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, 2009, 2010, 2011
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @section SRFI Support Modules
11 SRFI is an acronym for Scheme Request For Implementation. The SRFI
12 documents define a lot of syntactic and procedure extensions to standard
13 Scheme as defined in R5RS.
15 Guile has support for a number of SRFIs. This chapter gives an overview
16 over the available SRFIs and some usage hints. For complete
17 documentation, design rationales and further examples, we advise you to
18 get the relevant SRFI documents from the SRFI home page
19 @url{http://srfi.schemers.org}.
22 * About SRFI Usage:: What to know about Guile's SRFI support.
23 * SRFI-0:: cond-expand
24 * SRFI-1:: List library.
26 * SRFI-4:: Homogeneous numeric vector datatypes.
27 * SRFI-6:: Basic String Ports.
29 * SRFI-9:: define-record-type.
30 * SRFI-10:: Hash-Comma Reader Extension.
31 * SRFI-11:: let-values and let*-values.
32 * SRFI-13:: String library.
33 * SRFI-14:: Character-set library.
34 * SRFI-16:: case-lambda
35 * SRFI-17:: Generalized set!
36 * SRFI-18:: Multithreading support
37 * SRFI-19:: Time/Date library.
38 * SRFI-23:: Error reporting
39 * SRFI-26:: Specializing parameters
40 * SRFI-27:: Sources of Random Bits
41 * SRFI-30:: Nested multi-line block comments
42 * SRFI-31:: A special form `rec' for recursive evaluation
43 * SRFI-34:: Exception handling.
44 * SRFI-35:: Conditions.
45 * SRFI-37:: args-fold program argument processor
46 * SRFI-38:: External Representation for Data With Shared Structure
47 * SRFI-39:: Parameter objects
48 * SRFI-42:: Eager comprehensions
49 * SRFI-45:: Primitives for expressing iterative lazy algorithms
50 * SRFI-55:: Requiring Features.
51 * SRFI-60:: Integers as bits.
52 * SRFI-61:: A more general `cond' clause
53 * SRFI-67:: Compare procedures
54 * SRFI-69:: Basic hash tables.
55 * SRFI-88:: Keyword objects.
56 * SRFI-98:: Accessing environment variables.
60 @node About SRFI Usage
61 @subsection About SRFI Usage
63 @c FIXME::martin: Review me!
65 SRFI support in Guile is currently implemented partly in the core
66 library, and partly as add-on modules. That means that some SRFIs are
67 automatically available when the interpreter is started, whereas the
68 other SRFIs require you to use the appropriate support module
71 There are several reasons for this inconsistency. First, the feature
72 checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be
73 available immediately, because it must be there when the user wants to
74 check for the Scheme implementation, that is, before she can know that
75 it is safe to use @code{use-modules} to load SRFI support modules. The
76 second reason is that some features defined in SRFIs had been
77 implemented in Guile before the developers started to add SRFI
78 implementations as modules (for example SRFI-6 (@pxref{SRFI-6})). In
79 the future, it is possible that SRFIs in the core library might be
80 factored out into separate modules, requiring explicit module loading
81 when they are needed. So you should be prepared to have to use
82 @code{use-modules} someday in the future to access SRFI-6 bindings. If
83 you want, you can do that already. We have included the module
84 @code{(srfi srfi-6)} in the distribution, which currently does nothing,
85 but ensures that you can write future-safe code.
87 Generally, support for a specific SRFI is made available by using
88 modules named @code{(srfi srfi-@var{number})}, where @var{number} is the
89 number of the SRFI needed. Another possibility is to use the command
90 line option @code{--use-srfi}, which will load the necessary modules
91 automatically (@pxref{Invoking Guile}).
95 @subsection SRFI-0 - cond-expand
98 This SRFI lets a portable Scheme program test for the presence of
99 certain features, and adapt itself by using different blocks of code,
100 or fail if the necessary features are not available. There's no
101 module to load, this is in the Guile core.
103 A program designed only for Guile will generally not need this
104 mechanism, such a program can of course directly use the various
105 documented parts of Guile.
107 @deffn syntax cond-expand (feature body@dots{}) @dots{}
108 Expand to the @var{body} of the first clause whose @var{feature}
109 specification is satisfied. It is an error if no @var{feature} is
112 Features are symbols such as @code{srfi-1}, and a feature
113 specification can use @code{and}, @code{or} and @code{not} forms to
114 test combinations. The last clause can be an @code{else}, to be used
117 For example, define a private version of @code{alist-cons} if SRFI-1
124 (define (alist-cons key val alist)
125 (cons (cons key val) alist))))
128 Or demand a certain set of SRFIs (list operations, string ports,
129 @code{receive} and string operations), failing if they're not
133 (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13)
139 The Guile core has the following features,
143 guile-2 ;; starting from Guile 2.x
152 Other SRFI feature symbols are defined once their code has been loaded
153 with @code{use-modules}, since only then are their bindings available.
155 The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is
156 a good way to load SRFIs to satisfy @code{cond-expand} when running a
159 Testing the @code{guile} feature allows a program to adapt itself to
160 the Guile module system, but still run on other Scheme systems. For
161 example the following demands SRFI-8 (@code{receive}), but also knows
162 how to load it with the Guile mechanism.
168 (use-modules (srfi srfi-8))))
171 @cindex @code{guile-2} SRFI-0 feature
172 @cindex portability between 2.0 and older versions
173 Likewise, testing the @code{guile-2} feature allows code to be portable
174 between Guile 2.0 and previous versions of Guile. For instance, it
175 makes it possible to write code that accounts for Guile 2.0's compiler,
176 yet be correctly interpreted on 1.8 and earlier versions:
179 (cond-expand (guile-2 (eval-when (compile)
180 ;; This must be evaluated at compile time.
181 (fluid-set! current-reader my-reader)))
183 ;; Earlier versions of Guile do not have a
184 ;; separate compilation phase.
185 (fluid-set! current-reader my-reader)))
188 It should be noted that @code{cond-expand} is separate from the
189 @code{*features*} mechanism (@pxref{Feature Tracking}), feature
190 symbols in one are unrelated to those in the other.
194 @subsection SRFI-1 - List library
198 @c FIXME::martin: Review me!
200 The list library defined in SRFI-1 contains a lot of useful list
201 processing procedures for construction, examining, destructuring and
202 manipulating lists and pairs.
204 Since SRFI-1 also defines some procedures which are already contained
205 in R5RS and thus are supported by the Guile core library, some list
206 and pair procedures which appear in the SRFI-1 document may not appear
207 in this section. So when looking for a particular list/pair
208 processing procedure, you should also have a look at the sections
209 @ref{Lists} and @ref{Pairs}.
212 * SRFI-1 Constructors:: Constructing new lists.
213 * SRFI-1 Predicates:: Testing list for specific properties.
214 * SRFI-1 Selectors:: Selecting elements from lists.
215 * SRFI-1 Length Append etc:: Length calculation and list appending.
216 * SRFI-1 Fold and Map:: Higher-order list processing.
217 * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates.
218 * SRFI-1 Searching:: Search for elements.
219 * SRFI-1 Deleting:: Delete elements from lists.
220 * SRFI-1 Association Lists:: Handle association lists.
221 * SRFI-1 Set Operations:: Use lists for representing sets.
224 @node SRFI-1 Constructors
225 @subsubsection Constructors
226 @cindex list constructor
228 @c FIXME::martin: Review me!
230 New lists can be constructed by calling one of the following
233 @deffn {Scheme Procedure} xcons d a
234 Like @code{cons}, but with interchanged arguments. Useful mostly when
235 passed to higher-order procedures.
238 @deffn {Scheme Procedure} list-tabulate n init-proc
239 Return an @var{n}-element list, where each list element is produced by
240 applying the procedure @var{init-proc} to the corresponding list
241 index. The order in which @var{init-proc} is applied to the indices
245 @deffn {Scheme Procedure} list-copy lst
246 Return a new list containing the elements of the list @var{lst}.
248 This function differs from the core @code{list-copy} (@pxref{List
249 Constructors}) in accepting improper lists too. And if @var{lst} is
250 not a pair at all then it's treated as the final tail of an improper
251 list and simply returned.
254 @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{}
255 Return a circular list containing the given arguments @var{elt1}
259 @deffn {Scheme Procedure} iota count [start step]
260 Return a list containing @var{count} numbers, starting from
261 @var{start} and adding @var{step} each time. The default @var{start}
262 is 0, the default @var{step} is 1. For example,
265 (iota 6) @result{} (0 1 2 3 4 5)
266 (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5)
269 This function takes its name from the corresponding primitive in the
274 @node SRFI-1 Predicates
275 @subsubsection Predicates
276 @cindex list predicate
278 @c FIXME::martin: Review me!
280 The procedures in this section test specific properties of lists.
282 @deffn {Scheme Procedure} proper-list? obj
283 Return @code{#t} if @var{obj} is a proper list, or @code{#f}
284 otherwise. This is the same as the core @code{list?} (@pxref{List
287 A proper list is a list which ends with the empty list @code{()} in
288 the usual way. The empty list @code{()} itself is a proper list too.
291 (proper-list? '(1 2 3)) @result{} #t
292 (proper-list? '()) @result{} #t
296 @deffn {Scheme Procedure} circular-list? obj
297 Return @code{#t} if @var{obj} is a circular list, or @code{#f}
300 A circular list is a list where at some point the @code{cdr} refers
301 back to a previous pair in the list (either the start or some later
302 point), so that following the @code{cdr}s takes you around in a
306 (define x (list 1 2 3 4))
307 (set-cdr! (last-pair x) (cddr x))
308 x @result{} (1 2 3 4 3 4 3 4 ...)
309 (circular-list? x) @result{} #t
313 @deffn {Scheme Procedure} dotted-list? obj
314 Return @code{#t} if @var{obj} is a dotted list, or @code{#f}
317 A dotted list is a list where the @code{cdr} of the last pair is not
318 the empty list @code{()}. Any non-pair @var{obj} is also considered a
319 dotted list, with length zero.
322 (dotted-list? '(1 2 . 3)) @result{} #t
323 (dotted-list? 99) @result{} #t
327 It will be noted that any Scheme object passes exactly one of the
328 above three tests @code{proper-list?}, @code{circular-list?} and
329 @code{dotted-list?}. Non-lists are @code{dotted-list?}, finite lists
330 are either @code{proper-list?} or @code{dotted-list?}, and infinite
331 lists are @code{circular-list?}.
334 @deffn {Scheme Procedure} null-list? lst
335 Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f}
336 otherwise. If something else than a proper or circular list is passed
337 as @var{lst}, an error is signalled. This procedure is recommended
338 for checking for the end of a list in contexts where dotted lists are
342 @deffn {Scheme Procedure} not-pair? obj
343 Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise.
344 This is shorthand notation @code{(not (pair? @var{obj}))} and is
345 supposed to be used for end-of-list checking in contexts where dotted
349 @deffn {Scheme Procedure} list= elt= list1 @dots{}
350 Return @code{#t} if all argument lists are equal, @code{#f} otherwise.
351 List equality is determined by testing whether all lists have the same
352 length and the corresponding elements are equal in the sense of the
353 equality predicate @var{elt=}. If no or only one list is given,
354 @code{#t} is returned.
358 @node SRFI-1 Selectors
359 @subsubsection Selectors
360 @cindex list selector
362 @c FIXME::martin: Review me!
364 @deffn {Scheme Procedure} first pair
365 @deffnx {Scheme Procedure} second pair
366 @deffnx {Scheme Procedure} third pair
367 @deffnx {Scheme Procedure} fourth pair
368 @deffnx {Scheme Procedure} fifth pair
369 @deffnx {Scheme Procedure} sixth pair
370 @deffnx {Scheme Procedure} seventh pair
371 @deffnx {Scheme Procedure} eighth pair
372 @deffnx {Scheme Procedure} ninth pair
373 @deffnx {Scheme Procedure} tenth pair
374 These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}.
377 @deffn {Scheme Procedure} car+cdr pair
378 Return two values, the @sc{car} and the @sc{cdr} of @var{pair}.
381 @deffn {Scheme Procedure} take lst i
382 @deffnx {Scheme Procedure} take! lst i
383 Return a list containing the first @var{i} elements of @var{lst}.
385 @code{take!} may modify the structure of the argument list @var{lst}
386 in order to produce the result.
389 @deffn {Scheme Procedure} drop lst i
390 Return a list containing all but the first @var{i} elements of
394 @deffn {Scheme Procedure} take-right lst i
395 Return a list containing the @var{i} last elements of @var{lst}.
396 The return shares a common tail with @var{lst}.
399 @deffn {Scheme Procedure} drop-right lst i
400 @deffnx {Scheme Procedure} drop-right! lst i
401 Return a list containing all but the @var{i} last elements of
404 @code{drop-right} always returns a new list, even when @var{i} is
405 zero. @code{drop-right!} may modify the structure of the argument
406 list @var{lst} in order to produce the result.
409 @deffn {Scheme Procedure} split-at lst i
410 @deffnx {Scheme Procedure} split-at! lst i
411 Return two values, a list containing the first @var{i} elements of the
412 list @var{lst} and a list containing the remaining elements.
414 @code{split-at!} may modify the structure of the argument list
415 @var{lst} in order to produce the result.
418 @deffn {Scheme Procedure} last lst
419 Return the last element of the non-empty, finite list @var{lst}.
423 @node SRFI-1 Length Append etc
424 @subsubsection Length, Append, Concatenate, etc.
426 @c FIXME::martin: Review me!
428 @deffn {Scheme Procedure} length+ lst
429 Return the length of the argument list @var{lst}. When @var{lst} is a
430 circular list, @code{#f} is returned.
433 @deffn {Scheme Procedure} concatenate list-of-lists
434 @deffnx {Scheme Procedure} concatenate! list-of-lists
435 Construct a list by appending all lists in @var{list-of-lists}.
437 @code{concatenate!} may modify the structure of the given lists in
438 order to produce the result.
440 @code{concatenate} is the same as @code{(apply append
441 @var{list-of-lists})}. It exists because some Scheme implementations
442 have a limit on the number of arguments a function takes, which the
443 @code{apply} might exceed. In Guile there is no such limit.
446 @deffn {Scheme Procedure} append-reverse rev-head tail
447 @deffnx {Scheme Procedure} append-reverse! rev-head tail
448 Reverse @var{rev-head}, append @var{tail} to it, and return the
449 result. This is equivalent to @code{(append (reverse @var{rev-head})
450 @var{tail})}, but its implementation is more efficient.
453 (append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)
456 @code{append-reverse!} may modify @var{rev-head} in order to produce
460 @deffn {Scheme Procedure} zip lst1 lst2 @dots{}
461 Return a list as long as the shortest of the argument lists, where
462 each element is a list. The first list contains the first elements of
463 the argument lists, the second list contains the second elements, and
467 @deffn {Scheme Procedure} unzip1 lst
468 @deffnx {Scheme Procedure} unzip2 lst
469 @deffnx {Scheme Procedure} unzip3 lst
470 @deffnx {Scheme Procedure} unzip4 lst
471 @deffnx {Scheme Procedure} unzip5 lst
472 @code{unzip1} takes a list of lists, and returns a list containing the
473 first elements of each list, @code{unzip2} returns two lists, the
474 first containing the first elements of each lists and the second
475 containing the second elements of each lists, and so on.
478 @deffn {Scheme Procedure} count pred lst1 @dots{} lstN
479 Return a count of the number of times @var{pred} returns true when
480 called on elements from the given lists.
482 @var{pred} is called with @var{N} parameters @code{(@var{pred}
483 @var{elem1} @dots{} @var{elemN})}, each element being from the
484 corresponding @var{lst1} @dots{} @var{lstN}. The first call is with
485 the first element of each list, the second with the second element
486 from each, and so on.
488 Counting stops when the end of the shortest list is reached. At least
489 one list must be non-circular.
493 @node SRFI-1 Fold and Map
494 @subsubsection Fold, Unfold & Map
498 @c FIXME::martin: Review me!
500 @deffn {Scheme Procedure} fold proc init lst1 @dots{} lstN
501 @deffnx {Scheme Procedure} fold-right proc init lst1 @dots{} lstN
502 Apply @var{proc} to the elements of @var{lst1} @dots{} @var{lstN} to
503 build a result, and return that result.
505 Each @var{proc} call is @code{(@var{proc} @var{elem1} @dots{}
506 @var{elemN} @var{previous})}, where @var{elem1} is from @var{lst1},
507 through @var{elemN} from @var{lstN}. @var{previous} is the return
508 from the previous call to @var{proc}, or the given @var{init} for the
509 first call. If any list is empty, just @var{init} is returned.
511 @code{fold} works through the list elements from first to last. The
512 following shows a list reversal and the calls it makes,
515 (fold cons '() '(1 2 3))
523 @code{fold-right} works through the list elements from last to first,
524 ie.@: from the right. So for example the following finds the longest
525 string, and the last among equal longest,
528 (fold-right (lambda (str prev)
529 (if (> (string-length str) (string-length prev))
533 '("x" "abc" "xyz" "jk"))
537 If @var{lst1} through @var{lstN} have different lengths, @code{fold}
538 stops when the end of the shortest is reached; @code{fold-right}
539 commences at the last element of the shortest. Ie.@: elements past
540 the length of the shortest are ignored in the other @var{lst}s. At
541 least one @var{lst} must be non-circular.
543 @code{fold} should be preferred over @code{fold-right} if the order of
544 processing doesn't matter, or can be arranged either way, since
545 @code{fold} is a little more efficient.
547 The way @code{fold} builds a result from iterating is quite general,
548 it can do more than other iterations like say @code{map} or
549 @code{filter}. The following for example removes adjacent duplicate
550 elements from a list,
553 (define (delete-adjacent-duplicates lst)
554 (fold-right (lambda (elem ret)
555 (if (equal? elem (first ret))
560 (delete-adjacent-duplicates '(1 2 3 3 4 4 4 5))
561 @result{} (1 2 3 4 5)
564 Clearly the same sort of thing can be done with a @code{for-each} and
565 a variable in which to build the result, but a self-contained
566 @var{proc} can be re-used in multiple contexts, where a
567 @code{for-each} would have to be written out each time.
570 @deffn {Scheme Procedure} pair-fold proc init lst1 @dots{} lstN
571 @deffnx {Scheme Procedure} pair-fold-right proc init lst1 @dots{} lstN
572 The same as @code{fold} and @code{fold-right}, but apply @var{proc} to
573 the pairs of the lists instead of the list elements.
576 @deffn {Scheme Procedure} reduce proc default lst
577 @deffnx {Scheme Procedure} reduce-right proc default lst
578 @code{reduce} is a variant of @code{fold}, where the first call to
579 @var{proc} is on two elements from @var{lst}, rather than one element
580 and a given initial value.
582 If @var{lst} is empty, @code{reduce} returns @var{default} (this is
583 the only use for @var{default}). If @var{lst} has just one element
584 then that's the return value. Otherwise @var{proc} is called on the
585 elements of @var{lst}.
587 Each @var{proc} call is @code{(@var{proc} @var{elem} @var{previous})},
588 where @var{elem} is from @var{lst} (the second and subsequent elements
589 of @var{lst}), and @var{previous} is the return from the previous call
590 to @var{proc}. The first element of @var{lst} is the @var{previous}
591 for the first call to @var{proc}.
593 For example, the following adds a list of numbers, the calls made to
594 @code{+} are shown. (Of course @code{+} accepts multiple arguments
595 and can add a list directly, with @code{apply}.)
598 (reduce + 0 '(5 6 7)) @result{} 18
601 (+ 7 11) @result{} 18
604 @code{reduce} can be used instead of @code{fold} where the @var{init}
605 value is an ``identity'', meaning a value which under @var{proc}
606 doesn't change the result, in this case 0 is an identity since
607 @code{(+ 5 0)} is just 5. @code{reduce} avoids that unnecessary call.
609 @code{reduce-right} is a similar variation on @code{fold-right},
610 working from the end (ie.@: the right) of @var{lst}. The last element
611 of @var{lst} is the @var{previous} for the first call to @var{proc},
612 and the @var{elem} values go from the second last.
614 @code{reduce} should be preferred over @code{reduce-right} if the
615 order of processing doesn't matter, or can be arranged either way,
616 since @code{reduce} is a little more efficient.
619 @deffn {Scheme Procedure} unfold p f g seed [tail-gen]
620 @code{unfold} is defined as follows:
623 (unfold p f g seed) =
624 (if (p seed) (tail-gen seed)
626 (unfold p f g (g seed))))
631 Determines when to stop unfolding.
634 Maps each seed value to the corresponding list element.
637 Maps each seed value to next seed value.
640 The state value for the unfold.
643 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
646 @var{g} produces a series of seed values, which are mapped to list
647 elements by @var{f}. These elements are put into a list in
648 left-to-right order, and @var{p} tells when to stop unfolding.
651 @deffn {Scheme Procedure} unfold-right p f g seed [tail]
652 Construct a list with the following loop.
655 (let lp ((seed seed) (lis tail))
658 (cons (f seed) lis))))
663 Determines when to stop unfolding.
666 Maps each seed value to the corresponding list element.
669 Maps each seed value to next seed value.
672 The state value for the unfold.
675 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
680 @deffn {Scheme Procedure} map f lst1 lst2 @dots{}
681 Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and
682 return a list containing the results of the procedure applications.
683 This procedure is extended with respect to R5RS, because the argument
684 lists may have different lengths. The result list will have the same
685 length as the shortest argument lists. The order in which @var{f}
686 will be applied to the list element(s) is not specified.
689 @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{}
690 Apply the procedure @var{f} to each pair of corresponding elements of
691 the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not
692 specified. This procedure is extended with respect to R5RS, because
693 the argument lists may have different lengths. The shortest argument
694 list determines the number of times @var{f} is called. @var{f} will
695 be applied to the list elements in left-to-right order.
699 @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{}
700 @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{}
704 (apply append (map f clist1 clist2 ...))
710 (apply append! (map f clist1 clist2 ...))
713 Map @var{f} over the elements of the lists, just as in the @code{map}
714 function. However, the results of the applications are appended
715 together to make the final result. @code{append-map} uses
716 @code{append} to append the results together; @code{append-map!} uses
719 The dynamic order in which the various applications of @var{f} are
720 made is not specified.
723 @deffn {Scheme Procedure} map! f lst1 lst2 @dots{}
724 Linear-update variant of @code{map} -- @code{map!} is allowed, but not
725 required, to alter the cons cells of @var{lst1} to construct the
728 The dynamic order in which the various applications of @var{f} are
729 made is not specified. In the n-ary case, @var{lst2}, @var{lst3},
730 @dots{} must have at least as many elements as @var{lst1}.
733 @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{}
734 Like @code{for-each}, but applies the procedure @var{f} to the pairs
735 from which the argument lists are constructed, instead of the list
736 elements. The return value is not specified.
739 @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{}
740 Like @code{map}, but only results from the applications of @var{f}
741 which are true are saved in the result list.
745 @node SRFI-1 Filtering and Partitioning
746 @subsubsection Filtering and Partitioning
748 @cindex list partition
750 @c FIXME::martin: Review me!
752 Filtering means to collect all elements from a list which satisfy a
753 specific condition. Partitioning a list means to make two groups of
754 list elements, one which contains the elements satisfying a condition,
755 and the other for the elements which don't.
757 The @code{filter} and @code{filter!} functions are implemented in the
758 Guile core, @xref{List Modification}.
760 @deffn {Scheme Procedure} partition pred lst
761 @deffnx {Scheme Procedure} partition! pred lst
762 Split @var{lst} into those elements which do and don't satisfy the
763 predicate @var{pred}.
765 The return is two values (@pxref{Multiple Values}), the first being a
766 list of all elements from @var{lst} which satisfy @var{pred}, the
767 second a list of those which do not.
769 The elements in the result lists are in the same order as in @var{lst}
770 but the order in which the calls @code{(@var{pred} elem)} are made on
771 the list elements is unspecified.
773 @code{partition} does not change @var{lst}, but one of the returned
774 lists may share a tail with it. @code{partition!} may modify
775 @var{lst} to construct its return.
778 @deffn {Scheme Procedure} remove pred lst
779 @deffnx {Scheme Procedure} remove! pred lst
780 Return a list containing all elements from @var{lst} which do not
781 satisfy the predicate @var{pred}. The elements in the result list
782 have the same order as in @var{lst}. The order in which @var{pred} is
783 applied to the list elements is not specified.
785 @code{remove!} is allowed, but not required to modify the structure of
790 @node SRFI-1 Searching
791 @subsubsection Searching
794 @c FIXME::martin: Review me!
796 The procedures for searching elements in lists either accept a
797 predicate or a comparison object for determining which elements are to
800 @deffn {Scheme Procedure} find pred lst
801 Return the first element of @var{lst} which satisfies the predicate
802 @var{pred} and @code{#f} if no such element is found.
805 @deffn {Scheme Procedure} find-tail pred lst
806 Return the first pair of @var{lst} whose @sc{car} satisfies the
807 predicate @var{pred} and @code{#f} if no such element is found.
810 @deffn {Scheme Procedure} take-while pred lst
811 @deffnx {Scheme Procedure} take-while! pred lst
812 Return the longest initial prefix of @var{lst} whose elements all
813 satisfy the predicate @var{pred}.
815 @code{take-while!} is allowed, but not required to modify the input
816 list while producing the result.
819 @deffn {Scheme Procedure} drop-while pred lst
820 Drop the longest initial prefix of @var{lst} whose elements all
821 satisfy the predicate @var{pred}.
824 @deffn {Scheme Procedure} span pred lst
825 @deffnx {Scheme Procedure} span! pred lst
826 @deffnx {Scheme Procedure} break pred lst
827 @deffnx {Scheme Procedure} break! pred lst
828 @code{span} splits the list @var{lst} into the longest initial prefix
829 whose elements all satisfy the predicate @var{pred}, and the remaining
830 tail. @code{break} inverts the sense of the predicate.
832 @code{span!} and @code{break!} are allowed, but not required to modify
833 the structure of the input list @var{lst} in order to produce the
836 Note that the name @code{break} conflicts with the @code{break}
837 binding established by @code{while} (@pxref{while do}). Applications
838 wanting to use @code{break} from within a @code{while} loop will need
839 to make a new define under a different name.
842 @deffn {Scheme Procedure} any pred lst1 lst2 @dots{} lstN
843 Test whether any set of elements from @var{lst1} @dots{} lstN
844 satisfies @var{pred}. If so the return value is the return from the
845 successful @var{pred} call, or if not the return is @code{#f}.
847 Each @var{pred} call is @code{(@var{pred} @var{elem1} @dots{}
848 @var{elemN})} taking an element from each @var{lst}. The calls are
849 made successively for the first, second, etc elements of the lists,
850 stopping when @var{pred} returns non-@code{#f}, or when the end of the
851 shortest list is reached.
853 The @var{pred} call on the last set of elements (ie.@: when the end of
854 the shortest list has been reached), if that point is reached, is a
858 @deffn {Scheme Procedure} every pred lst1 lst2 @dots{} lstN
859 Test whether every set of elements from @var{lst1} @dots{} lstN
860 satisfies @var{pred}. If so the return value is the return from the
861 final @var{pred} call, or if not the return is @code{#f}.
863 Each @var{pred} call is @code{(@var{pred} @var{elem1} @dots{}
864 @var{elemN})} taking an element from each @var{lst}. The calls are
865 made successively for the first, second, etc elements of the lists,
866 stopping if @var{pred} returns @code{#f}, or when the end of any of
867 the lists is reached.
869 The @var{pred} call on the last set of elements (ie.@: when the end of
870 the shortest list has been reached) is a tail call.
872 If one of @var{lst1} @dots{} @var{lstN} is empty then no calls to
873 @var{pred} are made, and the return is @code{#t}.
876 @deffn {Scheme Procedure} list-index pred lst1 @dots{} lstN
877 Return the index of the first set of elements, one from each of
878 @var{lst1}@dots{}@var{lstN}, which satisfies @var{pred}.
880 @var{pred} is called as @code{(@var{pred} elem1 @dots{} elemN)}.
881 Searching stops when the end of the shortest @var{lst} is reached.
882 The return index starts from 0 for the first set of elements. If no
883 set of elements pass then the return is @code{#f}.
886 (list-index odd? '(2 4 6 9)) @result{} 3
887 (list-index = '(1 2 3) '(3 1 2)) @result{} #f
891 @deffn {Scheme Procedure} member x lst [=]
892 Return the first sublist of @var{lst} whose @sc{car} is equal to
893 @var{x}. If @var{x} does not appear in @var{lst}, return @code{#f}.
895 Equality is determined by @code{equal?}, or by the equality predicate
896 @var{=} if given. @var{=} is called @code{(= @var{x} elem)},
897 ie.@: with the given @var{x} first, so for example to find the first
898 element greater than 5,
901 (member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9)
904 This version of @code{member} extends the core @code{member}
905 (@pxref{List Searching}) by accepting an equality predicate.
909 @node SRFI-1 Deleting
910 @subsubsection Deleting
913 @deffn {Scheme Procedure} delete x lst [=]
914 @deffnx {Scheme Procedure} delete! x lst [=]
915 Return a list containing the elements of @var{lst} but with those
916 equal to @var{x} deleted. The returned elements will be in the same
917 order as they were in @var{lst}.
919 Equality is determined by the @var{=} predicate, or @code{equal?} if
920 not given. An equality call is made just once for each element, but
921 the order in which the calls are made on the elements is unspecified.
923 The equality calls are always @code{(= x elem)}, ie.@: the given @var{x}
924 is first. This means for instance elements greater than 5 can be
925 deleted with @code{(delete 5 lst <)}.
927 @code{delete} does not modify @var{lst}, but the return might share a
928 common tail with @var{lst}. @code{delete!} may modify the structure
929 of @var{lst} to construct its return.
931 These functions extend the core @code{delete} and @code{delete!}
932 (@pxref{List Modification}) in accepting an equality predicate. See
933 also @code{lset-difference} (@pxref{SRFI-1 Set Operations}) for
934 deleting multiple elements from a list.
937 @deffn {Scheme Procedure} delete-duplicates lst [=]
938 @deffnx {Scheme Procedure} delete-duplicates! lst [=]
939 Return a list containing the elements of @var{lst} but without
942 When elements are equal, only the first in @var{lst} is retained.
943 Equal elements can be anywhere in @var{lst}, they don't have to be
944 adjacent. The returned list will have the retained elements in the
945 same order as they were in @var{lst}.
947 Equality is determined by the @var{=} predicate, or @code{equal?} if
948 not given. Calls @code{(= x y)} are made with element @var{x} being
949 before @var{y} in @var{lst}. A call is made at most once for each
950 combination, but the sequence of the calls across the elements is
953 @code{delete-duplicates} does not modify @var{lst}, but the return
954 might share a common tail with @var{lst}. @code{delete-duplicates!}
955 may modify the structure of @var{lst} to construct its return.
957 In the worst case, this is an @math{O(N^2)} algorithm because it must
958 check each element against all those preceding it. For long lists it
959 is more efficient to sort and then compare only adjacent elements.
963 @node SRFI-1 Association Lists
964 @subsubsection Association Lists
965 @cindex association list
968 @c FIXME::martin: Review me!
970 Association lists are described in detail in section @ref{Association
971 Lists}. The present section only documents the additional procedures
972 for dealing with association lists defined by SRFI-1.
974 @deffn {Scheme Procedure} assoc key alist [=]
975 Return the pair from @var{alist} which matches @var{key}. This
976 extends the core @code{assoc} (@pxref{Retrieving Alist Entries}) by
977 taking an optional @var{=} comparison procedure.
979 The default comparison is @code{equal?}. If an @var{=} parameter is
980 given it's called @code{(@var{=} @var{key} @var{alistcar})}, i.e.@: the
981 given target @var{key} is the first argument, and a @code{car} from
982 @var{alist} is second.
984 For example a case-insensitive string lookup,
987 (assoc "yy" '(("XX" . 1) ("YY" . 2)) string-ci=?)
992 @deffn {Scheme Procedure} alist-cons key datum alist
993 Cons a new association @var{key} and @var{datum} onto @var{alist} and
994 return the result. This is equivalent to
997 (cons (cons @var{key} @var{datum}) @var{alist})
1000 @code{acons} (@pxref{Adding or Setting Alist Entries}) in the Guile
1001 core does the same thing.
1004 @deffn {Scheme Procedure} alist-copy alist
1005 Return a newly allocated copy of @var{alist}, that means that the
1006 spine of the list as well as the pairs are copied.
1009 @deffn {Scheme Procedure} alist-delete key alist [=]
1010 @deffnx {Scheme Procedure} alist-delete! key alist [=]
1011 Return a list containing the elements of @var{alist} but with those
1012 elements whose keys are equal to @var{key} deleted. The returned
1013 elements will be in the same order as they were in @var{alist}.
1015 Equality is determined by the @var{=} predicate, or @code{equal?} if
1016 not given. The order in which elements are tested is unspecified, but
1017 each equality call is made @code{(= key alistkey)}, i.e.@: the given
1018 @var{key} parameter is first and the key from @var{alist} second.
1019 This means for instance all associations with a key greater than 5 can
1020 be removed with @code{(alist-delete 5 alist <)}.
1022 @code{alist-delete} does not modify @var{alist}, but the return might
1023 share a common tail with @var{alist}. @code{alist-delete!} may modify
1024 the list structure of @var{alist} to construct its return.
1028 @node SRFI-1 Set Operations
1029 @subsubsection Set Operations on Lists
1030 @cindex list set operation
1032 Lists can be used to represent sets of objects. The procedures in
1033 this section operate on such lists as sets.
1035 Note that lists are not an efficient way to implement large sets. The
1036 procedures here typically take time @math{@var{m}@cross{}@var{n}} when
1037 operating on @var{m} and @var{n} element lists. Other data structures
1038 like trees, bitsets (@pxref{Bit Vectors}) or hash tables (@pxref{Hash
1039 Tables}) are faster.
1041 All these procedures take an equality predicate as the first argument.
1042 This predicate is used for testing the objects in the list sets for
1043 sameness. This predicate must be consistent with @code{eq?}
1044 (@pxref{Equality}) in the sense that if two list elements are
1045 @code{eq?} then they must also be equal under the predicate. This
1046 simply means a given object must be equal to itself.
1048 @deffn {Scheme Procedure} lset<= = list1 list2 @dots{}
1049 Return @code{#t} if each list is a subset of the one following it.
1050 Ie.@: @var{list1} a subset of @var{list2}, @var{list2} a subset of
1051 @var{list3}, etc, for as many lists as given. If only one list or no
1052 lists are given then the return is @code{#t}.
1054 A list @var{x} is a subset of @var{y} if each element of @var{x} is
1055 equal to some element in @var{y}. Elements are compared using the
1056 given @var{=} procedure, called as @code{(@var{=} xelem yelem)}.
1059 (lset<= eq?) @result{} #t
1060 (lset<= eqv? '(1 2 3) '(1)) @result{} #f
1061 (lset<= eqv? '(1 3 2) '(4 3 1 2)) @result{} #t
1065 @deffn {Scheme Procedure} lset= = list1 list2 @dots{}
1066 Return @code{#t} if all argument lists are set-equal. @var{list1} is
1067 compared to @var{list2}, @var{list2} to @var{list3}, etc, for as many
1068 lists as given. If only one list or no lists are given then the
1069 return is @code{#t}.
1071 Two lists @var{x} and @var{y} are set-equal if each element of @var{x}
1072 is equal to some element of @var{y} and conversely each element of
1073 @var{y} is equal to some element of @var{x}. The order of the
1074 elements in the lists doesn't matter. Element equality is determined
1075 with the given @var{=} procedure, called as @code{(@var{=} xelem
1076 yelem)}, but exactly which calls are made is unspecified.
1079 (lset= eq?) @result{} #t
1080 (lset= eqv? '(1 2 3) '(3 2 1)) @result{} #t
1081 (lset= string-ci=? '("a" "A" "b") '("B" "b" "a")) @result{} #t
1085 @deffn {Scheme Procedure} lset-adjoin = list elem1 @dots{}
1086 Add to @var{list} any of the given @var{elem}s not already in the
1087 list. @var{elem}s are @code{cons}ed onto the start of @var{list} (so
1088 the return shares a common tail with @var{list}), but the order
1089 they're added is unspecified.
1091 The given @var{=} procedure is used for comparing elements, called as
1092 @code{(@var{=} listelem elem)}, ie.@: the second argument is one of
1093 the given @var{elem} parameters.
1096 (lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3)
1100 @deffn {Scheme Procedure} lset-union = list1 list2 @dots{}
1101 @deffnx {Scheme Procedure} lset-union! = list1 list2 @dots{}
1102 Return the union of the argument list sets. The result is built by
1103 taking the union of @var{list1} and @var{list2}, then the union of
1104 that with @var{list3}, etc, for as many lists as given. For one list
1105 argument that list itself is the result, for no list arguments the
1106 result is the empty list.
1108 The union of two lists @var{x} and @var{y} is formed as follows. If
1109 @var{x} is empty then the result is @var{y}. Otherwise start with
1110 @var{x} as the result and consider each @var{y} element (from first to
1111 last). A @var{y} element not equal to something already in the result
1112 is @code{cons}ed onto the result.
1114 The given @var{=} procedure is used for comparing elements, called as
1115 @code{(@var{=} relem yelem)}. The first argument is from the result
1116 accumulated so far, and the second is from the list being union-ed in.
1117 But exactly which calls are made is otherwise unspecified.
1119 Notice that duplicate elements in @var{list1} (or the first non-empty
1120 list) are preserved, but that repeated elements in subsequent lists
1121 are only added once.
1124 (lset-union eqv?) @result{} ()
1125 (lset-union eqv? '(1 2 3)) @result{} (1 2 3)
1126 (lset-union eqv? '(1 2 1 3) '(2 4 5) '(5)) @result{} (5 4 1 2 1 3)
1129 @code{lset-union} doesn't change the given lists but the result may
1130 share a tail with the first non-empty list. @code{lset-union!} can
1131 modify all of the given lists to form the result.
1134 @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{}
1135 @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{}
1136 Return the intersection of @var{list1} with the other argument lists,
1137 meaning those elements of @var{list1} which are also in all of
1138 @var{list2} etc. For one list argument, just that list is returned.
1140 The test for an element of @var{list1} to be in the return is simply
1141 that it's equal to some element in each of @var{list2} etc. Notice
1142 this means an element appearing twice in @var{list1} but only once in
1143 each of @var{list2} etc will go into the return twice. The return has
1144 its elements in the same order as they were in @var{list1}.
1146 The given @var{=} procedure is used for comparing elements, called as
1147 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1148 and the second is from one of the subsequent lists. But exactly which
1149 calls are made and in what order is unspecified.
1152 (lset-intersection eqv? '(x y)) @result{} (x y)
1153 (lset-intersection eqv? '(1 2 3) '(4 3 2)) @result{} (2 3)
1154 (lset-intersection eqv? '(1 1 2 2) '(1 2) '(2 1) '(2)) @result{} (2 2)
1157 The return from @code{lset-intersection} may share a tail with
1158 @var{list1}. @code{lset-intersection!} may modify @var{list1} to form
1162 @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{}
1163 @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{}
1164 Return @var{list1} with any elements in @var{list2}, @var{list3} etc
1165 removed (ie.@: subtracted). For one list argument, just that list is
1168 The given @var{=} procedure is used for comparing elements, called as
1169 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1170 and the second from one of the subsequent lists. But exactly which
1171 calls are made and in what order is unspecified.
1174 (lset-difference eqv? '(x y)) @result{} (x y)
1175 (lset-difference eqv? '(1 2 3) '(3 1)) @result{} (2)
1176 (lset-difference eqv? '(1 2 3) '(3) '(2)) @result{} (1)
1179 The return from @code{lset-difference} may share a tail with
1180 @var{list1}. @code{lset-difference!} may modify @var{list1} to form
1184 @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{}
1185 @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{}
1186 Return two values (@pxref{Multiple Values}), the difference and
1187 intersection of the argument lists as per @code{lset-difference} and
1188 @code{lset-intersection} above.
1190 For two list arguments this partitions @var{list1} into those elements
1191 of @var{list1} which are in @var{list2} and not in @var{list2}. (But
1192 for more than two arguments there can be elements of @var{list1} which
1193 are neither part of the difference nor the intersection.)
1195 One of the return values from @code{lset-diff+intersection} may share
1196 a tail with @var{list1}. @code{lset-diff+intersection!} may modify
1197 @var{list1} to form its results.
1200 @deffn {Scheme Procedure} lset-xor = list1 list2 @dots{}
1201 @deffnx {Scheme Procedure} lset-xor! = list1 list2 @dots{}
1202 Return an XOR of the argument lists. For two lists this means those
1203 elements which are in exactly one of the lists. For more than two
1204 lists it means those elements which appear in an odd number of the
1207 To be precise, the XOR of two lists @var{x} and @var{y} is formed by
1208 taking those elements of @var{x} not equal to any element of @var{y},
1209 plus those elements of @var{y} not equal to any element of @var{x}.
1210 Equality is determined with the given @var{=} procedure, called as
1211 @code{(@var{=} e1 e2)}. One argument is from @var{x} and the other
1212 from @var{y}, but which way around is unspecified. Exactly which
1213 calls are made is also unspecified, as is the order of the elements in
1217 (lset-xor eqv? '(x y)) @result{} (x y)
1218 (lset-xor eqv? '(1 2 3) '(4 3 2)) @result{} (4 1)
1221 The return from @code{lset-xor} may share a tail with one of the list
1222 arguments. @code{lset-xor!} may modify @var{list1} to form its
1228 @subsection SRFI-2 - and-let*
1232 The following syntax can be obtained with
1235 (use-modules (srfi srfi-2))
1238 @deffn {library syntax} and-let* (clause @dots{}) body @dots{}
1239 A combination of @code{and} and @code{let*}.
1241 Each @var{clause} is evaluated in turn, and if @code{#f} is obtained
1242 then evaluation stops and @code{#f} is returned. If all are
1243 non-@code{#f} then @var{body} is evaluated and the last form gives the
1244 return value, or if @var{body} is empty then the result is @code{#t}.
1245 Each @var{clause} should be one of the following,
1249 Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}.
1250 Like @code{let*}, that binding is available to subsequent clauses.
1252 Evaluate @var{expr} and check for @code{#f}.
1254 Get the value bound to @var{symbol} and check for @code{#f}.
1257 Notice that @code{(expr)} has an ``extra'' pair of parentheses, for
1258 instance @code{((eq? x y))}. One way to remember this is to imagine
1259 the @code{symbol} in @code{(symbol expr)} is omitted.
1261 @code{and-let*} is good for calculations where a @code{#f} value means
1262 termination, but where a non-@code{#f} value is going to be needed in
1263 subsequent expressions.
1265 The following illustrates this, it returns text between brackets
1266 @samp{[...]} in a string, or @code{#f} if there are no such brackets
1267 (ie.@: either @code{string-index} gives @code{#f}).
1270 (define (extract-brackets str)
1271 (and-let* ((start (string-index str #\[))
1272 (end (string-index str #\] start)))
1273 (substring str (1+ start) end)))
1276 The following shows plain variables and expressions tested too.
1277 @code{diagnostic-levels} is taken to be an alist associating a
1278 diagnostic type with a level. @code{str} is printed only if the type
1279 is known and its level is high enough.
1282 (define (show-diagnostic type str)
1283 (and-let* (want-diagnostics
1284 (level (assq-ref diagnostic-levels type))
1285 ((>= level current-diagnostic-level)))
1289 The advantage of @code{and-let*} is that an extended sequence of
1290 expressions and tests doesn't require lots of nesting as would arise
1291 from separate @code{and} and @code{let*}, or from @code{cond} with
1298 @subsection SRFI-4 - Homogeneous numeric vector datatypes
1301 SRFI-4 provides an interface to uniform numeric vectors: vectors whose elements
1302 are all of a single numeric type. Guile offers uniform numeric vectors for
1303 signed and unsigned 8-bit, 16-bit, 32-bit, and 64-bit integers, two sizes of
1304 floating point values, and, as an extension to SRFI-4, complex floating-point
1305 numbers of these two sizes.
1307 The standard SRFI-4 procedures and data types may be included via loading the
1311 (use-modules (srfi srfi-4))
1314 This module is currently a part of the default Guile environment, but it is a
1315 good practice to explicitly import the module. In the future, using SRFI-4
1316 procedures without importing the SRFI-4 module will cause a deprecation message
1317 to be printed. (Of course, one may call the C functions at any time. Would that
1321 * SRFI-4 Overview:: The warp and weft of uniform numeric vectors.
1322 * SRFI-4 API:: Uniform vectors, from Scheme and from C.
1323 * SRFI-4 Generic Operations:: The general, operating on the specific.
1324 * SRFI-4 and Bytevectors:: SRFI-4 vectors are backed by bytevectors.
1325 * SRFI-4 Extensions:: Guile-specific extensions to the standard.
1328 @node SRFI-4 Overview
1329 @subsubsection SRFI-4 - Overview
1331 Uniform numeric vectors can be useful since they consume less memory
1332 than the non-uniform, general vectors. Also, since the types they can
1333 store correspond directly to C types, it is easier to work with them
1334 efficiently on a low level. Consider image processing as an example,
1335 where you want to apply a filter to some image. While you could store
1336 the pixels of an image in a general vector and write a general
1337 convolution function, things are much more efficient with uniform
1338 vectors: the convolution function knows that all pixels are unsigned
1339 8-bit values (say), and can use a very tight inner loop.
1341 This is implemented in Scheme by having the compiler notice calls to the SRFI-4
1342 accessors, and inline them to appropriate compiled code. From C you have access
1343 to the raw array; functions for efficiently working with uniform numeric vectors
1344 from C are listed at the end of this section.
1346 Uniform numeric vectors are the special case of one dimensional uniform
1349 There are 12 standard kinds of uniform numeric vectors, and they all have their
1350 own complement of constructors, accessors, and so on. Procedures that operate on
1351 a specific kind of uniform numeric vector have a ``tag'' in their name,
1352 indicating the element type.
1356 unsigned 8-bit integers
1359 signed 8-bit integers
1362 unsigned 16-bit integers
1365 signed 16-bit integers
1368 unsigned 32-bit integers
1371 signed 32-bit integers
1374 unsigned 64-bit integers
1377 signed 64-bit integers
1380 the C type @code{float}
1383 the C type @code{double}
1387 In addition, Guile supports uniform arrays of complex numbers, with the
1393 complex numbers in rectangular form with the real and imaginary part
1394 being a @code{float}
1397 complex numbers in rectangular form with the real and imaginary part
1398 being a @code{double}
1402 The external representation (ie.@: read syntax) for these vectors is
1403 similar to normal Scheme vectors, but with an additional tag from the
1404 tables above indicating the vector's type. For example,
1411 Note that the read syntax for floating-point here conflicts with
1412 @code{#f} for false. In Standard Scheme one can write @code{(1 #f3)}
1413 for a three element list @code{(1 #f 3)}, but for Guile @code{(1 #f3)}
1414 is invalid. @code{(1 #f 3)} is almost certainly what one should write
1415 anyway to make the intention clear, so this is rarely a problem.
1419 @subsubsection SRFI-4 - API
1421 Note that the @nicode{c32} and @nicode{c64} functions are only available from
1422 @nicode{(srfi srfi-4 gnu)}.
1424 @deffn {Scheme Procedure} u8vector? obj
1425 @deffnx {Scheme Procedure} s8vector? obj
1426 @deffnx {Scheme Procedure} u16vector? obj
1427 @deffnx {Scheme Procedure} s16vector? obj
1428 @deffnx {Scheme Procedure} u32vector? obj
1429 @deffnx {Scheme Procedure} s32vector? obj
1430 @deffnx {Scheme Procedure} u64vector? obj
1431 @deffnx {Scheme Procedure} s64vector? obj
1432 @deffnx {Scheme Procedure} f32vector? obj
1433 @deffnx {Scheme Procedure} f64vector? obj
1434 @deffnx {Scheme Procedure} c32vector? obj
1435 @deffnx {Scheme Procedure} c64vector? obj
1436 @deffnx {C Function} scm_u8vector_p (obj)
1437 @deffnx {C Function} scm_s8vector_p (obj)
1438 @deffnx {C Function} scm_u16vector_p (obj)
1439 @deffnx {C Function} scm_s16vector_p (obj)
1440 @deffnx {C Function} scm_u32vector_p (obj)
1441 @deffnx {C Function} scm_s32vector_p (obj)
1442 @deffnx {C Function} scm_u64vector_p (obj)
1443 @deffnx {C Function} scm_s64vector_p (obj)
1444 @deffnx {C Function} scm_f32vector_p (obj)
1445 @deffnx {C Function} scm_f64vector_p (obj)
1446 @deffnx {C Function} scm_c32vector_p (obj)
1447 @deffnx {C Function} scm_c64vector_p (obj)
1448 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1452 @deffn {Scheme Procedure} make-u8vector n [value]
1453 @deffnx {Scheme Procedure} make-s8vector n [value]
1454 @deffnx {Scheme Procedure} make-u16vector n [value]
1455 @deffnx {Scheme Procedure} make-s16vector n [value]
1456 @deffnx {Scheme Procedure} make-u32vector n [value]
1457 @deffnx {Scheme Procedure} make-s32vector n [value]
1458 @deffnx {Scheme Procedure} make-u64vector n [value]
1459 @deffnx {Scheme Procedure} make-s64vector n [value]
1460 @deffnx {Scheme Procedure} make-f32vector n [value]
1461 @deffnx {Scheme Procedure} make-f64vector n [value]
1462 @deffnx {Scheme Procedure} make-c32vector n [value]
1463 @deffnx {Scheme Procedure} make-c64vector n [value]
1464 @deffnx {C Function} scm_make_u8vector n [value]
1465 @deffnx {C Function} scm_make_s8vector n [value]
1466 @deffnx {C Function} scm_make_u16vector n [value]
1467 @deffnx {C Function} scm_make_s16vector n [value]
1468 @deffnx {C Function} scm_make_u32vector n [value]
1469 @deffnx {C Function} scm_make_s32vector n [value]
1470 @deffnx {C Function} scm_make_u64vector n [value]
1471 @deffnx {C Function} scm_make_s64vector n [value]
1472 @deffnx {C Function} scm_make_f32vector n [value]
1473 @deffnx {C Function} scm_make_f64vector n [value]
1474 @deffnx {C Function} scm_make_c32vector n [value]
1475 @deffnx {C Function} scm_make_c64vector n [value]
1476 Return a newly allocated homogeneous numeric vector holding @var{n}
1477 elements of the indicated type. If @var{value} is given, the vector
1478 is initialized with that value, otherwise the contents are
1482 @deffn {Scheme Procedure} u8vector value @dots{}
1483 @deffnx {Scheme Procedure} s8vector value @dots{}
1484 @deffnx {Scheme Procedure} u16vector value @dots{}
1485 @deffnx {Scheme Procedure} s16vector value @dots{}
1486 @deffnx {Scheme Procedure} u32vector value @dots{}
1487 @deffnx {Scheme Procedure} s32vector value @dots{}
1488 @deffnx {Scheme Procedure} u64vector value @dots{}
1489 @deffnx {Scheme Procedure} s64vector value @dots{}
1490 @deffnx {Scheme Procedure} f32vector value @dots{}
1491 @deffnx {Scheme Procedure} f64vector value @dots{}
1492 @deffnx {Scheme Procedure} c32vector value @dots{}
1493 @deffnx {Scheme Procedure} c64vector value @dots{}
1494 @deffnx {C Function} scm_u8vector (values)
1495 @deffnx {C Function} scm_s8vector (values)
1496 @deffnx {C Function} scm_u16vector (values)
1497 @deffnx {C Function} scm_s16vector (values)
1498 @deffnx {C Function} scm_u32vector (values)
1499 @deffnx {C Function} scm_s32vector (values)
1500 @deffnx {C Function} scm_u64vector (values)
1501 @deffnx {C Function} scm_s64vector (values)
1502 @deffnx {C Function} scm_f32vector (values)
1503 @deffnx {C Function} scm_f64vector (values)
1504 @deffnx {C Function} scm_c32vector (values)
1505 @deffnx {C Function} scm_c64vector (values)
1506 Return a newly allocated homogeneous numeric vector of the indicated
1507 type, holding the given parameter @var{value}s. The vector length is
1508 the number of parameters given.
1511 @deffn {Scheme Procedure} u8vector-length vec
1512 @deffnx {Scheme Procedure} s8vector-length vec
1513 @deffnx {Scheme Procedure} u16vector-length vec
1514 @deffnx {Scheme Procedure} s16vector-length vec
1515 @deffnx {Scheme Procedure} u32vector-length vec
1516 @deffnx {Scheme Procedure} s32vector-length vec
1517 @deffnx {Scheme Procedure} u64vector-length vec
1518 @deffnx {Scheme Procedure} s64vector-length vec
1519 @deffnx {Scheme Procedure} f32vector-length vec
1520 @deffnx {Scheme Procedure} f64vector-length vec
1521 @deffnx {Scheme Procedure} c32vector-length vec
1522 @deffnx {Scheme Procedure} c64vector-length vec
1523 @deffnx {C Function} scm_u8vector_length (vec)
1524 @deffnx {C Function} scm_s8vector_length (vec)
1525 @deffnx {C Function} scm_u16vector_length (vec)
1526 @deffnx {C Function} scm_s16vector_length (vec)
1527 @deffnx {C Function} scm_u32vector_length (vec)
1528 @deffnx {C Function} scm_s32vector_length (vec)
1529 @deffnx {C Function} scm_u64vector_length (vec)
1530 @deffnx {C Function} scm_s64vector_length (vec)
1531 @deffnx {C Function} scm_f32vector_length (vec)
1532 @deffnx {C Function} scm_f64vector_length (vec)
1533 @deffnx {C Function} scm_c32vector_length (vec)
1534 @deffnx {C Function} scm_c64vector_length (vec)
1535 Return the number of elements in @var{vec}.
1538 @deffn {Scheme Procedure} u8vector-ref vec i
1539 @deffnx {Scheme Procedure} s8vector-ref vec i
1540 @deffnx {Scheme Procedure} u16vector-ref vec i
1541 @deffnx {Scheme Procedure} s16vector-ref vec i
1542 @deffnx {Scheme Procedure} u32vector-ref vec i
1543 @deffnx {Scheme Procedure} s32vector-ref vec i
1544 @deffnx {Scheme Procedure} u64vector-ref vec i
1545 @deffnx {Scheme Procedure} s64vector-ref vec i
1546 @deffnx {Scheme Procedure} f32vector-ref vec i
1547 @deffnx {Scheme Procedure} f64vector-ref vec i
1548 @deffnx {Scheme Procedure} c32vector-ref vec i
1549 @deffnx {Scheme Procedure} c64vector-ref vec i
1550 @deffnx {C Function} scm_u8vector_ref (vec i)
1551 @deffnx {C Function} scm_s8vector_ref (vec i)
1552 @deffnx {C Function} scm_u16vector_ref (vec i)
1553 @deffnx {C Function} scm_s16vector_ref (vec i)
1554 @deffnx {C Function} scm_u32vector_ref (vec i)
1555 @deffnx {C Function} scm_s32vector_ref (vec i)
1556 @deffnx {C Function} scm_u64vector_ref (vec i)
1557 @deffnx {C Function} scm_s64vector_ref (vec i)
1558 @deffnx {C Function} scm_f32vector_ref (vec i)
1559 @deffnx {C Function} scm_f64vector_ref (vec i)
1560 @deffnx {C Function} scm_c32vector_ref (vec i)
1561 @deffnx {C Function} scm_c64vector_ref (vec i)
1562 Return the element at index @var{i} in @var{vec}. The first element
1563 in @var{vec} is index 0.
1566 @deffn {Scheme Procedure} u8vector-set! vec i value
1567 @deffnx {Scheme Procedure} s8vector-set! vec i value
1568 @deffnx {Scheme Procedure} u16vector-set! vec i value
1569 @deffnx {Scheme Procedure} s16vector-set! vec i value
1570 @deffnx {Scheme Procedure} u32vector-set! vec i value
1571 @deffnx {Scheme Procedure} s32vector-set! vec i value
1572 @deffnx {Scheme Procedure} u64vector-set! vec i value
1573 @deffnx {Scheme Procedure} s64vector-set! vec i value
1574 @deffnx {Scheme Procedure} f32vector-set! vec i value
1575 @deffnx {Scheme Procedure} f64vector-set! vec i value
1576 @deffnx {Scheme Procedure} c32vector-set! vec i value
1577 @deffnx {Scheme Procedure} c64vector-set! vec i value
1578 @deffnx {C Function} scm_u8vector_set_x (vec i value)
1579 @deffnx {C Function} scm_s8vector_set_x (vec i value)
1580 @deffnx {C Function} scm_u16vector_set_x (vec i value)
1581 @deffnx {C Function} scm_s16vector_set_x (vec i value)
1582 @deffnx {C Function} scm_u32vector_set_x (vec i value)
1583 @deffnx {C Function} scm_s32vector_set_x (vec i value)
1584 @deffnx {C Function} scm_u64vector_set_x (vec i value)
1585 @deffnx {C Function} scm_s64vector_set_x (vec i value)
1586 @deffnx {C Function} scm_f32vector_set_x (vec i value)
1587 @deffnx {C Function} scm_f64vector_set_x (vec i value)
1588 @deffnx {C Function} scm_c32vector_set_x (vec i value)
1589 @deffnx {C Function} scm_c64vector_set_x (vec i value)
1590 Set the element at index @var{i} in @var{vec} to @var{value}. The
1591 first element in @var{vec} is index 0. The return value is
1595 @deffn {Scheme Procedure} u8vector->list vec
1596 @deffnx {Scheme Procedure} s8vector->list vec
1597 @deffnx {Scheme Procedure} u16vector->list vec
1598 @deffnx {Scheme Procedure} s16vector->list vec
1599 @deffnx {Scheme Procedure} u32vector->list vec
1600 @deffnx {Scheme Procedure} s32vector->list vec
1601 @deffnx {Scheme Procedure} u64vector->list vec
1602 @deffnx {Scheme Procedure} s64vector->list vec
1603 @deffnx {Scheme Procedure} f32vector->list vec
1604 @deffnx {Scheme Procedure} f64vector->list vec
1605 @deffnx {Scheme Procedure} c32vector->list vec
1606 @deffnx {Scheme Procedure} c64vector->list vec
1607 @deffnx {C Function} scm_u8vector_to_list (vec)
1608 @deffnx {C Function} scm_s8vector_to_list (vec)
1609 @deffnx {C Function} scm_u16vector_to_list (vec)
1610 @deffnx {C Function} scm_s16vector_to_list (vec)
1611 @deffnx {C Function} scm_u32vector_to_list (vec)
1612 @deffnx {C Function} scm_s32vector_to_list (vec)
1613 @deffnx {C Function} scm_u64vector_to_list (vec)
1614 @deffnx {C Function} scm_s64vector_to_list (vec)
1615 @deffnx {C Function} scm_f32vector_to_list (vec)
1616 @deffnx {C Function} scm_f64vector_to_list (vec)
1617 @deffnx {C Function} scm_c32vector_to_list (vec)
1618 @deffnx {C Function} scm_c64vector_to_list (vec)
1619 Return a newly allocated list holding all elements of @var{vec}.
1622 @deffn {Scheme Procedure} list->u8vector lst
1623 @deffnx {Scheme Procedure} list->s8vector lst
1624 @deffnx {Scheme Procedure} list->u16vector lst
1625 @deffnx {Scheme Procedure} list->s16vector lst
1626 @deffnx {Scheme Procedure} list->u32vector lst
1627 @deffnx {Scheme Procedure} list->s32vector lst
1628 @deffnx {Scheme Procedure} list->u64vector lst
1629 @deffnx {Scheme Procedure} list->s64vector lst
1630 @deffnx {Scheme Procedure} list->f32vector lst
1631 @deffnx {Scheme Procedure} list->f64vector lst
1632 @deffnx {Scheme Procedure} list->c32vector lst
1633 @deffnx {Scheme Procedure} list->c64vector lst
1634 @deffnx {C Function} scm_list_to_u8vector (lst)
1635 @deffnx {C Function} scm_list_to_s8vector (lst)
1636 @deffnx {C Function} scm_list_to_u16vector (lst)
1637 @deffnx {C Function} scm_list_to_s16vector (lst)
1638 @deffnx {C Function} scm_list_to_u32vector (lst)
1639 @deffnx {C Function} scm_list_to_s32vector (lst)
1640 @deffnx {C Function} scm_list_to_u64vector (lst)
1641 @deffnx {C Function} scm_list_to_s64vector (lst)
1642 @deffnx {C Function} scm_list_to_f32vector (lst)
1643 @deffnx {C Function} scm_list_to_f64vector (lst)
1644 @deffnx {C Function} scm_list_to_c32vector (lst)
1645 @deffnx {C Function} scm_list_to_c64vector (lst)
1646 Return a newly allocated homogeneous numeric vector of the indicated type,
1647 initialized with the elements of the list @var{lst}.
1650 @deftypefn {C Function} SCM scm_take_u8vector (const scm_t_uint8 *data, size_t len)
1651 @deftypefnx {C Function} SCM scm_take_s8vector (const scm_t_int8 *data, size_t len)
1652 @deftypefnx {C Function} SCM scm_take_u16vector (const scm_t_uint16 *data, size_t len)
1653 @deftypefnx {C Function} SCM scm_take_s16vector (const scm_t_int16 *data, size_t len)
1654 @deftypefnx {C Function} SCM scm_take_u32vector (const scm_t_uint32 *data, size_t len)
1655 @deftypefnx {C Function} SCM scm_take_s32vector (const scm_t_int32 *data, size_t len)
1656 @deftypefnx {C Function} SCM scm_take_u64vector (const scm_t_uint64 *data, size_t len)
1657 @deftypefnx {C Function} SCM scm_take_s64vector (const scm_t_int64 *data, size_t len)
1658 @deftypefnx {C Function} SCM scm_take_f32vector (const float *data, size_t len)
1659 @deftypefnx {C Function} SCM scm_take_f64vector (const double *data, size_t len)
1660 @deftypefnx {C Function} SCM scm_take_c32vector (const float *data, size_t len)
1661 @deftypefnx {C Function} SCM scm_take_c64vector (const double *data, size_t len)
1662 Return a new uniform numeric vector of the indicated type and length
1663 that uses the memory pointed to by @var{data} to store its elements.
1664 This memory will eventually be freed with @code{free}. The argument
1665 @var{len} specifies the number of elements in @var{data}, not its size
1668 The @code{c32} and @code{c64} variants take a pointer to a C array of
1669 @code{float}s or @code{double}s. The real parts of the complex numbers
1670 are at even indices in that array, the corresponding imaginary parts are
1671 at the following odd index.
1674 @deftypefn {C Function} {const scm_t_uint8 *} scm_u8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1675 @deftypefnx {C Function} {const scm_t_int8 *} scm_s8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1676 @deftypefnx {C Function} {const scm_t_uint16 *} scm_u16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1677 @deftypefnx {C Function} {const scm_t_int16 *} scm_s16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1678 @deftypefnx {C Function} {const scm_t_uint32 *} scm_u32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1679 @deftypefnx {C Function} {const scm_t_int32 *} scm_s32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1680 @deftypefnx {C Function} {const scm_t_uint64 *} scm_u64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1681 @deftypefnx {C Function} {const scm_t_int64 *} scm_s64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1682 @deftypefnx {C Function} {const float *} scm_f32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1683 @deftypefnx {C Function} {const double *} scm_f64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1684 @deftypefnx {C Function} {const float *} scm_c32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1685 @deftypefnx {C Function} {const double *} scm_c64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1686 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1687 returns a pointer to the elements of a uniform numeric vector of the
1691 @deftypefn {C Function} {scm_t_uint8 *} scm_u8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1692 @deftypefnx {C Function} {scm_t_int8 *} scm_s8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1693 @deftypefnx {C Function} {scm_t_uint16 *} scm_u16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1694 @deftypefnx {C Function} {scm_t_int16 *} scm_s16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1695 @deftypefnx {C Function} {scm_t_uint32 *} scm_u32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1696 @deftypefnx {C Function} {scm_t_int32 *} scm_s32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1697 @deftypefnx {C Function} {scm_t_uint64 *} scm_u64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1698 @deftypefnx {C Function} {scm_t_int64 *} scm_s64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1699 @deftypefnx {C Function} {float *} scm_f32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1700 @deftypefnx {C Function} {double *} scm_f64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1701 @deftypefnx {C Function} {float *} scm_c32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1702 @deftypefnx {C Function} {double *} scm_c64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1703 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1704 C}), but returns a pointer to the elements of a uniform numeric vector
1705 of the indicated kind.
1708 @node SRFI-4 Generic Operations
1709 @subsubsection SRFI-4 - Generic operations
1711 Guile also provides procedures that operate on all types of uniform numeric
1712 vectors. In what is probably a bug, these procedures are currently available in
1713 the default environment as well; however prudent hackers will make sure to
1714 import @code{(srfi srfi-4 gnu)} before using these.
1716 @deftypefn {C Function} int scm_is_uniform_vector (SCM uvec)
1717 Return non-zero when @var{uvec} is a uniform numeric vector, zero
1721 @deftypefn {C Function} size_t scm_c_uniform_vector_length (SCM uvec)
1722 Return the number of elements of @var{uvec} as a @code{size_t}.
1725 @deffn {Scheme Procedure} uniform-vector? obj
1726 @deffnx {C Function} scm_uniform_vector_p (obj)
1727 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1731 @deffn {Scheme Procedure} uniform-vector-length vec
1732 @deffnx {C Function} scm_uniform_vector_length (vec)
1733 Return the number of elements in @var{vec}.
1736 @deffn {Scheme Procedure} uniform-vector-ref vec i
1737 @deffnx {C Function} scm_uniform_vector_ref (vec i)
1738 Return the element at index @var{i} in @var{vec}. The first element
1739 in @var{vec} is index 0.
1742 @deffn {Scheme Procedure} uniform-vector-set! vec i value
1743 @deffnx {C Function} scm_uniform_vector_set_x (vec i value)
1744 Set the element at index @var{i} in @var{vec} to @var{value}. The
1745 first element in @var{vec} is index 0. The return value is
1749 @deffn {Scheme Procedure} uniform-vector->list vec
1750 @deffnx {C Function} scm_uniform_vector_to_list (vec)
1751 Return a newly allocated list holding all elements of @var{vec}.
1754 @deftypefn {C Function} {const void *} scm_uniform_vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1755 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1756 returns a pointer to the elements of a uniform numeric vector.
1759 @deftypefn {C Function} {void *} scm_uniform_vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1760 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1761 C}), but returns a pointer to the elements of a uniform numeric vector.
1764 Unless you really need to the limited generality of these functions, it is best
1765 to use the type-specific functions, or the generalized vector accessors.
1767 @node SRFI-4 and Bytevectors
1768 @subsubsection SRFI-4 - Relation to bytevectors
1770 Guile implements SRFI-4 vectors using bytevectors (@pxref{Bytevectors}). Often
1771 when you have a numeric vector, you end up wanting to write its bytes somewhere,
1772 or have access to the underlying bytes, or read in bytes from somewhere else.
1773 Bytevectors are very good at this sort of thing. But the SRFI-4 APIs are nicer
1774 to use when doing number-crunching, because they are addressed by element and
1777 So as a compromise, Guile allows all bytevector functions to operate on numeric
1778 vectors. They address the underlying bytes in the native endianness, as one
1781 Following the same reasoning, that it's just bytes underneath, Guile also allows
1782 uniform vectors of a given type to be accessed as if they were of any type. One
1783 can fill a @nicode{u32vector}, and access its elements with
1784 @nicode{u8vector-ref}. One can use @nicode{f64vector-ref} on bytevectors. It's
1785 all the same to Guile.
1787 In this way, uniform numeric vectors may be written to and read from
1788 input/output ports using the procedures that operate on bytevectors.
1790 @xref{Bytevectors}, for more information.
1793 @node SRFI-4 Extensions
1794 @subsubsection SRFI-4 - Guile extensions
1796 Guile defines some useful extensions to SRFI-4, which are not available in the
1797 default Guile environment. They may be imported by loading the extensions
1801 (use-modules (srfi srfi-4 gnu))
1804 @deffn {Scheme Procedure} any->u8vector obj
1805 @deffnx {Scheme Procedure} any->s8vector obj
1806 @deffnx {Scheme Procedure} any->u16vector obj
1807 @deffnx {Scheme Procedure} any->s16vector obj
1808 @deffnx {Scheme Procedure} any->u32vector obj
1809 @deffnx {Scheme Procedure} any->s32vector obj
1810 @deffnx {Scheme Procedure} any->u64vector obj
1811 @deffnx {Scheme Procedure} any->s64vector obj
1812 @deffnx {Scheme Procedure} any->f32vector obj
1813 @deffnx {Scheme Procedure} any->f64vector obj
1814 @deffnx {Scheme Procedure} any->c32vector obj
1815 @deffnx {Scheme Procedure} any->c64vector obj
1816 @deffnx {C Function} scm_any_to_u8vector (obj)
1817 @deffnx {C Function} scm_any_to_s8vector (obj)
1818 @deffnx {C Function} scm_any_to_u16vector (obj)
1819 @deffnx {C Function} scm_any_to_s16vector (obj)
1820 @deffnx {C Function} scm_any_to_u32vector (obj)
1821 @deffnx {C Function} scm_any_to_s32vector (obj)
1822 @deffnx {C Function} scm_any_to_u64vector (obj)
1823 @deffnx {C Function} scm_any_to_s64vector (obj)
1824 @deffnx {C Function} scm_any_to_f32vector (obj)
1825 @deffnx {C Function} scm_any_to_f64vector (obj)
1826 @deffnx {C Function} scm_any_to_c32vector (obj)
1827 @deffnx {C Function} scm_any_to_c64vector (obj)
1828 Return a (maybe newly allocated) uniform numeric vector of the indicated
1829 type, initialized with the elements of @var{obj}, which must be a list,
1830 a vector, or a uniform vector. When @var{obj} is already a suitable
1831 uniform numeric vector, it is returned unchanged.
1836 @subsection SRFI-6 - Basic String Ports
1839 SRFI-6 defines the procedures @code{open-input-string},
1840 @code{open-output-string} and @code{get-output-string}. These
1841 procedures are included in the Guile core, so using this module does not
1842 make any difference at the moment. But it is possible that support for
1843 SRFI-6 will be factored out of the core library in the future, so using
1844 this module does not hurt, after all.
1847 @subsection SRFI-8 - receive
1850 @code{receive} is a syntax for making the handling of multiple-value
1851 procedures easier. It is documented in @xref{Multiple Values}.
1855 @subsection SRFI-9 - define-record-type
1859 This SRFI is a syntax for defining new record types and creating
1860 predicate, constructor, and field getter and setter functions. In
1861 Guile this is simply an alternate interface to the core record
1862 functionality (@pxref{Records}). It can be used with,
1865 (use-modules (srfi srfi-9))
1868 @deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{}
1870 Create a new record type, and make various @code{define}s for using
1871 it. This syntax can only occur at the top-level, not nested within
1874 @var{type} is bound to the record type, which is as per the return
1875 from the core @code{make-record-type}. @var{type} also provides the
1876 name for the record, as per @code{record-type-name}.
1878 @var{constructor} is bound to a function to be called as
1879 @code{(@var{constructor} fieldval @dots{})} to create a new record of
1880 this type. The arguments are initial values for the fields, one
1881 argument for each field, in the order they appear in the
1882 @code{define-record-type} form.
1884 The @var{fieldname}s provide the names for the record fields, as per
1885 the core @code{record-type-fields} etc, and are referred to in the
1886 subsequent accessor/modifier forms.
1888 @var{predicate} is bound to a function to be called as
1889 @code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f}
1890 according to whether @var{obj} is a record of this type.
1892 Each @var{accessor} is bound to a function to be called
1893 @code{(@var{accessor} record)} to retrieve the respective field from a
1894 @var{record}. Similarly each @var{modifier} is bound to a function to
1895 be called @code{(@var{modifier} record val)} to set the respective
1896 field in a @var{record}.
1900 An example will illustrate typical usage,
1903 (define-record-type employee-type
1904 (make-employee name age salary)
1906 (name get-employee-name)
1907 (age get-employee-age set-employee-age)
1908 (salary get-employee-salary set-employee-salary))
1911 This creates a new employee data type, with name, age and salary
1912 fields. Accessor functions are created for each field, but no
1913 modifier function for the name (the intention in this example being
1914 that it's established only when an employee object is created). These
1915 can all then be used as for example,
1918 employee-type @result{} #<record-type employee-type>
1920 (define fred (make-employee "Fred" 45 20000.00))
1922 (employee? fred) @result{} #t
1923 (get-employee-age fred) @result{} 45
1924 (set-employee-salary fred 25000.00) ;; pay rise
1927 The functions created by @code{define-record-type} are ordinary
1928 top-level @code{define}s. They can be redefined or @code{set!} as
1929 desired, exported from a module, etc.
1931 @unnumberedsubsubsec Non-toplevel Record Definitions
1933 The SRFI-9 specification explicitly disallows record definitions in a
1934 non-toplevel context, such as inside @code{lambda} body or inside a
1935 @var{let} block. However, Guile's implementation does not enforce that
1938 @unnumberedsubsubsec Custom Printers
1940 You may use @code{set-record-type-printer!} to customize the default printing
1941 behavior of records. This is a Guile extension and is not part of SRFI-9. It
1942 is located in the @nicode{(srfi srfi-9 gnu)} module.
1944 @deffn {Scheme Syntax} set-record-type-printer! name thunk
1945 Where @var{type} corresponds to the first argument of @code{define-record-type},
1946 and @var{thunk} is a procedure accepting two arguments, the record to print, and
1951 This example prints the employee's name in brackets, for instance @code{[Fred]}.
1954 (set-record-type-printer! employee-type
1955 (lambda (record port)
1956 (write-char #\[ port)
1957 (display (get-employee-name record) port)
1958 (write-char #\] port)))
1962 @subsection SRFI-10 - Hash-Comma Reader Extension
1967 This SRFI implements a reader extension @code{#,()} called hash-comma.
1968 It allows the reader to give new kinds of objects, for use both in
1969 data and as constants or literals in source code. This feature is
1973 (use-modules (srfi srfi-10))
1977 The new read syntax is of the form
1980 #,(@var{tag} @var{arg}@dots{})
1984 where @var{tag} is a symbol and the @var{arg}s are objects taken as
1985 parameters. @var{tag}s are registered with the following procedure.
1987 @deffn {Scheme Procedure} define-reader-ctor tag proc
1988 Register @var{proc} as the constructor for a hash-comma read syntax
1989 starting with symbol @var{tag}, i.e.@: @nicode{#,(@var{tag} arg@dots{})}.
1990 @var{proc} is called with the given arguments @code{(@var{proc}
1991 arg@dots{})} and the object it returns is the result of the read.
1995 For example, a syntax giving a list of @var{N} copies of an object.
1998 (define-reader-ctor 'repeat
2000 (make-list reps obj)))
2002 (display '#,(repeat 99 3))
2006 Notice the quote @nicode{'} when the @nicode{#,( )} is used. The
2007 @code{repeat} handler returns a list and the program must quote to use
2008 it literally, the same as any other list. Ie.
2011 (display '#,(repeat 99 3))
2013 (display '(99 99 99))
2016 When a handler returns an object which is self-evaluating, like a
2017 number or a string, then there's no need for quoting, just as there's
2018 no need when giving those directly as literals. For example an
2022 (define-reader-ctor 'sum
2025 (display #,(sum 123 456)) @print{} 579
2028 A typical use for @nicode{#,()} is to get a read syntax for objects
2029 which don't otherwise have one. For example, the following allows a
2030 hash table to be given literally, with tags and values, ready for fast
2034 (define-reader-ctor 'hash
2036 (let ((table (make-hash-table)))
2037 (for-each (lambda (elem)
2038 (apply hash-set! table elem))
2042 (define (animal->family animal)
2043 (hash-ref '#,(hash ("tiger" "cat")
2048 (animal->family "lion") @result{} "cat"
2051 Or for example the following is a syntax for a compiled regular
2052 expression (@pxref{Regular Expressions}).
2055 (use-modules (ice-9 regex))
2057 (define-reader-ctor 'regexp make-regexp)
2059 (define (extract-angs str)
2060 (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str)))
2062 (match:substring match 1))))
2064 (extract-angs "foo <BAR> quux") @result{} "BAR"
2068 @nicode{#,()} is somewhat similar to @code{define-macro}
2069 (@pxref{Macros}) in that handler code is run to produce a result, but
2070 @nicode{#,()} operates at the read stage, so it can appear in data for
2071 @code{read} (@pxref{Scheme Read}), not just in code to be executed.
2073 Because @nicode{#,()} is handled at read-time it has no direct access
2074 to variables etc. A symbol in the arguments is just a symbol, not a
2075 variable reference. The arguments are essentially constants, though
2076 the handler procedure can use them in any complicated way it might
2079 Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available
2080 globally, there's no need to use @code{(srfi srfi-10)} in later
2081 modules. Similarly the tags registered are global and can be used
2082 anywhere once registered.
2084 There's no attempt to record what previous @nicode{#,()} forms have
2085 been seen, if two identical forms occur then two calls are made to the
2086 handler procedure. The handler might like to maintain a cache or
2087 similar to avoid making copies of large objects, depending on expected
2090 In code the best uses of @nicode{#,()} are generally when there's a
2091 lot of objects of a particular kind as literals or constants. If
2092 there's just a few then some local variables and initializers are
2093 fine, but that becomes tedious and error prone when there's a lot, and
2094 the anonymous and compact syntax of @nicode{#,()} is much better.
2098 @subsection SRFI-11 - let-values
2103 This module implements the binding forms for multiple values
2104 @code{let-values} and @code{let*-values}. These forms are similar to
2105 @code{let} and @code{let*} (@pxref{Local Bindings}), but they support
2106 binding of the values returned by multiple-valued expressions.
2108 Write @code{(use-modules (srfi srfi-11))} to make the bindings
2112 (let-values (((x y) (values 1 2))
2113 ((z f) (values 3 4)))
2119 @code{let-values} performs all bindings simultaneously, which means that
2120 no expression in the binding clauses may refer to variables bound in the
2121 same clause list. @code{let*-values}, on the other hand, performs the
2122 bindings sequentially, just like @code{let*} does for single-valued
2127 @subsection SRFI-13 - String Library
2130 The SRFI-13 procedures are always available, @xref{Strings}.
2133 @subsection SRFI-14 - Character-set Library
2136 The SRFI-14 data type and procedures are always available,
2137 @xref{Character Sets}.
2140 @subsection SRFI-16 - case-lambda
2142 @cindex variable arity
2143 @cindex arity, variable
2145 SRFI-16 defines a variable-arity @code{lambda} form,
2146 @code{case-lambda}. This form is available in the default Guile
2147 environment. @xref{Case-lambda}, for more information.
2150 @subsection SRFI-17 - Generalized set!
2153 This SRFI implements a generalized @code{set!}, allowing some
2154 ``referencing'' functions to be used as the target location of a
2155 @code{set!}. This feature is available from
2158 (use-modules (srfi srfi-17))
2162 For example @code{vector-ref} is extended so that
2165 (set! (vector-ref vec idx) new-value)
2172 (vector-set! vec idx new-value)
2175 The idea is that a @code{vector-ref} expression identifies a location,
2176 which may be either fetched or stored. The same form is used for the
2177 location in both cases, encouraging visual clarity. This is similar
2178 to the idea of an ``lvalue'' in C.
2180 The mechanism for this kind of @code{set!} is in the Guile core
2181 (@pxref{Procedures with Setters}). This module adds definitions of
2182 the following functions as procedures with setters, allowing them to
2183 be targets of a @code{set!},
2186 @nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr},
2187 @nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr},
2188 @nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr},
2189 @nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr},
2190 @nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr},
2191 @nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr},
2192 @nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr},
2193 @nicode{cdddar}, @nicode{cddddr}
2195 @nicode{string-ref}, @nicode{vector-ref}
2198 The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as
2199 a procedure with setter, allowing the setter for a procedure to be
2200 changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}.
2201 Currently Guile does not implement this, a setter can only be
2202 specified on creation (@code{getter-with-setter} below).
2204 @defun getter-with-setter
2205 The same as the Guile core @code{make-procedure-with-setter}
2206 (@pxref{Procedures with Setters}).
2211 @subsection SRFI-18 - Multithreading support
2214 This is an implementation of the SRFI-18 threading and synchronization
2215 library. The functions and variables described here are provided by
2218 (use-modules (srfi srfi-18))
2221 As a general rule, the data types and functions in this SRFI-18
2222 implementation are compatible with the types and functions in Guile's
2223 core threading code. For example, mutexes created with the SRFI-18
2224 @code{make-mutex} function can be passed to the built-in Guile
2225 function @code{lock-mutex} (@pxref{Mutexes and Condition Variables}),
2226 and mutexes created with the built-in Guile function @code{make-mutex}
2227 can be passed to the SRFI-18 function @code{mutex-lock!}. Cases in
2228 which this does not hold true are noted in the following sections.
2231 * SRFI-18 Threads:: Executing code
2232 * SRFI-18 Mutexes:: Mutual exclusion devices
2233 * SRFI-18 Condition variables:: Synchronizing of groups of threads
2234 * SRFI-18 Time:: Representation of times and durations
2235 * SRFI-18 Exceptions:: Signalling and handling errors
2238 @node SRFI-18 Threads
2239 @subsubsection SRFI-18 Threads
2241 Threads created by SRFI-18 differ in two ways from threads created by
2242 Guile's built-in thread functions. First, a thread created by SRFI-18
2243 @code{make-thread} begins in a blocked state and will not start
2244 execution until @code{thread-start!} is called on it. Second, SRFI-18
2245 threads are constructed with a top-level exception handler that
2246 captures any exceptions that are thrown on thread exit. In all other
2247 regards, SRFI-18 threads are identical to normal Guile threads.
2249 @defun current-thread
2250 Returns the thread that called this function. This is the same
2251 procedure as the same-named built-in procedure @code{current-thread}
2256 Returns @code{#t} if @var{obj} is a thread, @code{#f} otherwise. This
2257 is the same procedure as the same-named built-in procedure
2258 @code{thread?} (@pxref{Threads}).
2261 @defun make-thread thunk [name]
2262 Call @code{thunk} in a new thread and with a new dynamic state,
2263 returning the new thread and optionally assigning it the object name
2264 @var{name}, which may be any Scheme object.
2266 Note that the name @code{make-thread} conflicts with the
2267 @code{(ice-9 threads)} function @code{make-thread}. Applications
2268 wanting to use both of these functions will need to refer to them by
2272 @defun thread-name thread
2273 Returns the name assigned to @var{thread} at the time of its creation,
2274 or @code{#f} if it was not given a name.
2277 @defun thread-specific thread
2278 @defunx thread-specific-set! thread obj
2279 Get or set the ``object-specific'' property of @var{thread}. In
2280 Guile's implementation of SRFI-18, this value is stored as an object
2281 property, and will be @code{#f} if not set.
2284 @defun thread-start! thread
2285 Unblocks @var{thread} and allows it to begin execution if it has not
2289 @defun thread-yield!
2290 If one or more threads are waiting to execute, calling
2291 @code{thread-yield!} forces an immediate context switch to one of them.
2292 Otherwise, @code{thread-yield!} has no effect. @code{thread-yield!}
2293 behaves identically to the Guile built-in function @code{yield}.
2296 @defun thread-sleep! timeout
2297 The current thread waits until the point specified by the time object
2298 @var{timeout} is reached (@pxref{SRFI-18 Time}). This blocks the
2299 thread only if @var{timeout} represents a point in the future. it is
2300 an error for @var{timeout} to be @code{#f}.
2303 @defun thread-terminate! thread
2304 Causes an abnormal termination of @var{thread}. If @var{thread} is
2305 not already terminated, all mutexes owned by @var{thread} become
2306 unlocked/abandoned. If @var{thread} is the current thread,
2307 @code{thread-terminate!} does not return. Otherwise
2308 @code{thread-terminate!} returns an unspecified value; the termination
2309 of @var{thread} will occur before @code{thread-terminate!} returns.
2310 Subsequent attempts to join on @var{thread} will cause a ``terminated
2311 thread exception'' to be raised.
2313 @code{thread-terminate!} is compatible with the thread cancellation
2314 procedures in the core threads API (@pxref{Threads}) in that if a
2315 cleanup handler has been installed for the target thread, it will be
2316 called before the thread exits and its return value (or exception, if
2317 any) will be stored for later retrieval via a call to
2318 @code{thread-join!}.
2321 @defun thread-join! thread [timeout [timeout-val]]
2322 Wait for @var{thread} to terminate and return its exit value. When a
2323 time value @var{timeout} is given, it specifies a point in time where
2324 the waiting should be aborted. When the waiting is aborted,
2325 @var{timeoutval} is returned if it is specified; otherwise, a
2326 @code{join-timeout-exception} exception is raised
2327 (@pxref{SRFI-18 Exceptions}). Exceptions may also be raised if the
2328 thread was terminated by a call to @code{thread-terminate!}
2329 (@code{terminated-thread-exception} will be raised) or if the thread
2330 exited by raising an exception that was handled by the top-level
2331 exception handler (@code{uncaught-exception} will be raised; the
2332 original exception can be retrieved using
2333 @code{uncaught-exception-reason}).
2337 @node SRFI-18 Mutexes
2338 @subsubsection SRFI-18 Mutexes
2340 The behavior of Guile's built-in mutexes is parameterized via a set of
2341 flags passed to the @code{make-mutex} procedure in the core
2342 (@pxref{Mutexes and Condition Variables}). To satisfy the requirements
2343 for mutexes specified by SRFI-18, the @code{make-mutex} procedure
2344 described below sets the following flags:
2347 @code{recursive}: the mutex can be locked recursively
2349 @code{unchecked-unlock}: attempts to unlock a mutex that is already
2350 unlocked will not raise an exception
2352 @code{allow-external-unlock}: the mutex can be unlocked by any thread,
2353 not just the thread that locked it originally
2356 @defun make-mutex [name]
2357 Returns a new mutex, optionally assigning it the object name
2358 @var{name}, which may be any Scheme object. The returned mutex will be
2359 created with the configuration described above. Note that the name
2360 @code{make-mutex} conflicts with Guile core function @code{make-mutex}.
2361 Applications wanting to use both of these functions will need to refer
2362 to them by different names.
2365 @defun mutex-name mutex
2366 Returns the name assigned to @var{mutex} at the time of its creation,
2367 or @code{#f} if it was not given a name.
2370 @defun mutex-specific mutex
2371 @defunx mutex-specific-set! mutex obj
2372 Get or set the ``object-specific'' property of @var{mutex}. In Guile's
2373 implementation of SRFI-18, this value is stored as an object property,
2374 and will be @code{#f} if not set.
2377 @defun mutex-state mutex
2378 Returns information about the state of @var{mutex}. Possible values
2382 thread @code{T}: the mutex is in the locked/owned state and thread T
2383 is the owner of the mutex
2385 symbol @code{not-owned}: the mutex is in the locked/not-owned state
2387 symbol @code{abandoned}: the mutex is in the unlocked/abandoned state
2389 symbol @code{not-abandoned}: the mutex is in the
2390 unlocked/not-abandoned state
2394 @defun mutex-lock! mutex [timeout [thread]]
2395 Lock @var{mutex}, optionally specifying a time object @var{timeout}
2396 after which to abort the lock attempt and a thread @var{thread} giving
2397 a new owner for @var{mutex} different than the current thread. This
2398 procedure has the same behavior as the @code{lock-mutex} procedure in
2402 @defun mutex-unlock! mutex [condition-variable [timeout]]
2403 Unlock @var{mutex}, optionally specifying a condition variable
2404 @var{condition-variable} on which to wait, either indefinitely or,
2405 optionally, until the time object @var{timeout} has passed, to be
2406 signalled. This procedure has the same behavior as the
2407 @code{unlock-mutex} procedure in the core library.
2411 @node SRFI-18 Condition variables
2412 @subsubsection SRFI-18 Condition variables
2414 SRFI-18 does not specify a ``wait'' function for condition variables.
2415 Waiting on a condition variable can be simulated using the SRFI-18
2416 @code{mutex-unlock!} function described in the previous section, or
2417 Guile's built-in @code{wait-condition-variable} procedure can be used.
2419 @defun condition-variable? obj
2420 Returns @code{#t} if @var{obj} is a condition variable, @code{#f}
2421 otherwise. This is the same procedure as the same-named built-in
2423 (@pxref{Mutexes and Condition Variables, @code{condition-variable?}}).
2426 @defun make-condition-variable [name]
2427 Returns a new condition variable, optionally assigning it the object
2428 name @var{name}, which may be any Scheme object. This procedure
2429 replaces a procedure of the same name in the core library.
2432 @defun condition-variable-name condition-variable
2433 Returns the name assigned to @var{thread} at the time of its creation,
2434 or @code{#f} if it was not given a name.
2437 @defun condition-variable-specific condition-variable
2438 @defunx condition-variable-specific-set! condition-variable obj
2439 Get or set the ``object-specific'' property of
2440 @var{condition-variable}. In Guile's implementation of SRFI-18, this
2441 value is stored as an object property, and will be @code{#f} if not
2445 @defun condition-variable-signal! condition-variable
2446 @defunx condition-variable-broadcast! condition-variable
2447 Wake up one thread that is waiting for @var{condition-variable}, in
2448 the case of @code{condition-variable-signal!}, or all threads waiting
2449 for it, in the case of @code{condition-variable-broadcast!}. The
2450 behavior of these procedures is equivalent to that of the procedures
2451 @code{signal-condition-variable} and
2452 @code{broadcast-condition-variable} in the core library.
2457 @subsubsection SRFI-18 Time
2459 The SRFI-18 time functions manipulate time in two formats: a
2460 ``time object'' type that represents an absolute point in time in some
2461 implementation-specific way; and the number of seconds since some
2462 unspecified ``epoch''. In Guile's implementation, the epoch is the
2463 Unix epoch, 00:00:00 UTC, January 1, 1970.
2466 Return the current time as a time object. This procedure replaces
2467 the procedure of the same name in the core library, which returns the
2468 current time in seconds since the epoch.
2472 Returns @code{#t} if @var{obj} is a time object, @code{#f} otherwise.
2475 @defun time->seconds time
2476 @defunx seconds->time seconds
2477 Convert between time objects and numerical values representing the
2478 number of seconds since the epoch. When converting from a time object
2479 to seconds, the return value is the number of seconds between
2480 @var{time} and the epoch. When converting from seconds to a time
2481 object, the return value is a time object that represents a time
2482 @var{seconds} seconds after the epoch.
2486 @node SRFI-18 Exceptions
2487 @subsubsection SRFI-18 Exceptions
2489 SRFI-18 exceptions are identical to the exceptions provided by
2490 Guile's implementation of SRFI-34. The behavior of exception
2491 handlers invoked to handle exceptions thrown from SRFI-18 functions,
2492 however, differs from the conventional behavior of SRFI-34 in that
2493 the continuation of the handler is the same as that of the call to
2494 the function. Handlers are called in a tail-recursive manner; the
2495 exceptions do not ``bubble up''.
2497 @defun current-exception-handler
2498 Returns the current exception handler.
2501 @defun with-exception-handler handler thunk
2502 Installs @var{handler} as the current exception handler and calls the
2503 procedure @var{thunk} with no arguments, returning its value as the
2504 value of the exception. @var{handler} must be a procedure that accepts
2505 a single argument. The current exception handler at the time this
2506 procedure is called will be restored after the call returns.
2510 Raise @var{obj} as an exception. This is the same procedure as the
2511 same-named procedure defined in SRFI 34.
2514 @defun join-timeout-exception? obj
2515 Returns @code{#t} if @var{obj} is an exception raised as the result of
2516 performing a timed join on a thread that does not exit within the
2517 specified timeout, @code{#f} otherwise.
2520 @defun abandoned-mutex-exception? obj
2521 Returns @code{#t} if @var{obj} is an exception raised as the result of
2522 attempting to lock a mutex that has been abandoned by its owner thread,
2523 @code{#f} otherwise.
2526 @defun terminated-thread-exception? obj
2527 Returns @code{#t} if @var{obj} is an exception raised as the result of
2528 joining on a thread that exited as the result of a call to
2529 @code{thread-terminate!}.
2532 @defun uncaught-exception? obj
2533 @defunx uncaught-exception-reason exc
2534 @code{uncaught-exception?} returns @code{#t} if @var{obj} is an
2535 exception thrown as the result of joining a thread that exited by
2536 raising an exception that was handled by the top-level exception
2537 handler installed by @code{make-thread}. When this occurs, the
2538 original exception is preserved as part of the exception thrown by
2539 @code{thread-join!} and can be accessed by calling
2540 @code{uncaught-exception-reason} on that exception. Note that
2541 because this exception-preservation mechanism is a side-effect of
2542 @code{make-thread}, joining on threads that exited as described above
2543 but were created by other means will not raise this
2544 @code{uncaught-exception} error.
2549 @subsection SRFI-19 - Time/Date Library
2554 This is an implementation of the SRFI-19 time/date library. The
2555 functions and variables described here are provided by
2558 (use-modules (srfi srfi-19))
2561 @strong{Caution}: The current code in this module incorrectly extends
2562 the Gregorian calendar leap year rule back prior to the introduction
2563 of those reforms in 1582 (or the appropriate year in various
2564 countries). The Julian calendar was used prior to 1582, and there
2565 were 10 days skipped for the reform, but the code doesn't implement
2568 This will be fixed some time. Until then calculations for 1583
2569 onwards are correct, but prior to that any day/month/year and day of
2570 the week calculations are wrong.
2573 * SRFI-19 Introduction::
2576 * SRFI-19 Time/Date conversions::
2577 * SRFI-19 Date to string::
2578 * SRFI-19 String to date::
2581 @node SRFI-19 Introduction
2582 @subsubsection SRFI-19 Introduction
2584 @cindex universal time
2588 This module implements time and date representations and calculations,
2589 in various time systems, including universal time (UTC) and atomic
2592 For those not familiar with these time systems, TAI is based on a
2593 fixed length second derived from oscillations of certain atoms. UTC
2594 differs from TAI by an integral number of seconds, which is increased
2595 or decreased at announced times to keep UTC aligned to a mean solar
2596 day (the orbit and rotation of the earth are not quite constant).
2599 So far, only increases in the TAI
2606 UTC difference have been needed. Such an increase is a ``leap
2607 second'', an extra second of TAI introduced at the end of a UTC day.
2608 When working entirely within UTC this is never seen, every day simply
2609 has 86400 seconds. But when converting from TAI to a UTC date, an
2610 extra 23:59:60 is present, where normally a day would end at 23:59:59.
2611 Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI
2614 @cindex system clock
2615 In the current implementation, the system clock is assumed to be UTC,
2616 and a table of leap seconds in the code converts to TAI. See comments
2617 in @file{srfi-19.scm} for how to update this table.
2620 @cindex modified julian day
2621 Also, for those not familiar with the terminology, a @dfn{Julian Day}
2622 is a real number which is a count of days and fraction of a day, in
2623 UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
2624 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from
2625 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time
2626 is julian day 2400000.5.
2628 @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
2629 @c noon, UTC), but this is incorrect. It looks like it might have
2630 @c arisen from the code incorrectly treating years a multiple of 100
2631 @c but not 400 prior to 1582 as non-leap years, where instead the Julian
2632 @c calendar should be used so all multiples of 4 before 1582 are leap
2637 @subsubsection SRFI-19 Time
2640 A @dfn{time} object has type, seconds and nanoseconds fields
2641 representing a point in time starting from some epoch. This is an
2642 arbitrary point in time, not just a time of day. Although times are
2643 represented in nanoseconds, the actual resolution may be lower.
2645 The following variables hold the possible time types. For instance
2646 @code{(current-time time-process)} would give the current CPU process
2650 Universal Coordinated Time (UTC).
2655 International Atomic Time (TAI).
2659 @defvar time-monotonic
2660 Monotonic time, meaning a monotonically increasing time starting from
2661 an unspecified epoch.
2663 Note that in the current implementation @code{time-monotonic} is the
2664 same as @code{time-tai}, and unfortunately is therefore affected by
2665 adjustments to the system clock. Perhaps this will change in the
2669 @defvar time-duration
2670 A duration, meaning simply a difference between two times.
2673 @defvar time-process
2674 CPU time spent in the current process, starting from when the process
2676 @cindex process time
2680 CPU time spent in the current thread. Not currently implemented.
2686 Return @code{#t} if @var{obj} is a time object, or @code{#f} if not.
2689 @defun make-time type nanoseconds seconds
2690 Create a time object with the given @var{type}, @var{seconds} and
2694 @defun time-type time
2695 @defunx time-nanosecond time
2696 @defunx time-second time
2697 @defunx set-time-type! time type
2698 @defunx set-time-nanosecond! time nsec
2699 @defunx set-time-second! time sec
2700 Get or set the type, seconds or nanoseconds fields of a time object.
2702 @code{set-time-type!} merely changes the field, it doesn't convert the
2703 time value. For conversions, see @ref{SRFI-19 Time/Date conversions}.
2706 @defun copy-time time
2707 Return a new time object, which is a copy of the given @var{time}.
2710 @defun current-time [type]
2711 Return the current time of the given @var{type}. The default
2712 @var{type} is @code{time-utc}.
2714 Note that the name @code{current-time} conflicts with the Guile core
2715 @code{current-time} function (@pxref{Time}) as well as the SRFI-18
2716 @code{current-time} function (@pxref{SRFI-18 Time}). Applications
2717 wanting to use more than one of these functions will need to refer to
2718 them by different names.
2721 @defun time-resolution [type]
2722 Return the resolution, in nanoseconds, of the given time @var{type}.
2723 The default @var{type} is @code{time-utc}.
2726 @defun time<=? t1 t2
2727 @defunx time<? t1 t2
2728 @defunx time=? t1 t2
2729 @defunx time>=? t1 t2
2730 @defunx time>? t1 t2
2731 Return @code{#t} or @code{#f} according to the respective relation
2732 between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2}
2733 must be the same time type.
2736 @defun time-difference t1 t2
2737 @defunx time-difference! t1 t2
2738 Return a time object of type @code{time-duration} representing the
2739 period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be
2742 @code{time-difference} returns a new time object,
2743 @code{time-difference!} may modify @var{t1} to form its return.
2746 @defun add-duration time duration
2747 @defunx add-duration! time duration
2748 @defunx subtract-duration time duration
2749 @defunx subtract-duration! time duration
2750 Return a time object which is @var{time} with the given @var{duration}
2751 added or subtracted. @var{duration} must be a time object of type
2752 @code{time-duration}.
2754 @code{add-duration} and @code{subtract-duration} return a new time
2755 object. @code{add-duration!} and @code{subtract-duration!} may modify
2756 the given @var{time} to form their return.
2761 @subsubsection SRFI-19 Date
2764 A @dfn{date} object represents a date in the Gregorian calendar and a
2765 time of day on that date in some timezone.
2767 The fields are year, month, day, hour, minute, second, nanoseconds and
2768 timezone. A date object is immutable, its fields can be read but they
2769 cannot be modified once the object is created.
2772 Return @code{#t} if @var{obj} is a date object, or @code{#f} if not.
2775 @defun make-date nsecs seconds minutes hours date month year zone-offset
2776 Create a new date object.
2778 @c FIXME: What can we say about the ranges of the values. The
2779 @c current code looks it doesn't normalize, but expects then in their
2780 @c usual range already.
2784 @defun date-nanosecond date
2785 Nanoseconds, 0 to 999999999.
2788 @defun date-second date
2789 Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working
2790 entirely within UTC, it's only when converting to or from TAI.
2793 @defun date-minute date
2797 @defun date-hour date
2801 @defun date-day date
2802 Day of the month, 1 to 31 (or less, according to the month).
2805 @defun date-month date
2809 @defun date-year date
2810 Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46
2811 B.C. There is no year 0, year @math{-1} is followed by year 1.
2814 @defun date-zone-offset date
2815 Time zone, an integer number of seconds east of Greenwich.
2818 @defun date-year-day date
2819 Day of the year, starting from 1 for 1st January.
2822 @defun date-week-day date
2823 Day of the week, starting from 0 for Sunday.
2826 @defun date-week-number date dstartw
2827 Week of the year, ignoring a first partial week. @var{dstartw} is the
2828 day of the week which is taken to start a week, 0 for Sunday, 1 for
2831 @c FIXME: The spec doesn't say whether numbering starts at 0 or 1.
2832 @c The code looks like it's 0, if that's the correct intention.
2836 @c The SRFI text doesn't actually give the default for tz-offset, but
2837 @c the reference implementation has the local timezone and the
2838 @c conversions functions all specify that, so it should be ok to
2839 @c document it here.
2841 @defun current-date [tz-offset]
2842 Return a date object representing the current date/time, in UTC offset
2843 by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and
2844 defaults to the local timezone.
2847 @defun current-julian-day
2849 Return the current Julian Day.
2852 @defun current-modified-julian-day
2853 @cindex modified julian day
2854 Return the current Modified Julian Day.
2858 @node SRFI-19 Time/Date conversions
2859 @subsubsection SRFI-19 Time/Date conversions
2860 @cindex time conversion
2861 @cindex date conversion
2863 @defun date->julian-day date
2864 @defunx date->modified-julian-day date
2865 @defunx date->time-monotonic date
2866 @defunx date->time-tai date
2867 @defunx date->time-utc date
2869 @defun julian-day->date jdn [tz-offset]
2870 @defunx julian-day->time-monotonic jdn
2871 @defunx julian-day->time-tai jdn
2872 @defunx julian-day->time-utc jdn
2874 @defun modified-julian-day->date jdn [tz-offset]
2875 @defunx modified-julian-day->time-monotonic jdn
2876 @defunx modified-julian-day->time-tai jdn
2877 @defunx modified-julian-day->time-utc jdn
2879 @defun time-monotonic->date time [tz-offset]
2880 @defunx time-monotonic->time-tai time
2881 @defunx time-monotonic->time-tai! time
2882 @defunx time-monotonic->time-utc time
2883 @defunx time-monotonic->time-utc! time
2885 @defun time-tai->date time [tz-offset]
2886 @defunx time-tai->julian-day time
2887 @defunx time-tai->modified-julian-day time
2888 @defunx time-tai->time-monotonic time
2889 @defunx time-tai->time-monotonic! time
2890 @defunx time-tai->time-utc time
2891 @defunx time-tai->time-utc! time
2893 @defun time-utc->date time [tz-offset]
2894 @defunx time-utc->julian-day time
2895 @defunx time-utc->modified-julian-day time
2896 @defunx time-utc->time-monotonic time
2897 @defunx time-utc->time-monotonic! time
2898 @defunx time-utc->time-tai time
2899 @defunx time-utc->time-tai! time
2901 Convert between dates, times and days of the respective types. For
2902 instance @code{time-tai->time-utc} accepts a @var{time} object of type
2903 @code{time-tai} and returns an object of type @code{time-utc}.
2905 The @code{!} variants may modify their @var{time} argument to form
2906 their return. The plain functions create a new object.
2908 For conversions to dates, @var{tz-offset} is seconds east of
2909 Greenwich. The default is the local timezone, at the given time, as
2910 provided by the system, using @code{localtime} (@pxref{Time}).
2912 On 32-bit systems, @code{localtime} is limited to a 32-bit
2913 @code{time_t}, so a default @var{tz-offset} is only available for
2914 times between Dec 1901 and Jan 2038. For prior dates an application
2915 might like to use the value in 1902, though some locations have zone
2916 changes prior to that. For future dates an application might like to
2917 assume today's rules extend indefinitely. But for correct daylight
2918 savings transitions it will be necessary to take an offset for the
2919 same day and time but a year in range and which has the same starting
2920 weekday and same leap/non-leap (to support rules like last Sunday in
2924 @node SRFI-19 Date to string
2925 @subsubsection SRFI-19 Date to string
2926 @cindex date to string
2927 @cindex string, from date
2929 @defun date->string date [format]
2930 Convert a date to a string under the control of a format.
2931 @var{format} should be a string containing @samp{~} escapes, which
2932 will be expanded as per the following conversion table. The default
2933 @var{format} is @samp{~c}, a locale-dependent date and time.
2935 Many of these conversion characters are the same as POSIX
2936 @code{strftime} (@pxref{Time}), but there are some extras and some
2939 @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM}
2940 @item @nicode{~~} @tab literal ~
2941 @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun}
2942 @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday}
2943 @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan}
2944 @item @nicode{~B} @tab locale full month, eg.@: @samp{January}
2945 @item @nicode{~c} @tab locale date and time, eg.@: @*
2946 @samp{Fri Jul 14 20:28:42-0400 2000}
2947 @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31}
2949 @c Spec says d/m/y, reference implementation says m/d/y.
2950 @c Apparently the reference code was the intention, but would like to
2951 @c see an errata published for the spec before contradicting it here.
2953 @c @item @nicode{~D} @tab date @nicode{~d/~m/~y}
2955 @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31}
2956 @item @nicode{~f} @tab seconds and fractional seconds,
2957 with locale decimal point, eg.@: @samp{5.2}
2958 @item @nicode{~h} @tab same as @nicode{~b}
2959 @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23}
2960 @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12}
2961 @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366}
2962 @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23}
2963 @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12}
2964 @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12}
2965 @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59}
2966 @item @nicode{~n} @tab newline
2967 @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999}
2968 @item @nicode{~p} @tab locale AM or PM
2969 @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p}
2970 @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC
2971 @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @*
2972 (usual limit is 59, 60 is a leap second)
2973 @item @nicode{~t} @tab horizontal tab character
2974 @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S}
2975 @item @nicode{~U} @tab week of year, Sunday first day of week,
2976 @samp{00} to @samp{52}
2977 @item @nicode{~V} @tab week of year, Monday first day of week,
2978 @samp{01} to @samp{53}
2979 @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6}
2980 @item @nicode{~W} @tab week of year, Monday first day of week,
2981 @samp{00} to @samp{52}
2983 @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale
2984 @c date. The reference code has ~x as the locale date and ~X as a
2985 @c locale time. The rule is apparently that the code should be
2986 @c believed, but would like to see an errata for the spec before
2987 @c contradicting it here.
2989 @c @item @nicode{~x} @tab week of year, Monday as first day of week,
2990 @c @samp{00} to @samp{53}
2991 @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00}
2993 @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99}
2994 @item @nicode{~Y} @tab year, full, eg.@: @samp{2003}
2995 @item @nicode{~z} @tab time zone, RFC-822 style
2996 @item @nicode{~Z} @tab time zone symbol (not currently implemented)
2997 @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d}
2998 @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~k:~M:~S~z}
2999 @item @nicode{~3} @tab ISO-8601 time, @samp{~k:~M:~S}
3000 @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~k:~M:~S~z}
3001 @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~k:~M:~S}
3005 Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently
3006 described here, since the specification and reference implementation
3009 Conversion is locale-dependent on systems that support it
3010 (@pxref{Accessing Locale Information}). @xref{Locales,
3011 @code{setlocale}}, for information on how to change the current
3015 @node SRFI-19 String to date
3016 @subsubsection SRFI-19 String to date
3017 @cindex string to date
3018 @cindex date, from string
3020 @c FIXME: Can we say what happens when an incomplete date is
3021 @c converted? I.e. fields left as 0, or what? The spec seems to be
3024 @defun string->date input template
3025 Convert an @var{input} string to a date under the control of a
3026 @var{template} string. Return a newly created date object.
3028 Literal characters in @var{template} must match characters in
3029 @var{input} and @samp{~} escapes must match the input forms described
3030 in the table below. ``Skip to'' means characters up to one of the
3031 given type are ignored, or ``no skip'' for no skipping. ``Read'' is
3032 what's then read, and ``Set'' is the field affected in the date
3035 For example @samp{~Y} skips input characters until a digit is reached,
3036 at which point it expects a year and stores that to the year field of
3039 @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}}
3051 @tab @nicode{char-alphabetic?}
3052 @tab locale abbreviated weekday name
3056 @tab @nicode{char-alphabetic?}
3057 @tab locale full weekday name
3060 @c Note that the SRFI spec says that ~b and ~B don't set anything,
3061 @c but that looks like a mistake. The reference implementation sets
3062 @c the month field, which seems sensible and is what we describe
3066 @tab @nicode{char-alphabetic?}
3067 @tab locale abbreviated month name
3068 @tab @nicode{date-month}
3071 @tab @nicode{char-alphabetic?}
3072 @tab locale full month name
3073 @tab @nicode{date-month}
3076 @tab @nicode{char-numeric?}
3078 @tab @nicode{date-day}
3082 @tab day of month, blank padded
3083 @tab @nicode{date-day}
3086 @tab same as @samp{~b}
3089 @tab @nicode{char-numeric?}
3091 @tab @nicode{date-hour}
3095 @tab hour, blank padded
3096 @tab @nicode{date-hour}
3099 @tab @nicode{char-numeric?}
3101 @tab @nicode{date-month}
3104 @tab @nicode{char-numeric?}
3106 @tab @nicode{date-minute}
3109 @tab @nicode{char-numeric?}
3111 @tab @nicode{date-second}
3116 @tab @nicode{date-year} within 50 years
3119 @tab @nicode{char-numeric?}
3121 @tab @nicode{date-year}
3126 @tab date-zone-offset
3129 Notice that the weekday matching forms don't affect the date object
3130 returned, instead the weekday will be derived from the day, month and
3133 Conversion is locale-dependent on systems that support it
3134 (@pxref{Accessing Locale Information}). @xref{Locales,
3135 @code{setlocale}}, for information on how to change the current
3140 @subsection SRFI-23 - Error Reporting
3143 The SRFI-23 @code{error} procedure is always available.
3146 @subsection SRFI-26 - specializing parameters
3148 @cindex parameter specialize
3149 @cindex argument specialize
3150 @cindex specialize parameter
3152 This SRFI provides a syntax for conveniently specializing selected
3153 parameters of a function. It can be used with,
3156 (use-modules (srfi srfi-26))
3159 @deffn {library syntax} cut slot @dots{}
3160 @deffnx {library syntax} cute slot @dots{}
3161 Return a new procedure which will make a call (@var{slot} @dots{}) but
3162 with selected parameters specialized to given expressions.
3164 An example will illustrate the idea. The following is a
3165 specialization of @code{write}, sending output to
3166 @code{my-output-port},
3169 (cut write <> my-output-port)
3171 (lambda (obj) (write obj my-output-port))
3174 The special symbol @code{<>} indicates a slot to be filled by an
3175 argument to the new procedure. @code{my-output-port} on the other
3176 hand is an expression to be evaluated and passed, ie.@: it specializes
3177 the behaviour of @code{write}.
3181 A slot to be filled by an argument from the created procedure.
3182 Arguments are assigned to @code{<>} slots in the order they appear in
3183 the @code{cut} form, there's no way to re-arrange arguments.
3185 The first argument to @code{cut} is usually a procedure (or expression
3186 giving a procedure), but @code{<>} is allowed there too. For example,
3191 (lambda (proc) (proc 1 2 3))
3195 A slot to be filled by all remaining arguments from the new procedure.
3196 This can only occur at the end of a @code{cut} form.
3198 For example, a procedure taking a variable number of arguments like
3199 @code{max} but in addition enforcing a lower bound,
3202 (define my-lower-bound 123)
3204 (cut max my-lower-bound <...>)
3206 (lambda arglist (apply max my-lower-bound arglist))
3210 For @code{cut} the specializing expressions are evaluated each time
3211 the new procedure is called. For @code{cute} they're evaluated just
3212 once, when the new procedure is created. The name @code{cute} stands
3213 for ``@code{cut} with evaluated arguments''. In all cases the
3214 evaluations take place in an unspecified order.
3216 The following illustrates the difference between @code{cut} and
3220 (cut format <> "the time is ~s" (current-time))
3222 (lambda (port) (format port "the time is ~s" (current-time)))
3224 (cute format <> "the time is ~s" (current-time))
3226 (let ((val (current-time)))
3227 (lambda (port) (format port "the time is ~s" val))
3230 (There's no provision for a mixture of @code{cut} and @code{cute}
3231 where some expressions would be evaluated every time but others
3232 evaluated only once.)
3234 @code{cut} is really just a shorthand for the sort of @code{lambda}
3235 forms shown in the above examples. But notice @code{cut} avoids the
3236 need to name unspecialized parameters, and is more compact. Use in
3237 functional programming style or just with @code{map}, @code{for-each}
3238 or similar is typical.
3241 (map (cut * 2 <>) '(1 2 3 4))
3243 (for-each (cut write <> my-port) my-list)
3248 @subsection SRFI-27 - Sources of Random Bits
3251 This subsection is based on the
3252 @uref{http://srfi.schemers.org/srfi-27/srfi-27.html, specification of
3253 SRFI-27} written by Sebastian Egner.
3255 @c The copyright notice and license text of the SRFI-27 specification is
3256 @c reproduced below:
3258 @c Copyright (C) Sebastian Egner (2002). All Rights Reserved.
3260 @c Permission is hereby granted, free of charge, to any person obtaining a
3261 @c copy of this software and associated documentation files (the
3262 @c "Software"), to deal in the Software without restriction, including
3263 @c without limitation the rights to use, copy, modify, merge, publish,
3264 @c distribute, sublicense, and/or sell copies of the Software, and to
3265 @c permit persons to whom the Software is furnished to do so, subject to
3266 @c the following conditions:
3268 @c The above copyright notice and this permission notice shall be included
3269 @c in all copies or substantial portions of the Software.
3271 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3272 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3273 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3274 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3275 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3276 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3277 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3279 This SRFI provides access to a (pseudo) random number generator; for
3280 Guile's built-in random number facilities, which SRFI-27 is implemented
3281 upon, @xref{Random}. With SRFI-27, random numbers are obtained from a
3282 @emph{random source}, which encapsulates a random number generation
3283 algorithm and its state.
3286 * SRFI-27 Default Random Source:: Obtaining random numbers
3287 * SRFI-27 Random Sources:: Creating and manipulating random sources
3288 * SRFI-27 Random Number Generators:: Obtaining random number generators
3291 @node SRFI-27 Default Random Source
3292 @subsubsection The Default Random Source
3295 @defun random-integer n
3296 Return a random number between zero (inclusive) and @var{n} (exclusive),
3297 using the default random source. The numbers returned have a uniform
3302 Return a random number in (0,1), using the default random source. The
3303 numbers returned have a uniform distribution.
3306 @defun default-random-source
3307 A random source from which @code{random-integer} and @code{random-real}
3308 have been derived using @code{random-source-make-integers} and
3309 @code{random-source-make-reals} (@pxref{SRFI-27 Random Number Generators}
3310 for those procedures). Note that an assignment to
3311 @code{default-random-source} does not change @code{random-integer} or
3312 @code{random-real}; it is also strongly recommended not to assign a new
3316 @node SRFI-27 Random Sources
3317 @subsubsection Random Sources
3320 @defun make-random-source
3321 Create a new random source. The stream of random numbers obtained from
3322 each random source created by this procedure will be identical, unless
3323 its state is changed by one of the procedures below.
3326 @defun random-source? object
3327 Tests whether @var{object} is a random source. Random sources are a
3331 @defun random-source-randomize! source
3332 Attempt to set the state of the random source to a truly random value.
3333 The current implementation uses a seed based on the current system time.
3336 @defun random-source-pseudo-randomize! source i j
3337 Changes the state of the random source s into the initial state of the
3338 (@var{i}, @var{j})-th independent random source, where @var{i} and
3339 @var{j} are non-negative integers. This procedure provides a mechanism
3340 to obtain a large number of independent random sources (usually all
3341 derived from the same backbone generator), indexed by two integers. In
3342 contrast to @code{random-source-randomize!}, this procedure is entirely
3346 The state associated with a random state can be obtained an reinstated
3347 with the following procedures:
3349 @defun random-source-state-ref source
3350 @defunx random-source-state-set! source state
3351 Get and set the state of a random source. No assumptions should be made
3352 about the nature of the state object, besides it having an external
3353 representation (i.e.@: it can be passed to @code{write} and subsequently
3357 @node SRFI-27 Random Number Generators
3358 @subsubsection Obtaining random number generator procedures
3361 @defun random-source-make-integers source
3362 Obtains a procedure to generate random integers using the random source
3363 @var{source}. The returned procedure takes a single argument @var{n},
3364 which must be a positive integer, and returns the next uniformly
3365 distributed random integer from the interval @{0, ..., @var{n}-1@} by
3366 advancing the state of @var{source}.
3368 If an application obtains and uses several generators for the same
3369 random source @var{source}, a call to any of these generators advances
3370 the state of @var{source}. Hence, the generators do not produce the
3371 same sequence of random integers each but rather share a state. This
3372 also holds for all other types of generators derived from a fixed random
3375 While the SRFI text specifies that ``Implementations that support
3376 concurrency make sure that the state of a generator is properly
3377 advanced'', this is currently not the case in Guile's implementation of
3378 SRFI-27, as it would cause a severe performance penalty. So in
3379 multi-threaded programs, you either must perform locking on random
3380 sources shared between threads yourself, or use different random sources
3381 for multiple threads.
3384 @defun random-source-make-reals source
3385 @defunx random-source-make-reals source unit
3386 Obtains a procedure to generate random real numbers @math{0 < x < 1}
3387 using the random source @var{source}. The procedure rand is called
3390 The optional parameter @var{unit} determines the type of numbers being
3391 produced by the returned procedure and the quantization of the output.
3392 @var{unit} must be a number such that @math{0 < @var{unit} < 1}. The
3393 numbers created by the returned procedure are of the same numerical type
3394 as @var{unit} and the potential output values are spaced by at most
3395 @var{unit}. One can imagine rand to create numbers as @var{x} *
3396 @var{unit} where @var{x} is a random integer in @{1, ...,
3397 floor(1/unit)-1@}. Note, however, that this need not be the way the
3398 values are actually created and that the actual resolution of rand can
3399 be much higher than unit. In case @var{unit} is absent it defaults to a
3400 reasonably small value (related to the width of the mantissa of an
3401 efficient number format).
3405 @subsection SRFI-30 - Nested Multi-line Comments
3408 Starting from version 2.0, Guile's @code{read} supports SRFI-30/R6RS
3409 nested multi-line comments by default, @ref{Block Comments}.
3412 @subsection SRFI-31 - A special form `rec' for recursive evaluation
3414 @cindex recursive expression
3417 SRFI-31 defines a special form that can be used to create
3418 self-referential expressions more conveniently. The syntax is as
3423 <rec expression> --> (rec <variable> <expression>)
3424 <rec expression> --> (rec (<variable>+) <body>)
3428 The first syntax can be used to create self-referential expressions,
3432 guile> (define tmp (rec ones (cons 1 (delay ones))))
3435 The second syntax can be used to create anonymous recursive functions:
3438 guile> (define tmp (rec (display-n item n)
3440 (begin (display n) (display-n (- n 1))))))
3448 @subsection SRFI-34 - Exception handling for programs
3451 Guile provides an implementation of
3452 @uref{http://srfi.schemers.org/srfi-34/srfi-34.html, SRFI-34's exception
3453 handling mechanisms} as an alternative to its own built-in mechanisms
3454 (@pxref{Exceptions}). It can be made available as follows:
3457 (use-modules (srfi srfi-34))
3460 @c FIXME: Document it.
3464 @subsection SRFI-35 - Conditions
3470 @uref{http://srfi.schemers.org/srfi-35/srfi-35.html, SRFI-35} implements
3471 @dfn{conditions}, a data structure akin to records designed to convey
3472 information about exceptional conditions between parts of a program. It
3473 is normally used in conjunction with SRFI-34's @code{raise}:
3476 (raise (condition (&message
3477 (message "An error occurred"))))
3480 Users can define @dfn{condition types} containing arbitrary information.
3481 Condition types may inherit from one another. This allows the part of
3482 the program that handles (or ``catches'') conditions to get accurate
3483 information about the exceptional condition that arose.
3485 SRFI-35 conditions are made available using:
3488 (use-modules (srfi srfi-35))
3491 The procedures available to manipulate condition types are the
3494 @deffn {Scheme Procedure} make-condition-type id parent field-names
3495 Return a new condition type named @var{id}, inheriting from
3496 @var{parent}, and with the fields whose names are listed in
3497 @var{field-names}. @var{field-names} must be a list of symbols and must
3498 not contain names already used by @var{parent} or one of its supertypes.
3501 @deffn {Scheme Procedure} condition-type? obj
3502 Return true if @var{obj} is a condition type.
3505 Conditions can be created and accessed with the following procedures:
3507 @deffn {Scheme Procedure} make-condition type . field+value
3508 Return a new condition of type @var{type} with fields initialized as
3509 specified by @var{field+value}, a sequence of field names (symbols) and
3510 values as in the following example:
3513 (let ((&ct (make-condition-type 'foo &condition '(a b c))))
3514 (make-condition &ct 'a 1 'b 2 'c 3))
3517 Note that all fields of @var{type} and its supertypes must be specified.
3520 @deffn {Scheme Procedure} make-compound-condition . conditions
3521 Return a new compound condition composed of @var{conditions}. The
3522 returned condition has the type of each condition of @var{conditions}
3523 (per @code{condition-has-type?}).
3526 @deffn {Scheme Procedure} condition-has-type? c type
3527 Return true if condition @var{c} has type @var{type}.
3530 @deffn {Scheme Procedure} condition-ref c field-name
3531 Return the value of the field named @var{field-name} from condition @var{c}.
3533 If @var{c} is a compound condition and several underlying condition
3534 types contain a field named @var{field-name}, then the value of the
3535 first such field is returned, using the order in which conditions were
3536 passed to @var{make-compound-condition}.
3539 @deffn {Scheme Procedure} extract-condition c type
3540 Return a condition of condition type @var{type} with the field values
3541 specified by @var{c}.
3543 If @var{c} is a compound condition, extract the field values from the
3544 subcondition belonging to @var{type} that appeared first in the call to
3545 @code{make-compound-condition} that created the condition.
3548 Convenience macros are also available to create condition types and
3551 @deffn {library syntax} define-condition-type type supertype predicate field-spec...
3552 Define a new condition type named @var{type} that inherits from
3553 @var{supertype}. In addition, bind @var{predicate} to a type predicate
3554 that returns true when passed a condition of type @var{type} or any of
3555 its subtypes. @var{field-spec} must have the form @code{(field
3556 accessor)} where @var{field} is the name of field of @var{type} and
3557 @var{accessor} is the name of a procedure to access field @var{field} in
3558 conditions of type @var{type}.
3560 The example below defines condition type @code{&foo}, inheriting from
3561 @code{&condition} with fields @code{a}, @code{b} and @code{c}:
3564 (define-condition-type &foo &condition
3572 @deffn {library syntax} condition type-field-bindings...
3573 Return a new condition, or compound condition, initialized according to
3574 @var{type-field-bindings}. Each @var{type-field-binding} must have the
3575 form @code{(type field-specs...)}, where @var{type} is the name of a
3576 variable bound to condition type; each @var{field-spec} must have the
3577 form @code{(field-name value)} where @var{field-name} is a symbol
3578 denoting the field being initialized to @var{value}. As for
3579 @code{make-condition}, all fields must be specified.
3581 The following example returns a simple condition:
3584 (condition (&message (message "An error occurred")))
3587 The one below returns a compound condition:
3590 (condition (&message (message "An error occurred"))
3595 Finally, SRFI-35 defines a several standard condition types.
3598 This condition type is the root of all condition types. It has no
3603 A condition type that carries a message describing the nature of the
3604 condition to humans.
3607 @deffn {Scheme Procedure} message-condition? c
3608 Return true if @var{c} is of type @code{&message} or one of its
3612 @deffn {Scheme Procedure} condition-message c
3613 Return the message associated with message condition @var{c}.
3617 This type describes conditions serious enough that they cannot safely be
3618 ignored. It has no fields.
3621 @deffn {Scheme Procedure} serious-condition? c
3622 Return true if @var{c} is of type @code{&serious} or one of its
3627 This condition describes errors, typically caused by something that has
3628 gone wrong in the interaction of the program with the external world or
3632 @deffn {Scheme Procedure} error? c
3633 Return true if @var{c} is of type @code{&error} or one of its subtypes.
3637 @subsection SRFI-37 - args-fold
3640 This is a processor for GNU @code{getopt_long}-style program
3641 arguments. It provides an alternative, less declarative interface
3642 than @code{getopt-long} in @code{(ice-9 getopt-long)}
3643 (@pxref{getopt-long,,The (ice-9 getopt-long) Module}). Unlike
3644 @code{getopt-long}, it supports repeated options and any number of
3645 short and long names per option. Access it with:
3648 (use-modules (srfi srfi-37))
3651 @acronym{SRFI}-37 principally provides an @code{option} type and the
3652 @code{args-fold} function. To use the library, create a set of
3653 options with @code{option} and use it as a specification for invoking
3656 Here is an example of a simple argument processor for the typical
3657 @samp{--version} and @samp{--help} options, which returns a backwards
3658 list of files given on the command line:
3661 (args-fold (cdr (program-arguments))
3662 (let ((display-and-exit-proc
3664 (lambda (opt name arg loads)
3665 (display msg) (quit)))))
3666 (list (option '(#\v "version") #f #f
3667 (display-and-exit-proc "Foo version 42.0\n"))
3668 (option '(#\h "help") #f #f
3669 (display-and-exit-proc
3670 "Usage: foo scheme-file ..."))))
3671 (lambda (opt name arg loads)
3672 (error "Unrecognized option `~A'" name))
3673 (lambda (op loads) (cons op loads))
3677 @deffn {Scheme Procedure} option names required-arg? optional-arg? processor
3678 Return an object that specifies a single kind of program option.
3680 @var{names} is a list of command-line option names, and should consist of
3681 characters for traditional @code{getopt} short options and strings for
3682 @code{getopt_long}-style long options.
3684 @var{required-arg?} and @var{optional-arg?} are mutually exclusive;
3685 one or both must be @code{#f}. If @var{required-arg?}, the option
3686 must be followed by an argument on the command line, such as
3687 @samp{--opt=value} for long options, or an error will be signalled.
3688 If @var{optional-arg?}, an argument will be taken if available.
3690 @var{processor} is a procedure that takes at least 3 arguments, called
3691 when @code{args-fold} encounters the option: the containing option
3692 object, the name used on the command line, and the argument given for
3693 the option (or @code{#f} if none). The rest of the arguments are
3694 @code{args-fold} ``seeds'', and the @var{processor} should return
3698 @deffn {Scheme Procedure} option-names opt
3699 @deffnx {Scheme Procedure} option-required-arg? opt
3700 @deffnx {Scheme Procedure} option-optional-arg? opt
3701 @deffnx {Scheme Procedure} option-processor opt
3702 Return the specified field of @var{opt}, an option object, as
3703 described above for @code{option}.
3706 @deffn {Scheme Procedure} args-fold args options unrecognized-option-proc operand-proc seeds @dots{}
3707 Process @var{args}, a list of program arguments such as that returned
3708 by @code{(cdr (program-arguments))}, in order against @var{options}, a
3709 list of option objects as described above. All functions called take
3710 the ``seeds'', or the last multiple-values as multiple arguments,
3711 starting with @var{seeds}, and must return the new seeds. Return the
3714 Call @code{unrecognized-option-proc}, which is like an option object's
3715 processor, for any options not found in @var{options}.
3717 Call @code{operand-proc} with any items on the command line that are
3718 not named options. This includes arguments after @samp{--}. It is
3719 called with the argument in question, as well as the seeds.
3723 @subsection SRFI-38 - External Representation for Data With Shared Structure
3726 This subsection is based on
3727 @uref{http://srfi.schemers.org/srfi-38/srfi-38.html, the specification
3728 of SRFI-38} written by Ray Dillinger.
3730 @c Copyright (C) Ray Dillinger 2003. All Rights Reserved.
3732 @c Permission is hereby granted, free of charge, to any person obtaining a
3733 @c copy of this software and associated documentation files (the
3734 @c "Software"), to deal in the Software without restriction, including
3735 @c without limitation the rights to use, copy, modify, merge, publish,
3736 @c distribute, sublicense, and/or sell copies of the Software, and to
3737 @c permit persons to whom the Software is furnished to do so, subject to
3738 @c the following conditions:
3740 @c The above copyright notice and this permission notice shall be included
3741 @c in all copies or substantial portions of the Software.
3743 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3744 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3745 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3746 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3747 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3748 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3749 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3751 This SRFI creates an alternative external representation for data
3752 written and read using @code{write-with-shared-structure} and
3753 @code{read-with-shared-structure}. It is identical to the grammar for
3754 external representation for data written and read with @code{write} and
3755 @code{read} given in section 7 of R5RS, except that the single
3759 <datum> --> <simple datum> | <compound datum>
3762 is replaced by the following five productions:
3765 <datum> --> <defining datum> | <nondefining datum> | <defined datum>
3766 <defining datum> --> #<indexnum>=<nondefining datum>
3767 <defined datum> --> #<indexnum>#
3768 <nondefining datum> --> <simple datum> | <compound datum>
3769 <indexnum> --> <digit 10>+
3772 @deffn {Scheme procedure} write-with-shared-structure obj
3773 @deffnx {Scheme procedure} write-with-shared-structure obj port
3774 @deffnx {Scheme procedure} write-with-shared-structure obj port optarg
3776 Writes an external representation of @var{obj} to the given port.
3777 Strings that appear in the written representation are enclosed in
3778 doublequotes, and within those strings backslash and doublequote
3779 characters are escaped by backslashes. Character objects are written
3780 using the @code{#\} notation.
3782 Objects which denote locations rather than values (cons cells, vectors,
3783 and non-zero-length strings in R5RS scheme; also Guile's structs,
3784 bytevectors and ports and hash-tables), if they appear at more than one
3785 point in the data being written, are preceded by @samp{#@var{N}=} the
3786 first time they are written and replaced by @samp{#@var{N}#} all
3787 subsequent times they are written, where @var{N} is a natural number
3788 used to identify that particular object. If objects which denote
3789 locations occur only once in the structure, then
3790 @code{write-with-shared-structure} must produce the same external
3791 representation for those objects as @code{write}.
3793 @code{write-with-shared-structure} terminates in finite time and
3794 produces a finite representation when writing finite data.
3796 @code{write-with-shared-structure} returns an unspecified value. The
3797 @var{port} argument may be omitted, in which case it defaults to the
3798 value returned by @code{(current-output-port)}. The @var{optarg}
3799 argument may also be omitted. If present, its effects on the output and
3800 return value are unspecified but @code{write-with-shared-structure} must
3801 still write a representation that can be read by
3802 @code{read-with-shared-structure}. Some implementations may wish to use
3803 @var{optarg} to specify formatting conventions, numeric radixes, or
3804 return values. Guile's implementation ignores @var{optarg}.
3806 For example, the code
3809 (begin (define a (cons 'val1 'val2))
3811 (write-with-shared-structure a))
3814 should produce the output @code{#1=(val1 . #1#)}. This shows a cons
3815 cell whose @code{cdr} contains itself.
3819 @deffn {Scheme procedure} read-with-shared-structure
3820 @deffnx {Scheme procedure} read-with-shared-structure port
3822 @code{read-with-shared-structure} converts the external representations
3823 of Scheme objects produced by @code{write-with-shared-structure} into
3824 Scheme objects. That is, it is a parser for the nonterminal
3825 @samp{<datum>} in the augmented external representation grammar defined
3826 above. @code{read-with-shared-structure} returns the next object
3827 parsable from the given input port, updating @var{port} to point to the
3828 first character past the end of the external representation of the
3831 If an end-of-file is encountered in the input before any characters are
3832 found that can begin an object, then an end-of-file object is returned.
3833 The port remains open, and further attempts to read it (by
3834 @code{read-with-shared-structure} or @code{read} will also return an
3835 end-of-file object. If an end of file is encountered after the
3836 beginning of an object's external representation, but the external
3837 representation is incomplete and therefore not parsable, an error is
3840 The @var{port} argument may be omitted, in which case it defaults to the
3841 value returned by @code{(current-input-port)}. It is an error to read
3847 @subsection SRFI-39 - Parameters
3849 @cindex parameter object
3852 This SRFI provides parameter objects, which implement dynamically
3853 bound locations for values. The functions below are available from
3856 (use-modules (srfi srfi-39))
3859 A parameter object is a procedure. Called with no arguments it
3860 returns its value, called with one argument it sets the value.
3863 (define my-param (make-parameter 123))
3864 (my-param) @result{} 123
3866 (my-param) @result{} 456
3869 The @code{parameterize} special form establishes new locations for
3870 parameters, those new locations having effect within the dynamic scope
3871 of the @code{parameterize} body. Leaving restores the previous
3872 locations, or re-entering through a saved continuation will again use
3876 (parameterize ((my-param 789))
3877 (my-param) @result{} 789
3879 (my-param) @result{} 456
3882 Parameters are like dynamically bound variables in other Lisp dialects.
3883 They allow an application to establish parameter settings (as the name
3884 suggests) just for the execution of a particular bit of code,
3885 restoring when done. Examples of such parameters might be
3886 case-sensitivity for a search, or a prompt for user input.
3888 Global variables are not as good as parameter objects for this sort of
3889 thing. Changes to them are visible to all threads, but in Guile
3890 parameter object locations are per-thread, thereby truly limiting the
3891 effect of @code{parameterize} to just its dynamic execution.
3893 Passing arguments to functions is thread-safe, but that soon becomes
3894 tedious when there's more than a few or when they need to pass down
3895 through several layers of calls before reaching the point they should
3896 affect. And introducing a new setting to existing code is often
3897 easier with a parameter object than adding arguments.
3901 @defun make-parameter init [converter]
3902 Return a new parameter object, with initial value @var{init}.
3904 A parameter object is a procedure. When called @code{(param)} it
3905 returns its value, or a call @code{(param val)} sets its value. For
3909 (define my-param (make-parameter 123))
3910 (my-param) @result{} 123
3913 (my-param) @result{} 456
3916 If a @var{converter} is given, then a call @code{(@var{converter}
3917 val)} is made for each value set, its return is the value stored.
3918 Such a call is made for the @var{init} initial value too.
3920 A @var{converter} allows values to be validated, or put into a
3921 canonical form. For example,
3924 (define my-param (make-parameter 123
3926 (if (not (number? val))
3927 (error "must be a number"))
3928 (inexact->exact val))))
3930 (my-param) @result{} 3/4
3934 @deffn {library syntax} parameterize ((param value) @dots{}) body @dots{}
3935 Establish a new dynamic scope with the given @var{param}s bound to new
3936 locations and set to the given @var{value}s. @var{body} is evaluated
3937 in that environment, the result is the return from the last form in
3940 Each @var{param} is an expression which is evaluated to get the
3941 parameter object. Often this will just be the name of a variable
3942 holding the object, but it can be anything that evaluates to a
3945 The @var{param} expressions and @var{value} expressions are all
3946 evaluated before establishing the new dynamic bindings, and they're
3947 evaluated in an unspecified order.
3952 (define prompt (make-parameter "Type something: "))
3957 (parameterize ((prompt "Type a number: "))
3963 @deffn {Parameter object} current-input-port [new-port]
3964 @deffnx {Parameter object} current-output-port [new-port]
3965 @deffnx {Parameter object} current-error-port [new-port]
3966 This SRFI extends the core @code{current-input-port} and
3967 @code{current-output-port}, making them parameter objects. The
3968 Guile-specific @code{current-error-port} is extended too, for
3969 consistency. (@pxref{Default Ports}.)
3971 This is an upwardly compatible extension, a plain call like
3972 @code{(current-input-port)} still returns the current input port, and
3973 @code{set-current-input-port} can still be used. But the port can now
3974 also be set with @code{(current-input-port my-port)} and bound
3975 dynamically with @code{parameterize}.
3978 @defun with-parameters* param-list value-list thunk
3979 Establish a new dynamic scope, as per @code{parameterize} above,
3980 taking parameters from @var{param-list} and corresponding values from
3981 @var{values-list}. A call @code{(@var{thunk})} is made in the new
3982 scope and the result from that @var{thunk} is the return from
3983 @code{with-parameters*}.
3985 This function is a Guile-specific addition to the SRFI, it's similar
3986 to the core @code{with-fluids*} (@pxref{Fluids and Dynamic States}).
3991 Parameter objects are implemented using fluids (@pxref{Fluids and
3992 Dynamic States}), so each dynamic state has it's own parameter
3993 locations. That includes the separate locations when outside any
3994 @code{parameterize} form. When a parameter is created it gets a
3995 separate initial location in each dynamic state, all initialized to
3996 the given @var{init} value.
3998 As alluded to above, because each thread usually has a separate
3999 dynamic state, each thread has it's own locations behind parameter
4000 objects, and changes in one thread are not visible to any other. When
4001 a new dynamic state or thread is created, the values of parameters in
4002 the originating context are copied, into new locations.
4004 SRFI-39 doesn't specify the interaction between parameter objects and
4005 threads, so the threading behaviour described here should be regarded
4009 @subsection SRFI-42 - Eager Comprehensions
4012 See @uref{http://srfi.schemers.org/srfi-42/srfi-42.html, the
4013 specification of SRFI-42}.
4016 @subsection SRFI-45 - Primitives for Expressing Iterative Lazy Algorithms
4019 This subsection is based on @uref{http://srfi.schemers.org/srfi-45/srfi-45.html, the
4020 specification of SRFI-45} written by Andr@'e van Tonder.
4022 @c Copyright (C) André van Tonder (2003). All Rights Reserved.
4024 @c Permission is hereby granted, free of charge, to any person obtaining a
4025 @c copy of this software and associated documentation files (the
4026 @c "Software"), to deal in the Software without restriction, including
4027 @c without limitation the rights to use, copy, modify, merge, publish,
4028 @c distribute, sublicense, and/or sell copies of the Software, and to
4029 @c permit persons to whom the Software is furnished to do so, subject to
4030 @c the following conditions:
4032 @c The above copyright notice and this permission notice shall be included
4033 @c in all copies or substantial portions of the Software.
4035 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
4036 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
4037 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
4038 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
4039 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
4040 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
4041 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
4043 Lazy evaluation is traditionally simulated in Scheme using @code{delay}
4044 and @code{force}. However, these primitives are not powerful enough to
4045 express a large class of lazy algorithms that are iterative. Indeed, it
4046 is folklore in the Scheme community that typical iterative lazy
4047 algorithms written using delay and force will often require unbounded
4050 This SRFI provides set of three operations: @{@code{lazy}, @code{delay},
4051 @code{force}@}, which allow the programmer to succinctly express lazy
4052 algorithms while retaining bounded space behavior in cases that are
4053 properly tail-recursive. A general recipe for using these primitives is
4054 provided. An additional procedure @code{eager} is provided for the
4055 construction of eager promises in cases where efficiency is a concern.
4057 Although this SRFI redefines @code{delay} and @code{force}, the
4058 extension is conservative in the sense that the semantics of the subset
4059 @{@code{delay}, @code{force}@} in isolation (i.e., as long as the
4060 program does not use @code{lazy}) agrees with that in R5RS. In other
4061 words, no program that uses the R5RS definitions of delay and force will
4062 break if those definition are replaced by the SRFI-45 definitions of
4065 @deffn {Scheme Syntax} delay expression
4066 Takes an expression of arbitrary type @var{a} and returns a promise of
4067 type @code{(Promise @var{a})} which at some point in the future may be
4068 asked (by the @code{force} procedure) to evaluate the expression and
4069 deliver the resulting value.
4072 @deffn {Scheme Syntax} lazy expression
4073 Takes an expression of type @code{(Promise @var{a})} and returns a
4074 promise of type @code{(Promise @var{a})} which at some point in the
4075 future may be asked (by the @code{force} procedure) to evaluate the
4076 expression and deliver the resulting promise.
4079 @deffn {Scheme Procedure} force expression
4080 Takes an argument of type @code{(Promise @var{a})} and returns a value
4081 of type @var{a} as follows: If a value of type @var{a} has been computed
4082 for the promise, this value is returned. Otherwise, the promise is
4083 first evaluated, then overwritten by the obtained promise or value, and
4084 then force is again applied (iteratively) to the promise.
4087 @deffn {Scheme Procedure} eager expression
4088 Takes an argument of type @var{a} and returns a value of type
4089 @code{(Promise @var{a})}. As opposed to @code{delay}, the argument is
4090 evaluated eagerly. Semantically, writing @code{(eager expression)} is
4091 equivalent to writing
4094 (let ((value expression)) (delay value)).
4097 However, the former is more efficient since it does not require
4098 unnecessary creation and evaluation of thunks. We also have the
4102 (delay expression) = (lazy (eager expression))
4106 The following reduction rules may be helpful for reasoning about these
4107 primitives. However, they do not express the memoization and memory
4108 usage semantics specified above:
4111 (force (delay expression)) -> expression
4112 (force (lazy expression)) -> (force expression)
4113 (force (eager value)) -> value
4116 @subsubheading Correct usage
4118 We now provide a general recipe for using the primitives @{@code{lazy},
4119 @code{delay}, @code{force}@} to express lazy algorithms in Scheme. The
4120 transformation is best described by way of an example: Consider the
4121 stream-filter algorithm, expressed in a hypothetical lazy language as
4124 (define (stream-filter p? s)
4129 (cons h (stream-filter p? t))
4130 (stream-filter p? t)))))
4133 This algorithm can be expressed as follows in Scheme:
4136 (define (stream-filter p? s)
4138 (if (null? (force s)) (delay '())
4139 (let ((h (car (force s)))
4140 (t (cdr (force s))))
4142 (delay (cons h (stream-filter p? t)))
4143 (stream-filter p? t))))))
4150 wrap all constructors (e.g., @code{'()}, @code{cons}) with @code{delay},
4152 apply @code{force} to arguments of deconstructors (e.g., @code{car},
4153 @code{cdr} and @code{null?}),
4155 wrap procedure bodies with @code{(lazy ...)}.
4159 @subsection SRFI-55 - Requiring Features
4162 SRFI-55 provides @code{require-extension} which is a portable
4163 mechanism to load selected SRFI modules. This is implemented in the
4164 Guile core, there's no module needed to get SRFI-55 itself.
4166 @deffn {library syntax} require-extension clause@dots{}
4167 Require each of the given @var{clause} features, throwing an error if
4168 any are unavailable.
4170 A @var{clause} is of the form @code{(@var{identifier} arg...)}. The
4171 only @var{identifier} currently supported is @code{srfi} and the
4172 arguments are SRFI numbers. For example to get SRFI-1 and SRFI-6,
4175 (require-extension (srfi 1 6))
4178 @code{require-extension} can only be used at the top-level.
4180 A Guile-specific program can simply @code{use-modules} to load SRFIs
4181 not already in the core, @code{require-extension} is for programs
4182 designed to be portable to other Scheme implementations.
4187 @subsection SRFI-60 - Integers as Bits
4189 @cindex integers as bits
4190 @cindex bitwise logical
4192 This SRFI provides various functions for treating integers as bits and
4193 for bitwise manipulations. These functions can be obtained with,
4196 (use-modules (srfi srfi-60))
4199 Integers are treated as infinite precision twos-complement, the same
4200 as in the core logical functions (@pxref{Bitwise Operations}). And
4201 likewise bit indexes start from 0 for the least significant bit. The
4202 following functions in this SRFI are already in the Guile core,
4211 @code{integer-length},
4217 @defun bitwise-and n1 ...
4218 @defunx bitwise-ior n1 ...
4219 @defunx bitwise-xor n1 ...
4220 @defunx bitwise-not n
4221 @defunx any-bits-set? j k
4222 @defunx bit-set? index n
4223 @defunx arithmetic-shift n count
4224 @defunx bit-field n start end
4226 Aliases for @code{logand}, @code{logior}, @code{logxor},
4227 @code{lognot}, @code{logtest}, @code{logbit?}, @code{ash},
4228 @code{bit-extract} and @code{logcount} respectively.
4230 Note that the name @code{bit-count} conflicts with @code{bit-count} in
4231 the core (@pxref{Bit Vectors}).
4234 @defun bitwise-if mask n1 n0
4235 @defunx bitwise-merge mask n1 n0
4236 Return an integer with bits selected from @var{n1} and @var{n0}
4237 according to @var{mask}. Those bits where @var{mask} has 1s are taken
4238 from @var{n1}, and those where @var{mask} has 0s are taken from
4242 (bitwise-if 3 #b0101 #b1010) @result{} 9
4246 @defun log2-binary-factors n
4247 @defunx first-set-bit n
4248 Return a count of how many factors of 2 are present in @var{n}. This
4249 is also the bit index of the lowest 1 bit in @var{n}. If @var{n} is
4250 0, the return is @math{-1}.
4253 (log2-binary-factors 6) @result{} 1
4254 (log2-binary-factors -8) @result{} 3
4258 @defun copy-bit index n newbit
4259 Return @var{n} with the bit at @var{index} set according to
4260 @var{newbit}. @var{newbit} should be @code{#t} to set the bit to 1,
4261 or @code{#f} to set it to 0. Bits other than at @var{index} are
4262 unchanged in the return.
4265 (copy-bit 1 #b0101 #t) @result{} 7
4269 @defun copy-bit-field n newbits start end
4270 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4271 (exclusive) changed to the value @var{newbits}.
4273 The least significant bit in @var{newbits} goes to @var{start}, the
4274 next to @math{@var{start}+1}, etc. Anything in @var{newbits} past the
4275 @var{end} given is ignored.
4278 (copy-bit-field #b10000 #b11 1 3) @result{} #b10110
4282 @defun rotate-bit-field n count start end
4283 Return @var{n} with the bit field from @var{start} (inclusive) to
4284 @var{end} (exclusive) rotated upwards by @var{count} bits.
4286 @var{count} can be positive or negative, and it can be more than the
4287 field width (it'll be reduced modulo the width).
4290 (rotate-bit-field #b0110 2 1 4) @result{} #b1010
4294 @defun reverse-bit-field n start end
4295 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4296 (exclusive) reversed.
4299 (reverse-bit-field #b101001 2 4) @result{} #b100101
4303 @defun integer->list n [len]
4304 Return bits from @var{n} in the form of a list of @code{#t} for 1 and
4305 @code{#f} for 0. The least significant @var{len} bits are returned,
4306 and the first list element is the most significant of those bits. If
4307 @var{len} is not given, the default is @code{(integer-length @var{n})}
4308 (@pxref{Bitwise Operations}).
4311 (integer->list 6) @result{} (#t #t #f)
4312 (integer->list 1 4) @result{} (#f #f #f #t)
4316 @defun list->integer lst
4317 @defunx booleans->integer bool@dots{}
4318 Return an integer formed bitwise from the given @var{lst} list of
4319 booleans, or for @code{booleans->integer} from the @var{bool}
4322 Each boolean is @code{#t} for a 1 and @code{#f} for a 0. The first
4323 element becomes the most significant bit in the return.
4326 (list->integer '(#t #f #t #f)) @result{} 10
4332 @subsection SRFI-61 - A more general @code{cond} clause
4334 This SRFI extends RnRS @code{cond} to support test expressions that
4335 return multiple values, as well as arbitrary definitions of test
4336 success. SRFI 61 is implemented in the Guile core; there's no module
4337 needed to get SRFI-61 itself. Extended @code{cond} is documented in
4338 @ref{if cond case,, Simple Conditional Evaluation}.
4341 @subsection SRFI-67 - Compare procedures
4344 See @uref{http://srfi.schemers.org/srfi-67/srfi-67.html, the
4345 specification of SRFI-67}.
4348 @subsection SRFI-69 - Basic hash tables
4351 This is a portable wrapper around Guile's built-in hash table and weak
4352 table support. @xref{Hash Tables}, for information on that built-in
4353 support. Above that, this hash-table interface provides association
4354 of equality and hash functions with tables at creation time, so
4355 variants of each function are not required, as well as a procedure
4356 that takes care of most uses for Guile hash table handles, which this
4357 SRFI does not provide as such.
4362 (use-modules (srfi srfi-69))
4366 * SRFI-69 Creating hash tables::
4367 * SRFI-69 Accessing table items::
4368 * SRFI-69 Table properties::
4369 * SRFI-69 Hash table algorithms::
4372 @node SRFI-69 Creating hash tables
4373 @subsubsection Creating hash tables
4375 @deffn {Scheme Procedure} make-hash-table [equal-proc hash-proc #:weak weakness start-size]
4376 Create and answer a new hash table with @var{equal-proc} as the
4377 equality function and @var{hash-proc} as the hashing function.
4379 By default, @var{equal-proc} is @code{equal?}. It can be any
4380 two-argument procedure, and should answer whether two keys are the
4381 same for this table's purposes.
4383 My default @var{hash-proc} assumes that @code{equal-proc} is no
4384 coarser than @code{equal?} unless it is literally @code{string-ci=?}.
4385 If provided, @var{hash-proc} should be a two-argument procedure that
4386 takes a key and the current table size, and answers a reasonably good
4387 hash integer between 0 (inclusive) and the size (exclusive).
4389 @var{weakness} should be @code{#f} or a symbol indicating how ``weak''
4394 An ordinary non-weak hash table. This is the default.
4397 When the key has no more non-weak references at GC, remove that entry.
4400 When the value has no more non-weak references at GC, remove that
4404 When either has no more non-weak references at GC, remove the
4408 As a legacy of the time when Guile couldn't grow hash tables,
4409 @var{start-size} is an optional integer argument that specifies the
4410 approximate starting size for the hash table, which will be rounded to
4411 an algorithmically-sounder number.
4414 By @dfn{coarser} than @code{equal?}, we mean that for all @var{x} and
4415 @var{y} values where @code{(@var{equal-proc} @var{x} @var{y})},
4416 @code{(equal? @var{x} @var{y})} as well. If that does not hold for
4417 your @var{equal-proc}, you must provide a @var{hash-proc}.
4419 In the case of weak tables, remember that @dfn{references} above
4420 always refers to @code{eq?}-wise references. Just because you have a
4421 reference to some string @code{"foo"} doesn't mean that an association
4422 with key @code{"foo"} in a weak-key table @emph{won't} be collected;
4423 it only counts as a reference if the two @code{"foo"}s are @code{eq?},
4424 regardless of @var{equal-proc}. As such, it is usually only sensible
4425 to use @code{eq?} and @code{hashq} as the equivalence and hash
4426 functions for a weak table. @xref{Weak References}, for more
4427 information on Guile's built-in weak table support.
4429 @deffn {Scheme Procedure} alist->hash-table alist [equal-proc hash-proc #:weak weakness start-size]
4430 As with @code{make-hash-table}, but initialize it with the
4431 associations in @var{alist}. Where keys are repeated in @var{alist},
4432 the leftmost association takes precedence.
4435 @node SRFI-69 Accessing table items
4436 @subsubsection Accessing table items
4438 @deffn {Scheme Procedure} hash-table-ref table key [default-thunk]
4439 @deffnx {Scheme Procedure} hash-table-ref/default table key default
4440 Answer the value associated with @var{key} in @var{table}. If
4441 @var{key} is not present, answer the result of invoking the thunk
4442 @var{default-thunk}, which signals an error instead by default.
4444 @code{hash-table-ref/default} is a variant that requires a third
4445 argument, @var{default}, and answers @var{default} itself instead of
4449 @deffn {Scheme Procedure} hash-table-set! table key new-value
4450 Set @var{key} to @var{new-value} in @var{table}.
4453 @deffn {Scheme Procedure} hash-table-delete! table key
4454 Remove the association of @var{key} in @var{table}, if present. If
4458 @deffn {Scheme Procedure} hash-table-exists? table key
4459 Answer whether @var{key} has an association in @var{table}.
4462 @deffn {Scheme Procedure} hash-table-update! table key modifier [default-thunk]
4463 @deffnx {Scheme Procedure} hash-table-update!/default table key modifier default
4464 Replace @var{key}'s associated value in @var{table} by invoking
4465 @var{modifier} with one argument, the old value.
4467 If @var{key} is not present, and @var{default-thunk} is provided,
4468 invoke it with no arguments to get the ``old value'' to be passed to
4469 @var{modifier} as above. If @var{default-thunk} is not provided in
4470 such a case, signal an error.
4472 @code{hash-table-update!/default} is a variant that requires the
4473 fourth argument, which is used directly as the ``old value'' rather
4474 than as a thunk to be invoked to retrieve the ``old value''.
4477 @node SRFI-69 Table properties
4478 @subsubsection Table properties
4480 @deffn {Scheme Procedure} hash-table-size table
4481 Answer the number of associations in @var{table}. This is guaranteed
4482 to run in constant time for non-weak tables.
4485 @deffn {Scheme Procedure} hash-table-keys table
4486 Answer an unordered list of the keys in @var{table}.
4489 @deffn {Scheme Procedure} hash-table-values table
4490 Answer an unordered list of the values in @var{table}.
4493 @deffn {Scheme Procedure} hash-table-walk table proc
4494 Invoke @var{proc} once for each association in @var{table}, passing
4495 the key and value as arguments.
4498 @deffn {Scheme Procedure} hash-table-fold table proc init
4499 Invoke @code{(@var{proc} @var{key} @var{value} @var{previous})} for
4500 each @var{key} and @var{value} in @var{table}, where @var{previous} is
4501 the result of the previous invocation, using @var{init} as the first
4502 @var{previous} value. Answer the final @var{proc} result.
4505 @deffn {Scheme Procedure} hash-table->alist table
4506 Answer an alist where each association in @var{table} is an
4507 association in the result.
4510 @node SRFI-69 Hash table algorithms
4511 @subsubsection Hash table algorithms
4513 Each hash table carries an @dfn{equivalence function} and a @dfn{hash
4514 function}, used to implement key lookups. Beginning users should
4515 follow the rules for consistency of the default @var{hash-proc}
4516 specified above. Advanced users can use these to implement their own
4517 equivalence and hash functions for specialized lookup semantics.
4519 @deffn {Scheme Procedure} hash-table-equivalence-function hash-table
4520 @deffnx {Scheme Procedure} hash-table-hash-function hash-table
4521 Answer the equivalence and hash function of @var{hash-table}, respectively.
4524 @deffn {Scheme Procedure} hash obj [size]
4525 @deffnx {Scheme Procedure} string-hash obj [size]
4526 @deffnx {Scheme Procedure} string-ci-hash obj [size]
4527 @deffnx {Scheme Procedure} hash-by-identity obj [size]
4528 Answer a hash value appropriate for equality predicate @code{equal?},
4529 @code{string=?}, @code{string-ci=?}, and @code{eq?}, respectively.
4532 @code{hash} is a backwards-compatible replacement for Guile's built-in
4536 @subsection SRFI-88 Keyword Objects
4538 @cindex keyword objects
4540 @uref{http://srfi.schemers.org/srfi-88/srfi-88.html, SRFI-88} provides
4541 @dfn{keyword objects}, which are equivalent to Guile's keywords
4542 (@pxref{Keywords}). SRFI-88 keywords can be entered using the
4543 @dfn{postfix keyword syntax}, which consists of an identifier followed
4544 by @code{:} (@pxref{Scheme Read, @code{postfix} keyword syntax}).
4545 SRFI-88 can be made available with:
4548 (use-modules (srfi srfi-88))
4551 Doing so installs the right reader option for keyword syntax, using
4552 @code{(read-set! keywords 'postfix)}. It also provides the procedures
4555 @deffn {Scheme Procedure} keyword? obj
4556 Return @code{#t} if @var{obj} is a keyword. This is the same procedure
4557 as the same-named built-in procedure (@pxref{Keyword Procedures,
4561 (keyword? foo:) @result{} #t
4562 (keyword? 'foo:) @result{} #t
4563 (keyword? "foo") @result{} #f
4567 @deffn {Scheme Procedure} keyword->string kw
4568 Return the name of @var{kw} as a string, i.e., without the trailing
4569 colon. The returned string may not be modified, e.g., with
4573 (keyword->string foo:) @result{} "foo"
4577 @deffn {Scheme Procedure} string->keyword str
4578 Return the keyword object whose name is @var{str}.
4581 (keyword->string (string->keyword "a b c")) @result{} "a b c"
4586 @subsection SRFI-98 Accessing environment variables.
4588 @cindex environment variables
4590 This is a portable wrapper around Guile's built-in support for
4591 interacting with the current environment, @xref{Runtime Environment}.
4593 @deffn {Scheme Procedure} get-environment-variable name
4594 Returns a string containing the value of the environment variable
4595 given by the string @code{name}, or @code{#f} if the named
4596 environment variable is not found. This is equivalent to
4597 @code{(getenv name)}.
4600 @deffn {Scheme Procedure} get-environment-variables
4601 Returns the names and values of all the environment variables as an
4602 association list in which both the keys and the values are strings.
4605 @c srfi-modules.texi ends here
4608 @c TeX-master: "guile.texi"