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, 2012, 2013
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.
57 * SRFI-105:: Curly-infix expressions.
61 @node About SRFI Usage
62 @subsection About SRFI Usage
64 @c FIXME::martin: Review me!
66 SRFI support in Guile is currently implemented partly in the core
67 library, and partly as add-on modules. That means that some SRFIs are
68 automatically available when the interpreter is started, whereas the
69 other SRFIs require you to use the appropriate support module
72 There are several reasons for this inconsistency. First, the feature
73 checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be
74 available immediately, because it must be there when the user wants to
75 check for the Scheme implementation, that is, before she can know that
76 it is safe to use @code{use-modules} to load SRFI support modules. The
77 second reason is that some features defined in SRFIs had been
78 implemented in Guile before the developers started to add SRFI
79 implementations as modules (for example SRFI-13 (@pxref{SRFI-13})). In
80 the future, it is possible that SRFIs in the core library might be
81 factored out into separate modules, requiring explicit module loading
82 when they are needed. So you should be prepared to have to use
83 @code{use-modules} someday in the future to access SRFI-13 bindings. If
84 you want, you can do that already. We have included the module
85 @code{(srfi srfi-13)} in the distribution, which currently does nothing,
86 but ensures that you can write future-safe code.
88 Generally, support for a specific SRFI is made available by using
89 modules named @code{(srfi srfi-@var{number})}, where @var{number} is the
90 number of the SRFI needed. Another possibility is to use the command
91 line option @code{--use-srfi}, which will load the necessary modules
92 automatically (@pxref{Invoking Guile}).
96 @subsection SRFI-0 - cond-expand
99 This SRFI lets a portable Scheme program test for the presence of
100 certain features, and adapt itself by using different blocks of code,
101 or fail if the necessary features are not available. There's no
102 module to load, this is in the Guile core.
104 A program designed only for Guile will generally not need this
105 mechanism, such a program can of course directly use the various
106 documented parts of Guile.
108 @deffn syntax cond-expand (feature body@dots{}) @dots{}
109 Expand to the @var{body} of the first clause whose @var{feature}
110 specification is satisfied. It is an error if no @var{feature} is
113 Features are symbols such as @code{srfi-1}, and a feature
114 specification can use @code{and}, @code{or} and @code{not} forms to
115 test combinations. The last clause can be an @code{else}, to be used
118 For example, define a private version of @code{alist-cons} if SRFI-1
125 (define (alist-cons key val alist)
126 (cons (cons key val) alist))))
129 Or demand a certain set of SRFIs (list operations, string ports,
130 @code{receive} and string operations), failing if they're not
134 (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13)
140 The Guile core has the following features,
144 guile-2 ;; starting from Guile 2.x
153 Other SRFI feature symbols are defined once their code has been loaded
154 with @code{use-modules}, since only then are their bindings available.
156 The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is
157 a good way to load SRFIs to satisfy @code{cond-expand} when running a
160 Testing the @code{guile} feature allows a program to adapt itself to
161 the Guile module system, but still run on other Scheme systems. For
162 example the following demands SRFI-8 (@code{receive}), but also knows
163 how to load it with the Guile mechanism.
169 (use-modules (srfi srfi-8))))
172 @cindex @code{guile-2} SRFI-0 feature
173 @cindex portability between 2.0 and older versions
174 Likewise, testing the @code{guile-2} feature allows code to be portable
175 between Guile 2.0 and previous versions of Guile. For instance, it
176 makes it possible to write code that accounts for Guile 2.0's compiler,
177 yet be correctly interpreted on 1.8 and earlier versions:
180 (cond-expand (guile-2 (eval-when (compile)
181 ;; This must be evaluated at compile time.
182 (fluid-set! current-reader my-reader)))
184 ;; Earlier versions of Guile do not have a
185 ;; separate compilation phase.
186 (fluid-set! current-reader my-reader)))
189 It should be noted that @code{cond-expand} is separate from the
190 @code{*features*} mechanism (@pxref{Feature Tracking}), feature
191 symbols in one are unrelated to those in the other.
195 @subsection SRFI-1 - List library
199 @c FIXME::martin: Review me!
201 The list library defined in SRFI-1 contains a lot of useful list
202 processing procedures for construction, examining, destructuring and
203 manipulating lists and pairs.
205 Since SRFI-1 also defines some procedures which are already contained
206 in R5RS and thus are supported by the Guile core library, some list
207 and pair procedures which appear in the SRFI-1 document may not appear
208 in this section. So when looking for a particular list/pair
209 processing procedure, you should also have a look at the sections
210 @ref{Lists} and @ref{Pairs}.
213 * SRFI-1 Constructors:: Constructing new lists.
214 * SRFI-1 Predicates:: Testing list for specific properties.
215 * SRFI-1 Selectors:: Selecting elements from lists.
216 * SRFI-1 Length Append etc:: Length calculation and list appending.
217 * SRFI-1 Fold and Map:: Higher-order list processing.
218 * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates.
219 * SRFI-1 Searching:: Search for elements.
220 * SRFI-1 Deleting:: Delete elements from lists.
221 * SRFI-1 Association Lists:: Handle association lists.
222 * SRFI-1 Set Operations:: Use lists for representing sets.
225 @node SRFI-1 Constructors
226 @subsubsection Constructors
227 @cindex list constructor
229 @c FIXME::martin: Review me!
231 New lists can be constructed by calling one of the following
234 @deffn {Scheme Procedure} xcons d a
235 Like @code{cons}, but with interchanged arguments. Useful mostly when
236 passed to higher-order procedures.
239 @deffn {Scheme Procedure} list-tabulate n init-proc
240 Return an @var{n}-element list, where each list element is produced by
241 applying the procedure @var{init-proc} to the corresponding list
242 index. The order in which @var{init-proc} is applied to the indices
246 @deffn {Scheme Procedure} list-copy lst
247 Return a new list containing the elements of the list @var{lst}.
249 This function differs from the core @code{list-copy} (@pxref{List
250 Constructors}) in accepting improper lists too. And if @var{lst} is
251 not a pair at all then it's treated as the final tail of an improper
252 list and simply returned.
255 @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{}
256 Return a circular list containing the given arguments @var{elt1}
260 @deffn {Scheme Procedure} iota count [start step]
261 Return a list containing @var{count} numbers, starting from
262 @var{start} and adding @var{step} each time. The default @var{start}
263 is 0, the default @var{step} is 1. For example,
266 (iota 6) @result{} (0 1 2 3 4 5)
267 (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5)
270 This function takes its name from the corresponding primitive in the
275 @node SRFI-1 Predicates
276 @subsubsection Predicates
277 @cindex list predicate
279 @c FIXME::martin: Review me!
281 The procedures in this section test specific properties of lists.
283 @deffn {Scheme Procedure} proper-list? obj
284 Return @code{#t} if @var{obj} is a proper list, or @code{#f}
285 otherwise. This is the same as the core @code{list?} (@pxref{List
288 A proper list is a list which ends with the empty list @code{()} in
289 the usual way. The empty list @code{()} itself is a proper list too.
292 (proper-list? '(1 2 3)) @result{} #t
293 (proper-list? '()) @result{} #t
297 @deffn {Scheme Procedure} circular-list? obj
298 Return @code{#t} if @var{obj} is a circular list, or @code{#f}
301 A circular list is a list where at some point the @code{cdr} refers
302 back to a previous pair in the list (either the start or some later
303 point), so that following the @code{cdr}s takes you around in a
307 (define x (list 1 2 3 4))
308 (set-cdr! (last-pair x) (cddr x))
309 x @result{} (1 2 3 4 3 4 3 4 ...)
310 (circular-list? x) @result{} #t
314 @deffn {Scheme Procedure} dotted-list? obj
315 Return @code{#t} if @var{obj} is a dotted list, or @code{#f}
318 A dotted list is a list where the @code{cdr} of the last pair is not
319 the empty list @code{()}. Any non-pair @var{obj} is also considered a
320 dotted list, with length zero.
323 (dotted-list? '(1 2 . 3)) @result{} #t
324 (dotted-list? 99) @result{} #t
328 It will be noted that any Scheme object passes exactly one of the
329 above three tests @code{proper-list?}, @code{circular-list?} and
330 @code{dotted-list?}. Non-lists are @code{dotted-list?}, finite lists
331 are either @code{proper-list?} or @code{dotted-list?}, and infinite
332 lists are @code{circular-list?}.
335 @deffn {Scheme Procedure} null-list? lst
336 Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f}
337 otherwise. If something else than a proper or circular list is passed
338 as @var{lst}, an error is signalled. This procedure is recommended
339 for checking for the end of a list in contexts where dotted lists are
343 @deffn {Scheme Procedure} not-pair? obj
344 Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise.
345 This is shorthand notation @code{(not (pair? @var{obj}))} and is
346 supposed to be used for end-of-list checking in contexts where dotted
350 @deffn {Scheme Procedure} list= elt= list1 @dots{}
351 Return @code{#t} if all argument lists are equal, @code{#f} otherwise.
352 List equality is determined by testing whether all lists have the same
353 length and the corresponding elements are equal in the sense of the
354 equality predicate @var{elt=}. If no or only one list is given,
355 @code{#t} is returned.
359 @node SRFI-1 Selectors
360 @subsubsection Selectors
361 @cindex list selector
363 @c FIXME::martin: Review me!
365 @deffn {Scheme Procedure} first pair
366 @deffnx {Scheme Procedure} second pair
367 @deffnx {Scheme Procedure} third pair
368 @deffnx {Scheme Procedure} fourth pair
369 @deffnx {Scheme Procedure} fifth pair
370 @deffnx {Scheme Procedure} sixth pair
371 @deffnx {Scheme Procedure} seventh pair
372 @deffnx {Scheme Procedure} eighth pair
373 @deffnx {Scheme Procedure} ninth pair
374 @deffnx {Scheme Procedure} tenth pair
375 These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}.
378 @deffn {Scheme Procedure} car+cdr pair
379 Return two values, the @sc{car} and the @sc{cdr} of @var{pair}.
382 @deffn {Scheme Procedure} take lst i
383 @deffnx {Scheme Procedure} take! lst i
384 Return a list containing the first @var{i} elements of @var{lst}.
386 @code{take!} may modify the structure of the argument list @var{lst}
387 in order to produce the result.
390 @deffn {Scheme Procedure} drop lst i
391 Return a list containing all but the first @var{i} elements of
395 @deffn {Scheme Procedure} take-right lst i
396 Return a list containing the @var{i} last elements of @var{lst}.
397 The return shares a common tail with @var{lst}.
400 @deffn {Scheme Procedure} drop-right lst i
401 @deffnx {Scheme Procedure} drop-right! lst i
402 Return a list containing all but the @var{i} last elements of
405 @code{drop-right} always returns a new list, even when @var{i} is
406 zero. @code{drop-right!} may modify the structure of the argument
407 list @var{lst} in order to produce the result.
410 @deffn {Scheme Procedure} split-at lst i
411 @deffnx {Scheme Procedure} split-at! lst i
412 Return two values, a list containing the first @var{i} elements of the
413 list @var{lst} and a list containing the remaining elements.
415 @code{split-at!} may modify the structure of the argument list
416 @var{lst} in order to produce the result.
419 @deffn {Scheme Procedure} last lst
420 Return the last element of the non-empty, finite list @var{lst}.
424 @node SRFI-1 Length Append etc
425 @subsubsection Length, Append, Concatenate, etc.
427 @c FIXME::martin: Review me!
429 @deffn {Scheme Procedure} length+ lst
430 Return the length of the argument list @var{lst}. When @var{lst} is a
431 circular list, @code{#f} is returned.
434 @deffn {Scheme Procedure} concatenate list-of-lists
435 @deffnx {Scheme Procedure} concatenate! list-of-lists
436 Construct a list by appending all lists in @var{list-of-lists}.
438 @code{concatenate!} may modify the structure of the given lists in
439 order to produce the result.
441 @code{concatenate} is the same as @code{(apply append
442 @var{list-of-lists})}. It exists because some Scheme implementations
443 have a limit on the number of arguments a function takes, which the
444 @code{apply} might exceed. In Guile there is no such limit.
447 @deffn {Scheme Procedure} append-reverse rev-head tail
448 @deffnx {Scheme Procedure} append-reverse! rev-head tail
449 Reverse @var{rev-head}, append @var{tail} to it, and return the
450 result. This is equivalent to @code{(append (reverse @var{rev-head})
451 @var{tail})}, but its implementation is more efficient.
454 (append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)
457 @code{append-reverse!} may modify @var{rev-head} in order to produce
461 @deffn {Scheme Procedure} zip lst1 lst2 @dots{}
462 Return a list as long as the shortest of the argument lists, where
463 each element is a list. The first list contains the first elements of
464 the argument lists, the second list contains the second elements, and
468 @deffn {Scheme Procedure} unzip1 lst
469 @deffnx {Scheme Procedure} unzip2 lst
470 @deffnx {Scheme Procedure} unzip3 lst
471 @deffnx {Scheme Procedure} unzip4 lst
472 @deffnx {Scheme Procedure} unzip5 lst
473 @code{unzip1} takes a list of lists, and returns a list containing the
474 first elements of each list, @code{unzip2} returns two lists, the
475 first containing the first elements of each lists and the second
476 containing the second elements of each lists, and so on.
479 @deffn {Scheme Procedure} count pred lst1 lst2 @dots{}
480 Return a count of the number of times @var{pred} returns true when
481 called on elements from the given lists.
483 @var{pred} is called with @var{N} parameters @code{(@var{pred}
484 @var{elem1} @dots{} @var{elemN} )}, each element being from the
485 corresponding list. The first call is with the first element of each
486 list, the second with the second element 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 lst2 @dots{}
501 @deffnx {Scheme Procedure} fold-right proc init lst1 lst2 @dots{}
502 Apply @var{proc} to the elements of @var{lst1} @var{lst2} @dots{} to
503 build a result, and return that result.
505 Each @var{proc} call is @code{(@var{proc} @var{elem1} @var{elem2}
506 @dots{} @var{previous})}, where @var{elem1} is from @var{lst1},
507 @var{elem2} is from @var{lst2}, and so on. @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} @var{lst2} @dots{} 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 the
540 length of the shortest are ignored in the other @var{lst}s. At least
541 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 lst2 @dots{}
571 @deffnx {Scheme Procedure} pair-fold-right proc init lst1 lst2 @dots{}
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{}
843 Test whether any set of elements from @var{lst1} @var{lst2} @dots{}
844 satisfies @var{pred}. If so, the return value is the return value from
845 the successful @var{pred} call, or if not, the return value is
848 If there are n list arguments, then @var{pred} must be a predicate
849 taking n arguments. Each @var{pred} call is @code{(@var{pred}
850 @var{elem1} @var{elem2} @dots{} )} taking an element from each
851 @var{lst}. The calls are made successively for the first, second, etc.
852 elements of the lists, stopping when @var{pred} returns non-@code{#f},
853 or when the end of the shortest list is reached.
855 The @var{pred} call on the last set of elements (i.e., when the end of
856 the shortest list has been reached), if that point is reached, is a
860 @deffn {Scheme Procedure} every pred lst1 lst2 @dots{}
861 Test whether every set of elements from @var{lst1} @var{lst2} @dots{}
862 satisfies @var{pred}. If so, the return value is the return from the
863 final @var{pred} call, or if not, the return value is @code{#f}.
865 If there are n list arguments, then @var{pred} must be a predicate
866 taking n arguments. Each @var{pred} call is @code{(@var{pred}
867 @var{elem1} @var{elem2 @dots{}})} taking an element from each
868 @var{lst}. The calls are made successively for the first, second, etc.
869 elements of the lists, stopping if @var{pred} returns @code{#f}, or when
870 the end of any of the lists is reached.
872 The @var{pred} call on the last set of elements (i.e., when the end of
873 the shortest list has been reached) is a tail call.
875 If one of @var{lst1} @var{lst2} @dots{}is empty then no calls to
876 @var{pred} are made, and the return value is @code{#t}.
879 @deffn {Scheme Procedure} list-index pred lst1 lst2 @dots{}
880 Return the index of the first set of elements, one from each of
881 @var{lst1} @var{lst2} @dots{}, which satisfies @var{pred}.
883 @var{pred} is called as @code{(@var{elem1} @var{elem2 @dots{}})}.
884 Searching stops when the end of the shortest @var{lst} is reached.
885 The return index starts from 0 for the first set of elements. If no
886 set of elements pass, then the return value is @code{#f}.
889 (list-index odd? '(2 4 6 9)) @result{} 3
890 (list-index = '(1 2 3) '(3 1 2)) @result{} #f
894 @deffn {Scheme Procedure} member x lst [=]
895 Return the first sublist of @var{lst} whose @sc{car} is equal to
896 @var{x}. If @var{x} does not appear in @var{lst}, return @code{#f}.
898 Equality is determined by @code{equal?}, or by the equality predicate
899 @var{=} if given. @var{=} is called @code{(= @var{x} elem)},
900 ie.@: with the given @var{x} first, so for example to find the first
901 element greater than 5,
904 (member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9)
907 This version of @code{member} extends the core @code{member}
908 (@pxref{List Searching}) by accepting an equality predicate.
912 @node SRFI-1 Deleting
913 @subsubsection Deleting
916 @deffn {Scheme Procedure} delete x lst [=]
917 @deffnx {Scheme Procedure} delete! x lst [=]
918 Return a list containing the elements of @var{lst} but with those
919 equal to @var{x} deleted. The returned elements will be in the same
920 order as they were in @var{lst}.
922 Equality is determined by the @var{=} predicate, or @code{equal?} if
923 not given. An equality call is made just once for each element, but
924 the order in which the calls are made on the elements is unspecified.
926 The equality calls are always @code{(= x elem)}, ie.@: the given @var{x}
927 is first. This means for instance elements greater than 5 can be
928 deleted with @code{(delete 5 lst <)}.
930 @code{delete} does not modify @var{lst}, but the return might share a
931 common tail with @var{lst}. @code{delete!} may modify the structure
932 of @var{lst} to construct its return.
934 These functions extend the core @code{delete} and @code{delete!}
935 (@pxref{List Modification}) in accepting an equality predicate. See
936 also @code{lset-difference} (@pxref{SRFI-1 Set Operations}) for
937 deleting multiple elements from a list.
940 @deffn {Scheme Procedure} delete-duplicates lst [=]
941 @deffnx {Scheme Procedure} delete-duplicates! lst [=]
942 Return a list containing the elements of @var{lst} but without
945 When elements are equal, only the first in @var{lst} is retained.
946 Equal elements can be anywhere in @var{lst}, they don't have to be
947 adjacent. The returned list will have the retained elements in the
948 same order as they were in @var{lst}.
950 Equality is determined by the @var{=} predicate, or @code{equal?} if
951 not given. Calls @code{(= x y)} are made with element @var{x} being
952 before @var{y} in @var{lst}. A call is made at most once for each
953 combination, but the sequence of the calls across the elements is
956 @code{delete-duplicates} does not modify @var{lst}, but the return
957 might share a common tail with @var{lst}. @code{delete-duplicates!}
958 may modify the structure of @var{lst} to construct its return.
960 In the worst case, this is an @math{O(N^2)} algorithm because it must
961 check each element against all those preceding it. For long lists it
962 is more efficient to sort and then compare only adjacent elements.
966 @node SRFI-1 Association Lists
967 @subsubsection Association Lists
968 @cindex association list
971 @c FIXME::martin: Review me!
973 Association lists are described in detail in section @ref{Association
974 Lists}. The present section only documents the additional procedures
975 for dealing with association lists defined by SRFI-1.
977 @deffn {Scheme Procedure} assoc key alist [=]
978 Return the pair from @var{alist} which matches @var{key}. This
979 extends the core @code{assoc} (@pxref{Retrieving Alist Entries}) by
980 taking an optional @var{=} comparison procedure.
982 The default comparison is @code{equal?}. If an @var{=} parameter is
983 given it's called @code{(@var{=} @var{key} @var{alistcar})}, i.e.@: the
984 given target @var{key} is the first argument, and a @code{car} from
985 @var{alist} is second.
987 For example a case-insensitive string lookup,
990 (assoc "yy" '(("XX" . 1) ("YY" . 2)) string-ci=?)
995 @deffn {Scheme Procedure} alist-cons key datum alist
996 Cons a new association @var{key} and @var{datum} onto @var{alist} and
997 return the result. This is equivalent to
1000 (cons (cons @var{key} @var{datum}) @var{alist})
1003 @code{acons} (@pxref{Adding or Setting Alist Entries}) in the Guile
1004 core does the same thing.
1007 @deffn {Scheme Procedure} alist-copy alist
1008 Return a newly allocated copy of @var{alist}, that means that the
1009 spine of the list as well as the pairs are copied.
1012 @deffn {Scheme Procedure} alist-delete key alist [=]
1013 @deffnx {Scheme Procedure} alist-delete! key alist [=]
1014 Return a list containing the elements of @var{alist} but with those
1015 elements whose keys are equal to @var{key} deleted. The returned
1016 elements will be in the same order as they were in @var{alist}.
1018 Equality is determined by the @var{=} predicate, or @code{equal?} if
1019 not given. The order in which elements are tested is unspecified, but
1020 each equality call is made @code{(= key alistkey)}, i.e.@: the given
1021 @var{key} parameter is first and the key from @var{alist} second.
1022 This means for instance all associations with a key greater than 5 can
1023 be removed with @code{(alist-delete 5 alist <)}.
1025 @code{alist-delete} does not modify @var{alist}, but the return might
1026 share a common tail with @var{alist}. @code{alist-delete!} may modify
1027 the list structure of @var{alist} to construct its return.
1031 @node SRFI-1 Set Operations
1032 @subsubsection Set Operations on Lists
1033 @cindex list set operation
1035 Lists can be used to represent sets of objects. The procedures in
1036 this section operate on such lists as sets.
1038 Note that lists are not an efficient way to implement large sets. The
1039 procedures here typically take time @math{@var{m}@cross{}@var{n}} when
1040 operating on @var{m} and @var{n} element lists. Other data structures
1041 like trees, bitsets (@pxref{Bit Vectors}) or hash tables (@pxref{Hash
1042 Tables}) are faster.
1044 All these procedures take an equality predicate as the first argument.
1045 This predicate is used for testing the objects in the list sets for
1046 sameness. This predicate must be consistent with @code{eq?}
1047 (@pxref{Equality}) in the sense that if two list elements are
1048 @code{eq?} then they must also be equal under the predicate. This
1049 simply means a given object must be equal to itself.
1051 @deffn {Scheme Procedure} lset<= = list @dots{}
1052 Return @code{#t} if each list is a subset of the one following it.
1053 I.e., @var{list1} is a subset of @var{list2}, @var{list2} is a subset of
1054 @var{list3}, etc., for as many lists as given. If only one list or no
1055 lists are given, the return value is @code{#t}.
1057 A list @var{x} is a subset of @var{y} if each element of @var{x} is
1058 equal to some element in @var{y}. Elements are compared using the
1059 given @var{=} procedure, called as @code{(@var{=} xelem yelem)}.
1062 (lset<= eq?) @result{} #t
1063 (lset<= eqv? '(1 2 3) '(1)) @result{} #f
1064 (lset<= eqv? '(1 3 2) '(4 3 1 2)) @result{} #t
1068 @deffn {Scheme Procedure} lset= = list @dots{}
1069 Return @code{#t} if all argument lists are set-equal. @var{list1} is
1070 compared to @var{list2}, @var{list2} to @var{list3}, etc., for as many
1071 lists as given. If only one list or no lists are given, the return
1074 Two lists @var{x} and @var{y} are set-equal if each element of @var{x}
1075 is equal to some element of @var{y} and conversely each element of
1076 @var{y} is equal to some element of @var{x}. The order of the
1077 elements in the lists doesn't matter. Element equality is determined
1078 with the given @var{=} procedure, called as @code{(@var{=} xelem
1079 yelem)}, but exactly which calls are made is unspecified.
1082 (lset= eq?) @result{} #t
1083 (lset= eqv? '(1 2 3) '(3 2 1)) @result{} #t
1084 (lset= string-ci=? '("a" "A" "b") '("B" "b" "a")) @result{} #t
1088 @deffn {Scheme Procedure} lset-adjoin = list elem @dots{}
1089 Add to @var{list} any of the given @var{elem}s not already in the list.
1090 @var{elem}s are @code{cons}ed onto the start of @var{list} (so the
1091 return value shares a common tail with @var{list}), but the order that
1092 the @var{elem}s are added is unspecified.
1094 The given @var{=} procedure is used for comparing elements, called as
1095 @code{(@var{=} listelem elem)}, i.e., the second argument is one of
1096 the given @var{elem} parameters.
1099 (lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3)
1103 @deffn {Scheme Procedure} lset-union = list @dots{}
1104 @deffnx {Scheme Procedure} lset-union! = list @dots{}
1105 Return the union of the argument list sets. The result is built by
1106 taking the union of @var{list1} and @var{list2}, then the union of
1107 that with @var{list3}, etc., for as many lists as given. For one list
1108 argument that list itself is the result, for no list arguments the
1109 result is the empty list.
1111 The union of two lists @var{x} and @var{y} is formed as follows. If
1112 @var{x} is empty then the result is @var{y}. Otherwise start with
1113 @var{x} as the result and consider each @var{y} element (from first to
1114 last). A @var{y} element not equal to something already in the result
1115 is @code{cons}ed onto the result.
1117 The given @var{=} procedure is used for comparing elements, called as
1118 @code{(@var{=} relem yelem)}. The first argument is from the result
1119 accumulated so far, and the second is from the list being union-ed in.
1120 But exactly which calls are made is otherwise unspecified.
1122 Notice that duplicate elements in @var{list1} (or the first non-empty
1123 list) are preserved, but that repeated elements in subsequent lists
1124 are only added once.
1127 (lset-union eqv?) @result{} ()
1128 (lset-union eqv? '(1 2 3)) @result{} (1 2 3)
1129 (lset-union eqv? '(1 2 1 3) '(2 4 5) '(5)) @result{} (5 4 1 2 1 3)
1132 @code{lset-union} doesn't change the given lists but the result may
1133 share a tail with the first non-empty list. @code{lset-union!} can
1134 modify all of the given lists to form the result.
1137 @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{}
1138 @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{}
1139 Return the intersection of @var{list1} with the other argument lists,
1140 meaning those elements of @var{list1} which are also in all of
1141 @var{list2} etc. For one list argument, just that list is returned.
1143 The test for an element of @var{list1} to be in the return is simply
1144 that it's equal to some element in each of @var{list2} etc. Notice
1145 this means an element appearing twice in @var{list1} but only once in
1146 each of @var{list2} etc will go into the return twice. The return has
1147 its elements in the same order as they were in @var{list1}.
1149 The given @var{=} procedure is used for comparing elements, called as
1150 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1151 and the second is from one of the subsequent lists. But exactly which
1152 calls are made and in what order is unspecified.
1155 (lset-intersection eqv? '(x y)) @result{} (x y)
1156 (lset-intersection eqv? '(1 2 3) '(4 3 2)) @result{} (2 3)
1157 (lset-intersection eqv? '(1 1 2 2) '(1 2) '(2 1) '(2)) @result{} (2 2)
1160 The return from @code{lset-intersection} may share a tail with
1161 @var{list1}. @code{lset-intersection!} may modify @var{list1} to form
1165 @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{}
1166 @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{}
1167 Return @var{list1} with any elements in @var{list2}, @var{list3} etc
1168 removed (ie.@: subtracted). For one list argument, just that list is
1171 The given @var{=} procedure is used for comparing elements, called as
1172 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1173 and the second from one of the subsequent lists. But exactly which
1174 calls are made and in what order is unspecified.
1177 (lset-difference eqv? '(x y)) @result{} (x y)
1178 (lset-difference eqv? '(1 2 3) '(3 1)) @result{} (2)
1179 (lset-difference eqv? '(1 2 3) '(3) '(2)) @result{} (1)
1182 The return from @code{lset-difference} may share a tail with
1183 @var{list1}. @code{lset-difference!} may modify @var{list1} to form
1187 @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{}
1188 @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{}
1189 Return two values (@pxref{Multiple Values}), the difference and
1190 intersection of the argument lists as per @code{lset-difference} and
1191 @code{lset-intersection} above.
1193 For two list arguments this partitions @var{list1} into those elements
1194 of @var{list1} which are in @var{list2} and not in @var{list2}. (But
1195 for more than two arguments there can be elements of @var{list1} which
1196 are neither part of the difference nor the intersection.)
1198 One of the return values from @code{lset-diff+intersection} may share
1199 a tail with @var{list1}. @code{lset-diff+intersection!} may modify
1200 @var{list1} to form its results.
1203 @deffn {Scheme Procedure} lset-xor = list @dots{}
1204 @deffnx {Scheme Procedure} lset-xor! = list @dots{}
1205 Return an XOR of the argument lists. For two lists this means those
1206 elements which are in exactly one of the lists. For more than two
1207 lists it means those elements which appear in an odd number of the
1210 To be precise, the XOR of two lists @var{x} and @var{y} is formed by
1211 taking those elements of @var{x} not equal to any element of @var{y},
1212 plus those elements of @var{y} not equal to any element of @var{x}.
1213 Equality is determined with the given @var{=} procedure, called as
1214 @code{(@var{=} e1 e2)}. One argument is from @var{x} and the other
1215 from @var{y}, but which way around is unspecified. Exactly which
1216 calls are made is also unspecified, as is the order of the elements in
1220 (lset-xor eqv? '(x y)) @result{} (x y)
1221 (lset-xor eqv? '(1 2 3) '(4 3 2)) @result{} (4 1)
1224 The return from @code{lset-xor} may share a tail with one of the list
1225 arguments. @code{lset-xor!} may modify @var{list1} to form its
1231 @subsection SRFI-2 - and-let*
1235 The following syntax can be obtained with
1238 (use-modules (srfi srfi-2))
1244 (use-modules (ice-9 and-let-star))
1247 @deffn {library syntax} and-let* (clause @dots{}) body @dots{}
1248 A combination of @code{and} and @code{let*}.
1250 Each @var{clause} is evaluated in turn, and if @code{#f} is obtained
1251 then evaluation stops and @code{#f} is returned. If all are
1252 non-@code{#f} then @var{body} is evaluated and the last form gives the
1253 return value, or if @var{body} is empty then the result is @code{#t}.
1254 Each @var{clause} should be one of the following,
1258 Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}.
1259 Like @code{let*}, that binding is available to subsequent clauses.
1261 Evaluate @var{expr} and check for @code{#f}.
1263 Get the value bound to @var{symbol} and check for @code{#f}.
1266 Notice that @code{(expr)} has an ``extra'' pair of parentheses, for
1267 instance @code{((eq? x y))}. One way to remember this is to imagine
1268 the @code{symbol} in @code{(symbol expr)} is omitted.
1270 @code{and-let*} is good for calculations where a @code{#f} value means
1271 termination, but where a non-@code{#f} value is going to be needed in
1272 subsequent expressions.
1274 The following illustrates this, it returns text between brackets
1275 @samp{[...]} in a string, or @code{#f} if there are no such brackets
1276 (ie.@: either @code{string-index} gives @code{#f}).
1279 (define (extract-brackets str)
1280 (and-let* ((start (string-index str #\[))
1281 (end (string-index str #\] start)))
1282 (substring str (1+ start) end)))
1285 The following shows plain variables and expressions tested too.
1286 @code{diagnostic-levels} is taken to be an alist associating a
1287 diagnostic type with a level. @code{str} is printed only if the type
1288 is known and its level is high enough.
1291 (define (show-diagnostic type str)
1292 (and-let* (want-diagnostics
1293 (level (assq-ref diagnostic-levels type))
1294 ((>= level current-diagnostic-level)))
1298 The advantage of @code{and-let*} is that an extended sequence of
1299 expressions and tests doesn't require lots of nesting as would arise
1300 from separate @code{and} and @code{let*}, or from @code{cond} with
1307 @subsection SRFI-4 - Homogeneous numeric vector datatypes
1310 SRFI-4 provides an interface to uniform numeric vectors: vectors whose elements
1311 are all of a single numeric type. Guile offers uniform numeric vectors for
1312 signed and unsigned 8-bit, 16-bit, 32-bit, and 64-bit integers, two sizes of
1313 floating point values, and, as an extension to SRFI-4, complex floating-point
1314 numbers of these two sizes.
1316 The standard SRFI-4 procedures and data types may be included via loading the
1320 (use-modules (srfi srfi-4))
1323 This module is currently a part of the default Guile environment, but it is a
1324 good practice to explicitly import the module. In the future, using SRFI-4
1325 procedures without importing the SRFI-4 module will cause a deprecation message
1326 to be printed. (Of course, one may call the C functions at any time. Would that
1330 * SRFI-4 Overview:: The warp and weft of uniform numeric vectors.
1331 * SRFI-4 API:: Uniform vectors, from Scheme and from C.
1332 * SRFI-4 Generic Operations:: The general, operating on the specific.
1333 * SRFI-4 and Bytevectors:: SRFI-4 vectors are backed by bytevectors.
1334 * SRFI-4 Extensions:: Guile-specific extensions to the standard.
1337 @node SRFI-4 Overview
1338 @subsubsection SRFI-4 - Overview
1340 Uniform numeric vectors can be useful since they consume less memory
1341 than the non-uniform, general vectors. Also, since the types they can
1342 store correspond directly to C types, it is easier to work with them
1343 efficiently on a low level. Consider image processing as an example,
1344 where you want to apply a filter to some image. While you could store
1345 the pixels of an image in a general vector and write a general
1346 convolution function, things are much more efficient with uniform
1347 vectors: the convolution function knows that all pixels are unsigned
1348 8-bit values (say), and can use a very tight inner loop.
1350 This is implemented in Scheme by having the compiler notice calls to the SRFI-4
1351 accessors, and inline them to appropriate compiled code. From C you have access
1352 to the raw array; functions for efficiently working with uniform numeric vectors
1353 from C are listed at the end of this section.
1355 Uniform numeric vectors are the special case of one dimensional uniform
1358 There are 12 standard kinds of uniform numeric vectors, and they all have their
1359 own complement of constructors, accessors, and so on. Procedures that operate on
1360 a specific kind of uniform numeric vector have a ``tag'' in their name,
1361 indicating the element type.
1365 unsigned 8-bit integers
1368 signed 8-bit integers
1371 unsigned 16-bit integers
1374 signed 16-bit integers
1377 unsigned 32-bit integers
1380 signed 32-bit integers
1383 unsigned 64-bit integers
1386 signed 64-bit integers
1389 the C type @code{float}
1392 the C type @code{double}
1396 In addition, Guile supports uniform arrays of complex numbers, with the
1402 complex numbers in rectangular form with the real and imaginary part
1403 being a @code{float}
1406 complex numbers in rectangular form with the real and imaginary part
1407 being a @code{double}
1411 The external representation (ie.@: read syntax) for these vectors is
1412 similar to normal Scheme vectors, but with an additional tag from the
1413 tables above indicating the vector's type. For example,
1420 Note that the read syntax for floating-point here conflicts with
1421 @code{#f} for false. In Standard Scheme one can write @code{(1 #f3)}
1422 for a three element list @code{(1 #f 3)}, but for Guile @code{(1 #f3)}
1423 is invalid. @code{(1 #f 3)} is almost certainly what one should write
1424 anyway to make the intention clear, so this is rarely a problem.
1428 @subsubsection SRFI-4 - API
1430 Note that the @nicode{c32} and @nicode{c64} functions are only available from
1431 @nicode{(srfi srfi-4 gnu)}.
1433 @deffn {Scheme Procedure} u8vector? obj
1434 @deffnx {Scheme Procedure} s8vector? obj
1435 @deffnx {Scheme Procedure} u16vector? obj
1436 @deffnx {Scheme Procedure} s16vector? obj
1437 @deffnx {Scheme Procedure} u32vector? obj
1438 @deffnx {Scheme Procedure} s32vector? obj
1439 @deffnx {Scheme Procedure} u64vector? obj
1440 @deffnx {Scheme Procedure} s64vector? obj
1441 @deffnx {Scheme Procedure} f32vector? obj
1442 @deffnx {Scheme Procedure} f64vector? obj
1443 @deffnx {Scheme Procedure} c32vector? obj
1444 @deffnx {Scheme Procedure} c64vector? obj
1445 @deffnx {C Function} scm_u8vector_p (obj)
1446 @deffnx {C Function} scm_s8vector_p (obj)
1447 @deffnx {C Function} scm_u16vector_p (obj)
1448 @deffnx {C Function} scm_s16vector_p (obj)
1449 @deffnx {C Function} scm_u32vector_p (obj)
1450 @deffnx {C Function} scm_s32vector_p (obj)
1451 @deffnx {C Function} scm_u64vector_p (obj)
1452 @deffnx {C Function} scm_s64vector_p (obj)
1453 @deffnx {C Function} scm_f32vector_p (obj)
1454 @deffnx {C Function} scm_f64vector_p (obj)
1455 @deffnx {C Function} scm_c32vector_p (obj)
1456 @deffnx {C Function} scm_c64vector_p (obj)
1457 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1461 @deffn {Scheme Procedure} make-u8vector n [value]
1462 @deffnx {Scheme Procedure} make-s8vector n [value]
1463 @deffnx {Scheme Procedure} make-u16vector n [value]
1464 @deffnx {Scheme Procedure} make-s16vector n [value]
1465 @deffnx {Scheme Procedure} make-u32vector n [value]
1466 @deffnx {Scheme Procedure} make-s32vector n [value]
1467 @deffnx {Scheme Procedure} make-u64vector n [value]
1468 @deffnx {Scheme Procedure} make-s64vector n [value]
1469 @deffnx {Scheme Procedure} make-f32vector n [value]
1470 @deffnx {Scheme Procedure} make-f64vector n [value]
1471 @deffnx {Scheme Procedure} make-c32vector n [value]
1472 @deffnx {Scheme Procedure} make-c64vector n [value]
1473 @deffnx {C Function} scm_make_u8vector (n, value)
1474 @deffnx {C Function} scm_make_s8vector (n, value)
1475 @deffnx {C Function} scm_make_u16vector (n, value)
1476 @deffnx {C Function} scm_make_s16vector (n, value)
1477 @deffnx {C Function} scm_make_u32vector (n, value)
1478 @deffnx {C Function} scm_make_s32vector (n, value)
1479 @deffnx {C Function} scm_make_u64vector (n, value)
1480 @deffnx {C Function} scm_make_s64vector (n, value)
1481 @deffnx {C Function} scm_make_f32vector (n, value)
1482 @deffnx {C Function} scm_make_f64vector (n, value)
1483 @deffnx {C Function} scm_make_c32vector (n, value)
1484 @deffnx {C Function} scm_make_c64vector (n, value)
1485 Return a newly allocated homogeneous numeric vector holding @var{n}
1486 elements of the indicated type. If @var{value} is given, the vector
1487 is initialized with that value, otherwise the contents are
1491 @deffn {Scheme Procedure} u8vector value @dots{}
1492 @deffnx {Scheme Procedure} s8vector value @dots{}
1493 @deffnx {Scheme Procedure} u16vector value @dots{}
1494 @deffnx {Scheme Procedure} s16vector value @dots{}
1495 @deffnx {Scheme Procedure} u32vector value @dots{}
1496 @deffnx {Scheme Procedure} s32vector value @dots{}
1497 @deffnx {Scheme Procedure} u64vector value @dots{}
1498 @deffnx {Scheme Procedure} s64vector value @dots{}
1499 @deffnx {Scheme Procedure} f32vector value @dots{}
1500 @deffnx {Scheme Procedure} f64vector value @dots{}
1501 @deffnx {Scheme Procedure} c32vector value @dots{}
1502 @deffnx {Scheme Procedure} c64vector value @dots{}
1503 @deffnx {C Function} scm_u8vector (values)
1504 @deffnx {C Function} scm_s8vector (values)
1505 @deffnx {C Function} scm_u16vector (values)
1506 @deffnx {C Function} scm_s16vector (values)
1507 @deffnx {C Function} scm_u32vector (values)
1508 @deffnx {C Function} scm_s32vector (values)
1509 @deffnx {C Function} scm_u64vector (values)
1510 @deffnx {C Function} scm_s64vector (values)
1511 @deffnx {C Function} scm_f32vector (values)
1512 @deffnx {C Function} scm_f64vector (values)
1513 @deffnx {C Function} scm_c32vector (values)
1514 @deffnx {C Function} scm_c64vector (values)
1515 Return a newly allocated homogeneous numeric vector of the indicated
1516 type, holding the given parameter @var{value}s. The vector length is
1517 the number of parameters given.
1520 @deffn {Scheme Procedure} u8vector-length vec
1521 @deffnx {Scheme Procedure} s8vector-length vec
1522 @deffnx {Scheme Procedure} u16vector-length vec
1523 @deffnx {Scheme Procedure} s16vector-length vec
1524 @deffnx {Scheme Procedure} u32vector-length vec
1525 @deffnx {Scheme Procedure} s32vector-length vec
1526 @deffnx {Scheme Procedure} u64vector-length vec
1527 @deffnx {Scheme Procedure} s64vector-length vec
1528 @deffnx {Scheme Procedure} f32vector-length vec
1529 @deffnx {Scheme Procedure} f64vector-length vec
1530 @deffnx {Scheme Procedure} c32vector-length vec
1531 @deffnx {Scheme Procedure} c64vector-length vec
1532 @deffnx {C Function} scm_u8vector_length (vec)
1533 @deffnx {C Function} scm_s8vector_length (vec)
1534 @deffnx {C Function} scm_u16vector_length (vec)
1535 @deffnx {C Function} scm_s16vector_length (vec)
1536 @deffnx {C Function} scm_u32vector_length (vec)
1537 @deffnx {C Function} scm_s32vector_length (vec)
1538 @deffnx {C Function} scm_u64vector_length (vec)
1539 @deffnx {C Function} scm_s64vector_length (vec)
1540 @deffnx {C Function} scm_f32vector_length (vec)
1541 @deffnx {C Function} scm_f64vector_length (vec)
1542 @deffnx {C Function} scm_c32vector_length (vec)
1543 @deffnx {C Function} scm_c64vector_length (vec)
1544 Return the number of elements in @var{vec}.
1547 @deffn {Scheme Procedure} u8vector-ref vec i
1548 @deffnx {Scheme Procedure} s8vector-ref vec i
1549 @deffnx {Scheme Procedure} u16vector-ref vec i
1550 @deffnx {Scheme Procedure} s16vector-ref vec i
1551 @deffnx {Scheme Procedure} u32vector-ref vec i
1552 @deffnx {Scheme Procedure} s32vector-ref vec i
1553 @deffnx {Scheme Procedure} u64vector-ref vec i
1554 @deffnx {Scheme Procedure} s64vector-ref vec i
1555 @deffnx {Scheme Procedure} f32vector-ref vec i
1556 @deffnx {Scheme Procedure} f64vector-ref vec i
1557 @deffnx {Scheme Procedure} c32vector-ref vec i
1558 @deffnx {Scheme Procedure} c64vector-ref vec i
1559 @deffnx {C Function} scm_u8vector_ref (vec, i)
1560 @deffnx {C Function} scm_s8vector_ref (vec, i)
1561 @deffnx {C Function} scm_u16vector_ref (vec, i)
1562 @deffnx {C Function} scm_s16vector_ref (vec, i)
1563 @deffnx {C Function} scm_u32vector_ref (vec, i)
1564 @deffnx {C Function} scm_s32vector_ref (vec, i)
1565 @deffnx {C Function} scm_u64vector_ref (vec, i)
1566 @deffnx {C Function} scm_s64vector_ref (vec, i)
1567 @deffnx {C Function} scm_f32vector_ref (vec, i)
1568 @deffnx {C Function} scm_f64vector_ref (vec, i)
1569 @deffnx {C Function} scm_c32vector_ref (vec, i)
1570 @deffnx {C Function} scm_c64vector_ref (vec, i)
1571 Return the element at index @var{i} in @var{vec}. The first element
1572 in @var{vec} is index 0.
1575 @deffn {Scheme Procedure} u8vector-set! vec i value
1576 @deffnx {Scheme Procedure} s8vector-set! vec i value
1577 @deffnx {Scheme Procedure} u16vector-set! vec i value
1578 @deffnx {Scheme Procedure} s16vector-set! vec i value
1579 @deffnx {Scheme Procedure} u32vector-set! vec i value
1580 @deffnx {Scheme Procedure} s32vector-set! vec i value
1581 @deffnx {Scheme Procedure} u64vector-set! vec i value
1582 @deffnx {Scheme Procedure} s64vector-set! vec i value
1583 @deffnx {Scheme Procedure} f32vector-set! vec i value
1584 @deffnx {Scheme Procedure} f64vector-set! vec i value
1585 @deffnx {Scheme Procedure} c32vector-set! vec i value
1586 @deffnx {Scheme Procedure} c64vector-set! vec i value
1587 @deffnx {C Function} scm_u8vector_set_x (vec, i, value)
1588 @deffnx {C Function} scm_s8vector_set_x (vec, i, value)
1589 @deffnx {C Function} scm_u16vector_set_x (vec, i, value)
1590 @deffnx {C Function} scm_s16vector_set_x (vec, i, value)
1591 @deffnx {C Function} scm_u32vector_set_x (vec, i, value)
1592 @deffnx {C Function} scm_s32vector_set_x (vec, i, value)
1593 @deffnx {C Function} scm_u64vector_set_x (vec, i, value)
1594 @deffnx {C Function} scm_s64vector_set_x (vec, i, value)
1595 @deffnx {C Function} scm_f32vector_set_x (vec, i, value)
1596 @deffnx {C Function} scm_f64vector_set_x (vec, i, value)
1597 @deffnx {C Function} scm_c32vector_set_x (vec, i, value)
1598 @deffnx {C Function} scm_c64vector_set_x (vec, i, value)
1599 Set the element at index @var{i} in @var{vec} to @var{value}. The
1600 first element in @var{vec} is index 0. The return value is
1604 @deffn {Scheme Procedure} u8vector->list vec
1605 @deffnx {Scheme Procedure} s8vector->list vec
1606 @deffnx {Scheme Procedure} u16vector->list vec
1607 @deffnx {Scheme Procedure} s16vector->list vec
1608 @deffnx {Scheme Procedure} u32vector->list vec
1609 @deffnx {Scheme Procedure} s32vector->list vec
1610 @deffnx {Scheme Procedure} u64vector->list vec
1611 @deffnx {Scheme Procedure} s64vector->list vec
1612 @deffnx {Scheme Procedure} f32vector->list vec
1613 @deffnx {Scheme Procedure} f64vector->list vec
1614 @deffnx {Scheme Procedure} c32vector->list vec
1615 @deffnx {Scheme Procedure} c64vector->list vec
1616 @deffnx {C Function} scm_u8vector_to_list (vec)
1617 @deffnx {C Function} scm_s8vector_to_list (vec)
1618 @deffnx {C Function} scm_u16vector_to_list (vec)
1619 @deffnx {C Function} scm_s16vector_to_list (vec)
1620 @deffnx {C Function} scm_u32vector_to_list (vec)
1621 @deffnx {C Function} scm_s32vector_to_list (vec)
1622 @deffnx {C Function} scm_u64vector_to_list (vec)
1623 @deffnx {C Function} scm_s64vector_to_list (vec)
1624 @deffnx {C Function} scm_f32vector_to_list (vec)
1625 @deffnx {C Function} scm_f64vector_to_list (vec)
1626 @deffnx {C Function} scm_c32vector_to_list (vec)
1627 @deffnx {C Function} scm_c64vector_to_list (vec)
1628 Return a newly allocated list holding all elements of @var{vec}.
1631 @deffn {Scheme Procedure} list->u8vector lst
1632 @deffnx {Scheme Procedure} list->s8vector lst
1633 @deffnx {Scheme Procedure} list->u16vector lst
1634 @deffnx {Scheme Procedure} list->s16vector lst
1635 @deffnx {Scheme Procedure} list->u32vector lst
1636 @deffnx {Scheme Procedure} list->s32vector lst
1637 @deffnx {Scheme Procedure} list->u64vector lst
1638 @deffnx {Scheme Procedure} list->s64vector lst
1639 @deffnx {Scheme Procedure} list->f32vector lst
1640 @deffnx {Scheme Procedure} list->f64vector lst
1641 @deffnx {Scheme Procedure} list->c32vector lst
1642 @deffnx {Scheme Procedure} list->c64vector lst
1643 @deffnx {C Function} scm_list_to_u8vector (lst)
1644 @deffnx {C Function} scm_list_to_s8vector (lst)
1645 @deffnx {C Function} scm_list_to_u16vector (lst)
1646 @deffnx {C Function} scm_list_to_s16vector (lst)
1647 @deffnx {C Function} scm_list_to_u32vector (lst)
1648 @deffnx {C Function} scm_list_to_s32vector (lst)
1649 @deffnx {C Function} scm_list_to_u64vector (lst)
1650 @deffnx {C Function} scm_list_to_s64vector (lst)
1651 @deffnx {C Function} scm_list_to_f32vector (lst)
1652 @deffnx {C Function} scm_list_to_f64vector (lst)
1653 @deffnx {C Function} scm_list_to_c32vector (lst)
1654 @deffnx {C Function} scm_list_to_c64vector (lst)
1655 Return a newly allocated homogeneous numeric vector of the indicated type,
1656 initialized with the elements of the list @var{lst}.
1659 @deftypefn {C Function} SCM scm_take_u8vector (const scm_t_uint8 *data, size_t len)
1660 @deftypefnx {C Function} SCM scm_take_s8vector (const scm_t_int8 *data, size_t len)
1661 @deftypefnx {C Function} SCM scm_take_u16vector (const scm_t_uint16 *data, size_t len)
1662 @deftypefnx {C Function} SCM scm_take_s16vector (const scm_t_int16 *data, size_t len)
1663 @deftypefnx {C Function} SCM scm_take_u32vector (const scm_t_uint32 *data, size_t len)
1664 @deftypefnx {C Function} SCM scm_take_s32vector (const scm_t_int32 *data, size_t len)
1665 @deftypefnx {C Function} SCM scm_take_u64vector (const scm_t_uint64 *data, size_t len)
1666 @deftypefnx {C Function} SCM scm_take_s64vector (const scm_t_int64 *data, size_t len)
1667 @deftypefnx {C Function} SCM scm_take_f32vector (const float *data, size_t len)
1668 @deftypefnx {C Function} SCM scm_take_f64vector (const double *data, size_t len)
1669 @deftypefnx {C Function} SCM scm_take_c32vector (const float *data, size_t len)
1670 @deftypefnx {C Function} SCM scm_take_c64vector (const double *data, size_t len)
1671 Return a new uniform numeric vector of the indicated type and length
1672 that uses the memory pointed to by @var{data} to store its elements.
1673 This memory will eventually be freed with @code{free}. The argument
1674 @var{len} specifies the number of elements in @var{data}, not its size
1677 The @code{c32} and @code{c64} variants take a pointer to a C array of
1678 @code{float}s or @code{double}s. The real parts of the complex numbers
1679 are at even indices in that array, the corresponding imaginary parts are
1680 at the following odd index.
1683 @deftypefn {C Function} {const scm_t_uint8 *} scm_u8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1684 @deftypefnx {C Function} {const scm_t_int8 *} scm_s8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1685 @deftypefnx {C Function} {const scm_t_uint16 *} scm_u16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1686 @deftypefnx {C Function} {const scm_t_int16 *} scm_s16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1687 @deftypefnx {C Function} {const scm_t_uint32 *} scm_u32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1688 @deftypefnx {C Function} {const scm_t_int32 *} scm_s32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1689 @deftypefnx {C Function} {const scm_t_uint64 *} scm_u64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1690 @deftypefnx {C Function} {const scm_t_int64 *} scm_s64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1691 @deftypefnx {C Function} {const float *} scm_f32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1692 @deftypefnx {C Function} {const double *} scm_f64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1693 @deftypefnx {C Function} {const float *} scm_c32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1694 @deftypefnx {C Function} {const double *} scm_c64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1695 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1696 returns a pointer to the elements of a uniform numeric vector of the
1700 @deftypefn {C Function} {scm_t_uint8 *} scm_u8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1701 @deftypefnx {C Function} {scm_t_int8 *} scm_s8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1702 @deftypefnx {C Function} {scm_t_uint16 *} scm_u16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1703 @deftypefnx {C Function} {scm_t_int16 *} scm_s16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1704 @deftypefnx {C Function} {scm_t_uint32 *} scm_u32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1705 @deftypefnx {C Function} {scm_t_int32 *} scm_s32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1706 @deftypefnx {C Function} {scm_t_uint64 *} scm_u64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1707 @deftypefnx {C Function} {scm_t_int64 *} scm_s64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1708 @deftypefnx {C Function} {float *} scm_f32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1709 @deftypefnx {C Function} {double *} scm_f64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1710 @deftypefnx {C Function} {float *} scm_c32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1711 @deftypefnx {C Function} {double *} scm_c64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1712 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1713 C}), but returns a pointer to the elements of a uniform numeric vector
1714 of the indicated kind.
1717 @node SRFI-4 Generic Operations
1718 @subsubsection SRFI-4 - Generic operations
1720 Guile also provides procedures that operate on all types of uniform numeric
1721 vectors. In what is probably a bug, these procedures are currently available in
1722 the default environment as well; however prudent hackers will make sure to
1723 import @code{(srfi srfi-4 gnu)} before using these.
1725 @deftypefn {C Function} int scm_is_uniform_vector (SCM uvec)
1726 Return non-zero when @var{uvec} is a uniform numeric vector, zero
1730 @deftypefn {C Function} size_t scm_c_uniform_vector_length (SCM uvec)
1731 Return the number of elements of @var{uvec} as a @code{size_t}.
1734 @deffn {Scheme Procedure} uniform-vector? obj
1735 @deffnx {C Function} scm_uniform_vector_p (obj)
1736 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1740 @deffn {Scheme Procedure} uniform-vector-length vec
1741 @deffnx {C Function} scm_uniform_vector_length (vec)
1742 Return the number of elements in @var{vec}.
1745 @deffn {Scheme Procedure} uniform-vector-ref vec i
1746 @deffnx {C Function} scm_uniform_vector_ref (vec, i)
1747 Return the element at index @var{i} in @var{vec}. The first element
1748 in @var{vec} is index 0.
1751 @deffn {Scheme Procedure} uniform-vector-set! vec i value
1752 @deffnx {C Function} scm_uniform_vector_set_x (vec, i, value)
1753 Set the element at index @var{i} in @var{vec} to @var{value}. The
1754 first element in @var{vec} is index 0. The return value is
1758 @deffn {Scheme Procedure} uniform-vector->list vec
1759 @deffnx {C Function} scm_uniform_vector_to_list (vec)
1760 Return a newly allocated list holding all elements of @var{vec}.
1763 @deftypefn {C Function} {const void *} scm_uniform_vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1764 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1765 returns a pointer to the elements of a uniform numeric vector.
1768 @deftypefn {C Function} {void *} scm_uniform_vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1769 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1770 C}), but returns a pointer to the elements of a uniform numeric vector.
1773 Unless you really need to the limited generality of these functions, it
1774 is best to use the type-specific functions, or the array accessors.
1776 @node SRFI-4 and Bytevectors
1777 @subsubsection SRFI-4 - Relation to bytevectors
1779 Guile implements SRFI-4 vectors using bytevectors (@pxref{Bytevectors}). Often
1780 when you have a numeric vector, you end up wanting to write its bytes somewhere,
1781 or have access to the underlying bytes, or read in bytes from somewhere else.
1782 Bytevectors are very good at this sort of thing. But the SRFI-4 APIs are nicer
1783 to use when doing number-crunching, because they are addressed by element and
1786 So as a compromise, Guile allows all bytevector functions to operate on numeric
1787 vectors. They address the underlying bytes in the native endianness, as one
1790 Following the same reasoning, that it's just bytes underneath, Guile also allows
1791 uniform vectors of a given type to be accessed as if they were of any type. One
1792 can fill a @nicode{u32vector}, and access its elements with
1793 @nicode{u8vector-ref}. One can use @nicode{f64vector-ref} on bytevectors. It's
1794 all the same to Guile.
1796 In this way, uniform numeric vectors may be written to and read from
1797 input/output ports using the procedures that operate on bytevectors.
1799 @xref{Bytevectors}, for more information.
1802 @node SRFI-4 Extensions
1803 @subsubsection SRFI-4 - Guile extensions
1805 Guile defines some useful extensions to SRFI-4, which are not available in the
1806 default Guile environment. They may be imported by loading the extensions
1810 (use-modules (srfi srfi-4 gnu))
1813 @deffn {Scheme Procedure} any->u8vector obj
1814 @deffnx {Scheme Procedure} any->s8vector obj
1815 @deffnx {Scheme Procedure} any->u16vector obj
1816 @deffnx {Scheme Procedure} any->s16vector obj
1817 @deffnx {Scheme Procedure} any->u32vector obj
1818 @deffnx {Scheme Procedure} any->s32vector obj
1819 @deffnx {Scheme Procedure} any->u64vector obj
1820 @deffnx {Scheme Procedure} any->s64vector obj
1821 @deffnx {Scheme Procedure} any->f32vector obj
1822 @deffnx {Scheme Procedure} any->f64vector obj
1823 @deffnx {Scheme Procedure} any->c32vector obj
1824 @deffnx {Scheme Procedure} any->c64vector obj
1825 @deffnx {C Function} scm_any_to_u8vector (obj)
1826 @deffnx {C Function} scm_any_to_s8vector (obj)
1827 @deffnx {C Function} scm_any_to_u16vector (obj)
1828 @deffnx {C Function} scm_any_to_s16vector (obj)
1829 @deffnx {C Function} scm_any_to_u32vector (obj)
1830 @deffnx {C Function} scm_any_to_s32vector (obj)
1831 @deffnx {C Function} scm_any_to_u64vector (obj)
1832 @deffnx {C Function} scm_any_to_s64vector (obj)
1833 @deffnx {C Function} scm_any_to_f32vector (obj)
1834 @deffnx {C Function} scm_any_to_f64vector (obj)
1835 @deffnx {C Function} scm_any_to_c32vector (obj)
1836 @deffnx {C Function} scm_any_to_c64vector (obj)
1837 Return a (maybe newly allocated) uniform numeric vector of the indicated
1838 type, initialized with the elements of @var{obj}, which must be a list,
1839 a vector, or a uniform vector. When @var{obj} is already a suitable
1840 uniform numeric vector, it is returned unchanged.
1845 @subsection SRFI-6 - Basic String Ports
1848 SRFI-6 defines the procedures @code{open-input-string},
1849 @code{open-output-string} and @code{get-output-string}.
1851 Note that although versions of these procedures are included in the
1852 Guile core, the core versions are not fully conformant with SRFI-6:
1853 attempts to read or write characters that are not supported by the
1854 current @code{%default-port-encoding} will fail.
1856 We therefore recommend that you import this module, which supports all
1860 (use-modules (srfi srfi-6))
1864 @subsection SRFI-8 - receive
1867 @code{receive} is a syntax for making the handling of multiple-value
1868 procedures easier. It is documented in @xref{Multiple Values}.
1872 @subsection SRFI-9 - define-record-type
1874 This SRFI is a syntax for defining new record types and creating
1875 predicate, constructor, and field getter and setter functions. It is
1876 documented in the ``Compound Data Types'' section of the manual
1877 (@pxref{SRFI-9 Records}).
1881 @subsection SRFI-10 - Hash-Comma Reader Extension
1886 This SRFI implements a reader extension @code{#,()} called hash-comma.
1887 It allows the reader to give new kinds of objects, for use both in
1888 data and as constants or literals in source code. This feature is
1892 (use-modules (srfi srfi-10))
1896 The new read syntax is of the form
1899 #,(@var{tag} @var{arg}@dots{})
1903 where @var{tag} is a symbol and the @var{arg}s are objects taken as
1904 parameters. @var{tag}s are registered with the following procedure.
1906 @deffn {Scheme Procedure} define-reader-ctor tag proc
1907 Register @var{proc} as the constructor for a hash-comma read syntax
1908 starting with symbol @var{tag}, i.e.@: @nicode{#,(@var{tag} arg@dots{})}.
1909 @var{proc} is called with the given arguments @code{(@var{proc}
1910 arg@dots{})} and the object it returns is the result of the read.
1914 For example, a syntax giving a list of @var{N} copies of an object.
1917 (define-reader-ctor 'repeat
1919 (make-list reps obj)))
1921 (display '#,(repeat 99 3))
1925 Notice the quote @nicode{'} when the @nicode{#,( )} is used. The
1926 @code{repeat} handler returns a list and the program must quote to use
1927 it literally, the same as any other list. Ie.
1930 (display '#,(repeat 99 3))
1932 (display '(99 99 99))
1935 When a handler returns an object which is self-evaluating, like a
1936 number or a string, then there's no need for quoting, just as there's
1937 no need when giving those directly as literals. For example an
1941 (define-reader-ctor 'sum
1944 (display #,(sum 123 456)) @print{} 579
1947 A typical use for @nicode{#,()} is to get a read syntax for objects
1948 which don't otherwise have one. For example, the following allows a
1949 hash table to be given literally, with tags and values, ready for fast
1953 (define-reader-ctor 'hash
1955 (let ((table (make-hash-table)))
1956 (for-each (lambda (elem)
1957 (apply hash-set! table elem))
1961 (define (animal->family animal)
1962 (hash-ref '#,(hash ("tiger" "cat")
1967 (animal->family "lion") @result{} "cat"
1970 Or for example the following is a syntax for a compiled regular
1971 expression (@pxref{Regular Expressions}).
1974 (use-modules (ice-9 regex))
1976 (define-reader-ctor 'regexp make-regexp)
1978 (define (extract-angs str)
1979 (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str)))
1981 (match:substring match 1))))
1983 (extract-angs "foo <BAR> quux") @result{} "BAR"
1987 @nicode{#,()} is somewhat similar to @code{define-macro}
1988 (@pxref{Macros}) in that handler code is run to produce a result, but
1989 @nicode{#,()} operates at the read stage, so it can appear in data for
1990 @code{read} (@pxref{Scheme Read}), not just in code to be executed.
1992 Because @nicode{#,()} is handled at read-time it has no direct access
1993 to variables etc. A symbol in the arguments is just a symbol, not a
1994 variable reference. The arguments are essentially constants, though
1995 the handler procedure can use them in any complicated way it might
1998 Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available
1999 globally, there's no need to use @code{(srfi srfi-10)} in later
2000 modules. Similarly the tags registered are global and can be used
2001 anywhere once registered.
2003 There's no attempt to record what previous @nicode{#,()} forms have
2004 been seen, if two identical forms occur then two calls are made to the
2005 handler procedure. The handler might like to maintain a cache or
2006 similar to avoid making copies of large objects, depending on expected
2009 In code the best uses of @nicode{#,()} are generally when there's a
2010 lot of objects of a particular kind as literals or constants. If
2011 there's just a few then some local variables and initializers are
2012 fine, but that becomes tedious and error prone when there's a lot, and
2013 the anonymous and compact syntax of @nicode{#,()} is much better.
2017 @subsection SRFI-11 - let-values
2022 This module implements the binding forms for multiple values
2023 @code{let-values} and @code{let*-values}. These forms are similar to
2024 @code{let} and @code{let*} (@pxref{Local Bindings}), but they support
2025 binding of the values returned by multiple-valued expressions.
2027 Write @code{(use-modules (srfi srfi-11))} to make the bindings
2031 (let-values (((x y) (values 1 2))
2032 ((z f) (values 3 4)))
2038 @code{let-values} performs all bindings simultaneously, which means that
2039 no expression in the binding clauses may refer to variables bound in the
2040 same clause list. @code{let*-values}, on the other hand, performs the
2041 bindings sequentially, just like @code{let*} does for single-valued
2046 @subsection SRFI-13 - String Library
2049 The SRFI-13 procedures are always available, @xref{Strings}.
2052 @subsection SRFI-14 - Character-set Library
2055 The SRFI-14 data type and procedures are always available,
2056 @xref{Character Sets}.
2059 @subsection SRFI-16 - case-lambda
2061 @cindex variable arity
2062 @cindex arity, variable
2064 SRFI-16 defines a variable-arity @code{lambda} form,
2065 @code{case-lambda}. This form is available in the default Guile
2066 environment. @xref{Case-lambda}, for more information.
2069 @subsection SRFI-17 - Generalized set!
2072 This SRFI implements a generalized @code{set!}, allowing some
2073 ``referencing'' functions to be used as the target location of a
2074 @code{set!}. This feature is available from
2077 (use-modules (srfi srfi-17))
2081 For example @code{vector-ref} is extended so that
2084 (set! (vector-ref vec idx) new-value)
2091 (vector-set! vec idx new-value)
2094 The idea is that a @code{vector-ref} expression identifies a location,
2095 which may be either fetched or stored. The same form is used for the
2096 location in both cases, encouraging visual clarity. This is similar
2097 to the idea of an ``lvalue'' in C.
2099 The mechanism for this kind of @code{set!} is in the Guile core
2100 (@pxref{Procedures with Setters}). This module adds definitions of
2101 the following functions as procedures with setters, allowing them to
2102 be targets of a @code{set!},
2105 @nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr},
2106 @nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr},
2107 @nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr},
2108 @nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr},
2109 @nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr},
2110 @nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr},
2111 @nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr},
2112 @nicode{cdddar}, @nicode{cddddr}
2114 @nicode{string-ref}, @nicode{vector-ref}
2117 The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as
2118 a procedure with setter, allowing the setter for a procedure to be
2119 changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}.
2120 Currently Guile does not implement this, a setter can only be
2121 specified on creation (@code{getter-with-setter} below).
2123 @defun getter-with-setter
2124 The same as the Guile core @code{make-procedure-with-setter}
2125 (@pxref{Procedures with Setters}).
2130 @subsection SRFI-18 - Multithreading support
2133 This is an implementation of the SRFI-18 threading and synchronization
2134 library. The functions and variables described here are provided by
2137 (use-modules (srfi srfi-18))
2140 As a general rule, the data types and functions in this SRFI-18
2141 implementation are compatible with the types and functions in Guile's
2142 core threading code. For example, mutexes created with the SRFI-18
2143 @code{make-mutex} function can be passed to the built-in Guile
2144 function @code{lock-mutex} (@pxref{Mutexes and Condition Variables}),
2145 and mutexes created with the built-in Guile function @code{make-mutex}
2146 can be passed to the SRFI-18 function @code{mutex-lock!}. Cases in
2147 which this does not hold true are noted in the following sections.
2150 * SRFI-18 Threads:: Executing code
2151 * SRFI-18 Mutexes:: Mutual exclusion devices
2152 * SRFI-18 Condition variables:: Synchronizing of groups of threads
2153 * SRFI-18 Time:: Representation of times and durations
2154 * SRFI-18 Exceptions:: Signalling and handling errors
2157 @node SRFI-18 Threads
2158 @subsubsection SRFI-18 Threads
2160 Threads created by SRFI-18 differ in two ways from threads created by
2161 Guile's built-in thread functions. First, a thread created by SRFI-18
2162 @code{make-thread} begins in a blocked state and will not start
2163 execution until @code{thread-start!} is called on it. Second, SRFI-18
2164 threads are constructed with a top-level exception handler that
2165 captures any exceptions that are thrown on thread exit. In all other
2166 regards, SRFI-18 threads are identical to normal Guile threads.
2168 @defun current-thread
2169 Returns the thread that called this function. This is the same
2170 procedure as the same-named built-in procedure @code{current-thread}
2175 Returns @code{#t} if @var{obj} is a thread, @code{#f} otherwise. This
2176 is the same procedure as the same-named built-in procedure
2177 @code{thread?} (@pxref{Threads}).
2180 @defun make-thread thunk [name]
2181 Call @code{thunk} in a new thread and with a new dynamic state,
2182 returning the new thread and optionally assigning it the object name
2183 @var{name}, which may be any Scheme object.
2185 Note that the name @code{make-thread} conflicts with the
2186 @code{(ice-9 threads)} function @code{make-thread}. Applications
2187 wanting to use both of these functions will need to refer to them by
2191 @defun thread-name thread
2192 Returns the name assigned to @var{thread} at the time of its creation,
2193 or @code{#f} if it was not given a name.
2196 @defun thread-specific thread
2197 @defunx thread-specific-set! thread obj
2198 Get or set the ``object-specific'' property of @var{thread}. In
2199 Guile's implementation of SRFI-18, this value is stored as an object
2200 property, and will be @code{#f} if not set.
2203 @defun thread-start! thread
2204 Unblocks @var{thread} and allows it to begin execution if it has not
2208 @defun thread-yield!
2209 If one or more threads are waiting to execute, calling
2210 @code{thread-yield!} forces an immediate context switch to one of them.
2211 Otherwise, @code{thread-yield!} has no effect. @code{thread-yield!}
2212 behaves identically to the Guile built-in function @code{yield}.
2215 @defun thread-sleep! timeout
2216 The current thread waits until the point specified by the time object
2217 @var{timeout} is reached (@pxref{SRFI-18 Time}). This blocks the
2218 thread only if @var{timeout} represents a point in the future. it is
2219 an error for @var{timeout} to be @code{#f}.
2222 @defun thread-terminate! thread
2223 Causes an abnormal termination of @var{thread}. If @var{thread} is
2224 not already terminated, all mutexes owned by @var{thread} become
2225 unlocked/abandoned. If @var{thread} is the current thread,
2226 @code{thread-terminate!} does not return. Otherwise
2227 @code{thread-terminate!} returns an unspecified value; the termination
2228 of @var{thread} will occur before @code{thread-terminate!} returns.
2229 Subsequent attempts to join on @var{thread} will cause a ``terminated
2230 thread exception'' to be raised.
2232 @code{thread-terminate!} is compatible with the thread cancellation
2233 procedures in the core threads API (@pxref{Threads}) in that if a
2234 cleanup handler has been installed for the target thread, it will be
2235 called before the thread exits and its return value (or exception, if
2236 any) will be stored for later retrieval via a call to
2237 @code{thread-join!}.
2240 @defun thread-join! thread [timeout [timeout-val]]
2241 Wait for @var{thread} to terminate and return its exit value. When a
2242 time value @var{timeout} is given, it specifies a point in time where
2243 the waiting should be aborted. When the waiting is aborted,
2244 @var{timeout-val} is returned if it is specified; otherwise, a
2245 @code{join-timeout-exception} exception is raised
2246 (@pxref{SRFI-18 Exceptions}). Exceptions may also be raised if the
2247 thread was terminated by a call to @code{thread-terminate!}
2248 (@code{terminated-thread-exception} will be raised) or if the thread
2249 exited by raising an exception that was handled by the top-level
2250 exception handler (@code{uncaught-exception} will be raised; the
2251 original exception can be retrieved using
2252 @code{uncaught-exception-reason}).
2256 @node SRFI-18 Mutexes
2257 @subsubsection SRFI-18 Mutexes
2259 The behavior of Guile's built-in mutexes is parameterized via a set of
2260 flags passed to the @code{make-mutex} procedure in the core
2261 (@pxref{Mutexes and Condition Variables}). To satisfy the requirements
2262 for mutexes specified by SRFI-18, the @code{make-mutex} procedure
2263 described below sets the following flags:
2266 @code{recursive}: the mutex can be locked recursively
2268 @code{unchecked-unlock}: attempts to unlock a mutex that is already
2269 unlocked will not raise an exception
2271 @code{allow-external-unlock}: the mutex can be unlocked by any thread,
2272 not just the thread that locked it originally
2275 @defun make-mutex [name]
2276 Returns a new mutex, optionally assigning it the object name
2277 @var{name}, which may be any Scheme object. The returned mutex will be
2278 created with the configuration described above. Note that the name
2279 @code{make-mutex} conflicts with Guile core function @code{make-mutex}.
2280 Applications wanting to use both of these functions will need to refer
2281 to them by different names.
2284 @defun mutex-name mutex
2285 Returns the name assigned to @var{mutex} at the time of its creation,
2286 or @code{#f} if it was not given a name.
2289 @defun mutex-specific mutex
2290 @defunx mutex-specific-set! mutex obj
2291 Get or set the ``object-specific'' property of @var{mutex}. In Guile's
2292 implementation of SRFI-18, this value is stored as an object property,
2293 and will be @code{#f} if not set.
2296 @defun mutex-state mutex
2297 Returns information about the state of @var{mutex}. Possible values
2301 thread @code{T}: the mutex is in the locked/owned state and thread T
2302 is the owner of the mutex
2304 symbol @code{not-owned}: the mutex is in the locked/not-owned state
2306 symbol @code{abandoned}: the mutex is in the unlocked/abandoned state
2308 symbol @code{not-abandoned}: the mutex is in the
2309 unlocked/not-abandoned state
2313 @defun mutex-lock! mutex [timeout [thread]]
2314 Lock @var{mutex}, optionally specifying a time object @var{timeout}
2315 after which to abort the lock attempt and a thread @var{thread} giving
2316 a new owner for @var{mutex} different than the current thread. This
2317 procedure has the same behavior as the @code{lock-mutex} procedure in
2321 @defun mutex-unlock! mutex [condition-variable [timeout]]
2322 Unlock @var{mutex}, optionally specifying a condition variable
2323 @var{condition-variable} on which to wait, either indefinitely or,
2324 optionally, until the time object @var{timeout} has passed, to be
2325 signalled. This procedure has the same behavior as the
2326 @code{unlock-mutex} procedure in the core library.
2330 @node SRFI-18 Condition variables
2331 @subsubsection SRFI-18 Condition variables
2333 SRFI-18 does not specify a ``wait'' function for condition variables.
2334 Waiting on a condition variable can be simulated using the SRFI-18
2335 @code{mutex-unlock!} function described in the previous section, or
2336 Guile's built-in @code{wait-condition-variable} procedure can be used.
2338 @defun condition-variable? obj
2339 Returns @code{#t} if @var{obj} is a condition variable, @code{#f}
2340 otherwise. This is the same procedure as the same-named built-in
2342 (@pxref{Mutexes and Condition Variables, @code{condition-variable?}}).
2345 @defun make-condition-variable [name]
2346 Returns a new condition variable, optionally assigning it the object
2347 name @var{name}, which may be any Scheme object. This procedure
2348 replaces a procedure of the same name in the core library.
2351 @defun condition-variable-name condition-variable
2352 Returns the name assigned to @var{condition-variable} at the time of its
2353 creation, or @code{#f} if it was not given a name.
2356 @defun condition-variable-specific condition-variable
2357 @defunx condition-variable-specific-set! condition-variable obj
2358 Get or set the ``object-specific'' property of
2359 @var{condition-variable}. In Guile's implementation of SRFI-18, this
2360 value is stored as an object property, and will be @code{#f} if not
2364 @defun condition-variable-signal! condition-variable
2365 @defunx condition-variable-broadcast! condition-variable
2366 Wake up one thread that is waiting for @var{condition-variable}, in
2367 the case of @code{condition-variable-signal!}, or all threads waiting
2368 for it, in the case of @code{condition-variable-broadcast!}. The
2369 behavior of these procedures is equivalent to that of the procedures
2370 @code{signal-condition-variable} and
2371 @code{broadcast-condition-variable} in the core library.
2376 @subsubsection SRFI-18 Time
2378 The SRFI-18 time functions manipulate time in two formats: a
2379 ``time object'' type that represents an absolute point in time in some
2380 implementation-specific way; and the number of seconds since some
2381 unspecified ``epoch''. In Guile's implementation, the epoch is the
2382 Unix epoch, 00:00:00 UTC, January 1, 1970.
2385 Return the current time as a time object. This procedure replaces
2386 the procedure of the same name in the core library, which returns the
2387 current time in seconds since the epoch.
2391 Returns @code{#t} if @var{obj} is a time object, @code{#f} otherwise.
2394 @defun time->seconds time
2395 @defunx seconds->time seconds
2396 Convert between time objects and numerical values representing the
2397 number of seconds since the epoch. When converting from a time object
2398 to seconds, the return value is the number of seconds between
2399 @var{time} and the epoch. When converting from seconds to a time
2400 object, the return value is a time object that represents a time
2401 @var{seconds} seconds after the epoch.
2405 @node SRFI-18 Exceptions
2406 @subsubsection SRFI-18 Exceptions
2408 SRFI-18 exceptions are identical to the exceptions provided by
2409 Guile's implementation of SRFI-34. The behavior of exception
2410 handlers invoked to handle exceptions thrown from SRFI-18 functions,
2411 however, differs from the conventional behavior of SRFI-34 in that
2412 the continuation of the handler is the same as that of the call to
2413 the function. Handlers are called in a tail-recursive manner; the
2414 exceptions do not ``bubble up''.
2416 @defun current-exception-handler
2417 Returns the current exception handler.
2420 @defun with-exception-handler handler thunk
2421 Installs @var{handler} as the current exception handler and calls the
2422 procedure @var{thunk} with no arguments, returning its value as the
2423 value of the exception. @var{handler} must be a procedure that accepts
2424 a single argument. The current exception handler at the time this
2425 procedure is called will be restored after the call returns.
2429 Raise @var{obj} as an exception. This is the same procedure as the
2430 same-named procedure defined in SRFI 34.
2433 @defun join-timeout-exception? obj
2434 Returns @code{#t} if @var{obj} is an exception raised as the result of
2435 performing a timed join on a thread that does not exit within the
2436 specified timeout, @code{#f} otherwise.
2439 @defun abandoned-mutex-exception? obj
2440 Returns @code{#t} if @var{obj} is an exception raised as the result of
2441 attempting to lock a mutex that has been abandoned by its owner thread,
2442 @code{#f} otherwise.
2445 @defun terminated-thread-exception? obj
2446 Returns @code{#t} if @var{obj} is an exception raised as the result of
2447 joining on a thread that exited as the result of a call to
2448 @code{thread-terminate!}.
2451 @defun uncaught-exception? obj
2452 @defunx uncaught-exception-reason exc
2453 @code{uncaught-exception?} returns @code{#t} if @var{obj} is an
2454 exception thrown as the result of joining a thread that exited by
2455 raising an exception that was handled by the top-level exception
2456 handler installed by @code{make-thread}. When this occurs, the
2457 original exception is preserved as part of the exception thrown by
2458 @code{thread-join!} and can be accessed by calling
2459 @code{uncaught-exception-reason} on that exception. Note that
2460 because this exception-preservation mechanism is a side-effect of
2461 @code{make-thread}, joining on threads that exited as described above
2462 but were created by other means will not raise this
2463 @code{uncaught-exception} error.
2468 @subsection SRFI-19 - Time/Date Library
2473 This is an implementation of the SRFI-19 time/date library. The
2474 functions and variables described here are provided by
2477 (use-modules (srfi srfi-19))
2480 @strong{Caution}: The current code in this module incorrectly extends
2481 the Gregorian calendar leap year rule back prior to the introduction
2482 of those reforms in 1582 (or the appropriate year in various
2483 countries). The Julian calendar was used prior to 1582, and there
2484 were 10 days skipped for the reform, but the code doesn't implement
2487 This will be fixed some time. Until then calculations for 1583
2488 onwards are correct, but prior to that any day/month/year and day of
2489 the week calculations are wrong.
2492 * SRFI-19 Introduction::
2495 * SRFI-19 Time/Date conversions::
2496 * SRFI-19 Date to string::
2497 * SRFI-19 String to date::
2500 @node SRFI-19 Introduction
2501 @subsubsection SRFI-19 Introduction
2503 @cindex universal time
2507 This module implements time and date representations and calculations,
2508 in various time systems, including universal time (UTC) and atomic
2511 For those not familiar with these time systems, TAI is based on a
2512 fixed length second derived from oscillations of certain atoms. UTC
2513 differs from TAI by an integral number of seconds, which is increased
2514 or decreased at announced times to keep UTC aligned to a mean solar
2515 day (the orbit and rotation of the earth are not quite constant).
2518 So far, only increases in the TAI
2525 UTC difference have been needed. Such an increase is a ``leap
2526 second'', an extra second of TAI introduced at the end of a UTC day.
2527 When working entirely within UTC this is never seen, every day simply
2528 has 86400 seconds. But when converting from TAI to a UTC date, an
2529 extra 23:59:60 is present, where normally a day would end at 23:59:59.
2530 Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI
2533 @cindex system clock
2534 In the current implementation, the system clock is assumed to be UTC,
2535 and a table of leap seconds in the code converts to TAI. See comments
2536 in @file{srfi-19.scm} for how to update this table.
2539 @cindex modified julian day
2540 Also, for those not familiar with the terminology, a @dfn{Julian Day}
2541 is a real number which is a count of days and fraction of a day, in
2542 UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
2543 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from
2544 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time
2545 is julian day 2400000.5.
2547 @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
2548 @c noon, UTC), but this is incorrect. It looks like it might have
2549 @c arisen from the code incorrectly treating years a multiple of 100
2550 @c but not 400 prior to 1582 as non-leap years, where instead the Julian
2551 @c calendar should be used so all multiples of 4 before 1582 are leap
2556 @subsubsection SRFI-19 Time
2559 A @dfn{time} object has type, seconds and nanoseconds fields
2560 representing a point in time starting from some epoch. This is an
2561 arbitrary point in time, not just a time of day. Although times are
2562 represented in nanoseconds, the actual resolution may be lower.
2564 The following variables hold the possible time types. For instance
2565 @code{(current-time time-process)} would give the current CPU process
2569 Universal Coordinated Time (UTC).
2574 International Atomic Time (TAI).
2578 @defvar time-monotonic
2579 Monotonic time, meaning a monotonically increasing time starting from
2580 an unspecified epoch.
2582 Note that in the current implementation @code{time-monotonic} is the
2583 same as @code{time-tai}, and unfortunately is therefore affected by
2584 adjustments to the system clock. Perhaps this will change in the
2588 @defvar time-duration
2589 A duration, meaning simply a difference between two times.
2592 @defvar time-process
2593 CPU time spent in the current process, starting from when the process
2595 @cindex process time
2599 CPU time spent in the current thread. Not currently implemented.
2605 Return @code{#t} if @var{obj} is a time object, or @code{#f} if not.
2608 @defun make-time type nanoseconds seconds
2609 Create a time object with the given @var{type}, @var{seconds} and
2613 @defun time-type time
2614 @defunx time-nanosecond time
2615 @defunx time-second time
2616 @defunx set-time-type! time type
2617 @defunx set-time-nanosecond! time nsec
2618 @defunx set-time-second! time sec
2619 Get or set the type, seconds or nanoseconds fields of a time object.
2621 @code{set-time-type!} merely changes the field, it doesn't convert the
2622 time value. For conversions, see @ref{SRFI-19 Time/Date conversions}.
2625 @defun copy-time time
2626 Return a new time object, which is a copy of the given @var{time}.
2629 @defun current-time [type]
2630 Return the current time of the given @var{type}. The default
2631 @var{type} is @code{time-utc}.
2633 Note that the name @code{current-time} conflicts with the Guile core
2634 @code{current-time} function (@pxref{Time}) as well as the SRFI-18
2635 @code{current-time} function (@pxref{SRFI-18 Time}). Applications
2636 wanting to use more than one of these functions will need to refer to
2637 them by different names.
2640 @defun time-resolution [type]
2641 Return the resolution, in nanoseconds, of the given time @var{type}.
2642 The default @var{type} is @code{time-utc}.
2645 @defun time<=? t1 t2
2646 @defunx time<? t1 t2
2647 @defunx time=? t1 t2
2648 @defunx time>=? t1 t2
2649 @defunx time>? t1 t2
2650 Return @code{#t} or @code{#f} according to the respective relation
2651 between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2}
2652 must be the same time type.
2655 @defun time-difference t1 t2
2656 @defunx time-difference! t1 t2
2657 Return a time object of type @code{time-duration} representing the
2658 period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be
2661 @code{time-difference} returns a new time object,
2662 @code{time-difference!} may modify @var{t1} to form its return.
2665 @defun add-duration time duration
2666 @defunx add-duration! time duration
2667 @defunx subtract-duration time duration
2668 @defunx subtract-duration! time duration
2669 Return a time object which is @var{time} with the given @var{duration}
2670 added or subtracted. @var{duration} must be a time object of type
2671 @code{time-duration}.
2673 @code{add-duration} and @code{subtract-duration} return a new time
2674 object. @code{add-duration!} and @code{subtract-duration!} may modify
2675 the given @var{time} to form their return.
2680 @subsubsection SRFI-19 Date
2683 A @dfn{date} object represents a date in the Gregorian calendar and a
2684 time of day on that date in some timezone.
2686 The fields are year, month, day, hour, minute, second, nanoseconds and
2687 timezone. A date object is immutable, its fields can be read but they
2688 cannot be modified once the object is created.
2691 Return @code{#t} if @var{obj} is a date object, or @code{#f} if not.
2694 @defun make-date nsecs seconds minutes hours date month year zone-offset
2695 Create a new date object.
2697 @c FIXME: What can we say about the ranges of the values. The
2698 @c current code looks it doesn't normalize, but expects then in their
2699 @c usual range already.
2703 @defun date-nanosecond date
2704 Nanoseconds, 0 to 999999999.
2707 @defun date-second date
2708 Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working
2709 entirely within UTC, it's only when converting to or from TAI.
2712 @defun date-minute date
2716 @defun date-hour date
2720 @defun date-day date
2721 Day of the month, 1 to 31 (or less, according to the month).
2724 @defun date-month date
2728 @defun date-year date
2729 Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46
2730 B.C. There is no year 0, year @math{-1} is followed by year 1.
2733 @defun date-zone-offset date
2734 Time zone, an integer number of seconds east of Greenwich.
2737 @defun date-year-day date
2738 Day of the year, starting from 1 for 1st January.
2741 @defun date-week-day date
2742 Day of the week, starting from 0 for Sunday.
2745 @defun date-week-number date dstartw
2746 Week of the year, ignoring a first partial week. @var{dstartw} is the
2747 day of the week which is taken to start a week, 0 for Sunday, 1 for
2750 @c FIXME: The spec doesn't say whether numbering starts at 0 or 1.
2751 @c The code looks like it's 0, if that's the correct intention.
2755 @c The SRFI text doesn't actually give the default for tz-offset, but
2756 @c the reference implementation has the local timezone and the
2757 @c conversions functions all specify that, so it should be ok to
2758 @c document it here.
2760 @defun current-date [tz-offset]
2761 Return a date object representing the current date/time, in UTC offset
2762 by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and
2763 defaults to the local timezone.
2766 @defun current-julian-day
2768 Return the current Julian Day.
2771 @defun current-modified-julian-day
2772 @cindex modified julian day
2773 Return the current Modified Julian Day.
2777 @node SRFI-19 Time/Date conversions
2778 @subsubsection SRFI-19 Time/Date conversions
2779 @cindex time conversion
2780 @cindex date conversion
2782 @defun date->julian-day date
2783 @defunx date->modified-julian-day date
2784 @defunx date->time-monotonic date
2785 @defunx date->time-tai date
2786 @defunx date->time-utc date
2788 @defun julian-day->date jdn [tz-offset]
2789 @defunx julian-day->time-monotonic jdn
2790 @defunx julian-day->time-tai jdn
2791 @defunx julian-day->time-utc jdn
2793 @defun modified-julian-day->date jdn [tz-offset]
2794 @defunx modified-julian-day->time-monotonic jdn
2795 @defunx modified-julian-day->time-tai jdn
2796 @defunx modified-julian-day->time-utc jdn
2798 @defun time-monotonic->date time [tz-offset]
2799 @defunx time-monotonic->time-tai time
2800 @defunx time-monotonic->time-tai! time
2801 @defunx time-monotonic->time-utc time
2802 @defunx time-monotonic->time-utc! time
2804 @defun time-tai->date time [tz-offset]
2805 @defunx time-tai->julian-day time
2806 @defunx time-tai->modified-julian-day time
2807 @defunx time-tai->time-monotonic time
2808 @defunx time-tai->time-monotonic! time
2809 @defunx time-tai->time-utc time
2810 @defunx time-tai->time-utc! time
2812 @defun time-utc->date time [tz-offset]
2813 @defunx time-utc->julian-day time
2814 @defunx time-utc->modified-julian-day time
2815 @defunx time-utc->time-monotonic time
2816 @defunx time-utc->time-monotonic! time
2817 @defunx time-utc->time-tai time
2818 @defunx time-utc->time-tai! time
2820 Convert between dates, times and days of the respective types. For
2821 instance @code{time-tai->time-utc} accepts a @var{time} object of type
2822 @code{time-tai} and returns an object of type @code{time-utc}.
2824 The @code{!} variants may modify their @var{time} argument to form
2825 their return. The plain functions create a new object.
2827 For conversions to dates, @var{tz-offset} is seconds east of
2828 Greenwich. The default is the local timezone, at the given time, as
2829 provided by the system, using @code{localtime} (@pxref{Time}).
2831 On 32-bit systems, @code{localtime} is limited to a 32-bit
2832 @code{time_t}, so a default @var{tz-offset} is only available for
2833 times between Dec 1901 and Jan 2038. For prior dates an application
2834 might like to use the value in 1902, though some locations have zone
2835 changes prior to that. For future dates an application might like to
2836 assume today's rules extend indefinitely. But for correct daylight
2837 savings transitions it will be necessary to take an offset for the
2838 same day and time but a year in range and which has the same starting
2839 weekday and same leap/non-leap (to support rules like last Sunday in
2843 @node SRFI-19 Date to string
2844 @subsubsection SRFI-19 Date to string
2845 @cindex date to string
2846 @cindex string, from date
2848 @defun date->string date [format]
2849 Convert a date to a string under the control of a format.
2850 @var{format} should be a string containing @samp{~} escapes, which
2851 will be expanded as per the following conversion table. The default
2852 @var{format} is @samp{~c}, a locale-dependent date and time.
2854 Many of these conversion characters are the same as POSIX
2855 @code{strftime} (@pxref{Time}), but there are some extras and some
2858 @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM}
2859 @item @nicode{~~} @tab literal ~
2860 @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun}
2861 @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday}
2862 @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan}
2863 @item @nicode{~B} @tab locale full month, eg.@: @samp{January}
2864 @item @nicode{~c} @tab locale date and time, eg.@: @*
2865 @samp{Fri Jul 14 20:28:42-0400 2000}
2866 @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31}
2868 @c Spec says d/m/y, reference implementation says m/d/y.
2869 @c Apparently the reference code was the intention, but would like to
2870 @c see an errata published for the spec before contradicting it here.
2872 @c @item @nicode{~D} @tab date @nicode{~d/~m/~y}
2874 @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31}
2875 @item @nicode{~f} @tab seconds and fractional seconds,
2876 with locale decimal point, eg.@: @samp{5.2}
2877 @item @nicode{~h} @tab same as @nicode{~b}
2878 @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23}
2879 @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12}
2880 @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366}
2881 @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23}
2882 @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12}
2883 @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12}
2884 @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59}
2885 @item @nicode{~n} @tab newline
2886 @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999}
2887 @item @nicode{~p} @tab locale AM or PM
2888 @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p}
2889 @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC
2890 @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @*
2891 (usual limit is 59, 60 is a leap second)
2892 @item @nicode{~t} @tab horizontal tab character
2893 @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S}
2894 @item @nicode{~U} @tab week of year, Sunday first day of week,
2895 @samp{00} to @samp{52}
2896 @item @nicode{~V} @tab week of year, Monday first day of week,
2897 @samp{01} to @samp{53}
2898 @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6}
2899 @item @nicode{~W} @tab week of year, Monday first day of week,
2900 @samp{00} to @samp{52}
2902 @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale
2903 @c date. The reference code has ~x as the locale date and ~X as a
2904 @c locale time. The rule is apparently that the code should be
2905 @c believed, but would like to see an errata for the spec before
2906 @c contradicting it here.
2908 @c @item @nicode{~x} @tab week of year, Monday as first day of week,
2909 @c @samp{00} to @samp{53}
2910 @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00}
2912 @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99}
2913 @item @nicode{~Y} @tab year, full, eg.@: @samp{2003}
2914 @item @nicode{~z} @tab time zone, RFC-822 style
2915 @item @nicode{~Z} @tab time zone symbol (not currently implemented)
2916 @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d}
2917 @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~H:~M:~S~z}
2918 @item @nicode{~3} @tab ISO-8601 time, @samp{~H:~M:~S}
2919 @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~H:~M:~S~z}
2920 @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~H:~M:~S}
2924 Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently
2925 described here, since the specification and reference implementation
2928 Conversion is locale-dependent on systems that support it
2929 (@pxref{Accessing Locale Information}). @xref{Locales,
2930 @code{setlocale}}, for information on how to change the current
2934 @node SRFI-19 String to date
2935 @subsubsection SRFI-19 String to date
2936 @cindex string to date
2937 @cindex date, from string
2939 @c FIXME: Can we say what happens when an incomplete date is
2940 @c converted? I.e. fields left as 0, or what? The spec seems to be
2943 @defun string->date input template
2944 Convert an @var{input} string to a date under the control of a
2945 @var{template} string. Return a newly created date object.
2947 Literal characters in @var{template} must match characters in
2948 @var{input} and @samp{~} escapes must match the input forms described
2949 in the table below. ``Skip to'' means characters up to one of the
2950 given type are ignored, or ``no skip'' for no skipping. ``Read'' is
2951 what's then read, and ``Set'' is the field affected in the date
2954 For example @samp{~Y} skips input characters until a digit is reached,
2955 at which point it expects a year and stores that to the year field of
2958 @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}}
2970 @tab @nicode{char-alphabetic?}
2971 @tab locale abbreviated weekday name
2975 @tab @nicode{char-alphabetic?}
2976 @tab locale full weekday name
2979 @c Note that the SRFI spec says that ~b and ~B don't set anything,
2980 @c but that looks like a mistake. The reference implementation sets
2981 @c the month field, which seems sensible and is what we describe
2985 @tab @nicode{char-alphabetic?}
2986 @tab locale abbreviated month name
2987 @tab @nicode{date-month}
2990 @tab @nicode{char-alphabetic?}
2991 @tab locale full month name
2992 @tab @nicode{date-month}
2995 @tab @nicode{char-numeric?}
2997 @tab @nicode{date-day}
3001 @tab day of month, blank padded
3002 @tab @nicode{date-day}
3005 @tab same as @samp{~b}
3008 @tab @nicode{char-numeric?}
3010 @tab @nicode{date-hour}
3014 @tab hour, blank padded
3015 @tab @nicode{date-hour}
3018 @tab @nicode{char-numeric?}
3020 @tab @nicode{date-month}
3023 @tab @nicode{char-numeric?}
3025 @tab @nicode{date-minute}
3028 @tab @nicode{char-numeric?}
3030 @tab @nicode{date-second}
3035 @tab @nicode{date-year} within 50 years
3038 @tab @nicode{char-numeric?}
3040 @tab @nicode{date-year}
3045 @tab date-zone-offset
3048 Notice that the weekday matching forms don't affect the date object
3049 returned, instead the weekday will be derived from the day, month and
3052 Conversion is locale-dependent on systems that support it
3053 (@pxref{Accessing Locale Information}). @xref{Locales,
3054 @code{setlocale}}, for information on how to change the current
3059 @subsection SRFI-23 - Error Reporting
3062 The SRFI-23 @code{error} procedure is always available.
3065 @subsection SRFI-26 - specializing parameters
3067 @cindex parameter specialize
3068 @cindex argument specialize
3069 @cindex specialize parameter
3071 This SRFI provides a syntax for conveniently specializing selected
3072 parameters of a function. It can be used with,
3075 (use-modules (srfi srfi-26))
3078 @deffn {library syntax} cut slot1 slot2 @dots{}
3079 @deffnx {library syntax} cute slot1 slot2 @dots{}
3080 Return a new procedure which will make a call (@var{slot1} @var{slot2}
3081 @dots{}) but with selected parameters specialized to given expressions.
3083 An example will illustrate the idea. The following is a
3084 specialization of @code{write}, sending output to
3085 @code{my-output-port},
3088 (cut write <> my-output-port)
3090 (lambda (obj) (write obj my-output-port))
3093 The special symbol @code{<>} indicates a slot to be filled by an
3094 argument to the new procedure. @code{my-output-port} on the other
3095 hand is an expression to be evaluated and passed, ie.@: it specializes
3096 the behaviour of @code{write}.
3100 A slot to be filled by an argument from the created procedure.
3101 Arguments are assigned to @code{<>} slots in the order they appear in
3102 the @code{cut} form, there's no way to re-arrange arguments.
3104 The first argument to @code{cut} is usually a procedure (or expression
3105 giving a procedure), but @code{<>} is allowed there too. For example,
3110 (lambda (proc) (proc 1 2 3))
3114 A slot to be filled by all remaining arguments from the new procedure.
3115 This can only occur at the end of a @code{cut} form.
3117 For example, a procedure taking a variable number of arguments like
3118 @code{max} but in addition enforcing a lower bound,
3121 (define my-lower-bound 123)
3123 (cut max my-lower-bound <...>)
3125 (lambda arglist (apply max my-lower-bound arglist))
3129 For @code{cut} the specializing expressions are evaluated each time
3130 the new procedure is called. For @code{cute} they're evaluated just
3131 once, when the new procedure is created. The name @code{cute} stands
3132 for ``@code{cut} with evaluated arguments''. In all cases the
3133 evaluations take place in an unspecified order.
3135 The following illustrates the difference between @code{cut} and
3139 (cut format <> "the time is ~s" (current-time))
3141 (lambda (port) (format port "the time is ~s" (current-time)))
3143 (cute format <> "the time is ~s" (current-time))
3145 (let ((val (current-time)))
3146 (lambda (port) (format port "the time is ~s" val))
3149 (There's no provision for a mixture of @code{cut} and @code{cute}
3150 where some expressions would be evaluated every time but others
3151 evaluated only once.)
3153 @code{cut} is really just a shorthand for the sort of @code{lambda}
3154 forms shown in the above examples. But notice @code{cut} avoids the
3155 need to name unspecialized parameters, and is more compact. Use in
3156 functional programming style or just with @code{map}, @code{for-each}
3157 or similar is typical.
3160 (map (cut * 2 <>) '(1 2 3 4))
3162 (for-each (cut write <> my-port) my-list)
3167 @subsection SRFI-27 - Sources of Random Bits
3170 This subsection is based on the
3171 @uref{http://srfi.schemers.org/srfi-27/srfi-27.html, specification of
3172 SRFI-27} written by Sebastian Egner.
3174 @c The copyright notice and license text of the SRFI-27 specification is
3175 @c reproduced below:
3177 @c Copyright (C) Sebastian Egner (2002). All Rights Reserved.
3179 @c Permission is hereby granted, free of charge, to any person obtaining a
3180 @c copy of this software and associated documentation files (the
3181 @c "Software"), to deal in the Software without restriction, including
3182 @c without limitation the rights to use, copy, modify, merge, publish,
3183 @c distribute, sublicense, and/or sell copies of the Software, and to
3184 @c permit persons to whom the Software is furnished to do so, subject to
3185 @c the following conditions:
3187 @c The above copyright notice and this permission notice shall be included
3188 @c in all copies or substantial portions of the Software.
3190 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3191 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3192 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3193 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3194 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3195 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3196 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3198 This SRFI provides access to a (pseudo) random number generator; for
3199 Guile's built-in random number facilities, which SRFI-27 is implemented
3200 upon, @xref{Random}. With SRFI-27, random numbers are obtained from a
3201 @emph{random source}, which encapsulates a random number generation
3202 algorithm and its state.
3205 * SRFI-27 Default Random Source:: Obtaining random numbers
3206 * SRFI-27 Random Sources:: Creating and manipulating random sources
3207 * SRFI-27 Random Number Generators:: Obtaining random number generators
3210 @node SRFI-27 Default Random Source
3211 @subsubsection The Default Random Source
3214 @defun random-integer n
3215 Return a random number between zero (inclusive) and @var{n} (exclusive),
3216 using the default random source. The numbers returned have a uniform
3221 Return a random number in (0,1), using the default random source. The
3222 numbers returned have a uniform distribution.
3225 @defun default-random-source
3226 A random source from which @code{random-integer} and @code{random-real}
3227 have been derived using @code{random-source-make-integers} and
3228 @code{random-source-make-reals} (@pxref{SRFI-27 Random Number Generators}
3229 for those procedures). Note that an assignment to
3230 @code{default-random-source} does not change @code{random-integer} or
3231 @code{random-real}; it is also strongly recommended not to assign a new
3235 @node SRFI-27 Random Sources
3236 @subsubsection Random Sources
3239 @defun make-random-source
3240 Create a new random source. The stream of random numbers obtained from
3241 each random source created by this procedure will be identical, unless
3242 its state is changed by one of the procedures below.
3245 @defun random-source? object
3246 Tests whether @var{object} is a random source. Random sources are a
3250 @defun random-source-randomize! source
3251 Attempt to set the state of the random source to a truly random value.
3252 The current implementation uses a seed based on the current system time.
3255 @defun random-source-pseudo-randomize! source i j
3256 Changes the state of the random source s into the initial state of the
3257 (@var{i}, @var{j})-th independent random source, where @var{i} and
3258 @var{j} are non-negative integers. This procedure provides a mechanism
3259 to obtain a large number of independent random sources (usually all
3260 derived from the same backbone generator), indexed by two integers. In
3261 contrast to @code{random-source-randomize!}, this procedure is entirely
3265 The state associated with a random state can be obtained an reinstated
3266 with the following procedures:
3268 @defun random-source-state-ref source
3269 @defunx random-source-state-set! source state
3270 Get and set the state of a random source. No assumptions should be made
3271 about the nature of the state object, besides it having an external
3272 representation (i.e.@: it can be passed to @code{write} and subsequently
3276 @node SRFI-27 Random Number Generators
3277 @subsubsection Obtaining random number generator procedures
3280 @defun random-source-make-integers source
3281 Obtains a procedure to generate random integers using the random source
3282 @var{source}. The returned procedure takes a single argument @var{n},
3283 which must be a positive integer, and returns the next uniformly
3284 distributed random integer from the interval @{0, ..., @var{n}-1@} by
3285 advancing the state of @var{source}.
3287 If an application obtains and uses several generators for the same
3288 random source @var{source}, a call to any of these generators advances
3289 the state of @var{source}. Hence, the generators do not produce the
3290 same sequence of random integers each but rather share a state. This
3291 also holds for all other types of generators derived from a fixed random
3294 While the SRFI text specifies that ``Implementations that support
3295 concurrency make sure that the state of a generator is properly
3296 advanced'', this is currently not the case in Guile's implementation of
3297 SRFI-27, as it would cause a severe performance penalty. So in
3298 multi-threaded programs, you either must perform locking on random
3299 sources shared between threads yourself, or use different random sources
3300 for multiple threads.
3303 @defun random-source-make-reals source
3304 @defunx random-source-make-reals source unit
3305 Obtains a procedure to generate random real numbers @math{0 < x < 1}
3306 using the random source @var{source}. The procedure rand is called
3309 The optional parameter @var{unit} determines the type of numbers being
3310 produced by the returned procedure and the quantization of the output.
3311 @var{unit} must be a number such that @math{0 < @var{unit} < 1}. The
3312 numbers created by the returned procedure are of the same numerical type
3313 as @var{unit} and the potential output values are spaced by at most
3314 @var{unit}. One can imagine rand to create numbers as @var{x} *
3315 @var{unit} where @var{x} is a random integer in @{1, ...,
3316 floor(1/unit)-1@}. Note, however, that this need not be the way the
3317 values are actually created and that the actual resolution of rand can
3318 be much higher than unit. In case @var{unit} is absent it defaults to a
3319 reasonably small value (related to the width of the mantissa of an
3320 efficient number format).
3324 @subsection SRFI-30 - Nested Multi-line Comments
3327 Starting from version 2.0, Guile's @code{read} supports SRFI-30/R6RS
3328 nested multi-line comments by default, @ref{Block Comments}.
3331 @subsection SRFI-31 - A special form `rec' for recursive evaluation
3333 @cindex recursive expression
3336 SRFI-31 defines a special form that can be used to create
3337 self-referential expressions more conveniently. The syntax is as
3342 <rec expression> --> (rec <variable> <expression>)
3343 <rec expression> --> (rec (<variable>+) <body>)
3347 The first syntax can be used to create self-referential expressions,
3351 guile> (define tmp (rec ones (cons 1 (delay ones))))
3354 The second syntax can be used to create anonymous recursive functions:
3357 guile> (define tmp (rec (display-n item n)
3359 (begin (display n) (display-n (- n 1))))))
3367 @subsection SRFI-34 - Exception handling for programs
3370 Guile provides an implementation of
3371 @uref{http://srfi.schemers.org/srfi-34/srfi-34.html, SRFI-34's exception
3372 handling mechanisms} as an alternative to its own built-in mechanisms
3373 (@pxref{Exceptions}). It can be made available as follows:
3376 (use-modules (srfi srfi-34))
3379 @c FIXME: Document it.
3383 @subsection SRFI-35 - Conditions
3389 @uref{http://srfi.schemers.org/srfi-35/srfi-35.html, SRFI-35} implements
3390 @dfn{conditions}, a data structure akin to records designed to convey
3391 information about exceptional conditions between parts of a program. It
3392 is normally used in conjunction with SRFI-34's @code{raise}:
3395 (raise (condition (&message
3396 (message "An error occurred"))))
3399 Users can define @dfn{condition types} containing arbitrary information.
3400 Condition types may inherit from one another. This allows the part of
3401 the program that handles (or ``catches'') conditions to get accurate
3402 information about the exceptional condition that arose.
3404 SRFI-35 conditions are made available using:
3407 (use-modules (srfi srfi-35))
3410 The procedures available to manipulate condition types are the
3413 @deffn {Scheme Procedure} make-condition-type id parent field-names
3414 Return a new condition type named @var{id}, inheriting from
3415 @var{parent}, and with the fields whose names are listed in
3416 @var{field-names}. @var{field-names} must be a list of symbols and must
3417 not contain names already used by @var{parent} or one of its supertypes.
3420 @deffn {Scheme Procedure} condition-type? obj
3421 Return true if @var{obj} is a condition type.
3424 Conditions can be created and accessed with the following procedures:
3426 @deffn {Scheme Procedure} make-condition type . field+value
3427 Return a new condition of type @var{type} with fields initialized as
3428 specified by @var{field+value}, a sequence of field names (symbols) and
3429 values as in the following example:
3432 (let ((&ct (make-condition-type 'foo &condition '(a b c))))
3433 (make-condition &ct 'a 1 'b 2 'c 3))
3436 Note that all fields of @var{type} and its supertypes must be specified.
3439 @deffn {Scheme Procedure} make-compound-condition condition1 condition2 @dots{}
3440 Return a new compound condition composed of @var{condition1}
3441 @var{condition2} @enddots{}. The returned condition has the type of
3442 each condition of condition1 condition2 @dots{} (per
3443 @code{condition-has-type?}).
3446 @deffn {Scheme Procedure} condition-has-type? c type
3447 Return true if condition @var{c} has type @var{type}.
3450 @deffn {Scheme Procedure} condition-ref c field-name
3451 Return the value of the field named @var{field-name} from condition @var{c}.
3453 If @var{c} is a compound condition and several underlying condition
3454 types contain a field named @var{field-name}, then the value of the
3455 first such field is returned, using the order in which conditions were
3456 passed to @code{make-compound-condition}.
3459 @deffn {Scheme Procedure} extract-condition c type
3460 Return a condition of condition type @var{type} with the field values
3461 specified by @var{c}.
3463 If @var{c} is a compound condition, extract the field values from the
3464 subcondition belonging to @var{type} that appeared first in the call to
3465 @code{make-compound-condition} that created the condition.
3468 Convenience macros are also available to create condition types and
3471 @deffn {library syntax} define-condition-type type supertype predicate field-spec...
3472 Define a new condition type named @var{type} that inherits from
3473 @var{supertype}. In addition, bind @var{predicate} to a type predicate
3474 that returns true when passed a condition of type @var{type} or any of
3475 its subtypes. @var{field-spec} must have the form @code{(field
3476 accessor)} where @var{field} is the name of field of @var{type} and
3477 @var{accessor} is the name of a procedure to access field @var{field} in
3478 conditions of type @var{type}.
3480 The example below defines condition type @code{&foo}, inheriting from
3481 @code{&condition} with fields @code{a}, @code{b} and @code{c}:
3484 (define-condition-type &foo &condition
3492 @deffn {library syntax} condition type-field-binding1 type-field-binding2 @dots{}
3493 Return a new condition or compound condition, initialized according to
3494 @var{type-field-binding1} @var{type-field-binding2} @enddots{}. Each
3495 @var{type-field-binding} must have the form @code{(type
3496 field-specs...)}, where @var{type} is the name of a variable bound to a
3497 condition type; each @var{field-spec} must have the form
3498 @code{(field-name value)} where @var{field-name} is a symbol denoting
3499 the field being initialized to @var{value}. As for
3500 @code{make-condition}, all fields must be specified.
3502 The following example returns a simple condition:
3505 (condition (&message (message "An error occurred")))
3508 The one below returns a compound condition:
3511 (condition (&message (message "An error occurred"))
3516 Finally, SRFI-35 defines a several standard condition types.
3519 This condition type is the root of all condition types. It has no
3524 A condition type that carries a message describing the nature of the
3525 condition to humans.
3528 @deffn {Scheme Procedure} message-condition? c
3529 Return true if @var{c} is of type @code{&message} or one of its
3533 @deffn {Scheme Procedure} condition-message c
3534 Return the message associated with message condition @var{c}.
3538 This type describes conditions serious enough that they cannot safely be
3539 ignored. It has no fields.
3542 @deffn {Scheme Procedure} serious-condition? c
3543 Return true if @var{c} is of type @code{&serious} or one of its
3548 This condition describes errors, typically caused by something that has
3549 gone wrong in the interaction of the program with the external world or
3553 @deffn {Scheme Procedure} error? c
3554 Return true if @var{c} is of type @code{&error} or one of its subtypes.
3558 @subsection SRFI-37 - args-fold
3561 This is a processor for GNU @code{getopt_long}-style program
3562 arguments. It provides an alternative, less declarative interface
3563 than @code{getopt-long} in @code{(ice-9 getopt-long)}
3564 (@pxref{getopt-long,,The (ice-9 getopt-long) Module}). Unlike
3565 @code{getopt-long}, it supports repeated options and any number of
3566 short and long names per option. Access it with:
3569 (use-modules (srfi srfi-37))
3572 @acronym{SRFI}-37 principally provides an @code{option} type and the
3573 @code{args-fold} function. To use the library, create a set of
3574 options with @code{option} and use it as a specification for invoking
3577 Here is an example of a simple argument processor for the typical
3578 @samp{--version} and @samp{--help} options, which returns a backwards
3579 list of files given on the command line:
3582 (args-fold (cdr (program-arguments))
3583 (let ((display-and-exit-proc
3585 (lambda (opt name arg loads)
3586 (display msg) (quit)))))
3587 (list (option '(#\v "version") #f #f
3588 (display-and-exit-proc "Foo version 42.0\n"))
3589 (option '(#\h "help") #f #f
3590 (display-and-exit-proc
3591 "Usage: foo scheme-file ..."))))
3592 (lambda (opt name arg loads)
3593 (error "Unrecognized option `~A'" name))
3594 (lambda (op loads) (cons op loads))
3598 @deffn {Scheme Procedure} option names required-arg? optional-arg? processor
3599 Return an object that specifies a single kind of program option.
3601 @var{names} is a list of command-line option names, and should consist of
3602 characters for traditional @code{getopt} short options and strings for
3603 @code{getopt_long}-style long options.
3605 @var{required-arg?} and @var{optional-arg?} are mutually exclusive;
3606 one or both must be @code{#f}. If @var{required-arg?}, the option
3607 must be followed by an argument on the command line, such as
3608 @samp{--opt=value} for long options, or an error will be signalled.
3609 If @var{optional-arg?}, an argument will be taken if available.
3611 @var{processor} is a procedure that takes at least 3 arguments, called
3612 when @code{args-fold} encounters the option: the containing option
3613 object, the name used on the command line, and the argument given for
3614 the option (or @code{#f} if none). The rest of the arguments are
3615 @code{args-fold} ``seeds'', and the @var{processor} should return
3619 @deffn {Scheme Procedure} option-names opt
3620 @deffnx {Scheme Procedure} option-required-arg? opt
3621 @deffnx {Scheme Procedure} option-optional-arg? opt
3622 @deffnx {Scheme Procedure} option-processor opt
3623 Return the specified field of @var{opt}, an option object, as
3624 described above for @code{option}.
3627 @deffn {Scheme Procedure} args-fold args options unrecognized-option-proc operand-proc seed @dots{}
3628 Process @var{args}, a list of program arguments such as that returned by
3629 @code{(cdr (program-arguments))}, in order against @var{options}, a list
3630 of option objects as described above. All functions called take the
3631 ``seeds'', or the last multiple-values as multiple arguments, starting
3632 with @var{seed} @dots{}, and must return the new seeds. Return the
3635 Call @code{unrecognized-option-proc}, which is like an option object's
3636 processor, for any options not found in @var{options}.
3638 Call @code{operand-proc} with any items on the command line that are
3639 not named options. This includes arguments after @samp{--}. It is
3640 called with the argument in question, as well as the seeds.
3644 @subsection SRFI-38 - External Representation for Data With Shared Structure
3647 This subsection is based on
3648 @uref{http://srfi.schemers.org/srfi-38/srfi-38.html, the specification
3649 of SRFI-38} written by Ray Dillinger.
3651 @c Copyright (C) Ray Dillinger 2003. All Rights Reserved.
3653 @c Permission is hereby granted, free of charge, to any person obtaining a
3654 @c copy of this software and associated documentation files (the
3655 @c "Software"), to deal in the Software without restriction, including
3656 @c without limitation the rights to use, copy, modify, merge, publish,
3657 @c distribute, sublicense, and/or sell copies of the Software, and to
3658 @c permit persons to whom the Software is furnished to do so, subject to
3659 @c the following conditions:
3661 @c The above copyright notice and this permission notice shall be included
3662 @c in all copies or substantial portions of the Software.
3664 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3665 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3666 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3667 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3668 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3669 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3670 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3672 This SRFI creates an alternative external representation for data
3673 written and read using @code{write-with-shared-structure} and
3674 @code{read-with-shared-structure}. It is identical to the grammar for
3675 external representation for data written and read with @code{write} and
3676 @code{read} given in section 7 of R5RS, except that the single
3680 <datum> --> <simple datum> | <compound datum>
3683 is replaced by the following five productions:
3686 <datum> --> <defining datum> | <nondefining datum> | <defined datum>
3687 <defining datum> --> #<indexnum>=<nondefining datum>
3688 <defined datum> --> #<indexnum>#
3689 <nondefining datum> --> <simple datum> | <compound datum>
3690 <indexnum> --> <digit 10>+
3693 @deffn {Scheme procedure} write-with-shared-structure obj
3694 @deffnx {Scheme procedure} write-with-shared-structure obj port
3695 @deffnx {Scheme procedure} write-with-shared-structure obj port optarg
3697 Writes an external representation of @var{obj} to the given port.
3698 Strings that appear in the written representation are enclosed in
3699 doublequotes, and within those strings backslash and doublequote
3700 characters are escaped by backslashes. Character objects are written
3701 using the @code{#\} notation.
3703 Objects which denote locations rather than values (cons cells, vectors,
3704 and non-zero-length strings in R5RS scheme; also Guile's structs,
3705 bytevectors and ports and hash-tables), if they appear at more than one
3706 point in the data being written, are preceded by @samp{#@var{N}=} the
3707 first time they are written and replaced by @samp{#@var{N}#} all
3708 subsequent times they are written, where @var{N} is a natural number
3709 used to identify that particular object. If objects which denote
3710 locations occur only once in the structure, then
3711 @code{write-with-shared-structure} must produce the same external
3712 representation for those objects as @code{write}.
3714 @code{write-with-shared-structure} terminates in finite time and
3715 produces a finite representation when writing finite data.
3717 @code{write-with-shared-structure} returns an unspecified value. The
3718 @var{port} argument may be omitted, in which case it defaults to the
3719 value returned by @code{(current-output-port)}. The @var{optarg}
3720 argument may also be omitted. If present, its effects on the output and
3721 return value are unspecified but @code{write-with-shared-structure} must
3722 still write a representation that can be read by
3723 @code{read-with-shared-structure}. Some implementations may wish to use
3724 @var{optarg} to specify formatting conventions, numeric radixes, or
3725 return values. Guile's implementation ignores @var{optarg}.
3727 For example, the code
3730 (begin (define a (cons 'val1 'val2))
3732 (write-with-shared-structure a))
3735 should produce the output @code{#1=(val1 . #1#)}. This shows a cons
3736 cell whose @code{cdr} contains itself.
3740 @deffn {Scheme procedure} read-with-shared-structure
3741 @deffnx {Scheme procedure} read-with-shared-structure port
3743 @code{read-with-shared-structure} converts the external representations
3744 of Scheme objects produced by @code{write-with-shared-structure} into
3745 Scheme objects. That is, it is a parser for the nonterminal
3746 @samp{<datum>} in the augmented external representation grammar defined
3747 above. @code{read-with-shared-structure} returns the next object
3748 parsable from the given input port, updating @var{port} to point to the
3749 first character past the end of the external representation of the
3752 If an end-of-file is encountered in the input before any characters are
3753 found that can begin an object, then an end-of-file object is returned.
3754 The port remains open, and further attempts to read it (by
3755 @code{read-with-shared-structure} or @code{read} will also return an
3756 end-of-file object. If an end of file is encountered after the
3757 beginning of an object's external representation, but the external
3758 representation is incomplete and therefore not parsable, an error is
3761 The @var{port} argument may be omitted, in which case it defaults to the
3762 value returned by @code{(current-input-port)}. It is an error to read
3768 @subsection SRFI-39 - Parameters
3771 This SRFI adds support for dynamically-scoped parameters. SRFI 39 is
3772 implemented in the Guile core; there's no module needed to get SRFI-39
3773 itself. Parameters are documented in @ref{Parameters}.
3775 This module does export one extra function: @code{with-parameters*}.
3776 This is a Guile-specific addition to the SRFI, similar to the core
3777 @code{with-fluids*} (@pxref{Fluids and Dynamic States}).
3779 @defun with-parameters* param-list value-list thunk
3780 Establish a new dynamic scope, as per @code{parameterize} above,
3781 taking parameters from @var{param-list} and corresponding values from
3782 @var{value-list}. A call @code{(@var{thunk})} is made in the new
3783 scope and the result from that @var{thunk} is the return from
3784 @code{with-parameters*}.
3788 @subsection SRFI-42 - Eager Comprehensions
3791 See @uref{http://srfi.schemers.org/srfi-42/srfi-42.html, the
3792 specification of SRFI-42}.
3795 @subsection SRFI-45 - Primitives for Expressing Iterative Lazy Algorithms
3798 This subsection is based on @uref{http://srfi.schemers.org/srfi-45/srfi-45.html, the
3799 specification of SRFI-45} written by Andr@'e van Tonder.
3801 @c Copyright (C) André van Tonder (2003). All Rights Reserved.
3803 @c Permission is hereby granted, free of charge, to any person obtaining a
3804 @c copy of this software and associated documentation files (the
3805 @c "Software"), to deal in the Software without restriction, including
3806 @c without limitation the rights to use, copy, modify, merge, publish,
3807 @c distribute, sublicense, and/or sell copies of the Software, and to
3808 @c permit persons to whom the Software is furnished to do so, subject to
3809 @c the following conditions:
3811 @c The above copyright notice and this permission notice shall be included
3812 @c in all copies or substantial portions of the Software.
3814 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3815 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3816 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3817 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3818 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3819 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3820 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3822 Lazy evaluation is traditionally simulated in Scheme using @code{delay}
3823 and @code{force}. However, these primitives are not powerful enough to
3824 express a large class of lazy algorithms that are iterative. Indeed, it
3825 is folklore in the Scheme community that typical iterative lazy
3826 algorithms written using delay and force will often require unbounded
3829 This SRFI provides set of three operations: @{@code{lazy}, @code{delay},
3830 @code{force}@}, which allow the programmer to succinctly express lazy
3831 algorithms while retaining bounded space behavior in cases that are
3832 properly tail-recursive. A general recipe for using these primitives is
3833 provided. An additional procedure @code{eager} is provided for the
3834 construction of eager promises in cases where efficiency is a concern.
3836 Although this SRFI redefines @code{delay} and @code{force}, the
3837 extension is conservative in the sense that the semantics of the subset
3838 @{@code{delay}, @code{force}@} in isolation (i.e., as long as the
3839 program does not use @code{lazy}) agrees with that in R5RS. In other
3840 words, no program that uses the R5RS definitions of delay and force will
3841 break if those definition are replaced by the SRFI-45 definitions of
3844 Guile compatibly extends SRFI-45 to support multiple values. It also
3845 adds @code{promise?} to the list of exports.
3847 @deffn {Scheme Procedure} promise? obj
3848 Return true if @var{obj} is an SRFI-45 promise, otherwise return false.
3851 @deffn {Scheme Syntax} delay expression
3852 Takes an expression and returns a promise which at some point in the
3853 future may be asked (by the @code{force} procedure) to evaluate the
3854 expression and deliver the resulting value(s).
3857 @deffn {Scheme Syntax} lazy expression
3858 Takes an expression (which must evaluate to a promise) and returns a
3859 promise which at some point in the future may be asked (by the
3860 @code{force} procedure) to evaluate the expression and deliver the
3864 @deffn {Scheme Procedure} force promise
3865 Takes a promise and returns the associated value(s) as follows: If
3866 value(s) have been computed for the promise, these value(s) are
3867 returned. Otherwise, the promise is first evaluated, then overwritten
3868 by the obtained promise or value(s), and then force is again applied
3869 (iteratively) to the promise.
3872 @deffn {Scheme Procedure} eager obj ...
3873 Takes any number of argument(s) and returns a promise. As opposed to
3874 @code{delay}, the argument(s) are evaluated eagerly. Semantically,
3875 writing @code{(eager expression)} is equivalent to writing
3878 (let ((value expression)) (delay value)).
3881 However, the former is more efficient since it does not require
3882 unnecessary creation and evaluation of thunks. For expressions that
3883 return a single value, we also have the equivalence
3886 (delay expression) = (lazy (eager expression))
3889 More generally, the following equivalence holds:
3892 (delay expression) = (lazy (call-with-values
3893 (lambda () expression)
3898 The following reduction rules may be helpful for reasoning about these
3899 primitives. However, they do not express the memoization and memory
3900 usage semantics specified above:
3903 (force (delay expression)) -> expression
3904 (force (lazy expression)) -> (force expression)
3905 (force (eager obj ...)) -> (values obj ...)
3908 @subsubheading Correct usage
3910 We now provide a general recipe for using the primitives @{@code{lazy},
3911 @code{delay}, @code{force}@} to express lazy algorithms in Scheme. The
3912 transformation is best described by way of an example: Consider the
3913 stream-filter algorithm, expressed in a hypothetical lazy language as
3916 (define (stream-filter p? s)
3921 (cons h (stream-filter p? t))
3922 (stream-filter p? t)))))
3925 This algorithm can be expressed as follows in Scheme:
3928 (define (stream-filter p? s)
3930 (if (null? (force s)) (delay '())
3931 (let ((h (car (force s)))
3932 (t (cdr (force s))))
3934 (delay (cons h (stream-filter p? t)))
3935 (stream-filter p? t))))))
3942 wrap all constructors (e.g., @code{'()}, @code{cons}) with @code{delay},
3944 apply @code{force} to arguments of deconstructors (e.g., @code{car},
3945 @code{cdr} and @code{null?}),
3947 wrap procedure bodies with @code{(lazy ...)}.
3951 @subsection SRFI-55 - Requiring Features
3954 SRFI-55 provides @code{require-extension} which is a portable
3955 mechanism to load selected SRFI modules. This is implemented in the
3956 Guile core, there's no module needed to get SRFI-55 itself.
3958 @deffn {library syntax} require-extension clause1 clause2 @dots{}
3959 Require the features of @var{clause1} @var{clause2} @dots{} , throwing
3960 an error if any are unavailable.
3962 A @var{clause} is of the form @code{(@var{identifier} arg...)}. The
3963 only @var{identifier} currently supported is @code{srfi} and the
3964 arguments are SRFI numbers. For example to get SRFI-1 and SRFI-6,
3967 (require-extension (srfi 1 6))
3970 @code{require-extension} can only be used at the top-level.
3972 A Guile-specific program can simply @code{use-modules} to load SRFIs
3973 not already in the core, @code{require-extension} is for programs
3974 designed to be portable to other Scheme implementations.
3979 @subsection SRFI-60 - Integers as Bits
3981 @cindex integers as bits
3982 @cindex bitwise logical
3984 This SRFI provides various functions for treating integers as bits and
3985 for bitwise manipulations. These functions can be obtained with,
3988 (use-modules (srfi srfi-60))
3991 Integers are treated as infinite precision twos-complement, the same
3992 as in the core logical functions (@pxref{Bitwise Operations}). And
3993 likewise bit indexes start from 0 for the least significant bit. The
3994 following functions in this SRFI are already in the Guile core,
4003 @code{integer-length},
4009 @defun bitwise-and n1 ...
4010 @defunx bitwise-ior n1 ...
4011 @defunx bitwise-xor n1 ...
4012 @defunx bitwise-not n
4013 @defunx any-bits-set? j k
4014 @defunx bit-set? index n
4015 @defunx arithmetic-shift n count
4016 @defunx bit-field n start end
4018 Aliases for @code{logand}, @code{logior}, @code{logxor},
4019 @code{lognot}, @code{logtest}, @code{logbit?}, @code{ash},
4020 @code{bit-extract} and @code{logcount} respectively.
4022 Note that the name @code{bit-count} conflicts with @code{bit-count} in
4023 the core (@pxref{Bit Vectors}).
4026 @defun bitwise-if mask n1 n0
4027 @defunx bitwise-merge mask n1 n0
4028 Return an integer with bits selected from @var{n1} and @var{n0}
4029 according to @var{mask}. Those bits where @var{mask} has 1s are taken
4030 from @var{n1}, and those where @var{mask} has 0s are taken from
4034 (bitwise-if 3 #b0101 #b1010) @result{} 9
4038 @defun log2-binary-factors n
4039 @defunx first-set-bit n
4040 Return a count of how many factors of 2 are present in @var{n}. This
4041 is also the bit index of the lowest 1 bit in @var{n}. If @var{n} is
4042 0, the return is @math{-1}.
4045 (log2-binary-factors 6) @result{} 1
4046 (log2-binary-factors -8) @result{} 3
4050 @defun copy-bit index n newbit
4051 Return @var{n} with the bit at @var{index} set according to
4052 @var{newbit}. @var{newbit} should be @code{#t} to set the bit to 1,
4053 or @code{#f} to set it to 0. Bits other than at @var{index} are
4054 unchanged in the return.
4057 (copy-bit 1 #b0101 #t) @result{} 7
4061 @defun copy-bit-field n newbits start end
4062 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4063 (exclusive) changed to the value @var{newbits}.
4065 The least significant bit in @var{newbits} goes to @var{start}, the
4066 next to @math{@var{start}+1}, etc. Anything in @var{newbits} past the
4067 @var{end} given is ignored.
4070 (copy-bit-field #b10000 #b11 1 3) @result{} #b10110
4074 @defun rotate-bit-field n count start end
4075 Return @var{n} with the bit field from @var{start} (inclusive) to
4076 @var{end} (exclusive) rotated upwards by @var{count} bits.
4078 @var{count} can be positive or negative, and it can be more than the
4079 field width (it'll be reduced modulo the width).
4082 (rotate-bit-field #b0110 2 1 4) @result{} #b1010
4086 @defun reverse-bit-field n start end
4087 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4088 (exclusive) reversed.
4091 (reverse-bit-field #b101001 2 4) @result{} #b100101
4095 @defun integer->list n [len]
4096 Return bits from @var{n} in the form of a list of @code{#t} for 1 and
4097 @code{#f} for 0. The least significant @var{len} bits are returned,
4098 and the first list element is the most significant of those bits. If
4099 @var{len} is not given, the default is @code{(integer-length @var{n})}
4100 (@pxref{Bitwise Operations}).
4103 (integer->list 6) @result{} (#t #t #f)
4104 (integer->list 1 4) @result{} (#f #f #f #t)
4108 @defun list->integer lst
4109 @defunx booleans->integer bool@dots{}
4110 Return an integer formed bitwise from the given @var{lst} list of
4111 booleans, or for @code{booleans->integer} from the @var{bool}
4114 Each boolean is @code{#t} for a 1 and @code{#f} for a 0. The first
4115 element becomes the most significant bit in the return.
4118 (list->integer '(#t #f #t #f)) @result{} 10
4124 @subsection SRFI-61 - A more general @code{cond} clause
4126 This SRFI extends RnRS @code{cond} to support test expressions that
4127 return multiple values, as well as arbitrary definitions of test
4128 success. SRFI 61 is implemented in the Guile core; there's no module
4129 needed to get SRFI-61 itself. Extended @code{cond} is documented in
4130 @ref{Conditionals,, Simple Conditional Evaluation}.
4133 @subsection SRFI-67 - Compare procedures
4136 See @uref{http://srfi.schemers.org/srfi-67/srfi-67.html, the
4137 specification of SRFI-67}.
4140 @subsection SRFI-69 - Basic hash tables
4143 This is a portable wrapper around Guile's built-in hash table and weak
4144 table support. @xref{Hash Tables}, for information on that built-in
4145 support. Above that, this hash-table interface provides association
4146 of equality and hash functions with tables at creation time, so
4147 variants of each function are not required, as well as a procedure
4148 that takes care of most uses for Guile hash table handles, which this
4149 SRFI does not provide as such.
4154 (use-modules (srfi srfi-69))
4158 * SRFI-69 Creating hash tables::
4159 * SRFI-69 Accessing table items::
4160 * SRFI-69 Table properties::
4161 * SRFI-69 Hash table algorithms::
4164 @node SRFI-69 Creating hash tables
4165 @subsubsection Creating hash tables
4167 @deffn {Scheme Procedure} make-hash-table [equal-proc hash-proc #:weak weakness start-size]
4168 Create and answer a new hash table with @var{equal-proc} as the
4169 equality function and @var{hash-proc} as the hashing function.
4171 By default, @var{equal-proc} is @code{equal?}. It can be any
4172 two-argument procedure, and should answer whether two keys are the
4173 same for this table's purposes.
4175 My default @var{hash-proc} assumes that @code{equal-proc} is no
4176 coarser than @code{equal?} unless it is literally @code{string-ci=?}.
4177 If provided, @var{hash-proc} should be a two-argument procedure that
4178 takes a key and the current table size, and answers a reasonably good
4179 hash integer between 0 (inclusive) and the size (exclusive).
4181 @var{weakness} should be @code{#f} or a symbol indicating how ``weak''
4186 An ordinary non-weak hash table. This is the default.
4189 When the key has no more non-weak references at GC, remove that entry.
4192 When the value has no more non-weak references at GC, remove that
4196 When either has no more non-weak references at GC, remove the
4200 As a legacy of the time when Guile couldn't grow hash tables,
4201 @var{start-size} is an optional integer argument that specifies the
4202 approximate starting size for the hash table, which will be rounded to
4203 an algorithmically-sounder number.
4206 By @dfn{coarser} than @code{equal?}, we mean that for all @var{x} and
4207 @var{y} values where @code{(@var{equal-proc} @var{x} @var{y})},
4208 @code{(equal? @var{x} @var{y})} as well. If that does not hold for
4209 your @var{equal-proc}, you must provide a @var{hash-proc}.
4211 In the case of weak tables, remember that @dfn{references} above
4212 always refers to @code{eq?}-wise references. Just because you have a
4213 reference to some string @code{"foo"} doesn't mean that an association
4214 with key @code{"foo"} in a weak-key table @emph{won't} be collected;
4215 it only counts as a reference if the two @code{"foo"}s are @code{eq?},
4216 regardless of @var{equal-proc}. As such, it is usually only sensible
4217 to use @code{eq?} and @code{hashq} as the equivalence and hash
4218 functions for a weak table. @xref{Weak References}, for more
4219 information on Guile's built-in weak table support.
4221 @deffn {Scheme Procedure} alist->hash-table alist [equal-proc hash-proc #:weak weakness start-size]
4222 As with @code{make-hash-table}, but initialize it with the
4223 associations in @var{alist}. Where keys are repeated in @var{alist},
4224 the leftmost association takes precedence.
4227 @node SRFI-69 Accessing table items
4228 @subsubsection Accessing table items
4230 @deffn {Scheme Procedure} hash-table-ref table key [default-thunk]
4231 @deffnx {Scheme Procedure} hash-table-ref/default table key default
4232 Answer the value associated with @var{key} in @var{table}. If
4233 @var{key} is not present, answer the result of invoking the thunk
4234 @var{default-thunk}, which signals an error instead by default.
4236 @code{hash-table-ref/default} is a variant that requires a third
4237 argument, @var{default}, and answers @var{default} itself instead of
4241 @deffn {Scheme Procedure} hash-table-set! table key new-value
4242 Set @var{key} to @var{new-value} in @var{table}.
4245 @deffn {Scheme Procedure} hash-table-delete! table key
4246 Remove the association of @var{key} in @var{table}, if present. If
4250 @deffn {Scheme Procedure} hash-table-exists? table key
4251 Answer whether @var{key} has an association in @var{table}.
4254 @deffn {Scheme Procedure} hash-table-update! table key modifier [default-thunk]
4255 @deffnx {Scheme Procedure} hash-table-update!/default table key modifier default
4256 Replace @var{key}'s associated value in @var{table} by invoking
4257 @var{modifier} with one argument, the old value.
4259 If @var{key} is not present, and @var{default-thunk} is provided,
4260 invoke it with no arguments to get the ``old value'' to be passed to
4261 @var{modifier} as above. If @var{default-thunk} is not provided in
4262 such a case, signal an error.
4264 @code{hash-table-update!/default} is a variant that requires the
4265 fourth argument, which is used directly as the ``old value'' rather
4266 than as a thunk to be invoked to retrieve the ``old value''.
4269 @node SRFI-69 Table properties
4270 @subsubsection Table properties
4272 @deffn {Scheme Procedure} hash-table-size table
4273 Answer the number of associations in @var{table}. This is guaranteed
4274 to run in constant time for non-weak tables.
4277 @deffn {Scheme Procedure} hash-table-keys table
4278 Answer an unordered list of the keys in @var{table}.
4281 @deffn {Scheme Procedure} hash-table-values table
4282 Answer an unordered list of the values in @var{table}.
4285 @deffn {Scheme Procedure} hash-table-walk table proc
4286 Invoke @var{proc} once for each association in @var{table}, passing
4287 the key and value as arguments.
4290 @deffn {Scheme Procedure} hash-table-fold table proc init
4291 Invoke @code{(@var{proc} @var{key} @var{value} @var{previous})} for
4292 each @var{key} and @var{value} in @var{table}, where @var{previous} is
4293 the result of the previous invocation, using @var{init} as the first
4294 @var{previous} value. Answer the final @var{proc} result.
4297 @deffn {Scheme Procedure} hash-table->alist table
4298 Answer an alist where each association in @var{table} is an
4299 association in the result.
4302 @node SRFI-69 Hash table algorithms
4303 @subsubsection Hash table algorithms
4305 Each hash table carries an @dfn{equivalence function} and a @dfn{hash
4306 function}, used to implement key lookups. Beginning users should
4307 follow the rules for consistency of the default @var{hash-proc}
4308 specified above. Advanced users can use these to implement their own
4309 equivalence and hash functions for specialized lookup semantics.
4311 @deffn {Scheme Procedure} hash-table-equivalence-function hash-table
4312 @deffnx {Scheme Procedure} hash-table-hash-function hash-table
4313 Answer the equivalence and hash function of @var{hash-table}, respectively.
4316 @deffn {Scheme Procedure} hash obj [size]
4317 @deffnx {Scheme Procedure} string-hash obj [size]
4318 @deffnx {Scheme Procedure} string-ci-hash obj [size]
4319 @deffnx {Scheme Procedure} hash-by-identity obj [size]
4320 Answer a hash value appropriate for equality predicate @code{equal?},
4321 @code{string=?}, @code{string-ci=?}, and @code{eq?}, respectively.
4324 @code{hash} is a backwards-compatible replacement for Guile's built-in
4328 @subsection SRFI-88 Keyword Objects
4330 @cindex keyword objects
4332 @uref{http://srfi.schemers.org/srfi-88/srfi-88.html, SRFI-88} provides
4333 @dfn{keyword objects}, which are equivalent to Guile's keywords
4334 (@pxref{Keywords}). SRFI-88 keywords can be entered using the
4335 @dfn{postfix keyword syntax}, which consists of an identifier followed
4336 by @code{:} (@pxref{Scheme Read, @code{postfix} keyword syntax}).
4337 SRFI-88 can be made available with:
4340 (use-modules (srfi srfi-88))
4343 Doing so installs the right reader option for keyword syntax, using
4344 @code{(read-set! keywords 'postfix)}. It also provides the procedures
4347 @deffn {Scheme Procedure} keyword? obj
4348 Return @code{#t} if @var{obj} is a keyword. This is the same procedure
4349 as the same-named built-in procedure (@pxref{Keyword Procedures,
4353 (keyword? foo:) @result{} #t
4354 (keyword? 'foo:) @result{} #t
4355 (keyword? "foo") @result{} #f
4359 @deffn {Scheme Procedure} keyword->string kw
4360 Return the name of @var{kw} as a string, i.e., without the trailing
4361 colon. The returned string may not be modified, e.g., with
4365 (keyword->string foo:) @result{} "foo"
4369 @deffn {Scheme Procedure} string->keyword str
4370 Return the keyword object whose name is @var{str}.
4373 (keyword->string (string->keyword "a b c")) @result{} "a b c"
4378 @subsection SRFI-98 Accessing environment variables.
4380 @cindex environment variables
4382 This is a portable wrapper around Guile's built-in support for
4383 interacting with the current environment, @xref{Runtime Environment}.
4385 @deffn {Scheme Procedure} get-environment-variable name
4386 Returns a string containing the value of the environment variable
4387 given by the string @code{name}, or @code{#f} if the named
4388 environment variable is not found. This is equivalent to
4389 @code{(getenv name)}.
4392 @deffn {Scheme Procedure} get-environment-variables
4393 Returns the names and values of all the environment variables as an
4394 association list in which both the keys and the values are strings.
4398 @subsection SRFI-105 Curly-infix expressions.
4401 @cindex curly-infix-and-bracket-lists
4403 Guile's built-in reader includes support for SRFI-105 curly-infix
4404 expressions. See @uref{http://srfi.schemers.org/srfi-105/srfi-105.html,
4405 the specification of SRFI-105}. Some examples:
4408 @{n <= 5@} @result{} (<= n 5)
4409 @{a + b + c@} @result{} (+ a b c)
4410 @{a * @{b + c@}@} @result{} (* a (+ b c))
4411 @{(- a) / b@} @result{} (/ (- a) b)
4412 @{-(a) / b@} @result{} (/ (- a) b) as well
4413 @{(f a b) + (g h)@} @result{} (+ (f a b) (g h))
4414 @{f(a b) + g(h)@} @result{} (+ (f a b) (g h)) as well
4415 @{f[a b] + g(h)@} @result{} (+ ($bracket-apply$ f a b) (g h))
4416 '@{a + f(b) + x@} @result{} '(+ a (f b) x)
4417 @{length(x) >= 6@} @result{} (>= (length x) 6)
4418 @{n-1 + n-2@} @result{} (+ n-1 n-2)
4419 @{n * factorial@{n - 1@}@} @result{} (* n (factorial (- n 1)))
4420 @{@{a > 0@} and @{b >= 1@}@} @result{} (and (> a 0) (>= b 1))
4421 @{f@{n - 1@}(x)@} @result{} ((f (- n 1)) x)
4422 @{a . z@} @result{} ($nfx$ a . z)
4423 @{a + b - c@} @result{} ($nfx$ a + b - c)
4426 To enable curly-infix expressions within a file, place the reader
4427 directive @code{#!curly-infix} before the first use of curly-infix
4428 notation. To globally enable curly-infix expressions in Guile's reader,
4429 set the @code{curly-infix} read option.
4431 Guile also implements the following non-standard extension to SRFI-105:
4432 if @code{curly-infix} is enabled and there is no other meaning assigned
4433 to square brackets (i.e. the @code{square-brackets} read option is
4434 turned off), then lists within square brackets are read as normal lists
4435 but with the special symbol @code{$bracket-list$} added to the front.
4436 To enable this combination of read options within a file, use the reader
4437 directive @code{#!curly-infix-and-bracket-lists}. For example:
4440 [a b] @result{} ($bracket-list$ a b)
4441 [a . b] @result{} ($bracket-list$ a . b)
4445 For more information on reader options, @xref{Scheme Read}.
4447 @c srfi-modules.texi ends here
4450 @c TeX-master: "guile.texi"