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
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @section SRFI Support Modules
11 SRFI is an acronym for Scheme Request For Implementation. The SRFI
12 documents define a lot of syntactic and procedure extensions to standard
13 Scheme as defined in R5RS.
15 Guile has support for a number of SRFIs. This chapter gives an overview
16 over the available SRFIs and some usage hints. For complete
17 documentation, design rationales and further examples, we advise you to
18 get the relevant SRFI documents from the SRFI home page
19 @url{http://srfi.schemers.org/}.
22 * About SRFI Usage:: What to know about Guile's SRFI support.
23 * SRFI-0:: cond-expand
24 * SRFI-1:: List library.
26 * SRFI-4:: Homogeneous numeric vector datatypes.
27 * SRFI-6:: Basic String Ports.
29 * SRFI-9:: define-record-type.
30 * SRFI-10:: Hash-Comma Reader Extension.
31 * SRFI-11:: let-values and let*-values.
32 * SRFI-13:: String library.
33 * SRFI-14:: Character-set library.
34 * SRFI-16:: case-lambda
35 * SRFI-17:: Generalized set!
36 * SRFI-18:: Multithreading support
37 * SRFI-19:: Time/Date library.
38 * SRFI-23:: Error reporting
39 * SRFI-26:: Specializing parameters
40 * SRFI-27:: Sources of Random Bits
41 * SRFI-30:: Nested multi-line block comments
42 * SRFI-31:: A special form `rec' for recursive evaluation
43 * SRFI-34:: Exception handling.
44 * SRFI-35:: Conditions.
45 * SRFI-37:: args-fold program argument processor
46 * SRFI-38:: External Representation for Data With Shared Structure
47 * SRFI-39:: Parameter objects
48 * SRFI-42:: Eager comprehensions
49 * SRFI-45:: Primitives for expressing iterative lazy algorithms
50 * SRFI-55:: Requiring Features.
51 * SRFI-60:: Integers as bits.
52 * SRFI-61:: A more general `cond' clause
53 * SRFI-67:: Compare procedures
54 * SRFI-69:: Basic hash tables.
55 * SRFI-88:: Keyword objects.
56 * SRFI-98:: Accessing environment variables.
60 @node About SRFI Usage
61 @subsection About SRFI Usage
63 @c FIXME::martin: Review me!
65 SRFI support in Guile is currently implemented partly in the core
66 library, and partly as add-on modules. That means that some SRFIs are
67 automatically available when the interpreter is started, whereas the
68 other SRFIs require you to use the appropriate support module
71 There are several reasons for this inconsistency. First, the feature
72 checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be
73 available immediately, because it must be there when the user wants to
74 check for the Scheme implementation, that is, before she can know that
75 it is safe to use @code{use-modules} to load SRFI support modules. The
76 second reason is that some features defined in SRFIs had been
77 implemented in Guile before the developers started to add SRFI
78 implementations as modules (for example SRFI-6 (@pxref{SRFI-6})). In
79 the future, it is possible that SRFIs in the core library might be
80 factored out into separate modules, requiring explicit module loading
81 when they are needed. So you should be prepared to have to use
82 @code{use-modules} someday in the future to access SRFI-6 bindings. If
83 you want, you can do that already. We have included the module
84 @code{(srfi srfi-6)} in the distribution, which currently does nothing,
85 but ensures that you can write future-safe code.
87 Generally, support for a specific SRFI is made available by using
88 modules named @code{(srfi srfi-@var{number})}, where @var{number} is the
89 number of the SRFI needed. Another possibility is to use the command
90 line option @code{--use-srfi}, which will load the necessary modules
91 automatically (@pxref{Invoking Guile}).
95 @subsection SRFI-0 - cond-expand
98 This SRFI lets a portable Scheme program test for the presence of
99 certain features, and adapt itself by using different blocks of code,
100 or fail if the necessary features are not available. There's no
101 module to load, this is in the Guile core.
103 A program designed only for Guile will generally not need this
104 mechanism, such a program can of course directly use the various
105 documented parts of Guile.
107 @deffn syntax cond-expand (feature body@dots{}) @dots{}
108 Expand to the @var{body} of the first clause whose @var{feature}
109 specification is satisfied. It is an error if no @var{feature} is
112 Features are symbols such as @code{srfi-1}, and a feature
113 specification can use @code{and}, @code{or} and @code{not} forms to
114 test combinations. The last clause can be an @code{else}, to be used
117 For example, define a private version of @code{alist-cons} if SRFI-1
124 (define (alist-cons key val alist)
125 (cons (cons key val) alist))))
128 Or demand a certain set of SRFIs (list operations, string ports,
129 @code{receive} and string operations), failing if they're not
133 (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13)
139 The Guile core has the following features,
143 guile-2 ;; starting from Guile 2.x
152 Other SRFI feature symbols are defined once their code has been loaded
153 with @code{use-modules}, since only then are their bindings available.
155 The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is
156 a good way to load SRFIs to satisfy @code{cond-expand} when running a
159 Testing the @code{guile} feature allows a program to adapt itself to
160 the Guile module system, but still run on other Scheme systems. For
161 example the following demands SRFI-8 (@code{receive}), but also knows
162 how to load it with the Guile mechanism.
168 (use-modules (srfi srfi-8))))
171 @cindex @code{guile-2} SRFI-0 feature
172 @cindex portability between 2.0 and older versions
173 Likewise, testing the @code{guile-2} feature allows code to be portable
174 between Guile 2.0 and previous versions of Guile. For instance, it
175 makes it possible to write code that accounts for Guile 2.0's compiler,
176 yet be correctly interpreted on 1.8 and earlier versions:
179 (cond-expand (guile-2 (eval-when (compile)
180 ;; This must be evaluated at compile time.
181 (fluid-set! current-reader my-reader)))
183 ;; Earlier versions of Guile do not have a
184 ;; separate compilation phase.
185 (fluid-set! current-reader my-reader)))
188 It should be noted that @code{cond-expand} is separate from the
189 @code{*features*} mechanism (@pxref{Feature Tracking}), feature
190 symbols in one are unrelated to those in the other.
194 @subsection SRFI-1 - List library
198 @c FIXME::martin: Review me!
200 The list library defined in SRFI-1 contains a lot of useful list
201 processing procedures for construction, examining, destructuring and
202 manipulating lists and pairs.
204 Since SRFI-1 also defines some procedures which are already contained
205 in R5RS and thus are supported by the Guile core library, some list
206 and pair procedures which appear in the SRFI-1 document may not appear
207 in this section. So when looking for a particular list/pair
208 processing procedure, you should also have a look at the sections
209 @ref{Lists} and @ref{Pairs}.
212 * SRFI-1 Constructors:: Constructing new lists.
213 * SRFI-1 Predicates:: Testing list for specific properties.
214 * SRFI-1 Selectors:: Selecting elements from lists.
215 * SRFI-1 Length Append etc:: Length calculation and list appending.
216 * SRFI-1 Fold and Map:: Higher-order list processing.
217 * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates.
218 * SRFI-1 Searching:: Search for elements.
219 * SRFI-1 Deleting:: Delete elements from lists.
220 * SRFI-1 Association Lists:: Handle association lists.
221 * SRFI-1 Set Operations:: Use lists for representing sets.
224 @node SRFI-1 Constructors
225 @subsubsection Constructors
226 @cindex list constructor
228 @c FIXME::martin: Review me!
230 New lists can be constructed by calling one of the following
233 @deffn {Scheme Procedure} xcons d a
234 Like @code{cons}, but with interchanged arguments. Useful mostly when
235 passed to higher-order procedures.
238 @deffn {Scheme Procedure} list-tabulate n init-proc
239 Return an @var{n}-element list, where each list element is produced by
240 applying the procedure @var{init-proc} to the corresponding list
241 index. The order in which @var{init-proc} is applied to the indices
245 @deffn {Scheme Procedure} list-copy lst
246 Return a new list containing the elements of the list @var{lst}.
248 This function differs from the core @code{list-copy} (@pxref{List
249 Constructors}) in accepting improper lists too. And if @var{lst} is
250 not a pair at all then it's treated as the final tail of an improper
251 list and simply returned.
254 @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{}
255 Return a circular list containing the given arguments @var{elt1}
259 @deffn {Scheme Procedure} iota count [start step]
260 Return a list containing @var{count} numbers, starting from
261 @var{start} and adding @var{step} each time. The default @var{start}
262 is 0, the default @var{step} is 1. For example,
265 (iota 6) @result{} (0 1 2 3 4 5)
266 (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5)
269 This function takes its name from the corresponding primitive in the
274 @node SRFI-1 Predicates
275 @subsubsection Predicates
276 @cindex list predicate
278 @c FIXME::martin: Review me!
280 The procedures in this section test specific properties of lists.
282 @deffn {Scheme Procedure} proper-list? obj
283 Return @code{#t} if @var{obj} is a proper list, or @code{#f}
284 otherwise. This is the same as the core @code{list?} (@pxref{List
287 A proper list is a list which ends with the empty list @code{()} in
288 the usual way. The empty list @code{()} itself is a proper list too.
291 (proper-list? '(1 2 3)) @result{} #t
292 (proper-list? '()) @result{} #t
296 @deffn {Scheme Procedure} circular-list? obj
297 Return @code{#t} if @var{obj} is a circular list, or @code{#f}
300 A circular list is a list where at some point the @code{cdr} refers
301 back to a previous pair in the list (either the start or some later
302 point), so that following the @code{cdr}s takes you around in a
306 (define x (list 1 2 3 4))
307 (set-cdr! (last-pair x) (cddr x))
308 x @result{} (1 2 3 4 3 4 3 4 ...)
309 (circular-list? x) @result{} #t
313 @deffn {Scheme Procedure} dotted-list? obj
314 Return @code{#t} if @var{obj} is a dotted list, or @code{#f}
317 A dotted list is a list where the @code{cdr} of the last pair is not
318 the empty list @code{()}. Any non-pair @var{obj} is also considered a
319 dotted list, with length zero.
322 (dotted-list? '(1 2 . 3)) @result{} #t
323 (dotted-list? 99) @result{} #t
327 It will be noted that any Scheme object passes exactly one of the
328 above three tests @code{proper-list?}, @code{circular-list?} and
329 @code{dotted-list?}. Non-lists are @code{dotted-list?}, finite lists
330 are either @code{proper-list?} or @code{dotted-list?}, and infinite
331 lists are @code{circular-list?}.
334 @deffn {Scheme Procedure} null-list? lst
335 Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f}
336 otherwise. If something else than a proper or circular list is passed
337 as @var{lst}, an error is signalled. This procedure is recommended
338 for checking for the end of a list in contexts where dotted lists are
342 @deffn {Scheme Procedure} not-pair? obj
343 Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise.
344 This is shorthand notation @code{(not (pair? @var{obj}))} and is
345 supposed to be used for end-of-list checking in contexts where dotted
349 @deffn {Scheme Procedure} list= elt= list1 @dots{}
350 Return @code{#t} if all argument lists are equal, @code{#f} otherwise.
351 List equality is determined by testing whether all lists have the same
352 length and the corresponding elements are equal in the sense of the
353 equality predicate @var{elt=}. If no or only one list is given,
354 @code{#t} is returned.
358 @node SRFI-1 Selectors
359 @subsubsection Selectors
360 @cindex list selector
362 @c FIXME::martin: Review me!
364 @deffn {Scheme Procedure} first pair
365 @deffnx {Scheme Procedure} second pair
366 @deffnx {Scheme Procedure} third pair
367 @deffnx {Scheme Procedure} fourth pair
368 @deffnx {Scheme Procedure} fifth pair
369 @deffnx {Scheme Procedure} sixth pair
370 @deffnx {Scheme Procedure} seventh pair
371 @deffnx {Scheme Procedure} eighth pair
372 @deffnx {Scheme Procedure} ninth pair
373 @deffnx {Scheme Procedure} tenth pair
374 These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}.
377 @deffn {Scheme Procedure} car+cdr pair
378 Return two values, the @sc{car} and the @sc{cdr} of @var{pair}.
381 @deffn {Scheme Procedure} take lst i
382 @deffnx {Scheme Procedure} take! lst i
383 Return a list containing the first @var{i} elements of @var{lst}.
385 @code{take!} may modify the structure of the argument list @var{lst}
386 in order to produce the result.
389 @deffn {Scheme Procedure} drop lst i
390 Return a list containing all but the first @var{i} elements of
394 @deffn {Scheme Procedure} take-right lst i
395 Return a list containing the @var{i} last elements of @var{lst}.
396 The return shares a common tail with @var{lst}.
399 @deffn {Scheme Procedure} drop-right lst i
400 @deffnx {Scheme Procedure} drop-right! lst i
401 Return a list containing all but the @var{i} last elements of
404 @code{drop-right} always returns a new list, even when @var{i} is
405 zero. @code{drop-right!} may modify the structure of the argument
406 list @var{lst} in order to produce the result.
409 @deffn {Scheme Procedure} split-at lst i
410 @deffnx {Scheme Procedure} split-at! lst i
411 Return two values, a list containing the first @var{i} elements of the
412 list @var{lst} and a list containing the remaining elements.
414 @code{split-at!} may modify the structure of the argument list
415 @var{lst} in order to produce the result.
418 @deffn {Scheme Procedure} last lst
419 Return the last element of the non-empty, finite list @var{lst}.
423 @node SRFI-1 Length Append etc
424 @subsubsection Length, Append, Concatenate, etc.
426 @c FIXME::martin: Review me!
428 @deffn {Scheme Procedure} length+ lst
429 Return the length of the argument list @var{lst}. When @var{lst} is a
430 circular list, @code{#f} is returned.
433 @deffn {Scheme Procedure} concatenate list-of-lists
434 @deffnx {Scheme Procedure} concatenate! list-of-lists
435 Construct a list by appending all lists in @var{list-of-lists}.
437 @code{concatenate!} may modify the structure of the given lists in
438 order to produce the result.
440 @code{concatenate} is the same as @code{(apply append
441 @var{list-of-lists})}. It exists because some Scheme implementations
442 have a limit on the number of arguments a function takes, which the
443 @code{apply} might exceed. In Guile there is no such limit.
446 @deffn {Scheme Procedure} append-reverse rev-head tail
447 @deffnx {Scheme Procedure} append-reverse! rev-head tail
448 Reverse @var{rev-head}, append @var{tail} to it, and return the
449 result. This is equivalent to @code{(append (reverse @var{rev-head})
450 @var{tail})}, but its implementation is more efficient.
453 (append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)
456 @code{append-reverse!} may modify @var{rev-head} in order to produce
460 @deffn {Scheme Procedure} zip lst1 lst2 @dots{}
461 Return a list as long as the shortest of the argument lists, where
462 each element is a list. The first list contains the first elements of
463 the argument lists, the second list contains the second elements, and
467 @deffn {Scheme Procedure} unzip1 lst
468 @deffnx {Scheme Procedure} unzip2 lst
469 @deffnx {Scheme Procedure} unzip3 lst
470 @deffnx {Scheme Procedure} unzip4 lst
471 @deffnx {Scheme Procedure} unzip5 lst
472 @code{unzip1} takes a list of lists, and returns a list containing the
473 first elements of each list, @code{unzip2} returns two lists, the
474 first containing the first elements of each lists and the second
475 containing the second elements of each lists, and so on.
478 @deffn {Scheme Procedure} count pred lst1 lst2 @dots{}
479 Return a count of the number of times @var{pred} returns true when
480 called on elements from the given lists.
482 @var{pred} is called with @var{N} parameters @code{(@var{pred}
483 @var{elem1} @dots{} @var{elemN} )}, each element being from the
484 corresponding list. The first call is with the first element of each
485 list, the second with the second element from each, and so on.
487 Counting stops when the end of the shortest list is reached. At least
488 one list must be non-circular.
492 @node SRFI-1 Fold and Map
493 @subsubsection Fold, Unfold & Map
497 @c FIXME::martin: Review me!
499 @deffn {Scheme Procedure} fold proc init lst1 lst2 @dots{}
500 @deffnx {Scheme Procedure} fold-right proc init lst1 lst2 @dots{}
501 Apply @var{proc} to the elements of @var{lst1} @var{lst2} @dots{} to
502 build a result, and return that result.
504 Each @var{proc} call is @code{(@var{proc} @var{elem1} @var{elem2}
505 @dots{} @var{previous})}, where @var{elem1} is from @var{lst1},
506 @var{elem2} is from @var{lst2}, and so on. @var{previous} is the return
507 from the previous call to @var{proc}, or the given @var{init} for the
508 first call. If any list is empty, just @var{init} is returned.
510 @code{fold} works through the list elements from first to last. The
511 following shows a list reversal and the calls it makes,
514 (fold cons '() '(1 2 3))
522 @code{fold-right} works through the list elements from last to first,
523 ie.@: from the right. So for example the following finds the longest
524 string, and the last among equal longest,
527 (fold-right (lambda (str prev)
528 (if (> (string-length str) (string-length prev))
532 '("x" "abc" "xyz" "jk"))
536 If @var{lst1} @var{lst2} @dots{} have different lengths, @code{fold}
537 stops when the end of the shortest is reached; @code{fold-right}
538 commences at the last element of the shortest. Ie.@: elements past the
539 length of the shortest are ignored in the other @var{lst}s. At least
540 one @var{lst} must be non-circular.
542 @code{fold} should be preferred over @code{fold-right} if the order of
543 processing doesn't matter, or can be arranged either way, since
544 @code{fold} is a little more efficient.
546 The way @code{fold} builds a result from iterating is quite general,
547 it can do more than other iterations like say @code{map} or
548 @code{filter}. The following for example removes adjacent duplicate
549 elements from a list,
552 (define (delete-adjacent-duplicates lst)
553 (fold-right (lambda (elem ret)
554 (if (equal? elem (first ret))
559 (delete-adjacent-duplicates '(1 2 3 3 4 4 4 5))
560 @result{} (1 2 3 4 5)
563 Clearly the same sort of thing can be done with a @code{for-each} and
564 a variable in which to build the result, but a self-contained
565 @var{proc} can be re-used in multiple contexts, where a
566 @code{for-each} would have to be written out each time.
569 @deffn {Scheme Procedure} pair-fold proc init lst1 lst2 @dots{}
570 @deffnx {Scheme Procedure} pair-fold-right proc init lst1 lst2 @dots{}
571 The same as @code{fold} and @code{fold-right}, but apply @var{proc} to
572 the pairs of the lists instead of the list elements.
575 @deffn {Scheme Procedure} reduce proc default lst
576 @deffnx {Scheme Procedure} reduce-right proc default lst
577 @code{reduce} is a variant of @code{fold}, where the first call to
578 @var{proc} is on two elements from @var{lst}, rather than one element
579 and a given initial value.
581 If @var{lst} is empty, @code{reduce} returns @var{default} (this is
582 the only use for @var{default}). If @var{lst} has just one element
583 then that's the return value. Otherwise @var{proc} is called on the
584 elements of @var{lst}.
586 Each @var{proc} call is @code{(@var{proc} @var{elem} @var{previous})},
587 where @var{elem} is from @var{lst} (the second and subsequent elements
588 of @var{lst}), and @var{previous} is the return from the previous call
589 to @var{proc}. The first element of @var{lst} is the @var{previous}
590 for the first call to @var{proc}.
592 For example, the following adds a list of numbers, the calls made to
593 @code{+} are shown. (Of course @code{+} accepts multiple arguments
594 and can add a list directly, with @code{apply}.)
597 (reduce + 0 '(5 6 7)) @result{} 18
600 (+ 7 11) @result{} 18
603 @code{reduce} can be used instead of @code{fold} where the @var{init}
604 value is an ``identity'', meaning a value which under @var{proc}
605 doesn't change the result, in this case 0 is an identity since
606 @code{(+ 5 0)} is just 5. @code{reduce} avoids that unnecessary call.
608 @code{reduce-right} is a similar variation on @code{fold-right},
609 working from the end (ie.@: the right) of @var{lst}. The last element
610 of @var{lst} is the @var{previous} for the first call to @var{proc},
611 and the @var{elem} values go from the second last.
613 @code{reduce} should be preferred over @code{reduce-right} if the
614 order of processing doesn't matter, or can be arranged either way,
615 since @code{reduce} is a little more efficient.
618 @deffn {Scheme Procedure} unfold p f g seed [tail-gen]
619 @code{unfold} is defined as follows:
622 (unfold p f g seed) =
623 (if (p seed) (tail-gen seed)
625 (unfold p f g (g seed))))
630 Determines when to stop unfolding.
633 Maps each seed value to the corresponding list element.
636 Maps each seed value to next seed value.
639 The state value for the unfold.
642 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
645 @var{g} produces a series of seed values, which are mapped to list
646 elements by @var{f}. These elements are put into a list in
647 left-to-right order, and @var{p} tells when to stop unfolding.
650 @deffn {Scheme Procedure} unfold-right p f g seed [tail]
651 Construct a list with the following loop.
654 (let lp ((seed seed) (lis tail))
657 (cons (f seed) lis))))
662 Determines when to stop unfolding.
665 Maps each seed value to the corresponding list element.
668 Maps each seed value to next seed value.
671 The state value for the unfold.
674 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
679 @deffn {Scheme Procedure} map f lst1 lst2 @dots{}
680 Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and
681 return a list containing the results of the procedure applications.
682 This procedure is extended with respect to R5RS, because the argument
683 lists may have different lengths. The result list will have the same
684 length as the shortest argument lists. The order in which @var{f}
685 will be applied to the list element(s) is not specified.
688 @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{}
689 Apply the procedure @var{f} to each pair of corresponding elements of
690 the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not
691 specified. This procedure is extended with respect to R5RS, because
692 the argument lists may have different lengths. The shortest argument
693 list determines the number of times @var{f} is called. @var{f} will
694 be applied to the list elements in left-to-right order.
698 @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{}
699 @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{}
703 (apply append (map f clist1 clist2 ...))
709 (apply append! (map f clist1 clist2 ...))
712 Map @var{f} over the elements of the lists, just as in the @code{map}
713 function. However, the results of the applications are appended
714 together to make the final result. @code{append-map} uses
715 @code{append} to append the results together; @code{append-map!} uses
718 The dynamic order in which the various applications of @var{f} are
719 made is not specified.
722 @deffn {Scheme Procedure} map! f lst1 lst2 @dots{}
723 Linear-update variant of @code{map} -- @code{map!} is allowed, but not
724 required, to alter the cons cells of @var{lst1} to construct the
727 The dynamic order in which the various applications of @var{f} are
728 made is not specified. In the n-ary case, @var{lst2}, @var{lst3},
729 @dots{} must have at least as many elements as @var{lst1}.
732 @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{}
733 Like @code{for-each}, but applies the procedure @var{f} to the pairs
734 from which the argument lists are constructed, instead of the list
735 elements. The return value is not specified.
738 @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{}
739 Like @code{map}, but only results from the applications of @var{f}
740 which are true are saved in the result list.
744 @node SRFI-1 Filtering and Partitioning
745 @subsubsection Filtering and Partitioning
747 @cindex list partition
749 @c FIXME::martin: Review me!
751 Filtering means to collect all elements from a list which satisfy a
752 specific condition. Partitioning a list means to make two groups of
753 list elements, one which contains the elements satisfying a condition,
754 and the other for the elements which don't.
756 The @code{filter} and @code{filter!} functions are implemented in the
757 Guile core, @xref{List Modification}.
759 @deffn {Scheme Procedure} partition pred lst
760 @deffnx {Scheme Procedure} partition! pred lst
761 Split @var{lst} into those elements which do and don't satisfy the
762 predicate @var{pred}.
764 The return is two values (@pxref{Multiple Values}), the first being a
765 list of all elements from @var{lst} which satisfy @var{pred}, the
766 second a list of those which do not.
768 The elements in the result lists are in the same order as in @var{lst}
769 but the order in which the calls @code{(@var{pred} elem)} are made on
770 the list elements is unspecified.
772 @code{partition} does not change @var{lst}, but one of the returned
773 lists may share a tail with it. @code{partition!} may modify
774 @var{lst} to construct its return.
777 @deffn {Scheme Procedure} remove pred lst
778 @deffnx {Scheme Procedure} remove! pred lst
779 Return a list containing all elements from @var{lst} which do not
780 satisfy the predicate @var{pred}. The elements in the result list
781 have the same order as in @var{lst}. The order in which @var{pred} is
782 applied to the list elements is not specified.
784 @code{remove!} is allowed, but not required to modify the structure of
789 @node SRFI-1 Searching
790 @subsubsection Searching
793 @c FIXME::martin: Review me!
795 The procedures for searching elements in lists either accept a
796 predicate or a comparison object for determining which elements are to
799 @deffn {Scheme Procedure} find pred lst
800 Return the first element of @var{lst} which satisfies the predicate
801 @var{pred} and @code{#f} if no such element is found.
804 @deffn {Scheme Procedure} find-tail pred lst
805 Return the first pair of @var{lst} whose @sc{car} satisfies the
806 predicate @var{pred} and @code{#f} if no such element is found.
809 @deffn {Scheme Procedure} take-while pred lst
810 @deffnx {Scheme Procedure} take-while! pred lst
811 Return the longest initial prefix of @var{lst} whose elements all
812 satisfy the predicate @var{pred}.
814 @code{take-while!} is allowed, but not required to modify the input
815 list while producing the result.
818 @deffn {Scheme Procedure} drop-while pred lst
819 Drop the longest initial prefix of @var{lst} whose elements all
820 satisfy the predicate @var{pred}.
823 @deffn {Scheme Procedure} span pred lst
824 @deffnx {Scheme Procedure} span! pred lst
825 @deffnx {Scheme Procedure} break pred lst
826 @deffnx {Scheme Procedure} break! pred lst
827 @code{span} splits the list @var{lst} into the longest initial prefix
828 whose elements all satisfy the predicate @var{pred}, and the remaining
829 tail. @code{break} inverts the sense of the predicate.
831 @code{span!} and @code{break!} are allowed, but not required to modify
832 the structure of the input list @var{lst} in order to produce the
835 Note that the name @code{break} conflicts with the @code{break}
836 binding established by @code{while} (@pxref{while do}). Applications
837 wanting to use @code{break} from within a @code{while} loop will need
838 to make a new define under a different name.
841 @deffn {Scheme Procedure} any pred lst1 lst2 @dots{}
842 Test whether any set of elements from @var{lst1} @var{lst2} @dots{}
843 satisfies @var{pred}. If so, the return value is the return value from
844 the successful @var{pred} call, or if not, the return value is
847 If there are n list arguments, then @var{pred} must be a predicate
848 taking n arguments. Each @var{pred} call is @code{(@var{pred}
849 @var{elem1} @var{elem2} @dots{} )} taking an element from each
850 @var{lst}. The calls are made successively for the first, second, etc.
851 elements of the lists, stopping when @var{pred} returns non-@code{#f},
852 or when the end of the shortest list is reached.
854 The @var{pred} call on the last set of elements (i.e., when the end of
855 the shortest list has been reached), if that point is reached, is a
859 @deffn {Scheme Procedure} every pred lst1 lst2 @dots{}
860 Test whether every set of elements from @var{lst1} @var{lst2} @dots{}
861 satisfies @var{pred}. If so, the return value is the return from the
862 final @var{pred} call, or if not, the return value is @code{#f}.
864 If there are n list arguments, then @var{pred} must be a predicate
865 taking n arguments. Each @var{pred} call is @code{(@var{pred}
866 @var{elem1} @var{elem2 @dots{}})} taking an element from each
867 @var{lst}. The calls are made successively for the first, second, etc.
868 elements of the lists, stopping if @var{pred} returns @code{#f}, or when
869 the end of any of the lists is reached.
871 The @var{pred} call on the last set of elements (i.e., when the end of
872 the shortest list has been reached) is a tail call.
874 If one of @var{lst1} @var{lst2} @dots{}is empty then no calls to
875 @var{pred} are made, and the return value is @code{#t}.
878 @deffn {Scheme Procedure} list-index pred lst1 lst2 @dots{}
879 Return the index of the first set of elements, one from each of
880 @var{lst1} @var{lst2} @dots{}, which satisfies @var{pred}.
882 @var{pred} is called as @code{(@var{elem1} @var{elem2 @dots{}})}.
883 Searching stops when the end of the shortest @var{lst} is reached.
884 The return index starts from 0 for the first set of elements. If no
885 set of elements pass, then the return value is @code{#f}.
888 (list-index odd? '(2 4 6 9)) @result{} 3
889 (list-index = '(1 2 3) '(3 1 2)) @result{} #f
893 @deffn {Scheme Procedure} member x lst [=]
894 Return the first sublist of @var{lst} whose @sc{car} is equal to
895 @var{x}. If @var{x} does not appear in @var{lst}, return @code{#f}.
897 Equality is determined by @code{equal?}, or by the equality predicate
898 @var{=} if given. @var{=} is called @code{(= @var{x} elem)},
899 ie.@: with the given @var{x} first, so for example to find the first
900 element greater than 5,
903 (member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9)
906 This version of @code{member} extends the core @code{member}
907 (@pxref{List Searching}) by accepting an equality predicate.
911 @node SRFI-1 Deleting
912 @subsubsection Deleting
915 @deffn {Scheme Procedure} delete x lst [=]
916 @deffnx {Scheme Procedure} delete! x lst [=]
917 Return a list containing the elements of @var{lst} but with those
918 equal to @var{x} deleted. The returned elements will be in the same
919 order as they were in @var{lst}.
921 Equality is determined by the @var{=} predicate, or @code{equal?} if
922 not given. An equality call is made just once for each element, but
923 the order in which the calls are made on the elements is unspecified.
925 The equality calls are always @code{(= x elem)}, ie.@: the given @var{x}
926 is first. This means for instance elements greater than 5 can be
927 deleted with @code{(delete 5 lst <)}.
929 @code{delete} does not modify @var{lst}, but the return might share a
930 common tail with @var{lst}. @code{delete!} may modify the structure
931 of @var{lst} to construct its return.
933 These functions extend the core @code{delete} and @code{delete!}
934 (@pxref{List Modification}) in accepting an equality predicate. See
935 also @code{lset-difference} (@pxref{SRFI-1 Set Operations}) for
936 deleting multiple elements from a list.
939 @deffn {Scheme Procedure} delete-duplicates lst [=]
940 @deffnx {Scheme Procedure} delete-duplicates! lst [=]
941 Return a list containing the elements of @var{lst} but without
944 When elements are equal, only the first in @var{lst} is retained.
945 Equal elements can be anywhere in @var{lst}, they don't have to be
946 adjacent. The returned list will have the retained elements in the
947 same order as they were in @var{lst}.
949 Equality is determined by the @var{=} predicate, or @code{equal?} if
950 not given. Calls @code{(= x y)} are made with element @var{x} being
951 before @var{y} in @var{lst}. A call is made at most once for each
952 combination, but the sequence of the calls across the elements is
955 @code{delete-duplicates} does not modify @var{lst}, but the return
956 might share a common tail with @var{lst}. @code{delete-duplicates!}
957 may modify the structure of @var{lst} to construct its return.
959 In the worst case, this is an @math{O(N^2)} algorithm because it must
960 check each element against all those preceding it. For long lists it
961 is more efficient to sort and then compare only adjacent elements.
965 @node SRFI-1 Association Lists
966 @subsubsection Association Lists
967 @cindex association list
970 @c FIXME::martin: Review me!
972 Association lists are described in detail in section @ref{Association
973 Lists}. The present section only documents the additional procedures
974 for dealing with association lists defined by SRFI-1.
976 @deffn {Scheme Procedure} assoc key alist [=]
977 Return the pair from @var{alist} which matches @var{key}. This
978 extends the core @code{assoc} (@pxref{Retrieving Alist Entries}) by
979 taking an optional @var{=} comparison procedure.
981 The default comparison is @code{equal?}. If an @var{=} parameter is
982 given it's called @code{(@var{=} @var{key} @var{alistcar})}, i.e.@: the
983 given target @var{key} is the first argument, and a @code{car} from
984 @var{alist} is second.
986 For example a case-insensitive string lookup,
989 (assoc "yy" '(("XX" . 1) ("YY" . 2)) string-ci=?)
994 @deffn {Scheme Procedure} alist-cons key datum alist
995 Cons a new association @var{key} and @var{datum} onto @var{alist} and
996 return the result. This is equivalent to
999 (cons (cons @var{key} @var{datum}) @var{alist})
1002 @code{acons} (@pxref{Adding or Setting Alist Entries}) in the Guile
1003 core does the same thing.
1006 @deffn {Scheme Procedure} alist-copy alist
1007 Return a newly allocated copy of @var{alist}, that means that the
1008 spine of the list as well as the pairs are copied.
1011 @deffn {Scheme Procedure} alist-delete key alist [=]
1012 @deffnx {Scheme Procedure} alist-delete! key alist [=]
1013 Return a list containing the elements of @var{alist} but with those
1014 elements whose keys are equal to @var{key} deleted. The returned
1015 elements will be in the same order as they were in @var{alist}.
1017 Equality is determined by the @var{=} predicate, or @code{equal?} if
1018 not given. The order in which elements are tested is unspecified, but
1019 each equality call is made @code{(= key alistkey)}, i.e.@: the given
1020 @var{key} parameter is first and the key from @var{alist} second.
1021 This means for instance all associations with a key greater than 5 can
1022 be removed with @code{(alist-delete 5 alist <)}.
1024 @code{alist-delete} does not modify @var{alist}, but the return might
1025 share a common tail with @var{alist}. @code{alist-delete!} may modify
1026 the list structure of @var{alist} to construct its return.
1030 @node SRFI-1 Set Operations
1031 @subsubsection Set Operations on Lists
1032 @cindex list set operation
1034 Lists can be used to represent sets of objects. The procedures in
1035 this section operate on such lists as sets.
1037 Note that lists are not an efficient way to implement large sets. The
1038 procedures here typically take time @math{@var{m}@cross{}@var{n}} when
1039 operating on @var{m} and @var{n} element lists. Other data structures
1040 like trees, bitsets (@pxref{Bit Vectors}) or hash tables (@pxref{Hash
1041 Tables}) are faster.
1043 All these procedures take an equality predicate as the first argument.
1044 This predicate is used for testing the objects in the list sets for
1045 sameness. This predicate must be consistent with @code{eq?}
1046 (@pxref{Equality}) in the sense that if two list elements are
1047 @code{eq?} then they must also be equal under the predicate. This
1048 simply means a given object must be equal to itself.
1050 @deffn {Scheme Procedure} lset<= = list @dots{}
1051 Return @code{#t} if each list is a subset of the one following it.
1052 I.e., @var{list1} is a subset of @var{list2}, @var{list2} is a subset of
1053 @var{list3}, etc., for as many lists as given. If only one list or no
1054 lists are given, the return value is @code{#t}.
1056 A list @var{x} is a subset of @var{y} if each element of @var{x} is
1057 equal to some element in @var{y}. Elements are compared using the
1058 given @var{=} procedure, called as @code{(@var{=} xelem yelem)}.
1061 (lset<= eq?) @result{} #t
1062 (lset<= eqv? '(1 2 3) '(1)) @result{} #f
1063 (lset<= eqv? '(1 3 2) '(4 3 1 2)) @result{} #t
1067 @deffn {Scheme Procedure} lset= = list @dots{}
1068 Return @code{#t} if all argument lists are set-equal. @var{list1} is
1069 compared to @var{list2}, @var{list2} to @var{list3}, etc., for as many
1070 lists as given. If only one list or no lists are given, the return
1073 Two lists @var{x} and @var{y} are set-equal if each element of @var{x}
1074 is equal to some element of @var{y} and conversely each element of
1075 @var{y} is equal to some element of @var{x}. The order of the
1076 elements in the lists doesn't matter. Element equality is determined
1077 with the given @var{=} procedure, called as @code{(@var{=} xelem
1078 yelem)}, but exactly which calls are made is unspecified.
1081 (lset= eq?) @result{} #t
1082 (lset= eqv? '(1 2 3) '(3 2 1)) @result{} #t
1083 (lset= string-ci=? '("a" "A" "b") '("B" "b" "a")) @result{} #t
1087 @deffn {Scheme Procedure} lset-adjoin = list elem @dots{}
1088 Add to @var{list} any of the given @var{elem}s not already in the list.
1089 @var{elem}s are @code{cons}ed onto the start of @var{list} (so the
1090 return value shares a common tail with @var{list}), but the order that
1091 the @var{elem}s are added is unspecified.
1093 The given @var{=} procedure is used for comparing elements, called as
1094 @code{(@var{=} listelem elem)}, i.e., the second argument is one of
1095 the given @var{elem} parameters.
1098 (lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3)
1102 @deffn {Scheme Procedure} lset-union = list @dots{}
1103 @deffnx {Scheme Procedure} lset-union! = list @dots{}
1104 Return the union of the argument list sets. The result is built by
1105 taking the union of @var{list1} and @var{list2}, then the union of
1106 that with @var{list3}, etc., for as many lists as given. For one list
1107 argument that list itself is the result, for no list arguments the
1108 result is the empty list.
1110 The union of two lists @var{x} and @var{y} is formed as follows. If
1111 @var{x} is empty then the result is @var{y}. Otherwise start with
1112 @var{x} as the result and consider each @var{y} element (from first to
1113 last). A @var{y} element not equal to something already in the result
1114 is @code{cons}ed onto the result.
1116 The given @var{=} procedure is used for comparing elements, called as
1117 @code{(@var{=} relem yelem)}. The first argument is from the result
1118 accumulated so far, and the second is from the list being union-ed in.
1119 But exactly which calls are made is otherwise unspecified.
1121 Notice that duplicate elements in @var{list1} (or the first non-empty
1122 list) are preserved, but that repeated elements in subsequent lists
1123 are only added once.
1126 (lset-union eqv?) @result{} ()
1127 (lset-union eqv? '(1 2 3)) @result{} (1 2 3)
1128 (lset-union eqv? '(1 2 1 3) '(2 4 5) '(5)) @result{} (5 4 1 2 1 3)
1131 @code{lset-union} doesn't change the given lists but the result may
1132 share a tail with the first non-empty list. @code{lset-union!} can
1133 modify all of the given lists to form the result.
1136 @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{}
1137 @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{}
1138 Return the intersection of @var{list1} with the other argument lists,
1139 meaning those elements of @var{list1} which are also in all of
1140 @var{list2} etc. For one list argument, just that list is returned.
1142 The test for an element of @var{list1} to be in the return is simply
1143 that it's equal to some element in each of @var{list2} etc. Notice
1144 this means an element appearing twice in @var{list1} but only once in
1145 each of @var{list2} etc will go into the return twice. The return has
1146 its elements in the same order as they were in @var{list1}.
1148 The given @var{=} procedure is used for comparing elements, called as
1149 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1150 and the second is from one of the subsequent lists. But exactly which
1151 calls are made and in what order is unspecified.
1154 (lset-intersection eqv? '(x y)) @result{} (x y)
1155 (lset-intersection eqv? '(1 2 3) '(4 3 2)) @result{} (2 3)
1156 (lset-intersection eqv? '(1 1 2 2) '(1 2) '(2 1) '(2)) @result{} (2 2)
1159 The return from @code{lset-intersection} may share a tail with
1160 @var{list1}. @code{lset-intersection!} may modify @var{list1} to form
1164 @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{}
1165 @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{}
1166 Return @var{list1} with any elements in @var{list2}, @var{list3} etc
1167 removed (ie.@: subtracted). For one list argument, just that list is
1170 The given @var{=} procedure is used for comparing elements, called as
1171 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1172 and the second from one of the subsequent lists. But exactly which
1173 calls are made and in what order is unspecified.
1176 (lset-difference eqv? '(x y)) @result{} (x y)
1177 (lset-difference eqv? '(1 2 3) '(3 1)) @result{} (2)
1178 (lset-difference eqv? '(1 2 3) '(3) '(2)) @result{} (1)
1181 The return from @code{lset-difference} may share a tail with
1182 @var{list1}. @code{lset-difference!} may modify @var{list1} to form
1186 @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{}
1187 @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{}
1188 Return two values (@pxref{Multiple Values}), the difference and
1189 intersection of the argument lists as per @code{lset-difference} and
1190 @code{lset-intersection} above.
1192 For two list arguments this partitions @var{list1} into those elements
1193 of @var{list1} which are in @var{list2} and not in @var{list2}. (But
1194 for more than two arguments there can be elements of @var{list1} which
1195 are neither part of the difference nor the intersection.)
1197 One of the return values from @code{lset-diff+intersection} may share
1198 a tail with @var{list1}. @code{lset-diff+intersection!} may modify
1199 @var{list1} to form its results.
1202 @deffn {Scheme Procedure} lset-xor = list @dots{}
1203 @deffnx {Scheme Procedure} lset-xor! = list @dots{}
1204 Return an XOR of the argument lists. For two lists this means those
1205 elements which are in exactly one of the lists. For more than two
1206 lists it means those elements which appear in an odd number of the
1209 To be precise, the XOR of two lists @var{x} and @var{y} is formed by
1210 taking those elements of @var{x} not equal to any element of @var{y},
1211 plus those elements of @var{y} not equal to any element of @var{x}.
1212 Equality is determined with the given @var{=} procedure, called as
1213 @code{(@var{=} e1 e2)}. One argument is from @var{x} and the other
1214 from @var{y}, but which way around is unspecified. Exactly which
1215 calls are made is also unspecified, as is the order of the elements in
1219 (lset-xor eqv? '(x y)) @result{} (x y)
1220 (lset-xor eqv? '(1 2 3) '(4 3 2)) @result{} (4 1)
1223 The return from @code{lset-xor} may share a tail with one of the list
1224 arguments. @code{lset-xor!} may modify @var{list1} to form its
1230 @subsection SRFI-2 - and-let*
1234 The following syntax can be obtained with
1237 (use-modules (srfi srfi-2))
1240 @deffn {library syntax} and-let* (clause @dots{}) body @dots{}
1241 A combination of @code{and} and @code{let*}.
1243 Each @var{clause} is evaluated in turn, and if @code{#f} is obtained
1244 then evaluation stops and @code{#f} is returned. If all are
1245 non-@code{#f} then @var{body} is evaluated and the last form gives the
1246 return value, or if @var{body} is empty then the result is @code{#t}.
1247 Each @var{clause} should be one of the following,
1251 Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}.
1252 Like @code{let*}, that binding is available to subsequent clauses.
1254 Evaluate @var{expr} and check for @code{#f}.
1256 Get the value bound to @var{symbol} and check for @code{#f}.
1259 Notice that @code{(expr)} has an ``extra'' pair of parentheses, for
1260 instance @code{((eq? x y))}. One way to remember this is to imagine
1261 the @code{symbol} in @code{(symbol expr)} is omitted.
1263 @code{and-let*} is good for calculations where a @code{#f} value means
1264 termination, but where a non-@code{#f} value is going to be needed in
1265 subsequent expressions.
1267 The following illustrates this, it returns text between brackets
1268 @samp{[...]} in a string, or @code{#f} if there are no such brackets
1269 (ie.@: either @code{string-index} gives @code{#f}).
1272 (define (extract-brackets str)
1273 (and-let* ((start (string-index str #\[))
1274 (end (string-index str #\] start)))
1275 (substring str (1+ start) end)))
1278 The following shows plain variables and expressions tested too.
1279 @code{diagnostic-levels} is taken to be an alist associating a
1280 diagnostic type with a level. @code{str} is printed only if the type
1281 is known and its level is high enough.
1284 (define (show-diagnostic type str)
1285 (and-let* (want-diagnostics
1286 (level (assq-ref diagnostic-levels type))
1287 ((>= level current-diagnostic-level)))
1291 The advantage of @code{and-let*} is that an extended sequence of
1292 expressions and tests doesn't require lots of nesting as would arise
1293 from separate @code{and} and @code{let*}, or from @code{cond} with
1300 @subsection SRFI-4 - Homogeneous numeric vector datatypes
1303 SRFI-4 provides an interface to uniform numeric vectors: vectors whose elements
1304 are all of a single numeric type. Guile offers uniform numeric vectors for
1305 signed and unsigned 8-bit, 16-bit, 32-bit, and 64-bit integers, two sizes of
1306 floating point values, and, as an extension to SRFI-4, complex floating-point
1307 numbers of these two sizes.
1309 The standard SRFI-4 procedures and data types may be included via loading the
1313 (use-modules (srfi srfi-4))
1316 This module is currently a part of the default Guile environment, but it is a
1317 good practice to explicitly import the module. In the future, using SRFI-4
1318 procedures without importing the SRFI-4 module will cause a deprecation message
1319 to be printed. (Of course, one may call the C functions at any time. Would that
1323 * SRFI-4 Overview:: The warp and weft of uniform numeric vectors.
1324 * SRFI-4 API:: Uniform vectors, from Scheme and from C.
1325 * SRFI-4 Generic Operations:: The general, operating on the specific.
1326 * SRFI-4 and Bytevectors:: SRFI-4 vectors are backed by bytevectors.
1327 * SRFI-4 Extensions:: Guile-specific extensions to the standard.
1330 @node SRFI-4 Overview
1331 @subsubsection SRFI-4 - Overview
1333 Uniform numeric vectors can be useful since they consume less memory
1334 than the non-uniform, general vectors. Also, since the types they can
1335 store correspond directly to C types, it is easier to work with them
1336 efficiently on a low level. Consider image processing as an example,
1337 where you want to apply a filter to some image. While you could store
1338 the pixels of an image in a general vector and write a general
1339 convolution function, things are much more efficient with uniform
1340 vectors: the convolution function knows that all pixels are unsigned
1341 8-bit values (say), and can use a very tight inner loop.
1343 This is implemented in Scheme by having the compiler notice calls to the SRFI-4
1344 accessors, and inline them to appropriate compiled code. From C you have access
1345 to the raw array; functions for efficiently working with uniform numeric vectors
1346 from C are listed at the end of this section.
1348 Uniform numeric vectors are the special case of one dimensional uniform
1351 There are 12 standard kinds of uniform numeric vectors, and they all have their
1352 own complement of constructors, accessors, and so on. Procedures that operate on
1353 a specific kind of uniform numeric vector have a ``tag'' in their name,
1354 indicating the element type.
1358 unsigned 8-bit integers
1361 signed 8-bit integers
1364 unsigned 16-bit integers
1367 signed 16-bit integers
1370 unsigned 32-bit integers
1373 signed 32-bit integers
1376 unsigned 64-bit integers
1379 signed 64-bit integers
1382 the C type @code{float}
1385 the C type @code{double}
1389 In addition, Guile supports uniform arrays of complex numbers, with the
1395 complex numbers in rectangular form with the real and imaginary part
1396 being a @code{float}
1399 complex numbers in rectangular form with the real and imaginary part
1400 being a @code{double}
1404 The external representation (ie.@: read syntax) for these vectors is
1405 similar to normal Scheme vectors, but with an additional tag from the
1406 tables above indicating the vector's type. For example,
1413 Note that the read syntax for floating-point here conflicts with
1414 @code{#f} for false. In Standard Scheme one can write @code{(1 #f3)}
1415 for a three element list @code{(1 #f 3)}, but for Guile @code{(1 #f3)}
1416 is invalid. @code{(1 #f 3)} is almost certainly what one should write
1417 anyway to make the intention clear, so this is rarely a problem.
1421 @subsubsection SRFI-4 - API
1423 Note that the @nicode{c32} and @nicode{c64} functions are only available from
1424 @nicode{(srfi srfi-4 gnu)}.
1426 @deffn {Scheme Procedure} u8vector? obj
1427 @deffnx {Scheme Procedure} s8vector? obj
1428 @deffnx {Scheme Procedure} u16vector? obj
1429 @deffnx {Scheme Procedure} s16vector? obj
1430 @deffnx {Scheme Procedure} u32vector? obj
1431 @deffnx {Scheme Procedure} s32vector? obj
1432 @deffnx {Scheme Procedure} u64vector? obj
1433 @deffnx {Scheme Procedure} s64vector? obj
1434 @deffnx {Scheme Procedure} f32vector? obj
1435 @deffnx {Scheme Procedure} f64vector? obj
1436 @deffnx {Scheme Procedure} c32vector? obj
1437 @deffnx {Scheme Procedure} c64vector? obj
1438 @deffnx {C Function} scm_u8vector_p (obj)
1439 @deffnx {C Function} scm_s8vector_p (obj)
1440 @deffnx {C Function} scm_u16vector_p (obj)
1441 @deffnx {C Function} scm_s16vector_p (obj)
1442 @deffnx {C Function} scm_u32vector_p (obj)
1443 @deffnx {C Function} scm_s32vector_p (obj)
1444 @deffnx {C Function} scm_u64vector_p (obj)
1445 @deffnx {C Function} scm_s64vector_p (obj)
1446 @deffnx {C Function} scm_f32vector_p (obj)
1447 @deffnx {C Function} scm_f64vector_p (obj)
1448 @deffnx {C Function} scm_c32vector_p (obj)
1449 @deffnx {C Function} scm_c64vector_p (obj)
1450 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1454 @deffn {Scheme Procedure} make-u8vector n [value]
1455 @deffnx {Scheme Procedure} make-s8vector n [value]
1456 @deffnx {Scheme Procedure} make-u16vector n [value]
1457 @deffnx {Scheme Procedure} make-s16vector n [value]
1458 @deffnx {Scheme Procedure} make-u32vector n [value]
1459 @deffnx {Scheme Procedure} make-s32vector n [value]
1460 @deffnx {Scheme Procedure} make-u64vector n [value]
1461 @deffnx {Scheme Procedure} make-s64vector n [value]
1462 @deffnx {Scheme Procedure} make-f32vector n [value]
1463 @deffnx {Scheme Procedure} make-f64vector n [value]
1464 @deffnx {Scheme Procedure} make-c32vector n [value]
1465 @deffnx {Scheme Procedure} make-c64vector n [value]
1466 @deffnx {C Function} scm_make_u8vector n [value]
1467 @deffnx {C Function} scm_make_s8vector n [value]
1468 @deffnx {C Function} scm_make_u16vector n [value]
1469 @deffnx {C Function} scm_make_s16vector n [value]
1470 @deffnx {C Function} scm_make_u32vector n [value]
1471 @deffnx {C Function} scm_make_s32vector n [value]
1472 @deffnx {C Function} scm_make_u64vector n [value]
1473 @deffnx {C Function} scm_make_s64vector n [value]
1474 @deffnx {C Function} scm_make_f32vector n [value]
1475 @deffnx {C Function} scm_make_f64vector n [value]
1476 @deffnx {C Function} scm_make_c32vector n [value]
1477 @deffnx {C Function} scm_make_c64vector n [value]
1478 Return a newly allocated homogeneous numeric vector holding @var{n}
1479 elements of the indicated type. If @var{value} is given, the vector
1480 is initialized with that value, otherwise the contents are
1484 @deffn {Scheme Procedure} u8vector value @dots{}
1485 @deffnx {Scheme Procedure} s8vector value @dots{}
1486 @deffnx {Scheme Procedure} u16vector value @dots{}
1487 @deffnx {Scheme Procedure} s16vector value @dots{}
1488 @deffnx {Scheme Procedure} u32vector value @dots{}
1489 @deffnx {Scheme Procedure} s32vector value @dots{}
1490 @deffnx {Scheme Procedure} u64vector value @dots{}
1491 @deffnx {Scheme Procedure} s64vector value @dots{}
1492 @deffnx {Scheme Procedure} f32vector value @dots{}
1493 @deffnx {Scheme Procedure} f64vector value @dots{}
1494 @deffnx {Scheme Procedure} c32vector value @dots{}
1495 @deffnx {Scheme Procedure} c64vector value @dots{}
1496 @deffnx {C Function} scm_u8vector (values)
1497 @deffnx {C Function} scm_s8vector (values)
1498 @deffnx {C Function} scm_u16vector (values)
1499 @deffnx {C Function} scm_s16vector (values)
1500 @deffnx {C Function} scm_u32vector (values)
1501 @deffnx {C Function} scm_s32vector (values)
1502 @deffnx {C Function} scm_u64vector (values)
1503 @deffnx {C Function} scm_s64vector (values)
1504 @deffnx {C Function} scm_f32vector (values)
1505 @deffnx {C Function} scm_f64vector (values)
1506 @deffnx {C Function} scm_c32vector (values)
1507 @deffnx {C Function} scm_c64vector (values)
1508 Return a newly allocated homogeneous numeric vector of the indicated
1509 type, holding the given parameter @var{value}s. The vector length is
1510 the number of parameters given.
1513 @deffn {Scheme Procedure} u8vector-length vec
1514 @deffnx {Scheme Procedure} s8vector-length vec
1515 @deffnx {Scheme Procedure} u16vector-length vec
1516 @deffnx {Scheme Procedure} s16vector-length vec
1517 @deffnx {Scheme Procedure} u32vector-length vec
1518 @deffnx {Scheme Procedure} s32vector-length vec
1519 @deffnx {Scheme Procedure} u64vector-length vec
1520 @deffnx {Scheme Procedure} s64vector-length vec
1521 @deffnx {Scheme Procedure} f32vector-length vec
1522 @deffnx {Scheme Procedure} f64vector-length vec
1523 @deffnx {Scheme Procedure} c32vector-length vec
1524 @deffnx {Scheme Procedure} c64vector-length vec
1525 @deffnx {C Function} scm_u8vector_length (vec)
1526 @deffnx {C Function} scm_s8vector_length (vec)
1527 @deffnx {C Function} scm_u16vector_length (vec)
1528 @deffnx {C Function} scm_s16vector_length (vec)
1529 @deffnx {C Function} scm_u32vector_length (vec)
1530 @deffnx {C Function} scm_s32vector_length (vec)
1531 @deffnx {C Function} scm_u64vector_length (vec)
1532 @deffnx {C Function} scm_s64vector_length (vec)
1533 @deffnx {C Function} scm_f32vector_length (vec)
1534 @deffnx {C Function} scm_f64vector_length (vec)
1535 @deffnx {C Function} scm_c32vector_length (vec)
1536 @deffnx {C Function} scm_c64vector_length (vec)
1537 Return the number of elements in @var{vec}.
1540 @deffn {Scheme Procedure} u8vector-ref vec i
1541 @deffnx {Scheme Procedure} s8vector-ref vec i
1542 @deffnx {Scheme Procedure} u16vector-ref vec i
1543 @deffnx {Scheme Procedure} s16vector-ref vec i
1544 @deffnx {Scheme Procedure} u32vector-ref vec i
1545 @deffnx {Scheme Procedure} s32vector-ref vec i
1546 @deffnx {Scheme Procedure} u64vector-ref vec i
1547 @deffnx {Scheme Procedure} s64vector-ref vec i
1548 @deffnx {Scheme Procedure} f32vector-ref vec i
1549 @deffnx {Scheme Procedure} f64vector-ref vec i
1550 @deffnx {Scheme Procedure} c32vector-ref vec i
1551 @deffnx {Scheme Procedure} c64vector-ref vec i
1552 @deffnx {C Function} scm_u8vector_ref (vec i)
1553 @deffnx {C Function} scm_s8vector_ref (vec i)
1554 @deffnx {C Function} scm_u16vector_ref (vec i)
1555 @deffnx {C Function} scm_s16vector_ref (vec i)
1556 @deffnx {C Function} scm_u32vector_ref (vec i)
1557 @deffnx {C Function} scm_s32vector_ref (vec i)
1558 @deffnx {C Function} scm_u64vector_ref (vec i)
1559 @deffnx {C Function} scm_s64vector_ref (vec i)
1560 @deffnx {C Function} scm_f32vector_ref (vec i)
1561 @deffnx {C Function} scm_f64vector_ref (vec i)
1562 @deffnx {C Function} scm_c32vector_ref (vec i)
1563 @deffnx {C Function} scm_c64vector_ref (vec i)
1564 Return the element at index @var{i} in @var{vec}. The first element
1565 in @var{vec} is index 0.
1568 @deffn {Scheme Procedure} u8vector-set! vec i value
1569 @deffnx {Scheme Procedure} s8vector-set! vec i value
1570 @deffnx {Scheme Procedure} u16vector-set! vec i value
1571 @deffnx {Scheme Procedure} s16vector-set! vec i value
1572 @deffnx {Scheme Procedure} u32vector-set! vec i value
1573 @deffnx {Scheme Procedure} s32vector-set! vec i value
1574 @deffnx {Scheme Procedure} u64vector-set! vec i value
1575 @deffnx {Scheme Procedure} s64vector-set! vec i value
1576 @deffnx {Scheme Procedure} f32vector-set! vec i value
1577 @deffnx {Scheme Procedure} f64vector-set! vec i value
1578 @deffnx {Scheme Procedure} c32vector-set! vec i value
1579 @deffnx {Scheme Procedure} c64vector-set! vec i value
1580 @deffnx {C Function} scm_u8vector_set_x (vec i value)
1581 @deffnx {C Function} scm_s8vector_set_x (vec i value)
1582 @deffnx {C Function} scm_u16vector_set_x (vec i value)
1583 @deffnx {C Function} scm_s16vector_set_x (vec i value)
1584 @deffnx {C Function} scm_u32vector_set_x (vec i value)
1585 @deffnx {C Function} scm_s32vector_set_x (vec i value)
1586 @deffnx {C Function} scm_u64vector_set_x (vec i value)
1587 @deffnx {C Function} scm_s64vector_set_x (vec i value)
1588 @deffnx {C Function} scm_f32vector_set_x (vec i value)
1589 @deffnx {C Function} scm_f64vector_set_x (vec i value)
1590 @deffnx {C Function} scm_c32vector_set_x (vec i value)
1591 @deffnx {C Function} scm_c64vector_set_x (vec i value)
1592 Set the element at index @var{i} in @var{vec} to @var{value}. The
1593 first element in @var{vec} is index 0. The return value is
1597 @deffn {Scheme Procedure} u8vector->list vec
1598 @deffnx {Scheme Procedure} s8vector->list vec
1599 @deffnx {Scheme Procedure} u16vector->list vec
1600 @deffnx {Scheme Procedure} s16vector->list vec
1601 @deffnx {Scheme Procedure} u32vector->list vec
1602 @deffnx {Scheme Procedure} s32vector->list vec
1603 @deffnx {Scheme Procedure} u64vector->list vec
1604 @deffnx {Scheme Procedure} s64vector->list vec
1605 @deffnx {Scheme Procedure} f32vector->list vec
1606 @deffnx {Scheme Procedure} f64vector->list vec
1607 @deffnx {Scheme Procedure} c32vector->list vec
1608 @deffnx {Scheme Procedure} c64vector->list vec
1609 @deffnx {C Function} scm_u8vector_to_list (vec)
1610 @deffnx {C Function} scm_s8vector_to_list (vec)
1611 @deffnx {C Function} scm_u16vector_to_list (vec)
1612 @deffnx {C Function} scm_s16vector_to_list (vec)
1613 @deffnx {C Function} scm_u32vector_to_list (vec)
1614 @deffnx {C Function} scm_s32vector_to_list (vec)
1615 @deffnx {C Function} scm_u64vector_to_list (vec)
1616 @deffnx {C Function} scm_s64vector_to_list (vec)
1617 @deffnx {C Function} scm_f32vector_to_list (vec)
1618 @deffnx {C Function} scm_f64vector_to_list (vec)
1619 @deffnx {C Function} scm_c32vector_to_list (vec)
1620 @deffnx {C Function} scm_c64vector_to_list (vec)
1621 Return a newly allocated list holding all elements of @var{vec}.
1624 @deffn {Scheme Procedure} list->u8vector lst
1625 @deffnx {Scheme Procedure} list->s8vector lst
1626 @deffnx {Scheme Procedure} list->u16vector lst
1627 @deffnx {Scheme Procedure} list->s16vector lst
1628 @deffnx {Scheme Procedure} list->u32vector lst
1629 @deffnx {Scheme Procedure} list->s32vector lst
1630 @deffnx {Scheme Procedure} list->u64vector lst
1631 @deffnx {Scheme Procedure} list->s64vector lst
1632 @deffnx {Scheme Procedure} list->f32vector lst
1633 @deffnx {Scheme Procedure} list->f64vector lst
1634 @deffnx {Scheme Procedure} list->c32vector lst
1635 @deffnx {Scheme Procedure} list->c64vector lst
1636 @deffnx {C Function} scm_list_to_u8vector (lst)
1637 @deffnx {C Function} scm_list_to_s8vector (lst)
1638 @deffnx {C Function} scm_list_to_u16vector (lst)
1639 @deffnx {C Function} scm_list_to_s16vector (lst)
1640 @deffnx {C Function} scm_list_to_u32vector (lst)
1641 @deffnx {C Function} scm_list_to_s32vector (lst)
1642 @deffnx {C Function} scm_list_to_u64vector (lst)
1643 @deffnx {C Function} scm_list_to_s64vector (lst)
1644 @deffnx {C Function} scm_list_to_f32vector (lst)
1645 @deffnx {C Function} scm_list_to_f64vector (lst)
1646 @deffnx {C Function} scm_list_to_c32vector (lst)
1647 @deffnx {C Function} scm_list_to_c64vector (lst)
1648 Return a newly allocated homogeneous numeric vector of the indicated type,
1649 initialized with the elements of the list @var{lst}.
1652 @deftypefn {C Function} SCM scm_take_u8vector (const scm_t_uint8 *data, size_t len)
1653 @deftypefnx {C Function} SCM scm_take_s8vector (const scm_t_int8 *data, size_t len)
1654 @deftypefnx {C Function} SCM scm_take_u16vector (const scm_t_uint16 *data, size_t len)
1655 @deftypefnx {C Function} SCM scm_take_s16vector (const scm_t_int16 *data, size_t len)
1656 @deftypefnx {C Function} SCM scm_take_u32vector (const scm_t_uint32 *data, size_t len)
1657 @deftypefnx {C Function} SCM scm_take_s32vector (const scm_t_int32 *data, size_t len)
1658 @deftypefnx {C Function} SCM scm_take_u64vector (const scm_t_uint64 *data, size_t len)
1659 @deftypefnx {C Function} SCM scm_take_s64vector (const scm_t_int64 *data, size_t len)
1660 @deftypefnx {C Function} SCM scm_take_f32vector (const float *data, size_t len)
1661 @deftypefnx {C Function} SCM scm_take_f64vector (const double *data, size_t len)
1662 @deftypefnx {C Function} SCM scm_take_c32vector (const float *data, size_t len)
1663 @deftypefnx {C Function} SCM scm_take_c64vector (const double *data, size_t len)
1664 Return a new uniform numeric vector of the indicated type and length
1665 that uses the memory pointed to by @var{data} to store its elements.
1666 This memory will eventually be freed with @code{free}. The argument
1667 @var{len} specifies the number of elements in @var{data}, not its size
1670 The @code{c32} and @code{c64} variants take a pointer to a C array of
1671 @code{float}s or @code{double}s. The real parts of the complex numbers
1672 are at even indices in that array, the corresponding imaginary parts are
1673 at the following odd index.
1676 @deftypefn {C Function} {const scm_t_uint8 *} scm_u8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1677 @deftypefnx {C Function} {const scm_t_int8 *} scm_s8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1678 @deftypefnx {C Function} {const scm_t_uint16 *} scm_u16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1679 @deftypefnx {C Function} {const scm_t_int16 *} scm_s16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1680 @deftypefnx {C Function} {const scm_t_uint32 *} scm_u32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1681 @deftypefnx {C Function} {const scm_t_int32 *} scm_s32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1682 @deftypefnx {C Function} {const scm_t_uint64 *} scm_u64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1683 @deftypefnx {C Function} {const scm_t_int64 *} scm_s64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1684 @deftypefnx {C Function} {const float *} scm_f32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1685 @deftypefnx {C Function} {const double *} scm_f64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1686 @deftypefnx {C Function} {const float *} scm_c32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1687 @deftypefnx {C Function} {const double *} scm_c64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1688 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1689 returns a pointer to the elements of a uniform numeric vector of the
1693 @deftypefn {C Function} {scm_t_uint8 *} scm_u8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1694 @deftypefnx {C Function} {scm_t_int8 *} scm_s8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1695 @deftypefnx {C Function} {scm_t_uint16 *} scm_u16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1696 @deftypefnx {C Function} {scm_t_int16 *} scm_s16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1697 @deftypefnx {C Function} {scm_t_uint32 *} scm_u32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1698 @deftypefnx {C Function} {scm_t_int32 *} scm_s32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1699 @deftypefnx {C Function} {scm_t_uint64 *} scm_u64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1700 @deftypefnx {C Function} {scm_t_int64 *} scm_s64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1701 @deftypefnx {C Function} {float *} scm_f32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1702 @deftypefnx {C Function} {double *} scm_f64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1703 @deftypefnx {C Function} {float *} scm_c32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1704 @deftypefnx {C Function} {double *} scm_c64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1705 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1706 C}), but returns a pointer to the elements of a uniform numeric vector
1707 of the indicated kind.
1710 @node SRFI-4 Generic Operations
1711 @subsubsection SRFI-4 - Generic operations
1713 Guile also provides procedures that operate on all types of uniform numeric
1714 vectors. In what is probably a bug, these procedures are currently available in
1715 the default environment as well; however prudent hackers will make sure to
1716 import @code{(srfi srfi-4 gnu)} before using these.
1718 @deftypefn {C Function} int scm_is_uniform_vector (SCM uvec)
1719 Return non-zero when @var{uvec} is a uniform numeric vector, zero
1723 @deftypefn {C Function} size_t scm_c_uniform_vector_length (SCM uvec)
1724 Return the number of elements of @var{uvec} as a @code{size_t}.
1727 @deffn {Scheme Procedure} uniform-vector? obj
1728 @deffnx {C Function} scm_uniform_vector_p (obj)
1729 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1733 @deffn {Scheme Procedure} uniform-vector-length vec
1734 @deffnx {C Function} scm_uniform_vector_length (vec)
1735 Return the number of elements in @var{vec}.
1738 @deffn {Scheme Procedure} uniform-vector-ref vec i
1739 @deffnx {C Function} scm_uniform_vector_ref (vec i)
1740 Return the element at index @var{i} in @var{vec}. The first element
1741 in @var{vec} is index 0.
1744 @deffn {Scheme Procedure} uniform-vector-set! vec i value
1745 @deffnx {C Function} scm_uniform_vector_set_x (vec i value)
1746 Set the element at index @var{i} in @var{vec} to @var{value}. The
1747 first element in @var{vec} is index 0. The return value is
1751 @deffn {Scheme Procedure} uniform-vector->list vec
1752 @deffnx {C Function} scm_uniform_vector_to_list (vec)
1753 Return a newly allocated list holding all elements of @var{vec}.
1756 @deftypefn {C Function} {const void *} scm_uniform_vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1757 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1758 returns a pointer to the elements of a uniform numeric vector.
1761 @deftypefn {C Function} {void *} scm_uniform_vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1762 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1763 C}), but returns a pointer to the elements of a uniform numeric vector.
1766 Unless you really need to the limited generality of these functions, it is best
1767 to use the type-specific functions, or the generalized vector accessors.
1769 @node SRFI-4 and Bytevectors
1770 @subsubsection SRFI-4 - Relation to bytevectors
1772 Guile implements SRFI-4 vectors using bytevectors (@pxref{Bytevectors}). Often
1773 when you have a numeric vector, you end up wanting to write its bytes somewhere,
1774 or have access to the underlying bytes, or read in bytes from somewhere else.
1775 Bytevectors are very good at this sort of thing. But the SRFI-4 APIs are nicer
1776 to use when doing number-crunching, because they are addressed by element and
1779 So as a compromise, Guile allows all bytevector functions to operate on numeric
1780 vectors. They address the underlying bytes in the native endianness, as one
1783 Following the same reasoning, that it's just bytes underneath, Guile also allows
1784 uniform vectors of a given type to be accessed as if they were of any type. One
1785 can fill a @nicode{u32vector}, and access its elements with
1786 @nicode{u8vector-ref}. One can use @nicode{f64vector-ref} on bytevectors. It's
1787 all the same to Guile.
1789 In this way, uniform numeric vectors may be written to and read from
1790 input/output ports using the procedures that operate on bytevectors.
1792 @xref{Bytevectors}, for more information.
1795 @node SRFI-4 Extensions
1796 @subsubsection SRFI-4 - Guile extensions
1798 Guile defines some useful extensions to SRFI-4, which are not available in the
1799 default Guile environment. They may be imported by loading the extensions
1803 (use-modules (srfi srfi-4 gnu))
1806 @deffn {Scheme Procedure} any->u8vector obj
1807 @deffnx {Scheme Procedure} any->s8vector obj
1808 @deffnx {Scheme Procedure} any->u16vector obj
1809 @deffnx {Scheme Procedure} any->s16vector obj
1810 @deffnx {Scheme Procedure} any->u32vector obj
1811 @deffnx {Scheme Procedure} any->s32vector obj
1812 @deffnx {Scheme Procedure} any->u64vector obj
1813 @deffnx {Scheme Procedure} any->s64vector obj
1814 @deffnx {Scheme Procedure} any->f32vector obj
1815 @deffnx {Scheme Procedure} any->f64vector obj
1816 @deffnx {Scheme Procedure} any->c32vector obj
1817 @deffnx {Scheme Procedure} any->c64vector obj
1818 @deffnx {C Function} scm_any_to_u8vector (obj)
1819 @deffnx {C Function} scm_any_to_s8vector (obj)
1820 @deffnx {C Function} scm_any_to_u16vector (obj)
1821 @deffnx {C Function} scm_any_to_s16vector (obj)
1822 @deffnx {C Function} scm_any_to_u32vector (obj)
1823 @deffnx {C Function} scm_any_to_s32vector (obj)
1824 @deffnx {C Function} scm_any_to_u64vector (obj)
1825 @deffnx {C Function} scm_any_to_s64vector (obj)
1826 @deffnx {C Function} scm_any_to_f32vector (obj)
1827 @deffnx {C Function} scm_any_to_f64vector (obj)
1828 @deffnx {C Function} scm_any_to_c32vector (obj)
1829 @deffnx {C Function} scm_any_to_c64vector (obj)
1830 Return a (maybe newly allocated) uniform numeric vector of the indicated
1831 type, initialized with the elements of @var{obj}, which must be a list,
1832 a vector, or a uniform vector. When @var{obj} is already a suitable
1833 uniform numeric vector, it is returned unchanged.
1838 @subsection SRFI-6 - Basic String Ports
1841 SRFI-6 defines the procedures @code{open-input-string},
1842 @code{open-output-string} and @code{get-output-string}. These
1843 procedures are included in the Guile core, so using this module does not
1844 make any difference at the moment. But it is possible that support for
1845 SRFI-6 will be factored out of the core library in the future, so using
1846 this module does not hurt, after all.
1849 @subsection SRFI-8 - receive
1852 @code{receive} is a syntax for making the handling of multiple-value
1853 procedures easier. It is documented in @xref{Multiple Values}.
1857 @subsection SRFI-9 - define-record-type
1861 This SRFI is a syntax for defining new record types and creating
1862 predicate, constructor, and field getter and setter functions. In
1863 Guile this is simply an alternate interface to the core record
1864 functionality (@pxref{Records}). It can be used with,
1867 (use-modules (srfi srfi-9))
1870 @deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{}
1872 Create a new record type, and make various @code{define}s for using
1873 it. This syntax can only occur at the top-level, not nested within
1876 @var{type} is bound to the record type, which is as per the return
1877 from the core @code{make-record-type}. @var{type} also provides the
1878 name for the record, as per @code{record-type-name}.
1880 @var{constructor} is bound to a function to be called as
1881 @code{(@var{constructor} fieldval @dots{})} to create a new record of
1882 this type. The arguments are initial values for the fields, one
1883 argument for each field, in the order they appear in the
1884 @code{define-record-type} form.
1886 The @var{fieldname}s provide the names for the record fields, as per
1887 the core @code{record-type-fields} etc, and are referred to in the
1888 subsequent accessor/modifier forms.
1890 @var{predicate} is bound to a function to be called as
1891 @code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f}
1892 according to whether @var{obj} is a record of this type.
1894 Each @var{accessor} is bound to a function to be called
1895 @code{(@var{accessor} record)} to retrieve the respective field from a
1896 @var{record}. Similarly each @var{modifier} is bound to a function to
1897 be called @code{(@var{modifier} record val)} to set the respective
1898 field in a @var{record}.
1902 An example will illustrate typical usage,
1905 (define-record-type employee-type
1906 (make-employee name age salary)
1908 (name get-employee-name)
1909 (age get-employee-age set-employee-age)
1910 (salary get-employee-salary set-employee-salary))
1913 This creates a new employee data type, with name, age and salary
1914 fields. Accessor functions are created for each field, but no
1915 modifier function for the name (the intention in this example being
1916 that it's established only when an employee object is created). These
1917 can all then be used as for example,
1920 employee-type @result{} #<record-type employee-type>
1922 (define fred (make-employee "Fred" 45 20000.00))
1924 (employee? fred) @result{} #t
1925 (get-employee-age fred) @result{} 45
1926 (set-employee-salary fred 25000.00) ;; pay rise
1929 The functions created by @code{define-record-type} are ordinary
1930 top-level @code{define}s. They can be redefined or @code{set!} as
1931 desired, exported from a module, etc.
1933 @unnumberedsubsubsec Non-toplevel Record Definitions
1935 The SRFI-9 specification explicitly disallows record definitions in a
1936 non-toplevel context, such as inside @code{lambda} body or inside a
1937 @var{let} block. However, Guile's implementation does not enforce that
1940 @unnumberedsubsubsec Custom Printers
1942 You may use @code{set-record-type-printer!} to customize the default printing
1943 behavior of records. This is a Guile extension and is not part of SRFI-9. It
1944 is located in the @nicode{(srfi srfi-9 gnu)} module.
1946 @deffn {Scheme Syntax} set-record-type-printer! name thunk
1947 Where @var{type} corresponds to the first argument of @code{define-record-type},
1948 and @var{thunk} is a procedure accepting two arguments, the record to print, and
1953 This example prints the employee's name in brackets, for instance @code{[Fred]}.
1956 (set-record-type-printer! employee-type
1957 (lambda (record port)
1958 (write-char #\[ port)
1959 (display (get-employee-name record) port)
1960 (write-char #\] port)))
1964 @subsection SRFI-10 - Hash-Comma Reader Extension
1969 This SRFI implements a reader extension @code{#,()} called hash-comma.
1970 It allows the reader to give new kinds of objects, for use both in
1971 data and as constants or literals in source code. This feature is
1975 (use-modules (srfi srfi-10))
1979 The new read syntax is of the form
1982 #,(@var{tag} @var{arg}@dots{})
1986 where @var{tag} is a symbol and the @var{arg}s are objects taken as
1987 parameters. @var{tag}s are registered with the following procedure.
1989 @deffn {Scheme Procedure} define-reader-ctor tag proc
1990 Register @var{proc} as the constructor for a hash-comma read syntax
1991 starting with symbol @var{tag}, i.e.@: @nicode{#,(@var{tag} arg@dots{})}.
1992 @var{proc} is called with the given arguments @code{(@var{proc}
1993 arg@dots{})} and the object it returns is the result of the read.
1997 For example, a syntax giving a list of @var{N} copies of an object.
2000 (define-reader-ctor 'repeat
2002 (make-list reps obj)))
2004 (display '#,(repeat 99 3))
2008 Notice the quote @nicode{'} when the @nicode{#,( )} is used. The
2009 @code{repeat} handler returns a list and the program must quote to use
2010 it literally, the same as any other list. Ie.
2013 (display '#,(repeat 99 3))
2015 (display '(99 99 99))
2018 When a handler returns an object which is self-evaluating, like a
2019 number or a string, then there's no need for quoting, just as there's
2020 no need when giving those directly as literals. For example an
2024 (define-reader-ctor 'sum
2027 (display #,(sum 123 456)) @print{} 579
2030 A typical use for @nicode{#,()} is to get a read syntax for objects
2031 which don't otherwise have one. For example, the following allows a
2032 hash table to be given literally, with tags and values, ready for fast
2036 (define-reader-ctor 'hash
2038 (let ((table (make-hash-table)))
2039 (for-each (lambda (elem)
2040 (apply hash-set! table elem))
2044 (define (animal->family animal)
2045 (hash-ref '#,(hash ("tiger" "cat")
2050 (animal->family "lion") @result{} "cat"
2053 Or for example the following is a syntax for a compiled regular
2054 expression (@pxref{Regular Expressions}).
2057 (use-modules (ice-9 regex))
2059 (define-reader-ctor 'regexp make-regexp)
2061 (define (extract-angs str)
2062 (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str)))
2064 (match:substring match 1))))
2066 (extract-angs "foo <BAR> quux") @result{} "BAR"
2070 @nicode{#,()} is somewhat similar to @code{define-macro}
2071 (@pxref{Macros}) in that handler code is run to produce a result, but
2072 @nicode{#,()} operates at the read stage, so it can appear in data for
2073 @code{read} (@pxref{Scheme Read}), not just in code to be executed.
2075 Because @nicode{#,()} is handled at read-time it has no direct access
2076 to variables etc. A symbol in the arguments is just a symbol, not a
2077 variable reference. The arguments are essentially constants, though
2078 the handler procedure can use them in any complicated way it might
2081 Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available
2082 globally, there's no need to use @code{(srfi srfi-10)} in later
2083 modules. Similarly the tags registered are global and can be used
2084 anywhere once registered.
2086 There's no attempt to record what previous @nicode{#,()} forms have
2087 been seen, if two identical forms occur then two calls are made to the
2088 handler procedure. The handler might like to maintain a cache or
2089 similar to avoid making copies of large objects, depending on expected
2092 In code the best uses of @nicode{#,()} are generally when there's a
2093 lot of objects of a particular kind as literals or constants. If
2094 there's just a few then some local variables and initializers are
2095 fine, but that becomes tedious and error prone when there's a lot, and
2096 the anonymous and compact syntax of @nicode{#,()} is much better.
2100 @subsection SRFI-11 - let-values
2105 This module implements the binding forms for multiple values
2106 @code{let-values} and @code{let*-values}. These forms are similar to
2107 @code{let} and @code{let*} (@pxref{Local Bindings}), but they support
2108 binding of the values returned by multiple-valued expressions.
2110 Write @code{(use-modules (srfi srfi-11))} to make the bindings
2114 (let-values (((x y) (values 1 2))
2115 ((z f) (values 3 4)))
2121 @code{let-values} performs all bindings simultaneously, which means that
2122 no expression in the binding clauses may refer to variables bound in the
2123 same clause list. @code{let*-values}, on the other hand, performs the
2124 bindings sequentially, just like @code{let*} does for single-valued
2129 @subsection SRFI-13 - String Library
2132 The SRFI-13 procedures are always available, @xref{Strings}.
2135 @subsection SRFI-14 - Character-set Library
2138 The SRFI-14 data type and procedures are always available,
2139 @xref{Character Sets}.
2142 @subsection SRFI-16 - case-lambda
2144 @cindex variable arity
2145 @cindex arity, variable
2147 SRFI-16 defines a variable-arity @code{lambda} form,
2148 @code{case-lambda}. This form is available in the default Guile
2149 environment. @xref{Case-lambda}, for more information.
2152 @subsection SRFI-17 - Generalized set!
2155 This SRFI implements a generalized @code{set!}, allowing some
2156 ``referencing'' functions to be used as the target location of a
2157 @code{set!}. This feature is available from
2160 (use-modules (srfi srfi-17))
2164 For example @code{vector-ref} is extended so that
2167 (set! (vector-ref vec idx) new-value)
2174 (vector-set! vec idx new-value)
2177 The idea is that a @code{vector-ref} expression identifies a location,
2178 which may be either fetched or stored. The same form is used for the
2179 location in both cases, encouraging visual clarity. This is similar
2180 to the idea of an ``lvalue'' in C.
2182 The mechanism for this kind of @code{set!} is in the Guile core
2183 (@pxref{Procedures with Setters}). This module adds definitions of
2184 the following functions as procedures with setters, allowing them to
2185 be targets of a @code{set!},
2188 @nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr},
2189 @nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr},
2190 @nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr},
2191 @nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr},
2192 @nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr},
2193 @nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr},
2194 @nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr},
2195 @nicode{cdddar}, @nicode{cddddr}
2197 @nicode{string-ref}, @nicode{vector-ref}
2200 The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as
2201 a procedure with setter, allowing the setter for a procedure to be
2202 changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}.
2203 Currently Guile does not implement this, a setter can only be
2204 specified on creation (@code{getter-with-setter} below).
2206 @defun getter-with-setter
2207 The same as the Guile core @code{make-procedure-with-setter}
2208 (@pxref{Procedures with Setters}).
2213 @subsection SRFI-18 - Multithreading support
2216 This is an implementation of the SRFI-18 threading and synchronization
2217 library. The functions and variables described here are provided by
2220 (use-modules (srfi srfi-18))
2223 As a general rule, the data types and functions in this SRFI-18
2224 implementation are compatible with the types and functions in Guile's
2225 core threading code. For example, mutexes created with the SRFI-18
2226 @code{make-mutex} function can be passed to the built-in Guile
2227 function @code{lock-mutex} (@pxref{Mutexes and Condition Variables}),
2228 and mutexes created with the built-in Guile function @code{make-mutex}
2229 can be passed to the SRFI-18 function @code{mutex-lock!}. Cases in
2230 which this does not hold true are noted in the following sections.
2233 * SRFI-18 Threads:: Executing code
2234 * SRFI-18 Mutexes:: Mutual exclusion devices
2235 * SRFI-18 Condition variables:: Synchronizing of groups of threads
2236 * SRFI-18 Time:: Representation of times and durations
2237 * SRFI-18 Exceptions:: Signalling and handling errors
2240 @node SRFI-18 Threads
2241 @subsubsection SRFI-18 Threads
2243 Threads created by SRFI-18 differ in two ways from threads created by
2244 Guile's built-in thread functions. First, a thread created by SRFI-18
2245 @code{make-thread} begins in a blocked state and will not start
2246 execution until @code{thread-start!} is called on it. Second, SRFI-18
2247 threads are constructed with a top-level exception handler that
2248 captures any exceptions that are thrown on thread exit. In all other
2249 regards, SRFI-18 threads are identical to normal Guile threads.
2251 @defun current-thread
2252 Returns the thread that called this function. This is the same
2253 procedure as the same-named built-in procedure @code{current-thread}
2258 Returns @code{#t} if @var{obj} is a thread, @code{#f} otherwise. This
2259 is the same procedure as the same-named built-in procedure
2260 @code{thread?} (@pxref{Threads}).
2263 @defun make-thread thunk [name]
2264 Call @code{thunk} in a new thread and with a new dynamic state,
2265 returning the new thread and optionally assigning it the object name
2266 @var{name}, which may be any Scheme object.
2268 Note that the name @code{make-thread} conflicts with the
2269 @code{(ice-9 threads)} function @code{make-thread}. Applications
2270 wanting to use both of these functions will need to refer to them by
2274 @defun thread-name thread
2275 Returns the name assigned to @var{thread} at the time of its creation,
2276 or @code{#f} if it was not given a name.
2279 @defun thread-specific thread
2280 @defunx thread-specific-set! thread obj
2281 Get or set the ``object-specific'' property of @var{thread}. In
2282 Guile's implementation of SRFI-18, this value is stored as an object
2283 property, and will be @code{#f} if not set.
2286 @defun thread-start! thread
2287 Unblocks @var{thread} and allows it to begin execution if it has not
2291 @defun thread-yield!
2292 If one or more threads are waiting to execute, calling
2293 @code{thread-yield!} forces an immediate context switch to one of them.
2294 Otherwise, @code{thread-yield!} has no effect. @code{thread-yield!}
2295 behaves identically to the Guile built-in function @code{yield}.
2298 @defun thread-sleep! timeout
2299 The current thread waits until the point specified by the time object
2300 @var{timeout} is reached (@pxref{SRFI-18 Time}). This blocks the
2301 thread only if @var{timeout} represents a point in the future. it is
2302 an error for @var{timeout} to be @code{#f}.
2305 @defun thread-terminate! thread
2306 Causes an abnormal termination of @var{thread}. If @var{thread} is
2307 not already terminated, all mutexes owned by @var{thread} become
2308 unlocked/abandoned. If @var{thread} is the current thread,
2309 @code{thread-terminate!} does not return. Otherwise
2310 @code{thread-terminate!} returns an unspecified value; the termination
2311 of @var{thread} will occur before @code{thread-terminate!} returns.
2312 Subsequent attempts to join on @var{thread} will cause a ``terminated
2313 thread exception'' to be raised.
2315 @code{thread-terminate!} is compatible with the thread cancellation
2316 procedures in the core threads API (@pxref{Threads}) in that if a
2317 cleanup handler has been installed for the target thread, it will be
2318 called before the thread exits and its return value (or exception, if
2319 any) will be stored for later retrieval via a call to
2320 @code{thread-join!}.
2323 @defun thread-join! thread [timeout [timeout-val]]
2324 Wait for @var{thread} to terminate and return its exit value. When a
2325 time value @var{timeout} is given, it specifies a point in time where
2326 the waiting should be aborted. When the waiting is aborted,
2327 @var{timeout-val} is returned if it is specified; otherwise, a
2328 @code{join-timeout-exception} exception is raised
2329 (@pxref{SRFI-18 Exceptions}). Exceptions may also be raised if the
2330 thread was terminated by a call to @code{thread-terminate!}
2331 (@code{terminated-thread-exception} will be raised) or if the thread
2332 exited by raising an exception that was handled by the top-level
2333 exception handler (@code{uncaught-exception} will be raised; the
2334 original exception can be retrieved using
2335 @code{uncaught-exception-reason}).
2339 @node SRFI-18 Mutexes
2340 @subsubsection SRFI-18 Mutexes
2342 The behavior of Guile's built-in mutexes is parameterized via a set of
2343 flags passed to the @code{make-mutex} procedure in the core
2344 (@pxref{Mutexes and Condition Variables}). To satisfy the requirements
2345 for mutexes specified by SRFI-18, the @code{make-mutex} procedure
2346 described below sets the following flags:
2349 @code{recursive}: the mutex can be locked recursively
2351 @code{unchecked-unlock}: attempts to unlock a mutex that is already
2352 unlocked will not raise an exception
2354 @code{allow-external-unlock}: the mutex can be unlocked by any thread,
2355 not just the thread that locked it originally
2358 @defun make-mutex [name]
2359 Returns a new mutex, optionally assigning it the object name
2360 @var{name}, which may be any Scheme object. The returned mutex will be
2361 created with the configuration described above. Note that the name
2362 @code{make-mutex} conflicts with Guile core function @code{make-mutex}.
2363 Applications wanting to use both of these functions will need to refer
2364 to them by different names.
2367 @defun mutex-name mutex
2368 Returns the name assigned to @var{mutex} at the time of its creation,
2369 or @code{#f} if it was not given a name.
2372 @defun mutex-specific mutex
2373 @defunx mutex-specific-set! mutex obj
2374 Get or set the ``object-specific'' property of @var{mutex}. In Guile's
2375 implementation of SRFI-18, this value is stored as an object property,
2376 and will be @code{#f} if not set.
2379 @defun mutex-state mutex
2380 Returns information about the state of @var{mutex}. Possible values
2384 thread @code{T}: the mutex is in the locked/owned state and thread T
2385 is the owner of the mutex
2387 symbol @code{not-owned}: the mutex is in the locked/not-owned state
2389 symbol @code{abandoned}: the mutex is in the unlocked/abandoned state
2391 symbol @code{not-abandoned}: the mutex is in the
2392 unlocked/not-abandoned state
2396 @defun mutex-lock! mutex [timeout [thread]]
2397 Lock @var{mutex}, optionally specifying a time object @var{timeout}
2398 after which to abort the lock attempt and a thread @var{thread} giving
2399 a new owner for @var{mutex} different than the current thread. This
2400 procedure has the same behavior as the @code{lock-mutex} procedure in
2404 @defun mutex-unlock! mutex [condition-variable [timeout]]
2405 Unlock @var{mutex}, optionally specifying a condition variable
2406 @var{condition-variable} on which to wait, either indefinitely or,
2407 optionally, until the time object @var{timeout} has passed, to be
2408 signalled. This procedure has the same behavior as the
2409 @code{unlock-mutex} procedure in the core library.
2413 @node SRFI-18 Condition variables
2414 @subsubsection SRFI-18 Condition variables
2416 SRFI-18 does not specify a ``wait'' function for condition variables.
2417 Waiting on a condition variable can be simulated using the SRFI-18
2418 @code{mutex-unlock!} function described in the previous section, or
2419 Guile's built-in @code{wait-condition-variable} procedure can be used.
2421 @defun condition-variable? obj
2422 Returns @code{#t} if @var{obj} is a condition variable, @code{#f}
2423 otherwise. This is the same procedure as the same-named built-in
2425 (@pxref{Mutexes and Condition Variables, @code{condition-variable?}}).
2428 @defun make-condition-variable [name]
2429 Returns a new condition variable, optionally assigning it the object
2430 name @var{name}, which may be any Scheme object. This procedure
2431 replaces a procedure of the same name in the core library.
2434 @defun condition-variable-name condition-variable
2435 Returns the name assigned to @var{condition-variable} at the time of its
2436 creation, or @code{#f} if it was not given a name.
2439 @defun condition-variable-specific condition-variable
2440 @defunx condition-variable-specific-set! condition-variable obj
2441 Get or set the ``object-specific'' property of
2442 @var{condition-variable}. In Guile's implementation of SRFI-18, this
2443 value is stored as an object property, and will be @code{#f} if not
2447 @defun condition-variable-signal! condition-variable
2448 @defunx condition-variable-broadcast! condition-variable
2449 Wake up one thread that is waiting for @var{condition-variable}, in
2450 the case of @code{condition-variable-signal!}, or all threads waiting
2451 for it, in the case of @code{condition-variable-broadcast!}. The
2452 behavior of these procedures is equivalent to that of the procedures
2453 @code{signal-condition-variable} and
2454 @code{broadcast-condition-variable} in the core library.
2459 @subsubsection SRFI-18 Time
2461 The SRFI-18 time functions manipulate time in two formats: a
2462 ``time object'' type that represents an absolute point in time in some
2463 implementation-specific way; and the number of seconds since some
2464 unspecified ``epoch''. In Guile's implementation, the epoch is the
2465 Unix epoch, 00:00:00 UTC, January 1, 1970.
2468 Return the current time as a time object. This procedure replaces
2469 the procedure of the same name in the core library, which returns the
2470 current time in seconds since the epoch.
2474 Returns @code{#t} if @var{obj} is a time object, @code{#f} otherwise.
2477 @defun time->seconds time
2478 @defunx seconds->time seconds
2479 Convert between time objects and numerical values representing the
2480 number of seconds since the epoch. When converting from a time object
2481 to seconds, the return value is the number of seconds between
2482 @var{time} and the epoch. When converting from seconds to a time
2483 object, the return value is a time object that represents a time
2484 @var{seconds} seconds after the epoch.
2488 @node SRFI-18 Exceptions
2489 @subsubsection SRFI-18 Exceptions
2491 SRFI-18 exceptions are identical to the exceptions provided by
2492 Guile's implementation of SRFI-34. The behavior of exception
2493 handlers invoked to handle exceptions thrown from SRFI-18 functions,
2494 however, differs from the conventional behavior of SRFI-34 in that
2495 the continuation of the handler is the same as that of the call to
2496 the function. Handlers are called in a tail-recursive manner; the
2497 exceptions do not ``bubble up''.
2499 @defun current-exception-handler
2500 Returns the current exception handler.
2503 @defun with-exception-handler handler thunk
2504 Installs @var{handler} as the current exception handler and calls the
2505 procedure @var{thunk} with no arguments, returning its value as the
2506 value of the exception. @var{handler} must be a procedure that accepts
2507 a single argument. The current exception handler at the time this
2508 procedure is called will be restored after the call returns.
2512 Raise @var{obj} as an exception. This is the same procedure as the
2513 same-named procedure defined in SRFI 34.
2516 @defun join-timeout-exception? obj
2517 Returns @code{#t} if @var{obj} is an exception raised as the result of
2518 performing a timed join on a thread that does not exit within the
2519 specified timeout, @code{#f} otherwise.
2522 @defun abandoned-mutex-exception? obj
2523 Returns @code{#t} if @var{obj} is an exception raised as the result of
2524 attempting to lock a mutex that has been abandoned by its owner thread,
2525 @code{#f} otherwise.
2528 @defun terminated-thread-exception? obj
2529 Returns @code{#t} if @var{obj} is an exception raised as the result of
2530 joining on a thread that exited as the result of a call to
2531 @code{thread-terminate!}.
2534 @defun uncaught-exception? obj
2535 @defunx uncaught-exception-reason exc
2536 @code{uncaught-exception?} returns @code{#t} if @var{obj} is an
2537 exception thrown as the result of joining a thread that exited by
2538 raising an exception that was handled by the top-level exception
2539 handler installed by @code{make-thread}. When this occurs, the
2540 original exception is preserved as part of the exception thrown by
2541 @code{thread-join!} and can be accessed by calling
2542 @code{uncaught-exception-reason} on that exception. Note that
2543 because this exception-preservation mechanism is a side-effect of
2544 @code{make-thread}, joining on threads that exited as described above
2545 but were created by other means will not raise this
2546 @code{uncaught-exception} error.
2551 @subsection SRFI-19 - Time/Date Library
2556 This is an implementation of the SRFI-19 time/date library. The
2557 functions and variables described here are provided by
2560 (use-modules (srfi srfi-19))
2563 @strong{Caution}: The current code in this module incorrectly extends
2564 the Gregorian calendar leap year rule back prior to the introduction
2565 of those reforms in 1582 (or the appropriate year in various
2566 countries). The Julian calendar was used prior to 1582, and there
2567 were 10 days skipped for the reform, but the code doesn't implement
2570 This will be fixed some time. Until then calculations for 1583
2571 onwards are correct, but prior to that any day/month/year and day of
2572 the week calculations are wrong.
2575 * SRFI-19 Introduction::
2578 * SRFI-19 Time/Date conversions::
2579 * SRFI-19 Date to string::
2580 * SRFI-19 String to date::
2583 @node SRFI-19 Introduction
2584 @subsubsection SRFI-19 Introduction
2586 @cindex universal time
2590 This module implements time and date representations and calculations,
2591 in various time systems, including universal time (UTC) and atomic
2594 For those not familiar with these time systems, TAI is based on a
2595 fixed length second derived from oscillations of certain atoms. UTC
2596 differs from TAI by an integral number of seconds, which is increased
2597 or decreased at announced times to keep UTC aligned to a mean solar
2598 day (the orbit and rotation of the earth are not quite constant).
2601 So far, only increases in the TAI
2608 UTC difference have been needed. Such an increase is a ``leap
2609 second'', an extra second of TAI introduced at the end of a UTC day.
2610 When working entirely within UTC this is never seen, every day simply
2611 has 86400 seconds. But when converting from TAI to a UTC date, an
2612 extra 23:59:60 is present, where normally a day would end at 23:59:59.
2613 Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI
2616 @cindex system clock
2617 In the current implementation, the system clock is assumed to be UTC,
2618 and a table of leap seconds in the code converts to TAI. See comments
2619 in @file{srfi-19.scm} for how to update this table.
2622 @cindex modified julian day
2623 Also, for those not familiar with the terminology, a @dfn{Julian Day}
2624 is a real number which is a count of days and fraction of a day, in
2625 UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
2626 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from
2627 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time
2628 is julian day 2400000.5.
2630 @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
2631 @c noon, UTC), but this is incorrect. It looks like it might have
2632 @c arisen from the code incorrectly treating years a multiple of 100
2633 @c but not 400 prior to 1582 as non-leap years, where instead the Julian
2634 @c calendar should be used so all multiples of 4 before 1582 are leap
2639 @subsubsection SRFI-19 Time
2642 A @dfn{time} object has type, seconds and nanoseconds fields
2643 representing a point in time starting from some epoch. This is an
2644 arbitrary point in time, not just a time of day. Although times are
2645 represented in nanoseconds, the actual resolution may be lower.
2647 The following variables hold the possible time types. For instance
2648 @code{(current-time time-process)} would give the current CPU process
2652 Universal Coordinated Time (UTC).
2657 International Atomic Time (TAI).
2661 @defvar time-monotonic
2662 Monotonic time, meaning a monotonically increasing time starting from
2663 an unspecified epoch.
2665 Note that in the current implementation @code{time-monotonic} is the
2666 same as @code{time-tai}, and unfortunately is therefore affected by
2667 adjustments to the system clock. Perhaps this will change in the
2671 @defvar time-duration
2672 A duration, meaning simply a difference between two times.
2675 @defvar time-process
2676 CPU time spent in the current process, starting from when the process
2678 @cindex process time
2682 CPU time spent in the current thread. Not currently implemented.
2688 Return @code{#t} if @var{obj} is a time object, or @code{#f} if not.
2691 @defun make-time type nanoseconds seconds
2692 Create a time object with the given @var{type}, @var{seconds} and
2696 @defun time-type time
2697 @defunx time-nanosecond time
2698 @defunx time-second time
2699 @defunx set-time-type! time type
2700 @defunx set-time-nanosecond! time nsec
2701 @defunx set-time-second! time sec
2702 Get or set the type, seconds or nanoseconds fields of a time object.
2704 @code{set-time-type!} merely changes the field, it doesn't convert the
2705 time value. For conversions, see @ref{SRFI-19 Time/Date conversions}.
2708 @defun copy-time time
2709 Return a new time object, which is a copy of the given @var{time}.
2712 @defun current-time [type]
2713 Return the current time of the given @var{type}. The default
2714 @var{type} is @code{time-utc}.
2716 Note that the name @code{current-time} conflicts with the Guile core
2717 @code{current-time} function (@pxref{Time}) as well as the SRFI-18
2718 @code{current-time} function (@pxref{SRFI-18 Time}). Applications
2719 wanting to use more than one of these functions will need to refer to
2720 them by different names.
2723 @defun time-resolution [type]
2724 Return the resolution, in nanoseconds, of the given time @var{type}.
2725 The default @var{type} is @code{time-utc}.
2728 @defun time<=? t1 t2
2729 @defunx time<? t1 t2
2730 @defunx time=? t1 t2
2731 @defunx time>=? t1 t2
2732 @defunx time>? t1 t2
2733 Return @code{#t} or @code{#f} according to the respective relation
2734 between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2}
2735 must be the same time type.
2738 @defun time-difference t1 t2
2739 @defunx time-difference! t1 t2
2740 Return a time object of type @code{time-duration} representing the
2741 period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be
2744 @code{time-difference} returns a new time object,
2745 @code{time-difference!} may modify @var{t1} to form its return.
2748 @defun add-duration time duration
2749 @defunx add-duration! time duration
2750 @defunx subtract-duration time duration
2751 @defunx subtract-duration! time duration
2752 Return a time object which is @var{time} with the given @var{duration}
2753 added or subtracted. @var{duration} must be a time object of type
2754 @code{time-duration}.
2756 @code{add-duration} and @code{subtract-duration} return a new time
2757 object. @code{add-duration!} and @code{subtract-duration!} may modify
2758 the given @var{time} to form their return.
2763 @subsubsection SRFI-19 Date
2766 A @dfn{date} object represents a date in the Gregorian calendar and a
2767 time of day on that date in some timezone.
2769 The fields are year, month, day, hour, minute, second, nanoseconds and
2770 timezone. A date object is immutable, its fields can be read but they
2771 cannot be modified once the object is created.
2774 Return @code{#t} if @var{obj} is a date object, or @code{#f} if not.
2777 @defun make-date nsecs seconds minutes hours date month year zone-offset
2778 Create a new date object.
2780 @c FIXME: What can we say about the ranges of the values. The
2781 @c current code looks it doesn't normalize, but expects then in their
2782 @c usual range already.
2786 @defun date-nanosecond date
2787 Nanoseconds, 0 to 999999999.
2790 @defun date-second date
2791 Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working
2792 entirely within UTC, it's only when converting to or from TAI.
2795 @defun date-minute date
2799 @defun date-hour date
2803 @defun date-day date
2804 Day of the month, 1 to 31 (or less, according to the month).
2807 @defun date-month date
2811 @defun date-year date
2812 Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46
2813 B.C. There is no year 0, year @math{-1} is followed by year 1.
2816 @defun date-zone-offset date
2817 Time zone, an integer number of seconds east of Greenwich.
2820 @defun date-year-day date
2821 Day of the year, starting from 1 for 1st January.
2824 @defun date-week-day date
2825 Day of the week, starting from 0 for Sunday.
2828 @defun date-week-number date dstartw
2829 Week of the year, ignoring a first partial week. @var{dstartw} is the
2830 day of the week which is taken to start a week, 0 for Sunday, 1 for
2833 @c FIXME: The spec doesn't say whether numbering starts at 0 or 1.
2834 @c The code looks like it's 0, if that's the correct intention.
2838 @c The SRFI text doesn't actually give the default for tz-offset, but
2839 @c the reference implementation has the local timezone and the
2840 @c conversions functions all specify that, so it should be ok to
2841 @c document it here.
2843 @defun current-date [tz-offset]
2844 Return a date object representing the current date/time, in UTC offset
2845 by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and
2846 defaults to the local timezone.
2849 @defun current-julian-day
2851 Return the current Julian Day.
2854 @defun current-modified-julian-day
2855 @cindex modified julian day
2856 Return the current Modified Julian Day.
2860 @node SRFI-19 Time/Date conversions
2861 @subsubsection SRFI-19 Time/Date conversions
2862 @cindex time conversion
2863 @cindex date conversion
2865 @defun date->julian-day date
2866 @defunx date->modified-julian-day date
2867 @defunx date->time-monotonic date
2868 @defunx date->time-tai date
2869 @defunx date->time-utc date
2871 @defun julian-day->date jdn [tz-offset]
2872 @defunx julian-day->time-monotonic jdn
2873 @defunx julian-day->time-tai jdn
2874 @defunx julian-day->time-utc jdn
2876 @defun modified-julian-day->date jdn [tz-offset]
2877 @defunx modified-julian-day->time-monotonic jdn
2878 @defunx modified-julian-day->time-tai jdn
2879 @defunx modified-julian-day->time-utc jdn
2881 @defun time-monotonic->date time [tz-offset]
2882 @defunx time-monotonic->time-tai time
2883 @defunx time-monotonic->time-tai! time
2884 @defunx time-monotonic->time-utc time
2885 @defunx time-monotonic->time-utc! time
2887 @defun time-tai->date time [tz-offset]
2888 @defunx time-tai->julian-day time
2889 @defunx time-tai->modified-julian-day time
2890 @defunx time-tai->time-monotonic time
2891 @defunx time-tai->time-monotonic! time
2892 @defunx time-tai->time-utc time
2893 @defunx time-tai->time-utc! time
2895 @defun time-utc->date time [tz-offset]
2896 @defunx time-utc->julian-day time
2897 @defunx time-utc->modified-julian-day time
2898 @defunx time-utc->time-monotonic time
2899 @defunx time-utc->time-monotonic! time
2900 @defunx time-utc->time-tai time
2901 @defunx time-utc->time-tai! time
2903 Convert between dates, times and days of the respective types. For
2904 instance @code{time-tai->time-utc} accepts a @var{time} object of type
2905 @code{time-tai} and returns an object of type @code{time-utc}.
2907 The @code{!} variants may modify their @var{time} argument to form
2908 their return. The plain functions create a new object.
2910 For conversions to dates, @var{tz-offset} is seconds east of
2911 Greenwich. The default is the local timezone, at the given time, as
2912 provided by the system, using @code{localtime} (@pxref{Time}).
2914 On 32-bit systems, @code{localtime} is limited to a 32-bit
2915 @code{time_t}, so a default @var{tz-offset} is only available for
2916 times between Dec 1901 and Jan 2038. For prior dates an application
2917 might like to use the value in 1902, though some locations have zone
2918 changes prior to that. For future dates an application might like to
2919 assume today's rules extend indefinitely. But for correct daylight
2920 savings transitions it will be necessary to take an offset for the
2921 same day and time but a year in range and which has the same starting
2922 weekday and same leap/non-leap (to support rules like last Sunday in
2926 @node SRFI-19 Date to string
2927 @subsubsection SRFI-19 Date to string
2928 @cindex date to string
2929 @cindex string, from date
2931 @defun date->string date [format]
2932 Convert a date to a string under the control of a format.
2933 @var{format} should be a string containing @samp{~} escapes, which
2934 will be expanded as per the following conversion table. The default
2935 @var{format} is @samp{~c}, a locale-dependent date and time.
2937 Many of these conversion characters are the same as POSIX
2938 @code{strftime} (@pxref{Time}), but there are some extras and some
2941 @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM}
2942 @item @nicode{~~} @tab literal ~
2943 @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun}
2944 @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday}
2945 @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan}
2946 @item @nicode{~B} @tab locale full month, eg.@: @samp{January}
2947 @item @nicode{~c} @tab locale date and time, eg.@: @*
2948 @samp{Fri Jul 14 20:28:42-0400 2000}
2949 @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31}
2951 @c Spec says d/m/y, reference implementation says m/d/y.
2952 @c Apparently the reference code was the intention, but would like to
2953 @c see an errata published for the spec before contradicting it here.
2955 @c @item @nicode{~D} @tab date @nicode{~d/~m/~y}
2957 @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31}
2958 @item @nicode{~f} @tab seconds and fractional seconds,
2959 with locale decimal point, eg.@: @samp{5.2}
2960 @item @nicode{~h} @tab same as @nicode{~b}
2961 @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23}
2962 @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12}
2963 @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366}
2964 @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23}
2965 @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12}
2966 @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12}
2967 @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59}
2968 @item @nicode{~n} @tab newline
2969 @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999}
2970 @item @nicode{~p} @tab locale AM or PM
2971 @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p}
2972 @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC
2973 @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @*
2974 (usual limit is 59, 60 is a leap second)
2975 @item @nicode{~t} @tab horizontal tab character
2976 @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S}
2977 @item @nicode{~U} @tab week of year, Sunday first day of week,
2978 @samp{00} to @samp{52}
2979 @item @nicode{~V} @tab week of year, Monday first day of week,
2980 @samp{01} to @samp{53}
2981 @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6}
2982 @item @nicode{~W} @tab week of year, Monday first day of week,
2983 @samp{00} to @samp{52}
2985 @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale
2986 @c date. The reference code has ~x as the locale date and ~X as a
2987 @c locale time. The rule is apparently that the code should be
2988 @c believed, but would like to see an errata for the spec before
2989 @c contradicting it here.
2991 @c @item @nicode{~x} @tab week of year, Monday as first day of week,
2992 @c @samp{00} to @samp{53}
2993 @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00}
2995 @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99}
2996 @item @nicode{~Y} @tab year, full, eg.@: @samp{2003}
2997 @item @nicode{~z} @tab time zone, RFC-822 style
2998 @item @nicode{~Z} @tab time zone symbol (not currently implemented)
2999 @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d}
3000 @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~k:~M:~S~z}
3001 @item @nicode{~3} @tab ISO-8601 time, @samp{~k:~M:~S}
3002 @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~k:~M:~S~z}
3003 @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~k:~M:~S}
3007 Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently
3008 described here, since the specification and reference implementation
3011 Conversion is locale-dependent on systems that support it
3012 (@pxref{Accessing Locale Information}). @xref{Locales,
3013 @code{setlocale}}, for information on how to change the current
3017 @node SRFI-19 String to date
3018 @subsubsection SRFI-19 String to date
3019 @cindex string to date
3020 @cindex date, from string
3022 @c FIXME: Can we say what happens when an incomplete date is
3023 @c converted? I.e. fields left as 0, or what? The spec seems to be
3026 @defun string->date input template
3027 Convert an @var{input} string to a date under the control of a
3028 @var{template} string. Return a newly created date object.
3030 Literal characters in @var{template} must match characters in
3031 @var{input} and @samp{~} escapes must match the input forms described
3032 in the table below. ``Skip to'' means characters up to one of the
3033 given type are ignored, or ``no skip'' for no skipping. ``Read'' is
3034 what's then read, and ``Set'' is the field affected in the date
3037 For example @samp{~Y} skips input characters until a digit is reached,
3038 at which point it expects a year and stores that to the year field of
3041 @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}}
3053 @tab @nicode{char-alphabetic?}
3054 @tab locale abbreviated weekday name
3058 @tab @nicode{char-alphabetic?}
3059 @tab locale full weekday name
3062 @c Note that the SRFI spec says that ~b and ~B don't set anything,
3063 @c but that looks like a mistake. The reference implementation sets
3064 @c the month field, which seems sensible and is what we describe
3068 @tab @nicode{char-alphabetic?}
3069 @tab locale abbreviated month name
3070 @tab @nicode{date-month}
3073 @tab @nicode{char-alphabetic?}
3074 @tab locale full month name
3075 @tab @nicode{date-month}
3078 @tab @nicode{char-numeric?}
3080 @tab @nicode{date-day}
3084 @tab day of month, blank padded
3085 @tab @nicode{date-day}
3088 @tab same as @samp{~b}
3091 @tab @nicode{char-numeric?}
3093 @tab @nicode{date-hour}
3097 @tab hour, blank padded
3098 @tab @nicode{date-hour}
3101 @tab @nicode{char-numeric?}
3103 @tab @nicode{date-month}
3106 @tab @nicode{char-numeric?}
3108 @tab @nicode{date-minute}
3111 @tab @nicode{char-numeric?}
3113 @tab @nicode{date-second}
3118 @tab @nicode{date-year} within 50 years
3121 @tab @nicode{char-numeric?}
3123 @tab @nicode{date-year}
3128 @tab date-zone-offset
3131 Notice that the weekday matching forms don't affect the date object
3132 returned, instead the weekday will be derived from the day, month and
3135 Conversion is locale-dependent on systems that support it
3136 (@pxref{Accessing Locale Information}). @xref{Locales,
3137 @code{setlocale}}, for information on how to change the current
3142 @subsection SRFI-23 - Error Reporting
3145 The SRFI-23 @code{error} procedure is always available.
3148 @subsection SRFI-26 - specializing parameters
3150 @cindex parameter specialize
3151 @cindex argument specialize
3152 @cindex specialize parameter
3154 This SRFI provides a syntax for conveniently specializing selected
3155 parameters of a function. It can be used with,
3158 (use-modules (srfi srfi-26))
3161 @deffn {library syntax} cut slot1 slot2 @dots{}
3162 @deffnx {library syntax} cute slot1 slot2 @dots{}
3163 Return a new procedure which will make a call (@var{slot1} @var{slot2}
3164 @dots{}) but with selected parameters specialized to given expressions.
3166 An example will illustrate the idea. The following is a
3167 specialization of @code{write}, sending output to
3168 @code{my-output-port},
3171 (cut write <> my-output-port)
3173 (lambda (obj) (write obj my-output-port))
3176 The special symbol @code{<>} indicates a slot to be filled by an
3177 argument to the new procedure. @code{my-output-port} on the other
3178 hand is an expression to be evaluated and passed, ie.@: it specializes
3179 the behaviour of @code{write}.
3183 A slot to be filled by an argument from the created procedure.
3184 Arguments are assigned to @code{<>} slots in the order they appear in
3185 the @code{cut} form, there's no way to re-arrange arguments.
3187 The first argument to @code{cut} is usually a procedure (or expression
3188 giving a procedure), but @code{<>} is allowed there too. For example,
3193 (lambda (proc) (proc 1 2 3))
3197 A slot to be filled by all remaining arguments from the new procedure.
3198 This can only occur at the end of a @code{cut} form.
3200 For example, a procedure taking a variable number of arguments like
3201 @code{max} but in addition enforcing a lower bound,
3204 (define my-lower-bound 123)
3206 (cut max my-lower-bound <...>)
3208 (lambda arglist (apply max my-lower-bound arglist))
3212 For @code{cut} the specializing expressions are evaluated each time
3213 the new procedure is called. For @code{cute} they're evaluated just
3214 once, when the new procedure is created. The name @code{cute} stands
3215 for ``@code{cut} with evaluated arguments''. In all cases the
3216 evaluations take place in an unspecified order.
3218 The following illustrates the difference between @code{cut} and
3222 (cut format <> "the time is ~s" (current-time))
3224 (lambda (port) (format port "the time is ~s" (current-time)))
3226 (cute format <> "the time is ~s" (current-time))
3228 (let ((val (current-time)))
3229 (lambda (port) (format port "the time is ~s" val))
3232 (There's no provision for a mixture of @code{cut} and @code{cute}
3233 where some expressions would be evaluated every time but others
3234 evaluated only once.)
3236 @code{cut} is really just a shorthand for the sort of @code{lambda}
3237 forms shown in the above examples. But notice @code{cut} avoids the
3238 need to name unspecialized parameters, and is more compact. Use in
3239 functional programming style or just with @code{map}, @code{for-each}
3240 or similar is typical.
3243 (map (cut * 2 <>) '(1 2 3 4))
3245 (for-each (cut write <> my-port) my-list)
3250 @subsection SRFI-27 - Sources of Random Bits
3253 This subsection is based on the
3254 @uref{http://srfi.schemers.org/srfi-27/srfi-27.html, specification of
3255 SRFI-27} written by Sebastian Egner.
3257 @c The copyright notice and license text of the SRFI-27 specification is
3258 @c reproduced below:
3260 @c Copyright (C) Sebastian Egner (2002). All Rights Reserved.
3262 @c Permission is hereby granted, free of charge, to any person obtaining a
3263 @c copy of this software and associated documentation files (the
3264 @c "Software"), to deal in the Software without restriction, including
3265 @c without limitation the rights to use, copy, modify, merge, publish,
3266 @c distribute, sublicense, and/or sell copies of the Software, and to
3267 @c permit persons to whom the Software is furnished to do so, subject to
3268 @c the following conditions:
3270 @c The above copyright notice and this permission notice shall be included
3271 @c in all copies or substantial portions of the Software.
3273 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3274 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3275 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3276 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3277 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3278 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3279 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3281 This SRFI provides access to a (pseudo) random number generator; for
3282 Guile's built-in random number facilities, which SRFI-27 is implemented
3283 upon, @xref{Random}. With SRFI-27, random numbers are obtained from a
3284 @emph{random source}, which encapsulates a random number generation
3285 algorithm and its state.
3288 * SRFI-27 Default Random Source:: Obtaining random numbers
3289 * SRFI-27 Random Sources:: Creating and manipulating random sources
3290 * SRFI-27 Random Number Generators:: Obtaining random number generators
3293 @node SRFI-27 Default Random Source
3294 @subsubsection The Default Random Source
3297 @defun random-integer n
3298 Return a random number between zero (inclusive) and @var{n} (exclusive),
3299 using the default random source. The numbers returned have a uniform
3304 Return a random number in (0,1), using the default random source. The
3305 numbers returned have a uniform distribution.
3308 @defun default-random-source
3309 A random source from which @code{random-integer} and @code{random-real}
3310 have been derived using @code{random-source-make-integers} and
3311 @code{random-source-make-reals} (@pxref{SRFI-27 Random Number Generators}
3312 for those procedures). Note that an assignment to
3313 @code{default-random-source} does not change @code{random-integer} or
3314 @code{random-real}; it is also strongly recommended not to assign a new
3318 @node SRFI-27 Random Sources
3319 @subsubsection Random Sources
3322 @defun make-random-source
3323 Create a new random source. The stream of random numbers obtained from
3324 each random source created by this procedure will be identical, unless
3325 its state is changed by one of the procedures below.
3328 @defun random-source? object
3329 Tests whether @var{object} is a random source. Random sources are a
3333 @defun random-source-randomize! source
3334 Attempt to set the state of the random source to a truly random value.
3335 The current implementation uses a seed based on the current system time.
3338 @defun random-source-pseudo-randomize! source i j
3339 Changes the state of the random source s into the initial state of the
3340 (@var{i}, @var{j})-th independent random source, where @var{i} and
3341 @var{j} are non-negative integers. This procedure provides a mechanism
3342 to obtain a large number of independent random sources (usually all
3343 derived from the same backbone generator), indexed by two integers. In
3344 contrast to @code{random-source-randomize!}, this procedure is entirely
3348 The state associated with a random state can be obtained an reinstated
3349 with the following procedures:
3351 @defun random-source-state-ref source
3352 @defunx random-source-state-set! source state
3353 Get and set the state of a random source. No assumptions should be made
3354 about the nature of the state object, besides it having an external
3355 representation (i.e.@: it can be passed to @code{write} and subsequently
3359 @node SRFI-27 Random Number Generators
3360 @subsubsection Obtaining random number generator procedures
3363 @defun random-source-make-integers source
3364 Obtains a procedure to generate random integers using the random source
3365 @var{source}. The returned procedure takes a single argument @var{n},
3366 which must be a positive integer, and returns the next uniformly
3367 distributed random integer from the interval @{0, ..., @var{n}-1@} by
3368 advancing the state of @var{source}.
3370 If an application obtains and uses several generators for the same
3371 random source @var{source}, a call to any of these generators advances
3372 the state of @var{source}. Hence, the generators do not produce the
3373 same sequence of random integers each but rather share a state. This
3374 also holds for all other types of generators derived from a fixed random
3377 While the SRFI text specifies that ``Implementations that support
3378 concurrency make sure that the state of a generator is properly
3379 advanced'', this is currently not the case in Guile's implementation of
3380 SRFI-27, as it would cause a severe performance penalty. So in
3381 multi-threaded programs, you either must perform locking on random
3382 sources shared between threads yourself, or use different random sources
3383 for multiple threads.
3386 @defun random-source-make-reals source
3387 @defunx random-source-make-reals source unit
3388 Obtains a procedure to generate random real numbers @math{0 < x < 1}
3389 using the random source @var{source}. The procedure rand is called
3392 The optional parameter @var{unit} determines the type of numbers being
3393 produced by the returned procedure and the quantization of the output.
3394 @var{unit} must be a number such that @math{0 < @var{unit} < 1}. The
3395 numbers created by the returned procedure are of the same numerical type
3396 as @var{unit} and the potential output values are spaced by at most
3397 @var{unit}. One can imagine rand to create numbers as @var{x} *
3398 @var{unit} where @var{x} is a random integer in @{1, ...,
3399 floor(1/unit)-1@}. Note, however, that this need not be the way the
3400 values are actually created and that the actual resolution of rand can
3401 be much higher than unit. In case @var{unit} is absent it defaults to a
3402 reasonably small value (related to the width of the mantissa of an
3403 efficient number format).
3407 @subsection SRFI-30 - Nested Multi-line Comments
3410 Starting from version 2.0, Guile's @code{read} supports SRFI-30/R6RS
3411 nested multi-line comments by default, @ref{Block Comments}.
3414 @subsection SRFI-31 - A special form `rec' for recursive evaluation
3416 @cindex recursive expression
3419 SRFI-31 defines a special form that can be used to create
3420 self-referential expressions more conveniently. The syntax is as
3425 <rec expression> --> (rec <variable> <expression>)
3426 <rec expression> --> (rec (<variable>+) <body>)
3430 The first syntax can be used to create self-referential expressions,
3434 guile> (define tmp (rec ones (cons 1 (delay ones))))
3437 The second syntax can be used to create anonymous recursive functions:
3440 guile> (define tmp (rec (display-n item n)
3442 (begin (display n) (display-n (- n 1))))))
3450 @subsection SRFI-34 - Exception handling for programs
3453 Guile provides an implementation of
3454 @uref{http://srfi.schemers.org/srfi-34/srfi-34.html, SRFI-34's exception
3455 handling mechanisms} as an alternative to its own built-in mechanisms
3456 (@pxref{Exceptions}). It can be made available as follows:
3459 (use-modules (srfi srfi-34))
3462 @c FIXME: Document it.
3466 @subsection SRFI-35 - Conditions
3472 @uref{http://srfi.schemers.org/srfi-35/srfi-35.html, SRFI-35} implements
3473 @dfn{conditions}, a data structure akin to records designed to convey
3474 information about exceptional conditions between parts of a program. It
3475 is normally used in conjunction with SRFI-34's @code{raise}:
3478 (raise (condition (&message
3479 (message "An error occurred"))))
3482 Users can define @dfn{condition types} containing arbitrary information.
3483 Condition types may inherit from one another. This allows the part of
3484 the program that handles (or ``catches'') conditions to get accurate
3485 information about the exceptional condition that arose.
3487 SRFI-35 conditions are made available using:
3490 (use-modules (srfi srfi-35))
3493 The procedures available to manipulate condition types are the
3496 @deffn {Scheme Procedure} make-condition-type id parent field-names
3497 Return a new condition type named @var{id}, inheriting from
3498 @var{parent}, and with the fields whose names are listed in
3499 @var{field-names}. @var{field-names} must be a list of symbols and must
3500 not contain names already used by @var{parent} or one of its supertypes.
3503 @deffn {Scheme Procedure} condition-type? obj
3504 Return true if @var{obj} is a condition type.
3507 Conditions can be created and accessed with the following procedures:
3509 @deffn {Scheme Procedure} make-condition type . field+value
3510 Return a new condition of type @var{type} with fields initialized as
3511 specified by @var{field+value}, a sequence of field names (symbols) and
3512 values as in the following example:
3515 (let ((&ct (make-condition-type 'foo &condition '(a b c))))
3516 (make-condition &ct 'a 1 'b 2 'c 3))
3519 Note that all fields of @var{type} and its supertypes must be specified.
3522 @deffn {Scheme Procedure} make-compound-condition condition1 condition2 @dots{}
3523 Return a new compound condition composed of @var{conditions}. The
3524 returned condition has the type of each condition of @var{conditions}
3525 (per @code{condition-has-type?}).
3528 @deffn {Scheme Procedure} condition-has-type? c type
3529 Return true if condition @var{c} has type @var{type}.
3532 @deffn {Scheme Procedure} condition-ref c field-name
3533 Return the value of the field named @var{field-name} from condition @var{c}.
3535 If @var{c} is a compound condition and several underlying condition
3536 types contain a field named @var{field-name}, then the value of the
3537 first such field is returned, using the order in which conditions were
3538 passed to @code{make-compound-condition}.
3541 @deffn {Scheme Procedure} extract-condition c type
3542 Return a condition of condition type @var{type} with the field values
3543 specified by @var{c}.
3545 If @var{c} is a compound condition, extract the field values from the
3546 subcondition belonging to @var{type} that appeared first in the call to
3547 @code{make-compound-condition} that created the condition.
3550 Convenience macros are also available to create condition types and
3553 @deffn {library syntax} define-condition-type type supertype predicate field-spec...
3554 Define a new condition type named @var{type} that inherits from
3555 @var{supertype}. In addition, bind @var{predicate} to a type predicate
3556 that returns true when passed a condition of type @var{type} or any of
3557 its subtypes. @var{field-spec} must have the form @code{(field
3558 accessor)} where @var{field} is the name of field of @var{type} and
3559 @var{accessor} is the name of a procedure to access field @var{field} in
3560 conditions of type @var{type}.
3562 The example below defines condition type @code{&foo}, inheriting from
3563 @code{&condition} with fields @code{a}, @code{b} and @code{c}:
3566 (define-condition-type &foo &condition
3574 @deffn {library syntax} condition type-field-binding1 type-field-binding2 @dots{}
3575 Return a new condition or compound condition, initialized according to
3576 @var{type-field-binding1} @var{type-field-binding2} @enddots{}. Each
3577 @var{type-field-binding} must have the form @code{(type
3578 field-specs...)}, where @var{type} is the name of a variable bound to a
3579 condition type; each @var{field-spec} must have the form
3580 @code{(field-name value)} where @var{field-name} is a symbol denoting
3581 the field being initialized to @var{value}. As for
3582 @code{make-condition}, all fields must be specified.
3584 The following example returns a simple condition:
3587 (condition (&message (message "An error occurred")))
3590 The one below returns a compound condition:
3593 (condition (&message (message "An error occurred"))
3598 Finally, SRFI-35 defines a several standard condition types.
3601 This condition type is the root of all condition types. It has no
3606 A condition type that carries a message describing the nature of the
3607 condition to humans.
3610 @deffn {Scheme Procedure} message-condition? c
3611 Return true if @var{c} is of type @code{&message} or one of its
3615 @deffn {Scheme Procedure} condition-message c
3616 Return the message associated with message condition @var{c}.
3620 This type describes conditions serious enough that they cannot safely be
3621 ignored. It has no fields.
3624 @deffn {Scheme Procedure} serious-condition? c
3625 Return true if @var{c} is of type @code{&serious} or one of its
3630 This condition describes errors, typically caused by something that has
3631 gone wrong in the interaction of the program with the external world or
3635 @deffn {Scheme Procedure} error? c
3636 Return true if @var{c} is of type @code{&error} or one of its subtypes.
3640 @subsection SRFI-37 - args-fold
3643 This is a processor for GNU @code{getopt_long}-style program
3644 arguments. It provides an alternative, less declarative interface
3645 than @code{getopt-long} in @code{(ice-9 getopt-long)}
3646 (@pxref{getopt-long,,The (ice-9 getopt-long) Module}). Unlike
3647 @code{getopt-long}, it supports repeated options and any number of
3648 short and long names per option. Access it with:
3651 (use-modules (srfi srfi-37))
3654 @acronym{SRFI}-37 principally provides an @code{option} type and the
3655 @code{args-fold} function. To use the library, create a set of
3656 options with @code{option} and use it as a specification for invoking
3659 Here is an example of a simple argument processor for the typical
3660 @samp{--version} and @samp{--help} options, which returns a backwards
3661 list of files given on the command line:
3664 (args-fold (cdr (program-arguments))
3665 (let ((display-and-exit-proc
3667 (lambda (opt name arg loads)
3668 (display msg) (quit)))))
3669 (list (option '(#\v "version") #f #f
3670 (display-and-exit-proc "Foo version 42.0\n"))
3671 (option '(#\h "help") #f #f
3672 (display-and-exit-proc
3673 "Usage: foo scheme-file ..."))))
3674 (lambda (opt name arg loads)
3675 (error "Unrecognized option `~A'" name))
3676 (lambda (op loads) (cons op loads))
3680 @deffn {Scheme Procedure} option names required-arg? optional-arg? processor
3681 Return an object that specifies a single kind of program option.
3683 @var{names} is a list of command-line option names, and should consist of
3684 characters for traditional @code{getopt} short options and strings for
3685 @code{getopt_long}-style long options.
3687 @var{required-arg?} and @var{optional-arg?} are mutually exclusive;
3688 one or both must be @code{#f}. If @var{required-arg?}, the option
3689 must be followed by an argument on the command line, such as
3690 @samp{--opt=value} for long options, or an error will be signalled.
3691 If @var{optional-arg?}, an argument will be taken if available.
3693 @var{processor} is a procedure that takes at least 3 arguments, called
3694 when @code{args-fold} encounters the option: the containing option
3695 object, the name used on the command line, and the argument given for
3696 the option (or @code{#f} if none). The rest of the arguments are
3697 @code{args-fold} ``seeds'', and the @var{processor} should return
3701 @deffn {Scheme Procedure} option-names opt
3702 @deffnx {Scheme Procedure} option-required-arg? opt
3703 @deffnx {Scheme Procedure} option-optional-arg? opt
3704 @deffnx {Scheme Procedure} option-processor opt
3705 Return the specified field of @var{opt}, an option object, as
3706 described above for @code{option}.
3709 @deffn {Scheme Procedure} args-fold args options unrecognized-option-proc operand-proc seed @dots{}
3710 Process @var{args}, a list of program arguments such as that returned by
3711 @code{(cdr (program-arguments))}, in order against @var{options}, a list
3712 of option objects as described above. All functions called take the
3713 ``seeds'', or the last multiple-values as multiple arguments, starting
3714 with @var{seed} @dots{}, and must return the new seeds. Return the
3717 Call @code{unrecognized-option-proc}, which is like an option object's
3718 processor, for any options not found in @var{options}.
3720 Call @code{operand-proc} with any items on the command line that are
3721 not named options. This includes arguments after @samp{--}. It is
3722 called with the argument in question, as well as the seeds.
3726 @subsection SRFI-38 - External Representation for Data With Shared Structure
3729 This subsection is based on
3730 @uref{http://srfi.schemers.org/srfi-38/srfi-38.html, the specification
3731 of SRFI-38} written by Ray Dillinger.
3733 @c Copyright (C) Ray Dillinger 2003. All Rights Reserved.
3735 @c Permission is hereby granted, free of charge, to any person obtaining a
3736 @c copy of this software and associated documentation files (the
3737 @c "Software"), to deal in the Software without restriction, including
3738 @c without limitation the rights to use, copy, modify, merge, publish,
3739 @c distribute, sublicense, and/or sell copies of the Software, and to
3740 @c permit persons to whom the Software is furnished to do so, subject to
3741 @c the following conditions:
3743 @c The above copyright notice and this permission notice shall be included
3744 @c in all copies or substantial portions of the Software.
3746 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3747 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3748 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3749 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3750 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3751 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3752 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3754 This SRFI creates an alternative external representation for data
3755 written and read using @code{write-with-shared-structure} and
3756 @code{read-with-shared-structure}. It is identical to the grammar for
3757 external representation for data written and read with @code{write} and
3758 @code{read} given in section 7 of R5RS, except that the single
3762 <datum> --> <simple datum> | <compound datum>
3765 is replaced by the following five productions:
3768 <datum> --> <defining datum> | <nondefining datum> | <defined datum>
3769 <defining datum> --> #<indexnum>=<nondefining datum>
3770 <defined datum> --> #<indexnum>#
3771 <nondefining datum> --> <simple datum> | <compound datum>
3772 <indexnum> --> <digit 10>+
3775 @deffn {Scheme procedure} write-with-shared-structure obj
3776 @deffnx {Scheme procedure} write-with-shared-structure obj port
3777 @deffnx {Scheme procedure} write-with-shared-structure obj port optarg
3779 Writes an external representation of @var{obj} to the given port.
3780 Strings that appear in the written representation are enclosed in
3781 doublequotes, and within those strings backslash and doublequote
3782 characters are escaped by backslashes. Character objects are written
3783 using the @code{#\} notation.
3785 Objects which denote locations rather than values (cons cells, vectors,
3786 and non-zero-length strings in R5RS scheme; also Guile's structs,
3787 bytevectors and ports and hash-tables), if they appear at more than one
3788 point in the data being written, are preceded by @samp{#@var{N}=} the
3789 first time they are written and replaced by @samp{#@var{N}#} all
3790 subsequent times they are written, where @var{N} is a natural number
3791 used to identify that particular object. If objects which denote
3792 locations occur only once in the structure, then
3793 @code{write-with-shared-structure} must produce the same external
3794 representation for those objects as @code{write}.
3796 @code{write-with-shared-structure} terminates in finite time and
3797 produces a finite representation when writing finite data.
3799 @code{write-with-shared-structure} returns an unspecified value. The
3800 @var{port} argument may be omitted, in which case it defaults to the
3801 value returned by @code{(current-output-port)}. The @var{optarg}
3802 argument may also be omitted. If present, its effects on the output and
3803 return value are unspecified but @code{write-with-shared-structure} must
3804 still write a representation that can be read by
3805 @code{read-with-shared-structure}. Some implementations may wish to use
3806 @var{optarg} to specify formatting conventions, numeric radixes, or
3807 return values. Guile's implementation ignores @var{optarg}.
3809 For example, the code
3812 (begin (define a (cons 'val1 'val2))
3814 (write-with-shared-structure a))
3817 should produce the output @code{#1=(val1 . #1#)}. This shows a cons
3818 cell whose @code{cdr} contains itself.
3822 @deffn {Scheme procedure} read-with-shared-structure
3823 @deffnx {Scheme procedure} read-with-shared-structure port
3825 @code{read-with-shared-structure} converts the external representations
3826 of Scheme objects produced by @code{write-with-shared-structure} into
3827 Scheme objects. That is, it is a parser for the nonterminal
3828 @samp{<datum>} in the augmented external representation grammar defined
3829 above. @code{read-with-shared-structure} returns the next object
3830 parsable from the given input port, updating @var{port} to point to the
3831 first character past the end of the external representation of the
3834 If an end-of-file is encountered in the input before any characters are
3835 found that can begin an object, then an end-of-file object is returned.
3836 The port remains open, and further attempts to read it (by
3837 @code{read-with-shared-structure} or @code{read} will also return an
3838 end-of-file object. If an end of file is encountered after the
3839 beginning of an object's external representation, but the external
3840 representation is incomplete and therefore not parsable, an error is
3843 The @var{port} argument may be omitted, in which case it defaults to the
3844 value returned by @code{(current-input-port)}. It is an error to read
3850 @subsection SRFI-39 - Parameters
3853 This SRFI adds support for dynamically-scoped parameters. SRFI 39 is
3854 implemented in the Guile core; there's no module needed to get SRFI-39
3855 itself. Parameters are documented in @ref{Parameters}.
3857 This module does export one extra function: @code{with-parameters*}.
3858 This is a Guile-specific addition to the SRFI, similar to the core
3859 @code{with-fluids*} (@pxref{Fluids and Dynamic States}).
3861 @defun with-parameters* param-list value-list thunk
3862 Establish a new dynamic scope, as per @code{parameterize} above,
3863 taking parameters from @var{param-list} and corresponding values from
3864 @var{value-list}. A call @code{(@var{thunk})} is made in the new
3865 scope and the result from that @var{thunk} is the return from
3866 @code{with-parameters*}.
3870 @subsection SRFI-42 - Eager Comprehensions
3873 See @uref{http://srfi.schemers.org/srfi-42/srfi-42.html, the
3874 specification of SRFI-42}.
3877 @subsection SRFI-45 - Primitives for Expressing Iterative Lazy Algorithms
3880 This subsection is based on @uref{http://srfi.schemers.org/srfi-45/srfi-45.html, the
3881 specification of SRFI-45} written by Andr@'e van Tonder.
3883 @c Copyright (C) André van Tonder (2003). All Rights Reserved.
3885 @c Permission is hereby granted, free of charge, to any person obtaining a
3886 @c copy of this software and associated documentation files (the
3887 @c "Software"), to deal in the Software without restriction, including
3888 @c without limitation the rights to use, copy, modify, merge, publish,
3889 @c distribute, sublicense, and/or sell copies of the Software, and to
3890 @c permit persons to whom the Software is furnished to do so, subject to
3891 @c the following conditions:
3893 @c The above copyright notice and this permission notice shall be included
3894 @c in all copies or substantial portions of the Software.
3896 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3897 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3898 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3899 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3900 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3901 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3902 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3904 Lazy evaluation is traditionally simulated in Scheme using @code{delay}
3905 and @code{force}. However, these primitives are not powerful enough to
3906 express a large class of lazy algorithms that are iterative. Indeed, it
3907 is folklore in the Scheme community that typical iterative lazy
3908 algorithms written using delay and force will often require unbounded
3911 This SRFI provides set of three operations: @{@code{lazy}, @code{delay},
3912 @code{force}@}, which allow the programmer to succinctly express lazy
3913 algorithms while retaining bounded space behavior in cases that are
3914 properly tail-recursive. A general recipe for using these primitives is
3915 provided. An additional procedure @code{eager} is provided for the
3916 construction of eager promises in cases where efficiency is a concern.
3918 Although this SRFI redefines @code{delay} and @code{force}, the
3919 extension is conservative in the sense that the semantics of the subset
3920 @{@code{delay}, @code{force}@} in isolation (i.e., as long as the
3921 program does not use @code{lazy}) agrees with that in R5RS. In other
3922 words, no program that uses the R5RS definitions of delay and force will
3923 break if those definition are replaced by the SRFI-45 definitions of
3926 @deffn {Scheme Syntax} delay expression
3927 Takes an expression of arbitrary type @var{a} and returns a promise of
3928 type @code{(Promise @var{a})} which at some point in the future may be
3929 asked (by the @code{force} procedure) to evaluate the expression and
3930 deliver the resulting value.
3933 @deffn {Scheme Syntax} lazy expression
3934 Takes an expression of type @code{(Promise @var{a})} and returns a
3935 promise of type @code{(Promise @var{a})} which at some point in the
3936 future may be asked (by the @code{force} procedure) to evaluate the
3937 expression and deliver the resulting promise.
3940 @deffn {Scheme Procedure} force expression
3941 Takes an argument of type @code{(Promise @var{a})} and returns a value
3942 of type @var{a} as follows: If a value of type @var{a} has been computed
3943 for the promise, this value is returned. Otherwise, the promise is
3944 first evaluated, then overwritten by the obtained promise or value, and
3945 then force is again applied (iteratively) to the promise.
3948 @deffn {Scheme Procedure} eager expression
3949 Takes an argument of type @var{a} and returns a value of type
3950 @code{(Promise @var{a})}. As opposed to @code{delay}, the argument is
3951 evaluated eagerly. Semantically, writing @code{(eager expression)} is
3952 equivalent to writing
3955 (let ((value expression)) (delay value)).
3958 However, the former is more efficient since it does not require
3959 unnecessary creation and evaluation of thunks. We also have the
3963 (delay expression) = (lazy (eager expression))
3967 The following reduction rules may be helpful for reasoning about these
3968 primitives. However, they do not express the memoization and memory
3969 usage semantics specified above:
3972 (force (delay expression)) -> expression
3973 (force (lazy expression)) -> (force expression)
3974 (force (eager value)) -> value
3977 @subsubheading Correct usage
3979 We now provide a general recipe for using the primitives @{@code{lazy},
3980 @code{delay}, @code{force}@} to express lazy algorithms in Scheme. The
3981 transformation is best described by way of an example: Consider the
3982 stream-filter algorithm, expressed in a hypothetical lazy language as
3985 (define (stream-filter p? s)
3990 (cons h (stream-filter p? t))
3991 (stream-filter p? t)))))
3994 This algorithm can be expressed as follows in Scheme:
3997 (define (stream-filter p? s)
3999 (if (null? (force s)) (delay '())
4000 (let ((h (car (force s)))
4001 (t (cdr (force s))))
4003 (delay (cons h (stream-filter p? t)))
4004 (stream-filter p? t))))))
4011 wrap all constructors (e.g., @code{'()}, @code{cons}) with @code{delay},
4013 apply @code{force} to arguments of deconstructors (e.g., @code{car},
4014 @code{cdr} and @code{null?}),
4016 wrap procedure bodies with @code{(lazy ...)}.
4020 @subsection SRFI-55 - Requiring Features
4023 SRFI-55 provides @code{require-extension} which is a portable
4024 mechanism to load selected SRFI modules. This is implemented in the
4025 Guile core, there's no module needed to get SRFI-55 itself.
4027 @deffn {library syntax} require-extension clause1 clause2 @dots{}
4028 Require the features of @var{clause1} @var{clause2} @dots{} , throwing
4029 an error if any are unavailable.
4031 A @var{clause} is of the form @code{(@var{identifier} arg...)}. The
4032 only @var{identifier} currently supported is @code{srfi} and the
4033 arguments are SRFI numbers. For example to get SRFI-1 and SRFI-6,
4036 (require-extension (srfi 1 6))
4039 @code{require-extension} can only be used at the top-level.
4041 A Guile-specific program can simply @code{use-modules} to load SRFIs
4042 not already in the core, @code{require-extension} is for programs
4043 designed to be portable to other Scheme implementations.
4048 @subsection SRFI-60 - Integers as Bits
4050 @cindex integers as bits
4051 @cindex bitwise logical
4053 This SRFI provides various functions for treating integers as bits and
4054 for bitwise manipulations. These functions can be obtained with,
4057 (use-modules (srfi srfi-60))
4060 Integers are treated as infinite precision twos-complement, the same
4061 as in the core logical functions (@pxref{Bitwise Operations}). And
4062 likewise bit indexes start from 0 for the least significant bit. The
4063 following functions in this SRFI are already in the Guile core,
4072 @code{integer-length},
4078 @defun bitwise-and n1 ...
4079 @defunx bitwise-ior n1 ...
4080 @defunx bitwise-xor n1 ...
4081 @defunx bitwise-not n
4082 @defunx any-bits-set? j k
4083 @defunx bit-set? index n
4084 @defunx arithmetic-shift n count
4085 @defunx bit-field n start end
4087 Aliases for @code{logand}, @code{logior}, @code{logxor},
4088 @code{lognot}, @code{logtest}, @code{logbit?}, @code{ash},
4089 @code{bit-extract} and @code{logcount} respectively.
4091 Note that the name @code{bit-count} conflicts with @code{bit-count} in
4092 the core (@pxref{Bit Vectors}).
4095 @defun bitwise-if mask n1 n0
4096 @defunx bitwise-merge mask n1 n0
4097 Return an integer with bits selected from @var{n1} and @var{n0}
4098 according to @var{mask}. Those bits where @var{mask} has 1s are taken
4099 from @var{n1}, and those where @var{mask} has 0s are taken from
4103 (bitwise-if 3 #b0101 #b1010) @result{} 9
4107 @defun log2-binary-factors n
4108 @defunx first-set-bit n
4109 Return a count of how many factors of 2 are present in @var{n}. This
4110 is also the bit index of the lowest 1 bit in @var{n}. If @var{n} is
4111 0, the return is @math{-1}.
4114 (log2-binary-factors 6) @result{} 1
4115 (log2-binary-factors -8) @result{} 3
4119 @defun copy-bit index n newbit
4120 Return @var{n} with the bit at @var{index} set according to
4121 @var{newbit}. @var{newbit} should be @code{#t} to set the bit to 1,
4122 or @code{#f} to set it to 0. Bits other than at @var{index} are
4123 unchanged in the return.
4126 (copy-bit 1 #b0101 #t) @result{} 7
4130 @defun copy-bit-field n newbits start end
4131 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4132 (exclusive) changed to the value @var{newbits}.
4134 The least significant bit in @var{newbits} goes to @var{start}, the
4135 next to @math{@var{start}+1}, etc. Anything in @var{newbits} past the
4136 @var{end} given is ignored.
4139 (copy-bit-field #b10000 #b11 1 3) @result{} #b10110
4143 @defun rotate-bit-field n count start end
4144 Return @var{n} with the bit field from @var{start} (inclusive) to
4145 @var{end} (exclusive) rotated upwards by @var{count} bits.
4147 @var{count} can be positive or negative, and it can be more than the
4148 field width (it'll be reduced modulo the width).
4151 (rotate-bit-field #b0110 2 1 4) @result{} #b1010
4155 @defun reverse-bit-field n start end
4156 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4157 (exclusive) reversed.
4160 (reverse-bit-field #b101001 2 4) @result{} #b100101
4164 @defun integer->list n [len]
4165 Return bits from @var{n} in the form of a list of @code{#t} for 1 and
4166 @code{#f} for 0. The least significant @var{len} bits are returned,
4167 and the first list element is the most significant of those bits. If
4168 @var{len} is not given, the default is @code{(integer-length @var{n})}
4169 (@pxref{Bitwise Operations}).
4172 (integer->list 6) @result{} (#t #t #f)
4173 (integer->list 1 4) @result{} (#f #f #f #t)
4177 @defun list->integer lst
4178 @defunx booleans->integer bool@dots{}
4179 Return an integer formed bitwise from the given @var{lst} list of
4180 booleans, or for @code{booleans->integer} from the @var{bool}
4183 Each boolean is @code{#t} for a 1 and @code{#f} for a 0. The first
4184 element becomes the most significant bit in the return.
4187 (list->integer '(#t #f #t #f)) @result{} 10
4193 @subsection SRFI-61 - A more general @code{cond} clause
4195 This SRFI extends RnRS @code{cond} to support test expressions that
4196 return multiple values, as well as arbitrary definitions of test
4197 success. SRFI 61 is implemented in the Guile core; there's no module
4198 needed to get SRFI-61 itself. Extended @code{cond} is documented in
4199 @ref{Conditionals,, Simple Conditional Evaluation}.
4202 @subsection SRFI-67 - Compare procedures
4205 See @uref{http://srfi.schemers.org/srfi-67/srfi-67.html, the
4206 specification of SRFI-67}.
4209 @subsection SRFI-69 - Basic hash tables
4212 This is a portable wrapper around Guile's built-in hash table and weak
4213 table support. @xref{Hash Tables}, for information on that built-in
4214 support. Above that, this hash-table interface provides association
4215 of equality and hash functions with tables at creation time, so
4216 variants of each function are not required, as well as a procedure
4217 that takes care of most uses for Guile hash table handles, which this
4218 SRFI does not provide as such.
4223 (use-modules (srfi srfi-69))
4227 * SRFI-69 Creating hash tables::
4228 * SRFI-69 Accessing table items::
4229 * SRFI-69 Table properties::
4230 * SRFI-69 Hash table algorithms::
4233 @node SRFI-69 Creating hash tables
4234 @subsubsection Creating hash tables
4236 @deffn {Scheme Procedure} make-hash-table [equal-proc hash-proc #:weak weakness start-size]
4237 Create and answer a new hash table with @var{equal-proc} as the
4238 equality function and @var{hash-proc} as the hashing function.
4240 By default, @var{equal-proc} is @code{equal?}. It can be any
4241 two-argument procedure, and should answer whether two keys are the
4242 same for this table's purposes.
4244 My default @var{hash-proc} assumes that @code{equal-proc} is no
4245 coarser than @code{equal?} unless it is literally @code{string-ci=?}.
4246 If provided, @var{hash-proc} should be a two-argument procedure that
4247 takes a key and the current table size, and answers a reasonably good
4248 hash integer between 0 (inclusive) and the size (exclusive).
4250 @var{weakness} should be @code{#f} or a symbol indicating how ``weak''
4255 An ordinary non-weak hash table. This is the default.
4258 When the key has no more non-weak references at GC, remove that entry.
4261 When the value has no more non-weak references at GC, remove that
4265 When either has no more non-weak references at GC, remove the
4269 As a legacy of the time when Guile couldn't grow hash tables,
4270 @var{start-size} is an optional integer argument that specifies the
4271 approximate starting size for the hash table, which will be rounded to
4272 an algorithmically-sounder number.
4275 By @dfn{coarser} than @code{equal?}, we mean that for all @var{x} and
4276 @var{y} values where @code{(@var{equal-proc} @var{x} @var{y})},
4277 @code{(equal? @var{x} @var{y})} as well. If that does not hold for
4278 your @var{equal-proc}, you must provide a @var{hash-proc}.
4280 In the case of weak tables, remember that @dfn{references} above
4281 always refers to @code{eq?}-wise references. Just because you have a
4282 reference to some string @code{"foo"} doesn't mean that an association
4283 with key @code{"foo"} in a weak-key table @emph{won't} be collected;
4284 it only counts as a reference if the two @code{"foo"}s are @code{eq?},
4285 regardless of @var{equal-proc}. As such, it is usually only sensible
4286 to use @code{eq?} and @code{hashq} as the equivalence and hash
4287 functions for a weak table. @xref{Weak References}, for more
4288 information on Guile's built-in weak table support.
4290 @deffn {Scheme Procedure} alist->hash-table alist [equal-proc hash-proc #:weak weakness start-size]
4291 As with @code{make-hash-table}, but initialize it with the
4292 associations in @var{alist}. Where keys are repeated in @var{alist},
4293 the leftmost association takes precedence.
4296 @node SRFI-69 Accessing table items
4297 @subsubsection Accessing table items
4299 @deffn {Scheme Procedure} hash-table-ref table key [default-thunk]
4300 @deffnx {Scheme Procedure} hash-table-ref/default table key default
4301 Answer the value associated with @var{key} in @var{table}. If
4302 @var{key} is not present, answer the result of invoking the thunk
4303 @var{default-thunk}, which signals an error instead by default.
4305 @code{hash-table-ref/default} is a variant that requires a third
4306 argument, @var{default}, and answers @var{default} itself instead of
4310 @deffn {Scheme Procedure} hash-table-set! table key new-value
4311 Set @var{key} to @var{new-value} in @var{table}.
4314 @deffn {Scheme Procedure} hash-table-delete! table key
4315 Remove the association of @var{key} in @var{table}, if present. If
4319 @deffn {Scheme Procedure} hash-table-exists? table key
4320 Answer whether @var{key} has an association in @var{table}.
4323 @deffn {Scheme Procedure} hash-table-update! table key modifier [default-thunk]
4324 @deffnx {Scheme Procedure} hash-table-update!/default table key modifier default
4325 Replace @var{key}'s associated value in @var{table} by invoking
4326 @var{modifier} with one argument, the old value.
4328 If @var{key} is not present, and @var{default-thunk} is provided,
4329 invoke it with no arguments to get the ``old value'' to be passed to
4330 @var{modifier} as above. If @var{default-thunk} is not provided in
4331 such a case, signal an error.
4333 @code{hash-table-update!/default} is a variant that requires the
4334 fourth argument, which is used directly as the ``old value'' rather
4335 than as a thunk to be invoked to retrieve the ``old value''.
4338 @node SRFI-69 Table properties
4339 @subsubsection Table properties
4341 @deffn {Scheme Procedure} hash-table-size table
4342 Answer the number of associations in @var{table}. This is guaranteed
4343 to run in constant time for non-weak tables.
4346 @deffn {Scheme Procedure} hash-table-keys table
4347 Answer an unordered list of the keys in @var{table}.
4350 @deffn {Scheme Procedure} hash-table-values table
4351 Answer an unordered list of the values in @var{table}.
4354 @deffn {Scheme Procedure} hash-table-walk table proc
4355 Invoke @var{proc} once for each association in @var{table}, passing
4356 the key and value as arguments.
4359 @deffn {Scheme Procedure} hash-table-fold table proc init
4360 Invoke @code{(@var{proc} @var{key} @var{value} @var{previous})} for
4361 each @var{key} and @var{value} in @var{table}, where @var{previous} is
4362 the result of the previous invocation, using @var{init} as the first
4363 @var{previous} value. Answer the final @var{proc} result.
4366 @deffn {Scheme Procedure} hash-table->alist table
4367 Answer an alist where each association in @var{table} is an
4368 association in the result.
4371 @node SRFI-69 Hash table algorithms
4372 @subsubsection Hash table algorithms
4374 Each hash table carries an @dfn{equivalence function} and a @dfn{hash
4375 function}, used to implement key lookups. Beginning users should
4376 follow the rules for consistency of the default @var{hash-proc}
4377 specified above. Advanced users can use these to implement their own
4378 equivalence and hash functions for specialized lookup semantics.
4380 @deffn {Scheme Procedure} hash-table-equivalence-function hash-table
4381 @deffnx {Scheme Procedure} hash-table-hash-function hash-table
4382 Answer the equivalence and hash function of @var{hash-table}, respectively.
4385 @deffn {Scheme Procedure} hash obj [size]
4386 @deffnx {Scheme Procedure} string-hash obj [size]
4387 @deffnx {Scheme Procedure} string-ci-hash obj [size]
4388 @deffnx {Scheme Procedure} hash-by-identity obj [size]
4389 Answer a hash value appropriate for equality predicate @code{equal?},
4390 @code{string=?}, @code{string-ci=?}, and @code{eq?}, respectively.
4393 @code{hash} is a backwards-compatible replacement for Guile's built-in
4397 @subsection SRFI-88 Keyword Objects
4399 @cindex keyword objects
4401 @uref{http://srfi.schemers.org/srfi-88/srfi-88.html, SRFI-88} provides
4402 @dfn{keyword objects}, which are equivalent to Guile's keywords
4403 (@pxref{Keywords}). SRFI-88 keywords can be entered using the
4404 @dfn{postfix keyword syntax}, which consists of an identifier followed
4405 by @code{:} (@pxref{Scheme Read, @code{postfix} keyword syntax}).
4406 SRFI-88 can be made available with:
4409 (use-modules (srfi srfi-88))
4412 Doing so installs the right reader option for keyword syntax, using
4413 @code{(read-set! keywords 'postfix)}. It also provides the procedures
4416 @deffn {Scheme Procedure} keyword? obj
4417 Return @code{#t} if @var{obj} is a keyword. This is the same procedure
4418 as the same-named built-in procedure (@pxref{Keyword Procedures,
4422 (keyword? foo:) @result{} #t
4423 (keyword? 'foo:) @result{} #t
4424 (keyword? "foo") @result{} #f
4428 @deffn {Scheme Procedure} keyword->string kw
4429 Return the name of @var{kw} as a string, i.e., without the trailing
4430 colon. The returned string may not be modified, e.g., with
4434 (keyword->string foo:) @result{} "foo"
4438 @deffn {Scheme Procedure} string->keyword str
4439 Return the keyword object whose name is @var{str}.
4442 (keyword->string (string->keyword "a b c")) @result{} "a b c"
4447 @subsection SRFI-98 Accessing environment variables.
4449 @cindex environment variables
4451 This is a portable wrapper around Guile's built-in support for
4452 interacting with the current environment, @xref{Runtime Environment}.
4454 @deffn {Scheme Procedure} get-environment-variable name
4455 Returns a string containing the value of the environment variable
4456 given by the string @code{name}, or @code{#f} if the named
4457 environment variable is not found. This is equivalent to
4458 @code{(getenv name)}.
4461 @deffn {Scheme Procedure} get-environment-variables
4462 Returns the names and values of all the environment variables as an
4463 association list in which both the keys and the values are strings.
4466 @c srfi-modules.texi ends here
4469 @c TeX-master: "guile.texi"