?} or @code{dotted-list?}, and infinite
307 lists are @code{circular-list?}.
310 @deffn {Scheme Procedure} null-list? lst
311 Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f}
312 otherwise. If something else than a proper or circular list is passed
313 as @var{lst}, an error is signalled. This procedure is recommended
314 for checking for the end of a list in contexts where dotted lists are
318 @deffn {Scheme Procedure} not-pair? obj
319 Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise.
320 This is shorthand notation @code{(not (pair? @var{obj}))} and is
321 supposed to be used for end-of-list checking in contexts where dotted
325 @deffn {Scheme Procedure} list= elt= list1 @dots{}
326 Return @code{#t} if all argument lists are equal, @code{#f} otherwise.
327 List equality is determined by testing whether all lists have the same
328 length and the corresponding elements are equal in the sense of the
329 equality predicate @var{elt=}. If no or only one list is given,
330 @code{#t} is returned.
334 @node SRFI-1 Selectors
335 @subsubsection Selectors
336 @cindex list selector
338 @c FIXME::martin: Review me!
340 @deffn {Scheme Procedure} first pair
341 @deffnx {Scheme Procedure} second pair
342 @deffnx {Scheme Procedure} third pair
343 @deffnx {Scheme Procedure} fourth pair
344 @deffnx {Scheme Procedure} fifth pair
345 @deffnx {Scheme Procedure} sixth pair
346 @deffnx {Scheme Procedure} seventh pair
347 @deffnx {Scheme Procedure} eighth pair
348 @deffnx {Scheme Procedure} ninth pair
349 @deffnx {Scheme Procedure} tenth pair
350 These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}.
353 @deffn {Scheme Procedure} car+cdr pair
354 Return two values, the @sc{car} and the @sc{cdr} of @var{pair}.
357 @deffn {Scheme Procedure} take lst i
358 @deffnx {Scheme Procedure} take! lst i
359 Return a list containing the first @var{i} elements of @var{lst}.
361 @code{take!} may modify the structure of the argument list @var{lst}
362 in order to produce the result.
365 @deffn {Scheme Procedure} drop lst i
366 Return a list containing all but the first @var{i} elements of
370 @deffn {Scheme Procedure} take-right lst i
371 Return the a list containing the @var{i} last elements of @var{lst}.
372 The return shares a common tail with @var{lst}.
375 @deffn {Scheme Procedure} drop-right lst i
376 @deffnx {Scheme Procedure} drop-right! lst i
377 Return the a list containing all but the @var{i} last elements of
380 @code{drop-right} always returns a new list, even when @var{i} is
381 zero. @code{drop-right!} may modify the structure of the argument
382 list @var{lst} in order to produce the result.
385 @deffn {Scheme Procedure} split-at lst i
386 @deffnx {Scheme Procedure} split-at! lst i
387 Return two values, a list containing the first @var{i} elements of the
388 list @var{lst} and a list containing the remaining elements.
390 @code{split-at!} may modify the structure of the argument list
391 @var{lst} in order to produce the result.
394 @deffn {Scheme Procedure} last lst
395 Return the last element of the non-empty, finite list @var{lst}.
399 @node SRFI-1 Length Append etc
400 @subsubsection Length, Append, Concatenate, etc.
402 @c FIXME::martin: Review me!
404 @deffn {Scheme Procedure} length+ lst
405 Return the length of the argument list @var{lst}. When @var{lst} is a
406 circular list, @code{#f} is returned.
409 @deffn {Scheme Procedure} concatenate list-of-lists
410 @deffnx {Scheme Procedure} concatenate! list-of-lists
411 Construct a list by appending all lists in @var{list-of-lists}.
413 @code{concatenate!} may modify the structure of the given lists in
414 order to produce the result.
416 @code{concatenate} is the same as @code{(apply append
417 @var{list-of-lists})}. It exists because some Scheme implementations
418 have a limit on the number of arguments a function takes, which the
419 @code{apply} might exceed. In Guile there is no such limit.
422 @deffn {Scheme Procedure} append-reverse rev-head tail
423 @deffnx {Scheme Procedure} append-reverse! rev-head tail
424 Reverse @var{rev-head}, append @var{tail} to it, and return the
425 result. This is equivalent to @code{(append (reverse @var{rev-head})
426 @var{tail})}, but its implementation is more efficient.
429 (append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)
432 @code{append-reverse!} may modify @var{rev-head} in order to produce
436 @deffn {Scheme Procedure} zip lst1 lst2 @dots{}
437 Return a list as long as the shortest of the argument lists, where
438 each element is a list. The first list contains the first elements of
439 the argument lists, the second list contains the second elements, and
443 @deffn {Scheme Procedure} unzip1 lst
444 @deffnx {Scheme Procedure} unzip2 lst
445 @deffnx {Scheme Procedure} unzip3 lst
446 @deffnx {Scheme Procedure} unzip4 lst
447 @deffnx {Scheme Procedure} unzip5 lst
448 @code{unzip1} takes a list of lists, and returns a list containing the
449 first elements of each list, @code{unzip2} returns two lists, the
450 first containing the first elements of each lists and the second
451 containing the second elements of each lists, and so on.
454 @deffn {Scheme Procedure} count pred lst1 @dots{} lstN
455 Return a count of the number of times @var{pred} returns true when
456 called on elements from the given lists.
458 @var{pred} is called with @var{N} parameters @code{(@var{pred}
459 @var{elem1} @dots{} @var{elemN})}, each element being from the
460 corresponding @var{lst1} @dots{} @var{lstN}. The first call is with
461 the first element of each list, the second with the second element
462 from each, and so on.
464 Counting stops when the end of the shortest list is reached. At least
465 one list must be non-circular.
469 @node SRFI-1 Fold and Map
470 @subsubsection Fold, Unfold & Map
474 @c FIXME::martin: Review me!
476 @deffn {Scheme Procedure} fold proc init lst1 @dots{} lstN
477 @deffnx {Scheme Procedure} fold-right proc init lst1 @dots{} lstN
478 Apply @var{proc} to the elements of @var{lst1} @dots{} @var{lstN} to
479 build a result, and return that result.
481 Each @var{proc} call is @code{(@var{proc} @var{elem1} @dots{}
482 @var{elemN} @var{previous})}, where @var{elem1} is from @var{lst1},
483 through @var{elemN} from @var{lstN}. @var{previous} is the return
484 from the previous call to @var{proc}, or the given @var{init} for the
485 first call. If any list is empty, just @var{init} is returned.
487 @code{fold} works through the list elements from first to last. The
488 following shows a list reversal and the calls it makes,
491 (fold cons '() '(1 2 3))
499 @code{fold-right} works through the list elements from last to first,
500 ie.@: from the right. So for example the following finds the longest
501 string, and the last among equal longest,
504 (fold-right (lambda (str prev)
505 (if (> (string-length str) (string-length prev))
509 '("x" "abc" "xyz" "jk"))
513 If @var{lst1} through @var{lstN} have different lengths, @code{fold}
514 stops when the end of the shortest is reached; @code{fold-right}
515 commences at the last element of the shortest. Ie.@: elements past
516 the length of the shortest are ignored in the other @var{lst}s. At
517 least one @var{lst} must be non-circular.
519 @code{fold} should be preferred over @code{fold-right} if the order of
520 processing doesn't matter, or can be arranged either way, since
521 @code{fold} is a little more efficient.
523 The way @code{fold} builds a result from iterating is quite general,
524 it can do more than other iterations like say @code{map} or
525 @code{filter}. The following for example removes adjacent duplicate
526 elements from a list,
529 (define (delete-adjacent-duplicates lst)
530 (fold-right (lambda (elem ret)
531 (if (equal? elem (first ret))
536 (delete-adjacent-duplicates '(1 2 3 3 4 4 4 5))
537 @result{} (1 2 3 4 5)
540 Clearly the same sort of thing can be done with a @code{for-each} and
541 a variable in which to build the result, but a self-contained
542 @var{proc} can be re-used in multiple contexts, where a
543 @code{for-each} would have to be written out each time.
546 @deffn {Scheme Procedure} pair-fold proc init lst1 @dots{} lstN
547 @deffnx {Scheme Procedure} pair-fold-right proc init lst1 @dots{} lstN
548 The same as @code{fold} and @code{fold-right}, but apply @var{proc} to
549 the pairs of the lists instead of the list elements.
552 @deffn {Scheme Procedure} reduce proc default lst
553 @deffnx {Scheme Procedure} reduce-right proc default lst
554 @code{reduce} is a variant of @code{fold}, where the first call to
555 @var{proc} is on two elements from @var{lst}, rather than one element
556 and a given initial value.
558 If @var{lst} is empty, @code{reduce} returns @var{default} (this is
559 the only use for @var{default}). If @var{lst} has just one element
560 then that's the return value. Otherwise @var{proc} is called on the
561 elements of @var{lst}.
563 Each @var{proc} call is @code{(@var{proc} @var{elem} @var{previous})},
564 where @var{elem} is from @var{lst} (the second and subsequent elements
565 of @var{lst}), and @var{previous} is the return from the previous call
566 to @var{proc}. The first element of @var{lst} is the @var{previous}
567 for the first call to @var{proc}.
569 For example, the following adds a list of numbers, the calls made to
570 @code{+} are shown. (Of course @code{+} accepts multiple arguments
571 and can add a list directly, with @code{apply}.)
574 (reduce + 0 '(5 6 7)) @result{} 18
577 (+ 7 11) @result{} 18
580 @code{reduce} can be used instead of @code{fold} where the @var{init}
581 value is an ``identity'', meaning a value which under @var{proc}
582 doesn't change the result, in this case 0 is an identity since
583 @code{(+ 5 0)} is just 5. @code{reduce} avoids that unnecessary call.
585 @code{reduce-right} is a similar variation on @code{fold-right},
586 working from the end (ie.@: the right) of @var{lst}. The last element
587 of @var{lst} is the @var{previous} for the first call to @var{proc},
588 and the @var{elem} values go from the second last.
590 @code{reduce} should be preferred over @code{reduce-right} if the
591 order of processing doesn't matter, or can be arranged either way,
592 since @code{reduce} is a little more efficient.
595 @deffn {Scheme Procedure} unfold p f g seed [tail-gen]
596 @code{unfold} is defined as follows:
599 (unfold p f g seed) =
600 (if (p seed) (tail-gen seed)
602 (unfold p f g (g seed))))
607 Determines when to stop unfolding.
610 Maps each seed value to the corresponding list element.
613 Maps each seed value to next seed valu.
616 The state value for the unfold.
619 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
622 @var{g} produces a series of seed values, which are mapped to list
623 elements by @var{f}. These elements are put into a list in
624 left-to-right order, and @var{p} tells when to stop unfolding.
627 @deffn {Scheme Procedure} unfold-right p f g seed [tail]
628 Construct a list with the following loop.
631 (let lp ((seed seed) (lis tail))
634 (cons (f seed) lis))))
639 Determines when to stop unfolding.
642 Maps each seed value to the corresponding list element.
645 Maps each seed value to next seed valu.
648 The state value for the unfold.
651 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
656 @deffn {Scheme Procedure} map f lst1 lst2 @dots{}
657 Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and
658 return a list containing the results of the procedure applications.
659 This procedure is extended with respect to R5RS, because the argument
660 lists may have different lengths. The result list will have the same
661 length as the shortest argument lists. The order in which @var{f}
662 will be applied to the list element(s) is not specified.
665 @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{}
666 Apply the procedure @var{f} to each pair of corresponding elements of
667 the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not
668 specified. This procedure is extended with respect to R5RS, because
669 the argument lists may have different lengths. The shortest argument
670 list determines the number of times @var{f} is called. @var{f} will
671 be applied to the list elements in left-to-right order.
675 @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{}
676 @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{}
680 (apply append (map f clist1 clist2 ...))
686 (apply append! (map f clist1 clist2 ...))
689 Map @var{f} over the elements of the lists, just as in the @code{map}
690 function. However, the results of the applications are appended
691 together to make the final result. @code{append-map} uses
692 @code{append} to append the results together; @code{append-map!} uses
695 The dynamic order in which the various applications of @var{f} are
696 made is not specified.
699 @deffn {Scheme Procedure} map! f lst1 lst2 @dots{}
700 Linear-update variant of @code{map} -- @code{map!} is allowed, but not
701 required, to alter the cons cells of @var{lst1} to construct the
704 The dynamic order in which the various applications of @var{f} are
705 made is not specified. In the n-ary case, @var{lst2}, @var{lst3},
706 @dots{} must have at least as many elements as @var{lst1}.
709 @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{}
710 Like @code{for-each}, but applies the procedure @var{f} to the pairs
711 from which the argument lists are constructed, instead of the list
712 elements. The return value is not specified.
715 @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{}
716 Like @code{map}, but only results from the applications of @var{f}
717 which are true are saved in the result list.
721 @node SRFI-1 Filtering and Partitioning
722 @subsubsection Filtering and Partitioning
724 @cindex list partition
726 @c FIXME::martin: Review me!
728 Filtering means to collect all elements from a list which satisfy a
729 specific condition. Partitioning a list means to make two groups of
730 list elements, one which contains the elements satisfying a condition,
731 and the other for the elements which don't.
733 The @code{filter} and @code{filter!} functions are implemented in the
734 Guile core, @xref{List Modification}.
736 @deffn {Scheme Procedure} partition pred lst
737 @deffnx {Scheme Procedure} partition! pred lst
738 Split @var{lst} into those elements which do and don't satisfy the
739 predicate @var{pred}.
741 The return is two values (@pxref{Multiple Values}), the first being a
742 list of all elements from @var{lst} which satisfy @var{pred}, the
743 second a list of those which do not.
745 The elements in the result lists are in the same order as in @var{lst}
746 but the order in which the calls @code{(@var{pred} elem)} are made on
747 the list elements is unspecified.
749 @code{partition} does not change @var{lst}, but one of the returned
750 lists may share a tail with it. @code{partition!} may modify
751 @var{lst} to construct its return.
754 @deffn {Scheme Procedure} remove pred lst
755 @deffnx {Scheme Procedure} remove! pred lst
756 Return a list containing all elements from @var{lst} which do not
757 satisfy the predicate @var{pred}. The elements in the result list
758 have the same order as in @var{lst}. The order in which @var{pred} is
759 applied to the list elements is not specified.
761 @code{remove!} is allowed, but not required to modify the structure of
766 @node SRFI-1 Searching
767 @subsubsection Searching
770 @c FIXME::martin: Review me!
772 The procedures for searching elements in lists either accept a
773 predicate or a comparison object for determining which elements are to
776 @deffn {Scheme Procedure} find pred lst
777 Return the first element of @var{lst} which satisfies the predicate
778 @var{pred} and @code{#f} if no such element is found.
781 @deffn {Scheme Procedure} find-tail pred lst
782 Return the first pair of @var{lst} whose @sc{car} satisfies the
783 predicate @var{pred} and @code{#f} if no such element is found.
786 @deffn {Scheme Procedure} take-while pred lst
787 @deffnx {Scheme Procedure} take-while! pred lst
788 Return the longest initial prefix of @var{lst} whose elements all
789 satisfy the predicate @var{pred}.
791 @code{take-while!} is allowed, but not required to modify the input
792 list while producing the result.
795 @deffn {Scheme Procedure} drop-while pred lst
796 Drop the longest initial prefix of @var{lst} whose elements all
797 satisfy the predicate @var{pred}.
800 @deffn {Scheme Procedure} span pred lst
801 @deffnx {Scheme Procedure} span! pred lst
802 @deffnx {Scheme Procedure} break pred lst
803 @deffnx {Scheme Procedure} break! pred lst
804 @code{span} splits the list @var{lst} into the longest initial prefix
805 whose elements all satisfy the predicate @var{pred}, and the remaining
806 tail. @code{break} inverts the sense of the predicate.
808 @code{span!} and @code{break!} are allowed, but not required to modify
809 the structure of the input list @var{lst} in order to produce the
812 Note that the name @code{break} conflicts with the @code{break}
813 binding established by @code{while} (@pxref{while do}). Applications
814 wanting to use @code{break} from within a @code{while} loop will need
815 to make a new define under a different name.
818 @deffn {Scheme Procedure} any pred lst1 lst2 @dots{} lstN
819 Test whether any set of elements from @var{lst1} @dots{} lstN
820 satisfies @var{pred}. If so the return value is the return from the
821 successful @var{pred} call, or if not the return is @code{#f}.
823 Each @var{pred} call is @code{(@var{pred} @var{elem1} @dots{}
824 @var{elemN})} taking an element from each @var{lst}. The calls are
825 made successively for the first, second, etc elements of the lists,
826 stopping when @var{pred} returns non-@code{#f}, or when the end of the
827 shortest list is reached.
829 The @var{pred} call on the last set of elements (ie.@: when the end of
830 the shortest list has been reached), if that point is reached, is a
834 @deffn {Scheme Procedure} every pred lst1 lst2 @dots{} lstN
835 Test whether every set of elements from @var{lst1} @dots{} lstN
836 satisfies @var{pred}. If so the return value is the return from the
837 final @var{pred} call, or if not the return is @code{#f}.
839 Each @var{pred} call is @code{(@var{pred} @var{elem1} @dots{}
840 @var{elemN})} taking an element from each @var{lst}. The calls are
841 made successively for the first, second, etc elements of the lists,
842 stopping if @var{pred} returns @code{#f}, or when the end of any of
843 the lists is reached.
845 The @var{pred} call on the last set of elements (ie.@: when the end of
846 the shortest list has been reached) is a tail call.
848 If one of @var{lst1} @dots{} @var{lstN} is empty then no calls to
849 @var{pred} are made, and the return is @code{#t}.
852 @deffn {Scheme Procedure} list-index pred lst1 @dots{} lstN
853 Return the index of the first set of elements, one from each of
854 @var{lst1}@dots{}@var{lstN}, which satisfies @var{pred}.
856 @var{pred} is called as @code{(@var{pred} elem1 @dots{} elemN)}.
857 Searching stops when the end of the shortest @var{lst} is reached.
858 The return index starts from 0 for the first set of elements. If no
859 set of elements pass then the return is @code{#f}.
862 (list-index odd? '(2 4 6 9)) @result{} 3
863 (list-index = '(1 2 3) '(3 1 2)) @result{} #f
867 @deffn {Scheme Procedure} member x lst [=]
868 Return the first sublist of @var{lst} whose @sc{car} is equal to
869 @var{x}. If @var{x} does not appear in @var{lst}, return @code{#f}.
871 Equality is determined by @code{equal?}, or by the equality predicate
872 @var{=} if given. @var{=} is called @code{(= @var{x} elem)},
873 ie.@: with the given @var{x} first, so for example to find the first
874 element greater than 5,
877 (member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9)
880 This version of @code{member} extends the core @code{member}
881 (@pxref{List Searching}) by accepting an equality predicate.
885 @node SRFI-1 Deleting
886 @subsubsection Deleting
889 @deffn {Scheme Procedure} delete x lst [=]
890 @deffnx {Scheme Procedure} delete! x lst [=]
891 Return a list containing the elements of @var{lst} but with those
892 equal to @var{x} deleted. The returned elements will be in the same
893 order as they were in @var{lst}.
895 Equality is determined by the @var{=} predicate, or @code{equal?} if
896 not given. An equality call is made just once for each element, but
897 the order in which the calls are made on the elements is unspecified.
899 The equality calls are always @code{(= x elem)}, ie.@: the given @var{x}
900 is first. This means for instance elements greater than 5 can be
901 deleted with @code{(delete 5 lst <)}.
903 @code{delete} does not modify @var{lst}, but the return might share a
904 common tail with @var{lst}. @code{delete!} may modify the structure
905 of @var{lst} to construct its return.
907 These functions extend the core @code{delete} and @code{delete!}
908 (@pxref{List Modification}) in accepting an equality predicate. See
909 also @code{lset-difference} (@pxref{SRFI-1 Set Operations}) for
910 deleting multiple elements from a list.
913 @deffn {Scheme Procedure} delete-duplicates lst [=]
914 @deffnx {Scheme Procedure} delete-duplicates! lst [=]
915 Return a list containing the elements of @var{lst} but without
918 When elements are equal, only the first in @var{lst} is retained.
919 Equal elements can be anywhere in @var{lst}, they don't have to be
920 adjacent. The returned list will have the retained elements in the
921 same order as they were in @var{lst}.
923 Equality is determined by the @var{=} predicate, or @code{equal?} if
924 not given. Calls @code{(= x y)} are made with element @var{x} being
925 before @var{y} in @var{lst}. A call is made at most once for each
926 combination, but the sequence of the calls across the elements is
929 @code{delete-duplicates} does not modify @var{lst}, but the return
930 might share a common tail with @var{lst}. @code{delete-duplicates!}
931 may modify the structure of @var{lst} to construct its return.
933 In the worst case, this is an @math{O(N^2)} algorithm because it must
934 check each element against all those preceding it. For long lists it
935 is more efficient to sort and then compare only adjacent elements.
939 @node SRFI-1 Association Lists
940 @subsubsection Association Lists
941 @cindex association list
944 @c FIXME::martin: Review me!
946 Association lists are described in detail in section @ref{Association
947 Lists}. The present section only documents the additional procedures
948 for dealing with association lists defined by SRFI-1.
950 @deffn {Scheme Procedure} assoc key alist [=]
951 Return the pair from @var{alist} which matches @var{key}. This
952 extends the core @code{assoc} (@pxref{Retrieving Alist Entries}) by
953 taking an optional @var{=} comparison procedure.
955 The default comparison is @code{equal?}. If an @var{=} parameter is
956 given it's called @code{(@var{=} @var{key} @var{alistcar})}, ie. the
957 given target @var{key} is the first argument, and a @code{car} from
958 @var{alist} is second.
960 For example a case-insensitive string lookup,
963 (assoc "yy" '(("XX" . 1) ("YY" . 2)) string-ci=?)
968 @deffn {Scheme Procedure} alist-cons key datum alist
969 Cons a new association @var{key} and @var{datum} onto @var{alist} and
970 return the result. This is equivalent to
973 (cons (cons @var{key} @var{datum}) @var{alist})
976 @code{acons} (@pxref{Adding or Setting Alist Entries}) in the Guile
977 core does the same thing.
980 @deffn {Scheme Procedure} alist-copy alist
981 Return a newly allocated copy of @var{alist}, that means that the
982 spine of the list as well as the pairs are copied.
985 @deffn {Scheme Procedure} alist-delete key alist [=]
986 @deffnx {Scheme Procedure} alist-delete! key alist [=]
987 Return a list containing the elements of @var{alist} but with those
988 elements whose keys are equal to @var{key} deleted. The returned
989 elements will be in the same order as they were in @var{alist}.
991 Equality is determined by the @var{=} predicate, or @code{equal?} if
992 not given. The order in which elements are tested is unspecified, but
993 each equality call is made @code{(= key alistkey)}, ie. the given
994 @var{key} parameter is first and the key from @var{alist} second.
995 This means for instance all associations with a key greater than 5 can
996 be removed with @code{(alist-delete 5 alist <)}.
998 @code{alist-delete} does not modify @var{alist}, but the return might
999 share a common tail with @var{alist}. @code{alist-delete!} may modify
1000 the list structure of @var{alist} to construct its return.
1004 @node SRFI-1 Set Operations
1005 @subsubsection Set Operations on Lists
1006 @cindex list set operation
1008 Lists can be used to represent sets of objects. The procedures in
1009 this section operate on such lists as sets.
1011 Note that lists are not an efficient way to implement large sets. The
1012 procedures here typically take time @math{@var{m}@cross{}@var{n}} when
1013 operating on @var{m} and @var{n} element lists. Other data structures
1014 like trees, bitsets (@pxref{Bit Vectors}) or hash tables (@pxref{Hash
1015 Tables}) are faster.
1017 All these procedures take an equality predicate as the first argument.
1018 This predicate is used for testing the objects in the list sets for
1019 sameness. This predicate must be consistent with @code{eq?}
1020 (@pxref{Equality}) in the sense that if two list elements are
1021 @code{eq?} then they must also be equal under the predicate. This
1022 simply means a given object must be equal to itself.
1024 @deffn {Scheme Procedure} lset<= = list1 list2 @dots{}
1025 Return @code{#t} if each list is a subset of the one following it.
1026 Ie.@: @var{list1} a subset of @var{list2}, @var{list2} a subset of
1027 @var{list3}, etc, for as many lists as given. If only one list or no
1028 lists are given then the return is @code{#t}.
1030 A list @var{x} is a subset of @var{y} if each element of @var{x} is
1031 equal to some element in @var{y}. Elements are compared using the
1032 given @var{=} procedure, called as @code{(@var{=} xelem yelem)}.
1035 (lset<= eq?) @result{} #t
1036 (lset<= eqv? '(1 2 3) '(1)) @result{} #f
1037 (lset<= eqv? '(1 3 2) '(4 3 1 2)) @result{} #t
1041 @deffn {Scheme Procedure} lset= = list1 list2 @dots{}
1042 Return @code{#t} if all argument lists are set-equal. @var{list1} is
1043 compared to @var{list2}, @var{list2} to @var{list3}, etc, for as many
1044 lists as given. If only one list or no lists are given then the
1045 return is @code{#t}.
1047 Two lists @var{x} and @var{y} are set-equal if each element of @var{x}
1048 is equal to some element of @var{y} and conversely each element of
1049 @var{y} is equal to some element of @var{x}. The order of the
1050 elements in the lists doesn't matter. Element equality is determined
1051 with the given @var{=} procedure, called as @code{(@var{=} xelem
1052 yelem)}, but exactly which calls are made is unspecified.
1055 (lset= eq?) @result{} #t
1056 (lset= eqv? '(1 2 3) '(3 2 1)) @result{} #t
1057 (lset= string-ci=? '("a" "A" "b") '("B" "b" "a")) @result{} #t
1061 @deffn {Scheme Procedure} lset-adjoin = list elem1 @dots{}
1062 Add to @var{list} any of the given @var{elem}s not already in the
1063 list. @var{elem}s are @code{cons}ed onto the start of @var{list} (so
1064 the return shares a common tail with @var{list}), but the order
1065 they're added is unspecified.
1067 The given @var{=} procedure is used for comparing elements, called as
1068 @code{(@var{=} listelem elem)}, ie.@: the second argument is one of
1069 the given @var{elem} parameters.
1072 (lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3)
1076 @deffn {Scheme Procedure} lset-union = list1 list2 @dots{}
1077 @deffnx {Scheme Procedure} lset-union! = list1 list2 @dots{}
1078 Return the union of the argument list sets. The result is built by
1079 taking the union of @var{list1} and @var{list2}, then the union of
1080 that with @var{list3}, etc, for as many lists as given. For one list
1081 argument that list itself is the result, for no list arguments the
1082 result is the empty list.
1084 The union of two lists @var{x} and @var{y} is formed as follows. If
1085 @var{x} is empty then the result is @var{y}. Otherwise start with
1086 @var{x} as the result and consider each @var{y} element (from first to
1087 last). A @var{y} element not equal to something already in the result
1088 is @code{cons}ed onto the result.
1090 The given @var{=} procedure is used for comparing elements, called as
1091 @code{(@var{=} relem yelem)}. The first argument is from the result
1092 accumulated so far, and the second is from the list being union-ed in.
1093 But exactly which calls are made is otherwise unspecified.
1095 Notice that duplicate elements in @var{list1} (or the first non-empty
1096 list) are preserved, but that repeated elements in subsequent lists
1097 are only added once.
1100 (lset-union eqv?) @result{} ()
1101 (lset-union eqv? '(1 2 3)) @result{} (1 2 3)
1102 (lset-union eqv? '(1 2 1 3) '(2 4 5) '(5)) @result{} (5 4 1 2 1 3)
1105 @code{lset-union} doesn't change the given lists but the result may
1106 share a tail with the first non-empty list. @code{lset-union!} can
1107 modify all of the given lists to form the result.
1110 @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{}
1111 @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{}
1112 Return the intersection of @var{list1} with the other argument lists,
1113 meaning those elements of @var{list1} which are also in all of
1114 @var{list2} etc. For one list argument, just that list is returned.
1116 The test for an element of @var{list1} to be in the return is simply
1117 that it's equal to some element in each of @var{list2} etc. Notice
1118 this means an element appearing twice in @var{list1} but only once in
1119 each of @var{list2} etc will go into the return twice. The return has
1120 its elements in the same order as they were in @var{list1}.
1122 The given @var{=} procedure is used for comparing elements, called as
1123 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1124 and the second is from one of the subsequent lists. But exactly which
1125 calls are made and in what order is unspecified.
1128 (lset-intersection eqv? '(x y)) @result{} (x y)
1129 (lset-intersection eqv? '(1 2 3) '(4 3 2)) @result{} (2 3)
1130 (lset-intersection eqv? '(1 1 2 2) '(1 2) '(2 1) '(2)) @result{} (2 2)
1133 The return from @code{lset-intersection} may share a tail with
1134 @var{list1}. @code{lset-intersection!} may modify @var{list1} to form
1138 @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{}
1139 @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{}
1140 Return @var{list1} with any elements in @var{list2}, @var{list3} etc
1141 removed (ie.@: subtracted). For one list argument, just that list is
1144 The given @var{=} procedure is used for comparing elements, called as
1145 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1146 and the second from one of the subsequent lists. But exactly which
1147 calls are made and in what order is unspecified.
1150 (lset-difference eqv? '(x y)) @result{} (x y)
1151 (lset-difference eqv? '(1 2 3) '(3 1)) @result{} (2)
1152 (lset-difference eqv? '(1 2 3) '(3) '(2)) @result{} (1)
1155 The return from @code{lset-difference} may share a tail with
1156 @var{list1}. @code{lset-difference!} may modify @var{list1} to form
1160 @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{}
1161 @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{}
1162 Return two values (@pxref{Multiple Values}), the difference and
1163 intersection of the argument lists as per @code{lset-difference} and
1164 @code{lset-intersection} above.
1166 For two list arguments this partitions @var{list1} into those elements
1167 of @var{list1} which are in @var{list2} and not in @var{list2}. (But
1168 for more than two arguments there can be elements of @var{list1} which
1169 are neither part of the difference nor the intersection.)
1171 One of the return values from @code{lset-diff+intersection} may share
1172 a tail with @var{list1}. @code{lset-diff+intersection!} may modify
1173 @var{list1} to form its results.
1176 @deffn {Scheme Procedure} lset-xor = list1 list2 @dots{}
1177 @deffnx {Scheme Procedure} lset-xor! = list1 list2 @dots{}
1178 Return an XOR of the argument lists. For two lists this means those
1179 elements which are in exactly one of the lists. For more than two
1180 lists it means those elements which appear in an odd number of the
1183 To be precise, the XOR of two lists @var{x} and @var{y} is formed by
1184 taking those elements of @var{x} not equal to any element of @var{y},
1185 plus those elements of @var{y} not equal to any element of @var{x}.
1186 Equality is determined with the given @var{=} procedure, called as
1187 @code{(@var{=} e1 e2)}. One argument is from @var{x} and the other
1188 from @var{y}, but which way around is unspecified. Exactly which
1189 calls are made is also unspecified, as is the order of the elements in
1193 (lset-xor eqv? '(x y)) @result{} (x y)
1194 (lset-xor eqv? '(1 2 3) '(4 3 2)) @result{} (4 1)
1197 The return from @code{lset-xor} may share a tail with one of the list
1198 arguments. @code{lset-xor!} may modify @var{list1} to form its
1204 @subsection SRFI-2 - and-let*
1208 The following syntax can be obtained with
1211 (use-modules (srfi srfi-2))
1214 @deffn {library syntax} and-let* (clause @dots{}) body @dots{}
1215 A combination of @code{and} and @code{let*}.
1217 Each @var{clause} is evaluated in turn, and if @code{#f} is obtained
1218 then evaluation stops and @code{#f} is returned. If all are
1219 non-@code{#f} then @var{body} is evaluated and the last form gives the
1220 return value, or if @var{body} is empty then the result is @code{#t}.
1221 Each @var{clause} should be one of the following,
1225 Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}.
1226 Like @code{let*}, that binding is available to subsequent clauses.
1228 Evaluate @var{expr} and check for @code{#f}.
1230 Get the value bound to @var{symbol} and check for @code{#f}.
1233 Notice that @code{(expr)} has an ``extra'' pair of parentheses, for
1234 instance @code{((eq? x y))}. One way to remember this is to imagine
1235 the @code{symbol} in @code{(symbol expr)} is omitted.
1237 @code{and-let*} is good for calculations where a @code{#f} value means
1238 termination, but where a non-@code{#f} value is going to be needed in
1239 subsequent expressions.
1241 The following illustrates this, it returns text between brackets
1242 @samp{[...]} in a string, or @code{#f} if there are no such brackets
1243 (ie.@: either @code{string-index} gives @code{#f}).
1246 (define (extract-brackets str)
1247 (and-let* ((start (string-index str #\[))
1248 (end (string-index str #\] start)))
1249 (substring str (1+ start) end)))
1252 The following shows plain variables and expressions tested too.
1253 @code{diagnostic-levels} is taken to be an alist associating a
1254 diagnostic type with a level. @code{str} is printed only if the type
1255 is known and its level is high enough.
1258 (define (show-diagnostic type str)
1259 (and-let* (want-diagnostics
1260 (level (assq-ref diagnostic-levels type))
1261 ((>= level current-diagnostic-level)))
1265 The advantage of @code{and-let*} is that an extended sequence of
1266 expressions and tests doesn't require lots of nesting as would arise
1267 from separate @code{and} and @code{let*}, or from @code{cond} with
1274 @subsection SRFI-4 - Homogeneous numeric vector datatypes
1277 The SRFI-4 procedures and data types are always available, @xref{Uniform
1281 @subsection SRFI-6 - Basic String Ports
1284 SRFI-6 defines the procedures @code{open-input-string},
1285 @code{open-output-string} and @code{get-output-string}. These
1286 procedures are included in the Guile core, so using this module does not
1287 make any difference at the moment. But it is possible that support for
1288 SRFI-6 will be factored out of the core library in the future, so using
1289 this module does not hurt, after all.
1292 @subsection SRFI-8 - receive
1295 @code{receive} is a syntax for making the handling of multiple-value
1296 procedures easier. It is documented in @xref{Multiple Values}.
1300 @subsection SRFI-9 - define-record-type
1304 This SRFI is a syntax for defining new record types and creating
1305 predicate, constructor, and field getter and setter functions. In
1306 Guile this is simply an alternate interface to the core record
1307 functionality (@pxref{Records}). It can be used with,
1310 (use-modules (srfi srfi-9))
1313 @deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{}
1315 Create a new record type, and make various @code{define}s for using
1316 it. This syntax can only occur at the top-level, not nested within
1319 @var{type} is bound to the record type, which is as per the return
1320 from the core @code{make-record-type}. @var{type} also provides the
1321 name for the record, as per @code{record-type-name}.
1323 @var{constructor} is bound to a function to be called as
1324 @code{(@var{constructor} fieldval @dots{})} to create a new record of
1325 this type. The arguments are initial values for the fields, one
1326 argument for each field, in the order they appear in the
1327 @code{define-record-type} form.
1329 The @var{fieldname}s provide the names for the record fields, as per
1330 the core @code{record-type-fields} etc, and are referred to in the
1331 subsequent accessor/modifier forms.
1333 @var{predictate} is bound to a function to be called as
1334 @code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f}
1335 according to whether @var{obj} is a record of this type.
1337 Each @var{accessor} is bound to a function to be called
1338 @code{(@var{accessor} record)} to retrieve the respective field from a
1339 @var{record}. Similarly each @var{modifier} is bound to a function to
1340 be called @code{(@var{modifier} record val)} to set the respective
1341 field in a @var{record}.
1345 An example will illustrate typical usage,
1348 (define-record-type employee-type
1349 (make-employee name age salary)
1351 (name get-employee-name)
1352 (age get-employee-age set-employee-age)
1353 (salary get-employee-salary set-employee-salary))
1356 This creates a new employee data type, with name, age and salary
1357 fields. Accessor functions are created for each field, but no
1358 modifier function for the name (the intention in this example being
1359 that it's established only when an employee object is created). These
1360 can all then be used as for example,
1363 employee-type @result{} #<record-type employee-type>
1365 (define fred (make-employee "Fred" 45 20000.00))
1367 (employee? fred) @result{} #t
1368 (get-employee-age fred) @result{} 45
1369 (set-employee-salary fred 25000.00) ;; pay rise
1372 The functions created by @code{define-record-type} are ordinary
1373 top-level @code{define}s. They can be redefined or @code{set!} as
1374 desired, exported from a module, etc.
1378 @subsection SRFI-10 - Hash-Comma Reader Extension
1383 This SRFI implements a reader extension @code{#,()} called hash-comma.
1384 It allows the reader to give new kinds of objects, for use both in
1385 data and as constants or literals in source code. This feature is
1389 (use-modules (srfi srfi-10))
1393 The new read syntax is of the form
1396 #,(@var{tag} @var{arg}@dots{})
1400 where @var{tag} is a symbol and the @var{arg}s are objects taken as
1401 parameters. @var{tag}s are registered with the following procedure.
1403 @deffn {Scheme Procedure} define-reader-ctor tag proc
1404 Register @var{proc} as the constructor for a hash-comma read syntax
1405 starting with symbol @var{tag}, ie. @nicode{#,(@var{tag} arg@dots{})}.
1406 @var{proc} is called with the given arguments @code{(@var{proc}
1407 arg@dots{})} and the object it returns is the result of the read.
1411 For example, a syntax giving a list of @var{N} copies of an object.
1414 (define-reader-ctor 'repeat
1416 (make-list reps obj)))
1418 (display '#,(repeat 99 3))
1422 Notice the quote @nicode{'} when the @nicode{#,( )} is used. The
1423 @code{repeat} handler returns a list and the program must quote to use
1424 it literally, the same as any other list. Ie.
1427 (display '#,(repeat 99 3))
1429 (display '(99 99 99))
1432 When a handler returns an object which is self-evaluating, like a
1433 number or a string, then there's no need for quoting, just as there's
1434 no need when giving those directly as literals. For example an
1438 (define-reader-ctor 'sum
1441 (display #,(sum 123 456)) @print{} 579
1444 A typical use for @nicode{#,()} is to get a read syntax for objects
1445 which don't otherwise have one. For example, the following allows a
1446 hash table to be given literally, with tags and values, ready for fast
1450 (define-reader-ctor 'hash
1452 (let ((table (make-hash-table)))
1453 (for-each (lambda (elem)
1454 (apply hash-set! table elem))
1458 (define (animal->family animal)
1459 (hash-ref '#,(hash ("tiger" "cat")
1464 (animal->family "lion") @result{} "cat"
1467 Or for example the following is a syntax for a compiled regular
1468 expression (@pxref{Regular Expressions}).
1471 (use-modules (ice-9 regex))
1473 (define-reader-ctor 'regexp make-regexp)
1475 (define (extract-angs str)
1476 (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str)))
1478 (match:substring match 1))))
1480 (extract-angs "foo <BAR> quux") @result{} "BAR"
1484 @nicode{#,()} is somewhat similar to @code{define-macro}
1485 (@pxref{Macros}) in that handler code is run to produce a result, but
1486 @nicode{#,()} operates at the read stage, so it can appear in data for
1487 @code{read} (@pxref{Scheme Read}), not just in code to be executed.
1489 Because @nicode{#,()} is handled at read-time it has no direct access
1490 to variables etc. A symbol in the arguments is just a symbol, not a
1491 variable reference. The arguments are essentially constants, though
1492 the handler procedure can use them in any complicated way it might
1495 Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available
1496 globally, there's no need to use @code{(srfi srfi-10)} in later
1497 modules. Similarly the tags registered are global and can be used
1498 anywhere once registered.
1500 There's no attempt to record what previous @nicode{#,()} forms have
1501 been seen, if two identical forms occur then two calls are made to the
1502 handler procedure. The handler might like to maintain a cache or
1503 similar to avoid making copies of large objects, depending on expected
1506 In code the best uses of @nicode{#,()} are generally when there's a
1507 lot of objects of a particular kind as literals or constants. If
1508 there's just a few then some local variables and initializers are
1509 fine, but that becomes tedious and error prone when there's a lot, and
1510 the anonymous and compact syntax of @nicode{#,()} is much better.
1514 @subsection SRFI-11 - let-values
1519 This module implements the binding forms for multiple values
1520 @code{let-values} and @code{let*-values}. These forms are similar to
1521 @code{let} and @code{let*} (@pxref{Local Bindings}), but they support
1522 binding of the values returned by multiple-valued expressions.
1524 Write @code{(use-modules (srfi srfi-11))} to make the bindings
1528 (let-values (((x y) (values 1 2))
1529 ((z f) (values 3 4)))
1535 @code{let-values} performs all bindings simultaneously, which means that
1536 no expression in the binding clauses may refer to variables bound in the
1537 same clause list. @code{let*-values}, on the other hand, performs the
1538 bindings sequentially, just like @code{let*} does for single-valued
1543 @subsection SRFI-13 - String Library
1546 The SRFI-13 procedures are always available, @xref{Strings}.
1549 @subsection SRFI-14 - Character-set Library
1552 The SRFI-14 data type and procedures are always available,
1553 @xref{Character Sets}.
1556 @subsection SRFI-16 - case-lambda
1558 @cindex variable arity
1559 @cindex arity, variable
1561 @c FIXME::martin: Review me!
1564 The syntactic form @code{case-lambda} creates procedures, just like
1565 @code{lambda}, but has syntactic extensions for writing procedures of
1566 varying arity easier.
1568 The syntax of the @code{case-lambda} form is defined in the following
1574 --> (case-lambda <case-lambda-clause>)
1575 <case-lambda-clause>
1576 --> (<formals> <definition-or-command>*)
1579 | (<identifier>* . <identifier>)
1584 The value returned by a @code{case-lambda} form is a procedure which
1585 matches the number of actual arguments against the formals in the
1586 various clauses, in order. @dfn{Formals} means a formal argument list
1587 just like with @code{lambda} (@pxref{Lambda}). The first matching clause
1588 is selected, the corresponding values from the actual parameter list are
1589 bound to the variable names in the clauses and the body of the clause is
1590 evaluated. If no clause matches, an error is signalled.
1592 The following (silly) definition creates a procedure @var{foo} which
1593 acts differently, depending on the number of actual arguments. If one
1594 argument is given, the constant @code{#t} is returned, two arguments are
1595 added and if more arguments are passed, their product is calculated.
1598 (define foo (case-lambda
1617 The last expression evaluates to 1 because the last clause is matched,
1618 @var{z} is bound to the empty list and the following multiplication,
1619 applied to zero arguments, yields 1.
1623 @subsection SRFI-17 - Generalized set!
1626 This SRFI implements a generalized @code{set!}, allowing some
1627 ``referencing'' functions to be used as the target location of a
1628 @code{set!}. This feature is available from
1631 (use-modules (srfi srfi-17))
1635 For example @code{vector-ref} is extended so that
1638 (set! (vector-ref vec idx) new-value)
1645 (vector-set! vec idx new-value)
1648 The idea is that a @code{vector-ref} expression identifies a location,
1649 which may be either fetched or stored. The same form is used for the
1650 location in both cases, encouraging visual clarity. This is similar
1651 to the idea of an ``lvalue'' in C.
1653 The mechanism for this kind of @code{set!} is in the Guile core
1654 (@pxref{Procedures with Setters}). This module adds definitions of
1655 the following functions as procedures with setters, allowing them to
1656 be targets of a @code{set!},
1659 @nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr},
1660 @nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr},
1661 @nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr},
1662 @nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr},
1663 @nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr},
1664 @nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr},
1665 @nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr},
1666 @nicode{cdddar}, @nicode{cddddr}
1668 @nicode{string-ref}, @nicode{vector-ref}
1671 The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as
1672 a procedure with setter, allowing the setter for a procedure to be
1673 changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}.
1674 Currently Guile does not implement this, a setter can only be
1675 specified on creation (@code{getter-with-setter} below).
1677 @defun getter-with-setter
1678 The same as the Guile core @code{make-procedure-with-setter}
1679 (@pxref{Procedures with Setters}).
1684 @subsection SRFI-18 - Multithreading support
1687 This is an implementation of the SRFI-18 threading and synchronization
1688 library. The functions and variables described here are provided by
1691 (use-modules (srfi srfi-18))
1694 As a general rule, the data types and functions in this SRFI-18
1695 implementation are compatible with the types and functions in Guile's
1696 core threading code. For example, mutexes created with the SRFI-18
1697 @code{make-mutex} function can be passed to the built-in Guile
1698 function @code{lock-mutex} (@pxref{Mutexes and Condition Variables}),
1699 and mutexes created with the built-in Guile function @code{make-mutex}
1700 can be passed to the SRFI-18 function @code{mutex-lock!}. Cases in
1701 which this does not hold true are noted in the following sections.
1704 * SRFI-18 Threads:: Executing code
1705 * SRFI-18 Mutexes:: Mutual exclusion devices
1706 * SRFI-18 Condition variables:: Synchronizing of groups of threads
1707 * SRFI-18 Time:: Representation of times and durations
1708 * SRFI-18 Exceptions:: Signalling and handling errors
1711 @node SRFI-18 Threads
1712 @subsubsection SRFI-18 Threads
1714 Threads created by SRFI-18 differ in two ways from threads created by
1715 Guile's built-in thread functions. First, a thread created by SRFI-18
1716 @code{make-thread} begins in a blocked state and will not start
1717 execution until @code{thread-start!} is called on it. Second, SRFI-18
1718 threads are constructed with a top-level exception handler that
1719 captures any exceptions that are thrown on thread exit. In all other
1720 regards, SRFI-18 threads are identical to normal Guile threads.
1722 @defun current-thread
1723 Returns the thread that called this function. This is the same
1724 procedure as the same-named built-in procedure @code{current-thread}
1729 Returns @code{#t} if @var{obj} is a thread, @code{#f} otherwise. This
1730 is the same procedure as the same-named built-in procedure
1731 @code{thread?} (@pxref{Threads}).
1734 @defun make-thread thunk [name]
1735 Call @code{thunk} in a new thread and with a new dynamic state,
1736 returning the new thread and optionally assigning it the object name
1737 @var{name}, which may be any Scheme object.
1739 Note that the name @code{make-thread} conflicts with the
1740 @code{(ice-9 threads)} function @code{make-thread}. Applications
1741 wanting to use both of these functions will need to refer to them by
1745 @defun thread-name thread
1746 Returns the name assigned to @var{thread} at the time of its creation,
1747 or @code{#f} if it was not given a name.
1750 @defun thread-specific thread
1751 @defunx thread-specific-set! thread obj
1752 Get or set the ``object-specific'' property of @var{thread}. In
1753 Guile's implementation of SRFI-18, this value is stored as an object
1754 property, and will be @code{#f} if not set.
1757 @defun thread-start! thread
1758 Unblocks @var{thread} and allows it to begin execution if it has not
1762 @defun thread-yield!
1763 If one or more threads are waiting to execute, calling
1764 @code{thread-yield!} forces an immediate context switch to one of them.
1765 Otherwise, @code{thread-yield!} has no effect. @code{thread-yield!}
1766 behaves identically to the Guile built-in function @code{yield}.
1769 @defun thread-sleep! timeout
1770 The current thread waits until the point specified by the time object
1771 @var{timeout} is reached (@pxref{SRFI-18 Time}). This blocks the
1772 thread only if @var{timeout} represents a point in the future. it is
1773 an error for @var{timeout} to be @code{#f}.
1776 @defun thread-terminate! thread
1777 Causes an abnormal termination of @var{thread}. If @var{thread} is
1778 not already terminated, all mutexes owned by @var{thread} become
1779 unlocked/abandoned. If @var{thread} is the current thread,
1780 @code{thread-terminate!} does not return. Otherwise
1781 @code{thread-terminate!} returns an unspecified value; the termination
1782 of @var{thread} will occur before @code{thread-terminate!} returns.
1783 Subsequent attempts to join on @var{thread} will cause a ``terminated
1784 thread exception'' to be raised.
1786 @code{thread-terminate!} is compatible with the thread cancellation
1787 procedures in the core threads API (@pxref{Threads}) in that if a
1788 cleanup handler has been installed for the target thread, it will be
1789 called before the thread exits and its return value (or exception, if
1790 any) will be stored for later retrieval via a call to
1791 @code{thread-join!}.
1794 @defun thread-join! thread [timeout [timeout-val]]
1795 Wait for @var{thread} to terminate and return its exit value. When a
1796 time value @var{timeout} is given, it specifies a point in time where
1797 the waiting should be aborted. When the waiting is aborted,
1798 @var{timeoutval} is returned if it is specified; otherwise, a
1799 @code{join-timeout-exception} exception is raised
1800 (@pxref{SRFI-18 Exceptions}). Exceptions may also be raised if the
1801 thread was terminated by a call to @code{thread-terminate!}
1802 (@code{terminated-thread-exception} will be raised) or if the thread
1803 exited by raising an exception that was handled by the top-level
1804 exception handler (@code{uncaught-exception} will be raised; the
1805 original exception can be retrieved using
1806 @code{uncaught-exception-reason}).
1810 @node SRFI-18 Mutexes
1811 @subsubsection SRFI-18 Mutexes
1813 The behavior of Guile's built-in mutexes is parameterized via a set of
1814 flags passed to the @code{make-mutex} procedure in the core
1815 (@pxref{Mutexes and Condition Variables}). To satisfy the requirements
1816 for mutexes specified by SRFI-18, the @code{make-mutex} procedure
1817 described below sets the following flags:
1820 @code{recursive}: the mutex can be locked recursively
1822 @code{unchecked-unlock}: attempts to unlock a mutex that is already
1823 unlocked will not raise an exception
1825 @code{allow-external-unlock}: the mutex can be unlocked by any thread,
1826 not just the thread that locked it originally
1829 @defun make-mutex [name]
1830 Returns a new mutex, optionally assigning it the object name
1831 @var{name}, which may be any Scheme object. The returned mutex will be
1832 created with the configuration described above. Note that the name
1833 @code{make-mutex} conflicts with Guile core function @code{make-mutex}.
1834 Applications wanting to use both of these functions will need to refer
1835 to them by different names.
1838 @defun mutex-name mutex
1839 Returns the name assigned to @var{mutex} at the time of its creation,
1840 or @code{#f} if it was not given a name.
1843 @defun mutex-specific mutex
1844 @defunx mutex-specific-set! mutex obj
1845 Get or set the ``object-specific'' property of @var{mutex}. In Guile's
1846 implementation of SRFI-18, this value is stored as an object property,
1847 and will be @code{#f} if not set.
1850 @defun mutex-state mutex
1851 Returns information about the state of @var{mutex}. Possible values
1855 thread @code{T}: the mutex is in the locked/owned state and thread T
1856 is the owner of the mutex
1858 symbol @code{not-owned}: the mutex is in the locked/not-owned state
1860 symbol @code{abandoned}: the mutex is in the unlocked/abandoned state
1862 symbol @code{not-abandoned}: the mutex is in the
1863 unlocked/not-abandoned state
1867 @defun mutex-lock! mutex [timeout [thread]]
1868 Lock @var{mutex}, optionally specifying a time object @var{timeout}
1869 after which to abort the lock attempt and a thread @var{thread} giving
1870 a new owner for @var{mutex} different than the current thread. This
1871 procedure has the same behavior as the @code{lock-mutex} procedure in
1875 @defun mutex-unlock! mutex [condition-variable [timeout]]
1876 Unlock @var{mutex}, optionally specifying a condition variable
1877 @var{condition-variable} on which to wait, either indefinitely or,
1878 optionally, until the time object @var{timeout} has passed, to be
1879 signalled. This procedure has the same behavior as the
1880 @code{unlock-mutex} procedure in the core library.
1884 @node SRFI-18 Condition variables
1885 @subsubsection SRFI-18 Condition variables
1887 SRFI-18 does not specify a ``wait'' function for condition variables.
1888 Waiting on a condition variable can be simulated using the SRFI-18
1889 @code{mutex-unlock!} function described in the previous section, or
1890 Guile's built-in @code{wait-condition-variable} procedure can be used.
1892 @defun condition-variable? obj
1893 Returns @code{#t} if @var{obj} is a condition variable, @code{#f}
1894 otherwise. This is the same procedure as the same-named built-in
1896 (@pxref{Mutexes and Condition Variables, @code{condition-variable?}}).
1899 @defun make-condition-variable [name]
1900 Returns a new condition variable, optionally assigning it the object
1901 name @var{name}, which may be any Scheme object. This procedure
1902 replaces a procedure of the same name in the core library.
1905 @defun condition-variable-name condition-variable
1906 Returns the name assigned to @var{thread} at the time of its creation,
1907 or @code{#f} if it was not given a name.
1910 @defun condition-variable-specific condition-variable
1911 @defunx condition-variable-specific-set! condition-variable obj
1912 Get or set the ``object-specific'' property of
1913 @var{condition-variable}. In Guile's implementation of SRFI-18, this
1914 value is stored as an object property, and will be @code{#f} if not
1918 @defun condition-variable-signal! condition-variable
1919 @defunx condition-variable-broadcast! condition-variable
1920 Wake up one thread that is waiting for @var{condition-variable}, in
1921 the case of @code{condition-variable-signal!}, or all threads waiting
1922 for it, in the case of @code{condition-variable-broadcast!}. The
1923 behavior of these procedures is equivalent to that of the procedures
1924 @code{signal-condition-variable} and
1925 @code{broadcast-condition-variable} in the core library.
1930 @subsubsection SRFI-18 Time
1932 The SRFI-18 time functions manipulate time in two formats: a
1933 ``time object'' type that represents an absolute point in time in some
1934 implementation-specific way; and the number of seconds since some
1935 unspecified ``epoch''. In Guile's implementation, the epoch is the
1936 Unix epoch, 00:00:00 UTC, January 1, 1970.
1939 Return the current time as a time object. This procedure replaces
1940 the procedure of the same name in the core library, which returns the
1941 current time in seconds since the epoch.
1945 Returns @code{#t} if @var{obj} is a time object, @code{#f} otherwise.
1948 @defun time->seconds time
1949 @defunx seconds->time seconds
1950 Convert between time objects and numerical values representing the
1951 number of seconds since the epoch. When converting from a time object
1952 to seconds, the return value is the number of seconds between
1953 @var{time} and the epoch. When converting from seconds to a time
1954 object, the return value is a time object that represents a time
1955 @var{seconds} seconds after the epoch.
1959 @node SRFI-18 Exceptions
1960 @subsubsection SRFI-18 Exceptions
1962 SRFI-18 exceptions are identical to the exceptions provided by
1963 Guile's implementation of SRFI-34. The behavior of exception
1964 handlers invoked to handle exceptions thrown from SRFI-18 functions,
1965 however, differs from the conventional behavior of SRFI-34 in that
1966 the continuation of the handler is the same as that of the call to
1967 the function. Handlers are called in a tail-recursive manner; the
1968 exceptions do not ``bubble up''.
1970 @defun current-exception-handler
1971 Returns the current exception handler.
1974 @defun with-exception-handler handler thunk
1975 Installs @var{handler} as the current exception handler and calls the
1976 procedure @var{thunk} with no arguments, returning its value as the
1977 value of the exception. @var{handler} must be a procedure that accepts
1978 a single argument. The current exception handler at the time this
1979 procedure is called will be restored after the call returns.
1983 Raise @var{obj} as an exception. This is the same procedure as the
1984 same-named procedure defined in SRFI 34.
1987 @defun join-timeout-exception? obj
1988 Returns @code{#t} if @var{obj} is an exception raised as the result of
1989 performing a timed join on a thread that does not exit within the
1990 specified timeout, @code{#f} otherwise.
1993 @defun abandoned-mutex-exception? obj
1994 Returns @code{#t} if @var{obj} is an exception raised as the result of
1995 attempting to lock a mutex that has been abandoned by its owner thread,
1996 @code{#f} otherwise.
1999 @defun terminated-thread-exception? obj
2000 Returns @code{#t} if @var{obj} is an exception raised as the result of
2001 joining on a thread that exited as the result of a call to
2002 @code{thread-terminate!}.
2005 @defun uncaught-exception? obj
2006 @defunx uncaught-exception-reason exc
2007 @code{uncaught-exception?} returns @code{#t} if @var{obj} is an
2008 exception thrown as the result of joining a thread that exited by
2009 raising an exception that was handled by the top-level exception
2010 handler installed by @code{make-thread}. When this occurs, the
2011 original exception is preserved as part of the exception thrown by
2012 @code{thread-join!} and can be accessed by calling
2013 @code{uncaught-exception-reason} on that exception. Note that
2014 because this exception-preservation mechanism is a side-effect of
2015 @code{make-thread}, joining on threads that exited as described above
2016 but were created by other means will not raise this
2017 @code{uncaught-exception} error.
2022 @subsection SRFI-19 - Time/Date Library
2027 This is an implementation of the SRFI-19 time/date library. The
2028 functions and variables described here are provided by
2031 (use-modules (srfi srfi-19))
2034 @strong{Caution}: The current code in this module incorrectly extends
2035 the Gregorian calendar leap year rule back prior to the introduction
2036 of those reforms in 1582 (or the appropriate year in various
2037 countries). The Julian calendar was used prior to 1582, and there
2038 were 10 days skipped for the reform, but the code doesn't implement
2041 This will be fixed some time. Until then calculations for 1583
2042 onwards are correct, but prior to that any day/month/year and day of
2043 the week calculations are wrong.
2046 * SRFI-19 Introduction::
2049 * SRFI-19 Time/Date conversions::
2050 * SRFI-19 Date to string::
2051 * SRFI-19 String to date::
2054 @node SRFI-19 Introduction
2055 @subsubsection SRFI-19 Introduction
2057 @cindex universal time
2061 This module implements time and date representations and calculations,
2062 in various time systems, including universal time (UTC) and atomic
2065 For those not familiar with these time systems, TAI is based on a
2066 fixed length second derived from oscillations of certain atoms. UTC
2067 differs from TAI by an integral number of seconds, which is increased
2068 or decreased at announced times to keep UTC aligned to a mean solar
2069 day (the orbit and rotation of the earth are not quite constant).
2072 So far, only increases in the TAI
2079 UTC difference have been needed. Such an increase is a ``leap
2080 second'', an extra second of TAI introduced at the end of a UTC day.
2081 When working entirely within UTC this is never seen, every day simply
2082 has 86400 seconds. But when converting from TAI to a UTC date, an
2083 extra 23:59:60 is present, where normally a day would end at 23:59:59.
2084 Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI
2087 @cindex system clock
2088 In the current implementation, the system clock is assumed to be UTC,
2089 and a table of leap seconds in the code converts to TAI. See comments
2090 in @file{srfi-19.scm} for how to update this table.
2093 @cindex modified julian day
2094 Also, for those not familiar with the terminology, a @dfn{Julian Day}
2095 is a real number which is a count of days and fraction of a day, in
2096 UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
2097 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from
2098 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time
2099 is julian day 2400000.5.
2101 @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
2102 @c noon, UTC), but this is incorrect. It looks like it might have
2103 @c arisen from the code incorrectly treating years a multiple of 100
2104 @c but not 400 prior to 1582 as non-leap years, where instead the Julian
2105 @c calendar should be used so all multiples of 4 before 1582 are leap
2110 @subsubsection SRFI-19 Time
2113 A @dfn{time} object has type, seconds and nanoseconds fields
2114 representing a point in time starting from some epoch. This is an
2115 arbitrary point in time, not just a time of day. Although times are
2116 represented in nanoseconds, the actual resolution may be lower.
2118 The following variables hold the possible time types. For instance
2119 @code{(current-time time-process)} would give the current CPU process
2123 Universal Coordinated Time (UTC).
2128 International Atomic Time (TAI).
2132 @defvar time-monotonic
2133 Monotonic time, meaning a monotonically increasing time starting from
2134 an unspecified epoch.
2136 Note that in the current implementation @code{time-monotonic} is the
2137 same as @code{time-tai}, and unfortunately is therefore affected by
2138 adjustments to the system clock. Perhaps this will change in the
2142 @defvar time-duration
2143 A duration, meaning simply a difference between two times.
2146 @defvar time-process
2147 CPU time spent in the current process, starting from when the process
2149 @cindex process time
2153 CPU time spent in the current thread. Not currently implemented.
2159 Return @code{#t} if @var{obj} is a time object, or @code{#f} if not.
2162 @defun make-time type nanoseconds seconds
2163 Create a time object with the given @var{type}, @var{seconds} and
2167 @defun time-type time
2168 @defunx time-nanosecond time
2169 @defunx time-second time
2170 @defunx set-time-type! time type
2171 @defunx set-time-nanosecond! time nsec
2172 @defunx set-time-second! time sec
2173 Get or set the type, seconds or nanoseconds fields of a time object.
2175 @code{set-time-type!} merely changes the field, it doesn't convert the
2176 time value. For conversions, see @ref{SRFI-19 Time/Date conversions}.
2179 @defun copy-time time
2180 Return a new time object, which is a copy of the given @var{time}.
2183 @defun current-time [type]
2184 Return the current time of the given @var{type}. The default
2185 @var{type} is @code{time-utc}.
2187 Note that the name @code{current-time} conflicts with the Guile core
2188 @code{current-time} function (@pxref{Time}) as well as the SRFI-18
2189 @code{current-time} function (@pxref{SRFI-18 Time}). Applications
2190 wanting to use more than one of these functions will need to refer to
2191 them by different names.
2194 @defun time-resolution [type]
2195 Return the resolution, in nanoseconds, of the given time @var{type}.
2196 The default @var{type} is @code{time-utc}.
2199 @defun time<=? t1 t2
2200 @defunx time<? t1 t2
2201 @defunx time=? t1 t2
2202 @defunx time>=? t1 t2
2203 @defunx time>? t1 t2
2204 Return @code{#t} or @code{#f} according to the respective relation
2205 between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2}
2206 must be the same time type.
2209 @defun time-difference t1 t2
2210 @defunx time-difference! t1 t2
2211 Return a time object of type @code{time-duration} representing the
2212 period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be
2215 @code{time-difference} returns a new time object,
2216 @code{time-difference!} may modify @var{t1} to form its return.
2219 @defun add-duration time duration
2220 @defunx add-duration! time duration
2221 @defunx subtract-duration time duration
2222 @defunx subtract-duration! time duration
2223 Return a time object which is @var{time} with the given @var{duration}
2224 added or subtracted. @var{duration} must be a time object of type
2225 @code{time-duration}.
2227 @code{add-duration} and @code{subtract-duration} return a new time
2228 object. @code{add-duration!} and @code{subtract-duration!} may modify
2229 the given @var{time} to form their return.
2234 @subsubsection SRFI-19 Date
2237 A @dfn{date} object represents a date in the Gregorian calendar and a
2238 time of day on that date in some timezone.
2240 The fields are year, month, day, hour, minute, second, nanoseconds and
2241 timezone. A date object is immutable, its fields can be read but they
2242 cannot be modified once the object is created.
2245 Return @code{#t} if @var{obj} is a date object, or @code{#f} if not.
2248 @defun make-date nsecs seconds minutes hours date month year zone-offset
2249 Create a new date object.
2251 @c FIXME: What can we say about the ranges of the values. The
2252 @c current code looks it doesn't normalize, but expects then in their
2253 @c usual range already.
2257 @defun date-nanosecond date
2258 Nanoseconds, 0 to 999999999.
2261 @defun date-second date
2262 Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working
2263 entirely within UTC, it's only when converting to or from TAI.
2266 @defun date-minute date
2270 @defun date-hour date
2274 @defun date-day date
2275 Day of the month, 1 to 31 (or less, according to the month).
2278 @defun date-month date
2282 @defun date-year date
2283 Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46
2284 B.C. There is no year 0, year @math{-1} is followed by year 1.
2287 @defun date-zone-offset date
2288 Time zone, an integer number of seconds east of Greenwich.
2291 @defun date-year-day date
2292 Day of the year, starting from 1 for 1st January.
2295 @defun date-week-day date
2296 Day of the week, starting from 0 for Sunday.
2299 @defun date-week-number date dstartw
2300 Week of the year, ignoring a first partial week. @var{dstartw} is the
2301 day of the week which is taken to start a week, 0 for Sunday, 1 for
2304 @c FIXME: The spec doesn't say whether numbering starts at 0 or 1.
2305 @c The code looks like it's 0, if that's the correct intention.
2309 @c The SRFI text doesn't actually give the default for tz-offset, but
2310 @c the reference implementation has the local timezone and the
2311 @c conversions functions all specify that, so it should be ok to
2312 @c document it here.
2314 @defun current-date [tz-offset]
2315 Return a date object representing the current date/time, in UTC offset
2316 by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and
2317 defaults to the local timezone.
2320 @defun current-julian-day
2322 Return the current Julian Day.
2325 @defun current-modified-julian-day
2326 @cindex modified julian day
2327 Return the current Modified Julian Day.
2331 @node SRFI-19 Time/Date conversions
2332 @subsubsection SRFI-19 Time/Date conversions
2333 @cindex time conversion
2334 @cindex date conversion
2336 @defun date->julian-day date
2337 @defunx date->modified-julian-day date
2338 @defunx date->time-monotonic date
2339 @defunx date->time-tai date
2340 @defunx date->time-utc date
2342 @defun julian-day->date jdn [tz-offset]
2343 @defunx julian-day->time-monotonic jdn
2344 @defunx julian-day->time-tai jdn
2345 @defunx julian-day->time-utc jdn
2347 @defun modified-julian-day->date jdn [tz-offset]
2348 @defunx modified-julian-day->time-monotonic jdn
2349 @defunx modified-julian-day->time-tai jdn
2350 @defunx modified-julian-day->time-utc jdn
2352 @defun time-monotonic->date time [tz-offset]
2353 @defunx time-monotonic->time-tai time
2354 @defunx time-monotonic->time-tai! time
2355 @defunx time-monotonic->time-utc time
2356 @defunx time-monotonic->time-utc! time
2358 @defun time-tai->date time [tz-offset]
2359 @defunx time-tai->julian-day time
2360 @defunx time-tai->modified-julian-day time
2361 @defunx time-tai->time-monotonic time
2362 @defunx time-tai->time-monotonic! time
2363 @defunx time-tai->time-utc time
2364 @defunx time-tai->time-utc! time
2366 @defun time-utc->date time [tz-offset]
2367 @defunx time-utc->julian-day time
2368 @defunx time-utc->modified-julian-day time
2369 @defunx time-utc->time-monotonic time
2370 @defunx time-utc->time-monotonic! time
2371 @defunx time-utc->time-tai time
2372 @defunx time-utc->time-tai! time
2374 Convert between dates, times and days of the respective types. For
2375 instance @code{time-tai->time-utc} accepts a @var{time} object of type
2376 @code{time-tai} and returns an object of type @code{time-utc}.
2378 The @code{!} variants may modify their @var{time} argument to form
2379 their return. The plain functions create a new object.
2381 For conversions to dates, @var{tz-offset} is seconds east of
2382 Greenwich. The default is the local timezone, at the given time, as
2383 provided by the system, using @code{localtime} (@pxref{Time}).
2385 On 32-bit systems, @code{localtime} is limited to a 32-bit
2386 @code{time_t}, so a default @var{tz-offset} is only available for
2387 times between Dec 1901 and Jan 2038. For prior dates an application
2388 might like to use the value in 1902, though some locations have zone
2389 changes prior to that. For future dates an application might like to
2390 assume today's rules extend indefinitely. But for correct daylight
2391 savings transitions it will be necessary to take an offset for the
2392 same day and time but a year in range and which has the same starting
2393 weekday and same leap/non-leap (to support rules like last Sunday in
2397 @node SRFI-19 Date to string
2398 @subsubsection SRFI-19 Date to string
2399 @cindex date to string
2400 @cindex string, from date
2402 @defun date->string date [format]
2403 Convert a date to a string under the control of a format.
2404 @var{format} should be a string containing @samp{~} escapes, which
2405 will be expanded as per the following conversion table. The default
2406 @var{format} is @samp{~c}, a locale-dependent date and time.
2408 Many of these conversion characters are the same as POSIX
2409 @code{strftime} (@pxref{Time}), but there are some extras and some
2412 @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM}
2413 @item @nicode{~~} @tab literal ~
2414 @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun}
2415 @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday}
2416 @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan}
2417 @item @nicode{~B} @tab locale full month, eg.@: @samp{January}
2418 @item @nicode{~c} @tab locale date and time, eg.@: @*
2419 @samp{Fri Jul 14 20:28:42-0400 2000}
2420 @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31}
2422 @c Spec says d/m/y, reference implementation says m/d/y.
2423 @c Apparently the reference code was the intention, but would like to
2424 @c see an errata published for the spec before contradicting it here.
2426 @c @item @nicode{~D} @tab date @nicode{~d/~m/~y}
2428 @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31}
2429 @item @nicode{~f} @tab seconds and fractional seconds,
2430 with locale decimal point, eg.@: @samp{5.2}
2431 @item @nicode{~h} @tab same as @nicode{~b}
2432 @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23}
2433 @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12}
2434 @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366}
2435 @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23}
2436 @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12}
2437 @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12}
2438 @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59}
2439 @item @nicode{~n} @tab newline
2440 @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999}
2441 @item @nicode{~p} @tab locale AM or PM
2442 @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p}
2443 @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC
2444 @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @*
2445 (usual limit is 59, 60 is a leap second)
2446 @item @nicode{~t} @tab horizontal tab character
2447 @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S}
2448 @item @nicode{~U} @tab week of year, Sunday first day of week,
2449 @samp{00} to @samp{52}
2450 @item @nicode{~V} @tab week of year, Monday first day of week,
2451 @samp{01} to @samp{53}
2452 @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6}
2453 @item @nicode{~W} @tab week of year, Monday first day of week,
2454 @samp{00} to @samp{52}
2456 @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale
2457 @c date. The reference code has ~x as the locale date and ~X as a
2458 @c locale time. The rule is apparently that the code should be
2459 @c believed, but would like to see an errata for the spec before
2460 @c contradicting it here.
2462 @c @item @nicode{~x} @tab week of year, Monday as first day of week,
2463 @c @samp{00} to @samp{53}
2464 @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00}
2466 @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99}
2467 @item @nicode{~Y} @tab year, full, eg.@: @samp{2003}
2468 @item @nicode{~z} @tab time zone, RFC-822 style
2469 @item @nicode{~Z} @tab time zone symbol (not currently implemented)
2470 @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d}
2471 @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~k:~M:~S~z}
2472 @item @nicode{~3} @tab ISO-8601 time, @samp{~k:~M:~S}
2473 @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~k:~M:~S~z}
2474 @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~k:~M:~S}
2478 Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently
2479 described here, since the specification and reference implementation
2482 Conversion is locale-dependent on systems that support it
2483 (@pxref{Accessing Locale Information}). @xref{Locales,
2484 @code{setlocale}}, for information on how to change the current
2488 @node SRFI-19 String to date
2489 @subsubsection SRFI-19 String to date
2490 @cindex string to date
2491 @cindex date, from string
2493 @c FIXME: Can we say what happens when an incomplete date is
2494 @c converted? Ie. fields left as 0, or what? The spec seems to be
2497 @defun string->date input template
2498 Convert an @var{input} string to a date under the control of a
2499 @var{template} string. Return a newly created date object.
2501 Literal characters in @var{template} must match characters in
2502 @var{input} and @samp{~} escapes must match the input forms described
2503 in the table below. ``Skip to'' means characters up to one of the
2504 given type are ignored, or ``no skip'' for no skipping. ``Read'' is
2505 what's then read, and ``Set'' is the field affected in the date
2508 For example @samp{~Y} skips input characters until a digit is reached,
2509 at which point it expects a year and stores that to the year field of
2512 @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}}
2524 @tab @nicode{char-alphabetic?}
2525 @tab locale abbreviated weekday name
2529 @tab @nicode{char-alphabetic?}
2530 @tab locale full weekday name
2533 @c Note that the SRFI spec says that ~b and ~B don't set anything,
2534 @c but that looks like a mistake. The reference implementation sets
2535 @c the month field, which seems sensible and is what we describe
2539 @tab @nicode{char-alphabetic?}
2540 @tab locale abbreviated month name
2541 @tab @nicode{date-month}
2544 @tab @nicode{char-alphabetic?}
2545 @tab locale full month name
2546 @tab @nicode{date-month}
2549 @tab @nicode{char-numeric?}
2551 @tab @nicode{date-day}
2555 @tab day of month, blank padded
2556 @tab @nicode{date-day}
2559 @tab same as @samp{~b}
2562 @tab @nicode{char-numeric?}
2564 @tab @nicode{date-hour}
2568 @tab hour, blank padded
2569 @tab @nicode{date-hour}
2572 @tab @nicode{char-numeric?}
2574 @tab @nicode{date-month}
2577 @tab @nicode{char-numeric?}
2579 @tab @nicode{date-minute}
2582 @tab @nicode{char-numeric?}
2584 @tab @nicode{date-second}
2589 @tab @nicode{date-year} within 50 years
2592 @tab @nicode{char-numeric?}
2594 @tab @nicode{date-year}
2599 @tab date-zone-offset
2602 Notice that the weekday matching forms don't affect the date object
2603 returned, instead the weekday will be derived from the day, month and
2606 Conversion is locale-dependent on systems that support it
2607 (@pxref{Accessing Locale Information}). @xref{Locales,
2608 @code{setlocale}}, for information on how to change the current
2614 @subsection SRFI-26 - specializing parameters
2616 @cindex parameter specialize
2617 @cindex argument specialize
2618 @cindex specialize parameter
2620 This SRFI provides a syntax for conveniently specializing selected
2621 parameters of a function. It can be used with,
2624 (use-modules (srfi srfi-26))
2627 @deffn {library syntax} cut slot @dots{}
2628 @deffnx {library syntax} cute slot @dots{}
2629 Return a new procedure which will make a call (@var{slot} @dots{}) but
2630 with selected parameters specialized to given expressions.
2632 An example will illustrate the idea. The following is a
2633 specialization of @code{write}, sending output to
2634 @code{my-output-port},
2637 (cut write <> my-output-port)
2639 (lambda (obj) (write obj my-output-port))
2642 The special symbol @code{<>} indicates a slot to be filled by an
2643 argument to the new procedure. @code{my-output-port} on the other
2644 hand is an expression to be evaluated and passed, ie.@: it specializes
2645 the behaviour of @code{write}.
2649 A slot to be filled by an argument from the created procedure.
2650 Arguments are assigned to @code{<>} slots in the order they appear in
2651 the @code{cut} form, there's no way to re-arrange arguments.
2653 The first argument to @code{cut} is usually a procedure (or expression
2654 giving a procedure), but @code{<>} is allowed there too. For example,
2659 (lambda (proc) (proc 1 2 3))
2663 A slot to be filled by all remaining arguments from the new procedure.
2664 This can only occur at the end of a @code{cut} form.
2666 For example, a procedure taking a variable number of arguments like
2667 @code{max} but in addition enforcing a lower bound,
2670 (define my-lower-bound 123)
2672 (cut max my-lower-bound <...>)
2674 (lambda arglist (apply max my-lower-bound arglist))
2678 For @code{cut} the specializing expressions are evaluated each time
2679 the new procedure is called. For @code{cute} they're evaluated just
2680 once, when the new procedure is created. The name @code{cute} stands
2681 for ``@code{cut} with evaluated arguments''. In all cases the
2682 evaluations take place in an unspecified order.
2684 The following illustrates the difference between @code{cut} and
2688 (cut format <> "the time is ~s" (current-time))
2690 (lambda (port) (format port "the time is ~s" (current-time)))
2692 (cute format <> "the time is ~s" (current-time))
2694 (let ((val (current-time)))
2695 (lambda (port) (format port "the time is ~s" val))
2698 (There's no provision for a mixture of @code{cut} and @code{cute}
2699 where some expressions would be evaluated every time but others
2700 evaluated only once.)
2702 @code{cut} is really just a shorthand for the sort of @code{lambda}
2703 forms shown in the above examples. But notice @code{cut} avoids the
2704 need to name unspecialized parameters, and is more compact. Use in
2705 functional programming style or just with @code{map}, @code{for-each}
2706 or similar is typical.
2709 (map (cut * 2 <>) '(1 2 3 4))
2711 (for-each (cut write <> my-port) my-list)
2716 @subsection SRFI-31 - A special form `rec' for recursive evaluation
2718 @cindex recursive expression
2721 SRFI-31 defines a special form that can be used to create
2722 self-referential expressions more conveniently. The syntax is as
2727 <rec expression> --> (rec <variable> <expression>)
2728 <rec expression> --> (rec (<variable>+) <body>)
2732 The first syntax can be used to create self-referential expressions,
2736 guile> (define tmp (rec ones (cons 1 (delay ones))))
2739 The second syntax can be used to create anonymous recursive functions:
2742 guile> (define tmp (rec (display-n item n)
2744 (begin (display n) (display-n (- n 1))))))
2752 @subsection SRFI-34 - Exception handling for programs
2755 Guile provides an implementation of
2756 @uref{http://srfi.schemers.org/srfi-34/srfi-34.html, SRFI-34's exception
2757 handling mechanisms} as an alternative to its own built-in mechanisms
2758 (@pxref{Exceptions}). It can be made available as follows:
2761 (use-modules (srfi srfi-34))
2764 @c FIXME: Document it.
2768 @subsection SRFI-35 - Conditions
2774 @uref{http://srfi.schemers.org/srfi-35/srfi-35.html, SRFI-35} implements
2775 @dfn{conditions}, a data structure akin to records designed to convey
2776 information about exceptional conditions between parts of a program. It
2777 is normally used in conjunction with SRFI-34's @code{raise}:
2780 (raise (condition (&message
2781 (message "An error occurred"))))
2784 Users can define @dfn{condition types} containing arbitrary information.
2785 Condition types may inherit from one another. This allows the part of
2786 the program that handles (or ``catches'') conditions to get accurate
2787 information about the exceptional condition that arose.
2789 SRFI-35 conditions are made available using:
2792 (use-modules (srfi srfi-35))
2795 The procedures available to manipulate condition types are the
2798 @deffn {Scheme Procedure} make-condition-type id parent field-names
2799 Return a new condition type named @var{id}, inheriting from
2800 @var{parent}, and with the fields whose names are listed in
2801 @var{field-names}. @var{field-names} must be a list of symbols and must
2802 not contain names already used by @var{parent} or one of its supertypes.
2805 @deffn {Scheme Procedure} condition-type? obj
2806 Return true if @var{obj} is a condition type.
2809 Conditions can be created and accessed with the following procedures:
2811 @deffn {Scheme Procedure} make-condition type . field+value
2812 Return a new condition of type @var{type} with fields initialized as
2813 specified by @var{field+value}, a sequence of field names (symbols) and
2814 values as in the following example:
2817 (let ((&ct (make-condition-type 'foo &condition '(a b c))))
2818 (make-condition &ct 'a 1 'b 2 'c 3))
2821 Note that all fields of @var{type} and its supertypes must be specified.
2824 @deffn {Scheme Procedure} make-compound-condition . conditions
2825 Return a new compound condition composed of @var{conditions}. The
2826 returned condition has the type of each condition of @var{conditions}
2827 (per @code{condition-has-type?}).
2830 @deffn {Scheme Procedure} condition-has-type? c type
2831 Return true if condition @var{c} has type @var{type}.
2834 @deffn {Scheme Procedure} condition-ref c field-name
2835 Return the value of the field named @var{field-name} from condition @var{c}.
2837 If @var{c} is a compound condition and several underlying condition
2838 types contain a field named @var{field-name}, then the value of the
2839 first such field is returned, using the order in which conditions were
2840 passed to @var{make-compound-condition}.
2843 @deffn {Scheme Procedure} extract-condition c type
2844 Return a condition of condition type @var{type} with the field values
2845 specified by @var{c}.
2847 If @var{c} is a compound condition, extract the field values from the
2848 subcondition belonging to @var{type} that appeared first in the call to
2849 @code{make-compound-condition} that created the the condition.
2852 Convenience macros are also available to create condition types and
2855 @deffn {library syntax} define-condition-type type supertype predicate field-spec...
2856 Define a new condition type named @var{type} that inherits from
2857 @var{supertype}. In addition, bind @var{predicate} to a type predicate
2858 that returns true when passed a condition of type @var{type} or any of
2859 its subtypes. @var{field-spec} must have the form @code{(field
2860 accessor)} where @var{field} is the name of field of @var{type} and
2861 @var{accessor} is the name of a procedure to access field @var{field} in
2862 conditions of type @var{type}.
2864 The example below defines condition type @code{&foo}, inheriting from
2865 @code{&condition} with fields @code{a}, @code{b} and @code{c}:
2868 (define-condition-type &foo &condition
2876 @deffn {library syntax} condition type-field-bindings...
2877 Return a new condition, or compound condition, initialized according to
2878 @var{type-field-bindings}. Each @var{type-field-binding} must have the
2879 form @code{(type field-specs...)}, where @var{type} is the name of a
2880 variable bound to condition type; each @var{field-spec} must have the
2881 form @code{(field-name value)} where @var{field-name} is a symbol
2882 denoting the field being initialized to @var{value}. As for
2883 @code{make-condition}, all fields must be specified.
2885 The following example returns a simple condition:
2888 (condition (&message (message "An error occurred")))
2891 The one below returns a compound condition:
2894 (condition (&message (message "An error occurred"))
2899 Finally, SRFI-35 defines a several standard condition types.
2902 This condition type is the root of all condition types. It has no
2907 A condition type that carries a message describing the nature of the
2908 condition to humans.
2911 @deffn {Scheme Procedure} message-condition? c
2912 Return true if @var{c} is of type @code{&message} or one of its
2916 @deffn {Scheme Procedure} condition-message c
2917 Return the message associated with message condition @var{c}.
2921 This type describes conditions serious enough that they cannot safely be
2922 ignored. It has no fields.
2925 @deffn {Scheme Procedure} serious-condition? c
2926 Return true if @var{c} is of type @code{&serious} or one of its
2931 This condition describes errors, typically caused by something that has
2932 gone wrong in the interaction of the program with the external world or
2936 @deffn {Scheme Procedure} error? c
2937 Return true if @var{c} is of type @code{&error} or one of its subtypes.
2942 @subsection SRFI-37 - args-fold
2945 This is a processor for GNU @code{getopt_long}-style program
2946 arguments. It provides an alternative, less declarative interface
2947 than @code{getopt-long} in @code{(ice-9 getopt-long)}
2948 (@pxref{getopt-long,,The (ice-9 getopt-long) Module}). Unlike
2949 @code{getopt-long}, it supports repeated options and any number of
2950 short and long names per option. Access it with:
2953 (use-modules (srfi srfi-37))
2956 @acronym{SRFI}-37 principally provides an @code{option} type and the
2957 @code{args-fold} function. To use the library, create a set of
2958 options with @code{option} and use it as a specification for invoking
2961 Here is an example of a simple argument processor for the typical
2962 @samp{--version} and @samp{--help} options, which returns a backwards
2963 list of files given on the command line:
2966 (args-fold (cdr (program-arguments))
2967 (let ((display-and-exit-proc
2969 (lambda (opt name arg loads)
2970 (display msg) (quit)))))
2971 (list (option '(#\v "version") #f #f
2972 (display-and-exit-proc "Foo version 42.0\n"))
2973 (option '(#\h "help") #f #f
2974 (display-and-exit-proc
2975 "Usage: foo scheme-file ..."))))
2976 (lambda (opt name arg loads)
2977 (error "Unrecognized option `~A'" name))
2978 (lambda (op loads) (cons op loads))
2982 @deffn {Scheme Procedure} option names required-arg? optional-arg? processor
2983 Return an object that specifies a single kind of program option.
2985 @var{names} is a list of command-line option names, and should consist of
2986 characters for traditional @code{getopt} short options and strings for
2987 @code{getopt_long}-style long options.
2989 @var{required-arg?} and @var{optional-arg?} are mutually exclusive;
2990 one or both must be @code{#f}. If @var{required-arg?}, the option
2991 must be followed by an argument on the command line, such as
2992 @samp{--opt=value} for long options, or an error will be signalled.
2993 If @var{optional-arg?}, an argument will be taken if available.
2995 @var{processor} is a procedure that takes at least 3 arguments, called
2996 when @code{args-fold} encounters the option: the containing option
2997 object, the name used on the command line, and the argument given for
2998 the option (or @code{#f} if none). The rest of the arguments are
2999 @code{args-fold} ``seeds'', and the @var{processor} should return
3003 @deffn {Scheme Procedure} option-names opt
3004 @deffnx {Scheme Procedure} option-required-arg? opt
3005 @deffnx {Scheme Procedure} option-optional-arg? opt
3006 @deffnx {Scheme Procedure} option-processor opt
3007 Return the specified field of @var{opt}, an option object, as
3008 described above for @code{option}.
3011 @deffn {Scheme Procedure} args-fold args options unrecognized-option-proc operand-proc seeds @dots{}
3012 Process @var{args}, a list of program arguments such as that returned
3013 by @code{(cdr (program-arguments))}, in order against @var{options}, a
3014 list of option objects as described above. All functions called take
3015 the ``seeds'', or the last multiple-values as multiple arguments,
3016 starting with @var{seeds}, and must return the new seeds. Return the
3019 Call @code{unrecognized-option-proc}, which is like an option object's
3020 processor, for any options not found in @var{options}.
3022 Call @code{operand-proc} with any items on the command line that are
3023 not named options. This includes arguments after @samp{--}. It is
3024 called with the argument in question, as well as the seeds.
3029 @subsection SRFI-39 - Parameters
3031 @cindex parameter object
3034 This SRFI provides parameter objects, which implement dynamically
3035 bound locations for values. The functions below are available from
3038 (use-modules (srfi srfi-39))
3041 A parameter object is a procedure. Called with no arguments it
3042 returns its value, called with one argument it sets the value.
3045 (define my-param (make-parameter 123))
3046 (my-param) @result{} 123
3048 (my-param) @result{} 456
3051 The @code{parameterize} special form establishes new locations for
3052 parameters, those new locations having effect within the dynamic scope
3053 of the @code{parameterize} body. Leaving restores the previous
3054 locations, or re-entering through a saved continuation will again use
3058 (parameterize ((my-param 789))
3059 (my-param) @result{} 789
3061 (my-param) @result{} 456
3064 Parameters are like dynamically bound variables in other Lisp dialets.
3065 They allow an application to establish parameter settings (as the name
3066 suggests) just for the execution of a particular bit of code,
3067 restoring when done. Examples of such parameters might be
3068 case-sensitivity for a search, or a prompt for user input.
3070 Global variables are not as good as parameter objects for this sort of
3071 thing. Changes to them are visible to all threads, but in Guile
3072 parameter object locations are per-thread, thereby truely limiting the
3073 effect of @code{parameterize} to just its dynamic execution.
3075 Passing arguments to functions is thread-safe, but that soon becomes
3076 tedious when there's more than a few or when they need to pass down
3077 through several layers of calls before reaching the point they should
3078 affect. And introducing a new setting to existing code is often
3079 easier with a parameter object than adding arguments.
3083 @defun make-parameter init [converter]
3084 Return a new parameter object, with initial value @var{init}.
3086 A parameter object is a procedure. When called @code{(param)} it
3087 returns its value, or a call @code{(param val)} sets its value. For
3091 (define my-param (make-parameter 123))
3092 (my-param) @result{} 123
3095 (my-param) @result{} 456
3098 If a @var{converter} is given, then a call @code{(@var{converter}
3099 val)} is made for each value set, its return is the value stored.
3100 Such a call is made for the @var{init} initial value too.
3102 A @var{converter} allows values to be validated, or put into a
3103 canonical form. For example,
3106 (define my-param (make-parameter 123
3108 (if (not (number? val))
3109 (error "must be a number"))
3110 (inexact->exact val))))
3112 (my-param) @result{} 3/4
3116 @deffn {library syntax} parameterize ((param value) @dots{}) body @dots{}
3117 Establish a new dynamic scope with the given @var{param}s bound to new
3118 locations and set to the given @var{value}s. @var{body} is evaluated
3119 in that environment, the result is the return from the last form in
3122 Each @var{param} is an expression which is evaluated to get the
3123 parameter object. Often this will just be the name of a variable
3124 holding the object, but it can be anything that evaluates to a
3127 The @var{param} expressions and @var{value} expressions are all
3128 evaluated before establishing the new dynamic bindings, and they're
3129 evaluated in an unspecified order.
3134 (define prompt (make-parameter "Type something: "))
3139 (parameterize ((prompt "Type a number: "))
3145 @deffn {Parameter object} current-input-port [new-port]
3146 @deffnx {Parameter object} current-output-port [new-port]
3147 @deffnx {Parameter object} current-error-port [new-port]
3148 This SRFI extends the core @code{current-input-port} and
3149 @code{current-output-port}, making them parameter objects. The
3150 Guile-specific @code{current-error-port} is extended too, for
3151 consistency. (@pxref{Default Ports}.)
3153 This is an upwardly compatible extension, a plain call like
3154 @code{(current-input-port)} still returns the current input port, and
3155 @code{set-current-input-port} can still be used. But the port can now
3156 also be set with @code{(current-input-port my-port)} and bound
3157 dynamically with @code{parameterize}.
3160 @defun with-parameters* param-list value-list thunk
3161 Establish a new dynamic scope, as per @code{parameterize} above,
3162 taking parameters from @var{param-list} and corresponding values from
3163 @var{values-list}. A call @code{(@var{thunk})} is made in the new
3164 scope and the result from that @var{thunk} is the return from
3165 @code{with-parameters*}.
3167 This function is a Guile-specific addition to the SRFI, it's similar
3168 to the core @code{with-fluids*} (@pxref{Fluids and Dynamic States}).
3173 Parameter objects are implemented using fluids (@pxref{Fluids and
3174 Dynamic States}), so each dynamic state has it's own parameter
3175 locations. That includes the separate locations when outside any
3176 @code{parameterize} form. When a parameter is created it gets a
3177 separate initial location in each dynamic state, all initialized to
3178 the given @var{init} value.
3180 As alluded to above, because each thread usually has a separate
3181 dynamic state, each thread has it's own locations behind parameter
3182 objects, and changes in one thread are not visible to any other. When
3183 a new dynamic state or thread is created, the values of parameters in
3184 the originating context are copied, into new locations.
3186 SRFI-39 doesn't specify the interaction between parameter objects and
3187 threads, so the threading behaviour described here should be regarded
3192 @subsection SRFI-55 - Requiring Features
3195 SRFI-55 provides @code{require-extension} which is a portable
3196 mechanism to load selected SRFI modules. This is implemented in the
3197 Guile core, there's no module needed to get SRFI-55 itself.
3199 @deffn {library syntax} require-extension clause@dots{}
3200 Require each of the given @var{clause} features, throwing an error if
3201 any are unavailable.
3203 A @var{clause} is of the form @code{(@var{identifier} arg...)}. The
3204 only @var{identifier} currently supported is @code{srfi} and the
3205 arguments are SRFI numbers. For example to get SRFI-1 and SRFI-6,
3208 (require-extension (srfi 1 6))
3211 @code{require-extension} can only be used at the top-level.
3213 A Guile-specific program can simply @code{use-modules} to load SRFIs
3214 not already in the core, @code{require-extension} is for programs
3215 designed to be portable to other Scheme implementations.
3220 @subsection SRFI-60 - Integers as Bits
3222 @cindex integers as bits
3223 @cindex bitwise logical
3225 This SRFI provides various functions for treating integers as bits and
3226 for bitwise manipulations. These functions can be obtained with,
3229 (use-modules (srfi srfi-60))
3232 Integers are treated as infinite precision twos-complement, the same
3233 as in the core logical functions (@pxref{Bitwise Operations}). And
3234 likewise bit indexes start from 0 for the least significant bit. The
3235 following functions in this SRFI are already in the Guile core,
3244 @code{integer-length},
3250 @defun bitwise-and n1 ...
3251 @defunx bitwise-ior n1 ...
3252 @defunx bitwise-xor n1 ...
3253 @defunx bitwise-not n
3254 @defunx any-bits-set? j k
3255 @defunx bit-set? index n
3256 @defunx arithmetic-shift n count
3257 @defunx bit-field n start end
3259 Aliases for @code{logand}, @code{logior}, @code{logxor},
3260 @code{lognot}, @code{logtest}, @code{logbit?}, @code{ash},
3261 @code{bit-extract} and @code{logcount} respectively.
3263 Note that the name @code{bit-count} conflicts with @code{bit-count} in
3264 the core (@pxref{Bit Vectors}).
3267 @defun bitwise-if mask n1 n0
3268 @defunx bitwise-merge mask n1 n0
3269 Return an integer with bits selected from @var{n1} and @var{n0}
3270 according to @var{mask}. Those bits where @var{mask} has 1s are taken
3271 from @var{n1}, and those where @var{mask} has 0s are taken from
3275 (bitwise-if 3 #b0101 #b1010) @result{} 9
3279 @defun log2-binary-factors n
3280 @defunx first-set-bit n
3281 Return a count of how many factors of 2 are present in @var{n}. This
3282 is also the bit index of the lowest 1 bit in @var{n}. If @var{n} is
3283 0, the return is @math{-1}.
3286 (log2-binary-factors 6) @result{} 1
3287 (log2-binary-factors -8) @result{} 3
3291 @defun copy-bit index n newbit
3292 Return @var{n} with the bit at @var{index} set according to
3293 @var{newbit}. @var{newbit} should be @code{#t} to set the bit to 1,
3294 or @code{#f} to set it to 0. Bits other than at @var{index} are
3295 unchanged in the return.
3298 (copy-bit 1 #b0101 #t) @result{} 7
3302 @defun copy-bit-field n newbits start end
3303 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
3304 (exclusive) changed to the value @var{newbits}.
3306 The least significant bit in @var{newbits} goes to @var{start}, the
3307 next to @math{@var{start}+1}, etc. Anything in @var{newbits} past the
3308 @var{end} given is ignored.
3311 (copy-bit-field #b10000 #b11 1 3) @result{} #b10110
3315 @defun rotate-bit-field n count start end
3316 Return @var{n} with the bit field from @var{start} (inclusive) to
3317 @var{end} (exclusive) rotated upwards by @var{count} bits.
3319 @var{count} can be positive or negative, and it can be more than the
3320 field width (it'll be reduced modulo the width).
3323 (rotate-bit-field #b0110 2 1 4) @result{} #b1010
3327 @defun reverse-bit-field n start end
3328 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
3329 (exclusive) reversed.
3332 (reverse-bit-field #b101001 2 4) @result{} #b100101
3336 @defun integer->list n [len]
3337 Return bits from @var{n} in the form of a list of @code{#t} for 1 and
3338 @code{#f} for 0. The least significant @var{len} bits are returned,
3339 and the first list element is the most significant of those bits. If
3340 @var{len} is not given, the default is @code{(integer-length @var{n})}
3341 (@pxref{Bitwise Operations}).
3344 (integer->list 6) @result{} (#t #t #f)
3345 (integer->list 1 4) @result{} (#f #f #f #t)
3349 @defun list->integer lst
3350 @defunx booleans->integer bool@dots{}
3351 Return an integer formed bitwise from the given @var{lst} list of
3352 booleans, or for @code{booleans->integer} from the @var{bool}
3355 Each boolean is @code{#t} for a 1 and @code{#f} for a 0. The first
3356 element becomes the most significant bit in the return.
3359 (list->integer '(#t #f #t #f)) @result{} 10
3365 @subsection SRFI-61 - A more general @code{cond} clause
3367 This SRFI extends RnRS @code{cond} to support test expressions that
3368 return multiple values, as well as arbitrary definitions of test
3369 success. SRFI 61 is implemented in the Guile core; there's no module
3370 needed to get SRFI-61 itself. Extended @code{cond} is documented in
3371 @ref{if cond case,, Simple Conditional Evaluation}.
3375 @subsection SRFI-69 - Basic hash tables
3378 This is a portable wrapper around Guile's built-in hash table and weak
3379 table support. @xref{Hash Tables}, for information on that built-in
3380 support. Above that, this hash-table interface provides association
3381 of equality and hash functions with tables at creation time, so
3382 variants of each function are not required, as well as a procedure
3383 that takes care of most uses for Guile hash table handles, which this
3384 SRFI does not provide as such.
3389 (use-modules (srfi srfi-69))
3393 * SRFI-69 Creating hash tables::
3394 * SRFI-69 Accessing table items::
3395 * SRFI-69 Table properties::
3396 * SRFI-69 Hash table algorithms::
3399 @node SRFI-69 Creating hash tables
3400 @subsubsection Creating hash tables
3402 @deffn {Scheme Procedure} make-hash-table [equal-proc hash-proc #:weak weakness start-size]
3403 Create and answer a new hash table with @var{equal-proc} as the
3404 equality function and @var{hash-proc} as the hashing function.
3406 By default, @var{equal-proc} is @code{equal?}. It can be any
3407 two-argument procedure, and should answer whether two keys are the
3408 same for this table's purposes.
3410 My default @var{hash-proc} assumes that @code{equal-proc} is no
3411 coarser than @code{equal?} unless it is literally @code{string-ci=?}.
3412 If provided, @var{hash-proc} should be a two-argument procedure that
3413 takes a key and the current table size, and answers a reasonably good
3414 hash integer between 0 (inclusive) and the size (exclusive).
3416 @var{weakness} should be @code{#f} or a symbol indicating how ``weak''
3421 An ordinary non-weak hash table. This is the default.
3424 When the key has no more non-weak references at GC, remove that entry.
3427 When the value has no more non-weak references at GC, remove that
3431 When either has no more non-weak references at GC, remove the
3435 As a legacy of the time when Guile couldn't grow hash tables,
3436 @var{start-size} is an optional integer argument that specifies the
3437 approximate starting size for the hash table, which will be rounded to
3438 an algorithmically-sounder number.
3441 By @dfn{coarser} than @code{equal?}, we mean that for all @var{x} and
3442 @var{y} values where @code{(@var{equal-proc} @var{x} @var{y})},
3443 @code{(equal? @var{x} @var{y})} as well. If that does not hold for
3444 your @var{equal-proc}, you must provide a @var{hash-proc}.
3446 In the case of weak tables, remember that @dfn{references} above
3447 always refers to @code{eq?}-wise references. Just because you have a
3448 reference to some string @code{"foo"} doesn't mean that an association
3449 with key @code{"foo"} in a weak-key table @emph{won't} be collected;
3450 it only counts as a reference if the two @code{"foo"}s are @code{eq?},
3451 regardless of @var{equal-proc}. As such, it is usually only sensible
3452 to use @code{eq?} and @code{hashq} as the equivalence and hash
3453 functions for a weak table. @xref{Weak References}, for more
3454 information on Guile's built-in weak table support.
3456 @deffn {Scheme Procedure} alist->hash-table alist [equal-proc hash-proc #:weak weakness start-size]
3457 As with @code{make-hash-table}, but initialize it with the
3458 associations in @var{alist}. Where keys are repeated in @var{alist},
3459 the leftmost association takes precedence.
3462 @node SRFI-69 Accessing table items
3463 @subsubsection Accessing table items
3465 @deffn {Scheme Procedure} hash-table-ref table key [default-thunk]
3466 @deffnx {Scheme Procedure} hash-table-ref/default table key default
3467 Answer the value associated with @var{key} in @var{table}. If
3468 @var{key} is not present, answer the result of invoking the thunk
3469 @var{default-thunk}, which signals an error instead by default.
3471 @code{hash-table-ref/default} is a variant that requires a third
3472 argument, @var{default}, and answers @var{default} itself instead of
3476 @deffn {Scheme Procedure} hash-table-set! table key new-value
3477 Set @var{key} to @var{new-value} in @var{table}.
3480 @deffn {Scheme Procedure} hash-table-delete! table key
3481 Remove the association of @var{key} in @var{table}, if present. If
3485 @deffn {Scheme Procedure} hash-table-exists? table key
3486 Answer whether @var{key} has an association in @var{table}.
3489 @deffn {Scheme Procedure} hash-table-update! table key modifier [default-thunk]
3490 @deffnx {Scheme Procedure} hash-table-update!/default table key modifier default
3491 Replace @var{key}'s associated value in @var{table} by invoking
3492 @var{modifier} with one argument, the old value.
3494 If @var{key} is not present, and @var{default-thunk} is provided,
3495 invoke it with no arguments to get the ``old value'' to be passed to
3496 @var{modifier} as above. If @var{default-thunk} is not provided in
3497 such a case, signal an error.
3499 @code{hash-table-update!/default} is a variant that requires the
3500 fourth argument, which is used directly as the ``old value'' rather
3501 than as a thunk to be invoked to retrieve the ``old value''.
3504 @node SRFI-69 Table properties
3505 @subsubsection Table properties
3507 @deffn {Scheme Procedure} hash-table-size table
3508 Answer the number of associations in @var{table}. This is guaranteed
3509 to run in constant time for non-weak tables.
3512 @deffn {Scheme Procedure} hash-table-keys table
3513 Answer an unordered list of the keys in @var{table}.
3516 @deffn {Scheme Procedure} hash-table-values table
3517 Answer an unordered list of the values in @var{table}.
3520 @deffn {Scheme Procedure} hash-table-walk table proc
3521 Invoke @var{proc} once for each association in @var{table}, passing
3522 the key and value as arguments.
3525 @deffn {Scheme Procedure} hash-table-fold table proc init
3526 Invoke @code{(@var{proc} @var{key} @var{value} @var{previous})} for
3527 each @var{key} and @var{value} in @var{table}, where @var{previous} is
3528 the result of the previous invocation, using @var{init} as the first
3529 @var{previous} value. Answer the final @var{proc} result.
3532 @deffn {Scheme Procedure} hash-table->alist table
3533 Answer an alist where each association in @var{table} is an
3534 association in the result.
3537 @node SRFI-69 Hash table algorithms
3538 @subsubsection Hash table algorithms
3540 Each hash table carries an @dfn{equivalence function} and a @dfn{hash
3541 function}, used to implement key lookups. Beginning users should
3542 follow the rules for consistency of the default @var{hash-proc}
3543 specified above. Advanced users can use these to implement their own
3544 equivalence and hash functions for specialized lookup semantics.
3546 @deffn {Scheme Procedure} hash-table-equivalence-function hash-table
3547 @deffnx {Scheme Procedure} hash-table-hash-function hash-table
3548 Answer the equivalence and hash function of @var{hash-table}, respectively.
3551 @deffn {Scheme Procedure} hash obj [size]
3552 @deffnx {Scheme Procedure} string-hash obj [size]
3553 @deffnx {Scheme Procedure} string-ci-hash obj [size]
3554 @deffnx {Scheme Procedure} hash-by-identity obj [size]
3555 Answer a hash value appropriate for equality predicate @code{equal?},
3556 @code{string=?}, @code{string-ci=?}, and @code{eq?}, respectively.
3559 @code{hash} is a backwards-compatible replacement for Guile's built-in
3563 @subsection SRFI-88 Keyword Objects
3565 @cindex keyword objects
3567 @uref{http://srfi.schemers.org/srfi-88/srfi-88.html, SRFI-88} provides
3568 @dfn{keyword objects}, which are equivalent to Guile's keywords
3569 (@pxref{Keywords}). SRFI-88 keywords can be entered using the
3570 @dfn{postfix keyword syntax}, which consists of an identifier followed
3571 by @code{:} (@pxref{Reader options, @code{postfix} keyword syntax}).
3572 SRFI-88 can be made available with:
3575 (use-modules (srfi srfi-88))
3578 Doing so installs the right reader option for keyword syntax, using
3579 @code{(read-set! keywords 'postfix)}. It also provides the procedures
3582 @deffn {Scheme Procedure} keyword? obj
3583 Return @code{#t} if @var{obj} is a keyword. This is the same procedure
3584 as the same-named built-in procedure (@pxref{Keyword Procedures,
3588 (keyword? foo:) @result{} #t
3589 (keyword? 'foo:) @result{} #t
3590 (keyword? "foo") @result{} #f
3594 @deffn {Scheme Procedure} keyword->string kw
3595 Return the name of @var{kw} as a string, i.e., without the trailing
3596 colon. The returned string may not be modified, e.g., with
3600 (keyword->string foo:) @result{} "foo"
3604 @deffn {Scheme Procedure} string->keyword str
3605 Return the keyword object whose name is @var{str}.
3608 (keyword->string (string->keyword "a b c")) @result{} "a b c"
3613 @subsection SRFI-98 Accessing environment variables.
3615 @cindex environment variables
3617 This is a portable wrapper around Guile's built-in support for
3618 interacting with the current environment, @xref{Runtime Environment}.
3620 @deffn {Scheme Procedure} get-environment-variable name
3621 Returns a string containing the value of the environment variable
3622 given by the string @code{name}, or @code{#f} if the named
3623 environment variable is not found. This is equivalent to
3624 @code{(getenv name)}.
3627 @deffn {Scheme Procedure} get-environment-variables
3628 Returns the names and values of all the environment variables as an
3629 association list in which both the keys and the values are strings.
3632 @c srfi-modules.texi ends here
3635 @c TeX-master: "guile.texi"