2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @section SRFI Support Modules
11 SRFI is an acronym for Scheme Request For Implementation. The SRFI
12 documents define a lot of syntactic and procedure extensions to standard
13 Scheme as defined in R5RS.
15 Guile has support for a number of SRFIs. This chapter gives an overview
16 over the available SRFIs and some usage hints. For complete
17 documentation, design rationales and further examples, we advise you to
18 get the relevant SRFI documents from the SRFI home page
19 @url{http://srfi.schemers.org/}.
22 * About SRFI Usage:: What to know about Guile's SRFI support.
23 * SRFI-0:: cond-expand
24 * SRFI-1:: List library.
26 * SRFI-4:: Homogeneous numeric vector datatypes.
27 * SRFI-6:: Basic String Ports.
29 * SRFI-9:: define-record-type.
30 * SRFI-10:: Hash-Comma Reader Extension.
31 * SRFI-11:: let-values and let*-values.
32 * SRFI-13:: String library.
33 * SRFI-14:: Character-set library.
34 * SRFI-16:: case-lambda
35 * SRFI-17:: Generalized set!
36 * SRFI-18:: Multithreading support
37 * SRFI-19:: Time/Date library.
38 * SRFI-23:: Error reporting
39 * SRFI-26:: Specializing parameters
40 * SRFI-27:: Sources of Random Bits
41 * SRFI-30:: Nested multi-line block comments
42 * SRFI-31:: A special form `rec' for recursive evaluation
43 * SRFI-34:: Exception handling.
44 * SRFI-35:: Conditions.
45 * SRFI-37:: args-fold program argument processor
46 * SRFI-38:: External Representation for Data With Shared Structure
47 * SRFI-39:: Parameter objects
49 * SRFI-42:: Eager comprehensions
50 * SRFI-45:: Primitives for expressing iterative lazy algorithms
51 * SRFI-55:: Requiring Features.
52 * SRFI-60:: Integers as bits.
53 * SRFI-61:: A more general `cond' clause
54 * SRFI-67:: Compare procedures
55 * SRFI-69:: Basic hash tables.
56 * SRFI-88:: Keyword objects.
57 * SRFI-98:: Accessing environment variables.
58 * SRFI-105:: Curly-infix expressions.
62 @node About SRFI Usage
63 @subsection About SRFI Usage
65 @c FIXME::martin: Review me!
67 SRFI support in Guile is currently implemented partly in the core
68 library, and partly as add-on modules. That means that some SRFIs are
69 automatically available when the interpreter is started, whereas the
70 other SRFIs require you to use the appropriate support module
73 There are several reasons for this inconsistency. First, the feature
74 checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be
75 available immediately, because it must be there when the user wants to
76 check for the Scheme implementation, that is, before she can know that
77 it is safe to use @code{use-modules} to load SRFI support modules. The
78 second reason is that some features defined in SRFIs had been
79 implemented in Guile before the developers started to add SRFI
80 implementations as modules (for example SRFI-13 (@pxref{SRFI-13})). In
81 the future, it is possible that SRFIs in the core library might be
82 factored out into separate modules, requiring explicit module loading
83 when they are needed. So you should be prepared to have to use
84 @code{use-modules} someday in the future to access SRFI-13 bindings. If
85 you want, you can do that already. We have included the module
86 @code{(srfi srfi-13)} in the distribution, which currently does nothing,
87 but ensures that you can write future-safe code.
89 Generally, support for a specific SRFI is made available by using
90 modules named @code{(srfi srfi-@var{number})}, where @var{number} is the
91 number of the SRFI needed. Another possibility is to use the command
92 line option @code{--use-srfi}, which will load the necessary modules
93 automatically (@pxref{Invoking Guile}).
97 @subsection SRFI-0 - cond-expand
100 This SRFI lets a portable Scheme program test for the presence of
101 certain features, and adapt itself by using different blocks of code,
102 or fail if the necessary features are not available. There's no
103 module to load, this is in the Guile core.
105 A program designed only for Guile will generally not need this
106 mechanism, such a program can of course directly use the various
107 documented parts of Guile.
109 @deffn syntax cond-expand (feature body@dots{}) @dots{}
110 Expand to the @var{body} of the first clause whose @var{feature}
111 specification is satisfied. It is an error if no @var{feature} is
114 Features are symbols such as @code{srfi-1}, and a feature
115 specification can use @code{and}, @code{or} and @code{not} forms to
116 test combinations. The last clause can be an @code{else}, to be used
119 For example, define a private version of @code{alist-cons} if SRFI-1
126 (define (alist-cons key val alist)
127 (cons (cons key val) alist))))
130 Or demand a certain set of SRFIs (list operations, string ports,
131 @code{receive} and string operations), failing if they're not
135 (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13)
141 The Guile core has the following features,
145 guile-2 ;; starting from Guile 2.x
159 Other SRFI feature symbols are defined once their code has been loaded
160 with @code{use-modules}, since only then are their bindings available.
162 The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is
163 a good way to load SRFIs to satisfy @code{cond-expand} when running a
166 Testing the @code{guile} feature allows a program to adapt itself to
167 the Guile module system, but still run on other Scheme systems. For
168 example the following demands SRFI-8 (@code{receive}), but also knows
169 how to load it with the Guile mechanism.
175 (use-modules (srfi srfi-8))))
178 @cindex @code{guile-2} SRFI-0 feature
179 @cindex portability between 2.0 and older versions
180 Likewise, testing the @code{guile-2} feature allows code to be portable
181 between Guile 2.@var{x} and previous versions of Guile. For instance, it
182 makes it possible to write code that accounts for Guile 2.@var{x}'s compiler,
183 yet be correctly interpreted on 1.8 and earlier versions:
186 (cond-expand (guile-2 (eval-when (compile)
187 ;; This must be evaluated at compile time.
188 (fluid-set! current-reader my-reader)))
190 ;; Earlier versions of Guile do not have a
191 ;; separate compilation phase.
192 (fluid-set! current-reader my-reader)))
195 It should be noted that @code{cond-expand} is separate from the
196 @code{*features*} mechanism (@pxref{Feature Tracking}), feature
197 symbols in one are unrelated to those in the other.
201 @subsection SRFI-1 - List library
205 @c FIXME::martin: Review me!
207 The list library defined in SRFI-1 contains a lot of useful list
208 processing procedures for construction, examining, destructuring and
209 manipulating lists and pairs.
211 Since SRFI-1 also defines some procedures which are already contained
212 in R5RS and thus are supported by the Guile core library, some list
213 and pair procedures which appear in the SRFI-1 document may not appear
214 in this section. So when looking for a particular list/pair
215 processing procedure, you should also have a look at the sections
216 @ref{Lists} and @ref{Pairs}.
219 * SRFI-1 Constructors:: Constructing new lists.
220 * SRFI-1 Predicates:: Testing list for specific properties.
221 * SRFI-1 Selectors:: Selecting elements from lists.
222 * SRFI-1 Length Append etc:: Length calculation and list appending.
223 * SRFI-1 Fold and Map:: Higher-order list processing.
224 * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates.
225 * SRFI-1 Searching:: Search for elements.
226 * SRFI-1 Deleting:: Delete elements from lists.
227 * SRFI-1 Association Lists:: Handle association lists.
228 * SRFI-1 Set Operations:: Use lists for representing sets.
231 @node SRFI-1 Constructors
232 @subsubsection Constructors
233 @cindex list constructor
235 @c FIXME::martin: Review me!
237 New lists can be constructed by calling one of the following
240 @deffn {Scheme Procedure} xcons d a
241 Like @code{cons}, but with interchanged arguments. Useful mostly when
242 passed to higher-order procedures.
245 @deffn {Scheme Procedure} list-tabulate n init-proc
246 Return an @var{n}-element list, where each list element is produced by
247 applying the procedure @var{init-proc} to the corresponding list
248 index. The order in which @var{init-proc} is applied to the indices
252 @deffn {Scheme Procedure} list-copy lst
253 Return a new list containing the elements of the list @var{lst}.
255 This function differs from the core @code{list-copy} (@pxref{List
256 Constructors}) in accepting improper lists too. And if @var{lst} is
257 not a pair at all then it's treated as the final tail of an improper
258 list and simply returned.
261 @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{}
262 Return a circular list containing the given arguments @var{elt1}
266 @deffn {Scheme Procedure} iota count [start step]
267 Return a list containing @var{count} numbers, starting from
268 @var{start} and adding @var{step} each time. The default @var{start}
269 is 0, the default @var{step} is 1. For example,
272 (iota 6) @result{} (0 1 2 3 4 5)
273 (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5)
276 This function takes its name from the corresponding primitive in the
281 @node SRFI-1 Predicates
282 @subsubsection Predicates
283 @cindex list predicate
285 @c FIXME::martin: Review me!
287 The procedures in this section test specific properties of lists.
289 @deffn {Scheme Procedure} proper-list? obj
290 Return @code{#t} if @var{obj} is a proper list, or @code{#f}
291 otherwise. This is the same as the core @code{list?} (@pxref{List
294 A proper list is a list which ends with the empty list @code{()} in
295 the usual way. The empty list @code{()} itself is a proper list too.
298 (proper-list? '(1 2 3)) @result{} #t
299 (proper-list? '()) @result{} #t
303 @deffn {Scheme Procedure} circular-list? obj
304 Return @code{#t} if @var{obj} is a circular list, or @code{#f}
307 A circular list is a list where at some point the @code{cdr} refers
308 back to a previous pair in the list (either the start or some later
309 point), so that following the @code{cdr}s takes you around in a
313 (define x (list 1 2 3 4))
314 (set-cdr! (last-pair x) (cddr x))
315 x @result{} (1 2 3 4 3 4 3 4 ...)
316 (circular-list? x) @result{} #t
320 @deffn {Scheme Procedure} dotted-list? obj
321 Return @code{#t} if @var{obj} is a dotted list, or @code{#f}
324 A dotted list is a list where the @code{cdr} of the last pair is not
325 the empty list @code{()}. Any non-pair @var{obj} is also considered a
326 dotted list, with length zero.
329 (dotted-list? '(1 2 . 3)) @result{} #t
330 (dotted-list? 99) @result{} #t
334 It will be noted that any Scheme object passes exactly one of the
335 above three tests @code{proper-list?}, @code{circular-list?} and
336 @code{dotted-list?}. Non-lists are @code{dotted-list?}, finite lists
337 are either @code{proper-list?} or @code{dotted-list?}, and infinite
338 lists are @code{circular-list?}.
341 @deffn {Scheme Procedure} null-list? lst
342 Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f}
343 otherwise. If something else than a proper or circular list is passed
344 as @var{lst}, an error is signalled. This procedure is recommended
345 for checking for the end of a list in contexts where dotted lists are
349 @deffn {Scheme Procedure} not-pair? obj
350 Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise.
351 This is shorthand notation @code{(not (pair? @var{obj}))} and is
352 supposed to be used for end-of-list checking in contexts where dotted
356 @deffn {Scheme Procedure} list= elt= list1 @dots{}
357 Return @code{#t} if all argument lists are equal, @code{#f} otherwise.
358 List equality is determined by testing whether all lists have the same
359 length and the corresponding elements are equal in the sense of the
360 equality predicate @var{elt=}. If no or only one list is given,
361 @code{#t} is returned.
365 @node SRFI-1 Selectors
366 @subsubsection Selectors
367 @cindex list selector
369 @c FIXME::martin: Review me!
371 @deffn {Scheme Procedure} first pair
372 @deffnx {Scheme Procedure} second pair
373 @deffnx {Scheme Procedure} third pair
374 @deffnx {Scheme Procedure} fourth pair
375 @deffnx {Scheme Procedure} fifth pair
376 @deffnx {Scheme Procedure} sixth pair
377 @deffnx {Scheme Procedure} seventh pair
378 @deffnx {Scheme Procedure} eighth pair
379 @deffnx {Scheme Procedure} ninth pair
380 @deffnx {Scheme Procedure} tenth pair
381 These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}.
384 @deffn {Scheme Procedure} car+cdr pair
385 Return two values, the @sc{car} and the @sc{cdr} of @var{pair}.
388 @deffn {Scheme Procedure} take lst i
389 @deffnx {Scheme Procedure} take! lst i
390 Return a list containing the first @var{i} elements of @var{lst}.
392 @code{take!} may modify the structure of the argument list @var{lst}
393 in order to produce the result.
396 @deffn {Scheme Procedure} drop lst i
397 Return a list containing all but the first @var{i} elements of
401 @deffn {Scheme Procedure} take-right lst i
402 Return a list containing the @var{i} last elements of @var{lst}.
403 The return shares a common tail with @var{lst}.
406 @deffn {Scheme Procedure} drop-right lst i
407 @deffnx {Scheme Procedure} drop-right! lst i
408 Return a list containing all but the @var{i} last elements of
411 @code{drop-right} always returns a new list, even when @var{i} is
412 zero. @code{drop-right!} may modify the structure of the argument
413 list @var{lst} in order to produce the result.
416 @deffn {Scheme Procedure} split-at lst i
417 @deffnx {Scheme Procedure} split-at! lst i
418 Return two values, a list containing the first @var{i} elements of the
419 list @var{lst} and a list containing the remaining elements.
421 @code{split-at!} may modify the structure of the argument list
422 @var{lst} in order to produce the result.
425 @deffn {Scheme Procedure} last lst
426 Return the last element of the non-empty, finite list @var{lst}.
430 @node SRFI-1 Length Append etc
431 @subsubsection Length, Append, Concatenate, etc.
433 @c FIXME::martin: Review me!
435 @deffn {Scheme Procedure} length+ lst
436 Return the length of the argument list @var{lst}. When @var{lst} is a
437 circular list, @code{#f} is returned.
440 @deffn {Scheme Procedure} concatenate list-of-lists
441 @deffnx {Scheme Procedure} concatenate! list-of-lists
442 Construct a list by appending all lists in @var{list-of-lists}.
444 @code{concatenate!} may modify the structure of the given lists in
445 order to produce the result.
447 @code{concatenate} is the same as @code{(apply append
448 @var{list-of-lists})}. It exists because some Scheme implementations
449 have a limit on the number of arguments a function takes, which the
450 @code{apply} might exceed. In Guile there is no such limit.
453 @deffn {Scheme Procedure} append-reverse rev-head tail
454 @deffnx {Scheme Procedure} append-reverse! rev-head tail
455 Reverse @var{rev-head}, append @var{tail} to it, and return the
456 result. This is equivalent to @code{(append (reverse @var{rev-head})
457 @var{tail})}, but its implementation is more efficient.
460 (append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)
463 @code{append-reverse!} may modify @var{rev-head} in order to produce
467 @deffn {Scheme Procedure} zip lst1 lst2 @dots{}
468 Return a list as long as the shortest of the argument lists, where
469 each element is a list. The first list contains the first elements of
470 the argument lists, the second list contains the second elements, and
474 @deffn {Scheme Procedure} unzip1 lst
475 @deffnx {Scheme Procedure} unzip2 lst
476 @deffnx {Scheme Procedure} unzip3 lst
477 @deffnx {Scheme Procedure} unzip4 lst
478 @deffnx {Scheme Procedure} unzip5 lst
479 @code{unzip1} takes a list of lists, and returns a list containing the
480 first elements of each list, @code{unzip2} returns two lists, the
481 first containing the first elements of each lists and the second
482 containing the second elements of each lists, and so on.
485 @deffn {Scheme Procedure} count pred lst1 lst2 @dots{}
486 Return a count of the number of times @var{pred} returns true when
487 called on elements from the given lists.
489 @var{pred} is called with @var{N} parameters @code{(@var{pred}
490 @var{elem1} @dots{} @var{elemN} )}, each element being from the
491 corresponding list. The first call is with the first element of each
492 list, the second with the second element from each, and so on.
494 Counting stops when the end of the shortest list is reached. At least
495 one list must be non-circular.
499 @node SRFI-1 Fold and Map
500 @subsubsection Fold, Unfold & Map
504 @c FIXME::martin: Review me!
506 @deffn {Scheme Procedure} fold proc init lst1 lst2 @dots{}
507 @deffnx {Scheme Procedure} fold-right proc init lst1 lst2 @dots{}
508 Apply @var{proc} to the elements of @var{lst1} @var{lst2} @dots{} to
509 build a result, and return that result.
511 Each @var{proc} call is @code{(@var{proc} @var{elem1} @var{elem2}
512 @dots{} @var{previous})}, where @var{elem1} is from @var{lst1},
513 @var{elem2} is from @var{lst2}, and so on. @var{previous} is the return
514 from the previous call to @var{proc}, or the given @var{init} for the
515 first call. If any list is empty, just @var{init} is returned.
517 @code{fold} works through the list elements from first to last. The
518 following shows a list reversal and the calls it makes,
521 (fold cons '() '(1 2 3))
529 @code{fold-right} works through the list elements from last to first,
530 ie.@: from the right. So for example the following finds the longest
531 string, and the last among equal longest,
534 (fold-right (lambda (str prev)
535 (if (> (string-length str) (string-length prev))
539 '("x" "abc" "xyz" "jk"))
543 If @var{lst1} @var{lst2} @dots{} have different lengths, @code{fold}
544 stops when the end of the shortest is reached; @code{fold-right}
545 commences at the last element of the shortest. Ie.@: elements past the
546 length of the shortest are ignored in the other @var{lst}s. At least
547 one @var{lst} must be non-circular.
549 @code{fold} should be preferred over @code{fold-right} if the order of
550 processing doesn't matter, or can be arranged either way, since
551 @code{fold} is a little more efficient.
553 The way @code{fold} builds a result from iterating is quite general,
554 it can do more than other iterations like say @code{map} or
555 @code{filter}. The following for example removes adjacent duplicate
556 elements from a list,
559 (define (delete-adjacent-duplicates lst)
560 (fold-right (lambda (elem ret)
561 (if (equal? elem (first ret))
566 (delete-adjacent-duplicates '(1 2 3 3 4 4 4 5))
567 @result{} (1 2 3 4 5)
570 Clearly the same sort of thing can be done with a @code{for-each} and
571 a variable in which to build the result, but a self-contained
572 @var{proc} can be re-used in multiple contexts, where a
573 @code{for-each} would have to be written out each time.
576 @deffn {Scheme Procedure} pair-fold proc init lst1 lst2 @dots{}
577 @deffnx {Scheme Procedure} pair-fold-right proc init lst1 lst2 @dots{}
578 The same as @code{fold} and @code{fold-right}, but apply @var{proc} to
579 the pairs of the lists instead of the list elements.
582 @deffn {Scheme Procedure} reduce proc default lst
583 @deffnx {Scheme Procedure} reduce-right proc default lst
584 @code{reduce} is a variant of @code{fold}, where the first call to
585 @var{proc} is on two elements from @var{lst}, rather than one element
586 and a given initial value.
588 If @var{lst} is empty, @code{reduce} returns @var{default} (this is
589 the only use for @var{default}). If @var{lst} has just one element
590 then that's the return value. Otherwise @var{proc} is called on the
591 elements of @var{lst}.
593 Each @var{proc} call is @code{(@var{proc} @var{elem} @var{previous})},
594 where @var{elem} is from @var{lst} (the second and subsequent elements
595 of @var{lst}), and @var{previous} is the return from the previous call
596 to @var{proc}. The first element of @var{lst} is the @var{previous}
597 for the first call to @var{proc}.
599 For example, the following adds a list of numbers, the calls made to
600 @code{+} are shown. (Of course @code{+} accepts multiple arguments
601 and can add a list directly, with @code{apply}.)
604 (reduce + 0 '(5 6 7)) @result{} 18
607 (+ 7 11) @result{} 18
610 @code{reduce} can be used instead of @code{fold} where the @var{init}
611 value is an ``identity'', meaning a value which under @var{proc}
612 doesn't change the result, in this case 0 is an identity since
613 @code{(+ 5 0)} is just 5. @code{reduce} avoids that unnecessary call.
615 @code{reduce-right} is a similar variation on @code{fold-right},
616 working from the end (ie.@: the right) of @var{lst}. The last element
617 of @var{lst} is the @var{previous} for the first call to @var{proc},
618 and the @var{elem} values go from the second last.
620 @code{reduce} should be preferred over @code{reduce-right} if the
621 order of processing doesn't matter, or can be arranged either way,
622 since @code{reduce} is a little more efficient.
625 @deffn {Scheme Procedure} unfold p f g seed [tail-gen]
626 @code{unfold} is defined as follows:
629 (unfold p f g seed) =
630 (if (p seed) (tail-gen seed)
632 (unfold p f g (g seed))))
637 Determines when to stop unfolding.
640 Maps each seed value to the corresponding list element.
643 Maps each seed value to next seed value.
646 The state value for the unfold.
649 Creates the tail of the list; defaults to @code{(lambda (x) '())}.
652 @var{g} produces a series of seed values, which are mapped to list
653 elements by @var{f}. These elements are put into a list in
654 left-to-right order, and @var{p} tells when to stop unfolding.
657 @deffn {Scheme Procedure} unfold-right p f g seed [tail]
658 Construct a list with the following loop.
661 (let lp ((seed seed) (lis tail))
664 (cons (f seed) lis))))
669 Determines when to stop unfolding.
672 Maps each seed value to the corresponding list element.
675 Maps each seed value to next seed value.
678 The state value for the unfold.
681 The tail of the list; defaults to @code{'()}.
686 @deffn {Scheme Procedure} map f lst1 lst2 @dots{}
687 Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and
688 return a list containing the results of the procedure applications.
689 This procedure is extended with respect to R5RS, because the argument
690 lists may have different lengths. The result list will have the same
691 length as the shortest argument lists. The order in which @var{f}
692 will be applied to the list element(s) is not specified.
695 @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{}
696 Apply the procedure @var{f} to each pair of corresponding elements of
697 the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not
698 specified. This procedure is extended with respect to R5RS, because
699 the argument lists may have different lengths. The shortest argument
700 list determines the number of times @var{f} is called. @var{f} will
701 be applied to the list elements in left-to-right order.
705 @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{}
706 @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{}
710 (apply append (map f clist1 clist2 ...))
716 (apply append! (map f clist1 clist2 ...))
719 Map @var{f} over the elements of the lists, just as in the @code{map}
720 function. However, the results of the applications are appended
721 together to make the final result. @code{append-map} uses
722 @code{append} to append the results together; @code{append-map!} uses
725 The dynamic order in which the various applications of @var{f} are
726 made is not specified.
729 @deffn {Scheme Procedure} map! f lst1 lst2 @dots{}
730 Linear-update variant of @code{map} -- @code{map!} is allowed, but not
731 required, to alter the cons cells of @var{lst1} to construct the
734 The dynamic order in which the various applications of @var{f} are
735 made is not specified. In the n-ary case, @var{lst2}, @var{lst3},
736 @dots{} must have at least as many elements as @var{lst1}.
739 @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{}
740 Like @code{for-each}, but applies the procedure @var{f} to the pairs
741 from which the argument lists are constructed, instead of the list
742 elements. The return value is not specified.
745 @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{}
746 Like @code{map}, but only results from the applications of @var{f}
747 which are true are saved in the result list.
751 @node SRFI-1 Filtering and Partitioning
752 @subsubsection Filtering and Partitioning
754 @cindex list partition
756 @c FIXME::martin: Review me!
758 Filtering means to collect all elements from a list which satisfy a
759 specific condition. Partitioning a list means to make two groups of
760 list elements, one which contains the elements satisfying a condition,
761 and the other for the elements which don't.
763 The @code{filter} and @code{filter!} functions are implemented in the
764 Guile core, @xref{List Modification}.
766 @deffn {Scheme Procedure} partition pred lst
767 @deffnx {Scheme Procedure} partition! pred lst
768 Split @var{lst} into those elements which do and don't satisfy the
769 predicate @var{pred}.
771 The return is two values (@pxref{Multiple Values}), the first being a
772 list of all elements from @var{lst} which satisfy @var{pred}, the
773 second a list of those which do not.
775 The elements in the result lists are in the same order as in @var{lst}
776 but the order in which the calls @code{(@var{pred} elem)} are made on
777 the list elements is unspecified.
779 @code{partition} does not change @var{lst}, but one of the returned
780 lists may share a tail with it. @code{partition!} may modify
781 @var{lst} to construct its return.
784 @deffn {Scheme Procedure} remove pred lst
785 @deffnx {Scheme Procedure} remove! pred lst
786 Return a list containing all elements from @var{lst} which do not
787 satisfy the predicate @var{pred}. The elements in the result list
788 have the same order as in @var{lst}. The order in which @var{pred} is
789 applied to the list elements is not specified.
791 @code{remove!} is allowed, but not required to modify the structure of
796 @node SRFI-1 Searching
797 @subsubsection Searching
800 @c FIXME::martin: Review me!
802 The procedures for searching elements in lists either accept a
803 predicate or a comparison object for determining which elements are to
806 @deffn {Scheme Procedure} find pred lst
807 Return the first element of @var{lst} which satisfies the predicate
808 @var{pred} and @code{#f} if no such element is found.
811 @deffn {Scheme Procedure} find-tail pred lst
812 Return the first pair of @var{lst} whose @sc{car} satisfies the
813 predicate @var{pred} and @code{#f} if no such element is found.
816 @deffn {Scheme Procedure} take-while pred lst
817 @deffnx {Scheme Procedure} take-while! pred lst
818 Return the longest initial prefix of @var{lst} whose elements all
819 satisfy the predicate @var{pred}.
821 @code{take-while!} is allowed, but not required to modify the input
822 list while producing the result.
825 @deffn {Scheme Procedure} drop-while pred lst
826 Drop the longest initial prefix of @var{lst} whose elements all
827 satisfy the predicate @var{pred}.
830 @deffn {Scheme Procedure} span pred lst
831 @deffnx {Scheme Procedure} span! pred lst
832 @deffnx {Scheme Procedure} break pred lst
833 @deffnx {Scheme Procedure} break! pred lst
834 @code{span} splits the list @var{lst} into the longest initial prefix
835 whose elements all satisfy the predicate @var{pred}, and the remaining
836 tail. @code{break} inverts the sense of the predicate.
838 @code{span!} and @code{break!} are allowed, but not required to modify
839 the structure of the input list @var{lst} in order to produce the
842 Note that the name @code{break} conflicts with the @code{break}
843 binding established by @code{while} (@pxref{while do}). Applications
844 wanting to use @code{break} from within a @code{while} loop will need
845 to make a new define under a different name.
848 @deffn {Scheme Procedure} any pred lst1 lst2 @dots{}
849 Test whether any set of elements from @var{lst1} @var{lst2} @dots{}
850 satisfies @var{pred}. If so, the return value is the return value from
851 the successful @var{pred} call, or if not, the return value is
854 If there are n list arguments, then @var{pred} must be a predicate
855 taking n arguments. Each @var{pred} call is @code{(@var{pred}
856 @var{elem1} @var{elem2} @dots{} )} taking an element from each
857 @var{lst}. The calls are made successively for the first, second, etc.
858 elements of the lists, stopping when @var{pred} returns non-@code{#f},
859 or when the end of the shortest list is reached.
861 The @var{pred} call on the last set of elements (i.e., when the end of
862 the shortest list has been reached), if that point is reached, is a
866 @deffn {Scheme Procedure} every pred lst1 lst2 @dots{}
867 Test whether every set of elements from @var{lst1} @var{lst2} @dots{}
868 satisfies @var{pred}. If so, the return value is the return from the
869 final @var{pred} call, or if not, the return value is @code{#f}.
871 If there are n list arguments, then @var{pred} must be a predicate
872 taking n arguments. Each @var{pred} call is @code{(@var{pred}
873 @var{elem1} @var{elem2 @dots{}})} taking an element from each
874 @var{lst}. The calls are made successively for the first, second, etc.
875 elements of the lists, stopping if @var{pred} returns @code{#f}, or when
876 the end of any of the lists is reached.
878 The @var{pred} call on the last set of elements (i.e., when the end of
879 the shortest list has been reached) is a tail call.
881 If one of @var{lst1} @var{lst2} @dots{}is empty then no calls to
882 @var{pred} are made, and the return value is @code{#t}.
885 @deffn {Scheme Procedure} list-index pred lst1 lst2 @dots{}
886 Return the index of the first set of elements, one from each of
887 @var{lst1} @var{lst2} @dots{}, which satisfies @var{pred}.
889 @var{pred} is called as @code{(@var{elem1} @var{elem2 @dots{}})}.
890 Searching stops when the end of the shortest @var{lst} is reached.
891 The return index starts from 0 for the first set of elements. If no
892 set of elements pass, then the return value is @code{#f}.
895 (list-index odd? '(2 4 6 9)) @result{} 3
896 (list-index = '(1 2 3) '(3 1 2)) @result{} #f
900 @deffn {Scheme Procedure} member x lst [=]
901 Return the first sublist of @var{lst} whose @sc{car} is equal to
902 @var{x}. If @var{x} does not appear in @var{lst}, return @code{#f}.
904 Equality is determined by @code{equal?}, or by the equality predicate
905 @var{=} if given. @var{=} is called @code{(= @var{x} elem)},
906 ie.@: with the given @var{x} first, so for example to find the first
907 element greater than 5,
910 (member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9)
913 This version of @code{member} extends the core @code{member}
914 (@pxref{List Searching}) by accepting an equality predicate.
918 @node SRFI-1 Deleting
919 @subsubsection Deleting
922 @deffn {Scheme Procedure} delete x lst [=]
923 @deffnx {Scheme Procedure} delete! x lst [=]
924 Return a list containing the elements of @var{lst} but with those
925 equal to @var{x} deleted. The returned elements will be in the same
926 order as they were in @var{lst}.
928 Equality is determined by the @var{=} predicate, or @code{equal?} if
929 not given. An equality call is made just once for each element, but
930 the order in which the calls are made on the elements is unspecified.
932 The equality calls are always @code{(= x elem)}, ie.@: the given @var{x}
933 is first. This means for instance elements greater than 5 can be
934 deleted with @code{(delete 5 lst <)}.
936 @code{delete} does not modify @var{lst}, but the return might share a
937 common tail with @var{lst}. @code{delete!} may modify the structure
938 of @var{lst} to construct its return.
940 These functions extend the core @code{delete} and @code{delete!}
941 (@pxref{List Modification}) in accepting an equality predicate. See
942 also @code{lset-difference} (@pxref{SRFI-1 Set Operations}) for
943 deleting multiple elements from a list.
946 @deffn {Scheme Procedure} delete-duplicates lst [=]
947 @deffnx {Scheme Procedure} delete-duplicates! lst [=]
948 Return a list containing the elements of @var{lst} but without
951 When elements are equal, only the first in @var{lst} is retained.
952 Equal elements can be anywhere in @var{lst}, they don't have to be
953 adjacent. The returned list will have the retained elements in the
954 same order as they were in @var{lst}.
956 Equality is determined by the @var{=} predicate, or @code{equal?} if
957 not given. Calls @code{(= x y)} are made with element @var{x} being
958 before @var{y} in @var{lst}. A call is made at most once for each
959 combination, but the sequence of the calls across the elements is
962 @code{delete-duplicates} does not modify @var{lst}, but the return
963 might share a common tail with @var{lst}. @code{delete-duplicates!}
964 may modify the structure of @var{lst} to construct its return.
966 In the worst case, this is an @math{O(N^2)} algorithm because it must
967 check each element against all those preceding it. For long lists it
968 is more efficient to sort and then compare only adjacent elements.
972 @node SRFI-1 Association Lists
973 @subsubsection Association Lists
974 @cindex association list
977 @c FIXME::martin: Review me!
979 Association lists are described in detail in section @ref{Association
980 Lists}. The present section only documents the additional procedures
981 for dealing with association lists defined by SRFI-1.
983 @deffn {Scheme Procedure} assoc key alist [=]
984 Return the pair from @var{alist} which matches @var{key}. This
985 extends the core @code{assoc} (@pxref{Retrieving Alist Entries}) by
986 taking an optional @var{=} comparison procedure.
988 The default comparison is @code{equal?}. If an @var{=} parameter is
989 given it's called @code{(@var{=} @var{key} @var{alistcar})}, i.e.@: the
990 given target @var{key} is the first argument, and a @code{car} from
991 @var{alist} is second.
993 For example a case-insensitive string lookup,
996 (assoc "yy" '(("XX" . 1) ("YY" . 2)) string-ci=?)
1001 @deffn {Scheme Procedure} alist-cons key datum alist
1002 Cons a new association @var{key} and @var{datum} onto @var{alist} and
1003 return the result. This is equivalent to
1006 (cons (cons @var{key} @var{datum}) @var{alist})
1009 @code{acons} (@pxref{Adding or Setting Alist Entries}) in the Guile
1010 core does the same thing.
1013 @deffn {Scheme Procedure} alist-copy alist
1014 Return a newly allocated copy of @var{alist}, that means that the
1015 spine of the list as well as the pairs are copied.
1018 @deffn {Scheme Procedure} alist-delete key alist [=]
1019 @deffnx {Scheme Procedure} alist-delete! key alist [=]
1020 Return a list containing the elements of @var{alist} but with those
1021 elements whose keys are equal to @var{key} deleted. The returned
1022 elements will be in the same order as they were in @var{alist}.
1024 Equality is determined by the @var{=} predicate, or @code{equal?} if
1025 not given. The order in which elements are tested is unspecified, but
1026 each equality call is made @code{(= key alistkey)}, i.e.@: the given
1027 @var{key} parameter is first and the key from @var{alist} second.
1028 This means for instance all associations with a key greater than 5 can
1029 be removed with @code{(alist-delete 5 alist <)}.
1031 @code{alist-delete} does not modify @var{alist}, but the return might
1032 share a common tail with @var{alist}. @code{alist-delete!} may modify
1033 the list structure of @var{alist} to construct its return.
1037 @node SRFI-1 Set Operations
1038 @subsubsection Set Operations on Lists
1039 @cindex list set operation
1041 Lists can be used to represent sets of objects. The procedures in
1042 this section operate on such lists as sets.
1044 Note that lists are not an efficient way to implement large sets. The
1045 procedures here typically take time @math{@var{m}@cross{}@var{n}} when
1046 operating on @var{m} and @var{n} element lists. Other data structures
1047 like trees, bitsets (@pxref{Bit Vectors}) or hash tables (@pxref{Hash
1048 Tables}) are faster.
1050 All these procedures take an equality predicate as the first argument.
1051 This predicate is used for testing the objects in the list sets for
1052 sameness. This predicate must be consistent with @code{eq?}
1053 (@pxref{Equality}) in the sense that if two list elements are
1054 @code{eq?} then they must also be equal under the predicate. This
1055 simply means a given object must be equal to itself.
1057 @deffn {Scheme Procedure} lset<= = list @dots{}
1058 Return @code{#t} if each list is a subset of the one following it.
1059 I.e., @var{list1} is a subset of @var{list2}, @var{list2} is a subset of
1060 @var{list3}, etc., for as many lists as given. If only one list or no
1061 lists are given, the return value is @code{#t}.
1063 A list @var{x} is a subset of @var{y} if each element of @var{x} is
1064 equal to some element in @var{y}. Elements are compared using the
1065 given @var{=} procedure, called as @code{(@var{=} xelem yelem)}.
1068 (lset<= eq?) @result{} #t
1069 (lset<= eqv? '(1 2 3) '(1)) @result{} #f
1070 (lset<= eqv? '(1 3 2) '(4 3 1 2)) @result{} #t
1074 @deffn {Scheme Procedure} lset= = list @dots{}
1075 Return @code{#t} if all argument lists are set-equal. @var{list1} is
1076 compared to @var{list2}, @var{list2} to @var{list3}, etc., for as many
1077 lists as given. If only one list or no lists are given, the return
1080 Two lists @var{x} and @var{y} are set-equal if each element of @var{x}
1081 is equal to some element of @var{y} and conversely each element of
1082 @var{y} is equal to some element of @var{x}. The order of the
1083 elements in the lists doesn't matter. Element equality is determined
1084 with the given @var{=} procedure, called as @code{(@var{=} xelem
1085 yelem)}, but exactly which calls are made is unspecified.
1088 (lset= eq?) @result{} #t
1089 (lset= eqv? '(1 2 3) '(3 2 1)) @result{} #t
1090 (lset= string-ci=? '("a" "A" "b") '("B" "b" "a")) @result{} #t
1094 @deffn {Scheme Procedure} lset-adjoin = list elem @dots{}
1095 Add to @var{list} any of the given @var{elem}s not already in the list.
1096 @var{elem}s are @code{cons}ed onto the start of @var{list} (so the
1097 return value shares a common tail with @var{list}), but the order that
1098 the @var{elem}s are added is unspecified.
1100 The given @var{=} procedure is used for comparing elements, called as
1101 @code{(@var{=} listelem elem)}, i.e., the second argument is one of
1102 the given @var{elem} parameters.
1105 (lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3)
1109 @deffn {Scheme Procedure} lset-union = list @dots{}
1110 @deffnx {Scheme Procedure} lset-union! = list @dots{}
1111 Return the union of the argument list sets. The result is built by
1112 taking the union of @var{list1} and @var{list2}, then the union of
1113 that with @var{list3}, etc., for as many lists as given. For one list
1114 argument that list itself is the result, for no list arguments the
1115 result is the empty list.
1117 The union of two lists @var{x} and @var{y} is formed as follows. If
1118 @var{x} is empty then the result is @var{y}. Otherwise start with
1119 @var{x} as the result and consider each @var{y} element (from first to
1120 last). A @var{y} element not equal to something already in the result
1121 is @code{cons}ed onto the result.
1123 The given @var{=} procedure is used for comparing elements, called as
1124 @code{(@var{=} relem yelem)}. The first argument is from the result
1125 accumulated so far, and the second is from the list being union-ed in.
1126 But exactly which calls are made is otherwise unspecified.
1128 Notice that duplicate elements in @var{list1} (or the first non-empty
1129 list) are preserved, but that repeated elements in subsequent lists
1130 are only added once.
1133 (lset-union eqv?) @result{} ()
1134 (lset-union eqv? '(1 2 3)) @result{} (1 2 3)
1135 (lset-union eqv? '(1 2 1 3) '(2 4 5) '(5)) @result{} (5 4 1 2 1 3)
1138 @code{lset-union} doesn't change the given lists but the result may
1139 share a tail with the first non-empty list. @code{lset-union!} can
1140 modify all of the given lists to form the result.
1143 @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{}
1144 @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{}
1145 Return the intersection of @var{list1} with the other argument lists,
1146 meaning those elements of @var{list1} which are also in all of
1147 @var{list2} etc. For one list argument, just that list is returned.
1149 The test for an element of @var{list1} to be in the return is simply
1150 that it's equal to some element in each of @var{list2} etc. Notice
1151 this means an element appearing twice in @var{list1} but only once in
1152 each of @var{list2} etc will go into the return twice. The return has
1153 its elements in the same order as they were in @var{list1}.
1155 The given @var{=} procedure is used for comparing elements, called as
1156 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1157 and the second is from one of the subsequent lists. But exactly which
1158 calls are made and in what order is unspecified.
1161 (lset-intersection eqv? '(x y)) @result{} (x y)
1162 (lset-intersection eqv? '(1 2 3) '(4 3 2)) @result{} (2 3)
1163 (lset-intersection eqv? '(1 1 2 2) '(1 2) '(2 1) '(2)) @result{} (2 2)
1166 The return from @code{lset-intersection} may share a tail with
1167 @var{list1}. @code{lset-intersection!} may modify @var{list1} to form
1171 @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{}
1172 @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{}
1173 Return @var{list1} with any elements in @var{list2}, @var{list3} etc
1174 removed (ie.@: subtracted). For one list argument, just that list is
1177 The given @var{=} procedure is used for comparing elements, called as
1178 @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1}
1179 and the second from one of the subsequent lists. But exactly which
1180 calls are made and in what order is unspecified.
1183 (lset-difference eqv? '(x y)) @result{} (x y)
1184 (lset-difference eqv? '(1 2 3) '(3 1)) @result{} (2)
1185 (lset-difference eqv? '(1 2 3) '(3) '(2)) @result{} (1)
1188 The return from @code{lset-difference} may share a tail with
1189 @var{list1}. @code{lset-difference!} may modify @var{list1} to form
1193 @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{}
1194 @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{}
1195 Return two values (@pxref{Multiple Values}), the difference and
1196 intersection of the argument lists as per @code{lset-difference} and
1197 @code{lset-intersection} above.
1199 For two list arguments this partitions @var{list1} into those elements
1200 of @var{list1} which are in @var{list2} and not in @var{list2}. (But
1201 for more than two arguments there can be elements of @var{list1} which
1202 are neither part of the difference nor the intersection.)
1204 One of the return values from @code{lset-diff+intersection} may share
1205 a tail with @var{list1}. @code{lset-diff+intersection!} may modify
1206 @var{list1} to form its results.
1209 @deffn {Scheme Procedure} lset-xor = list @dots{}
1210 @deffnx {Scheme Procedure} lset-xor! = list @dots{}
1211 Return an XOR of the argument lists. For two lists this means those
1212 elements which are in exactly one of the lists. For more than two
1213 lists it means those elements which appear in an odd number of the
1216 To be precise, the XOR of two lists @var{x} and @var{y} is formed by
1217 taking those elements of @var{x} not equal to any element of @var{y},
1218 plus those elements of @var{y} not equal to any element of @var{x}.
1219 Equality is determined with the given @var{=} procedure, called as
1220 @code{(@var{=} e1 e2)}. One argument is from @var{x} and the other
1221 from @var{y}, but which way around is unspecified. Exactly which
1222 calls are made is also unspecified, as is the order of the elements in
1226 (lset-xor eqv? '(x y)) @result{} (x y)
1227 (lset-xor eqv? '(1 2 3) '(4 3 2)) @result{} (4 1)
1230 The return from @code{lset-xor} may share a tail with one of the list
1231 arguments. @code{lset-xor!} may modify @var{list1} to form its
1237 @subsection SRFI-2 - and-let*
1241 The following syntax can be obtained with
1244 (use-modules (srfi srfi-2))
1250 (use-modules (ice-9 and-let-star))
1253 @deffn {library syntax} and-let* (clause @dots{}) body @dots{}
1254 A combination of @code{and} and @code{let*}.
1256 Each @var{clause} is evaluated in turn, and if @code{#f} is obtained
1257 then evaluation stops and @code{#f} is returned. If all are
1258 non-@code{#f} then @var{body} is evaluated and the last form gives the
1259 return value, or if @var{body} is empty then the result is @code{#t}.
1260 Each @var{clause} should be one of the following,
1264 Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}.
1265 Like @code{let*}, that binding is available to subsequent clauses.
1267 Evaluate @var{expr} and check for @code{#f}.
1269 Get the value bound to @var{symbol} and check for @code{#f}.
1272 Notice that @code{(expr)} has an ``extra'' pair of parentheses, for
1273 instance @code{((eq? x y))}. One way to remember this is to imagine
1274 the @code{symbol} in @code{(symbol expr)} is omitted.
1276 @code{and-let*} is good for calculations where a @code{#f} value means
1277 termination, but where a non-@code{#f} value is going to be needed in
1278 subsequent expressions.
1280 The following illustrates this, it returns text between brackets
1281 @samp{[...]} in a string, or @code{#f} if there are no such brackets
1282 (ie.@: either @code{string-index} gives @code{#f}).
1285 (define (extract-brackets str)
1286 (and-let* ((start (string-index str #\[))
1287 (end (string-index str #\] start)))
1288 (substring str (1+ start) end)))
1291 The following shows plain variables and expressions tested too.
1292 @code{diagnostic-levels} is taken to be an alist associating a
1293 diagnostic type with a level. @code{str} is printed only if the type
1294 is known and its level is high enough.
1297 (define (show-diagnostic type str)
1298 (and-let* (want-diagnostics
1299 (level (assq-ref diagnostic-levels type))
1300 ((>= level current-diagnostic-level)))
1304 The advantage of @code{and-let*} is that an extended sequence of
1305 expressions and tests doesn't require lots of nesting as would arise
1306 from separate @code{and} and @code{let*}, or from @code{cond} with
1313 @subsection SRFI-4 - Homogeneous numeric vector datatypes
1316 SRFI-4 provides an interface to uniform numeric vectors: vectors whose elements
1317 are all of a single numeric type. Guile offers uniform numeric vectors for
1318 signed and unsigned 8-bit, 16-bit, 32-bit, and 64-bit integers, two sizes of
1319 floating point values, and, as an extension to SRFI-4, complex floating-point
1320 numbers of these two sizes.
1322 The standard SRFI-4 procedures and data types may be included via loading the
1326 (use-modules (srfi srfi-4))
1329 This module is currently a part of the default Guile environment, but it is a
1330 good practice to explicitly import the module. In the future, using SRFI-4
1331 procedures without importing the SRFI-4 module will cause a deprecation message
1332 to be printed. (Of course, one may call the C functions at any time. Would that
1336 * SRFI-4 Overview:: The warp and weft of uniform numeric vectors.
1337 * SRFI-4 API:: Uniform vectors, from Scheme and from C.
1338 * SRFI-4 Generic Operations:: The general, operating on the specific.
1339 * SRFI-4 and Bytevectors:: SRFI-4 vectors are backed by bytevectors.
1340 * SRFI-4 Extensions:: Guile-specific extensions to the standard.
1343 @node SRFI-4 Overview
1344 @subsubsection SRFI-4 - Overview
1346 Uniform numeric vectors can be useful since they consume less memory
1347 than the non-uniform, general vectors. Also, since the types they can
1348 store correspond directly to C types, it is easier to work with them
1349 efficiently on a low level. Consider image processing as an example,
1350 where you want to apply a filter to some image. While you could store
1351 the pixels of an image in a general vector and write a general
1352 convolution function, things are much more efficient with uniform
1353 vectors: the convolution function knows that all pixels are unsigned
1354 8-bit values (say), and can use a very tight inner loop.
1356 This is implemented in Scheme by having the compiler notice calls to the SRFI-4
1357 accessors, and inline them to appropriate compiled code. From C you have access
1358 to the raw array; functions for efficiently working with uniform numeric vectors
1359 from C are listed at the end of this section.
1361 Uniform numeric vectors are the special case of one dimensional uniform
1364 There are 12 standard kinds of uniform numeric vectors, and they all have their
1365 own complement of constructors, accessors, and so on. Procedures that operate on
1366 a specific kind of uniform numeric vector have a ``tag'' in their name,
1367 indicating the element type.
1371 unsigned 8-bit integers
1374 signed 8-bit integers
1377 unsigned 16-bit integers
1380 signed 16-bit integers
1383 unsigned 32-bit integers
1386 signed 32-bit integers
1389 unsigned 64-bit integers
1392 signed 64-bit integers
1395 the C type @code{float}
1398 the C type @code{double}
1402 In addition, Guile supports uniform arrays of complex numbers, with the
1408 complex numbers in rectangular form with the real and imaginary part
1409 being a @code{float}
1412 complex numbers in rectangular form with the real and imaginary part
1413 being a @code{double}
1417 The external representation (ie.@: read syntax) for these vectors is
1418 similar to normal Scheme vectors, but with an additional tag from the
1419 tables above indicating the vector's type. For example,
1426 Note that the read syntax for floating-point here conflicts with
1427 @code{#f} for false. In Standard Scheme one can write @code{(1 #f3)}
1428 for a three element list @code{(1 #f 3)}, but for Guile @code{(1 #f3)}
1429 is invalid. @code{(1 #f 3)} is almost certainly what one should write
1430 anyway to make the intention clear, so this is rarely a problem.
1434 @subsubsection SRFI-4 - API
1436 Note that the @nicode{c32} and @nicode{c64} functions are only available from
1437 @nicode{(srfi srfi-4 gnu)}.
1439 @deffn {Scheme Procedure} u8vector? obj
1440 @deffnx {Scheme Procedure} s8vector? obj
1441 @deffnx {Scheme Procedure} u16vector? obj
1442 @deffnx {Scheme Procedure} s16vector? obj
1443 @deffnx {Scheme Procedure} u32vector? obj
1444 @deffnx {Scheme Procedure} s32vector? obj
1445 @deffnx {Scheme Procedure} u64vector? obj
1446 @deffnx {Scheme Procedure} s64vector? obj
1447 @deffnx {Scheme Procedure} f32vector? obj
1448 @deffnx {Scheme Procedure} f64vector? obj
1449 @deffnx {Scheme Procedure} c32vector? obj
1450 @deffnx {Scheme Procedure} c64vector? obj
1451 @deffnx {C Function} scm_u8vector_p (obj)
1452 @deffnx {C Function} scm_s8vector_p (obj)
1453 @deffnx {C Function} scm_u16vector_p (obj)
1454 @deffnx {C Function} scm_s16vector_p (obj)
1455 @deffnx {C Function} scm_u32vector_p (obj)
1456 @deffnx {C Function} scm_s32vector_p (obj)
1457 @deffnx {C Function} scm_u64vector_p (obj)
1458 @deffnx {C Function} scm_s64vector_p (obj)
1459 @deffnx {C Function} scm_f32vector_p (obj)
1460 @deffnx {C Function} scm_f64vector_p (obj)
1461 @deffnx {C Function} scm_c32vector_p (obj)
1462 @deffnx {C Function} scm_c64vector_p (obj)
1463 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1467 @deffn {Scheme Procedure} make-u8vector n [value]
1468 @deffnx {Scheme Procedure} make-s8vector n [value]
1469 @deffnx {Scheme Procedure} make-u16vector n [value]
1470 @deffnx {Scheme Procedure} make-s16vector n [value]
1471 @deffnx {Scheme Procedure} make-u32vector n [value]
1472 @deffnx {Scheme Procedure} make-s32vector n [value]
1473 @deffnx {Scheme Procedure} make-u64vector n [value]
1474 @deffnx {Scheme Procedure} make-s64vector n [value]
1475 @deffnx {Scheme Procedure} make-f32vector n [value]
1476 @deffnx {Scheme Procedure} make-f64vector n [value]
1477 @deffnx {Scheme Procedure} make-c32vector n [value]
1478 @deffnx {Scheme Procedure} make-c64vector n [value]
1479 @deffnx {C Function} scm_make_u8vector (n, value)
1480 @deffnx {C Function} scm_make_s8vector (n, value)
1481 @deffnx {C Function} scm_make_u16vector (n, value)
1482 @deffnx {C Function} scm_make_s16vector (n, value)
1483 @deffnx {C Function} scm_make_u32vector (n, value)
1484 @deffnx {C Function} scm_make_s32vector (n, value)
1485 @deffnx {C Function} scm_make_u64vector (n, value)
1486 @deffnx {C Function} scm_make_s64vector (n, value)
1487 @deffnx {C Function} scm_make_f32vector (n, value)
1488 @deffnx {C Function} scm_make_f64vector (n, value)
1489 @deffnx {C Function} scm_make_c32vector (n, value)
1490 @deffnx {C Function} scm_make_c64vector (n, value)
1491 Return a newly allocated homogeneous numeric vector holding @var{n}
1492 elements of the indicated type. If @var{value} is given, the vector
1493 is initialized with that value, otherwise the contents are
1497 @deffn {Scheme Procedure} u8vector value @dots{}
1498 @deffnx {Scheme Procedure} s8vector value @dots{}
1499 @deffnx {Scheme Procedure} u16vector value @dots{}
1500 @deffnx {Scheme Procedure} s16vector value @dots{}
1501 @deffnx {Scheme Procedure} u32vector value @dots{}
1502 @deffnx {Scheme Procedure} s32vector value @dots{}
1503 @deffnx {Scheme Procedure} u64vector value @dots{}
1504 @deffnx {Scheme Procedure} s64vector value @dots{}
1505 @deffnx {Scheme Procedure} f32vector value @dots{}
1506 @deffnx {Scheme Procedure} f64vector value @dots{}
1507 @deffnx {Scheme Procedure} c32vector value @dots{}
1508 @deffnx {Scheme Procedure} c64vector value @dots{}
1509 @deffnx {C Function} scm_u8vector (values)
1510 @deffnx {C Function} scm_s8vector (values)
1511 @deffnx {C Function} scm_u16vector (values)
1512 @deffnx {C Function} scm_s16vector (values)
1513 @deffnx {C Function} scm_u32vector (values)
1514 @deffnx {C Function} scm_s32vector (values)
1515 @deffnx {C Function} scm_u64vector (values)
1516 @deffnx {C Function} scm_s64vector (values)
1517 @deffnx {C Function} scm_f32vector (values)
1518 @deffnx {C Function} scm_f64vector (values)
1519 @deffnx {C Function} scm_c32vector (values)
1520 @deffnx {C Function} scm_c64vector (values)
1521 Return a newly allocated homogeneous numeric vector of the indicated
1522 type, holding the given parameter @var{value}s. The vector length is
1523 the number of parameters given.
1526 @deffn {Scheme Procedure} u8vector-length vec
1527 @deffnx {Scheme Procedure} s8vector-length vec
1528 @deffnx {Scheme Procedure} u16vector-length vec
1529 @deffnx {Scheme Procedure} s16vector-length vec
1530 @deffnx {Scheme Procedure} u32vector-length vec
1531 @deffnx {Scheme Procedure} s32vector-length vec
1532 @deffnx {Scheme Procedure} u64vector-length vec
1533 @deffnx {Scheme Procedure} s64vector-length vec
1534 @deffnx {Scheme Procedure} f32vector-length vec
1535 @deffnx {Scheme Procedure} f64vector-length vec
1536 @deffnx {Scheme Procedure} c32vector-length vec
1537 @deffnx {Scheme Procedure} c64vector-length vec
1538 @deffnx {C Function} scm_u8vector_length (vec)
1539 @deffnx {C Function} scm_s8vector_length (vec)
1540 @deffnx {C Function} scm_u16vector_length (vec)
1541 @deffnx {C Function} scm_s16vector_length (vec)
1542 @deffnx {C Function} scm_u32vector_length (vec)
1543 @deffnx {C Function} scm_s32vector_length (vec)
1544 @deffnx {C Function} scm_u64vector_length (vec)
1545 @deffnx {C Function} scm_s64vector_length (vec)
1546 @deffnx {C Function} scm_f32vector_length (vec)
1547 @deffnx {C Function} scm_f64vector_length (vec)
1548 @deffnx {C Function} scm_c32vector_length (vec)
1549 @deffnx {C Function} scm_c64vector_length (vec)
1550 Return the number of elements in @var{vec}.
1553 @deffn {Scheme Procedure} u8vector-ref vec i
1554 @deffnx {Scheme Procedure} s8vector-ref vec i
1555 @deffnx {Scheme Procedure} u16vector-ref vec i
1556 @deffnx {Scheme Procedure} s16vector-ref vec i
1557 @deffnx {Scheme Procedure} u32vector-ref vec i
1558 @deffnx {Scheme Procedure} s32vector-ref vec i
1559 @deffnx {Scheme Procedure} u64vector-ref vec i
1560 @deffnx {Scheme Procedure} s64vector-ref vec i
1561 @deffnx {Scheme Procedure} f32vector-ref vec i
1562 @deffnx {Scheme Procedure} f64vector-ref vec i
1563 @deffnx {Scheme Procedure} c32vector-ref vec i
1564 @deffnx {Scheme Procedure} c64vector-ref vec i
1565 @deffnx {C Function} scm_u8vector_ref (vec, i)
1566 @deffnx {C Function} scm_s8vector_ref (vec, i)
1567 @deffnx {C Function} scm_u16vector_ref (vec, i)
1568 @deffnx {C Function} scm_s16vector_ref (vec, i)
1569 @deffnx {C Function} scm_u32vector_ref (vec, i)
1570 @deffnx {C Function} scm_s32vector_ref (vec, i)
1571 @deffnx {C Function} scm_u64vector_ref (vec, i)
1572 @deffnx {C Function} scm_s64vector_ref (vec, i)
1573 @deffnx {C Function} scm_f32vector_ref (vec, i)
1574 @deffnx {C Function} scm_f64vector_ref (vec, i)
1575 @deffnx {C Function} scm_c32vector_ref (vec, i)
1576 @deffnx {C Function} scm_c64vector_ref (vec, i)
1577 Return the element at index @var{i} in @var{vec}. The first element
1578 in @var{vec} is index 0.
1581 @deffn {Scheme Procedure} u8vector-set! vec i value
1582 @deffnx {Scheme Procedure} s8vector-set! vec i value
1583 @deffnx {Scheme Procedure} u16vector-set! vec i value
1584 @deffnx {Scheme Procedure} s16vector-set! vec i value
1585 @deffnx {Scheme Procedure} u32vector-set! vec i value
1586 @deffnx {Scheme Procedure} s32vector-set! vec i value
1587 @deffnx {Scheme Procedure} u64vector-set! vec i value
1588 @deffnx {Scheme Procedure} s64vector-set! vec i value
1589 @deffnx {Scheme Procedure} f32vector-set! vec i value
1590 @deffnx {Scheme Procedure} f64vector-set! vec i value
1591 @deffnx {Scheme Procedure} c32vector-set! vec i value
1592 @deffnx {Scheme Procedure} c64vector-set! vec i value
1593 @deffnx {C Function} scm_u8vector_set_x (vec, i, value)
1594 @deffnx {C Function} scm_s8vector_set_x (vec, i, value)
1595 @deffnx {C Function} scm_u16vector_set_x (vec, i, value)
1596 @deffnx {C Function} scm_s16vector_set_x (vec, i, value)
1597 @deffnx {C Function} scm_u32vector_set_x (vec, i, value)
1598 @deffnx {C Function} scm_s32vector_set_x (vec, i, value)
1599 @deffnx {C Function} scm_u64vector_set_x (vec, i, value)
1600 @deffnx {C Function} scm_s64vector_set_x (vec, i, value)
1601 @deffnx {C Function} scm_f32vector_set_x (vec, i, value)
1602 @deffnx {C Function} scm_f64vector_set_x (vec, i, value)
1603 @deffnx {C Function} scm_c32vector_set_x (vec, i, value)
1604 @deffnx {C Function} scm_c64vector_set_x (vec, i, value)
1605 Set the element at index @var{i} in @var{vec} to @var{value}. The
1606 first element in @var{vec} is index 0. The return value is
1610 @deffn {Scheme Procedure} u8vector->list vec
1611 @deffnx {Scheme Procedure} s8vector->list vec
1612 @deffnx {Scheme Procedure} u16vector->list vec
1613 @deffnx {Scheme Procedure} s16vector->list vec
1614 @deffnx {Scheme Procedure} u32vector->list vec
1615 @deffnx {Scheme Procedure} s32vector->list vec
1616 @deffnx {Scheme Procedure} u64vector->list vec
1617 @deffnx {Scheme Procedure} s64vector->list vec
1618 @deffnx {Scheme Procedure} f32vector->list vec
1619 @deffnx {Scheme Procedure} f64vector->list vec
1620 @deffnx {Scheme Procedure} c32vector->list vec
1621 @deffnx {Scheme Procedure} c64vector->list vec
1622 @deffnx {C Function} scm_u8vector_to_list (vec)
1623 @deffnx {C Function} scm_s8vector_to_list (vec)
1624 @deffnx {C Function} scm_u16vector_to_list (vec)
1625 @deffnx {C Function} scm_s16vector_to_list (vec)
1626 @deffnx {C Function} scm_u32vector_to_list (vec)
1627 @deffnx {C Function} scm_s32vector_to_list (vec)
1628 @deffnx {C Function} scm_u64vector_to_list (vec)
1629 @deffnx {C Function} scm_s64vector_to_list (vec)
1630 @deffnx {C Function} scm_f32vector_to_list (vec)
1631 @deffnx {C Function} scm_f64vector_to_list (vec)
1632 @deffnx {C Function} scm_c32vector_to_list (vec)
1633 @deffnx {C Function} scm_c64vector_to_list (vec)
1634 Return a newly allocated list holding all elements of @var{vec}.
1637 @deffn {Scheme Procedure} list->u8vector lst
1638 @deffnx {Scheme Procedure} list->s8vector lst
1639 @deffnx {Scheme Procedure} list->u16vector lst
1640 @deffnx {Scheme Procedure} list->s16vector lst
1641 @deffnx {Scheme Procedure} list->u32vector lst
1642 @deffnx {Scheme Procedure} list->s32vector lst
1643 @deffnx {Scheme Procedure} list->u64vector lst
1644 @deffnx {Scheme Procedure} list->s64vector lst
1645 @deffnx {Scheme Procedure} list->f32vector lst
1646 @deffnx {Scheme Procedure} list->f64vector lst
1647 @deffnx {Scheme Procedure} list->c32vector lst
1648 @deffnx {Scheme Procedure} list->c64vector lst
1649 @deffnx {C Function} scm_list_to_u8vector (lst)
1650 @deffnx {C Function} scm_list_to_s8vector (lst)
1651 @deffnx {C Function} scm_list_to_u16vector (lst)
1652 @deffnx {C Function} scm_list_to_s16vector (lst)
1653 @deffnx {C Function} scm_list_to_u32vector (lst)
1654 @deffnx {C Function} scm_list_to_s32vector (lst)
1655 @deffnx {C Function} scm_list_to_u64vector (lst)
1656 @deffnx {C Function} scm_list_to_s64vector (lst)
1657 @deffnx {C Function} scm_list_to_f32vector (lst)
1658 @deffnx {C Function} scm_list_to_f64vector (lst)
1659 @deffnx {C Function} scm_list_to_c32vector (lst)
1660 @deffnx {C Function} scm_list_to_c64vector (lst)
1661 Return a newly allocated homogeneous numeric vector of the indicated type,
1662 initialized with the elements of the list @var{lst}.
1665 @deftypefn {C Function} SCM scm_take_u8vector (const scm_t_uint8 *data, size_t len)
1666 @deftypefnx {C Function} SCM scm_take_s8vector (const scm_t_int8 *data, size_t len)
1667 @deftypefnx {C Function} SCM scm_take_u16vector (const scm_t_uint16 *data, size_t len)
1668 @deftypefnx {C Function} SCM scm_take_s16vector (const scm_t_int16 *data, size_t len)
1669 @deftypefnx {C Function} SCM scm_take_u32vector (const scm_t_uint32 *data, size_t len)
1670 @deftypefnx {C Function} SCM scm_take_s32vector (const scm_t_int32 *data, size_t len)
1671 @deftypefnx {C Function} SCM scm_take_u64vector (const scm_t_uint64 *data, size_t len)
1672 @deftypefnx {C Function} SCM scm_take_s64vector (const scm_t_int64 *data, size_t len)
1673 @deftypefnx {C Function} SCM scm_take_f32vector (const float *data, size_t len)
1674 @deftypefnx {C Function} SCM scm_take_f64vector (const double *data, size_t len)
1675 @deftypefnx {C Function} SCM scm_take_c32vector (const float *data, size_t len)
1676 @deftypefnx {C Function} SCM scm_take_c64vector (const double *data, size_t len)
1677 Return a new uniform numeric vector of the indicated type and length
1678 that uses the memory pointed to by @var{data} to store its elements.
1679 This memory will eventually be freed with @code{free}. The argument
1680 @var{len} specifies the number of elements in @var{data}, not its size
1683 The @code{c32} and @code{c64} variants take a pointer to a C array of
1684 @code{float}s or @code{double}s. The real parts of the complex numbers
1685 are at even indices in that array, the corresponding imaginary parts are
1686 at the following odd index.
1689 @deftypefn {C Function} {const scm_t_uint8 *} scm_u8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1690 @deftypefnx {C Function} {const scm_t_int8 *} scm_s8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1691 @deftypefnx {C Function} {const scm_t_uint16 *} scm_u16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1692 @deftypefnx {C Function} {const scm_t_int16 *} scm_s16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1693 @deftypefnx {C Function} {const scm_t_uint32 *} scm_u32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1694 @deftypefnx {C Function} {const scm_t_int32 *} scm_s32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1695 @deftypefnx {C Function} {const scm_t_uint64 *} scm_u64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1696 @deftypefnx {C Function} {const scm_t_int64 *} scm_s64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1697 @deftypefnx {C Function} {const float *} scm_f32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1698 @deftypefnx {C Function} {const double *} scm_f64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1699 @deftypefnx {C Function} {const float *} scm_c32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1700 @deftypefnx {C Function} {const double *} scm_c64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1701 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1702 returns a pointer to the elements of a uniform numeric vector of the
1706 @deftypefn {C Function} {scm_t_uint8 *} scm_u8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1707 @deftypefnx {C Function} {scm_t_int8 *} scm_s8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1708 @deftypefnx {C Function} {scm_t_uint16 *} scm_u16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1709 @deftypefnx {C Function} {scm_t_int16 *} scm_s16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1710 @deftypefnx {C Function} {scm_t_uint32 *} scm_u32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1711 @deftypefnx {C Function} {scm_t_int32 *} scm_s32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1712 @deftypefnx {C Function} {scm_t_uint64 *} scm_u64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1713 @deftypefnx {C Function} {scm_t_int64 *} scm_s64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1714 @deftypefnx {C Function} {float *} scm_f32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1715 @deftypefnx {C Function} {double *} scm_f64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1716 @deftypefnx {C Function} {float *} scm_c32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1717 @deftypefnx {C Function} {double *} scm_c64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1718 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1719 C}), but returns a pointer to the elements of a uniform numeric vector
1720 of the indicated kind.
1723 @node SRFI-4 Generic Operations
1724 @subsubsection SRFI-4 - Generic operations
1726 Guile also provides procedures that operate on all types of uniform numeric
1727 vectors. In what is probably a bug, these procedures are currently available in
1728 the default environment as well; however prudent hackers will make sure to
1729 import @code{(srfi srfi-4 gnu)} before using these.
1731 @deftypefn {C Function} int scm_is_uniform_vector (SCM uvec)
1732 Return non-zero when @var{uvec} is a uniform numeric vector, zero
1736 @deftypefn {C Function} size_t scm_c_uniform_vector_length (SCM uvec)
1737 Return the number of elements of @var{uvec} as a @code{size_t}.
1740 @deffn {Scheme Procedure} uniform-vector? obj
1741 @deffnx {C Function} scm_uniform_vector_p (obj)
1742 Return @code{#t} if @var{obj} is a homogeneous numeric vector of the
1746 @deffn {Scheme Procedure} uniform-vector-length vec
1747 @deffnx {C Function} scm_uniform_vector_length (vec)
1748 Return the number of elements in @var{vec}.
1751 @deffn {Scheme Procedure} uniform-vector-ref vec i
1752 @deffnx {C Function} scm_uniform_vector_ref (vec, i)
1753 Return the element at index @var{i} in @var{vec}. The first element
1754 in @var{vec} is index 0.
1757 @deffn {Scheme Procedure} uniform-vector-set! vec i value
1758 @deffnx {C Function} scm_uniform_vector_set_x (vec, i, value)
1759 Set the element at index @var{i} in @var{vec} to @var{value}. The
1760 first element in @var{vec} is index 0. The return value is
1764 @deffn {Scheme Procedure} uniform-vector->list vec
1765 @deffnx {C Function} scm_uniform_vector_to_list (vec)
1766 Return a newly allocated list holding all elements of @var{vec}.
1769 @deftypefn {C Function} {const void *} scm_uniform_vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1770 Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but
1771 returns a pointer to the elements of a uniform numeric vector.
1774 @deftypefn {C Function} {void *} scm_uniform_vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)
1775 Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from
1776 C}), but returns a pointer to the elements of a uniform numeric vector.
1779 Unless you really need to the limited generality of these functions, it
1780 is best to use the type-specific functions, or the array accessors.
1782 @node SRFI-4 and Bytevectors
1783 @subsubsection SRFI-4 - Relation to bytevectors
1785 Guile implements SRFI-4 vectors using bytevectors (@pxref{Bytevectors}). Often
1786 when you have a numeric vector, you end up wanting to write its bytes somewhere,
1787 or have access to the underlying bytes, or read in bytes from somewhere else.
1788 Bytevectors are very good at this sort of thing. But the SRFI-4 APIs are nicer
1789 to use when doing number-crunching, because they are addressed by element and
1792 So as a compromise, Guile allows all bytevector functions to operate on numeric
1793 vectors. They address the underlying bytes in the native endianness, as one
1796 Following the same reasoning, that it's just bytes underneath, Guile also allows
1797 uniform vectors of a given type to be accessed as if they were of any type. One
1798 can fill a @nicode{u32vector}, and access its elements with
1799 @nicode{u8vector-ref}. One can use @nicode{f64vector-ref} on bytevectors. It's
1800 all the same to Guile.
1802 In this way, uniform numeric vectors may be written to and read from
1803 input/output ports using the procedures that operate on bytevectors.
1805 @xref{Bytevectors}, for more information.
1808 @node SRFI-4 Extensions
1809 @subsubsection SRFI-4 - Guile extensions
1811 Guile defines some useful extensions to SRFI-4, which are not available in the
1812 default Guile environment. They may be imported by loading the extensions
1816 (use-modules (srfi srfi-4 gnu))
1819 @deffn {Scheme Procedure} any->u8vector obj
1820 @deffnx {Scheme Procedure} any->s8vector obj
1821 @deffnx {Scheme Procedure} any->u16vector obj
1822 @deffnx {Scheme Procedure} any->s16vector obj
1823 @deffnx {Scheme Procedure} any->u32vector obj
1824 @deffnx {Scheme Procedure} any->s32vector obj
1825 @deffnx {Scheme Procedure} any->u64vector obj
1826 @deffnx {Scheme Procedure} any->s64vector obj
1827 @deffnx {Scheme Procedure} any->f32vector obj
1828 @deffnx {Scheme Procedure} any->f64vector obj
1829 @deffnx {Scheme Procedure} any->c32vector obj
1830 @deffnx {Scheme Procedure} any->c64vector obj
1831 @deffnx {C Function} scm_any_to_u8vector (obj)
1832 @deffnx {C Function} scm_any_to_s8vector (obj)
1833 @deffnx {C Function} scm_any_to_u16vector (obj)
1834 @deffnx {C Function} scm_any_to_s16vector (obj)
1835 @deffnx {C Function} scm_any_to_u32vector (obj)
1836 @deffnx {C Function} scm_any_to_s32vector (obj)
1837 @deffnx {C Function} scm_any_to_u64vector (obj)
1838 @deffnx {C Function} scm_any_to_s64vector (obj)
1839 @deffnx {C Function} scm_any_to_f32vector (obj)
1840 @deffnx {C Function} scm_any_to_f64vector (obj)
1841 @deffnx {C Function} scm_any_to_c32vector (obj)
1842 @deffnx {C Function} scm_any_to_c64vector (obj)
1843 Return a (maybe newly allocated) uniform numeric vector of the indicated
1844 type, initialized with the elements of @var{obj}, which must be a list,
1845 a vector, or a uniform vector. When @var{obj} is already a suitable
1846 uniform numeric vector, it is returned unchanged.
1851 @subsection SRFI-6 - Basic String Ports
1854 SRFI-6 defines the procedures @code{open-input-string},
1855 @code{open-output-string} and @code{get-output-string}. These
1856 procedures are included in the Guile core, so using this module does not
1857 make any difference at the moment. But it is possible that support for
1858 SRFI-6 will be factored out of the core library in the future, so using
1859 this module does not hurt, after all.
1862 @subsection SRFI-8 - receive
1865 @code{receive} is a syntax for making the handling of multiple-value
1866 procedures easier. It is documented in @xref{Multiple Values}.
1870 @subsection SRFI-9 - define-record-type
1872 This SRFI is a syntax for defining new record types and creating
1873 predicate, constructor, and field getter and setter functions. It is
1874 documented in the ``Compound Data Types'' section of the manual
1875 (@pxref{SRFI-9 Records}).
1879 @subsection SRFI-10 - Hash-Comma Reader Extension
1884 This SRFI implements a reader extension @code{#,()} called hash-comma.
1885 It allows the reader to give new kinds of objects, for use both in
1886 data and as constants or literals in source code. This feature is
1890 (use-modules (srfi srfi-10))
1894 The new read syntax is of the form
1897 #,(@var{tag} @var{arg}@dots{})
1901 where @var{tag} is a symbol and the @var{arg}s are objects taken as
1902 parameters. @var{tag}s are registered with the following procedure.
1904 @deffn {Scheme Procedure} define-reader-ctor tag proc
1905 Register @var{proc} as the constructor for a hash-comma read syntax
1906 starting with symbol @var{tag}, i.e.@: @nicode{#,(@var{tag} arg@dots{})}.
1907 @var{proc} is called with the given arguments @code{(@var{proc}
1908 arg@dots{})} and the object it returns is the result of the read.
1912 For example, a syntax giving a list of @var{N} copies of an object.
1915 (define-reader-ctor 'repeat
1917 (make-list reps obj)))
1919 (display '#,(repeat 99 3))
1923 Notice the quote @nicode{'} when the @nicode{#,( )} is used. The
1924 @code{repeat} handler returns a list and the program must quote to use
1925 it literally, the same as any other list. Ie.
1928 (display '#,(repeat 99 3))
1930 (display '(99 99 99))
1933 When a handler returns an object which is self-evaluating, like a
1934 number or a string, then there's no need for quoting, just as there's
1935 no need when giving those directly as literals. For example an
1939 (define-reader-ctor 'sum
1942 (display #,(sum 123 456)) @print{} 579
1945 A typical use for @nicode{#,()} is to get a read syntax for objects
1946 which don't otherwise have one. For example, the following allows a
1947 hash table to be given literally, with tags and values, ready for fast
1951 (define-reader-ctor 'hash
1953 (let ((table (make-hash-table)))
1954 (for-each (lambda (elem)
1955 (apply hash-set! table elem))
1959 (define (animal->family animal)
1960 (hash-ref '#,(hash ("tiger" "cat")
1965 (animal->family "lion") @result{} "cat"
1968 Or for example the following is a syntax for a compiled regular
1969 expression (@pxref{Regular Expressions}).
1972 (use-modules (ice-9 regex))
1974 (define-reader-ctor 'regexp make-regexp)
1976 (define (extract-angs str)
1977 (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str)))
1979 (match:substring match 1))))
1981 (extract-angs "foo <BAR> quux") @result{} "BAR"
1985 @nicode{#,()} is somewhat similar to @code{define-macro}
1986 (@pxref{Macros}) in that handler code is run to produce a result, but
1987 @nicode{#,()} operates at the read stage, so it can appear in data for
1988 @code{read} (@pxref{Scheme Read}), not just in code to be executed.
1990 Because @nicode{#,()} is handled at read-time it has no direct access
1991 to variables etc. A symbol in the arguments is just a symbol, not a
1992 variable reference. The arguments are essentially constants, though
1993 the handler procedure can use them in any complicated way it might
1996 Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available
1997 globally, there's no need to use @code{(srfi srfi-10)} in later
1998 modules. Similarly the tags registered are global and can be used
1999 anywhere once registered.
2001 There's no attempt to record what previous @nicode{#,()} forms have
2002 been seen, if two identical forms occur then two calls are made to the
2003 handler procedure. The handler might like to maintain a cache or
2004 similar to avoid making copies of large objects, depending on expected
2007 In code the best uses of @nicode{#,()} are generally when there's a
2008 lot of objects of a particular kind as literals or constants. If
2009 there's just a few then some local variables and initializers are
2010 fine, but that becomes tedious and error prone when there's a lot, and
2011 the anonymous and compact syntax of @nicode{#,()} is much better.
2015 @subsection SRFI-11 - let-values
2020 This module implements the binding forms for multiple values
2021 @code{let-values} and @code{let*-values}. These forms are similar to
2022 @code{let} and @code{let*} (@pxref{Local Bindings}), but they support
2023 binding of the values returned by multiple-valued expressions.
2025 Write @code{(use-modules (srfi srfi-11))} to make the bindings
2029 (let-values (((x y) (values 1 2))
2030 ((z f) (values 3 4)))
2036 @code{let-values} performs all bindings simultaneously, which means that
2037 no expression in the binding clauses may refer to variables bound in the
2038 same clause list. @code{let*-values}, on the other hand, performs the
2039 bindings sequentially, just like @code{let*} does for single-valued
2044 @subsection SRFI-13 - String Library
2047 The SRFI-13 procedures are always available, @xref{Strings}.
2050 @subsection SRFI-14 - Character-set Library
2053 The SRFI-14 data type and procedures are always available,
2054 @xref{Character Sets}.
2057 @subsection SRFI-16 - case-lambda
2059 @cindex variable arity
2060 @cindex arity, variable
2062 SRFI-16 defines a variable-arity @code{lambda} form,
2063 @code{case-lambda}. This form is available in the default Guile
2064 environment. @xref{Case-lambda}, for more information.
2067 @subsection SRFI-17 - Generalized set!
2070 This SRFI implements a generalized @code{set!}, allowing some
2071 ``referencing'' functions to be used as the target location of a
2072 @code{set!}. This feature is available from
2075 (use-modules (srfi srfi-17))
2079 For example @code{vector-ref} is extended so that
2082 (set! (vector-ref vec idx) new-value)
2089 (vector-set! vec idx new-value)
2092 The idea is that a @code{vector-ref} expression identifies a location,
2093 which may be either fetched or stored. The same form is used for the
2094 location in both cases, encouraging visual clarity. This is similar
2095 to the idea of an ``lvalue'' in C.
2097 The mechanism for this kind of @code{set!} is in the Guile core
2098 (@pxref{Procedures with Setters}). This module adds definitions of
2099 the following functions as procedures with setters, allowing them to
2100 be targets of a @code{set!},
2103 @nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr},
2104 @nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr},
2105 @nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr},
2106 @nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr},
2107 @nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr},
2108 @nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr},
2109 @nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr},
2110 @nicode{cdddar}, @nicode{cddddr}
2112 @nicode{string-ref}, @nicode{vector-ref}
2115 The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as
2116 a procedure with setter, allowing the setter for a procedure to be
2117 changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}.
2118 Currently Guile does not implement this, a setter can only be
2119 specified on creation (@code{getter-with-setter} below).
2121 @defun getter-with-setter
2122 The same as the Guile core @code{make-procedure-with-setter}
2123 (@pxref{Procedures with Setters}).
2128 @subsection SRFI-18 - Multithreading support
2131 This is an implementation of the SRFI-18 threading and synchronization
2132 library. The functions and variables described here are provided by
2135 (use-modules (srfi srfi-18))
2138 As a general rule, the data types and functions in this SRFI-18
2139 implementation are compatible with the types and functions in Guile's
2140 core threading code. For example, mutexes created with the SRFI-18
2141 @code{make-mutex} function can be passed to the built-in Guile
2142 function @code{lock-mutex} (@pxref{Mutexes and Condition Variables}),
2143 and mutexes created with the built-in Guile function @code{make-mutex}
2144 can be passed to the SRFI-18 function @code{mutex-lock!}. Cases in
2145 which this does not hold true are noted in the following sections.
2148 * SRFI-18 Threads:: Executing code
2149 * SRFI-18 Mutexes:: Mutual exclusion devices
2150 * SRFI-18 Condition variables:: Synchronizing of groups of threads
2151 * SRFI-18 Time:: Representation of times and durations
2152 * SRFI-18 Exceptions:: Signalling and handling errors
2155 @node SRFI-18 Threads
2156 @subsubsection SRFI-18 Threads
2158 Threads created by SRFI-18 differ in two ways from threads created by
2159 Guile's built-in thread functions. First, a thread created by SRFI-18
2160 @code{make-thread} begins in a blocked state and will not start
2161 execution until @code{thread-start!} is called on it. Second, SRFI-18
2162 threads are constructed with a top-level exception handler that
2163 captures any exceptions that are thrown on thread exit. In all other
2164 regards, SRFI-18 threads are identical to normal Guile threads.
2166 @defun current-thread
2167 Returns the thread that called this function. This is the same
2168 procedure as the same-named built-in procedure @code{current-thread}
2173 Returns @code{#t} if @var{obj} is a thread, @code{#f} otherwise. This
2174 is the same procedure as the same-named built-in procedure
2175 @code{thread?} (@pxref{Threads}).
2178 @defun make-thread thunk [name]
2179 Call @code{thunk} in a new thread and with a new dynamic state,
2180 returning the new thread and optionally assigning it the object name
2181 @var{name}, which may be any Scheme object.
2183 Note that the name @code{make-thread} conflicts with the
2184 @code{(ice-9 threads)} function @code{make-thread}. Applications
2185 wanting to use both of these functions will need to refer to them by
2189 @defun thread-name thread
2190 Returns the name assigned to @var{thread} at the time of its creation,
2191 or @code{#f} if it was not given a name.
2194 @defun thread-specific thread
2195 @defunx thread-specific-set! thread obj
2196 Get or set the ``object-specific'' property of @var{thread}. In
2197 Guile's implementation of SRFI-18, this value is stored as an object
2198 property, and will be @code{#f} if not set.
2201 @defun thread-start! thread
2202 Unblocks @var{thread} and allows it to begin execution if it has not
2206 @defun thread-yield!
2207 If one or more threads are waiting to execute, calling
2208 @code{thread-yield!} forces an immediate context switch to one of them.
2209 Otherwise, @code{thread-yield!} has no effect. @code{thread-yield!}
2210 behaves identically to the Guile built-in function @code{yield}.
2213 @defun thread-sleep! timeout
2214 The current thread waits until the point specified by the time object
2215 @var{timeout} is reached (@pxref{SRFI-18 Time}). This blocks the
2216 thread only if @var{timeout} represents a point in the future. it is
2217 an error for @var{timeout} to be @code{#f}.
2220 @defun thread-terminate! thread
2221 Causes an abnormal termination of @var{thread}. If @var{thread} is
2222 not already terminated, all mutexes owned by @var{thread} become
2223 unlocked/abandoned. If @var{thread} is the current thread,
2224 @code{thread-terminate!} does not return. Otherwise
2225 @code{thread-terminate!} returns an unspecified value; the termination
2226 of @var{thread} will occur before @code{thread-terminate!} returns.
2227 Subsequent attempts to join on @var{thread} will cause a ``terminated
2228 thread exception'' to be raised.
2230 @code{thread-terminate!} is compatible with the thread cancellation
2231 procedures in the core threads API (@pxref{Threads}) in that if a
2232 cleanup handler has been installed for the target thread, it will be
2233 called before the thread exits and its return value (or exception, if
2234 any) will be stored for later retrieval via a call to
2235 @code{thread-join!}.
2238 @defun thread-join! thread [timeout [timeout-val]]
2239 Wait for @var{thread} to terminate and return its exit value. When a
2240 time value @var{timeout} is given, it specifies a point in time where
2241 the waiting should be aborted. When the waiting is aborted,
2242 @var{timeout-val} is returned if it is specified; otherwise, a
2243 @code{join-timeout-exception} exception is raised
2244 (@pxref{SRFI-18 Exceptions}). Exceptions may also be raised if the
2245 thread was terminated by a call to @code{thread-terminate!}
2246 (@code{terminated-thread-exception} will be raised) or if the thread
2247 exited by raising an exception that was handled by the top-level
2248 exception handler (@code{uncaught-exception} will be raised; the
2249 original exception can be retrieved using
2250 @code{uncaught-exception-reason}).
2254 @node SRFI-18 Mutexes
2255 @subsubsection SRFI-18 Mutexes
2257 The behavior of Guile's built-in mutexes is parameterized via a set of
2258 flags passed to the @code{make-mutex} procedure in the core
2259 (@pxref{Mutexes and Condition Variables}). To satisfy the requirements
2260 for mutexes specified by SRFI-18, the @code{make-mutex} procedure
2261 described below sets the following flags:
2264 @code{recursive}: the mutex can be locked recursively
2266 @code{unchecked-unlock}: attempts to unlock a mutex that is already
2267 unlocked will not raise an exception
2269 @code{allow-external-unlock}: the mutex can be unlocked by any thread,
2270 not just the thread that locked it originally
2273 @defun make-mutex [name]
2274 Returns a new mutex, optionally assigning it the object name
2275 @var{name}, which may be any Scheme object. The returned mutex will be
2276 created with the configuration described above. Note that the name
2277 @code{make-mutex} conflicts with Guile core function @code{make-mutex}.
2278 Applications wanting to use both of these functions will need to refer
2279 to them by different names.
2282 @defun mutex-name mutex
2283 Returns the name assigned to @var{mutex} at the time of its creation,
2284 or @code{#f} if it was not given a name.
2287 @defun mutex-specific mutex
2288 @defunx mutex-specific-set! mutex obj
2289 Get or set the ``object-specific'' property of @var{mutex}. In Guile's
2290 implementation of SRFI-18, this value is stored as an object property,
2291 and will be @code{#f} if not set.
2294 @defun mutex-state mutex
2295 Returns information about the state of @var{mutex}. Possible values
2299 thread @code{T}: the mutex is in the locked/owned state and thread T
2300 is the owner of the mutex
2302 symbol @code{not-owned}: the mutex is in the locked/not-owned state
2304 symbol @code{abandoned}: the mutex is in the unlocked/abandoned state
2306 symbol @code{not-abandoned}: the mutex is in the
2307 unlocked/not-abandoned state
2311 @defun mutex-lock! mutex [timeout [thread]]
2312 Lock @var{mutex}, optionally specifying a time object @var{timeout}
2313 after which to abort the lock attempt and a thread @var{thread} giving
2314 a new owner for @var{mutex} different than the current thread. This
2315 procedure has the same behavior as the @code{lock-mutex} procedure in
2319 @defun mutex-unlock! mutex [condition-variable [timeout]]
2320 Unlock @var{mutex}, optionally specifying a condition variable
2321 @var{condition-variable} on which to wait, either indefinitely or,
2322 optionally, until the time object @var{timeout} has passed, to be
2323 signalled. This procedure has the same behavior as the
2324 @code{unlock-mutex} procedure in the core library.
2328 @node SRFI-18 Condition variables
2329 @subsubsection SRFI-18 Condition variables
2331 SRFI-18 does not specify a ``wait'' function for condition variables.
2332 Waiting on a condition variable can be simulated using the SRFI-18
2333 @code{mutex-unlock!} function described in the previous section, or
2334 Guile's built-in @code{wait-condition-variable} procedure can be used.
2336 @defun condition-variable? obj
2337 Returns @code{#t} if @var{obj} is a condition variable, @code{#f}
2338 otherwise. This is the same procedure as the same-named built-in
2340 (@pxref{Mutexes and Condition Variables, @code{condition-variable?}}).
2343 @defun make-condition-variable [name]
2344 Returns a new condition variable, optionally assigning it the object
2345 name @var{name}, which may be any Scheme object. This procedure
2346 replaces a procedure of the same name in the core library.
2349 @defun condition-variable-name condition-variable
2350 Returns the name assigned to @var{condition-variable} at the time of its
2351 creation, or @code{#f} if it was not given a name.
2354 @defun condition-variable-specific condition-variable
2355 @defunx condition-variable-specific-set! condition-variable obj
2356 Get or set the ``object-specific'' property of
2357 @var{condition-variable}. In Guile's implementation of SRFI-18, this
2358 value is stored as an object property, and will be @code{#f} if not
2362 @defun condition-variable-signal! condition-variable
2363 @defunx condition-variable-broadcast! condition-variable
2364 Wake up one thread that is waiting for @var{condition-variable}, in
2365 the case of @code{condition-variable-signal!}, or all threads waiting
2366 for it, in the case of @code{condition-variable-broadcast!}. The
2367 behavior of these procedures is equivalent to that of the procedures
2368 @code{signal-condition-variable} and
2369 @code{broadcast-condition-variable} in the core library.
2374 @subsubsection SRFI-18 Time
2376 The SRFI-18 time functions manipulate time in two formats: a
2377 ``time object'' type that represents an absolute point in time in some
2378 implementation-specific way; and the number of seconds since some
2379 unspecified ``epoch''. In Guile's implementation, the epoch is the
2380 Unix epoch, 00:00:00 UTC, January 1, 1970.
2383 Return the current time as a time object. This procedure replaces
2384 the procedure of the same name in the core library, which returns the
2385 current time in seconds since the epoch.
2389 Returns @code{#t} if @var{obj} is a time object, @code{#f} otherwise.
2392 @defun time->seconds time
2393 @defunx seconds->time seconds
2394 Convert between time objects and numerical values representing the
2395 number of seconds since the epoch. When converting from a time object
2396 to seconds, the return value is the number of seconds between
2397 @var{time} and the epoch. When converting from seconds to a time
2398 object, the return value is a time object that represents a time
2399 @var{seconds} seconds after the epoch.
2403 @node SRFI-18 Exceptions
2404 @subsubsection SRFI-18 Exceptions
2406 SRFI-18 exceptions are identical to the exceptions provided by
2407 Guile's implementation of SRFI-34. The behavior of exception
2408 handlers invoked to handle exceptions thrown from SRFI-18 functions,
2409 however, differs from the conventional behavior of SRFI-34 in that
2410 the continuation of the handler is the same as that of the call to
2411 the function. Handlers are called in a tail-recursive manner; the
2412 exceptions do not ``bubble up''.
2414 @defun current-exception-handler
2415 Returns the current exception handler.
2418 @defun with-exception-handler handler thunk
2419 Installs @var{handler} as the current exception handler and calls the
2420 procedure @var{thunk} with no arguments, returning its value as the
2421 value of the exception. @var{handler} must be a procedure that accepts
2422 a single argument. The current exception handler at the time this
2423 procedure is called will be restored after the call returns.
2427 Raise @var{obj} as an exception. This is the same procedure as the
2428 same-named procedure defined in SRFI 34.
2431 @defun join-timeout-exception? obj
2432 Returns @code{#t} if @var{obj} is an exception raised as the result of
2433 performing a timed join on a thread that does not exit within the
2434 specified timeout, @code{#f} otherwise.
2437 @defun abandoned-mutex-exception? obj
2438 Returns @code{#t} if @var{obj} is an exception raised as the result of
2439 attempting to lock a mutex that has been abandoned by its owner thread,
2440 @code{#f} otherwise.
2443 @defun terminated-thread-exception? obj
2444 Returns @code{#t} if @var{obj} is an exception raised as the result of
2445 joining on a thread that exited as the result of a call to
2446 @code{thread-terminate!}.
2449 @defun uncaught-exception? obj
2450 @defunx uncaught-exception-reason exc
2451 @code{uncaught-exception?} returns @code{#t} if @var{obj} is an
2452 exception thrown as the result of joining a thread that exited by
2453 raising an exception that was handled by the top-level exception
2454 handler installed by @code{make-thread}. When this occurs, the
2455 original exception is preserved as part of the exception thrown by
2456 @code{thread-join!} and can be accessed by calling
2457 @code{uncaught-exception-reason} on that exception. Note that
2458 because this exception-preservation mechanism is a side-effect of
2459 @code{make-thread}, joining on threads that exited as described above
2460 but were created by other means will not raise this
2461 @code{uncaught-exception} error.
2466 @subsection SRFI-19 - Time/Date Library
2471 This is an implementation of the SRFI-19 time/date library. The
2472 functions and variables described here are provided by
2475 (use-modules (srfi srfi-19))
2478 @strong{Caution}: The current code in this module incorrectly extends
2479 the Gregorian calendar leap year rule back prior to the introduction
2480 of those reforms in 1582 (or the appropriate year in various
2481 countries). The Julian calendar was used prior to 1582, and there
2482 were 10 days skipped for the reform, but the code doesn't implement
2485 This will be fixed some time. Until then calculations for 1583
2486 onwards are correct, but prior to that any day/month/year and day of
2487 the week calculations are wrong.
2490 * SRFI-19 Introduction::
2493 * SRFI-19 Time/Date conversions::
2494 * SRFI-19 Date to string::
2495 * SRFI-19 String to date::
2498 @node SRFI-19 Introduction
2499 @subsubsection SRFI-19 Introduction
2501 @cindex universal time
2505 This module implements time and date representations and calculations,
2506 in various time systems, including universal time (UTC) and atomic
2509 For those not familiar with these time systems, TAI is based on a
2510 fixed length second derived from oscillations of certain atoms. UTC
2511 differs from TAI by an integral number of seconds, which is increased
2512 or decreased at announced times to keep UTC aligned to a mean solar
2513 day (the orbit and rotation of the earth are not quite constant).
2516 So far, only increases in the TAI
2523 UTC difference have been needed. Such an increase is a ``leap
2524 second'', an extra second of TAI introduced at the end of a UTC day.
2525 When working entirely within UTC this is never seen, every day simply
2526 has 86400 seconds. But when converting from TAI to a UTC date, an
2527 extra 23:59:60 is present, where normally a day would end at 23:59:59.
2528 Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI
2531 @cindex system clock
2532 In the current implementation, the system clock is assumed to be UTC,
2533 and a table of leap seconds in the code converts to TAI. See comments
2534 in @file{srfi-19.scm} for how to update this table.
2537 @cindex modified julian day
2538 Also, for those not familiar with the terminology, a @dfn{Julian Day}
2539 is a real number which is a count of days and fraction of a day, in
2540 UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
2541 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from
2542 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time
2543 is julian day 2400000.5.
2545 @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
2546 @c noon, UTC), but this is incorrect. It looks like it might have
2547 @c arisen from the code incorrectly treating years a multiple of 100
2548 @c but not 400 prior to 1582 as non-leap years, where instead the Julian
2549 @c calendar should be used so all multiples of 4 before 1582 are leap
2554 @subsubsection SRFI-19 Time
2557 A @dfn{time} object has type, seconds and nanoseconds fields
2558 representing a point in time starting from some epoch. This is an
2559 arbitrary point in time, not just a time of day. Although times are
2560 represented in nanoseconds, the actual resolution may be lower.
2562 The following variables hold the possible time types. For instance
2563 @code{(current-time time-process)} would give the current CPU process
2567 Universal Coordinated Time (UTC).
2572 International Atomic Time (TAI).
2576 @defvar time-monotonic
2577 Monotonic time, meaning a monotonically increasing time starting from
2578 an unspecified epoch.
2580 Note that in the current implementation @code{time-monotonic} is the
2581 same as @code{time-tai}, and unfortunately is therefore affected by
2582 adjustments to the system clock. Perhaps this will change in the
2586 @defvar time-duration
2587 A duration, meaning simply a difference between two times.
2590 @defvar time-process
2591 CPU time spent in the current process, starting from when the process
2593 @cindex process time
2597 CPU time spent in the current thread. Not currently implemented.
2603 Return @code{#t} if @var{obj} is a time object, or @code{#f} if not.
2606 @defun make-time type nanoseconds seconds
2607 Create a time object with the given @var{type}, @var{seconds} and
2611 @defun time-type time
2612 @defunx time-nanosecond time
2613 @defunx time-second time
2614 @defunx set-time-type! time type
2615 @defunx set-time-nanosecond! time nsec
2616 @defunx set-time-second! time sec
2617 Get or set the type, seconds or nanoseconds fields of a time object.
2619 @code{set-time-type!} merely changes the field, it doesn't convert the
2620 time value. For conversions, see @ref{SRFI-19 Time/Date conversions}.
2623 @defun copy-time time
2624 Return a new time object, which is a copy of the given @var{time}.
2627 @defun current-time [type]
2628 Return the current time of the given @var{type}. The default
2629 @var{type} is @code{time-utc}.
2631 Note that the name @code{current-time} conflicts with the Guile core
2632 @code{current-time} function (@pxref{Time}) as well as the SRFI-18
2633 @code{current-time} function (@pxref{SRFI-18 Time}). Applications
2634 wanting to use more than one of these functions will need to refer to
2635 them by different names.
2638 @defun time-resolution [type]
2639 Return the resolution, in nanoseconds, of the given time @var{type}.
2640 The default @var{type} is @code{time-utc}.
2643 @defun time<=? t1 t2
2644 @defunx time<? t1 t2
2645 @defunx time=? t1 t2
2646 @defunx time>=? t1 t2
2647 @defunx time>? t1 t2
2648 Return @code{#t} or @code{#f} according to the respective relation
2649 between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2}
2650 must be the same time type.
2653 @defun time-difference t1 t2
2654 @defunx time-difference! t1 t2
2655 Return a time object of type @code{time-duration} representing the
2656 period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be
2659 @code{time-difference} returns a new time object,
2660 @code{time-difference!} may modify @var{t1} to form its return.
2663 @defun add-duration time duration
2664 @defunx add-duration! time duration
2665 @defunx subtract-duration time duration
2666 @defunx subtract-duration! time duration
2667 Return a time object which is @var{time} with the given @var{duration}
2668 added or subtracted. @var{duration} must be a time object of type
2669 @code{time-duration}.
2671 @code{add-duration} and @code{subtract-duration} return a new time
2672 object. @code{add-duration!} and @code{subtract-duration!} may modify
2673 the given @var{time} to form their return.
2678 @subsubsection SRFI-19 Date
2681 A @dfn{date} object represents a date in the Gregorian calendar and a
2682 time of day on that date in some timezone.
2684 The fields are year, month, day, hour, minute, second, nanoseconds and
2685 timezone. A date object is immutable, its fields can be read but they
2686 cannot be modified once the object is created.
2689 Return @code{#t} if @var{obj} is a date object, or @code{#f} if not.
2692 @defun make-date nsecs seconds minutes hours date month year zone-offset
2693 Create a new date object.
2695 @c FIXME: What can we say about the ranges of the values. The
2696 @c current code looks it doesn't normalize, but expects then in their
2697 @c usual range already.
2701 @defun date-nanosecond date
2702 Nanoseconds, 0 to 999999999.
2705 @defun date-second date
2706 Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working
2707 entirely within UTC, it's only when converting to or from TAI.
2710 @defun date-minute date
2714 @defun date-hour date
2718 @defun date-day date
2719 Day of the month, 1 to 31 (or less, according to the month).
2722 @defun date-month date
2726 @defun date-year date
2727 Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46
2728 B.C. There is no year 0, year @math{-1} is followed by year 1.
2731 @defun date-zone-offset date
2732 Time zone, an integer number of seconds east of Greenwich.
2735 @defun date-year-day date
2736 Day of the year, starting from 1 for 1st January.
2739 @defun date-week-day date
2740 Day of the week, starting from 0 for Sunday.
2743 @defun date-week-number date dstartw
2744 Week of the year, ignoring a first partial week. @var{dstartw} is the
2745 day of the week which is taken to start a week, 0 for Sunday, 1 for
2748 @c FIXME: The spec doesn't say whether numbering starts at 0 or 1.
2749 @c The code looks like it's 0, if that's the correct intention.
2753 @c The SRFI text doesn't actually give the default for tz-offset, but
2754 @c the reference implementation has the local timezone and the
2755 @c conversions functions all specify that, so it should be ok to
2756 @c document it here.
2758 @defun current-date [tz-offset]
2759 Return a date object representing the current date/time, in UTC offset
2760 by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and
2761 defaults to the local timezone.
2764 @defun current-julian-day
2766 Return the current Julian Day.
2769 @defun current-modified-julian-day
2770 @cindex modified julian day
2771 Return the current Modified Julian Day.
2775 @node SRFI-19 Time/Date conversions
2776 @subsubsection SRFI-19 Time/Date conversions
2777 @cindex time conversion
2778 @cindex date conversion
2780 @defun date->julian-day date
2781 @defunx date->modified-julian-day date
2782 @defunx date->time-monotonic date
2783 @defunx date->time-tai date
2784 @defunx date->time-utc date
2786 @defun julian-day->date jdn [tz-offset]
2787 @defunx julian-day->time-monotonic jdn
2788 @defunx julian-day->time-tai jdn
2789 @defunx julian-day->time-utc jdn
2791 @defun modified-julian-day->date jdn [tz-offset]
2792 @defunx modified-julian-day->time-monotonic jdn
2793 @defunx modified-julian-day->time-tai jdn
2794 @defunx modified-julian-day->time-utc jdn
2796 @defun time-monotonic->date time [tz-offset]
2797 @defunx time-monotonic->time-tai time
2798 @defunx time-monotonic->time-tai! time
2799 @defunx time-monotonic->time-utc time
2800 @defunx time-monotonic->time-utc! time
2802 @defun time-tai->date time [tz-offset]
2803 @defunx time-tai->julian-day time
2804 @defunx time-tai->modified-julian-day time
2805 @defunx time-tai->time-monotonic time
2806 @defunx time-tai->time-monotonic! time
2807 @defunx time-tai->time-utc time
2808 @defunx time-tai->time-utc! time
2810 @defun time-utc->date time [tz-offset]
2811 @defunx time-utc->julian-day time
2812 @defunx time-utc->modified-julian-day time
2813 @defunx time-utc->time-monotonic time
2814 @defunx time-utc->time-monotonic! time
2815 @defunx time-utc->time-tai time
2816 @defunx time-utc->time-tai! time
2818 Convert between dates, times and days of the respective types. For
2819 instance @code{time-tai->time-utc} accepts a @var{time} object of type
2820 @code{time-tai} and returns an object of type @code{time-utc}.
2822 The @code{!} variants may modify their @var{time} argument to form
2823 their return. The plain functions create a new object.
2825 For conversions to dates, @var{tz-offset} is seconds east of
2826 Greenwich. The default is the local timezone, at the given time, as
2827 provided by the system, using @code{localtime} (@pxref{Time}).
2829 On 32-bit systems, @code{localtime} is limited to a 32-bit
2830 @code{time_t}, so a default @var{tz-offset} is only available for
2831 times between Dec 1901 and Jan 2038. For prior dates an application
2832 might like to use the value in 1902, though some locations have zone
2833 changes prior to that. For future dates an application might like to
2834 assume today's rules extend indefinitely. But for correct daylight
2835 savings transitions it will be necessary to take an offset for the
2836 same day and time but a year in range and which has the same starting
2837 weekday and same leap/non-leap (to support rules like last Sunday in
2841 @node SRFI-19 Date to string
2842 @subsubsection SRFI-19 Date to string
2843 @cindex date to string
2844 @cindex string, from date
2846 @defun date->string date [format]
2847 Convert a date to a string under the control of a format.
2848 @var{format} should be a string containing @samp{~} escapes, which
2849 will be expanded as per the following conversion table. The default
2850 @var{format} is @samp{~c}, a locale-dependent date and time.
2852 Many of these conversion characters are the same as POSIX
2853 @code{strftime} (@pxref{Time}), but there are some extras and some
2856 @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM}
2857 @item @nicode{~~} @tab literal ~
2858 @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun}
2859 @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday}
2860 @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan}
2861 @item @nicode{~B} @tab locale full month, eg.@: @samp{January}
2862 @item @nicode{~c} @tab locale date and time, eg.@: @*
2863 @samp{Fri Jul 14 20:28:42-0400 2000}
2864 @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31}
2866 @c Spec says d/m/y, reference implementation says m/d/y.
2867 @c Apparently the reference code was the intention, but would like to
2868 @c see an errata published for the spec before contradicting it here.
2870 @c @item @nicode{~D} @tab date @nicode{~d/~m/~y}
2872 @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31}
2873 @item @nicode{~f} @tab seconds and fractional seconds,
2874 with locale decimal point, eg.@: @samp{5.2}
2875 @item @nicode{~h} @tab same as @nicode{~b}
2876 @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23}
2877 @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12}
2878 @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366}
2879 @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23}
2880 @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12}
2881 @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12}
2882 @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59}
2883 @item @nicode{~n} @tab newline
2884 @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999}
2885 @item @nicode{~p} @tab locale AM or PM
2886 @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p}
2887 @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC
2888 @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @*
2889 (usual limit is 59, 60 is a leap second)
2890 @item @nicode{~t} @tab horizontal tab character
2891 @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S}
2892 @item @nicode{~U} @tab week of year, Sunday first day of week,
2893 @samp{00} to @samp{52}
2894 @item @nicode{~V} @tab week of year, Monday first day of week,
2895 @samp{01} to @samp{53}
2896 @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6}
2897 @item @nicode{~W} @tab week of year, Monday first day of week,
2898 @samp{00} to @samp{52}
2900 @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale
2901 @c date. The reference code has ~x as the locale date and ~X as a
2902 @c locale time. The rule is apparently that the code should be
2903 @c believed, but would like to see an errata for the spec before
2904 @c contradicting it here.
2906 @c @item @nicode{~x} @tab week of year, Monday as first day of week,
2907 @c @samp{00} to @samp{53}
2908 @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00}
2910 @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99}
2911 @item @nicode{~Y} @tab year, full, eg.@: @samp{2003}
2912 @item @nicode{~z} @tab time zone, RFC-822 style
2913 @item @nicode{~Z} @tab time zone symbol (not currently implemented)
2914 @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d}
2915 @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~H:~M:~S~z}
2916 @item @nicode{~3} @tab ISO-8601 time, @samp{~H:~M:~S}
2917 @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~H:~M:~S~z}
2918 @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~H:~M:~S}
2922 Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently
2923 described here, since the specification and reference implementation
2926 Conversion is locale-dependent on systems that support it
2927 (@pxref{Accessing Locale Information}). @xref{Locales,
2928 @code{setlocale}}, for information on how to change the current
2932 @node SRFI-19 String to date
2933 @subsubsection SRFI-19 String to date
2934 @cindex string to date
2935 @cindex date, from string
2937 @c FIXME: Can we say what happens when an incomplete date is
2938 @c converted? I.e. fields left as 0, or what? The spec seems to be
2941 @defun string->date input template
2942 Convert an @var{input} string to a date under the control of a
2943 @var{template} string. Return a newly created date object.
2945 Literal characters in @var{template} must match characters in
2946 @var{input} and @samp{~} escapes must match the input forms described
2947 in the table below. ``Skip to'' means characters up to one of the
2948 given type are ignored, or ``no skip'' for no skipping. ``Read'' is
2949 what's then read, and ``Set'' is the field affected in the date
2952 For example @samp{~Y} skips input characters until a digit is reached,
2953 at which point it expects a year and stores that to the year field of
2956 @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}}
2968 @tab @nicode{char-alphabetic?}
2969 @tab locale abbreviated weekday name
2973 @tab @nicode{char-alphabetic?}
2974 @tab locale full weekday name
2977 @c Note that the SRFI spec says that ~b and ~B don't set anything,
2978 @c but that looks like a mistake. The reference implementation sets
2979 @c the month field, which seems sensible and is what we describe
2983 @tab @nicode{char-alphabetic?}
2984 @tab locale abbreviated month name
2985 @tab @nicode{date-month}
2988 @tab @nicode{char-alphabetic?}
2989 @tab locale full month name
2990 @tab @nicode{date-month}
2993 @tab @nicode{char-numeric?}
2995 @tab @nicode{date-day}
2999 @tab day of month, blank padded
3000 @tab @nicode{date-day}
3003 @tab same as @samp{~b}
3006 @tab @nicode{char-numeric?}
3008 @tab @nicode{date-hour}
3012 @tab hour, blank padded
3013 @tab @nicode{date-hour}
3016 @tab @nicode{char-numeric?}
3018 @tab @nicode{date-month}
3021 @tab @nicode{char-numeric?}
3023 @tab @nicode{date-minute}
3026 @tab @nicode{char-numeric?}
3028 @tab @nicode{date-second}
3033 @tab @nicode{date-year} within 50 years
3036 @tab @nicode{char-numeric?}
3038 @tab @nicode{date-year}
3043 @tab date-zone-offset
3046 Notice that the weekday matching forms don't affect the date object
3047 returned, instead the weekday will be derived from the day, month and
3050 Conversion is locale-dependent on systems that support it
3051 (@pxref{Accessing Locale Information}). @xref{Locales,
3052 @code{setlocale}}, for information on how to change the current
3057 @subsection SRFI-23 - Error Reporting
3060 The SRFI-23 @code{error} procedure is always available.
3063 @subsection SRFI-26 - specializing parameters
3065 @cindex parameter specialize
3066 @cindex argument specialize
3067 @cindex specialize parameter
3069 This SRFI provides a syntax for conveniently specializing selected
3070 parameters of a function. It can be used with,
3073 (use-modules (srfi srfi-26))
3076 @deffn {library syntax} cut slot1 slot2 @dots{}
3077 @deffnx {library syntax} cute slot1 slot2 @dots{}
3078 Return a new procedure which will make a call (@var{slot1} @var{slot2}
3079 @dots{}) but with selected parameters specialized to given expressions.
3081 An example will illustrate the idea. The following is a
3082 specialization of @code{write}, sending output to
3083 @code{my-output-port},
3086 (cut write <> my-output-port)
3088 (lambda (obj) (write obj my-output-port))
3091 The special symbol @code{<>} indicates a slot to be filled by an
3092 argument to the new procedure. @code{my-output-port} on the other
3093 hand is an expression to be evaluated and passed, ie.@: it specializes
3094 the behaviour of @code{write}.
3098 A slot to be filled by an argument from the created procedure.
3099 Arguments are assigned to @code{<>} slots in the order they appear in
3100 the @code{cut} form, there's no way to re-arrange arguments.
3102 The first argument to @code{cut} is usually a procedure (or expression
3103 giving a procedure), but @code{<>} is allowed there too. For example,
3108 (lambda (proc) (proc 1 2 3))
3112 A slot to be filled by all remaining arguments from the new procedure.
3113 This can only occur at the end of a @code{cut} form.
3115 For example, a procedure taking a variable number of arguments like
3116 @code{max} but in addition enforcing a lower bound,
3119 (define my-lower-bound 123)
3121 (cut max my-lower-bound <...>)
3123 (lambda arglist (apply max my-lower-bound arglist))
3127 For @code{cut} the specializing expressions are evaluated each time
3128 the new procedure is called. For @code{cute} they're evaluated just
3129 once, when the new procedure is created. The name @code{cute} stands
3130 for ``@code{cut} with evaluated arguments''. In all cases the
3131 evaluations take place in an unspecified order.
3133 The following illustrates the difference between @code{cut} and
3137 (cut format <> "the time is ~s" (current-time))
3139 (lambda (port) (format port "the time is ~s" (current-time)))
3141 (cute format <> "the time is ~s" (current-time))
3143 (let ((val (current-time)))
3144 (lambda (port) (format port "the time is ~s" val))
3147 (There's no provision for a mixture of @code{cut} and @code{cute}
3148 where some expressions would be evaluated every time but others
3149 evaluated only once.)
3151 @code{cut} is really just a shorthand for the sort of @code{lambda}
3152 forms shown in the above examples. But notice @code{cut} avoids the
3153 need to name unspecialized parameters, and is more compact. Use in
3154 functional programming style or just with @code{map}, @code{for-each}
3155 or similar is typical.
3158 (map (cut * 2 <>) '(1 2 3 4))
3160 (for-each (cut write <> my-port) my-list)
3165 @subsection SRFI-27 - Sources of Random Bits
3168 This subsection is based on the
3169 @uref{http://srfi.schemers.org/srfi-27/srfi-27.html, specification of
3170 SRFI-27} written by Sebastian Egner.
3172 @c The copyright notice and license text of the SRFI-27 specification is
3173 @c reproduced below:
3175 @c Copyright (C) Sebastian Egner (2002). All Rights Reserved.
3177 @c Permission is hereby granted, free of charge, to any person obtaining a
3178 @c copy of this software and associated documentation files (the
3179 @c "Software"), to deal in the Software without restriction, including
3180 @c without limitation the rights to use, copy, modify, merge, publish,
3181 @c distribute, sublicense, and/or sell copies of the Software, and to
3182 @c permit persons to whom the Software is furnished to do so, subject to
3183 @c the following conditions:
3185 @c The above copyright notice and this permission notice shall be included
3186 @c in all copies or substantial portions of the Software.
3188 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3189 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3190 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3191 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3192 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3193 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3194 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3196 This SRFI provides access to a (pseudo) random number generator; for
3197 Guile's built-in random number facilities, which SRFI-27 is implemented
3198 upon, @xref{Random}. With SRFI-27, random numbers are obtained from a
3199 @emph{random source}, which encapsulates a random number generation
3200 algorithm and its state.
3203 * SRFI-27 Default Random Source:: Obtaining random numbers
3204 * SRFI-27 Random Sources:: Creating and manipulating random sources
3205 * SRFI-27 Random Number Generators:: Obtaining random number generators
3208 @node SRFI-27 Default Random Source
3209 @subsubsection The Default Random Source
3212 @defun random-integer n
3213 Return a random number between zero (inclusive) and @var{n} (exclusive),
3214 using the default random source. The numbers returned have a uniform
3219 Return a random number in (0,1), using the default random source. The
3220 numbers returned have a uniform distribution.
3223 @defun default-random-source
3224 A random source from which @code{random-integer} and @code{random-real}
3225 have been derived using @code{random-source-make-integers} and
3226 @code{random-source-make-reals} (@pxref{SRFI-27 Random Number Generators}
3227 for those procedures). Note that an assignment to
3228 @code{default-random-source} does not change @code{random-integer} or
3229 @code{random-real}; it is also strongly recommended not to assign a new
3233 @node SRFI-27 Random Sources
3234 @subsubsection Random Sources
3237 @defun make-random-source
3238 Create a new random source. The stream of random numbers obtained from
3239 each random source created by this procedure will be identical, unless
3240 its state is changed by one of the procedures below.
3243 @defun random-source? object
3244 Tests whether @var{object} is a random source. Random sources are a
3248 @defun random-source-randomize! source
3249 Attempt to set the state of the random source to a truly random value.
3250 The current implementation uses a seed based on the current system time.
3253 @defun random-source-pseudo-randomize! source i j
3254 Changes the state of the random source s into the initial state of the
3255 (@var{i}, @var{j})-th independent random source, where @var{i} and
3256 @var{j} are non-negative integers. This procedure provides a mechanism
3257 to obtain a large number of independent random sources (usually all
3258 derived from the same backbone generator), indexed by two integers. In
3259 contrast to @code{random-source-randomize!}, this procedure is entirely
3263 The state associated with a random state can be obtained an reinstated
3264 with the following procedures:
3266 @defun random-source-state-ref source
3267 @defunx random-source-state-set! source state
3268 Get and set the state of a random source. No assumptions should be made
3269 about the nature of the state object, besides it having an external
3270 representation (i.e.@: it can be passed to @code{write} and subsequently
3274 @node SRFI-27 Random Number Generators
3275 @subsubsection Obtaining random number generator procedures
3278 @defun random-source-make-integers source
3279 Obtains a procedure to generate random integers using the random source
3280 @var{source}. The returned procedure takes a single argument @var{n},
3281 which must be a positive integer, and returns the next uniformly
3282 distributed random integer from the interval @{0, ..., @var{n}-1@} by
3283 advancing the state of @var{source}.
3285 If an application obtains and uses several generators for the same
3286 random source @var{source}, a call to any of these generators advances
3287 the state of @var{source}. Hence, the generators do not produce the
3288 same sequence of random integers each but rather share a state. This
3289 also holds for all other types of generators derived from a fixed random
3292 While the SRFI text specifies that ``Implementations that support
3293 concurrency make sure that the state of a generator is properly
3294 advanced'', this is currently not the case in Guile's implementation of
3295 SRFI-27, as it would cause a severe performance penalty. So in
3296 multi-threaded programs, you either must perform locking on random
3297 sources shared between threads yourself, or use different random sources
3298 for multiple threads.
3301 @defun random-source-make-reals source
3302 @defunx random-source-make-reals source unit
3303 Obtains a procedure to generate random real numbers @math{0 < x < 1}
3304 using the random source @var{source}. The procedure rand is called
3307 The optional parameter @var{unit} determines the type of numbers being
3308 produced by the returned procedure and the quantization of the output.
3309 @var{unit} must be a number such that @math{0 < @var{unit} < 1}. The
3310 numbers created by the returned procedure are of the same numerical type
3311 as @var{unit} and the potential output values are spaced by at most
3312 @var{unit}. One can imagine rand to create numbers as @var{x} *
3313 @var{unit} where @var{x} is a random integer in @{1, ...,
3314 floor(1/unit)-1@}. Note, however, that this need not be the way the
3315 values are actually created and that the actual resolution of rand can
3316 be much higher than unit. In case @var{unit} is absent it defaults to a
3317 reasonably small value (related to the width of the mantissa of an
3318 efficient number format).
3322 @subsection SRFI-30 - Nested Multi-line Comments
3325 Starting from version 2.0, Guile's @code{read} supports SRFI-30/R6RS
3326 nested multi-line comments by default, @ref{Block Comments}.
3329 @subsection SRFI-31 - A special form `rec' for recursive evaluation
3331 @cindex recursive expression
3334 SRFI-31 defines a special form that can be used to create
3335 self-referential expressions more conveniently. The syntax is as
3340 <rec expression> --> (rec <variable> <expression>)
3341 <rec expression> --> (rec (<variable>+) <body>)
3345 The first syntax can be used to create self-referential expressions,
3349 guile> (define tmp (rec ones (cons 1 (delay ones))))
3352 The second syntax can be used to create anonymous recursive functions:
3355 guile> (define tmp (rec (display-n item n)
3357 (begin (display n) (display-n (- n 1))))))
3365 @subsection SRFI-34 - Exception handling for programs
3368 Guile provides an implementation of
3369 @uref{http://srfi.schemers.org/srfi-34/srfi-34.html, SRFI-34's exception
3370 handling mechanisms} as an alternative to its own built-in mechanisms
3371 (@pxref{Exceptions}). It can be made available as follows:
3374 (use-modules (srfi srfi-34))
3377 @c FIXME: Document it.
3381 @subsection SRFI-35 - Conditions
3387 @uref{http://srfi.schemers.org/srfi-35/srfi-35.html, SRFI-35} implements
3388 @dfn{conditions}, a data structure akin to records designed to convey
3389 information about exceptional conditions between parts of a program. It
3390 is normally used in conjunction with SRFI-34's @code{raise}:
3393 (raise (condition (&message
3394 (message "An error occurred"))))
3397 Users can define @dfn{condition types} containing arbitrary information.
3398 Condition types may inherit from one another. This allows the part of
3399 the program that handles (or ``catches'') conditions to get accurate
3400 information about the exceptional condition that arose.
3402 SRFI-35 conditions are made available using:
3405 (use-modules (srfi srfi-35))
3408 The procedures available to manipulate condition types are the
3411 @deffn {Scheme Procedure} make-condition-type id parent field-names
3412 Return a new condition type named @var{id}, inheriting from
3413 @var{parent}, and with the fields whose names are listed in
3414 @var{field-names}. @var{field-names} must be a list of symbols and must
3415 not contain names already used by @var{parent} or one of its supertypes.
3418 @deffn {Scheme Procedure} condition-type? obj
3419 Return true if @var{obj} is a condition type.
3422 Conditions can be created and accessed with the following procedures:
3424 @deffn {Scheme Procedure} make-condition type . field+value
3425 Return a new condition of type @var{type} with fields initialized as
3426 specified by @var{field+value}, a sequence of field names (symbols) and
3427 values as in the following example:
3430 (let ((&ct (make-condition-type 'foo &condition '(a b c))))
3431 (make-condition &ct 'a 1 'b 2 'c 3))
3434 Note that all fields of @var{type} and its supertypes must be specified.
3437 @deffn {Scheme Procedure} make-compound-condition condition1 condition2 @dots{}
3438 Return a new compound condition composed of @var{condition1}
3439 @var{condition2} @enddots{}. The returned condition has the type of
3440 each condition of condition1 condition2 @dots{} (per
3441 @code{condition-has-type?}).
3444 @deffn {Scheme Procedure} condition-has-type? c type
3445 Return true if condition @var{c} has type @var{type}.
3448 @deffn {Scheme Procedure} condition-ref c field-name
3449 Return the value of the field named @var{field-name} from condition @var{c}.
3451 If @var{c} is a compound condition and several underlying condition
3452 types contain a field named @var{field-name}, then the value of the
3453 first such field is returned, using the order in which conditions were
3454 passed to @code{make-compound-condition}.
3457 @deffn {Scheme Procedure} extract-condition c type
3458 Return a condition of condition type @var{type} with the field values
3459 specified by @var{c}.
3461 If @var{c} is a compound condition, extract the field values from the
3462 subcondition belonging to @var{type} that appeared first in the call to
3463 @code{make-compound-condition} that created the condition.
3466 Convenience macros are also available to create condition types and
3469 @deffn {library syntax} define-condition-type type supertype predicate field-spec...
3470 Define a new condition type named @var{type} that inherits from
3471 @var{supertype}. In addition, bind @var{predicate} to a type predicate
3472 that returns true when passed a condition of type @var{type} or any of
3473 its subtypes. @var{field-spec} must have the form @code{(field
3474 accessor)} where @var{field} is the name of field of @var{type} and
3475 @var{accessor} is the name of a procedure to access field @var{field} in
3476 conditions of type @var{type}.
3478 The example below defines condition type @code{&foo}, inheriting from
3479 @code{&condition} with fields @code{a}, @code{b} and @code{c}:
3482 (define-condition-type &foo &condition
3490 @deffn {library syntax} condition type-field-binding1 type-field-binding2 @dots{}
3491 Return a new condition or compound condition, initialized according to
3492 @var{type-field-binding1} @var{type-field-binding2} @enddots{}. Each
3493 @var{type-field-binding} must have the form @code{(type
3494 field-specs...)}, where @var{type} is the name of a variable bound to a
3495 condition type; each @var{field-spec} must have the form
3496 @code{(field-name value)} where @var{field-name} is a symbol denoting
3497 the field being initialized to @var{value}. As for
3498 @code{make-condition}, all fields must be specified.
3500 The following example returns a simple condition:
3503 (condition (&message (message "An error occurred")))
3506 The one below returns a compound condition:
3509 (condition (&message (message "An error occurred"))
3514 Finally, SRFI-35 defines a several standard condition types.
3517 This condition type is the root of all condition types. It has no
3522 A condition type that carries a message describing the nature of the
3523 condition to humans.
3526 @deffn {Scheme Procedure} message-condition? c
3527 Return true if @var{c} is of type @code{&message} or one of its
3531 @deffn {Scheme Procedure} condition-message c
3532 Return the message associated with message condition @var{c}.
3536 This type describes conditions serious enough that they cannot safely be
3537 ignored. It has no fields.
3540 @deffn {Scheme Procedure} serious-condition? c
3541 Return true if @var{c} is of type @code{&serious} or one of its
3546 This condition describes errors, typically caused by something that has
3547 gone wrong in the interaction of the program with the external world or
3551 @deffn {Scheme Procedure} error? c
3552 Return true if @var{c} is of type @code{&error} or one of its subtypes.
3556 @subsection SRFI-37 - args-fold
3559 This is a processor for GNU @code{getopt_long}-style program
3560 arguments. It provides an alternative, less declarative interface
3561 than @code{getopt-long} in @code{(ice-9 getopt-long)}
3562 (@pxref{getopt-long,,The (ice-9 getopt-long) Module}). Unlike
3563 @code{getopt-long}, it supports repeated options and any number of
3564 short and long names per option. Access it with:
3567 (use-modules (srfi srfi-37))
3570 @acronym{SRFI}-37 principally provides an @code{option} type and the
3571 @code{args-fold} function. To use the library, create a set of
3572 options with @code{option} and use it as a specification for invoking
3575 Here is an example of a simple argument processor for the typical
3576 @samp{--version} and @samp{--help} options, which returns a backwards
3577 list of files given on the command line:
3580 (args-fold (cdr (program-arguments))
3581 (let ((display-and-exit-proc
3583 (lambda (opt name arg loads)
3584 (display msg) (quit)))))
3585 (list (option '(#\v "version") #f #f
3586 (display-and-exit-proc "Foo version 42.0\n"))
3587 (option '(#\h "help") #f #f
3588 (display-and-exit-proc
3589 "Usage: foo scheme-file ..."))))
3590 (lambda (opt name arg loads)
3591 (error "Unrecognized option `~A'" name))
3592 (lambda (op loads) (cons op loads))
3596 @deffn {Scheme Procedure} option names required-arg? optional-arg? processor
3597 Return an object that specifies a single kind of program option.
3599 @var{names} is a list of command-line option names, and should consist of
3600 characters for traditional @code{getopt} short options and strings for
3601 @code{getopt_long}-style long options.
3603 @var{required-arg?} and @var{optional-arg?} are mutually exclusive;
3604 one or both must be @code{#f}. If @var{required-arg?}, the option
3605 must be followed by an argument on the command line, such as
3606 @samp{--opt=value} for long options, or an error will be signalled.
3607 If @var{optional-arg?}, an argument will be taken if available.
3609 @var{processor} is a procedure that takes at least 3 arguments, called
3610 when @code{args-fold} encounters the option: the containing option
3611 object, the name used on the command line, and the argument given for
3612 the option (or @code{#f} if none). The rest of the arguments are
3613 @code{args-fold} ``seeds'', and the @var{processor} should return
3617 @deffn {Scheme Procedure} option-names opt
3618 @deffnx {Scheme Procedure} option-required-arg? opt
3619 @deffnx {Scheme Procedure} option-optional-arg? opt
3620 @deffnx {Scheme Procedure} option-processor opt
3621 Return the specified field of @var{opt}, an option object, as
3622 described above for @code{option}.
3625 @deffn {Scheme Procedure} args-fold args options unrecognized-option-proc operand-proc seed @dots{}
3626 Process @var{args}, a list of program arguments such as that returned by
3627 @code{(cdr (program-arguments))}, in order against @var{options}, a list
3628 of option objects as described above. All functions called take the
3629 ``seeds'', or the last multiple-values as multiple arguments, starting
3630 with @var{seed} @dots{}, and must return the new seeds. Return the
3633 Call @code{unrecognized-option-proc}, which is like an option object's
3634 processor, for any options not found in @var{options}.
3636 Call @code{operand-proc} with any items on the command line that are
3637 not named options. This includes arguments after @samp{--}. It is
3638 called with the argument in question, as well as the seeds.
3642 @subsection SRFI-38 - External Representation for Data With Shared Structure
3645 This subsection is based on
3646 @uref{http://srfi.schemers.org/srfi-38/srfi-38.html, the specification
3647 of SRFI-38} written by Ray Dillinger.
3649 @c Copyright (C) Ray Dillinger 2003. All Rights Reserved.
3651 @c Permission is hereby granted, free of charge, to any person obtaining a
3652 @c copy of this software and associated documentation files (the
3653 @c "Software"), to deal in the Software without restriction, including
3654 @c without limitation the rights to use, copy, modify, merge, publish,
3655 @c distribute, sublicense, and/or sell copies of the Software, and to
3656 @c permit persons to whom the Software is furnished to do so, subject to
3657 @c the following conditions:
3659 @c The above copyright notice and this permission notice shall be included
3660 @c in all copies or substantial portions of the Software.
3662 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3663 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3664 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3665 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3666 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3667 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3668 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3670 This SRFI creates an alternative external representation for data
3671 written and read using @code{write-with-shared-structure} and
3672 @code{read-with-shared-structure}. It is identical to the grammar for
3673 external representation for data written and read with @code{write} and
3674 @code{read} given in section 7 of R5RS, except that the single
3678 <datum> --> <simple datum> | <compound datum>
3681 is replaced by the following five productions:
3684 <datum> --> <defining datum> | <nondefining datum> | <defined datum>
3685 <defining datum> --> #<indexnum>=<nondefining datum>
3686 <defined datum> --> #<indexnum>#
3687 <nondefining datum> --> <simple datum> | <compound datum>
3688 <indexnum> --> <digit 10>+
3691 @deffn {Scheme procedure} write-with-shared-structure obj
3692 @deffnx {Scheme procedure} write-with-shared-structure obj port
3693 @deffnx {Scheme procedure} write-with-shared-structure obj port optarg
3695 Writes an external representation of @var{obj} to the given port.
3696 Strings that appear in the written representation are enclosed in
3697 doublequotes, and within those strings backslash and doublequote
3698 characters are escaped by backslashes. Character objects are written
3699 using the @code{#\} notation.
3701 Objects which denote locations rather than values (cons cells, vectors,
3702 and non-zero-length strings in R5RS scheme; also Guile's structs,
3703 bytevectors and ports and hash-tables), if they appear at more than one
3704 point in the data being written, are preceded by @samp{#@var{N}=} the
3705 first time they are written and replaced by @samp{#@var{N}#} all
3706 subsequent times they are written, where @var{N} is a natural number
3707 used to identify that particular object. If objects which denote
3708 locations occur only once in the structure, then
3709 @code{write-with-shared-structure} must produce the same external
3710 representation for those objects as @code{write}.
3712 @code{write-with-shared-structure} terminates in finite time and
3713 produces a finite representation when writing finite data.
3715 @code{write-with-shared-structure} returns an unspecified value. The
3716 @var{port} argument may be omitted, in which case it defaults to the
3717 value returned by @code{(current-output-port)}. The @var{optarg}
3718 argument may also be omitted. If present, its effects on the output and
3719 return value are unspecified but @code{write-with-shared-structure} must
3720 still write a representation that can be read by
3721 @code{read-with-shared-structure}. Some implementations may wish to use
3722 @var{optarg} to specify formatting conventions, numeric radixes, or
3723 return values. Guile's implementation ignores @var{optarg}.
3725 For example, the code
3728 (begin (define a (cons 'val1 'val2))
3730 (write-with-shared-structure a))
3733 should produce the output @code{#1=(val1 . #1#)}. This shows a cons
3734 cell whose @code{cdr} contains itself.
3738 @deffn {Scheme procedure} read-with-shared-structure
3739 @deffnx {Scheme procedure} read-with-shared-structure port
3741 @code{read-with-shared-structure} converts the external representations
3742 of Scheme objects produced by @code{write-with-shared-structure} into
3743 Scheme objects. That is, it is a parser for the nonterminal
3744 @samp{<datum>} in the augmented external representation grammar defined
3745 above. @code{read-with-shared-structure} returns the next object
3746 parsable from the given input port, updating @var{port} to point to the
3747 first character past the end of the external representation of the
3750 If an end-of-file is encountered in the input before any characters are
3751 found that can begin an object, then an end-of-file object is returned.
3752 The port remains open, and further attempts to read it (by
3753 @code{read-with-shared-structure} or @code{read} will also return an
3754 end-of-file object. If an end of file is encountered after the
3755 beginning of an object's external representation, but the external
3756 representation is incomplete and therefore not parsable, an error is
3759 The @var{port} argument may be omitted, in which case it defaults to the
3760 value returned by @code{(current-input-port)}. It is an error to read
3766 @subsection SRFI-39 - Parameters
3769 This SRFI adds support for dynamically-scoped parameters. SRFI 39 is
3770 implemented in the Guile core; there's no module needed to get SRFI-39
3771 itself. Parameters are documented in @ref{Parameters}.
3773 This module does export one extra function: @code{with-parameters*}.
3774 This is a Guile-specific addition to the SRFI, similar to the core
3775 @code{with-fluids*} (@pxref{Fluids and Dynamic States}).
3777 @defun with-parameters* param-list value-list thunk
3778 Establish a new dynamic scope, as per @code{parameterize} above,
3779 taking parameters from @var{param-list} and corresponding values from
3780 @var{value-list}. A call @code{(@var{thunk})} is made in the new
3781 scope and the result from that @var{thunk} is the return from
3782 @code{with-parameters*}.
3786 @subsection SRFI-41 - Streams
3789 This subsection is based on the
3790 @uref{http://srfi.schemers.org/srfi-41/srfi-41.html, specification of
3791 SRFI-41} by Philip L.@: Bewig.
3793 @c The copyright notice and license text of the SRFI-41 specification is
3794 @c reproduced below:
3796 @c Copyright (C) Philip L. Bewig (2007). All Rights Reserved.
3798 @c Permission is hereby granted, free of charge, to any person obtaining a
3799 @c copy of this software and associated documentation files (the
3800 @c "Software"), to deal in the Software without restriction, including
3801 @c without limitation the rights to use, copy, modify, merge, publish,
3802 @c distribute, sublicense, and/or sell copies of the Software, and to
3803 @c permit persons to whom the Software is furnished to do so, subject to
3804 @c the following conditions:
3806 @c The above copyright notice and this permission notice shall be included
3807 @c in all copies or substantial portions of the Software.
3809 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
3810 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
3811 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
3812 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
3813 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
3814 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
3815 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
3818 This SRFI implements streams, sometimes called lazy lists, a sequential
3819 data structure containing elements computed only on demand. A stream is
3820 either null or is a pair with a stream in its cdr. Since elements of a
3821 stream are computed only when accessed, streams can be infinite. Once
3822 computed, the value of a stream element is cached in case it is needed
3823 again. SRFI-41 can be made available with:
3826 (use-modules (srfi srfi-41))
3830 * SRFI-41 Stream Fundamentals::
3831 * SRFI-41 Stream Primitives::
3832 * SRFI-41 Stream Library::
3835 @node SRFI-41 Stream Fundamentals
3836 @subsubsection SRFI-41 Stream Fundamentals
3838 SRFI-41 Streams are based on two mutually-recursive abstract data types:
3839 An object of the @code{stream} abstract data type is a promise that,
3840 when forced, is either @code{stream-null} or is an object of type
3841 @code{stream-pair}. An object of the @code{stream-pair} abstract data
3842 type contains a @code{stream-car} and a @code{stream-cdr}, which must be
3843 a @code{stream}. The essential feature of streams is the systematic
3844 suspensions of the recursive promises between the two data types.
3846 The object stored in the @code{stream-car} of a @code{stream-pair} is a
3847 promise that is forced the first time the @code{stream-car} is accessed;
3848 its value is cached in case it is needed again. The object may have any
3849 type, and different stream elements may have different types. If the
3850 @code{stream-car} is never accessed, the object stored there is never
3851 evaluated. Likewise, the @code{stream-cdr} is a promise to return a
3852 stream, and is only forced on demand.
3854 @node SRFI-41 Stream Primitives
3855 @subsubsection SRFI-41 Stream Primitives
3857 This library provides eight operators: constructors for
3858 @code{stream-null} and @code{stream-pair}s, type predicates for streams
3859 and the two kinds of streams, accessors for both fields of a
3860 @code{stream-pair}, and a lambda that creates procedures that return
3863 @defvr {Scheme Variable} stream-null
3864 A promise that, when forced, is a single object, distinguishable from
3865 all other objects, that represents the null stream. @code{stream-null}
3866 is immutable and unique.
3869 @deffn {Scheme Syntax} stream-cons object-expr stream-expr
3870 Creates a newly-allocated stream containing a promise that, when forced,
3871 is a @code{stream-pair} with @var{object-expr} in its @code{stream-car}
3872 and @var{stream-expr} in its @code{stream-cdr}. Neither
3873 @var{object-expr} nor @var{stream-expr} is evaluated when
3874 @code{stream-cons} is called.
3876 Once created, a @code{stream-pair} is immutable; there is no
3877 @code{stream-set-car!} or @code{stream-set-cdr!} that modifies an
3878 existing stream-pair. There is no dotted-pair or improper stream as
3882 @deffn {Scheme Procedure} stream? object
3883 Returns true if @var{object} is a stream, otherwise returns false. If
3884 @var{object} is a stream, its promise will not be forced. If
3885 @code{(stream? obj)} returns true, then one of @code{(stream-null? obj)}
3886 or @code{(stream-pair? obj)} will return true and the other will return
3890 @deffn {Scheme Procedure} stream-null? object
3891 Returns true if @var{object} is the distinguished null stream, otherwise
3892 returns false. If @var{object} is a stream, its promise will be forced.
3895 @deffn {Scheme Procedure} stream-pair? object
3896 Returns true if @var{object} is a @code{stream-pair} constructed by
3897 @code{stream-cons}, otherwise returns false. If @var{object} is a
3898 stream, its promise will be forced.
3901 @deffn {Scheme Procedure} stream-car stream
3902 Returns the object stored in the @code{stream-car} of @var{stream}. An
3903 error is signalled if the argument is not a @code{stream-pair}. This
3904 causes the @var{object-expr} passed to @code{stream-cons} to be
3905 evaluated if it had not yet been; the value is cached in case it is
3909 @deffn {Scheme Procedure} stream-cdr stream
3910 Returns the stream stored in the @code{stream-cdr} of @var{stream}. An
3911 error is signalled if the argument is not a @code{stream-pair}.
3914 @deffn {Scheme Syntax} stream-lambda formals body @dots{}
3915 Creates a procedure that returns a promise to evaluate the @var{body} of
3916 the procedure. The last @var{body} expression to be evaluated must
3917 yield a stream. As with normal @code{lambda}, @var{formals} may be a
3918 single variable name, in which case all the formal arguments are
3919 collected into a single list, or a list of variable names, which may be
3920 null if there are no arguments, proper if there are an exact number of
3921 arguments, or dotted if a fixed number of arguments is to be followed by
3922 zero or more arguments collected into a list. @var{Body} must contain
3923 at least one expression, and may contain internal definitions preceding
3924 any expressions to be evaluated.
3934 (stream-car strm123) @result{} 1
3935 (stream-car (stream-cdr strm123) @result{} 2
3939 (stream-cons (/ 1 0) stream-null))) @result{} #f
3941 (stream? (list 1 2 3)) @result{} #f
3944 (stream-lambda (f x)
3945 (stream-cons x (iter f (f x)))))
3947 (define nats (iter (lambda (x) (+ x 1)) 0))
3949 (stream-car (stream-cdr nats)) @result{} 1
3952 (stream-lambda (s1 s2)
3954 (+ (stream-car s1) (stream-car s2))
3955 (stream-add (stream-cdr s1)
3958 (define evens (stream-add nats nats))
3960 (stream-car evens) @result{} 0
3961 (stream-car (stream-cdr evens)) @result{} 2
3962 (stream-car (stream-cdr (stream-cdr evens))) @result{} 4
3965 @node SRFI-41 Stream Library
3966 @subsubsection SRFI-41 Stream Library
3968 @deffn {Scheme Syntax} define-stream (name args @dots{}) body @dots{}
3969 Creates a procedure that returns a stream, and may appear anywhere a
3970 normal @code{define} may appear, including as an internal definition.
3971 It may contain internal definitions of its own. The defined procedure
3972 takes arguments in the same way as @code{stream-lambda}.
3973 @code{define-stream} is syntactic sugar on @code{stream-lambda}; see
3974 also @code{stream-let}, which is also a sugaring of
3975 @code{stream-lambda}.
3977 A simple version of @code{stream-map} that takes only a single input
3978 stream calls itself recursively:
3981 (define-stream (stream-map proc strm)
3982 (if (stream-null? strm)
3985 (proc (stream-car strm))
3986 (stream-map proc (stream-cdr strm))))))
3990 @deffn {Scheme Procedure} list->stream list
3991 Returns a newly-allocated stream containing the elements from
3995 @deffn {Scheme Procedure} port->stream [port]
3996 Returns a newly-allocated stream containing in its elements the
3997 characters on the port. If @var{port} is not given it defaults to the
3998 current input port. The returned stream has finite length and is
3999 terminated by @code{stream-null}.
4001 It looks like one use of @code{port->stream} would be this:
4005 (with-input-from-file filename
4006 (lambda () (port->stream))))
4009 But that fails, because @code{with-input-from-file} is eager, and closes
4010 the input port prematurely, before the first character is read. To read
4011 a file into a stream, say:
4014 (define-stream (file->stream filename)
4015 (let ((p (open-input-file filename)))
4016 (stream-let loop ((c (read-char p)))
4018 (begin (close-input-port p)
4021 (loop (read-char p)))))))
4025 @deffn {Scheme Syntax} stream object-expr @dots{}
4026 Creates a newly-allocated stream containing in its elements the objects,
4027 in order. The @var{object-expr}s are evaluated when they are accessed,
4028 not when the stream is created. If no objects are given, as in
4029 (stream), the null stream is returned. See also @code{list->stream}.
4032 (define strm123 (stream 1 2 3))
4034 ; (/ 1 0) not evaluated when stream is created
4035 (define s (stream 1 (/ 1 0) -1))
4039 @deffn {Scheme Procedure} stream->list [n] stream
4040 Returns a newly-allocated list containing in its elements the first
4041 @var{n} items in @var{stream}. If @var{stream} has less than @var{n}
4042 items, all the items in the stream will be included in the returned
4043 list. If @var{n} is not given it defaults to infinity, which means that
4044 unless @var{stream} is finite @code{stream->list} will never return.
4048 (stream-map (lambda (x) (* x x))
4050 @result{} (0 1 4 9 16 25 36 49 64 81)
4054 @deffn {Scheme Procedure} stream-append stream @dots{}
4055 Returns a newly-allocated stream containing in its elements those
4056 elements contained in its input @var{stream}s, in order of input. If
4057 any of the input streams is infinite, no elements of any of the
4058 succeeding input streams will appear in the output stream. See also
4059 @code{stream-concat}.
4062 @deffn {Scheme Procedure} stream-concat stream
4063 Takes a @var{stream} consisting of one or more streams and returns a
4064 newly-allocated stream containing all the elements of the input streams.
4065 If any of the streams in the input @var{stream} is infinite, any
4066 remaining streams in the input stream will never appear in the output
4067 stream. See also @code{stream-append}.
4070 @deffn {Scheme Procedure} stream-constant object @dots{}
4071 Returns a newly-allocated stream containing in its elements the
4072 @var{object}s, repeating in succession forever.
4075 (stream-constant 1) @result{} 1 1 1 @dots{}
4076 (stream-constant #t #f) @result{} #t #f #t #f #t #f @dots{}
4080 @deffn {Scheme Procedure} stream-drop n stream
4081 Returns the suffix of the input @var{stream} that starts at the next
4082 element after the first @var{n} elements. The output stream shares
4083 structure with the input @var{stream}; thus, promises forced in one
4084 instance of the stream are also forced in the other instance of the
4085 stream. If the input @var{stream} has less than @var{n} elements,
4086 @code{stream-drop} returns the null stream. See also
4090 @deffn {Scheme Procedure} stream-drop-while pred stream
4091 Returns the suffix of the input @var{stream} that starts at the first
4092 element @var{x} for which @code{(pred x)} returns false. The output
4093 stream shares structure with the input @var{stream}. See also
4094 @code{stream-take-while}.
4097 @deffn {Scheme Procedure} stream-filter pred stream
4098 Returns a newly-allocated stream that contains only those elements
4099 @var{x} of the input @var{stream} which satisfy the predicate
4103 (stream-filter odd? (stream-from 0))
4104 @result{} 1 3 5 7 9 @dots{}
4108 @deffn {Scheme Procedure} stream-fold proc base stream
4109 Applies a binary procedure @var{proc} to @var{base} and the first
4110 element of @var{stream} to compute a new @var{base}, then applies the
4111 procedure to the new @var{base} and the next element of @var{stream} to
4112 compute a succeeding @var{base}, and so on, accumulating a value that is
4113 finally returned as the value of @code{stream-fold} when the end of the
4114 stream is reached. @var{stream} must be finite, or @code{stream-fold}
4115 will enter an infinite loop. See also @code{stream-scan}, which is
4116 similar to @code{stream-fold}, but useful for infinite streams. For
4117 readers familiar with other functional languages, this is a left-fold;
4118 there is no corresponding right-fold, since right-fold relies on finite
4119 streams that are fully-evaluated, in which case they may as well be
4120 converted to a list.
4123 @deffn {Scheme Procedure} stream-for-each proc stream @dots{}
4124 Applies @var{proc} element-wise to corresponding elements of the input
4125 @var{stream}s for side-effects; it returns nothing.
4126 @code{stream-for-each} stops as soon as any of its input streams is
4130 @deffn {Scheme Procedure} stream-from first [step]
4131 Creates a newly-allocated stream that contains @var{first} as its first
4132 element and increments each succeeding element by @var{step}. If
4133 @var{step} is not given it defaults to 1. @var{first} and @var{step}
4134 may be of any numeric type. @code{stream-from} is frequently useful as
4135 a generator in @code{stream-of} expressions. See also
4136 @code{stream-range} for a similar procedure that creates finite streams.
4139 @deffn {Scheme Procedure} stream-iterate proc base
4140 Creates a newly-allocated stream containing @var{base} in its first
4141 element and applies @var{proc} to each element in turn to determine the
4142 succeeding element. See also @code{stream-unfold} and
4143 @code{stream-unfolds}.
4146 @deffn {Scheme Procedure} stream-length stream
4147 Returns the number of elements in the @var{stream}; it does not evaluate
4148 its elements. @code{stream-length} may only be used on finite streams;
4149 it enters an infinite loop with infinite streams.
4152 @deffn {Scheme Syntax} stream-let tag ((var expr) @dots{}) body @dots{}
4153 Creates a local scope that binds each variable to the value of its
4154 corresponding expression. It additionally binds @var{tag} to a
4155 procedure which takes the bound variables as arguments and @var{body} as
4156 its defining expressions, binding the @var{tag} with
4157 @code{stream-lambda}. @var{tag} is in scope within body, and may be
4158 called recursively. When the expanded expression defined by the
4159 @code{stream-let} is evaluated, @code{stream-let} evaluates the
4160 expressions in its @var{body} in an environment containing the
4161 newly-bound variables, returning the value of the last expression
4162 evaluated, which must yield a stream.
4164 @code{stream-let} provides syntactic sugar on @code{stream-lambda}, in
4165 the same manner as normal @code{let} provides syntactic sugar on normal
4166 @code{lambda}. However, unlike normal @code{let}, the @var{tag} is
4167 required, not optional, because unnamed @code{stream-let} is
4170 For example, @code{stream-member} returns the first @code{stream-pair}
4171 of the input @var{strm} with a @code{stream-car} @var{x} that satisfies
4172 @code{(eql? obj x)}, or the null stream if @var{x} is not present in
4176 (define-stream (stream-member eql? obj strm)
4177 (stream-let loop ((strm strm))
4178 (cond ((stream-null? strm) strm)
4179 ((eql? obj (stream-car strm)) strm)
4180 (else (loop (stream-cdr strm))))))
4184 @deffn {Scheme Procedure} stream-map proc stream @dots{}
4185 Applies @var{proc} element-wise to corresponding elements of the input
4186 @var{stream}s, returning a newly-allocated stream containing elements
4187 that are the results of those procedure applications. The output stream
4188 has as many elements as the minimum-length input stream, and may be
4192 @deffn {Scheme Syntax} stream-match stream clause @dots{}
4193 Provides pattern-matching for streams. The input @var{stream} is an
4194 expression that evaluates to a stream. Clauses are of the form
4195 @code{(pattern [fender] expression)}, consisting of a @var{pattern} that
4196 matches a stream of a particular shape, an optional @var{fender} that
4197 must succeed if the pattern is to match, and an @var{expression} that is
4198 evaluated if the pattern matches. There are four types of patterns:
4202 () matches the null stream.
4205 (@var{pat0} @var{pat1} @dots{}) matches a finite stream with length
4206 exactly equal to the number of pattern elements.
4209 (@var{pat0} @var{pat1} @dots{} @code{.} @var{pat-rest}) matches an
4210 infinite stream, or a finite stream with length at least as great as the
4211 number of pattern elements before the literal dot.
4214 @var{pat} matches an entire stream. Should always appear last in the
4215 list of clauses; it's not an error to appear elsewhere, but subsequent
4216 clauses could never match.
4219 Each pattern element may be either:
4223 An identifier, which matches any stream element. Additionally, the
4224 value of the stream element is bound to the variable named by the
4225 identifier, which is in scope in the @var{fender} and @var{expression}
4226 of the corresponding @var{clause}. Each identifier in a single pattern
4230 A literal underscore (@code{_}), which matches any stream element but
4231 creates no bindings.
4234 The @var{pattern}s are tested in order, left-to-right, until a matching
4235 pattern is found; if @var{fender} is present, it must evaluate to a true
4236 value for the match to be successful. Pattern variables are bound in
4237 the corresponding @var{fender} and @var{expression}. Once the matching
4238 @var{pattern} is found, the corresponding @var{expression} is evaluated
4239 and returned as the result of the match. An error is signaled if no
4240 pattern matches the input @var{stream}.
4242 @code{stream-match} is often used to distinguish null streams from
4243 non-null streams, binding @var{head} and @var{tail}:
4249 ((head . tail) (+ 1 (len tail)))))
4252 Fenders can test the common case where two stream elements must be
4253 identical; the @code{else} pattern is an identifier bound to the entire
4254 stream, not a keyword as in @code{cond}.
4258 ((x y . _) (equal? x y) 'ok)
4262 A more complex example uses two nested matchers to match two different
4263 stream arguments; @code{(stream-merge lt? . strms)} stably merges two or
4264 more streams ordered by the @code{lt?} predicate:
4267 (define-stream (stream-merge lt? . strms)
4268 (define-stream (merge xx yy)
4269 (stream-match xx (() yy) ((x . xs)
4270 (stream-match yy (() xx) ((y . ys)
4272 (stream-cons y (merge xx ys))
4273 (stream-cons x (merge xs yy))))))))
4274 (stream-let loop ((strms strms))
4275 (cond ((null? strms) stream-null)
4276 ((null? (cdr strms)) (car strms))
4277 (else (merge (car strms)
4278 (apply stream-merge lt?
4283 @deffn {Scheme Syntax} stream-of expr clause @dots{}
4284 Provides the syntax of stream comprehensions, which generate streams by
4285 means of looping expressions. The result is a stream of objects of the
4286 type returned by @var{expr}. There are four types of clauses:
4290 (@var{var} @code{in} @var{stream-expr}) loops over the elements of
4291 @var{stream-expr}, in order from the start of the stream, binding each
4292 element of the stream in turn to @var{var}. @code{stream-from} and
4293 @code{stream-range} are frequently useful as generators for
4297 (@var{var} @code{is} @var{expr}) binds @var{var} to the value obtained
4298 by evaluating @var{expr}.
4301 (@var{pred} @var{expr}) includes in the output stream only those
4302 elements @var{x} which satisfy the predicate @var{pred}.
4305 The scope of variables bound in the stream comprehension is the clauses
4306 to the right of the binding clause (but not the binding clause itself)
4307 plus the result expression.
4309 When two or more generators are present, the loops are processed as if
4310 they are nested from left to right; that is, the rightmost generator
4311 varies fastest. A consequence of this is that only the first generator
4312 may be infinite and all subsequent generators must be finite. If no
4313 generators are present, the result of a stream comprehension is a stream
4314 containing the result expression; thus, @samp{(stream-of 1)} produces a
4315 finite stream containing only the element 1.
4319 (x in (stream-range 0 10))
4321 @result{} 0 4 16 36 64
4323 (stream-of (list a b)
4324 (a in (stream-range 1 4))
4325 (b in (stream-range 1 3)))
4326 @result{} (1 1) (1 2) (2 1) (2 2) (3 1) (3 2)
4328 (stream-of (list i j)
4329 (i in (stream-range 1 5))
4330 (j in (stream-range (+ i 1) 5)))
4331 @result{} (1 2) (1 3) (1 4) (2 3) (2 4) (3 4)
4335 @deffn {Scheme Procedure} stream-range first past [step]
4336 Creates a newly-allocated stream that contains @var{first} as its first
4337 element and increments each succeeding element by @var{step}. The
4338 stream is finite and ends before @var{past}, which is not an element of
4339 the stream. If @var{step} is not given it defaults to 1 if @var{first}
4340 is less than past and -1 otherwise. @var{first}, @var{past} and
4341 @var{step} may be of any real numeric type. @code{stream-range} is
4342 frequently useful as a generator in @code{stream-of} expressions. See
4343 also @code{stream-from} for a similar procedure that creates infinite
4347 (stream-range 0 10) @result{} 0 1 2 3 4 5 6 7 8 9
4348 (stream-range 0 10 2) @result{} 0 2 4 6 8
4351 Successive elements of the stream are calculated by adding @var{step} to
4352 @var{first}, so if any of @var{first}, @var{past} or @var{step} are
4353 inexact, the length of the output stream may differ from
4354 @code{(ceiling (- (/ (- past first) step) 1)}.
4357 @deffn {Scheme Procedure} stream-ref stream n
4358 Returns the @var{n}th element of stream, counting from zero. An error
4359 is signaled if @var{n} is greater than or equal to the length of stream.
4364 (stream-scan * 1 (stream-from 1))
4369 @deffn {Scheme Procedure} stream-reverse stream
4370 Returns a newly-allocated stream containing the elements of the input
4371 @var{stream} but in reverse order. @code{stream-reverse} may only be
4372 used with finite streams; it enters an infinite loop with infinite
4373 streams. @code{stream-reverse} does not force evaluation of the
4374 elements of the stream.
4377 @deffn {Scheme Procedure} stream-scan proc base stream
4378 Accumulates the partial folds of an input @var{stream} into a
4379 newly-allocated output stream. The output stream is the @var{base}
4380 followed by @code{(stream-fold proc base (stream-take i stream))} for
4381 each of the first @var{i} elements of @var{stream}.
4384 (stream-scan + 0 (stream-from 1))
4385 @result{} (stream 0 1 3 6 10 15 @dots{})
4387 (stream-scan * 1 (stream-from 1))
4388 @result{} (stream 1 1 2 6 24 120 @dots{})
4392 @deffn {Scheme Procedure} stream-take n stream
4393 Returns a newly-allocated stream containing the first @var{n} elements
4394 of the input @var{stream}. If the input @var{stream} has less than
4395 @var{n} elements, so does the output stream. See also
4399 @deffn {Scheme Procedure} stream-take-while pred stream
4400 Takes a predicate and a @code{stream} and returns a newly-allocated
4401 stream containing those elements @code{x} that form the maximal prefix
4402 of the input stream which satisfy @var{pred}. See also
4403 @code{stream-drop-while}.
4406 @deffn {Scheme Procedure} stream-unfold map pred gen base
4407 The fundamental recursive stream constructor. It constructs a stream by
4408 repeatedly applying @var{gen} to successive values of @var{base}, in the
4409 manner of @code{stream-iterate}, then applying @var{map} to each of the
4410 values so generated, appending each of the mapped values to the output
4411 stream as long as @code{(pred? base)} returns a true value. See also
4412 @code{stream-iterate} and @code{stream-unfolds}.
4414 The expression below creates the finite stream @samp{0 1 4 9 16 25 36 49
4415 64 81}. Initially the @var{base} is 0, which is less than 10, so
4416 @var{map} squares the @var{base} and the mapped value becomes the first
4417 element of the output stream. Then @var{gen} increments the @var{base}
4418 by 1, so it becomes 1; this is less than 10, so @var{map} squares the
4419 new @var{base} and 1 becomes the second element of the output stream.
4420 And so on, until the base becomes 10, when @var{pred} stops the
4421 recursion and stream-null ends the output stream.
4425 (lambda (x) (expt x 2)) ; map
4426 (lambda (x) (< x 10)) ; pred?
4427 (lambda (x) (+ x 1)) ; gen
4432 @deffn {Scheme Procedure} stream-unfolds proc seed
4433 Returns @var{n} newly-allocated streams containing those elements
4434 produced by successive calls to the generator @var{proc}, which takes
4435 the current @var{seed} as its argument and returns @var{n}+1 values
4437 (@var{proc} @var{seed}) @result{} @var{seed} @var{result_0} @dots{} @var{result_n-1}
4439 where the returned @var{seed} is the input @var{seed} to the next call
4440 to the generator and @var{result_i} indicates how to produce the next
4441 element of the @var{i}th result stream:
4445 (@var{value}): @var{value} is the next car of the result stream.
4448 @code{#f}: no value produced by this iteration of the generator
4449 @var{proc} for the result stream.
4452 (): the end of the result stream.
4455 It may require multiple calls of @var{proc} to produce the next element
4456 of any particular result stream. See also @code{stream-iterate} and
4457 @code{stream-unfold}.
4460 (define (stream-partition pred? strm)
4463 (if (stream-null? s)
4465 (let ((a (stream-car s))
4468 (values d (list a) #f)
4469 (values d #f (list a))))))
4474 (stream-partition odd?
4475 (stream-range 1 6)))
4476 (lambda (odds evens)
4477 (list (stream->list odds)
4478 (stream->list evens))))
4479 @result{} ((1 3 5) (2 4))
4483 @deffn {Scheme Procedure} stream-zip stream @dots{}
4484 Returns a newly-allocated stream in which each element is a list (not a
4485 stream) of the corresponding elements of the input @var{stream}s. The
4486 output stream is as long as the shortest input @var{stream}, if any of
4487 the input @var{stream}s is finite, or is infinite if all the input
4488 @var{stream}s are infinite.
4492 @subsection SRFI-42 - Eager Comprehensions
4495 See @uref{http://srfi.schemers.org/srfi-42/srfi-42.html, the
4496 specification of SRFI-42}.
4499 @subsection SRFI-45 - Primitives for Expressing Iterative Lazy Algorithms
4502 This subsection is based on @uref{http://srfi.schemers.org/srfi-45/srfi-45.html, the
4503 specification of SRFI-45} written by Andr@'e van Tonder.
4505 @c Copyright (C) André van Tonder (2003). All Rights Reserved.
4507 @c Permission is hereby granted, free of charge, to any person obtaining a
4508 @c copy of this software and associated documentation files (the
4509 @c "Software"), to deal in the Software without restriction, including
4510 @c without limitation the rights to use, copy, modify, merge, publish,
4511 @c distribute, sublicense, and/or sell copies of the Software, and to
4512 @c permit persons to whom the Software is furnished to do so, subject to
4513 @c the following conditions:
4515 @c The above copyright notice and this permission notice shall be included
4516 @c in all copies or substantial portions of the Software.
4518 @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
4519 @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
4520 @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
4521 @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
4522 @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
4523 @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
4524 @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
4526 Lazy evaluation is traditionally simulated in Scheme using @code{delay}
4527 and @code{force}. However, these primitives are not powerful enough to
4528 express a large class of lazy algorithms that are iterative. Indeed, it
4529 is folklore in the Scheme community that typical iterative lazy
4530 algorithms written using delay and force will often require unbounded
4533 This SRFI provides set of three operations: @{@code{lazy}, @code{delay},
4534 @code{force}@}, which allow the programmer to succinctly express lazy
4535 algorithms while retaining bounded space behavior in cases that are
4536 properly tail-recursive. A general recipe for using these primitives is
4537 provided. An additional procedure @code{eager} is provided for the
4538 construction of eager promises in cases where efficiency is a concern.
4540 Although this SRFI redefines @code{delay} and @code{force}, the
4541 extension is conservative in the sense that the semantics of the subset
4542 @{@code{delay}, @code{force}@} in isolation (i.e., as long as the
4543 program does not use @code{lazy}) agrees with that in R5RS. In other
4544 words, no program that uses the R5RS definitions of delay and force will
4545 break if those definition are replaced by the SRFI-45 definitions of
4548 Guile also adds @code{promise?} to the list of exports, which is not
4549 part of the official SRFI-45.
4551 @deffn {Scheme Procedure} promise? obj
4552 Return true if @var{obj} is an SRFI-45 promise, otherwise return false.
4555 @deffn {Scheme Syntax} delay expression
4556 Takes an expression of arbitrary type @var{a} and returns a promise of
4557 type @code{(Promise @var{a})} which at some point in the future may be
4558 asked (by the @code{force} procedure) to evaluate the expression and
4559 deliver the resulting value.
4562 @deffn {Scheme Syntax} lazy expression
4563 Takes an expression of type @code{(Promise @var{a})} and returns a
4564 promise of type @code{(Promise @var{a})} which at some point in the
4565 future may be asked (by the @code{force} procedure) to evaluate the
4566 expression and deliver the resulting promise.
4569 @deffn {Scheme Procedure} force expression
4570 Takes an argument of type @code{(Promise @var{a})} and returns a value
4571 of type @var{a} as follows: If a value of type @var{a} has been computed
4572 for the promise, this value is returned. Otherwise, the promise is
4573 first evaluated, then overwritten by the obtained promise or value, and
4574 then force is again applied (iteratively) to the promise.
4577 @deffn {Scheme Procedure} eager expression
4578 Takes an argument of type @var{a} and returns a value of type
4579 @code{(Promise @var{a})}. As opposed to @code{delay}, the argument is
4580 evaluated eagerly. Semantically, writing @code{(eager expression)} is
4581 equivalent to writing
4584 (let ((value expression)) (delay value)).
4587 However, the former is more efficient since it does not require
4588 unnecessary creation and evaluation of thunks. We also have the
4592 (delay expression) = (lazy (eager expression))
4596 The following reduction rules may be helpful for reasoning about these
4597 primitives. However, they do not express the memoization and memory
4598 usage semantics specified above:
4601 (force (delay expression)) -> expression
4602 (force (lazy expression)) -> (force expression)
4603 (force (eager value)) -> value
4606 @subsubheading Correct usage
4608 We now provide a general recipe for using the primitives @{@code{lazy},
4609 @code{delay}, @code{force}@} to express lazy algorithms in Scheme. The
4610 transformation is best described by way of an example: Consider the
4611 stream-filter algorithm, expressed in a hypothetical lazy language as
4614 (define (stream-filter p? s)
4619 (cons h (stream-filter p? t))
4620 (stream-filter p? t)))))
4623 This algorithm can be expressed as follows in Scheme:
4626 (define (stream-filter p? s)
4628 (if (null? (force s)) (delay '())
4629 (let ((h (car (force s)))
4630 (t (cdr (force s))))
4632 (delay (cons h (stream-filter p? t)))
4633 (stream-filter p? t))))))
4640 wrap all constructors (e.g., @code{'()}, @code{cons}) with @code{delay},
4642 apply @code{force} to arguments of deconstructors (e.g., @code{car},
4643 @code{cdr} and @code{null?}),
4645 wrap procedure bodies with @code{(lazy ...)}.
4649 @subsection SRFI-55 - Requiring Features
4652 SRFI-55 provides @code{require-extension} which is a portable
4653 mechanism to load selected SRFI modules. This is implemented in the
4654 Guile core, there's no module needed to get SRFI-55 itself.
4656 @deffn {library syntax} require-extension clause1 clause2 @dots{}
4657 Require the features of @var{clause1} @var{clause2} @dots{} , throwing
4658 an error if any are unavailable.
4660 A @var{clause} is of the form @code{(@var{identifier} arg...)}. The
4661 only @var{identifier} currently supported is @code{srfi} and the
4662 arguments are SRFI numbers. For example to get SRFI-1 and SRFI-6,
4665 (require-extension (srfi 1 6))
4668 @code{require-extension} can only be used at the top-level.
4670 A Guile-specific program can simply @code{use-modules} to load SRFIs
4671 not already in the core, @code{require-extension} is for programs
4672 designed to be portable to other Scheme implementations.
4677 @subsection SRFI-60 - Integers as Bits
4679 @cindex integers as bits
4680 @cindex bitwise logical
4682 This SRFI provides various functions for treating integers as bits and
4683 for bitwise manipulations. These functions can be obtained with,
4686 (use-modules (srfi srfi-60))
4689 Integers are treated as infinite precision twos-complement, the same
4690 as in the core logical functions (@pxref{Bitwise Operations}). And
4691 likewise bit indexes start from 0 for the least significant bit. The
4692 following functions in this SRFI are already in the Guile core,
4701 @code{integer-length},
4707 @defun bitwise-and n1 ...
4708 @defunx bitwise-ior n1 ...
4709 @defunx bitwise-xor n1 ...
4710 @defunx bitwise-not n
4711 @defunx any-bits-set? j k
4712 @defunx bit-set? index n
4713 @defunx arithmetic-shift n count
4714 @defunx bit-field n start end
4716 Aliases for @code{logand}, @code{logior}, @code{logxor},
4717 @code{lognot}, @code{logtest}, @code{logbit?}, @code{ash},
4718 @code{bit-extract} and @code{logcount} respectively.
4720 Note that the name @code{bit-count} conflicts with @code{bit-count} in
4721 the core (@pxref{Bit Vectors}).
4724 @defun bitwise-if mask n1 n0
4725 @defunx bitwise-merge mask n1 n0
4726 Return an integer with bits selected from @var{n1} and @var{n0}
4727 according to @var{mask}. Those bits where @var{mask} has 1s are taken
4728 from @var{n1}, and those where @var{mask} has 0s are taken from
4732 (bitwise-if 3 #b0101 #b1010) @result{} 9
4736 @defun log2-binary-factors n
4737 @defunx first-set-bit n
4738 Return a count of how many factors of 2 are present in @var{n}. This
4739 is also the bit index of the lowest 1 bit in @var{n}. If @var{n} is
4740 0, the return is @math{-1}.
4743 (log2-binary-factors 6) @result{} 1
4744 (log2-binary-factors -8) @result{} 3
4748 @defun copy-bit index n newbit
4749 Return @var{n} with the bit at @var{index} set according to
4750 @var{newbit}. @var{newbit} should be @code{#t} to set the bit to 1,
4751 or @code{#f} to set it to 0. Bits other than at @var{index} are
4752 unchanged in the return.
4755 (copy-bit 1 #b0101 #t) @result{} 7
4759 @defun copy-bit-field n newbits start end
4760 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4761 (exclusive) changed to the value @var{newbits}.
4763 The least significant bit in @var{newbits} goes to @var{start}, the
4764 next to @math{@var{start}+1}, etc. Anything in @var{newbits} past the
4765 @var{end} given is ignored.
4768 (copy-bit-field #b10000 #b11 1 3) @result{} #b10110
4772 @defun rotate-bit-field n count start end
4773 Return @var{n} with the bit field from @var{start} (inclusive) to
4774 @var{end} (exclusive) rotated upwards by @var{count} bits.
4776 @var{count} can be positive or negative, and it can be more than the
4777 field width (it'll be reduced modulo the width).
4780 (rotate-bit-field #b0110 2 1 4) @result{} #b1010
4784 @defun reverse-bit-field n start end
4785 Return @var{n} with the bits from @var{start} (inclusive) to @var{end}
4786 (exclusive) reversed.
4789 (reverse-bit-field #b101001 2 4) @result{} #b100101
4793 @defun integer->list n [len]
4794 Return bits from @var{n} in the form of a list of @code{#t} for 1 and
4795 @code{#f} for 0. The least significant @var{len} bits are returned,
4796 and the first list element is the most significant of those bits. If
4797 @var{len} is not given, the default is @code{(integer-length @var{n})}
4798 (@pxref{Bitwise Operations}).
4801 (integer->list 6) @result{} (#t #t #f)
4802 (integer->list 1 4) @result{} (#f #f #f #t)
4806 @defun list->integer lst
4807 @defunx booleans->integer bool@dots{}
4808 Return an integer formed bitwise from the given @var{lst} list of
4809 booleans, or for @code{booleans->integer} from the @var{bool}
4812 Each boolean is @code{#t} for a 1 and @code{#f} for a 0. The first
4813 element becomes the most significant bit in the return.
4816 (list->integer '(#t #f #t #f)) @result{} 10
4822 @subsection SRFI-61 - A more general @code{cond} clause
4824 This SRFI extends RnRS @code{cond} to support test expressions that
4825 return multiple values, as well as arbitrary definitions of test
4826 success. SRFI 61 is implemented in the Guile core; there's no module
4827 needed to get SRFI-61 itself. Extended @code{cond} is documented in
4828 @ref{Conditionals,, Simple Conditional Evaluation}.
4831 @subsection SRFI-67 - Compare procedures
4834 See @uref{http://srfi.schemers.org/srfi-67/srfi-67.html, the
4835 specification of SRFI-67}.
4838 @subsection SRFI-69 - Basic hash tables
4841 This is a portable wrapper around Guile's built-in hash table and weak
4842 table support. @xref{Hash Tables}, for information on that built-in
4843 support. Above that, this hash-table interface provides association
4844 of equality and hash functions with tables at creation time, so
4845 variants of each function are not required, as well as a procedure
4846 that takes care of most uses for Guile hash table handles, which this
4847 SRFI does not provide as such.
4852 (use-modules (srfi srfi-69))
4856 * SRFI-69 Creating hash tables::
4857 * SRFI-69 Accessing table items::
4858 * SRFI-69 Table properties::
4859 * SRFI-69 Hash table algorithms::
4862 @node SRFI-69 Creating hash tables
4863 @subsubsection Creating hash tables
4865 @deffn {Scheme Procedure} make-hash-table [equal-proc hash-proc #:weak weakness start-size]
4866 Create and answer a new hash table with @var{equal-proc} as the
4867 equality function and @var{hash-proc} as the hashing function.
4869 By default, @var{equal-proc} is @code{equal?}. It can be any
4870 two-argument procedure, and should answer whether two keys are the
4871 same for this table's purposes.
4873 My default @var{hash-proc} assumes that @code{equal-proc} is no
4874 coarser than @code{equal?} unless it is literally @code{string-ci=?}.
4875 If provided, @var{hash-proc} should be a two-argument procedure that
4876 takes a key and the current table size, and answers a reasonably good
4877 hash integer between 0 (inclusive) and the size (exclusive).
4879 @var{weakness} should be @code{#f} or a symbol indicating how ``weak''
4884 An ordinary non-weak hash table. This is the default.
4887 When the key has no more non-weak references at GC, remove that entry.
4890 When the value has no more non-weak references at GC, remove that
4894 When either has no more non-weak references at GC, remove the
4898 As a legacy of the time when Guile couldn't grow hash tables,
4899 @var{start-size} is an optional integer argument that specifies the
4900 approximate starting size for the hash table, which will be rounded to
4901 an algorithmically-sounder number.
4904 By @dfn{coarser} than @code{equal?}, we mean that for all @var{x} and
4905 @var{y} values where @code{(@var{equal-proc} @var{x} @var{y})},
4906 @code{(equal? @var{x} @var{y})} as well. If that does not hold for
4907 your @var{equal-proc}, you must provide a @var{hash-proc}.
4909 In the case of weak tables, remember that @dfn{references} above
4910 always refers to @code{eq?}-wise references. Just because you have a
4911 reference to some string @code{"foo"} doesn't mean that an association
4912 with key @code{"foo"} in a weak-key table @emph{won't} be collected;
4913 it only counts as a reference if the two @code{"foo"}s are @code{eq?},
4914 regardless of @var{equal-proc}. As such, it is usually only sensible
4915 to use @code{eq?} and @code{hashq} as the equivalence and hash
4916 functions for a weak table. @xref{Weak References}, for more
4917 information on Guile's built-in weak table support.
4919 @deffn {Scheme Procedure} alist->hash-table alist [equal-proc hash-proc #:weak weakness start-size]
4920 As with @code{make-hash-table}, but initialize it with the
4921 associations in @var{alist}. Where keys are repeated in @var{alist},
4922 the leftmost association takes precedence.
4925 @node SRFI-69 Accessing table items
4926 @subsubsection Accessing table items
4928 @deffn {Scheme Procedure} hash-table-ref table key [default-thunk]
4929 @deffnx {Scheme Procedure} hash-table-ref/default table key default
4930 Answer the value associated with @var{key} in @var{table}. If
4931 @var{key} is not present, answer the result of invoking the thunk
4932 @var{default-thunk}, which signals an error instead by default.
4934 @code{hash-table-ref/default} is a variant that requires a third
4935 argument, @var{default}, and answers @var{default} itself instead of
4939 @deffn {Scheme Procedure} hash-table-set! table key new-value
4940 Set @var{key} to @var{new-value} in @var{table}.
4943 @deffn {Scheme Procedure} hash-table-delete! table key
4944 Remove the association of @var{key} in @var{table}, if present. If
4948 @deffn {Scheme Procedure} hash-table-exists? table key
4949 Answer whether @var{key} has an association in @var{table}.
4952 @deffn {Scheme Procedure} hash-table-update! table key modifier [default-thunk]
4953 @deffnx {Scheme Procedure} hash-table-update!/default table key modifier default
4954 Replace @var{key}'s associated value in @var{table} by invoking
4955 @var{modifier} with one argument, the old value.
4957 If @var{key} is not present, and @var{default-thunk} is provided,
4958 invoke it with no arguments to get the ``old value'' to be passed to
4959 @var{modifier} as above. If @var{default-thunk} is not provided in
4960 such a case, signal an error.
4962 @code{hash-table-update!/default} is a variant that requires the
4963 fourth argument, which is used directly as the ``old value'' rather
4964 than as a thunk to be invoked to retrieve the ``old value''.
4967 @node SRFI-69 Table properties
4968 @subsubsection Table properties
4970 @deffn {Scheme Procedure} hash-table-size table
4971 Answer the number of associations in @var{table}. This is guaranteed
4972 to run in constant time for non-weak tables.
4975 @deffn {Scheme Procedure} hash-table-keys table
4976 Answer an unordered list of the keys in @var{table}.
4979 @deffn {Scheme Procedure} hash-table-values table
4980 Answer an unordered list of the values in @var{table}.
4983 @deffn {Scheme Procedure} hash-table-walk table proc
4984 Invoke @var{proc} once for each association in @var{table}, passing
4985 the key and value as arguments.
4988 @deffn {Scheme Procedure} hash-table-fold table proc init
4989 Invoke @code{(@var{proc} @var{key} @var{value} @var{previous})} for
4990 each @var{key} and @var{value} in @var{table}, where @var{previous} is
4991 the result of the previous invocation, using @var{init} as the first
4992 @var{previous} value. Answer the final @var{proc} result.
4995 @deffn {Scheme Procedure} hash-table->alist table
4996 Answer an alist where each association in @var{table} is an
4997 association in the result.
5000 @node SRFI-69 Hash table algorithms
5001 @subsubsection Hash table algorithms
5003 Each hash table carries an @dfn{equivalence function} and a @dfn{hash
5004 function}, used to implement key lookups. Beginning users should
5005 follow the rules for consistency of the default @var{hash-proc}
5006 specified above. Advanced users can use these to implement their own
5007 equivalence and hash functions for specialized lookup semantics.
5009 @deffn {Scheme Procedure} hash-table-equivalence-function hash-table
5010 @deffnx {Scheme Procedure} hash-table-hash-function hash-table
5011 Answer the equivalence and hash function of @var{hash-table}, respectively.
5014 @deffn {Scheme Procedure} hash obj [size]
5015 @deffnx {Scheme Procedure} string-hash obj [size]
5016 @deffnx {Scheme Procedure} string-ci-hash obj [size]
5017 @deffnx {Scheme Procedure} hash-by-identity obj [size]
5018 Answer a hash value appropriate for equality predicate @code{equal?},
5019 @code{string=?}, @code{string-ci=?}, and @code{eq?}, respectively.
5022 @code{hash} is a backwards-compatible replacement for Guile's built-in
5026 @subsection SRFI-88 Keyword Objects
5028 @cindex keyword objects
5030 @uref{http://srfi.schemers.org/srfi-88/srfi-88.html, SRFI-88} provides
5031 @dfn{keyword objects}, which are equivalent to Guile's keywords
5032 (@pxref{Keywords}). SRFI-88 keywords can be entered using the
5033 @dfn{postfix keyword syntax}, which consists of an identifier followed
5034 by @code{:} (@pxref{Scheme Read, @code{postfix} keyword syntax}).
5035 SRFI-88 can be made available with:
5038 (use-modules (srfi srfi-88))
5041 Doing so installs the right reader option for keyword syntax, using
5042 @code{(read-set! keywords 'postfix)}. It also provides the procedures
5045 @deffn {Scheme Procedure} keyword? obj
5046 Return @code{#t} if @var{obj} is a keyword. This is the same procedure
5047 as the same-named built-in procedure (@pxref{Keyword Procedures,
5051 (keyword? foo:) @result{} #t
5052 (keyword? 'foo:) @result{} #t
5053 (keyword? "foo") @result{} #f
5057 @deffn {Scheme Procedure} keyword->string kw
5058 Return the name of @var{kw} as a string, i.e., without the trailing
5059 colon. The returned string may not be modified, e.g., with
5063 (keyword->string foo:) @result{} "foo"
5067 @deffn {Scheme Procedure} string->keyword str
5068 Return the keyword object whose name is @var{str}.
5071 (keyword->string (string->keyword "a b c")) @result{} "a b c"
5076 @subsection SRFI-98 Accessing environment variables.
5078 @cindex environment variables
5080 This is a portable wrapper around Guile's built-in support for
5081 interacting with the current environment, @xref{Runtime Environment}.
5083 @deffn {Scheme Procedure} get-environment-variable name
5084 Returns a string containing the value of the environment variable
5085 given by the string @code{name}, or @code{#f} if the named
5086 environment variable is not found. This is equivalent to
5087 @code{(getenv name)}.
5090 @deffn {Scheme Procedure} get-environment-variables
5091 Returns the names and values of all the environment variables as an
5092 association list in which both the keys and the values are strings.
5096 @subsection SRFI-105 Curly-infix expressions.
5099 @cindex curly-infix-and-bracket-lists
5101 Guile's built-in reader includes support for SRFI-105 curly-infix
5102 expressions. See @uref{http://srfi.schemers.org/srfi-105/srfi-105.html,
5103 the specification of SRFI-105}. Some examples:
5106 @{n <= 5@} @result{} (<= n 5)
5107 @{a + b + c@} @result{} (+ a b c)
5108 @{a * @{b + c@}@} @result{} (* a (+ b c))
5109 @{(- a) / b@} @result{} (/ (- a) b)
5110 @{-(a) / b@} @result{} (/ (- a) b) as well
5111 @{(f a b) + (g h)@} @result{} (+ (f a b) (g h))
5112 @{f(a b) + g(h)@} @result{} (+ (f a b) (g h)) as well
5113 @{f[a b] + g(h)@} @result{} (+ ($bracket-apply$ f a b) (g h))
5114 '@{a + f(b) + x@} @result{} '(+ a (f b) x)
5115 @{length(x) >= 6@} @result{} (>= (length x) 6)
5116 @{n-1 + n-2@} @result{} (+ n-1 n-2)
5117 @{n * factorial@{n - 1@}@} @result{} (* n (factorial (- n 1)))
5118 @{@{a > 0@} and @{b >= 1@}@} @result{} (and (> a 0) (>= b 1))
5119 @{f@{n - 1@}(x)@} @result{} ((f (- n 1)) x)
5120 @{a . z@} @result{} ($nfx$ a . z)
5121 @{a + b - c@} @result{} ($nfx$ a + b - c)
5124 To enable curly-infix expressions within a file, place the reader
5125 directive @code{#!curly-infix} before the first use of curly-infix
5126 notation. To globally enable curly-infix expressions in Guile's reader,
5127 set the @code{curly-infix} read option.
5129 Guile also implements the following non-standard extension to SRFI-105:
5130 if @code{curly-infix} is enabled and there is no other meaning assigned
5131 to square brackets (i.e. the @code{square-brackets} read option is
5132 turned off), then lists within square brackets are read as normal lists
5133 but with the special symbol @code{$bracket-list$} added to the front.
5134 To enable this combination of read options within a file, use the reader
5135 directive @code{#!curly-infix-and-bracket-lists}. For example:
5138 [a b] @result{} ($bracket-list$ a b)
5139 [a . b] @result{} ($bracket-list$ a . b)
5143 For more information on reader options, @xref{Scheme Read}.
5145 @c srfi-modules.texi ends here
5148 @c TeX-master: "guile.texi"