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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Guile Reference Manual. | |
61d50919 MW |
3 | @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, |
4 | @c 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc. | |
2da09c3f MV |
5 | @c See the file guile.texi for copying conditions. |
6 | ||
a0e07ba4 | 7 | @node SRFI Support |
3229f68b | 8 | @section SRFI Support Modules |
8742c48b | 9 | @cindex SRFI |
a0e07ba4 NJ |
10 | |
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. | |
14 | ||
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 | |
4b4b1e0b | 19 | @url{http://srfi.schemers.org/}. |
a0e07ba4 NJ |
20 | |
21 | @menu | |
22 | * About SRFI Usage:: What to know about Guile's SRFI support. | |
23 | * SRFI-0:: cond-expand | |
24 | * SRFI-1:: List library. | |
25 | * SRFI-2:: and-let*. | |
26 | * SRFI-4:: Homogeneous numeric vector datatypes. | |
27 | * SRFI-6:: Basic String Ports. | |
28 | * SRFI-8:: receive. | |
29 | * SRFI-9:: define-record-type. | |
30 | * SRFI-10:: Hash-Comma Reader Extension. | |
c010924a | 31 | * SRFI-11:: let-values and let*-values. |
a0e07ba4 NJ |
32 | * SRFI-13:: String library. |
33 | * SRFI-14:: Character-set library. | |
34 | * SRFI-16:: case-lambda | |
35 | * SRFI-17:: Generalized set! | |
e68f492a | 36 | * SRFI-18:: Multithreading support |
bfc9c8e0 | 37 | * SRFI-19:: Time/Date library. |
8e9af854 | 38 | * SRFI-23:: Error reporting |
1de8c1ae | 39 | * SRFI-26:: Specializing parameters |
56ec46a7 | 40 | * SRFI-27:: Sources of Random Bits |
620c8965 | 41 | * SRFI-30:: Nested multi-line block comments |
8638c417 | 42 | * SRFI-31:: A special form `rec' for recursive evaluation |
f50ca8da LC |
43 | * SRFI-34:: Exception handling. |
44 | * SRFI-35:: Conditions. | |
d4c38221 | 45 | * SRFI-37:: args-fold program argument processor |
12708eeb | 46 | * SRFI-38:: External Representation for Data With Shared Structure |
eeadfda1 | 47 | * SRFI-39:: Parameter objects |
50d08cd8 | 48 | * SRFI-41:: Streams. |
fdc8fd46 | 49 | * SRFI-42:: Eager comprehensions |
f16a2007 | 50 | * SRFI-45:: Primitives for expressing iterative lazy algorithms |
4ea9becb | 51 | * SRFI-55:: Requiring Features. |
8503beb8 | 52 | * SRFI-60:: Integers as bits. |
43ed3b69 | 53 | * SRFI-61:: A more general `cond' clause |
b306fae0 | 54 | * SRFI-62:: S-expression comments. |
8175a07e | 55 | * SRFI-67:: Compare procedures |
1317062f | 56 | * SRFI-69:: Basic hash tables. |
da81e75d | 57 | * SRFI-87:: => in case clauses. |
189681f5 | 58 | * SRFI-88:: Keyword objects. |
922d417b | 59 | * SRFI-98:: Accessing environment variables. |
bf9eb54a | 60 | * SRFI-105:: Curly-infix expressions. |
a0e07ba4 NJ |
61 | @end menu |
62 | ||
63 | ||
64 | @node About SRFI Usage | |
3229f68b | 65 | @subsection About SRFI Usage |
a0e07ba4 NJ |
66 | |
67 | @c FIXME::martin: Review me! | |
68 | ||
69 | SRFI support in Guile is currently implemented partly in the core | |
70 | library, and partly as add-on modules. That means that some SRFIs are | |
71 | automatically available when the interpreter is started, whereas the | |
72 | other SRFIs require you to use the appropriate support module | |
12991fed | 73 | explicitly. |
a0e07ba4 NJ |
74 | |
75 | There are several reasons for this inconsistency. First, the feature | |
76 | checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be | |
77 | available immediately, because it must be there when the user wants to | |
78 | check for the Scheme implementation, that is, before she can know that | |
79 | it is safe to use @code{use-modules} to load SRFI support modules. The | |
80 | second reason is that some features defined in SRFIs had been | |
81 | implemented in Guile before the developers started to add SRFI | |
8edab37f | 82 | implementations as modules (for example SRFI-13 (@pxref{SRFI-13})). In |
a0e07ba4 NJ |
83 | the future, it is possible that SRFIs in the core library might be |
84 | factored out into separate modules, requiring explicit module loading | |
85 | when they are needed. So you should be prepared to have to use | |
8edab37f | 86 | @code{use-modules} someday in the future to access SRFI-13 bindings. If |
a0e07ba4 | 87 | you want, you can do that already. We have included the module |
8edab37f | 88 | @code{(srfi srfi-13)} in the distribution, which currently does nothing, |
a0e07ba4 NJ |
89 | but ensures that you can write future-safe code. |
90 | ||
91 | Generally, support for a specific SRFI is made available by using | |
92 | modules named @code{(srfi srfi-@var{number})}, where @var{number} is the | |
93 | number of the SRFI needed. Another possibility is to use the command | |
94 | line option @code{--use-srfi}, which will load the necessary modules | |
95 | automatically (@pxref{Invoking Guile}). | |
96 | ||
97 | ||
98 | @node SRFI-0 | |
3229f68b | 99 | @subsection SRFI-0 - cond-expand |
8742c48b | 100 | @cindex SRFI-0 |
a0e07ba4 | 101 | |
5eef0f61 KR |
102 | This SRFI lets a portable Scheme program test for the presence of |
103 | certain features, and adapt itself by using different blocks of code, | |
104 | or fail if the necessary features are not available. There's no | |
105 | module to load, this is in the Guile core. | |
a0e07ba4 | 106 | |
5eef0f61 KR |
107 | A program designed only for Guile will generally not need this |
108 | mechanism, such a program can of course directly use the various | |
109 | documented parts of Guile. | |
a0e07ba4 | 110 | |
5eef0f61 KR |
111 | @deffn syntax cond-expand (feature body@dots{}) @dots{} |
112 | Expand to the @var{body} of the first clause whose @var{feature} | |
113 | specification is satisfied. It is an error if no @var{feature} is | |
a0e07ba4 NJ |
114 | satisfied. |
115 | ||
5eef0f61 KR |
116 | Features are symbols such as @code{srfi-1}, and a feature |
117 | specification can use @code{and}, @code{or} and @code{not} forms to | |
118 | test combinations. The last clause can be an @code{else}, to be used | |
119 | if no other passes. | |
a0e07ba4 | 120 | |
5eef0f61 KR |
121 | For example, define a private version of @code{alist-cons} if SRFI-1 |
122 | is not available. | |
a0e07ba4 | 123 | |
5eef0f61 KR |
124 | @example |
125 | (cond-expand (srfi-1 | |
126 | ) | |
127 | (else | |
128 | (define (alist-cons key val alist) | |
129 | (cons (cons key val) alist)))) | |
130 | @end example | |
a0e07ba4 | 131 | |
5eef0f61 KR |
132 | Or demand a certain set of SRFIs (list operations, string ports, |
133 | @code{receive} and string operations), failing if they're not | |
134 | available. | |
a0e07ba4 | 135 | |
5eef0f61 KR |
136 | @example |
137 | (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13) | |
138 | )) | |
139 | @end example | |
140 | @end deffn | |
a0e07ba4 | 141 | |
f38d22c5 KR |
142 | @noindent |
143 | The Guile core has the following features, | |
144 | ||
145 | @example | |
146 | guile | |
60c8ad9e | 147 | guile-2 ;; starting from Guile 2.x |
f38d22c5 KR |
148 | r5rs |
149 | srfi-0 | |
150 | srfi-4 | |
f38d22c5 KR |
151 | srfi-13 |
152 | srfi-14 | |
61d50919 | 153 | srfi-16 |
edb6de0b | 154 | srfi-23 |
61d50919 | 155 | srfi-30 |
edb6de0b MW |
156 | srfi-39 |
157 | srfi-55 | |
158 | srfi-61 | |
b306fae0 | 159 | srfi-62 |
da81e75d | 160 | srfi-87 |
edb6de0b | 161 | srfi-105 |
f38d22c5 KR |
162 | @end example |
163 | ||
164 | Other SRFI feature symbols are defined once their code has been loaded | |
165 | with @code{use-modules}, since only then are their bindings available. | |
a0e07ba4 | 166 | |
5eef0f61 KR |
167 | The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is |
168 | a good way to load SRFIs to satisfy @code{cond-expand} when running a | |
169 | portable program. | |
a0e07ba4 | 170 | |
5eef0f61 KR |
171 | Testing the @code{guile} feature allows a program to adapt itself to |
172 | the Guile module system, but still run on other Scheme systems. For | |
173 | example the following demands SRFI-8 (@code{receive}), but also knows | |
174 | how to load it with the Guile mechanism. | |
a0e07ba4 NJ |
175 | |
176 | @example | |
5eef0f61 KR |
177 | (cond-expand (srfi-8 |
178 | ) | |
179 | (guile | |
180 | (use-modules (srfi srfi-8)))) | |
a0e07ba4 NJ |
181 | @end example |
182 | ||
60c8ad9e LC |
183 | @cindex @code{guile-2} SRFI-0 feature |
184 | @cindex portability between 2.0 and older versions | |
185 | Likewise, testing the @code{guile-2} feature allows code to be portable | |
186 | between Guile 2.0 and previous versions of Guile. For instance, it | |
187 | makes it possible to write code that accounts for Guile 2.0's compiler, | |
188 | yet be correctly interpreted on 1.8 and earlier versions: | |
189 | ||
190 | @example | |
191 | (cond-expand (guile-2 (eval-when (compile) | |
192 | ;; This must be evaluated at compile time. | |
193 | (fluid-set! current-reader my-reader))) | |
194 | (guile | |
195 | ;; Earlier versions of Guile do not have a | |
196 | ;; separate compilation phase. | |
197 | (fluid-set! current-reader my-reader))) | |
198 | @end example | |
199 | ||
5eef0f61 KR |
200 | It should be noted that @code{cond-expand} is separate from the |
201 | @code{*features*} mechanism (@pxref{Feature Tracking}), feature | |
202 | symbols in one are unrelated to those in the other. | |
a0e07ba4 NJ |
203 | |
204 | ||
205 | @node SRFI-1 | |
3229f68b | 206 | @subsection SRFI-1 - List library |
8742c48b | 207 | @cindex SRFI-1 |
7c2e18cd | 208 | @cindex list |
a0e07ba4 NJ |
209 | |
210 | @c FIXME::martin: Review me! | |
211 | ||
212 | The list library defined in SRFI-1 contains a lot of useful list | |
213 | processing procedures for construction, examining, destructuring and | |
214 | manipulating lists and pairs. | |
215 | ||
216 | Since SRFI-1 also defines some procedures which are already contained | |
217 | in R5RS and thus are supported by the Guile core library, some list | |
218 | and pair procedures which appear in the SRFI-1 document may not appear | |
219 | in this section. So when looking for a particular list/pair | |
220 | processing procedure, you should also have a look at the sections | |
221 | @ref{Lists} and @ref{Pairs}. | |
222 | ||
223 | @menu | |
224 | * SRFI-1 Constructors:: Constructing new lists. | |
225 | * SRFI-1 Predicates:: Testing list for specific properties. | |
226 | * SRFI-1 Selectors:: Selecting elements from lists. | |
227 | * SRFI-1 Length Append etc:: Length calculation and list appending. | |
228 | * SRFI-1 Fold and Map:: Higher-order list processing. | |
229 | * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates. | |
85a9b4ed | 230 | * SRFI-1 Searching:: Search for elements. |
a0e07ba4 NJ |
231 | * SRFI-1 Deleting:: Delete elements from lists. |
232 | * SRFI-1 Association Lists:: Handle association lists. | |
233 | * SRFI-1 Set Operations:: Use lists for representing sets. | |
234 | @end menu | |
235 | ||
236 | @node SRFI-1 Constructors | |
3229f68b | 237 | @subsubsection Constructors |
7c2e18cd | 238 | @cindex list constructor |
a0e07ba4 NJ |
239 | |
240 | @c FIXME::martin: Review me! | |
241 | ||
242 | New lists can be constructed by calling one of the following | |
243 | procedures. | |
244 | ||
8f85c0c6 | 245 | @deffn {Scheme Procedure} xcons d a |
a0e07ba4 NJ |
246 | Like @code{cons}, but with interchanged arguments. Useful mostly when |
247 | passed to higher-order procedures. | |
248 | @end deffn | |
249 | ||
8f85c0c6 | 250 | @deffn {Scheme Procedure} list-tabulate n init-proc |
a0e07ba4 NJ |
251 | Return an @var{n}-element list, where each list element is produced by |
252 | applying the procedure @var{init-proc} to the corresponding list | |
253 | index. The order in which @var{init-proc} is applied to the indices | |
254 | is not specified. | |
255 | @end deffn | |
256 | ||
57066448 KR |
257 | @deffn {Scheme Procedure} list-copy lst |
258 | Return a new list containing the elements of the list @var{lst}. | |
259 | ||
260 | This function differs from the core @code{list-copy} (@pxref{List | |
261 | Constructors}) in accepting improper lists too. And if @var{lst} is | |
262 | not a pair at all then it's treated as the final tail of an improper | |
263 | list and simply returned. | |
264 | @end deffn | |
265 | ||
8f85c0c6 | 266 | @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{} |
a0e07ba4 NJ |
267 | Return a circular list containing the given arguments @var{elt1} |
268 | @var{elt2} @dots{}. | |
269 | @end deffn | |
270 | ||
8f85c0c6 | 271 | @deffn {Scheme Procedure} iota count [start step] |
256853db KR |
272 | Return a list containing @var{count} numbers, starting from |
273 | @var{start} and adding @var{step} each time. The default @var{start} | |
274 | is 0, the default @var{step} is 1. For example, | |
a0e07ba4 | 275 | |
256853db KR |
276 | @example |
277 | (iota 6) @result{} (0 1 2 3 4 5) | |
278 | (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5) | |
279 | @end example | |
a0e07ba4 | 280 | |
256853db KR |
281 | This function takes its name from the corresponding primitive in the |
282 | APL language. | |
a0e07ba4 NJ |
283 | @end deffn |
284 | ||
285 | ||
286 | @node SRFI-1 Predicates | |
3229f68b | 287 | @subsubsection Predicates |
7c2e18cd | 288 | @cindex list predicate |
a0e07ba4 NJ |
289 | |
290 | @c FIXME::martin: Review me! | |
291 | ||
292 | The procedures in this section test specific properties of lists. | |
293 | ||
8f85c0c6 | 294 | @deffn {Scheme Procedure} proper-list? obj |
f18f87aa KR |
295 | Return @code{#t} if @var{obj} is a proper list, or @code{#f} |
296 | otherwise. This is the same as the core @code{list?} (@pxref{List | |
297 | Predicates}). | |
298 | ||
299 | A proper list is a list which ends with the empty list @code{()} in | |
300 | the usual way. The empty list @code{()} itself is a proper list too. | |
301 | ||
302 | @example | |
303 | (proper-list? '(1 2 3)) @result{} #t | |
304 | (proper-list? '()) @result{} #t | |
305 | @end example | |
a0e07ba4 NJ |
306 | @end deffn |
307 | ||
8f85c0c6 | 308 | @deffn {Scheme Procedure} circular-list? obj |
f18f87aa KR |
309 | Return @code{#t} if @var{obj} is a circular list, or @code{#f} |
310 | otherwise. | |
311 | ||
312 | A circular list is a list where at some point the @code{cdr} refers | |
313 | back to a previous pair in the list (either the start or some later | |
314 | point), so that following the @code{cdr}s takes you around in a | |
315 | circle, with no end. | |
316 | ||
317 | @example | |
318 | (define x (list 1 2 3 4)) | |
319 | (set-cdr! (last-pair x) (cddr x)) | |
320 | x @result{} (1 2 3 4 3 4 3 4 ...) | |
321 | (circular-list? x) @result{} #t | |
322 | @end example | |
a0e07ba4 NJ |
323 | @end deffn |
324 | ||
8f85c0c6 | 325 | @deffn {Scheme Procedure} dotted-list? obj |
f18f87aa KR |
326 | Return @code{#t} if @var{obj} is a dotted list, or @code{#f} |
327 | otherwise. | |
328 | ||
329 | A dotted list is a list where the @code{cdr} of the last pair is not | |
330 | the empty list @code{()}. Any non-pair @var{obj} is also considered a | |
331 | dotted list, with length zero. | |
332 | ||
333 | @example | |
334 | (dotted-list? '(1 2 . 3)) @result{} #t | |
335 | (dotted-list? 99) @result{} #t | |
336 | @end example | |
a0e07ba4 NJ |
337 | @end deffn |
338 | ||
f18f87aa KR |
339 | It will be noted that any Scheme object passes exactly one of the |
340 | above three tests @code{proper-list?}, @code{circular-list?} and | |
341 | @code{dotted-list?}. Non-lists are @code{dotted-list?}, finite lists | |
342 | are either @code{proper-list?} or @code{dotted-list?}, and infinite | |
343 | lists are @code{circular-list?}. | |
344 | ||
345 | @sp 1 | |
8f85c0c6 | 346 | @deffn {Scheme Procedure} null-list? lst |
a0e07ba4 NJ |
347 | Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f} |
348 | otherwise. If something else than a proper or circular list is passed | |
85a9b4ed | 349 | as @var{lst}, an error is signalled. This procedure is recommended |
a0e07ba4 NJ |
350 | for checking for the end of a list in contexts where dotted lists are |
351 | not allowed. | |
352 | @end deffn | |
353 | ||
8f85c0c6 | 354 | @deffn {Scheme Procedure} not-pair? obj |
a0e07ba4 NJ |
355 | Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise. |
356 | This is shorthand notation @code{(not (pair? @var{obj}))} and is | |
357 | supposed to be used for end-of-list checking in contexts where dotted | |
358 | lists are allowed. | |
359 | @end deffn | |
360 | ||
8f85c0c6 | 361 | @deffn {Scheme Procedure} list= elt= list1 @dots{} |
a0e07ba4 NJ |
362 | Return @code{#t} if all argument lists are equal, @code{#f} otherwise. |
363 | List equality is determined by testing whether all lists have the same | |
364 | length and the corresponding elements are equal in the sense of the | |
365 | equality predicate @var{elt=}. If no or only one list is given, | |
366 | @code{#t} is returned. | |
367 | @end deffn | |
368 | ||
369 | ||
370 | @node SRFI-1 Selectors | |
3229f68b | 371 | @subsubsection Selectors |
7c2e18cd | 372 | @cindex list selector |
a0e07ba4 NJ |
373 | |
374 | @c FIXME::martin: Review me! | |
375 | ||
8f85c0c6 NJ |
376 | @deffn {Scheme Procedure} first pair |
377 | @deffnx {Scheme Procedure} second pair | |
378 | @deffnx {Scheme Procedure} third pair | |
379 | @deffnx {Scheme Procedure} fourth pair | |
380 | @deffnx {Scheme Procedure} fifth pair | |
381 | @deffnx {Scheme Procedure} sixth pair | |
382 | @deffnx {Scheme Procedure} seventh pair | |
383 | @deffnx {Scheme Procedure} eighth pair | |
384 | @deffnx {Scheme Procedure} ninth pair | |
385 | @deffnx {Scheme Procedure} tenth pair | |
a0e07ba4 NJ |
386 | These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}. |
387 | @end deffn | |
388 | ||
8f85c0c6 | 389 | @deffn {Scheme Procedure} car+cdr pair |
a0e07ba4 NJ |
390 | Return two values, the @sc{car} and the @sc{cdr} of @var{pair}. |
391 | @end deffn | |
392 | ||
8f85c0c6 NJ |
393 | @deffn {Scheme Procedure} take lst i |
394 | @deffnx {Scheme Procedure} take! lst i | |
a0e07ba4 NJ |
395 | Return a list containing the first @var{i} elements of @var{lst}. |
396 | ||
397 | @code{take!} may modify the structure of the argument list @var{lst} | |
398 | in order to produce the result. | |
399 | @end deffn | |
400 | ||
8f85c0c6 | 401 | @deffn {Scheme Procedure} drop lst i |
a0e07ba4 NJ |
402 | Return a list containing all but the first @var{i} elements of |
403 | @var{lst}. | |
404 | @end deffn | |
405 | ||
8f85c0c6 | 406 | @deffn {Scheme Procedure} take-right lst i |
ecb87335 | 407 | Return a list containing the @var{i} last elements of @var{lst}. |
64bf8517 | 408 | The return shares a common tail with @var{lst}. |
a0e07ba4 NJ |
409 | @end deffn |
410 | ||
8f85c0c6 NJ |
411 | @deffn {Scheme Procedure} drop-right lst i |
412 | @deffnx {Scheme Procedure} drop-right! lst i | |
ecb87335 | 413 | Return a list containing all but the @var{i} last elements of |
a0e07ba4 NJ |
414 | @var{lst}. |
415 | ||
64bf8517 KR |
416 | @code{drop-right} always returns a new list, even when @var{i} is |
417 | zero. @code{drop-right!} may modify the structure of the argument | |
418 | list @var{lst} in order to produce the result. | |
a0e07ba4 NJ |
419 | @end deffn |
420 | ||
8f85c0c6 NJ |
421 | @deffn {Scheme Procedure} split-at lst i |
422 | @deffnx {Scheme Procedure} split-at! lst i | |
a0e07ba4 NJ |
423 | Return two values, a list containing the first @var{i} elements of the |
424 | list @var{lst} and a list containing the remaining elements. | |
425 | ||
426 | @code{split-at!} may modify the structure of the argument list | |
427 | @var{lst} in order to produce the result. | |
428 | @end deffn | |
429 | ||
8f85c0c6 | 430 | @deffn {Scheme Procedure} last lst |
a0e07ba4 NJ |
431 | Return the last element of the non-empty, finite list @var{lst}. |
432 | @end deffn | |
433 | ||
434 | ||
435 | @node SRFI-1 Length Append etc | |
3229f68b | 436 | @subsubsection Length, Append, Concatenate, etc. |
a0e07ba4 NJ |
437 | |
438 | @c FIXME::martin: Review me! | |
439 | ||
8f85c0c6 | 440 | @deffn {Scheme Procedure} length+ lst |
a0e07ba4 NJ |
441 | Return the length of the argument list @var{lst}. When @var{lst} is a |
442 | circular list, @code{#f} is returned. | |
443 | @end deffn | |
444 | ||
8f85c0c6 NJ |
445 | @deffn {Scheme Procedure} concatenate list-of-lists |
446 | @deffnx {Scheme Procedure} concatenate! list-of-lists | |
a0e07ba4 NJ |
447 | Construct a list by appending all lists in @var{list-of-lists}. |
448 | ||
449 | @code{concatenate!} may modify the structure of the given lists in | |
450 | order to produce the result. | |
a3e856f2 KR |
451 | |
452 | @code{concatenate} is the same as @code{(apply append | |
453 | @var{list-of-lists})}. It exists because some Scheme implementations | |
454 | have a limit on the number of arguments a function takes, which the | |
455 | @code{apply} might exceed. In Guile there is no such limit. | |
a0e07ba4 NJ |
456 | @end deffn |
457 | ||
8f85c0c6 NJ |
458 | @deffn {Scheme Procedure} append-reverse rev-head tail |
459 | @deffnx {Scheme Procedure} append-reverse! rev-head tail | |
23f2b9a3 KR |
460 | Reverse @var{rev-head}, append @var{tail} to it, and return the |
461 | result. This is equivalent to @code{(append (reverse @var{rev-head}) | |
462 | @var{tail})}, but its implementation is more efficient. | |
463 | ||
464 | @example | |
465 | (append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6) | |
466 | @end example | |
a0e07ba4 NJ |
467 | |
468 | @code{append-reverse!} may modify @var{rev-head} in order to produce | |
469 | the result. | |
470 | @end deffn | |
471 | ||
8f85c0c6 | 472 | @deffn {Scheme Procedure} zip lst1 lst2 @dots{} |
a0e07ba4 NJ |
473 | Return a list as long as the shortest of the argument lists, where |
474 | each element is a list. The first list contains the first elements of | |
475 | the argument lists, the second list contains the second elements, and | |
476 | so on. | |
477 | @end deffn | |
478 | ||
8f85c0c6 NJ |
479 | @deffn {Scheme Procedure} unzip1 lst |
480 | @deffnx {Scheme Procedure} unzip2 lst | |
481 | @deffnx {Scheme Procedure} unzip3 lst | |
482 | @deffnx {Scheme Procedure} unzip4 lst | |
483 | @deffnx {Scheme Procedure} unzip5 lst | |
a0e07ba4 NJ |
484 | @code{unzip1} takes a list of lists, and returns a list containing the |
485 | first elements of each list, @code{unzip2} returns two lists, the | |
486 | first containing the first elements of each lists and the second | |
487 | containing the second elements of each lists, and so on. | |
488 | @end deffn | |
489 | ||
df0a1002 | 490 | @deffn {Scheme Procedure} count pred lst1 lst2 @dots{} |
e508c863 KR |
491 | Return a count of the number of times @var{pred} returns true when |
492 | called on elements from the given lists. | |
493 | ||
494 | @var{pred} is called with @var{N} parameters @code{(@var{pred} | |
df0a1002 BT |
495 | @var{elem1} @dots{} @var{elemN} )}, each element being from the |
496 | corresponding list. The first call is with the first element of each | |
497 | list, the second with the second element from each, and so on. | |
e508c863 KR |
498 | |
499 | Counting stops when the end of the shortest list is reached. At least | |
500 | one list must be non-circular. | |
501 | @end deffn | |
502 | ||
a0e07ba4 NJ |
503 | |
504 | @node SRFI-1 Fold and Map | |
3229f68b | 505 | @subsubsection Fold, Unfold & Map |
7c2e18cd KR |
506 | @cindex list fold |
507 | @cindex list map | |
a0e07ba4 NJ |
508 | |
509 | @c FIXME::martin: Review me! | |
510 | ||
df0a1002 BT |
511 | @deffn {Scheme Procedure} fold proc init lst1 lst2 @dots{} |
512 | @deffnx {Scheme Procedure} fold-right proc init lst1 lst2 @dots{} | |
513 | Apply @var{proc} to the elements of @var{lst1} @var{lst2} @dots{} to | |
1e181a08 | 514 | build a result, and return that result. |
a0e07ba4 | 515 | |
df0a1002 BT |
516 | Each @var{proc} call is @code{(@var{proc} @var{elem1} @var{elem2} |
517 | @dots{} @var{previous})}, where @var{elem1} is from @var{lst1}, | |
518 | @var{elem2} is from @var{lst2}, and so on. @var{previous} is the return | |
1e181a08 KR |
519 | from the previous call to @var{proc}, or the given @var{init} for the |
520 | first call. If any list is empty, just @var{init} is returned. | |
a0e07ba4 | 521 | |
1e181a08 KR |
522 | @code{fold} works through the list elements from first to last. The |
523 | following shows a list reversal and the calls it makes, | |
a0e07ba4 | 524 | |
1e181a08 KR |
525 | @example |
526 | (fold cons '() '(1 2 3)) | |
a0e07ba4 | 527 | |
1e181a08 KR |
528 | (cons 1 '()) |
529 | (cons 2 '(1)) | |
530 | (cons 3 '(2 1) | |
531 | @result{} (3 2 1) | |
532 | @end example | |
a0e07ba4 | 533 | |
1e181a08 KR |
534 | @code{fold-right} works through the list elements from last to first, |
535 | ie.@: from the right. So for example the following finds the longest | |
536 | string, and the last among equal longest, | |
537 | ||
538 | @example | |
539 | (fold-right (lambda (str prev) | |
540 | (if (> (string-length str) (string-length prev)) | |
541 | str | |
542 | prev)) | |
543 | "" | |
544 | '("x" "abc" "xyz" "jk")) | |
545 | @result{} "xyz" | |
546 | @end example | |
a0e07ba4 | 547 | |
df0a1002 | 548 | If @var{lst1} @var{lst2} @dots{} have different lengths, @code{fold} |
1e181a08 | 549 | stops when the end of the shortest is reached; @code{fold-right} |
df0a1002 BT |
550 | commences at the last element of the shortest. Ie.@: elements past the |
551 | length of the shortest are ignored in the other @var{lst}s. At least | |
552 | one @var{lst} must be non-circular. | |
1e181a08 KR |
553 | |
554 | @code{fold} should be preferred over @code{fold-right} if the order of | |
555 | processing doesn't matter, or can be arranged either way, since | |
556 | @code{fold} is a little more efficient. | |
557 | ||
558 | The way @code{fold} builds a result from iterating is quite general, | |
559 | it can do more than other iterations like say @code{map} or | |
560 | @code{filter}. The following for example removes adjacent duplicate | |
561 | elements from a list, | |
562 | ||
563 | @example | |
564 | (define (delete-adjacent-duplicates lst) | |
565 | (fold-right (lambda (elem ret) | |
566 | (if (equal? elem (first ret)) | |
567 | ret | |
568 | (cons elem ret))) | |
569 | (list (last lst)) | |
570 | lst)) | |
571 | (delete-adjacent-duplicates '(1 2 3 3 4 4 4 5)) | |
572 | @result{} (1 2 3 4 5) | |
573 | @end example | |
574 | ||
575 | Clearly the same sort of thing can be done with a @code{for-each} and | |
5f708db6 KR |
576 | a variable in which to build the result, but a self-contained |
577 | @var{proc} can be re-used in multiple contexts, where a | |
578 | @code{for-each} would have to be written out each time. | |
a0e07ba4 NJ |
579 | @end deffn |
580 | ||
df0a1002 BT |
581 | @deffn {Scheme Procedure} pair-fold proc init lst1 lst2 @dots{} |
582 | @deffnx {Scheme Procedure} pair-fold-right proc init lst1 lst2 @dots{} | |
1e181a08 KR |
583 | The same as @code{fold} and @code{fold-right}, but apply @var{proc} to |
584 | the pairs of the lists instead of the list elements. | |
a0e07ba4 NJ |
585 | @end deffn |
586 | ||
5f708db6 KR |
587 | @deffn {Scheme Procedure} reduce proc default lst |
588 | @deffnx {Scheme Procedure} reduce-right proc default lst | |
589 | @code{reduce} is a variant of @code{fold}, where the first call to | |
590 | @var{proc} is on two elements from @var{lst}, rather than one element | |
591 | and a given initial value. | |
1e181a08 | 592 | |
5f708db6 KR |
593 | If @var{lst} is empty, @code{reduce} returns @var{default} (this is |
594 | the only use for @var{default}). If @var{lst} has just one element | |
595 | then that's the return value. Otherwise @var{proc} is called on the | |
596 | elements of @var{lst}. | |
1e181a08 | 597 | |
5f708db6 KR |
598 | Each @var{proc} call is @code{(@var{proc} @var{elem} @var{previous})}, |
599 | where @var{elem} is from @var{lst} (the second and subsequent elements | |
600 | of @var{lst}), and @var{previous} is the return from the previous call | |
601 | to @var{proc}. The first element of @var{lst} is the @var{previous} | |
602 | for the first call to @var{proc}. | |
1e181a08 | 603 | |
5f708db6 KR |
604 | For example, the following adds a list of numbers, the calls made to |
605 | @code{+} are shown. (Of course @code{+} accepts multiple arguments | |
606 | and can add a list directly, with @code{apply}.) | |
1e181a08 KR |
607 | |
608 | @example | |
5f708db6 KR |
609 | (reduce + 0 '(5 6 7)) @result{} 18 |
610 | ||
611 | (+ 6 5) @result{} 11 | |
612 | (+ 7 11) @result{} 18 | |
1e181a08 KR |
613 | @end example |
614 | ||
5f708db6 KR |
615 | @code{reduce} can be used instead of @code{fold} where the @var{init} |
616 | value is an ``identity'', meaning a value which under @var{proc} | |
617 | doesn't change the result, in this case 0 is an identity since | |
618 | @code{(+ 5 0)} is just 5. @code{reduce} avoids that unnecessary call. | |
1e181a08 KR |
619 | |
620 | @code{reduce-right} is a similar variation on @code{fold-right}, | |
5f708db6 KR |
621 | working from the end (ie.@: the right) of @var{lst}. The last element |
622 | of @var{lst} is the @var{previous} for the first call to @var{proc}, | |
623 | and the @var{elem} values go from the second last. | |
1e181a08 KR |
624 | |
625 | @code{reduce} should be preferred over @code{reduce-right} if the | |
626 | order of processing doesn't matter, or can be arranged either way, | |
627 | since @code{reduce} is a little more efficient. | |
a0e07ba4 NJ |
628 | @end deffn |
629 | ||
8f85c0c6 | 630 | @deffn {Scheme Procedure} unfold p f g seed [tail-gen] |
a0e07ba4 NJ |
631 | @code{unfold} is defined as follows: |
632 | ||
633 | @lisp | |
634 | (unfold p f g seed) = | |
635 | (if (p seed) (tail-gen seed) | |
636 | (cons (f seed) | |
637 | (unfold p f g (g seed)))) | |
638 | @end lisp | |
639 | ||
640 | @table @var | |
641 | @item p | |
642 | Determines when to stop unfolding. | |
643 | ||
644 | @item f | |
645 | Maps each seed value to the corresponding list element. | |
646 | ||
647 | @item g | |
ecb87335 | 648 | Maps each seed value to next seed value. |
a0e07ba4 NJ |
649 | |
650 | @item seed | |
651 | The state value for the unfold. | |
652 | ||
653 | @item tail-gen | |
654 | Creates the tail of the list; defaults to @code{(lambda (x) '())}. | |
655 | @end table | |
656 | ||
657 | @var{g} produces a series of seed values, which are mapped to list | |
658 | elements by @var{f}. These elements are put into a list in | |
659 | left-to-right order, and @var{p} tells when to stop unfolding. | |
660 | @end deffn | |
661 | ||
8f85c0c6 | 662 | @deffn {Scheme Procedure} unfold-right p f g seed [tail] |
a0e07ba4 NJ |
663 | Construct a list with the following loop. |
664 | ||
665 | @lisp | |
666 | (let lp ((seed seed) (lis tail)) | |
667 | (if (p seed) lis | |
668 | (lp (g seed) | |
669 | (cons (f seed) lis)))) | |
670 | @end lisp | |
671 | ||
672 | @table @var | |
673 | @item p | |
674 | Determines when to stop unfolding. | |
675 | ||
676 | @item f | |
677 | Maps each seed value to the corresponding list element. | |
678 | ||
679 | @item g | |
ecb87335 | 680 | Maps each seed value to next seed value. |
a0e07ba4 NJ |
681 | |
682 | @item seed | |
683 | The state value for the unfold. | |
684 | ||
9cdf0ac6 IP |
685 | @item tail |
686 | The tail of the list; defaults to @code{'()}. | |
a0e07ba4 NJ |
687 | @end table |
688 | ||
689 | @end deffn | |
690 | ||
8f85c0c6 | 691 | @deffn {Scheme Procedure} map f lst1 lst2 @dots{} |
a0e07ba4 NJ |
692 | Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and |
693 | return a list containing the results of the procedure applications. | |
694 | This procedure is extended with respect to R5RS, because the argument | |
695 | lists may have different lengths. The result list will have the same | |
696 | length as the shortest argument lists. The order in which @var{f} | |
697 | will be applied to the list element(s) is not specified. | |
698 | @end deffn | |
699 | ||
8f85c0c6 | 700 | @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{} |
a0e07ba4 NJ |
701 | Apply the procedure @var{f} to each pair of corresponding elements of |
702 | the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not | |
703 | specified. This procedure is extended with respect to R5RS, because | |
704 | the argument lists may have different lengths. The shortest argument | |
705 | list determines the number of times @var{f} is called. @var{f} will | |
85a9b4ed | 706 | be applied to the list elements in left-to-right order. |
a0e07ba4 NJ |
707 | |
708 | @end deffn | |
709 | ||
8f85c0c6 NJ |
710 | @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{} |
711 | @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{} | |
12991fed | 712 | Equivalent to |
a0e07ba4 NJ |
713 | |
714 | @lisp | |
12991fed | 715 | (apply append (map f clist1 clist2 ...)) |
a0e07ba4 NJ |
716 | @end lisp |
717 | ||
12991fed | 718 | and |
a0e07ba4 NJ |
719 | |
720 | @lisp | |
12991fed | 721 | (apply append! (map f clist1 clist2 ...)) |
a0e07ba4 NJ |
722 | @end lisp |
723 | ||
724 | Map @var{f} over the elements of the lists, just as in the @code{map} | |
725 | function. However, the results of the applications are appended | |
726 | together to make the final result. @code{append-map} uses | |
727 | @code{append} to append the results together; @code{append-map!} uses | |
728 | @code{append!}. | |
729 | ||
730 | The dynamic order in which the various applications of @var{f} are | |
731 | made is not specified. | |
732 | @end deffn | |
733 | ||
8f85c0c6 | 734 | @deffn {Scheme Procedure} map! f lst1 lst2 @dots{} |
a0e07ba4 NJ |
735 | Linear-update variant of @code{map} -- @code{map!} is allowed, but not |
736 | required, to alter the cons cells of @var{lst1} to construct the | |
737 | result list. | |
738 | ||
739 | The dynamic order in which the various applications of @var{f} are | |
740 | made is not specified. In the n-ary case, @var{lst2}, @var{lst3}, | |
741 | @dots{} must have at least as many elements as @var{lst1}. | |
742 | @end deffn | |
743 | ||
8f85c0c6 | 744 | @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{} |
a0e07ba4 NJ |
745 | Like @code{for-each}, but applies the procedure @var{f} to the pairs |
746 | from which the argument lists are constructed, instead of the list | |
747 | elements. The return value is not specified. | |
748 | @end deffn | |
749 | ||
8f85c0c6 | 750 | @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{} |
a0e07ba4 NJ |
751 | Like @code{map}, but only results from the applications of @var{f} |
752 | which are true are saved in the result list. | |
753 | @end deffn | |
754 | ||
755 | ||
756 | @node SRFI-1 Filtering and Partitioning | |
3229f68b | 757 | @subsubsection Filtering and Partitioning |
7c2e18cd KR |
758 | @cindex list filter |
759 | @cindex list partition | |
a0e07ba4 NJ |
760 | |
761 | @c FIXME::martin: Review me! | |
762 | ||
763 | Filtering means to collect all elements from a list which satisfy a | |
764 | specific condition. Partitioning a list means to make two groups of | |
765 | list elements, one which contains the elements satisfying a condition, | |
766 | and the other for the elements which don't. | |
767 | ||
60e25dc4 KR |
768 | The @code{filter} and @code{filter!} functions are implemented in the |
769 | Guile core, @xref{List Modification}. | |
a0e07ba4 | 770 | |
8f85c0c6 NJ |
771 | @deffn {Scheme Procedure} partition pred lst |
772 | @deffnx {Scheme Procedure} partition! pred lst | |
193239f1 KR |
773 | Split @var{lst} into those elements which do and don't satisfy the |
774 | predicate @var{pred}. | |
a0e07ba4 | 775 | |
193239f1 KR |
776 | The return is two values (@pxref{Multiple Values}), the first being a |
777 | list of all elements from @var{lst} which satisfy @var{pred}, the | |
778 | second a list of those which do not. | |
779 | ||
780 | The elements in the result lists are in the same order as in @var{lst} | |
781 | but the order in which the calls @code{(@var{pred} elem)} are made on | |
782 | the list elements is unspecified. | |
783 | ||
784 | @code{partition} does not change @var{lst}, but one of the returned | |
785 | lists may share a tail with it. @code{partition!} may modify | |
786 | @var{lst} to construct its return. | |
a0e07ba4 NJ |
787 | @end deffn |
788 | ||
8f85c0c6 NJ |
789 | @deffn {Scheme Procedure} remove pred lst |
790 | @deffnx {Scheme Procedure} remove! pred lst | |
a0e07ba4 NJ |
791 | Return a list containing all elements from @var{lst} which do not |
792 | satisfy the predicate @var{pred}. The elements in the result list | |
793 | have the same order as in @var{lst}. The order in which @var{pred} is | |
794 | applied to the list elements is not specified. | |
795 | ||
796 | @code{remove!} is allowed, but not required to modify the structure of | |
797 | the input list. | |
798 | @end deffn | |
799 | ||
800 | ||
801 | @node SRFI-1 Searching | |
3229f68b | 802 | @subsubsection Searching |
7c2e18cd | 803 | @cindex list search |
a0e07ba4 NJ |
804 | |
805 | @c FIXME::martin: Review me! | |
806 | ||
807 | The procedures for searching elements in lists either accept a | |
808 | predicate or a comparison object for determining which elements are to | |
809 | be searched. | |
810 | ||
8f85c0c6 | 811 | @deffn {Scheme Procedure} find pred lst |
a0e07ba4 NJ |
812 | Return the first element of @var{lst} which satisfies the predicate |
813 | @var{pred} and @code{#f} if no such element is found. | |
814 | @end deffn | |
815 | ||
8f85c0c6 | 816 | @deffn {Scheme Procedure} find-tail pred lst |
a0e07ba4 NJ |
817 | Return the first pair of @var{lst} whose @sc{car} satisfies the |
818 | predicate @var{pred} and @code{#f} if no such element is found. | |
819 | @end deffn | |
820 | ||
8f85c0c6 NJ |
821 | @deffn {Scheme Procedure} take-while pred lst |
822 | @deffnx {Scheme Procedure} take-while! pred lst | |
a0e07ba4 NJ |
823 | Return the longest initial prefix of @var{lst} whose elements all |
824 | satisfy the predicate @var{pred}. | |
825 | ||
826 | @code{take-while!} is allowed, but not required to modify the input | |
827 | list while producing the result. | |
828 | @end deffn | |
829 | ||
8f85c0c6 | 830 | @deffn {Scheme Procedure} drop-while pred lst |
a0e07ba4 NJ |
831 | Drop the longest initial prefix of @var{lst} whose elements all |
832 | satisfy the predicate @var{pred}. | |
833 | @end deffn | |
834 | ||
8f85c0c6 NJ |
835 | @deffn {Scheme Procedure} span pred lst |
836 | @deffnx {Scheme Procedure} span! pred lst | |
837 | @deffnx {Scheme Procedure} break pred lst | |
838 | @deffnx {Scheme Procedure} break! pred lst | |
a0e07ba4 NJ |
839 | @code{span} splits the list @var{lst} into the longest initial prefix |
840 | whose elements all satisfy the predicate @var{pred}, and the remaining | |
841 | tail. @code{break} inverts the sense of the predicate. | |
842 | ||
843 | @code{span!} and @code{break!} are allowed, but not required to modify | |
844 | the structure of the input list @var{lst} in order to produce the | |
845 | result. | |
3e73b6f9 KR |
846 | |
847 | Note that the name @code{break} conflicts with the @code{break} | |
848 | binding established by @code{while} (@pxref{while do}). Applications | |
849 | wanting to use @code{break} from within a @code{while} loop will need | |
850 | to make a new define under a different name. | |
a0e07ba4 NJ |
851 | @end deffn |
852 | ||
df0a1002 BT |
853 | @deffn {Scheme Procedure} any pred lst1 lst2 @dots{} |
854 | Test whether any set of elements from @var{lst1} @var{lst2} @dots{} | |
855 | satisfies @var{pred}. If so, the return value is the return value from | |
856 | the successful @var{pred} call, or if not, the return value is | |
857 | @code{#f}. | |
62705beb | 858 | |
df0a1002 BT |
859 | If there are n list arguments, then @var{pred} must be a predicate |
860 | taking n arguments. Each @var{pred} call is @code{(@var{pred} | |
861 | @var{elem1} @var{elem2} @dots{} )} taking an element from each | |
862 | @var{lst}. The calls are made successively for the first, second, etc. | |
863 | elements of the lists, stopping when @var{pred} returns non-@code{#f}, | |
864 | or when the end of the shortest list is reached. | |
62705beb | 865 | |
df0a1002 | 866 | The @var{pred} call on the last set of elements (i.e., when the end of |
62705beb KR |
867 | the shortest list has been reached), if that point is reached, is a |
868 | tail call. | |
869 | @end deffn | |
870 | ||
df0a1002 BT |
871 | @deffn {Scheme Procedure} every pred lst1 lst2 @dots{} |
872 | Test whether every set of elements from @var{lst1} @var{lst2} @dots{} | |
873 | satisfies @var{pred}. If so, the return value is the return from the | |
874 | final @var{pred} call, or if not, the return value is @code{#f}. | |
62705beb | 875 | |
df0a1002 BT |
876 | If there are n list arguments, then @var{pred} must be a predicate |
877 | taking n arguments. Each @var{pred} call is @code{(@var{pred} | |
878 | @var{elem1} @var{elem2 @dots{}})} taking an element from each | |
879 | @var{lst}. The calls are made successively for the first, second, etc. | |
880 | elements of the lists, stopping if @var{pred} returns @code{#f}, or when | |
881 | the end of any of the lists is reached. | |
62705beb | 882 | |
df0a1002 | 883 | The @var{pred} call on the last set of elements (i.e., when the end of |
62705beb KR |
884 | the shortest list has been reached) is a tail call. |
885 | ||
df0a1002 BT |
886 | If one of @var{lst1} @var{lst2} @dots{}is empty then no calls to |
887 | @var{pred} are made, and the return value is @code{#t}. | |
a0e07ba4 NJ |
888 | @end deffn |
889 | ||
df0a1002 | 890 | @deffn {Scheme Procedure} list-index pred lst1 lst2 @dots{} |
d1736abf | 891 | Return the index of the first set of elements, one from each of |
df0a1002 | 892 | @var{lst1} @var{lst2} @dots{}, which satisfies @var{pred}. |
d1736abf | 893 | |
df0a1002 | 894 | @var{pred} is called as @code{(@var{elem1} @var{elem2 @dots{}})}. |
d1736abf KR |
895 | Searching stops when the end of the shortest @var{lst} is reached. |
896 | The return index starts from 0 for the first set of elements. If no | |
df0a1002 | 897 | set of elements pass, then the return value is @code{#f}. |
0166e7f2 KR |
898 | |
899 | @example | |
900 | (list-index odd? '(2 4 6 9)) @result{} 3 | |
901 | (list-index = '(1 2 3) '(3 1 2)) @result{} #f | |
902 | @end example | |
a0e07ba4 NJ |
903 | @end deffn |
904 | ||
8f85c0c6 | 905 | @deffn {Scheme Procedure} member x lst [=] |
a0e07ba4 | 906 | Return the first sublist of @var{lst} whose @sc{car} is equal to |
ca04a5ae | 907 | @var{x}. If @var{x} does not appear in @var{lst}, return @code{#f}. |
ea6ea01b | 908 | |
ca04a5ae KR |
909 | Equality is determined by @code{equal?}, or by the equality predicate |
910 | @var{=} if given. @var{=} is called @code{(= @var{x} elem)}, | |
911 | ie.@: with the given @var{x} first, so for example to find the first | |
912 | element greater than 5, | |
913 | ||
914 | @example | |
915 | (member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9) | |
916 | @end example | |
917 | ||
918 | This version of @code{member} extends the core @code{member} | |
919 | (@pxref{List Searching}) by accepting an equality predicate. | |
a0e07ba4 NJ |
920 | @end deffn |
921 | ||
922 | ||
923 | @node SRFI-1 Deleting | |
3229f68b | 924 | @subsubsection Deleting |
7c2e18cd | 925 | @cindex list delete |
a0e07ba4 | 926 | |
8f85c0c6 NJ |
927 | @deffn {Scheme Procedure} delete x lst [=] |
928 | @deffnx {Scheme Procedure} delete! x lst [=] | |
b6b9376a KR |
929 | Return a list containing the elements of @var{lst} but with those |
930 | equal to @var{x} deleted. The returned elements will be in the same | |
931 | order as they were in @var{lst}. | |
932 | ||
933 | Equality is determined by the @var{=} predicate, or @code{equal?} if | |
934 | not given. An equality call is made just once for each element, but | |
935 | the order in which the calls are made on the elements is unspecified. | |
a0e07ba4 | 936 | |
243bdb63 | 937 | The equality calls are always @code{(= x elem)}, ie.@: the given @var{x} |
b6b9376a KR |
938 | is first. This means for instance elements greater than 5 can be |
939 | deleted with @code{(delete 5 lst <)}. | |
940 | ||
941 | @code{delete} does not modify @var{lst}, but the return might share a | |
942 | common tail with @var{lst}. @code{delete!} may modify the structure | |
943 | of @var{lst} to construct its return. | |
ea6ea01b | 944 | |
4eb21177 KR |
945 | These functions extend the core @code{delete} and @code{delete!} |
946 | (@pxref{List Modification}) in accepting an equality predicate. See | |
947 | also @code{lset-difference} (@pxref{SRFI-1 Set Operations}) for | |
948 | deleting multiple elements from a list. | |
a0e07ba4 NJ |
949 | @end deffn |
950 | ||
8f85c0c6 NJ |
951 | @deffn {Scheme Procedure} delete-duplicates lst [=] |
952 | @deffnx {Scheme Procedure} delete-duplicates! lst [=] | |
b6b9376a KR |
953 | Return a list containing the elements of @var{lst} but without |
954 | duplicates. | |
955 | ||
956 | When elements are equal, only the first in @var{lst} is retained. | |
957 | Equal elements can be anywhere in @var{lst}, they don't have to be | |
958 | adjacent. The returned list will have the retained elements in the | |
959 | same order as they were in @var{lst}. | |
960 | ||
961 | Equality is determined by the @var{=} predicate, or @code{equal?} if | |
962 | not given. Calls @code{(= x y)} are made with element @var{x} being | |
963 | before @var{y} in @var{lst}. A call is made at most once for each | |
964 | combination, but the sequence of the calls across the elements is | |
965 | unspecified. | |
966 | ||
967 | @code{delete-duplicates} does not modify @var{lst}, but the return | |
968 | might share a common tail with @var{lst}. @code{delete-duplicates!} | |
969 | may modify the structure of @var{lst} to construct its return. | |
970 | ||
971 | In the worst case, this is an @math{O(N^2)} algorithm because it must | |
972 | check each element against all those preceding it. For long lists it | |
973 | is more efficient to sort and then compare only adjacent elements. | |
a0e07ba4 NJ |
974 | @end deffn |
975 | ||
976 | ||
977 | @node SRFI-1 Association Lists | |
3229f68b | 978 | @subsubsection Association Lists |
7c2e18cd KR |
979 | @cindex association list |
980 | @cindex alist | |
a0e07ba4 NJ |
981 | |
982 | @c FIXME::martin: Review me! | |
983 | ||
984 | Association lists are described in detail in section @ref{Association | |
985 | Lists}. The present section only documents the additional procedures | |
986 | for dealing with association lists defined by SRFI-1. | |
987 | ||
8f85c0c6 | 988 | @deffn {Scheme Procedure} assoc key alist [=] |
23f2b9a3 KR |
989 | Return the pair from @var{alist} which matches @var{key}. This |
990 | extends the core @code{assoc} (@pxref{Retrieving Alist Entries}) by | |
991 | taking an optional @var{=} comparison procedure. | |
992 | ||
993 | The default comparison is @code{equal?}. If an @var{=} parameter is | |
679cceed | 994 | given it's called @code{(@var{=} @var{key} @var{alistcar})}, i.e.@: the |
23f2b9a3 KR |
995 | given target @var{key} is the first argument, and a @code{car} from |
996 | @var{alist} is second. | |
ea6ea01b | 997 | |
23f2b9a3 KR |
998 | For example a case-insensitive string lookup, |
999 | ||
1000 | @example | |
1001 | (assoc "yy" '(("XX" . 1) ("YY" . 2)) string-ci=?) | |
1002 | @result{} ("YY" . 2) | |
1003 | @end example | |
a0e07ba4 NJ |
1004 | @end deffn |
1005 | ||
8f85c0c6 | 1006 | @deffn {Scheme Procedure} alist-cons key datum alist |
5e5999f9 KR |
1007 | Cons a new association @var{key} and @var{datum} onto @var{alist} and |
1008 | return the result. This is equivalent to | |
a0e07ba4 NJ |
1009 | |
1010 | @lisp | |
1011 | (cons (cons @var{key} @var{datum}) @var{alist}) | |
1012 | @end lisp | |
1013 | ||
5e5999f9 KR |
1014 | @code{acons} (@pxref{Adding or Setting Alist Entries}) in the Guile |
1015 | core does the same thing. | |
a0e07ba4 NJ |
1016 | @end deffn |
1017 | ||
8f85c0c6 | 1018 | @deffn {Scheme Procedure} alist-copy alist |
a0e07ba4 NJ |
1019 | Return a newly allocated copy of @var{alist}, that means that the |
1020 | spine of the list as well as the pairs are copied. | |
1021 | @end deffn | |
1022 | ||
8f85c0c6 NJ |
1023 | @deffn {Scheme Procedure} alist-delete key alist [=] |
1024 | @deffnx {Scheme Procedure} alist-delete! key alist [=] | |
bd35f1f0 KR |
1025 | Return a list containing the elements of @var{alist} but with those |
1026 | elements whose keys are equal to @var{key} deleted. The returned | |
1027 | elements will be in the same order as they were in @var{alist}. | |
a0e07ba4 | 1028 | |
bd35f1f0 KR |
1029 | Equality is determined by the @var{=} predicate, or @code{equal?} if |
1030 | not given. The order in which elements are tested is unspecified, but | |
679cceed | 1031 | each equality call is made @code{(= key alistkey)}, i.e.@: the given |
bd35f1f0 KR |
1032 | @var{key} parameter is first and the key from @var{alist} second. |
1033 | This means for instance all associations with a key greater than 5 can | |
1034 | be removed with @code{(alist-delete 5 alist <)}. | |
1035 | ||
1036 | @code{alist-delete} does not modify @var{alist}, but the return might | |
1037 | share a common tail with @var{alist}. @code{alist-delete!} may modify | |
1038 | the list structure of @var{alist} to construct its return. | |
a0e07ba4 NJ |
1039 | @end deffn |
1040 | ||
1041 | ||
1042 | @node SRFI-1 Set Operations | |
3229f68b | 1043 | @subsubsection Set Operations on Lists |
7c2e18cd | 1044 | @cindex list set operation |
a0e07ba4 | 1045 | |
4eb21177 KR |
1046 | Lists can be used to represent sets of objects. The procedures in |
1047 | this section operate on such lists as sets. | |
1048 | ||
1049 | Note that lists are not an efficient way to implement large sets. The | |
9aa0c3dd | 1050 | procedures here typically take time @math{@var{m}@cross{}@var{n}} when |
4eb21177 KR |
1051 | operating on @var{m} and @var{n} element lists. Other data structures |
1052 | like trees, bitsets (@pxref{Bit Vectors}) or hash tables (@pxref{Hash | |
1053 | Tables}) are faster. | |
1054 | ||
1055 | All these procedures take an equality predicate as the first argument. | |
1056 | This predicate is used for testing the objects in the list sets for | |
1057 | sameness. This predicate must be consistent with @code{eq?} | |
1058 | (@pxref{Equality}) in the sense that if two list elements are | |
1059 | @code{eq?} then they must also be equal under the predicate. This | |
1060 | simply means a given object must be equal to itself. | |
a0e07ba4 | 1061 | |
df0a1002 | 1062 | @deffn {Scheme Procedure} lset<= = list @dots{} |
4eb21177 | 1063 | Return @code{#t} if each list is a subset of the one following it. |
df0a1002 BT |
1064 | I.e., @var{list1} is a subset of @var{list2}, @var{list2} is a subset of |
1065 | @var{list3}, etc., for as many lists as given. If only one list or no | |
1066 | lists are given, the return value is @code{#t}. | |
4eb21177 KR |
1067 | |
1068 | A list @var{x} is a subset of @var{y} if each element of @var{x} is | |
1069 | equal to some element in @var{y}. Elements are compared using the | |
1070 | given @var{=} procedure, called as @code{(@var{=} xelem yelem)}. | |
1071 | ||
1072 | @example | |
1073 | (lset<= eq?) @result{} #t | |
1074 | (lset<= eqv? '(1 2 3) '(1)) @result{} #f | |
1075 | (lset<= eqv? '(1 3 2) '(4 3 1 2)) @result{} #t | |
1076 | @end example | |
a0e07ba4 NJ |
1077 | @end deffn |
1078 | ||
df0a1002 | 1079 | @deffn {Scheme Procedure} lset= = list @dots{} |
4eb21177 | 1080 | Return @code{#t} if all argument lists are set-equal. @var{list1} is |
df0a1002 BT |
1081 | compared to @var{list2}, @var{list2} to @var{list3}, etc., for as many |
1082 | lists as given. If only one list or no lists are given, the return | |
1083 | value is @code{#t}. | |
4eb21177 KR |
1084 | |
1085 | Two lists @var{x} and @var{y} are set-equal if each element of @var{x} | |
1086 | is equal to some element of @var{y} and conversely each element of | |
1087 | @var{y} is equal to some element of @var{x}. The order of the | |
1088 | elements in the lists doesn't matter. Element equality is determined | |
1089 | with the given @var{=} procedure, called as @code{(@var{=} xelem | |
1090 | yelem)}, but exactly which calls are made is unspecified. | |
1091 | ||
1092 | @example | |
1093 | (lset= eq?) @result{} #t | |
1094 | (lset= eqv? '(1 2 3) '(3 2 1)) @result{} #t | |
1095 | (lset= string-ci=? '("a" "A" "b") '("B" "b" "a")) @result{} #t | |
1096 | @end example | |
a0e07ba4 NJ |
1097 | @end deffn |
1098 | ||
df0a1002 BT |
1099 | @deffn {Scheme Procedure} lset-adjoin = list elem @dots{} |
1100 | Add to @var{list} any of the given @var{elem}s not already in the list. | |
1101 | @var{elem}s are @code{cons}ed onto the start of @var{list} (so the | |
1102 | return value shares a common tail with @var{list}), but the order that | |
1103 | the @var{elem}s are added is unspecified. | |
4eb21177 KR |
1104 | |
1105 | The given @var{=} procedure is used for comparing elements, called as | |
df0a1002 | 1106 | @code{(@var{=} listelem elem)}, i.e., the second argument is one of |
4eb21177 KR |
1107 | the given @var{elem} parameters. |
1108 | ||
1109 | @example | |
1110 | (lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3) | |
1111 | @end example | |
a0e07ba4 NJ |
1112 | @end deffn |
1113 | ||
df0a1002 BT |
1114 | @deffn {Scheme Procedure} lset-union = list @dots{} |
1115 | @deffnx {Scheme Procedure} lset-union! = list @dots{} | |
4eb21177 KR |
1116 | Return the union of the argument list sets. The result is built by |
1117 | taking the union of @var{list1} and @var{list2}, then the union of | |
df0a1002 | 1118 | that with @var{list3}, etc., for as many lists as given. For one list |
4eb21177 KR |
1119 | argument that list itself is the result, for no list arguments the |
1120 | result is the empty list. | |
1121 | ||
1122 | The union of two lists @var{x} and @var{y} is formed as follows. If | |
1123 | @var{x} is empty then the result is @var{y}. Otherwise start with | |
1124 | @var{x} as the result and consider each @var{y} element (from first to | |
1125 | last). A @var{y} element not equal to something already in the result | |
1126 | is @code{cons}ed onto the result. | |
1127 | ||
1128 | The given @var{=} procedure is used for comparing elements, called as | |
1129 | @code{(@var{=} relem yelem)}. The first argument is from the result | |
1130 | accumulated so far, and the second is from the list being union-ed in. | |
1131 | But exactly which calls are made is otherwise unspecified. | |
1132 | ||
1133 | Notice that duplicate elements in @var{list1} (or the first non-empty | |
1134 | list) are preserved, but that repeated elements in subsequent lists | |
1135 | are only added once. | |
1136 | ||
1137 | @example | |
1138 | (lset-union eqv?) @result{} () | |
1139 | (lset-union eqv? '(1 2 3)) @result{} (1 2 3) | |
1140 | (lset-union eqv? '(1 2 1 3) '(2 4 5) '(5)) @result{} (5 4 1 2 1 3) | |
1141 | @end example | |
1142 | ||
1143 | @code{lset-union} doesn't change the given lists but the result may | |
1144 | share a tail with the first non-empty list. @code{lset-union!} can | |
1145 | modify all of the given lists to form the result. | |
a0e07ba4 NJ |
1146 | @end deffn |
1147 | ||
8f85c0c6 NJ |
1148 | @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{} |
1149 | @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{} | |
4eb21177 KR |
1150 | Return the intersection of @var{list1} with the other argument lists, |
1151 | meaning those elements of @var{list1} which are also in all of | |
1152 | @var{list2} etc. For one list argument, just that list is returned. | |
1153 | ||
1154 | The test for an element of @var{list1} to be in the return is simply | |
1155 | that it's equal to some element in each of @var{list2} etc. Notice | |
1156 | this means an element appearing twice in @var{list1} but only once in | |
1157 | each of @var{list2} etc will go into the return twice. The return has | |
1158 | its elements in the same order as they were in @var{list1}. | |
1159 | ||
1160 | The given @var{=} procedure is used for comparing elements, called as | |
1161 | @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1} | |
1162 | and the second is from one of the subsequent lists. But exactly which | |
1163 | calls are made and in what order is unspecified. | |
1164 | ||
1165 | @example | |
1166 | (lset-intersection eqv? '(x y)) @result{} (x y) | |
1167 | (lset-intersection eqv? '(1 2 3) '(4 3 2)) @result{} (2 3) | |
1168 | (lset-intersection eqv? '(1 1 2 2) '(1 2) '(2 1) '(2)) @result{} (2 2) | |
1169 | @end example | |
1170 | ||
1171 | The return from @code{lset-intersection} may share a tail with | |
1172 | @var{list1}. @code{lset-intersection!} may modify @var{list1} to form | |
1173 | its result. | |
a0e07ba4 NJ |
1174 | @end deffn |
1175 | ||
8f85c0c6 NJ |
1176 | @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{} |
1177 | @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{} | |
4eb21177 KR |
1178 | Return @var{list1} with any elements in @var{list2}, @var{list3} etc |
1179 | removed (ie.@: subtracted). For one list argument, just that list is | |
1180 | returned. | |
1181 | ||
1182 | The given @var{=} procedure is used for comparing elements, called as | |
1183 | @code{(@var{=} elem1 elemN)}. The first argument is from @var{list1} | |
1184 | and the second from one of the subsequent lists. But exactly which | |
1185 | calls are made and in what order is unspecified. | |
a0e07ba4 | 1186 | |
4eb21177 KR |
1187 | @example |
1188 | (lset-difference eqv? '(x y)) @result{} (x y) | |
1189 | (lset-difference eqv? '(1 2 3) '(3 1)) @result{} (2) | |
1190 | (lset-difference eqv? '(1 2 3) '(3) '(2)) @result{} (1) | |
1191 | @end example | |
1192 | ||
1193 | The return from @code{lset-difference} may share a tail with | |
1194 | @var{list1}. @code{lset-difference!} may modify @var{list1} to form | |
1195 | its result. | |
a0e07ba4 NJ |
1196 | @end deffn |
1197 | ||
8f85c0c6 NJ |
1198 | @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{} |
1199 | @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{} | |
4eb21177 KR |
1200 | Return two values (@pxref{Multiple Values}), the difference and |
1201 | intersection of the argument lists as per @code{lset-difference} and | |
1202 | @code{lset-intersection} above. | |
1203 | ||
1204 | For two list arguments this partitions @var{list1} into those elements | |
1205 | of @var{list1} which are in @var{list2} and not in @var{list2}. (But | |
1206 | for more than two arguments there can be elements of @var{list1} which | |
1207 | are neither part of the difference nor the intersection.) | |
1208 | ||
1209 | One of the return values from @code{lset-diff+intersection} may share | |
1210 | a tail with @var{list1}. @code{lset-diff+intersection!} may modify | |
1211 | @var{list1} to form its results. | |
1212 | @end deffn | |
1213 | ||
df0a1002 BT |
1214 | @deffn {Scheme Procedure} lset-xor = list @dots{} |
1215 | @deffnx {Scheme Procedure} lset-xor! = list @dots{} | |
4eb21177 KR |
1216 | Return an XOR of the argument lists. For two lists this means those |
1217 | elements which are in exactly one of the lists. For more than two | |
1218 | lists it means those elements which appear in an odd number of the | |
1219 | lists. | |
1220 | ||
1221 | To be precise, the XOR of two lists @var{x} and @var{y} is formed by | |
1222 | taking those elements of @var{x} not equal to any element of @var{y}, | |
1223 | plus those elements of @var{y} not equal to any element of @var{x}. | |
1224 | Equality is determined with the given @var{=} procedure, called as | |
1225 | @code{(@var{=} e1 e2)}. One argument is from @var{x} and the other | |
1226 | from @var{y}, but which way around is unspecified. Exactly which | |
1227 | calls are made is also unspecified, as is the order of the elements in | |
1228 | the result. | |
1229 | ||
1230 | @example | |
1231 | (lset-xor eqv? '(x y)) @result{} (x y) | |
1232 | (lset-xor eqv? '(1 2 3) '(4 3 2)) @result{} (4 1) | |
1233 | @end example | |
1234 | ||
1235 | The return from @code{lset-xor} may share a tail with one of the list | |
1236 | arguments. @code{lset-xor!} may modify @var{list1} to form its | |
1237 | result. | |
a0e07ba4 NJ |
1238 | @end deffn |
1239 | ||
1240 | ||
1241 | @node SRFI-2 | |
3229f68b | 1242 | @subsection SRFI-2 - and-let* |
8742c48b | 1243 | @cindex SRFI-2 |
a0e07ba4 | 1244 | |
4fd0db14 KR |
1245 | @noindent |
1246 | The following syntax can be obtained with | |
a0e07ba4 | 1247 | |
4fd0db14 KR |
1248 | @lisp |
1249 | (use-modules (srfi srfi-2)) | |
1250 | @end lisp | |
a0e07ba4 | 1251 | |
abd731ff NL |
1252 | or alternatively |
1253 | ||
1254 | @lisp | |
1255 | (use-modules (ice-9 and-let-star)) | |
1256 | @end lisp | |
1257 | ||
4fd0db14 KR |
1258 | @deffn {library syntax} and-let* (clause @dots{}) body @dots{} |
1259 | A combination of @code{and} and @code{let*}. | |
1260 | ||
1261 | Each @var{clause} is evaluated in turn, and if @code{#f} is obtained | |
1262 | then evaluation stops and @code{#f} is returned. If all are | |
1263 | non-@code{#f} then @var{body} is evaluated and the last form gives the | |
6b1a6e4c KR |
1264 | return value, or if @var{body} is empty then the result is @code{#t}. |
1265 | Each @var{clause} should be one of the following, | |
4fd0db14 KR |
1266 | |
1267 | @table @code | |
1268 | @item (symbol expr) | |
1269 | Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}. | |
1270 | Like @code{let*}, that binding is available to subsequent clauses. | |
1271 | @item (expr) | |
1272 | Evaluate @var{expr} and check for @code{#f}. | |
1273 | @item symbol | |
1274 | Get the value bound to @var{symbol} and check for @code{#f}. | |
1275 | @end table | |
a0e07ba4 | 1276 | |
4fd0db14 KR |
1277 | Notice that @code{(expr)} has an ``extra'' pair of parentheses, for |
1278 | instance @code{((eq? x y))}. One way to remember this is to imagine | |
1279 | the @code{symbol} in @code{(symbol expr)} is omitted. | |
a0e07ba4 | 1280 | |
4fd0db14 KR |
1281 | @code{and-let*} is good for calculations where a @code{#f} value means |
1282 | termination, but where a non-@code{#f} value is going to be needed in | |
1283 | subsequent expressions. | |
1284 | ||
1285 | The following illustrates this, it returns text between brackets | |
1286 | @samp{[...]} in a string, or @code{#f} if there are no such brackets | |
1287 | (ie.@: either @code{string-index} gives @code{#f}). | |
1288 | ||
1289 | @example | |
1290 | (define (extract-brackets str) | |
1291 | (and-let* ((start (string-index str #\[)) | |
1292 | (end (string-index str #\] start))) | |
1293 | (substring str (1+ start) end))) | |
1294 | @end example | |
1295 | ||
1296 | The following shows plain variables and expressions tested too. | |
1297 | @code{diagnostic-levels} is taken to be an alist associating a | |
1298 | diagnostic type with a level. @code{str} is printed only if the type | |
1299 | is known and its level is high enough. | |
1300 | ||
1301 | @example | |
1302 | (define (show-diagnostic type str) | |
1303 | (and-let* (want-diagnostics | |
1304 | (level (assq-ref diagnostic-levels type)) | |
1305 | ((>= level current-diagnostic-level))) | |
1306 | (display str))) | |
1307 | @end example | |
1308 | ||
1309 | The advantage of @code{and-let*} is that an extended sequence of | |
1310 | expressions and tests doesn't require lots of nesting as would arise | |
1311 | from separate @code{and} and @code{let*}, or from @code{cond} with | |
1312 | @code{=>}. | |
1313 | ||
1314 | @end deffn | |
a0e07ba4 NJ |
1315 | |
1316 | ||
1317 | @node SRFI-4 | |
3229f68b | 1318 | @subsection SRFI-4 - Homogeneous numeric vector datatypes |
8742c48b | 1319 | @cindex SRFI-4 |
a0e07ba4 | 1320 | |
27219b32 AW |
1321 | SRFI-4 provides an interface to uniform numeric vectors: vectors whose elements |
1322 | are all of a single numeric type. Guile offers uniform numeric vectors for | |
1323 | signed and unsigned 8-bit, 16-bit, 32-bit, and 64-bit integers, two sizes of | |
1324 | floating point values, and, as an extension to SRFI-4, complex floating-point | |
1325 | numbers of these two sizes. | |
1326 | ||
1327 | The standard SRFI-4 procedures and data types may be included via loading the | |
1328 | appropriate module: | |
1329 | ||
1330 | @example | |
1331 | (use-modules (srfi srfi-4)) | |
1332 | @end example | |
1333 | ||
1334 | This module is currently a part of the default Guile environment, but it is a | |
1335 | good practice to explicitly import the module. In the future, using SRFI-4 | |
1336 | procedures without importing the SRFI-4 module will cause a deprecation message | |
1337 | to be printed. (Of course, one may call the C functions at any time. Would that | |
1338 | C had modules!) | |
1339 | ||
1340 | @menu | |
1341 | * SRFI-4 Overview:: The warp and weft of uniform numeric vectors. | |
1342 | * SRFI-4 API:: Uniform vectors, from Scheme and from C. | |
1343 | * SRFI-4 Generic Operations:: The general, operating on the specific. | |
1344 | * SRFI-4 and Bytevectors:: SRFI-4 vectors are backed by bytevectors. | |
1345 | * SRFI-4 Extensions:: Guile-specific extensions to the standard. | |
1346 | @end menu | |
1347 | ||
1348 | @node SRFI-4 Overview | |
1349 | @subsubsection SRFI-4 - Overview | |
1350 | ||
1351 | Uniform numeric vectors can be useful since they consume less memory | |
1352 | than the non-uniform, general vectors. Also, since the types they can | |
1353 | store correspond directly to C types, it is easier to work with them | |
1354 | efficiently on a low level. Consider image processing as an example, | |
1355 | where you want to apply a filter to some image. While you could store | |
1356 | the pixels of an image in a general vector and write a general | |
1357 | convolution function, things are much more efficient with uniform | |
1358 | vectors: the convolution function knows that all pixels are unsigned | |
1359 | 8-bit values (say), and can use a very tight inner loop. | |
1360 | ||
1361 | This is implemented in Scheme by having the compiler notice calls to the SRFI-4 | |
1362 | accessors, and inline them to appropriate compiled code. From C you have access | |
1363 | to the raw array; functions for efficiently working with uniform numeric vectors | |
1364 | from C are listed at the end of this section. | |
1365 | ||
1366 | Uniform numeric vectors are the special case of one dimensional uniform | |
1367 | numeric arrays. | |
1368 | ||
1369 | There are 12 standard kinds of uniform numeric vectors, and they all have their | |
1370 | own complement of constructors, accessors, and so on. Procedures that operate on | |
1371 | a specific kind of uniform numeric vector have a ``tag'' in their name, | |
1372 | indicating the element type. | |
1373 | ||
1374 | @table @nicode | |
1375 | @item u8 | |
1376 | unsigned 8-bit integers | |
1377 | ||
1378 | @item s8 | |
1379 | signed 8-bit integers | |
1380 | ||
1381 | @item u16 | |
1382 | unsigned 16-bit integers | |
1383 | ||
1384 | @item s16 | |
1385 | signed 16-bit integers | |
1386 | ||
1387 | @item u32 | |
1388 | unsigned 32-bit integers | |
1389 | ||
1390 | @item s32 | |
1391 | signed 32-bit integers | |
1392 | ||
1393 | @item u64 | |
1394 | unsigned 64-bit integers | |
1395 | ||
1396 | @item s64 | |
1397 | signed 64-bit integers | |
1398 | ||
1399 | @item f32 | |
1400 | the C type @code{float} | |
1401 | ||
1402 | @item f64 | |
1403 | the C type @code{double} | |
1404 | ||
1405 | @end table | |
1406 | ||
1407 | In addition, Guile supports uniform arrays of complex numbers, with the | |
1408 | nonstandard tags: | |
1409 | ||
1410 | @table @nicode | |
1411 | ||
1412 | @item c32 | |
1413 | complex numbers in rectangular form with the real and imaginary part | |
1414 | being a @code{float} | |
1415 | ||
1416 | @item c64 | |
1417 | complex numbers in rectangular form with the real and imaginary part | |
1418 | being a @code{double} | |
1419 | ||
1420 | @end table | |
1421 | ||
1422 | The external representation (ie.@: read syntax) for these vectors is | |
1423 | similar to normal Scheme vectors, but with an additional tag from the | |
1424 | tables above indicating the vector's type. For example, | |
1425 | ||
1426 | @lisp | |
1427 | #u16(1 2 3) | |
1428 | #f64(3.1415 2.71) | |
1429 | @end lisp | |
1430 | ||
1431 | Note that the read syntax for floating-point here conflicts with | |
1432 | @code{#f} for false. In Standard Scheme one can write @code{(1 #f3)} | |
1433 | for a three element list @code{(1 #f 3)}, but for Guile @code{(1 #f3)} | |
1434 | is invalid. @code{(1 #f 3)} is almost certainly what one should write | |
1435 | anyway to make the intention clear, so this is rarely a problem. | |
1436 | ||
1437 | ||
1438 | @node SRFI-4 API | |
1439 | @subsubsection SRFI-4 - API | |
1440 | ||
1441 | Note that the @nicode{c32} and @nicode{c64} functions are only available from | |
1442 | @nicode{(srfi srfi-4 gnu)}. | |
1443 | ||
1444 | @deffn {Scheme Procedure} u8vector? obj | |
1445 | @deffnx {Scheme Procedure} s8vector? obj | |
1446 | @deffnx {Scheme Procedure} u16vector? obj | |
1447 | @deffnx {Scheme Procedure} s16vector? obj | |
1448 | @deffnx {Scheme Procedure} u32vector? obj | |
1449 | @deffnx {Scheme Procedure} s32vector? obj | |
1450 | @deffnx {Scheme Procedure} u64vector? obj | |
1451 | @deffnx {Scheme Procedure} s64vector? obj | |
1452 | @deffnx {Scheme Procedure} f32vector? obj | |
1453 | @deffnx {Scheme Procedure} f64vector? obj | |
1454 | @deffnx {Scheme Procedure} c32vector? obj | |
1455 | @deffnx {Scheme Procedure} c64vector? obj | |
1456 | @deffnx {C Function} scm_u8vector_p (obj) | |
1457 | @deffnx {C Function} scm_s8vector_p (obj) | |
1458 | @deffnx {C Function} scm_u16vector_p (obj) | |
1459 | @deffnx {C Function} scm_s16vector_p (obj) | |
1460 | @deffnx {C Function} scm_u32vector_p (obj) | |
1461 | @deffnx {C Function} scm_s32vector_p (obj) | |
1462 | @deffnx {C Function} scm_u64vector_p (obj) | |
1463 | @deffnx {C Function} scm_s64vector_p (obj) | |
1464 | @deffnx {C Function} scm_f32vector_p (obj) | |
1465 | @deffnx {C Function} scm_f64vector_p (obj) | |
1466 | @deffnx {C Function} scm_c32vector_p (obj) | |
1467 | @deffnx {C Function} scm_c64vector_p (obj) | |
1468 | Return @code{#t} if @var{obj} is a homogeneous numeric vector of the | |
1469 | indicated type. | |
1470 | @end deffn | |
1471 | ||
1472 | @deffn {Scheme Procedure} make-u8vector n [value] | |
1473 | @deffnx {Scheme Procedure} make-s8vector n [value] | |
1474 | @deffnx {Scheme Procedure} make-u16vector n [value] | |
1475 | @deffnx {Scheme Procedure} make-s16vector n [value] | |
1476 | @deffnx {Scheme Procedure} make-u32vector n [value] | |
1477 | @deffnx {Scheme Procedure} make-s32vector n [value] | |
1478 | @deffnx {Scheme Procedure} make-u64vector n [value] | |
1479 | @deffnx {Scheme Procedure} make-s64vector n [value] | |
1480 | @deffnx {Scheme Procedure} make-f32vector n [value] | |
1481 | @deffnx {Scheme Procedure} make-f64vector n [value] | |
1482 | @deffnx {Scheme Procedure} make-c32vector n [value] | |
1483 | @deffnx {Scheme Procedure} make-c64vector n [value] | |
5f6ffd66 BT |
1484 | @deffnx {C Function} scm_make_u8vector (n, value) |
1485 | @deffnx {C Function} scm_make_s8vector (n, value) | |
1486 | @deffnx {C Function} scm_make_u16vector (n, value) | |
1487 | @deffnx {C Function} scm_make_s16vector (n, value) | |
1488 | @deffnx {C Function} scm_make_u32vector (n, value) | |
1489 | @deffnx {C Function} scm_make_s32vector (n, value) | |
1490 | @deffnx {C Function} scm_make_u64vector (n, value) | |
1491 | @deffnx {C Function} scm_make_s64vector (n, value) | |
1492 | @deffnx {C Function} scm_make_f32vector (n, value) | |
1493 | @deffnx {C Function} scm_make_f64vector (n, value) | |
1494 | @deffnx {C Function} scm_make_c32vector (n, value) | |
1495 | @deffnx {C Function} scm_make_c64vector (n, value) | |
27219b32 AW |
1496 | Return a newly allocated homogeneous numeric vector holding @var{n} |
1497 | elements of the indicated type. If @var{value} is given, the vector | |
1498 | is initialized with that value, otherwise the contents are | |
1499 | unspecified. | |
1500 | @end deffn | |
1501 | ||
1502 | @deffn {Scheme Procedure} u8vector value @dots{} | |
1503 | @deffnx {Scheme Procedure} s8vector value @dots{} | |
1504 | @deffnx {Scheme Procedure} u16vector value @dots{} | |
1505 | @deffnx {Scheme Procedure} s16vector value @dots{} | |
1506 | @deffnx {Scheme Procedure} u32vector value @dots{} | |
1507 | @deffnx {Scheme Procedure} s32vector value @dots{} | |
1508 | @deffnx {Scheme Procedure} u64vector value @dots{} | |
1509 | @deffnx {Scheme Procedure} s64vector value @dots{} | |
1510 | @deffnx {Scheme Procedure} f32vector value @dots{} | |
1511 | @deffnx {Scheme Procedure} f64vector value @dots{} | |
1512 | @deffnx {Scheme Procedure} c32vector value @dots{} | |
1513 | @deffnx {Scheme Procedure} c64vector value @dots{} | |
1514 | @deffnx {C Function} scm_u8vector (values) | |
1515 | @deffnx {C Function} scm_s8vector (values) | |
1516 | @deffnx {C Function} scm_u16vector (values) | |
1517 | @deffnx {C Function} scm_s16vector (values) | |
1518 | @deffnx {C Function} scm_u32vector (values) | |
1519 | @deffnx {C Function} scm_s32vector (values) | |
1520 | @deffnx {C Function} scm_u64vector (values) | |
1521 | @deffnx {C Function} scm_s64vector (values) | |
1522 | @deffnx {C Function} scm_f32vector (values) | |
1523 | @deffnx {C Function} scm_f64vector (values) | |
1524 | @deffnx {C Function} scm_c32vector (values) | |
1525 | @deffnx {C Function} scm_c64vector (values) | |
1526 | Return a newly allocated homogeneous numeric vector of the indicated | |
1527 | type, holding the given parameter @var{value}s. The vector length is | |
1528 | the number of parameters given. | |
1529 | @end deffn | |
1530 | ||
1531 | @deffn {Scheme Procedure} u8vector-length vec | |
1532 | @deffnx {Scheme Procedure} s8vector-length vec | |
1533 | @deffnx {Scheme Procedure} u16vector-length vec | |
1534 | @deffnx {Scheme Procedure} s16vector-length vec | |
1535 | @deffnx {Scheme Procedure} u32vector-length vec | |
1536 | @deffnx {Scheme Procedure} s32vector-length vec | |
1537 | @deffnx {Scheme Procedure} u64vector-length vec | |
1538 | @deffnx {Scheme Procedure} s64vector-length vec | |
1539 | @deffnx {Scheme Procedure} f32vector-length vec | |
1540 | @deffnx {Scheme Procedure} f64vector-length vec | |
1541 | @deffnx {Scheme Procedure} c32vector-length vec | |
1542 | @deffnx {Scheme Procedure} c64vector-length vec | |
1543 | @deffnx {C Function} scm_u8vector_length (vec) | |
1544 | @deffnx {C Function} scm_s8vector_length (vec) | |
1545 | @deffnx {C Function} scm_u16vector_length (vec) | |
1546 | @deffnx {C Function} scm_s16vector_length (vec) | |
1547 | @deffnx {C Function} scm_u32vector_length (vec) | |
1548 | @deffnx {C Function} scm_s32vector_length (vec) | |
1549 | @deffnx {C Function} scm_u64vector_length (vec) | |
1550 | @deffnx {C Function} scm_s64vector_length (vec) | |
1551 | @deffnx {C Function} scm_f32vector_length (vec) | |
1552 | @deffnx {C Function} scm_f64vector_length (vec) | |
1553 | @deffnx {C Function} scm_c32vector_length (vec) | |
1554 | @deffnx {C Function} scm_c64vector_length (vec) | |
1555 | Return the number of elements in @var{vec}. | |
1556 | @end deffn | |
1557 | ||
1558 | @deffn {Scheme Procedure} u8vector-ref vec i | |
1559 | @deffnx {Scheme Procedure} s8vector-ref vec i | |
1560 | @deffnx {Scheme Procedure} u16vector-ref vec i | |
1561 | @deffnx {Scheme Procedure} s16vector-ref vec i | |
1562 | @deffnx {Scheme Procedure} u32vector-ref vec i | |
1563 | @deffnx {Scheme Procedure} s32vector-ref vec i | |
1564 | @deffnx {Scheme Procedure} u64vector-ref vec i | |
1565 | @deffnx {Scheme Procedure} s64vector-ref vec i | |
1566 | @deffnx {Scheme Procedure} f32vector-ref vec i | |
1567 | @deffnx {Scheme Procedure} f64vector-ref vec i | |
1568 | @deffnx {Scheme Procedure} c32vector-ref vec i | |
1569 | @deffnx {Scheme Procedure} c64vector-ref vec i | |
5f6ffd66 BT |
1570 | @deffnx {C Function} scm_u8vector_ref (vec, i) |
1571 | @deffnx {C Function} scm_s8vector_ref (vec, i) | |
1572 | @deffnx {C Function} scm_u16vector_ref (vec, i) | |
1573 | @deffnx {C Function} scm_s16vector_ref (vec, i) | |
1574 | @deffnx {C Function} scm_u32vector_ref (vec, i) | |
1575 | @deffnx {C Function} scm_s32vector_ref (vec, i) | |
1576 | @deffnx {C Function} scm_u64vector_ref (vec, i) | |
1577 | @deffnx {C Function} scm_s64vector_ref (vec, i) | |
1578 | @deffnx {C Function} scm_f32vector_ref (vec, i) | |
1579 | @deffnx {C Function} scm_f64vector_ref (vec, i) | |
1580 | @deffnx {C Function} scm_c32vector_ref (vec, i) | |
1581 | @deffnx {C Function} scm_c64vector_ref (vec, i) | |
27219b32 AW |
1582 | Return the element at index @var{i} in @var{vec}. The first element |
1583 | in @var{vec} is index 0. | |
1584 | @end deffn | |
1585 | ||
1586 | @deffn {Scheme Procedure} u8vector-set! vec i value | |
1587 | @deffnx {Scheme Procedure} s8vector-set! vec i value | |
1588 | @deffnx {Scheme Procedure} u16vector-set! vec i value | |
1589 | @deffnx {Scheme Procedure} s16vector-set! vec i value | |
1590 | @deffnx {Scheme Procedure} u32vector-set! vec i value | |
1591 | @deffnx {Scheme Procedure} s32vector-set! vec i value | |
1592 | @deffnx {Scheme Procedure} u64vector-set! vec i value | |
1593 | @deffnx {Scheme Procedure} s64vector-set! vec i value | |
1594 | @deffnx {Scheme Procedure} f32vector-set! vec i value | |
1595 | @deffnx {Scheme Procedure} f64vector-set! vec i value | |
1596 | @deffnx {Scheme Procedure} c32vector-set! vec i value | |
1597 | @deffnx {Scheme Procedure} c64vector-set! vec i value | |
5f6ffd66 BT |
1598 | @deffnx {C Function} scm_u8vector_set_x (vec, i, value) |
1599 | @deffnx {C Function} scm_s8vector_set_x (vec, i, value) | |
1600 | @deffnx {C Function} scm_u16vector_set_x (vec, i, value) | |
1601 | @deffnx {C Function} scm_s16vector_set_x (vec, i, value) | |
1602 | @deffnx {C Function} scm_u32vector_set_x (vec, i, value) | |
1603 | @deffnx {C Function} scm_s32vector_set_x (vec, i, value) | |
1604 | @deffnx {C Function} scm_u64vector_set_x (vec, i, value) | |
1605 | @deffnx {C Function} scm_s64vector_set_x (vec, i, value) | |
1606 | @deffnx {C Function} scm_f32vector_set_x (vec, i, value) | |
1607 | @deffnx {C Function} scm_f64vector_set_x (vec, i, value) | |
1608 | @deffnx {C Function} scm_c32vector_set_x (vec, i, value) | |
1609 | @deffnx {C Function} scm_c64vector_set_x (vec, i, value) | |
27219b32 AW |
1610 | Set the element at index @var{i} in @var{vec} to @var{value}. The |
1611 | first element in @var{vec} is index 0. The return value is | |
1612 | unspecified. | |
1613 | @end deffn | |
1614 | ||
1615 | @deffn {Scheme Procedure} u8vector->list vec | |
1616 | @deffnx {Scheme Procedure} s8vector->list vec | |
1617 | @deffnx {Scheme Procedure} u16vector->list vec | |
1618 | @deffnx {Scheme Procedure} s16vector->list vec | |
1619 | @deffnx {Scheme Procedure} u32vector->list vec | |
1620 | @deffnx {Scheme Procedure} s32vector->list vec | |
1621 | @deffnx {Scheme Procedure} u64vector->list vec | |
1622 | @deffnx {Scheme Procedure} s64vector->list vec | |
1623 | @deffnx {Scheme Procedure} f32vector->list vec | |
1624 | @deffnx {Scheme Procedure} f64vector->list vec | |
1625 | @deffnx {Scheme Procedure} c32vector->list vec | |
1626 | @deffnx {Scheme Procedure} c64vector->list vec | |
1627 | @deffnx {C Function} scm_u8vector_to_list (vec) | |
1628 | @deffnx {C Function} scm_s8vector_to_list (vec) | |
1629 | @deffnx {C Function} scm_u16vector_to_list (vec) | |
1630 | @deffnx {C Function} scm_s16vector_to_list (vec) | |
1631 | @deffnx {C Function} scm_u32vector_to_list (vec) | |
1632 | @deffnx {C Function} scm_s32vector_to_list (vec) | |
1633 | @deffnx {C Function} scm_u64vector_to_list (vec) | |
1634 | @deffnx {C Function} scm_s64vector_to_list (vec) | |
1635 | @deffnx {C Function} scm_f32vector_to_list (vec) | |
1636 | @deffnx {C Function} scm_f64vector_to_list (vec) | |
1637 | @deffnx {C Function} scm_c32vector_to_list (vec) | |
1638 | @deffnx {C Function} scm_c64vector_to_list (vec) | |
1639 | Return a newly allocated list holding all elements of @var{vec}. | |
1640 | @end deffn | |
1641 | ||
1642 | @deffn {Scheme Procedure} list->u8vector lst | |
1643 | @deffnx {Scheme Procedure} list->s8vector lst | |
1644 | @deffnx {Scheme Procedure} list->u16vector lst | |
1645 | @deffnx {Scheme Procedure} list->s16vector lst | |
1646 | @deffnx {Scheme Procedure} list->u32vector lst | |
1647 | @deffnx {Scheme Procedure} list->s32vector lst | |
1648 | @deffnx {Scheme Procedure} list->u64vector lst | |
1649 | @deffnx {Scheme Procedure} list->s64vector lst | |
1650 | @deffnx {Scheme Procedure} list->f32vector lst | |
1651 | @deffnx {Scheme Procedure} list->f64vector lst | |
1652 | @deffnx {Scheme Procedure} list->c32vector lst | |
1653 | @deffnx {Scheme Procedure} list->c64vector lst | |
1654 | @deffnx {C Function} scm_list_to_u8vector (lst) | |
1655 | @deffnx {C Function} scm_list_to_s8vector (lst) | |
1656 | @deffnx {C Function} scm_list_to_u16vector (lst) | |
1657 | @deffnx {C Function} scm_list_to_s16vector (lst) | |
1658 | @deffnx {C Function} scm_list_to_u32vector (lst) | |
1659 | @deffnx {C Function} scm_list_to_s32vector (lst) | |
1660 | @deffnx {C Function} scm_list_to_u64vector (lst) | |
1661 | @deffnx {C Function} scm_list_to_s64vector (lst) | |
1662 | @deffnx {C Function} scm_list_to_f32vector (lst) | |
1663 | @deffnx {C Function} scm_list_to_f64vector (lst) | |
1664 | @deffnx {C Function} scm_list_to_c32vector (lst) | |
1665 | @deffnx {C Function} scm_list_to_c64vector (lst) | |
1666 | Return a newly allocated homogeneous numeric vector of the indicated type, | |
1667 | initialized with the elements of the list @var{lst}. | |
1668 | @end deffn | |
1669 | ||
1670 | @deftypefn {C Function} SCM scm_take_u8vector (const scm_t_uint8 *data, size_t len) | |
1671 | @deftypefnx {C Function} SCM scm_take_s8vector (const scm_t_int8 *data, size_t len) | |
1672 | @deftypefnx {C Function} SCM scm_take_u16vector (const scm_t_uint16 *data, size_t len) | |
1673 | @deftypefnx {C Function} SCM scm_take_s16vector (const scm_t_int16 *data, size_t len) | |
1674 | @deftypefnx {C Function} SCM scm_take_u32vector (const scm_t_uint32 *data, size_t len) | |
1675 | @deftypefnx {C Function} SCM scm_take_s32vector (const scm_t_int32 *data, size_t len) | |
1676 | @deftypefnx {C Function} SCM scm_take_u64vector (const scm_t_uint64 *data, size_t len) | |
1677 | @deftypefnx {C Function} SCM scm_take_s64vector (const scm_t_int64 *data, size_t len) | |
1678 | @deftypefnx {C Function} SCM scm_take_f32vector (const float *data, size_t len) | |
1679 | @deftypefnx {C Function} SCM scm_take_f64vector (const double *data, size_t len) | |
1680 | @deftypefnx {C Function} SCM scm_take_c32vector (const float *data, size_t len) | |
1681 | @deftypefnx {C Function} SCM scm_take_c64vector (const double *data, size_t len) | |
1682 | Return a new uniform numeric vector of the indicated type and length | |
1683 | that uses the memory pointed to by @var{data} to store its elements. | |
1684 | This memory will eventually be freed with @code{free}. The argument | |
1685 | @var{len} specifies the number of elements in @var{data}, not its size | |
1686 | in bytes. | |
1687 | ||
1688 | The @code{c32} and @code{c64} variants take a pointer to a C array of | |
1689 | @code{float}s or @code{double}s. The real parts of the complex numbers | |
1690 | are at even indices in that array, the corresponding imaginary parts are | |
1691 | at the following odd index. | |
1692 | @end deftypefn | |
1693 | ||
1694 | @deftypefn {C Function} {const scm_t_uint8 *} scm_u8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1695 | @deftypefnx {C Function} {const scm_t_int8 *} scm_s8vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1696 | @deftypefnx {C Function} {const scm_t_uint16 *} scm_u16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1697 | @deftypefnx {C Function} {const scm_t_int16 *} scm_s16vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1698 | @deftypefnx {C Function} {const scm_t_uint32 *} scm_u32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1699 | @deftypefnx {C Function} {const scm_t_int32 *} scm_s32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1700 | @deftypefnx {C Function} {const scm_t_uint64 *} scm_u64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1701 | @deftypefnx {C Function} {const scm_t_int64 *} scm_s64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
ecb87335 | 1702 | @deftypefnx {C Function} {const float *} scm_f32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) |
27219b32 AW |
1703 | @deftypefnx {C Function} {const double *} scm_f64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) |
1704 | @deftypefnx {C Function} {const float *} scm_c32vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1705 | @deftypefnx {C Function} {const double *} scm_c64vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1706 | Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but | |
1707 | returns a pointer to the elements of a uniform numeric vector of the | |
1708 | indicated kind. | |
1709 | @end deftypefn | |
1710 | ||
1711 | @deftypefn {C Function} {scm_t_uint8 *} scm_u8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1712 | @deftypefnx {C Function} {scm_t_int8 *} scm_s8vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1713 | @deftypefnx {C Function} {scm_t_uint16 *} scm_u16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1714 | @deftypefnx {C Function} {scm_t_int16 *} scm_s16vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1715 | @deftypefnx {C Function} {scm_t_uint32 *} scm_u32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1716 | @deftypefnx {C Function} {scm_t_int32 *} scm_s32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1717 | @deftypefnx {C Function} {scm_t_uint64 *} scm_u64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1718 | @deftypefnx {C Function} {scm_t_int64 *} scm_s64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
ecb87335 | 1719 | @deftypefnx {C Function} {float *} scm_f32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) |
27219b32 AW |
1720 | @deftypefnx {C Function} {double *} scm_f64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) |
1721 | @deftypefnx {C Function} {float *} scm_c32vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1722 | @deftypefnx {C Function} {double *} scm_c64vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1723 | Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from | |
1724 | C}), but returns a pointer to the elements of a uniform numeric vector | |
1725 | of the indicated kind. | |
1726 | @end deftypefn | |
1727 | ||
1728 | @node SRFI-4 Generic Operations | |
1729 | @subsubsection SRFI-4 - Generic operations | |
1730 | ||
1731 | Guile also provides procedures that operate on all types of uniform numeric | |
1732 | vectors. In what is probably a bug, these procedures are currently available in | |
1733 | the default environment as well; however prudent hackers will make sure to | |
1734 | import @code{(srfi srfi-4 gnu)} before using these. | |
1735 | ||
1736 | @deftypefn {C Function} int scm_is_uniform_vector (SCM uvec) | |
1737 | Return non-zero when @var{uvec} is a uniform numeric vector, zero | |
1738 | otherwise. | |
1739 | @end deftypefn | |
1740 | ||
1741 | @deftypefn {C Function} size_t scm_c_uniform_vector_length (SCM uvec) | |
1742 | Return the number of elements of @var{uvec} as a @code{size_t}. | |
1743 | @end deftypefn | |
1744 | ||
1745 | @deffn {Scheme Procedure} uniform-vector? obj | |
1746 | @deffnx {C Function} scm_uniform_vector_p (obj) | |
1747 | Return @code{#t} if @var{obj} is a homogeneous numeric vector of the | |
1748 | indicated type. | |
1749 | @end deffn | |
1750 | ||
1751 | @deffn {Scheme Procedure} uniform-vector-length vec | |
1752 | @deffnx {C Function} scm_uniform_vector_length (vec) | |
1753 | Return the number of elements in @var{vec}. | |
1754 | @end deffn | |
1755 | ||
1756 | @deffn {Scheme Procedure} uniform-vector-ref vec i | |
5f6ffd66 | 1757 | @deffnx {C Function} scm_uniform_vector_ref (vec, i) |
27219b32 AW |
1758 | Return the element at index @var{i} in @var{vec}. The first element |
1759 | in @var{vec} is index 0. | |
1760 | @end deffn | |
1761 | ||
1762 | @deffn {Scheme Procedure} uniform-vector-set! vec i value | |
5f6ffd66 | 1763 | @deffnx {C Function} scm_uniform_vector_set_x (vec, i, value) |
27219b32 AW |
1764 | Set the element at index @var{i} in @var{vec} to @var{value}. The |
1765 | first element in @var{vec} is index 0. The return value is | |
1766 | unspecified. | |
1767 | @end deffn | |
1768 | ||
1769 | @deffn {Scheme Procedure} uniform-vector->list vec | |
1770 | @deffnx {C Function} scm_uniform_vector_to_list (vec) | |
1771 | Return a newly allocated list holding all elements of @var{vec}. | |
1772 | @end deffn | |
1773 | ||
1774 | @deftypefn {C Function} {const void *} scm_uniform_vector_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1775 | Like @code{scm_vector_elements} (@pxref{Vector Accessing from C}), but | |
1776 | returns a pointer to the elements of a uniform numeric vector. | |
1777 | @end deftypefn | |
1778 | ||
1779 | @deftypefn {C Function} {void *} scm_uniform_vector_writable_elements (SCM vec, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp) | |
1780 | Like @code{scm_vector_writable_elements} (@pxref{Vector Accessing from | |
1781 | C}), but returns a pointer to the elements of a uniform numeric vector. | |
1782 | @end deftypefn | |
1783 | ||
118ff892 AW |
1784 | Unless you really need to the limited generality of these functions, it |
1785 | is best to use the type-specific functions, or the array accessors. | |
27219b32 AW |
1786 | |
1787 | @node SRFI-4 and Bytevectors | |
1788 | @subsubsection SRFI-4 - Relation to bytevectors | |
1789 | ||
1790 | Guile implements SRFI-4 vectors using bytevectors (@pxref{Bytevectors}). Often | |
1791 | when you have a numeric vector, you end up wanting to write its bytes somewhere, | |
1792 | or have access to the underlying bytes, or read in bytes from somewhere else. | |
1793 | Bytevectors are very good at this sort of thing. But the SRFI-4 APIs are nicer | |
1794 | to use when doing number-crunching, because they are addressed by element and | |
1795 | not by byte. | |
1796 | ||
1797 | So as a compromise, Guile allows all bytevector functions to operate on numeric | |
1798 | vectors. They address the underlying bytes in the native endianness, as one | |
1799 | would expect. | |
1800 | ||
1801 | Following the same reasoning, that it's just bytes underneath, Guile also allows | |
1802 | uniform vectors of a given type to be accessed as if they were of any type. One | |
1803 | can fill a @nicode{u32vector}, and access its elements with | |
1804 | @nicode{u8vector-ref}. One can use @nicode{f64vector-ref} on bytevectors. It's | |
1805 | all the same to Guile. | |
1806 | ||
1807 | In this way, uniform numeric vectors may be written to and read from | |
1808 | input/output ports using the procedures that operate on bytevectors. | |
1809 | ||
1810 | @xref{Bytevectors}, for more information. | |
1811 | ||
1812 | ||
1813 | @node SRFI-4 Extensions | |
1814 | @subsubsection SRFI-4 - Guile extensions | |
1815 | ||
1816 | Guile defines some useful extensions to SRFI-4, which are not available in the | |
1817 | default Guile environment. They may be imported by loading the extensions | |
1818 | module: | |
1819 | ||
1820 | @example | |
1821 | (use-modules (srfi srfi-4 gnu)) | |
1822 | @end example | |
1823 | ||
1824 | @deffn {Scheme Procedure} any->u8vector obj | |
1825 | @deffnx {Scheme Procedure} any->s8vector obj | |
1826 | @deffnx {Scheme Procedure} any->u16vector obj | |
1827 | @deffnx {Scheme Procedure} any->s16vector obj | |
1828 | @deffnx {Scheme Procedure} any->u32vector obj | |
1829 | @deffnx {Scheme Procedure} any->s32vector obj | |
1830 | @deffnx {Scheme Procedure} any->u64vector obj | |
1831 | @deffnx {Scheme Procedure} any->s64vector obj | |
1832 | @deffnx {Scheme Procedure} any->f32vector obj | |
1833 | @deffnx {Scheme Procedure} any->f64vector obj | |
1834 | @deffnx {Scheme Procedure} any->c32vector obj | |
1835 | @deffnx {Scheme Procedure} any->c64vector obj | |
1836 | @deffnx {C Function} scm_any_to_u8vector (obj) | |
1837 | @deffnx {C Function} scm_any_to_s8vector (obj) | |
1838 | @deffnx {C Function} scm_any_to_u16vector (obj) | |
1839 | @deffnx {C Function} scm_any_to_s16vector (obj) | |
1840 | @deffnx {C Function} scm_any_to_u32vector (obj) | |
1841 | @deffnx {C Function} scm_any_to_s32vector (obj) | |
1842 | @deffnx {C Function} scm_any_to_u64vector (obj) | |
1843 | @deffnx {C Function} scm_any_to_s64vector (obj) | |
1844 | @deffnx {C Function} scm_any_to_f32vector (obj) | |
1845 | @deffnx {C Function} scm_any_to_f64vector (obj) | |
1846 | @deffnx {C Function} scm_any_to_c32vector (obj) | |
1847 | @deffnx {C Function} scm_any_to_c64vector (obj) | |
1848 | Return a (maybe newly allocated) uniform numeric vector of the indicated | |
1849 | type, initialized with the elements of @var{obj}, which must be a list, | |
1850 | a vector, or a uniform vector. When @var{obj} is already a suitable | |
1851 | uniform numeric vector, it is returned unchanged. | |
1852 | @end deffn | |
1853 | ||
a0e07ba4 NJ |
1854 | |
1855 | @node SRFI-6 | |
3229f68b | 1856 | @subsection SRFI-6 - Basic String Ports |
8742c48b | 1857 | @cindex SRFI-6 |
a0e07ba4 NJ |
1858 | |
1859 | SRFI-6 defines the procedures @code{open-input-string}, | |
8edab37f MW |
1860 | @code{open-output-string} and @code{get-output-string}. |
1861 | ||
1862 | Note that although versions of these procedures are included in the | |
1863 | Guile core, the core versions are not fully conformant with SRFI-6: | |
1864 | attempts to read or write characters that are not supported by the | |
1865 | current @code{%default-port-encoding} will fail. | |
1866 | ||
1867 | We therefore recommend that you import this module, which supports all | |
1868 | characters: | |
1869 | ||
1870 | @example | |
1871 | (use-modules (srfi srfi-6)) | |
1872 | @end example | |
a0e07ba4 NJ |
1873 | |
1874 | @node SRFI-8 | |
3229f68b | 1875 | @subsection SRFI-8 - receive |
8742c48b | 1876 | @cindex SRFI-8 |
a0e07ba4 NJ |
1877 | |
1878 | @code{receive} is a syntax for making the handling of multiple-value | |
1879 | procedures easier. It is documented in @xref{Multiple Values}. | |
1880 | ||
1881 | ||
1882 | @node SRFI-9 | |
3229f68b | 1883 | @subsection SRFI-9 - define-record-type |
a0e07ba4 | 1884 | |
6afe385d | 1885 | This SRFI is a syntax for defining new record types and creating |
ec7e4f77 LC |
1886 | predicate, constructor, and field getter and setter functions. It is |
1887 | documented in the ``Compound Data Types'' section of the manual | |
1888 | (@pxref{SRFI-9 Records}). | |
a0e07ba4 | 1889 | |
a0e07ba4 NJ |
1890 | |
1891 | @node SRFI-10 | |
3229f68b | 1892 | @subsection SRFI-10 - Hash-Comma Reader Extension |
8742c48b | 1893 | @cindex SRFI-10 |
a0e07ba4 NJ |
1894 | |
1895 | @cindex hash-comma | |
1896 | @cindex #,() | |
633acbe2 KR |
1897 | This SRFI implements a reader extension @code{#,()} called hash-comma. |
1898 | It allows the reader to give new kinds of objects, for use both in | |
1899 | data and as constants or literals in source code. This feature is | |
1900 | available with | |
a0e07ba4 | 1901 | |
633acbe2 KR |
1902 | @example |
1903 | (use-modules (srfi srfi-10)) | |
1904 | @end example | |
1905 | ||
1906 | @noindent | |
1907 | The new read syntax is of the form | |
a0e07ba4 NJ |
1908 | |
1909 | @example | |
633acbe2 | 1910 | #,(@var{tag} @var{arg}@dots{}) |
a0e07ba4 NJ |
1911 | @end example |
1912 | ||
633acbe2 KR |
1913 | @noindent |
1914 | where @var{tag} is a symbol and the @var{arg}s are objects taken as | |
1915 | parameters. @var{tag}s are registered with the following procedure. | |
a0e07ba4 | 1916 | |
633acbe2 KR |
1917 | @deffn {Scheme Procedure} define-reader-ctor tag proc |
1918 | Register @var{proc} as the constructor for a hash-comma read syntax | |
679cceed | 1919 | starting with symbol @var{tag}, i.e.@: @nicode{#,(@var{tag} arg@dots{})}. |
633acbe2 KR |
1920 | @var{proc} is called with the given arguments @code{(@var{proc} |
1921 | arg@dots{})} and the object it returns is the result of the read. | |
1922 | @end deffn | |
a0e07ba4 | 1923 | |
633acbe2 KR |
1924 | @noindent |
1925 | For example, a syntax giving a list of @var{N} copies of an object. | |
1926 | ||
1927 | @example | |
1928 | (define-reader-ctor 'repeat | |
1929 | (lambda (obj reps) | |
1930 | (make-list reps obj))) | |
1931 | ||
1932 | (display '#,(repeat 99 3)) | |
1933 | @print{} (99 99 99) | |
1934 | @end example | |
1935 | ||
1936 | Notice the quote @nicode{'} when the @nicode{#,( )} is used. The | |
1937 | @code{repeat} handler returns a list and the program must quote to use | |
1938 | it literally, the same as any other list. Ie. | |
1939 | ||
1940 | @example | |
1941 | (display '#,(repeat 99 3)) | |
a0e07ba4 | 1942 | @result{} |
633acbe2 KR |
1943 | (display '(99 99 99)) |
1944 | @end example | |
a0e07ba4 | 1945 | |
633acbe2 KR |
1946 | When a handler returns an object which is self-evaluating, like a |
1947 | number or a string, then there's no need for quoting, just as there's | |
1948 | no need when giving those directly as literals. For example an | |
1949 | addition, | |
a0e07ba4 | 1950 | |
633acbe2 KR |
1951 | @example |
1952 | (define-reader-ctor 'sum | |
1953 | (lambda (x y) | |
1954 | (+ x y))) | |
1955 | (display #,(sum 123 456)) @print{} 579 | |
1956 | @end example | |
1957 | ||
1958 | A typical use for @nicode{#,()} is to get a read syntax for objects | |
1959 | which don't otherwise have one. For example, the following allows a | |
1960 | hash table to be given literally, with tags and values, ready for fast | |
1961 | lookup. | |
1962 | ||
1963 | @example | |
1964 | (define-reader-ctor 'hash | |
1965 | (lambda elems | |
1966 | (let ((table (make-hash-table))) | |
1967 | (for-each (lambda (elem) | |
01549abb KR |
1968 | (apply hash-set! table elem)) |
1969 | elems) | |
633acbe2 KR |
1970 | table))) |
1971 | ||
1972 | (define (animal->family animal) | |
1973 | (hash-ref '#,(hash ("tiger" "cat") | |
1974 | ("lion" "cat") | |
1975 | ("wolf" "dog")) | |
1976 | animal)) | |
1977 | ||
1978 | (animal->family "lion") @result{} "cat" | |
1979 | @end example | |
1980 | ||
1981 | Or for example the following is a syntax for a compiled regular | |
1982 | expression (@pxref{Regular Expressions}). | |
1983 | ||
1984 | @example | |
1985 | (use-modules (ice-9 regex)) | |
1986 | ||
1987 | (define-reader-ctor 'regexp make-regexp) | |
1988 | ||
1989 | (define (extract-angs str) | |
1990 | (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str))) | |
1991 | (and match | |
1992 | (match:substring match 1)))) | |
1993 | ||
1994 | (extract-angs "foo <BAR> quux") @result{} "BAR" | |
1995 | @end example | |
1996 | ||
1997 | @sp 1 | |
1998 | @nicode{#,()} is somewhat similar to @code{define-macro} | |
1999 | (@pxref{Macros}) in that handler code is run to produce a result, but | |
2000 | @nicode{#,()} operates at the read stage, so it can appear in data for | |
2001 | @code{read} (@pxref{Scheme Read}), not just in code to be executed. | |
2002 | ||
2003 | Because @nicode{#,()} is handled at read-time it has no direct access | |
2004 | to variables etc. A symbol in the arguments is just a symbol, not a | |
2005 | variable reference. The arguments are essentially constants, though | |
2006 | the handler procedure can use them in any complicated way it might | |
2007 | want. | |
2008 | ||
2009 | Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available | |
2010 | globally, there's no need to use @code{(srfi srfi-10)} in later | |
2011 | modules. Similarly the tags registered are global and can be used | |
2012 | anywhere once registered. | |
2013 | ||
2014 | There's no attempt to record what previous @nicode{#,()} forms have | |
2015 | been seen, if two identical forms occur then two calls are made to the | |
2016 | handler procedure. The handler might like to maintain a cache or | |
2017 | similar to avoid making copies of large objects, depending on expected | |
2018 | usage. | |
2019 | ||
2020 | In code the best uses of @nicode{#,()} are generally when there's a | |
2021 | lot of objects of a particular kind as literals or constants. If | |
2022 | there's just a few then some local variables and initializers are | |
2023 | fine, but that becomes tedious and error prone when there's a lot, and | |
2024 | the anonymous and compact syntax of @nicode{#,()} is much better. | |
a0e07ba4 NJ |
2025 | |
2026 | ||
2027 | @node SRFI-11 | |
3229f68b | 2028 | @subsection SRFI-11 - let-values |
8742c48b | 2029 | @cindex SRFI-11 |
a0e07ba4 | 2030 | |
8742c48b | 2031 | @findex let-values |
c010924a | 2032 | @findex let*-values |
a0e07ba4 | 2033 | This module implements the binding forms for multiple values |
c010924a | 2034 | @code{let-values} and @code{let*-values}. These forms are similar to |
a0e07ba4 NJ |
2035 | @code{let} and @code{let*} (@pxref{Local Bindings}), but they support |
2036 | binding of the values returned by multiple-valued expressions. | |
2037 | ||
2038 | Write @code{(use-modules (srfi srfi-11))} to make the bindings | |
2039 | available. | |
2040 | ||
2041 | @lisp | |
2042 | (let-values (((x y) (values 1 2)) | |
2043 | ((z f) (values 3 4))) | |
2044 | (+ x y z f)) | |
2045 | @result{} | |
2046 | 10 | |
2047 | @end lisp | |
2048 | ||
2049 | @code{let-values} performs all bindings simultaneously, which means that | |
2050 | no expression in the binding clauses may refer to variables bound in the | |
c010924a | 2051 | same clause list. @code{let*-values}, on the other hand, performs the |
a0e07ba4 NJ |
2052 | bindings sequentially, just like @code{let*} does for single-valued |
2053 | expressions. | |
2054 | ||
2055 | ||
2056 | @node SRFI-13 | |
3229f68b | 2057 | @subsection SRFI-13 - String Library |
8742c48b | 2058 | @cindex SRFI-13 |
a0e07ba4 | 2059 | |
5676b4fa | 2060 | The SRFI-13 procedures are always available, @xref{Strings}. |
a0e07ba4 NJ |
2061 | |
2062 | @node SRFI-14 | |
3229f68b | 2063 | @subsection SRFI-14 - Character-set Library |
8742c48b | 2064 | @cindex SRFI-14 |
a0e07ba4 | 2065 | |
050ab45f MV |
2066 | The SRFI-14 data type and procedures are always available, |
2067 | @xref{Character Sets}. | |
a0e07ba4 NJ |
2068 | |
2069 | @node SRFI-16 | |
3229f68b | 2070 | @subsection SRFI-16 - case-lambda |
8742c48b | 2071 | @cindex SRFI-16 |
7c2e18cd KR |
2072 | @cindex variable arity |
2073 | @cindex arity, variable | |
a0e07ba4 | 2074 | |
f916cbc4 AW |
2075 | SRFI-16 defines a variable-arity @code{lambda} form, |
2076 | @code{case-lambda}. This form is available in the default Guile | |
2077 | environment. @xref{Case-lambda}, for more information. | |
a0e07ba4 NJ |
2078 | |
2079 | @node SRFI-17 | |
3229f68b | 2080 | @subsection SRFI-17 - Generalized set! |
8742c48b | 2081 | @cindex SRFI-17 |
a0e07ba4 | 2082 | |
9a18d8d4 KR |
2083 | This SRFI implements a generalized @code{set!}, allowing some |
2084 | ``referencing'' functions to be used as the target location of a | |
2085 | @code{set!}. This feature is available from | |
2086 | ||
2087 | @example | |
2088 | (use-modules (srfi srfi-17)) | |
2089 | @end example | |
2090 | ||
2091 | @noindent | |
2092 | For example @code{vector-ref} is extended so that | |
2093 | ||
2094 | @example | |
2095 | (set! (vector-ref vec idx) new-value) | |
2096 | @end example | |
2097 | ||
2098 | @noindent | |
2099 | is equivalent to | |
2100 | ||
2101 | @example | |
2102 | (vector-set! vec idx new-value) | |
2103 | @end example | |
2104 | ||
2105 | The idea is that a @code{vector-ref} expression identifies a location, | |
2106 | which may be either fetched or stored. The same form is used for the | |
2107 | location in both cases, encouraging visual clarity. This is similar | |
2108 | to the idea of an ``lvalue'' in C. | |
2109 | ||
2110 | The mechanism for this kind of @code{set!} is in the Guile core | |
2111 | (@pxref{Procedures with Setters}). This module adds definitions of | |
2112 | the following functions as procedures with setters, allowing them to | |
2113 | be targets of a @code{set!}, | |
2114 | ||
2115 | @quotation | |
2116 | @nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr}, | |
2117 | @nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr}, | |
2118 | @nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr}, | |
2119 | @nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr}, | |
2120 | @nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr}, | |
2121 | @nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr}, | |
2122 | @nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr}, | |
2123 | @nicode{cdddar}, @nicode{cddddr} | |
2124 | ||
2125 | @nicode{string-ref}, @nicode{vector-ref} | |
2126 | @end quotation | |
2127 | ||
2128 | The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as | |
2129 | a procedure with setter, allowing the setter for a procedure to be | |
2130 | changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}. | |
2131 | Currently Guile does not implement this, a setter can only be | |
2132 | specified on creation (@code{getter-with-setter} below). | |
2133 | ||
2134 | @defun getter-with-setter | |
2135 | The same as the Guile core @code{make-procedure-with-setter} | |
2136 | (@pxref{Procedures with Setters}). | |
2137 | @end defun | |
a0e07ba4 | 2138 | |
12991fed | 2139 | |
e68f492a JG |
2140 | @node SRFI-18 |
2141 | @subsection SRFI-18 - Multithreading support | |
2142 | @cindex SRFI-18 | |
2143 | ||
2144 | This is an implementation of the SRFI-18 threading and synchronization | |
2145 | library. The functions and variables described here are provided by | |
2146 | ||
2147 | @example | |
2148 | (use-modules (srfi srfi-18)) | |
2149 | @end example | |
2150 | ||
2151 | As a general rule, the data types and functions in this SRFI-18 | |
2152 | implementation are compatible with the types and functions in Guile's | |
2153 | core threading code. For example, mutexes created with the SRFI-18 | |
2154 | @code{make-mutex} function can be passed to the built-in Guile | |
2155 | function @code{lock-mutex} (@pxref{Mutexes and Condition Variables}), | |
2156 | and mutexes created with the built-in Guile function @code{make-mutex} | |
2157 | can be passed to the SRFI-18 function @code{mutex-lock!}. Cases in | |
2158 | which this does not hold true are noted in the following sections. | |
2159 | ||
2160 | @menu | |
2161 | * SRFI-18 Threads:: Executing code | |
2162 | * SRFI-18 Mutexes:: Mutual exclusion devices | |
2163 | * SRFI-18 Condition variables:: Synchronizing of groups of threads | |
2164 | * SRFI-18 Time:: Representation of times and durations | |
2165 | * SRFI-18 Exceptions:: Signalling and handling errors | |
2166 | @end menu | |
2167 | ||
2168 | @node SRFI-18 Threads | |
2169 | @subsubsection SRFI-18 Threads | |
2170 | ||
2171 | Threads created by SRFI-18 differ in two ways from threads created by | |
2172 | Guile's built-in thread functions. First, a thread created by SRFI-18 | |
2173 | @code{make-thread} begins in a blocked state and will not start | |
2174 | execution until @code{thread-start!} is called on it. Second, SRFI-18 | |
2175 | threads are constructed with a top-level exception handler that | |
2176 | captures any exceptions that are thrown on thread exit. In all other | |
2177 | regards, SRFI-18 threads are identical to normal Guile threads. | |
2178 | ||
2179 | @defun current-thread | |
2180 | Returns the thread that called this function. This is the same | |
2181 | procedure as the same-named built-in procedure @code{current-thread} | |
2182 | (@pxref{Threads}). | |
2183 | @end defun | |
2184 | ||
2185 | @defun thread? obj | |
2186 | Returns @code{#t} if @var{obj} is a thread, @code{#f} otherwise. This | |
2187 | is the same procedure as the same-named built-in procedure | |
2188 | @code{thread?} (@pxref{Threads}). | |
2189 | @end defun | |
2190 | ||
2191 | @defun make-thread thunk [name] | |
2192 | Call @code{thunk} in a new thread and with a new dynamic state, | |
2193 | returning the new thread and optionally assigning it the object name | |
2194 | @var{name}, which may be any Scheme object. | |
2195 | ||
2196 | Note that the name @code{make-thread} conflicts with the | |
2197 | @code{(ice-9 threads)} function @code{make-thread}. Applications | |
2198 | wanting to use both of these functions will need to refer to them by | |
2199 | different names. | |
2200 | @end defun | |
2201 | ||
2202 | @defun thread-name thread | |
2203 | Returns the name assigned to @var{thread} at the time of its creation, | |
2204 | or @code{#f} if it was not given a name. | |
2205 | @end defun | |
2206 | ||
2207 | @defun thread-specific thread | |
2208 | @defunx thread-specific-set! thread obj | |
2209 | Get or set the ``object-specific'' property of @var{thread}. In | |
2210 | Guile's implementation of SRFI-18, this value is stored as an object | |
2211 | property, and will be @code{#f} if not set. | |
2212 | @end defun | |
2213 | ||
2214 | @defun thread-start! thread | |
2215 | Unblocks @var{thread} and allows it to begin execution if it has not | |
2216 | done so already. | |
2217 | @end defun | |
2218 | ||
2219 | @defun thread-yield! | |
2220 | If one or more threads are waiting to execute, calling | |
2221 | @code{thread-yield!} forces an immediate context switch to one of them. | |
2222 | Otherwise, @code{thread-yield!} has no effect. @code{thread-yield!} | |
2223 | behaves identically to the Guile built-in function @code{yield}. | |
2224 | @end defun | |
2225 | ||
2226 | @defun thread-sleep! timeout | |
2227 | The current thread waits until the point specified by the time object | |
2228 | @var{timeout} is reached (@pxref{SRFI-18 Time}). This blocks the | |
2229 | thread only if @var{timeout} represents a point in the future. it is | |
2230 | an error for @var{timeout} to be @code{#f}. | |
2231 | @end defun | |
2232 | ||
2233 | @defun thread-terminate! thread | |
2234 | Causes an abnormal termination of @var{thread}. If @var{thread} is | |
2235 | not already terminated, all mutexes owned by @var{thread} become | |
2236 | unlocked/abandoned. If @var{thread} is the current thread, | |
2237 | @code{thread-terminate!} does not return. Otherwise | |
2238 | @code{thread-terminate!} returns an unspecified value; the termination | |
2239 | of @var{thread} will occur before @code{thread-terminate!} returns. | |
2240 | Subsequent attempts to join on @var{thread} will cause a ``terminated | |
2241 | thread exception'' to be raised. | |
2242 | ||
2243 | @code{thread-terminate!} is compatible with the thread cancellation | |
2244 | procedures in the core threads API (@pxref{Threads}) in that if a | |
2245 | cleanup handler has been installed for the target thread, it will be | |
2246 | called before the thread exits and its return value (or exception, if | |
2247 | any) will be stored for later retrieval via a call to | |
2248 | @code{thread-join!}. | |
2249 | @end defun | |
2250 | ||
2251 | @defun thread-join! thread [timeout [timeout-val]] | |
2252 | Wait for @var{thread} to terminate and return its exit value. When a | |
2253 | time value @var{timeout} is given, it specifies a point in time where | |
2254 | the waiting should be aborted. When the waiting is aborted, | |
64de6db5 | 2255 | @var{timeout-val} is returned if it is specified; otherwise, a |
e68f492a JG |
2256 | @code{join-timeout-exception} exception is raised |
2257 | (@pxref{SRFI-18 Exceptions}). Exceptions may also be raised if the | |
2258 | thread was terminated by a call to @code{thread-terminate!} | |
2259 | (@code{terminated-thread-exception} will be raised) or if the thread | |
2260 | exited by raising an exception that was handled by the top-level | |
2261 | exception handler (@code{uncaught-exception} will be raised; the | |
2262 | original exception can be retrieved using | |
2263 | @code{uncaught-exception-reason}). | |
2264 | @end defun | |
2265 | ||
2266 | ||
2267 | @node SRFI-18 Mutexes | |
2268 | @subsubsection SRFI-18 Mutexes | |
2269 | ||
2270 | The behavior of Guile's built-in mutexes is parameterized via a set of | |
2271 | flags passed to the @code{make-mutex} procedure in the core | |
2272 | (@pxref{Mutexes and Condition Variables}). To satisfy the requirements | |
2273 | for mutexes specified by SRFI-18, the @code{make-mutex} procedure | |
2274 | described below sets the following flags: | |
2275 | @itemize @bullet | |
2276 | @item | |
2277 | @code{recursive}: the mutex can be locked recursively | |
2278 | @item | |
2279 | @code{unchecked-unlock}: attempts to unlock a mutex that is already | |
2280 | unlocked will not raise an exception | |
2281 | @item | |
2282 | @code{allow-external-unlock}: the mutex can be unlocked by any thread, | |
2283 | not just the thread that locked it originally | |
2284 | @end itemize | |
2285 | ||
2286 | @defun make-mutex [name] | |
2287 | Returns a new mutex, optionally assigning it the object name | |
2288 | @var{name}, which may be any Scheme object. The returned mutex will be | |
2289 | created with the configuration described above. Note that the name | |
2290 | @code{make-mutex} conflicts with Guile core function @code{make-mutex}. | |
2291 | Applications wanting to use both of these functions will need to refer | |
2292 | to them by different names. | |
2293 | @end defun | |
2294 | ||
2295 | @defun mutex-name mutex | |
2296 | Returns the name assigned to @var{mutex} at the time of its creation, | |
2297 | or @code{#f} if it was not given a name. | |
2298 | @end defun | |
2299 | ||
2300 | @defun mutex-specific mutex | |
2301 | @defunx mutex-specific-set! mutex obj | |
2302 | Get or set the ``object-specific'' property of @var{mutex}. In Guile's | |
2303 | implementation of SRFI-18, this value is stored as an object property, | |
2304 | and will be @code{#f} if not set. | |
2305 | @end defun | |
2306 | ||
2307 | @defun mutex-state mutex | |
2308 | Returns information about the state of @var{mutex}. Possible values | |
2309 | are: | |
2310 | @itemize @bullet | |
2311 | @item | |
2312 | thread @code{T}: the mutex is in the locked/owned state and thread T | |
2313 | is the owner of the mutex | |
2314 | @item | |
2315 | symbol @code{not-owned}: the mutex is in the locked/not-owned state | |
2316 | @item | |
2317 | symbol @code{abandoned}: the mutex is in the unlocked/abandoned state | |
2318 | @item | |
2319 | symbol @code{not-abandoned}: the mutex is in the | |
2320 | unlocked/not-abandoned state | |
2321 | @end itemize | |
2322 | @end defun | |
2323 | ||
2324 | @defun mutex-lock! mutex [timeout [thread]] | |
2325 | Lock @var{mutex}, optionally specifying a time object @var{timeout} | |
2326 | after which to abort the lock attempt and a thread @var{thread} giving | |
2327 | a new owner for @var{mutex} different than the current thread. This | |
2328 | procedure has the same behavior as the @code{lock-mutex} procedure in | |
2329 | the core library. | |
2330 | @end defun | |
2331 | ||
2332 | @defun mutex-unlock! mutex [condition-variable [timeout]] | |
2333 | Unlock @var{mutex}, optionally specifying a condition variable | |
2334 | @var{condition-variable} on which to wait, either indefinitely or, | |
2335 | optionally, until the time object @var{timeout} has passed, to be | |
2336 | signalled. This procedure has the same behavior as the | |
2337 | @code{unlock-mutex} procedure in the core library. | |
2338 | @end defun | |
2339 | ||
2340 | ||
2341 | @node SRFI-18 Condition variables | |
2342 | @subsubsection SRFI-18 Condition variables | |
2343 | ||
2344 | SRFI-18 does not specify a ``wait'' function for condition variables. | |
2345 | Waiting on a condition variable can be simulated using the SRFI-18 | |
2346 | @code{mutex-unlock!} function described in the previous section, or | |
2347 | Guile's built-in @code{wait-condition-variable} procedure can be used. | |
2348 | ||
2349 | @defun condition-variable? obj | |
2350 | Returns @code{#t} if @var{obj} is a condition variable, @code{#f} | |
2351 | otherwise. This is the same procedure as the same-named built-in | |
2352 | procedure | |
2353 | (@pxref{Mutexes and Condition Variables, @code{condition-variable?}}). | |
2354 | @end defun | |
2355 | ||
2356 | @defun make-condition-variable [name] | |
2357 | Returns a new condition variable, optionally assigning it the object | |
2358 | name @var{name}, which may be any Scheme object. This procedure | |
2359 | replaces a procedure of the same name in the core library. | |
2360 | @end defun | |
2361 | ||
2362 | @defun condition-variable-name condition-variable | |
64de6db5 BT |
2363 | Returns the name assigned to @var{condition-variable} at the time of its |
2364 | creation, or @code{#f} if it was not given a name. | |
e68f492a JG |
2365 | @end defun |
2366 | ||
2367 | @defun condition-variable-specific condition-variable | |
2368 | @defunx condition-variable-specific-set! condition-variable obj | |
2369 | Get or set the ``object-specific'' property of | |
2370 | @var{condition-variable}. In Guile's implementation of SRFI-18, this | |
2371 | value is stored as an object property, and will be @code{#f} if not | |
2372 | set. | |
2373 | @end defun | |
2374 | ||
2375 | @defun condition-variable-signal! condition-variable | |
2376 | @defunx condition-variable-broadcast! condition-variable | |
2377 | Wake up one thread that is waiting for @var{condition-variable}, in | |
2378 | the case of @code{condition-variable-signal!}, or all threads waiting | |
2379 | for it, in the case of @code{condition-variable-broadcast!}. The | |
2380 | behavior of these procedures is equivalent to that of the procedures | |
2381 | @code{signal-condition-variable} and | |
2382 | @code{broadcast-condition-variable} in the core library. | |
2383 | @end defun | |
2384 | ||
2385 | ||
2386 | @node SRFI-18 Time | |
2387 | @subsubsection SRFI-18 Time | |
2388 | ||
2389 | The SRFI-18 time functions manipulate time in two formats: a | |
2390 | ``time object'' type that represents an absolute point in time in some | |
2391 | implementation-specific way; and the number of seconds since some | |
2392 | unspecified ``epoch''. In Guile's implementation, the epoch is the | |
2393 | Unix epoch, 00:00:00 UTC, January 1, 1970. | |
2394 | ||
2395 | @defun current-time | |
2396 | Return the current time as a time object. This procedure replaces | |
2397 | the procedure of the same name in the core library, which returns the | |
2398 | current time in seconds since the epoch. | |
2399 | @end defun | |
2400 | ||
2401 | @defun time? obj | |
2402 | Returns @code{#t} if @var{obj} is a time object, @code{#f} otherwise. | |
2403 | @end defun | |
2404 | ||
2405 | @defun time->seconds time | |
2406 | @defunx seconds->time seconds | |
2407 | Convert between time objects and numerical values representing the | |
2408 | number of seconds since the epoch. When converting from a time object | |
2409 | to seconds, the return value is the number of seconds between | |
2410 | @var{time} and the epoch. When converting from seconds to a time | |
2411 | object, the return value is a time object that represents a time | |
2412 | @var{seconds} seconds after the epoch. | |
2413 | @end defun | |
2414 | ||
2415 | ||
2416 | @node SRFI-18 Exceptions | |
2417 | @subsubsection SRFI-18 Exceptions | |
2418 | ||
2419 | SRFI-18 exceptions are identical to the exceptions provided by | |
2420 | Guile's implementation of SRFI-34. The behavior of exception | |
2421 | handlers invoked to handle exceptions thrown from SRFI-18 functions, | |
2422 | however, differs from the conventional behavior of SRFI-34 in that | |
2423 | the continuation of the handler is the same as that of the call to | |
2424 | the function. Handlers are called in a tail-recursive manner; the | |
2425 | exceptions do not ``bubble up''. | |
2426 | ||
2427 | @defun current-exception-handler | |
2428 | Returns the current exception handler. | |
2429 | @end defun | |
2430 | ||
2431 | @defun with-exception-handler handler thunk | |
2432 | Installs @var{handler} as the current exception handler and calls the | |
2433 | procedure @var{thunk} with no arguments, returning its value as the | |
2434 | value of the exception. @var{handler} must be a procedure that accepts | |
2435 | a single argument. The current exception handler at the time this | |
2436 | procedure is called will be restored after the call returns. | |
2437 | @end defun | |
2438 | ||
2439 | @defun raise obj | |
2440 | Raise @var{obj} as an exception. This is the same procedure as the | |
2441 | same-named procedure defined in SRFI 34. | |
2442 | @end defun | |
2443 | ||
2444 | @defun join-timeout-exception? obj | |
2445 | Returns @code{#t} if @var{obj} is an exception raised as the result of | |
2446 | performing a timed join on a thread that does not exit within the | |
2447 | specified timeout, @code{#f} otherwise. | |
2448 | @end defun | |
2449 | ||
2450 | @defun abandoned-mutex-exception? obj | |
2451 | Returns @code{#t} if @var{obj} is an exception raised as the result of | |
2452 | attempting to lock a mutex that has been abandoned by its owner thread, | |
2453 | @code{#f} otherwise. | |
2454 | @end defun | |
2455 | ||
2456 | @defun terminated-thread-exception? obj | |
2457 | Returns @code{#t} if @var{obj} is an exception raised as the result of | |
2458 | joining on a thread that exited as the result of a call to | |
2459 | @code{thread-terminate!}. | |
2460 | @end defun | |
2461 | ||
2462 | @defun uncaught-exception? obj | |
2463 | @defunx uncaught-exception-reason exc | |
2464 | @code{uncaught-exception?} returns @code{#t} if @var{obj} is an | |
2465 | exception thrown as the result of joining a thread that exited by | |
2466 | raising an exception that was handled by the top-level exception | |
2467 | handler installed by @code{make-thread}. When this occurs, the | |
2468 | original exception is preserved as part of the exception thrown by | |
2469 | @code{thread-join!} and can be accessed by calling | |
2470 | @code{uncaught-exception-reason} on that exception. Note that | |
2471 | because this exception-preservation mechanism is a side-effect of | |
2472 | @code{make-thread}, joining on threads that exited as described above | |
2473 | but were created by other means will not raise this | |
2474 | @code{uncaught-exception} error. | |
2475 | @end defun | |
2476 | ||
2477 | ||
12991fed | 2478 | @node SRFI-19 |
3229f68b | 2479 | @subsection SRFI-19 - Time/Date Library |
8742c48b | 2480 | @cindex SRFI-19 |
7c2e18cd KR |
2481 | @cindex time |
2482 | @cindex date | |
12991fed | 2483 | |
85600a0f KR |
2484 | This is an implementation of the SRFI-19 time/date library. The |
2485 | functions and variables described here are provided by | |
12991fed TTN |
2486 | |
2487 | @example | |
85600a0f | 2488 | (use-modules (srfi srfi-19)) |
12991fed TTN |
2489 | @end example |
2490 | ||
7d281fa5 KR |
2491 | @strong{Caution}: The current code in this module incorrectly extends |
2492 | the Gregorian calendar leap year rule back prior to the introduction | |
2493 | of those reforms in 1582 (or the appropriate year in various | |
2494 | countries). The Julian calendar was used prior to 1582, and there | |
2495 | were 10 days skipped for the reform, but the code doesn't implement | |
2496 | that. | |
2497 | ||
2498 | This will be fixed some time. Until then calculations for 1583 | |
2499 | onwards are correct, but prior to that any day/month/year and day of | |
2500 | the week calculations are wrong. | |
2501 | ||
85600a0f KR |
2502 | @menu |
2503 | * SRFI-19 Introduction:: | |
2504 | * SRFI-19 Time:: | |
2505 | * SRFI-19 Date:: | |
2506 | * SRFI-19 Time/Date conversions:: | |
2507 | * SRFI-19 Date to string:: | |
2508 | * SRFI-19 String to date:: | |
2509 | @end menu | |
12991fed | 2510 | |
85600a0f | 2511 | @node SRFI-19 Introduction |
3229f68b | 2512 | @subsubsection SRFI-19 Introduction |
85600a0f KR |
2513 | |
2514 | @cindex universal time | |
2515 | @cindex atomic time | |
2516 | @cindex UTC | |
2517 | @cindex TAI | |
2518 | This module implements time and date representations and calculations, | |
2519 | in various time systems, including universal time (UTC) and atomic | |
2520 | time (TAI). | |
2521 | ||
2522 | For those not familiar with these time systems, TAI is based on a | |
2523 | fixed length second derived from oscillations of certain atoms. UTC | |
2524 | differs from TAI by an integral number of seconds, which is increased | |
2525 | or decreased at announced times to keep UTC aligned to a mean solar | |
2526 | day (the orbit and rotation of the earth are not quite constant). | |
2527 | ||
2528 | @cindex leap second | |
2529 | So far, only increases in the TAI | |
2530 | @tex | |
2531 | $\leftrightarrow$ | |
2532 | @end tex | |
2533 | @ifnottex | |
2534 | <-> | |
2535 | @end ifnottex | |
2536 | UTC difference have been needed. Such an increase is a ``leap | |
2537 | second'', an extra second of TAI introduced at the end of a UTC day. | |
2538 | When working entirely within UTC this is never seen, every day simply | |
2539 | has 86400 seconds. But when converting from TAI to a UTC date, an | |
2540 | extra 23:59:60 is present, where normally a day would end at 23:59:59. | |
2541 | Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI | |
2542 | seconds. | |
2543 | ||
2544 | @cindex system clock | |
2545 | In the current implementation, the system clock is assumed to be UTC, | |
2546 | and a table of leap seconds in the code converts to TAI. See comments | |
2547 | in @file{srfi-19.scm} for how to update this table. | |
2548 | ||
2549 | @cindex julian day | |
2550 | @cindex modified julian day | |
2551 | Also, for those not familiar with the terminology, a @dfn{Julian Day} | |
2552 | is a real number which is a count of days and fraction of a day, in | |
2553 | UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan | |
7c2e18cd KR |
2554 | 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from |
2555 | 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time | |
2556 | is julian day 2400000.5. | |
85600a0f KR |
2557 | |
2558 | @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at | |
2559 | @c noon, UTC), but this is incorrect. It looks like it might have | |
2560 | @c arisen from the code incorrectly treating years a multiple of 100 | |
7c2e18cd | 2561 | @c but not 400 prior to 1582 as non-leap years, where instead the Julian |
85600a0f KR |
2562 | @c calendar should be used so all multiples of 4 before 1582 are leap |
2563 | @c years. | |
2564 | ||
2565 | ||
2566 | @node SRFI-19 Time | |
3229f68b | 2567 | @subsubsection SRFI-19 Time |
85600a0f KR |
2568 | @cindex time |
2569 | ||
2570 | A @dfn{time} object has type, seconds and nanoseconds fields | |
2571 | representing a point in time starting from some epoch. This is an | |
2572 | arbitrary point in time, not just a time of day. Although times are | |
2573 | represented in nanoseconds, the actual resolution may be lower. | |
2574 | ||
2575 | The following variables hold the possible time types. For instance | |
2576 | @code{(current-time time-process)} would give the current CPU process | |
2577 | time. | |
2578 | ||
2579 | @defvar time-utc | |
2580 | Universal Coordinated Time (UTC). | |
2581 | @cindex UTC | |
2582 | @end defvar | |
12991fed | 2583 | |
85600a0f KR |
2584 | @defvar time-tai |
2585 | International Atomic Time (TAI). | |
2586 | @cindex TAI | |
2587 | @end defvar | |
12991fed | 2588 | |
85600a0f KR |
2589 | @defvar time-monotonic |
2590 | Monotonic time, meaning a monotonically increasing time starting from | |
2591 | an unspecified epoch. | |
12991fed | 2592 | |
85600a0f KR |
2593 | Note that in the current implementation @code{time-monotonic} is the |
2594 | same as @code{time-tai}, and unfortunately is therefore affected by | |
2595 | adjustments to the system clock. Perhaps this will change in the | |
2596 | future. | |
2597 | @end defvar | |
12991fed | 2598 | |
85600a0f KR |
2599 | @defvar time-duration |
2600 | A duration, meaning simply a difference between two times. | |
2601 | @end defvar | |
12991fed | 2602 | |
85600a0f KR |
2603 | @defvar time-process |
2604 | CPU time spent in the current process, starting from when the process | |
2605 | began. | |
2606 | @cindex process time | |
2607 | @end defvar | |
12991fed | 2608 | |
85600a0f KR |
2609 | @defvar time-thread |
2610 | CPU time spent in the current thread. Not currently implemented. | |
2611 | @cindex thread time | |
2612 | @end defvar | |
12991fed | 2613 | |
85600a0f KR |
2614 | @sp 1 |
2615 | @defun time? obj | |
2616 | Return @code{#t} if @var{obj} is a time object, or @code{#f} if not. | |
2617 | @end defun | |
2618 | ||
2619 | @defun make-time type nanoseconds seconds | |
2620 | Create a time object with the given @var{type}, @var{seconds} and | |
2621 | @var{nanoseconds}. | |
2622 | @end defun | |
2623 | ||
2624 | @defun time-type time | |
2625 | @defunx time-nanosecond time | |
2626 | @defunx time-second time | |
2627 | @defunx set-time-type! time type | |
2628 | @defunx set-time-nanosecond! time nsec | |
2629 | @defunx set-time-second! time sec | |
2630 | Get or set the type, seconds or nanoseconds fields of a time object. | |
2631 | ||
2632 | @code{set-time-type!} merely changes the field, it doesn't convert the | |
2633 | time value. For conversions, see @ref{SRFI-19 Time/Date conversions}. | |
2634 | @end defun | |
2635 | ||
2636 | @defun copy-time time | |
2637 | Return a new time object, which is a copy of the given @var{time}. | |
2638 | @end defun | |
2639 | ||
2640 | @defun current-time [type] | |
2641 | Return the current time of the given @var{type}. The default | |
2642 | @var{type} is @code{time-utc}. | |
2643 | ||
2644 | Note that the name @code{current-time} conflicts with the Guile core | |
e68f492a JG |
2645 | @code{current-time} function (@pxref{Time}) as well as the SRFI-18 |
2646 | @code{current-time} function (@pxref{SRFI-18 Time}). Applications | |
2647 | wanting to use more than one of these functions will need to refer to | |
2648 | them by different names. | |
85600a0f KR |
2649 | @end defun |
2650 | ||
2651 | @defun time-resolution [type] | |
2652 | Return the resolution, in nanoseconds, of the given time @var{type}. | |
2653 | The default @var{type} is @code{time-utc}. | |
2654 | @end defun | |
2655 | ||
2656 | @defun time<=? t1 t2 | |
2657 | @defunx time<? t1 t2 | |
2658 | @defunx time=? t1 t2 | |
2659 | @defunx time>=? t1 t2 | |
2660 | @defunx time>? t1 t2 | |
2661 | Return @code{#t} or @code{#f} according to the respective relation | |
2662 | between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2} | |
2663 | must be the same time type. | |
2664 | @end defun | |
2665 | ||
2666 | @defun time-difference t1 t2 | |
2667 | @defunx time-difference! t1 t2 | |
2668 | Return a time object of type @code{time-duration} representing the | |
2669 | period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be | |
2670 | the same time type. | |
2671 | ||
2672 | @code{time-difference} returns a new time object, | |
2673 | @code{time-difference!} may modify @var{t1} to form its return. | |
2674 | @end defun | |
2675 | ||
2676 | @defun add-duration time duration | |
2677 | @defunx add-duration! time duration | |
2678 | @defunx subtract-duration time duration | |
2679 | @defunx subtract-duration! time duration | |
2680 | Return a time object which is @var{time} with the given @var{duration} | |
2681 | added or subtracted. @var{duration} must be a time object of type | |
2682 | @code{time-duration}. | |
2683 | ||
2684 | @code{add-duration} and @code{subtract-duration} return a new time | |
2685 | object. @code{add-duration!} and @code{subtract-duration!} may modify | |
2686 | the given @var{time} to form their return. | |
2687 | @end defun | |
2688 | ||
2689 | ||
2690 | @node SRFI-19 Date | |
3229f68b | 2691 | @subsubsection SRFI-19 Date |
85600a0f KR |
2692 | @cindex date |
2693 | ||
2694 | A @dfn{date} object represents a date in the Gregorian calendar and a | |
2695 | time of day on that date in some timezone. | |
2696 | ||
2697 | The fields are year, month, day, hour, minute, second, nanoseconds and | |
2698 | timezone. A date object is immutable, its fields can be read but they | |
2699 | cannot be modified once the object is created. | |
2700 | ||
2701 | @defun date? obj | |
2702 | Return @code{#t} if @var{obj} is a date object, or @code{#f} if not. | |
2703 | @end defun | |
2704 | ||
2705 | @defun make-date nsecs seconds minutes hours date month year zone-offset | |
2706 | Create a new date object. | |
2707 | @c | |
2708 | @c FIXME: What can we say about the ranges of the values. The | |
2709 | @c current code looks it doesn't normalize, but expects then in their | |
2710 | @c usual range already. | |
2711 | @c | |
2712 | @end defun | |
2713 | ||
2714 | @defun date-nanosecond date | |
2715 | Nanoseconds, 0 to 999999999. | |
2716 | @end defun | |
2717 | ||
2718 | @defun date-second date | |
7c2e18cd KR |
2719 | Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working |
2720 | entirely within UTC, it's only when converting to or from TAI. | |
85600a0f KR |
2721 | @end defun |
2722 | ||
2723 | @defun date-minute date | |
2724 | Minutes, 0 to 59. | |
2725 | @end defun | |
2726 | ||
2727 | @defun date-hour date | |
2728 | Hour, 0 to 23. | |
2729 | @end defun | |
2730 | ||
2731 | @defun date-day date | |
2732 | Day of the month, 1 to 31 (or less, according to the month). | |
2733 | @end defun | |
2734 | ||
2735 | @defun date-month date | |
2736 | Month, 1 to 12. | |
2737 | @end defun | |
2738 | ||
2739 | @defun date-year date | |
7c2e18cd KR |
2740 | Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46 |
2741 | B.C. There is no year 0, year @math{-1} is followed by year 1. | |
85600a0f KR |
2742 | @end defun |
2743 | ||
2744 | @defun date-zone-offset date | |
2745 | Time zone, an integer number of seconds east of Greenwich. | |
2746 | @end defun | |
2747 | ||
2748 | @defun date-year-day date | |
2749 | Day of the year, starting from 1 for 1st January. | |
2750 | @end defun | |
2751 | ||
2752 | @defun date-week-day date | |
2753 | Day of the week, starting from 0 for Sunday. | |
2754 | @end defun | |
2755 | ||
2756 | @defun date-week-number date dstartw | |
2757 | Week of the year, ignoring a first partial week. @var{dstartw} is the | |
2758 | day of the week which is taken to start a week, 0 for Sunday, 1 for | |
2759 | Monday, etc. | |
2760 | @c | |
2761 | @c FIXME: The spec doesn't say whether numbering starts at 0 or 1. | |
2762 | @c The code looks like it's 0, if that's the correct intention. | |
2763 | @c | |
2764 | @end defun | |
2765 | ||
2766 | @c The SRFI text doesn't actually give the default for tz-offset, but | |
2767 | @c the reference implementation has the local timezone and the | |
2768 | @c conversions functions all specify that, so it should be ok to | |
2769 | @c document it here. | |
2770 | @c | |
2771 | @defun current-date [tz-offset] | |
7c2e18cd KR |
2772 | Return a date object representing the current date/time, in UTC offset |
2773 | by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and | |
2774 | defaults to the local timezone. | |
85600a0f KR |
2775 | @end defun |
2776 | ||
2777 | @defun current-julian-day | |
2778 | @cindex julian day | |
2779 | Return the current Julian Day. | |
2780 | @end defun | |
2781 | ||
2782 | @defun current-modified-julian-day | |
2783 | @cindex modified julian day | |
2784 | Return the current Modified Julian Day. | |
2785 | @end defun | |
2786 | ||
2787 | ||
2788 | @node SRFI-19 Time/Date conversions | |
3229f68b | 2789 | @subsubsection SRFI-19 Time/Date conversions |
7c2e18cd KR |
2790 | @cindex time conversion |
2791 | @cindex date conversion | |
85600a0f KR |
2792 | |
2793 | @defun date->julian-day date | |
2794 | @defunx date->modified-julian-day date | |
2795 | @defunx date->time-monotonic date | |
2796 | @defunx date->time-tai date | |
2797 | @defunx date->time-utc date | |
2798 | @end defun | |
2799 | @defun julian-day->date jdn [tz-offset] | |
2800 | @defunx julian-day->time-monotonic jdn | |
2801 | @defunx julian-day->time-tai jdn | |
2802 | @defunx julian-day->time-utc jdn | |
2803 | @end defun | |
2804 | @defun modified-julian-day->date jdn [tz-offset] | |
2805 | @defunx modified-julian-day->time-monotonic jdn | |
2806 | @defunx modified-julian-day->time-tai jdn | |
2807 | @defunx modified-julian-day->time-utc jdn | |
2808 | @end defun | |
2809 | @defun time-monotonic->date time [tz-offset] | |
2810 | @defunx time-monotonic->time-tai time | |
2811 | @defunx time-monotonic->time-tai! time | |
2812 | @defunx time-monotonic->time-utc time | |
2813 | @defunx time-monotonic->time-utc! time | |
2814 | @end defun | |
2815 | @defun time-tai->date time [tz-offset] | |
2816 | @defunx time-tai->julian-day time | |
2817 | @defunx time-tai->modified-julian-day time | |
2818 | @defunx time-tai->time-monotonic time | |
2819 | @defunx time-tai->time-monotonic! time | |
2820 | @defunx time-tai->time-utc time | |
2821 | @defunx time-tai->time-utc! time | |
2822 | @end defun | |
2823 | @defun time-utc->date time [tz-offset] | |
2824 | @defunx time-utc->julian-day time | |
2825 | @defunx time-utc->modified-julian-day time | |
2826 | @defunx time-utc->time-monotonic time | |
2827 | @defunx time-utc->time-monotonic! time | |
2828 | @defunx time-utc->time-tai time | |
2829 | @defunx time-utc->time-tai! time | |
2830 | @sp 1 | |
2831 | Convert between dates, times and days of the respective types. For | |
2832 | instance @code{time-tai->time-utc} accepts a @var{time} object of type | |
2833 | @code{time-tai} and returns an object of type @code{time-utc}. | |
2834 | ||
85600a0f KR |
2835 | The @code{!} variants may modify their @var{time} argument to form |
2836 | their return. The plain functions create a new object. | |
702e6e09 KR |
2837 | |
2838 | For conversions to dates, @var{tz-offset} is seconds east of | |
2839 | Greenwich. The default is the local timezone, at the given time, as | |
2840 | provided by the system, using @code{localtime} (@pxref{Time}). | |
2841 | ||
2842 | On 32-bit systems, @code{localtime} is limited to a 32-bit | |
2843 | @code{time_t}, so a default @var{tz-offset} is only available for | |
2844 | times between Dec 1901 and Jan 2038. For prior dates an application | |
2845 | might like to use the value in 1902, though some locations have zone | |
2846 | changes prior to that. For future dates an application might like to | |
2847 | assume today's rules extend indefinitely. But for correct daylight | |
2848 | savings transitions it will be necessary to take an offset for the | |
2849 | same day and time but a year in range and which has the same starting | |
2850 | weekday and same leap/non-leap (to support rules like last Sunday in | |
2851 | October). | |
85600a0f KR |
2852 | @end defun |
2853 | ||
2854 | @node SRFI-19 Date to string | |
3229f68b | 2855 | @subsubsection SRFI-19 Date to string |
85600a0f | 2856 | @cindex date to string |
7c2e18cd | 2857 | @cindex string, from date |
85600a0f KR |
2858 | |
2859 | @defun date->string date [format] | |
2860 | Convert a date to a string under the control of a format. | |
2861 | @var{format} should be a string containing @samp{~} escapes, which | |
2862 | will be expanded as per the following conversion table. The default | |
2863 | @var{format} is @samp{~c}, a locale-dependent date and time. | |
2864 | ||
2865 | Many of these conversion characters are the same as POSIX | |
2866 | @code{strftime} (@pxref{Time}), but there are some extras and some | |
2867 | variations. | |
2868 | ||
2869 | @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM} | |
2870 | @item @nicode{~~} @tab literal ~ | |
2871 | @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun} | |
2872 | @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday} | |
2873 | @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan} | |
2874 | @item @nicode{~B} @tab locale full month, eg.@: @samp{January} | |
2875 | @item @nicode{~c} @tab locale date and time, eg.@: @* | |
2876 | @samp{Fri Jul 14 20:28:42-0400 2000} | |
2877 | @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31} | |
2878 | ||
2879 | @c Spec says d/m/y, reference implementation says m/d/y. | |
2880 | @c Apparently the reference code was the intention, but would like to | |
2881 | @c see an errata published for the spec before contradicting it here. | |
2882 | @c | |
2883 | @c @item @nicode{~D} @tab date @nicode{~d/~m/~y} | |
2884 | ||
2885 | @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31} | |
2886 | @item @nicode{~f} @tab seconds and fractional seconds, | |
2887 | with locale decimal point, eg.@: @samp{5.2} | |
2888 | @item @nicode{~h} @tab same as @nicode{~b} | |
2889 | @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23} | |
2890 | @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12} | |
2891 | @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366} | |
2892 | @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23} | |
2893 | @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12} | |
2894 | @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12} | |
2895 | @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59} | |
2896 | @item @nicode{~n} @tab newline | |
2897 | @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999} | |
2898 | @item @nicode{~p} @tab locale AM or PM | |
2899 | @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p} | |
2900 | @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC | |
2901 | @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @* | |
2902 | (usual limit is 59, 60 is a leap second) | |
2903 | @item @nicode{~t} @tab horizontal tab character | |
2904 | @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S} | |
2905 | @item @nicode{~U} @tab week of year, Sunday first day of week, | |
2906 | @samp{00} to @samp{52} | |
2907 | @item @nicode{~V} @tab week of year, Monday first day of week, | |
2908 | @samp{01} to @samp{53} | |
2909 | @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6} | |
2910 | @item @nicode{~W} @tab week of year, Monday first day of week, | |
2911 | @samp{00} to @samp{52} | |
2912 | ||
2913 | @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale | |
2914 | @c date. The reference code has ~x as the locale date and ~X as a | |
2915 | @c locale time. The rule is apparently that the code should be | |
2916 | @c believed, but would like to see an errata for the spec before | |
2917 | @c contradicting it here. | |
2918 | @c | |
2919 | @c @item @nicode{~x} @tab week of year, Monday as first day of week, | |
2920 | @c @samp{00} to @samp{53} | |
2921 | @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00} | |
2922 | ||
2923 | @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99} | |
2924 | @item @nicode{~Y} @tab year, full, eg.@: @samp{2003} | |
2925 | @item @nicode{~z} @tab time zone, RFC-822 style | |
2926 | @item @nicode{~Z} @tab time zone symbol (not currently implemented) | |
2927 | @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d} | |
d6bd1826 IP |
2928 | @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~H:~M:~S~z} |
2929 | @item @nicode{~3} @tab ISO-8601 time, @samp{~H:~M:~S} | |
2930 | @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~H:~M:~S~z} | |
2931 | @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~H:~M:~S} | |
85600a0f KR |
2932 | @end multitable |
2933 | @end defun | |
2934 | ||
2935 | Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently | |
2936 | described here, since the specification and reference implementation | |
2937 | differ. | |
2938 | ||
a2f00b9b LC |
2939 | Conversion is locale-dependent on systems that support it |
2940 | (@pxref{Accessing Locale Information}). @xref{Locales, | |
2941 | @code{setlocale}}, for information on how to change the current | |
2942 | locale. | |
85600a0f KR |
2943 | |
2944 | ||
2945 | @node SRFI-19 String to date | |
3229f68b | 2946 | @subsubsection SRFI-19 String to date |
85600a0f | 2947 | @cindex string to date |
7c2e18cd | 2948 | @cindex date, from string |
85600a0f KR |
2949 | |
2950 | @c FIXME: Can we say what happens when an incomplete date is | |
679cceed | 2951 | @c converted? I.e. fields left as 0, or what? The spec seems to be |
85600a0f KR |
2952 | @c silent on this. |
2953 | ||
2954 | @defun string->date input template | |
2955 | Convert an @var{input} string to a date under the control of a | |
2956 | @var{template} string. Return a newly created date object. | |
2957 | ||
2958 | Literal characters in @var{template} must match characters in | |
2959 | @var{input} and @samp{~} escapes must match the input forms described | |
2960 | in the table below. ``Skip to'' means characters up to one of the | |
2961 | given type are ignored, or ``no skip'' for no skipping. ``Read'' is | |
2962 | what's then read, and ``Set'' is the field affected in the date | |
2963 | object. | |
2964 | ||
2965 | For example @samp{~Y} skips input characters until a digit is reached, | |
2966 | at which point it expects a year and stores that to the year field of | |
2967 | the date. | |
2968 | ||
2969 | @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}} | |
2970 | @item | |
2971 | @tab Skip to | |
2972 | @tab Read | |
2973 | @tab Set | |
2974 | ||
2975 | @item @nicode{~~} | |
2976 | @tab no skip | |
2977 | @tab literal ~ | |
2978 | @tab nothing | |
2979 | ||
2980 | @item @nicode{~a} | |
2981 | @tab @nicode{char-alphabetic?} | |
2982 | @tab locale abbreviated weekday name | |
2983 | @tab nothing | |
2984 | ||
2985 | @item @nicode{~A} | |
2986 | @tab @nicode{char-alphabetic?} | |
2987 | @tab locale full weekday name | |
2988 | @tab nothing | |
2989 | ||
2990 | @c Note that the SRFI spec says that ~b and ~B don't set anything, | |
2991 | @c but that looks like a mistake. The reference implementation sets | |
2992 | @c the month field, which seems sensible and is what we describe | |
2993 | @c here. | |
2994 | ||
2995 | @item @nicode{~b} | |
2996 | @tab @nicode{char-alphabetic?} | |
2997 | @tab locale abbreviated month name | |
2998 | @tab @nicode{date-month} | |
2999 | ||
3000 | @item @nicode{~B} | |
3001 | @tab @nicode{char-alphabetic?} | |
3002 | @tab locale full month name | |
3003 | @tab @nicode{date-month} | |
3004 | ||
3005 | @item @nicode{~d} | |
3006 | @tab @nicode{char-numeric?} | |
3007 | @tab day of month | |
3008 | @tab @nicode{date-day} | |
3009 | ||
3010 | @item @nicode{~e} | |
3011 | @tab no skip | |
3012 | @tab day of month, blank padded | |
3013 | @tab @nicode{date-day} | |
3014 | ||
3015 | @item @nicode{~h} | |
3016 | @tab same as @samp{~b} | |
3017 | ||
3018 | @item @nicode{~H} | |
3019 | @tab @nicode{char-numeric?} | |
3020 | @tab hour | |
3021 | @tab @nicode{date-hour} | |
3022 | ||
3023 | @item @nicode{~k} | |
3024 | @tab no skip | |
3025 | @tab hour, blank padded | |
3026 | @tab @nicode{date-hour} | |
3027 | ||
3028 | @item @nicode{~m} | |
3029 | @tab @nicode{char-numeric?} | |
3030 | @tab month | |
3031 | @tab @nicode{date-month} | |
3032 | ||
3033 | @item @nicode{~M} | |
3034 | @tab @nicode{char-numeric?} | |
3035 | @tab minute | |
3036 | @tab @nicode{date-minute} | |
3037 | ||
3038 | @item @nicode{~S} | |
3039 | @tab @nicode{char-numeric?} | |
3040 | @tab second | |
3041 | @tab @nicode{date-second} | |
3042 | ||
3043 | @item @nicode{~y} | |
3044 | @tab no skip | |
3045 | @tab 2-digit year | |
3046 | @tab @nicode{date-year} within 50 years | |
3047 | ||
3048 | @item @nicode{~Y} | |
3049 | @tab @nicode{char-numeric?} | |
3050 | @tab year | |
3051 | @tab @nicode{date-year} | |
3052 | ||
3053 | @item @nicode{~z} | |
3054 | @tab no skip | |
3055 | @tab time zone | |
3056 | @tab date-zone-offset | |
3057 | @end multitable | |
3058 | ||
3059 | Notice that the weekday matching forms don't affect the date object | |
3060 | returned, instead the weekday will be derived from the day, month and | |
3061 | year. | |
3062 | ||
a2f00b9b LC |
3063 | Conversion is locale-dependent on systems that support it |
3064 | (@pxref{Accessing Locale Information}). @xref{Locales, | |
3065 | @code{setlocale}}, for information on how to change the current | |
3066 | locale. | |
85600a0f | 3067 | @end defun |
12991fed | 3068 | |
8e9af854 NL |
3069 | @node SRFI-23 |
3070 | @subsection SRFI-23 - Error Reporting | |
3071 | @cindex SRFI-23 | |
3072 | ||
3073 | The SRFI-23 @code{error} procedure is always available. | |
1de8c1ae | 3074 | |
b0b55bd6 | 3075 | @node SRFI-26 |
3229f68b | 3076 | @subsection SRFI-26 - specializing parameters |
1de8c1ae | 3077 | @cindex SRFI-26 |
7c2e18cd KR |
3078 | @cindex parameter specialize |
3079 | @cindex argument specialize | |
3080 | @cindex specialize parameter | |
1de8c1ae KR |
3081 | |
3082 | This SRFI provides a syntax for conveniently specializing selected | |
3083 | parameters of a function. It can be used with, | |
3084 | ||
3085 | @example | |
3086 | (use-modules (srfi srfi-26)) | |
3087 | @end example | |
3088 | ||
df0a1002 BT |
3089 | @deffn {library syntax} cut slot1 slot2 @dots{} |
3090 | @deffnx {library syntax} cute slot1 slot2 @dots{} | |
3091 | Return a new procedure which will make a call (@var{slot1} @var{slot2} | |
3092 | @dots{}) but with selected parameters specialized to given expressions. | |
1de8c1ae KR |
3093 | |
3094 | An example will illustrate the idea. The following is a | |
3095 | specialization of @code{write}, sending output to | |
3096 | @code{my-output-port}, | |
3097 | ||
3098 | @example | |
3099 | (cut write <> my-output-port) | |
3100 | @result{} | |
3101 | (lambda (obj) (write obj my-output-port)) | |
3102 | @end example | |
3103 | ||
3104 | The special symbol @code{<>} indicates a slot to be filled by an | |
3105 | argument to the new procedure. @code{my-output-port} on the other | |
3106 | hand is an expression to be evaluated and passed, ie.@: it specializes | |
3107 | the behaviour of @code{write}. | |
3108 | ||
3109 | @table @nicode | |
3110 | @item <> | |
3111 | A slot to be filled by an argument from the created procedure. | |
3112 | Arguments are assigned to @code{<>} slots in the order they appear in | |
3113 | the @code{cut} form, there's no way to re-arrange arguments. | |
3114 | ||
3115 | The first argument to @code{cut} is usually a procedure (or expression | |
3116 | giving a procedure), but @code{<>} is allowed there too. For example, | |
3117 | ||
3118 | @example | |
3119 | (cut <> 1 2 3) | |
3120 | @result{} | |
3121 | (lambda (proc) (proc 1 2 3)) | |
3122 | @end example | |
3123 | ||
3124 | @item <...> | |
3125 | A slot to be filled by all remaining arguments from the new procedure. | |
3126 | This can only occur at the end of a @code{cut} form. | |
3127 | ||
3128 | For example, a procedure taking a variable number of arguments like | |
3129 | @code{max} but in addition enforcing a lower bound, | |
3130 | ||
3131 | @example | |
3132 | (define my-lower-bound 123) | |
3133 | ||
3134 | (cut max my-lower-bound <...>) | |
3135 | @result{} | |
3136 | (lambda arglist (apply max my-lower-bound arglist)) | |
3137 | @end example | |
3138 | @end table | |
3139 | ||
3140 | For @code{cut} the specializing expressions are evaluated each time | |
3141 | the new procedure is called. For @code{cute} they're evaluated just | |
3142 | once, when the new procedure is created. The name @code{cute} stands | |
3143 | for ``@code{cut} with evaluated arguments''. In all cases the | |
3144 | evaluations take place in an unspecified order. | |
3145 | ||
3146 | The following illustrates the difference between @code{cut} and | |
3147 | @code{cute}, | |
3148 | ||
3149 | @example | |
3150 | (cut format <> "the time is ~s" (current-time)) | |
3151 | @result{} | |
3152 | (lambda (port) (format port "the time is ~s" (current-time))) | |
3153 | ||
3154 | (cute format <> "the time is ~s" (current-time)) | |
3155 | @result{} | |
3156 | (let ((val (current-time))) | |
3157 | (lambda (port) (format port "the time is ~s" val)) | |
3158 | @end example | |
3159 | ||
3160 | (There's no provision for a mixture of @code{cut} and @code{cute} | |
3161 | where some expressions would be evaluated every time but others | |
3162 | evaluated only once.) | |
3163 | ||
3164 | @code{cut} is really just a shorthand for the sort of @code{lambda} | |
3165 | forms shown in the above examples. But notice @code{cut} avoids the | |
3166 | need to name unspecialized parameters, and is more compact. Use in | |
3167 | functional programming style or just with @code{map}, @code{for-each} | |
3168 | or similar is typical. | |
3169 | ||
3170 | @example | |
3171 | (map (cut * 2 <>) '(1 2 3 4)) | |
3172 | ||
3173 | (for-each (cut write <> my-port) my-list) | |
3174 | @end example | |
3175 | @end deffn | |
b0b55bd6 | 3176 | |
56ec46a7 AR |
3177 | @node SRFI-27 |
3178 | @subsection SRFI-27 - Sources of Random Bits | |
3179 | @cindex SRFI-27 | |
3180 | ||
6e3d49a0 AR |
3181 | This subsection is based on the |
3182 | @uref{http://srfi.schemers.org/srfi-27/srfi-27.html, specification of | |
3183 | SRFI-27} written by Sebastian Egner. | |
3184 | ||
3185 | @c The copyright notice and license text of the SRFI-27 specification is | |
3186 | @c reproduced below: | |
56ec46a7 AR |
3187 | |
3188 | @c Copyright (C) Sebastian Egner (2002). All Rights Reserved. | |
3189 | ||
3190 | @c Permission is hereby granted, free of charge, to any person obtaining a | |
3191 | @c copy of this software and associated documentation files (the | |
3192 | @c "Software"), to deal in the Software without restriction, including | |
3193 | @c without limitation the rights to use, copy, modify, merge, publish, | |
3194 | @c distribute, sublicense, and/or sell copies of the Software, and to | |
3195 | @c permit persons to whom the Software is furnished to do so, subject to | |
3196 | @c the following conditions: | |
3197 | ||
3198 | @c The above copyright notice and this permission notice shall be included | |
3199 | @c in all copies or substantial portions of the Software. | |
3200 | ||
3201 | @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS | |
3202 | @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF | |
3203 | @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | |
3204 | @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE | |
3205 | @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION | |
3206 | @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION | |
3207 | @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. | |
3208 | ||
56ec46a7 AR |
3209 | This SRFI provides access to a (pseudo) random number generator; for |
3210 | Guile's built-in random number facilities, which SRFI-27 is implemented | |
3211 | upon, @xref{Random}. With SRFI-27, random numbers are obtained from a | |
3212 | @emph{random source}, which encapsulates a random number generation | |
3213 | algorithm and its state. | |
3214 | ||
3215 | @menu | |
3216 | * SRFI-27 Default Random Source:: Obtaining random numbers | |
3217 | * SRFI-27 Random Sources:: Creating and manipulating random sources | |
3218 | * SRFI-27 Random Number Generators:: Obtaining random number generators | |
3219 | @end menu | |
3220 | ||
3221 | @node SRFI-27 Default Random Source | |
3222 | @subsubsection The Default Random Source | |
3223 | @cindex SRFI-27 | |
3224 | ||
3225 | @defun random-integer n | |
3226 | Return a random number between zero (inclusive) and @var{n} (exclusive), | |
3227 | using the default random source. The numbers returned have a uniform | |
3228 | distribution. | |
3229 | @end defun | |
3230 | ||
3231 | @defun random-real | |
3232 | Return a random number in (0,1), using the default random source. The | |
3233 | numbers returned have a uniform distribution. | |
3234 | @end defun | |
3235 | ||
3236 | @defun default-random-source | |
3237 | A random source from which @code{random-integer} and @code{random-real} | |
3238 | have been derived using @code{random-source-make-integers} and | |
3239 | @code{random-source-make-reals} (@pxref{SRFI-27 Random Number Generators} | |
3240 | for those procedures). Note that an assignment to | |
3241 | @code{default-random-source} does not change @code{random-integer} or | |
3242 | @code{random-real}; it is also strongly recommended not to assign a new | |
3243 | value. | |
3244 | @end defun | |
3245 | ||
3246 | @node SRFI-27 Random Sources | |
3247 | @subsubsection Random Sources | |
3248 | @cindex SRFI-27 | |
3249 | ||
3250 | @defun make-random-source | |
3251 | Create a new random source. The stream of random numbers obtained from | |
3252 | each random source created by this procedure will be identical, unless | |
3253 | its state is changed by one of the procedures below. | |
3254 | @end defun | |
3255 | ||
3256 | @defun random-source? object | |
3257 | Tests whether @var{object} is a random source. Random sources are a | |
3258 | disjoint type. | |
3259 | @end defun | |
3260 | ||
3261 | @defun random-source-randomize! source | |
3262 | Attempt to set the state of the random source to a truly random value. | |
3263 | The current implementation uses a seed based on the current system time. | |
3264 | @end defun | |
3265 | ||
3266 | @defun random-source-pseudo-randomize! source i j | |
3267 | Changes the state of the random source s into the initial state of the | |
3268 | (@var{i}, @var{j})-th independent random source, where @var{i} and | |
3269 | @var{j} are non-negative integers. This procedure provides a mechanism | |
3270 | to obtain a large number of independent random sources (usually all | |
3271 | derived from the same backbone generator), indexed by two integers. In | |
3272 | contrast to @code{random-source-randomize!}, this procedure is entirely | |
3273 | deterministic. | |
3274 | @end defun | |
3275 | ||
3276 | The state associated with a random state can be obtained an reinstated | |
3277 | with the following procedures: | |
3278 | ||
3279 | @defun random-source-state-ref source | |
3280 | @defunx random-source-state-set! source state | |
3281 | Get and set the state of a random source. No assumptions should be made | |
3282 | about the nature of the state object, besides it having an external | |
679cceed | 3283 | representation (i.e.@: it can be passed to @code{write} and subsequently |
56ec46a7 AR |
3284 | @code{read} back). |
3285 | @end defun | |
3286 | ||
3287 | @node SRFI-27 Random Number Generators | |
3288 | @subsubsection Obtaining random number generator procedures | |
3289 | @cindex SRFI-27 | |
3290 | ||
3291 | @defun random-source-make-integers source | |
3292 | Obtains a procedure to generate random integers using the random source | |
3293 | @var{source}. The returned procedure takes a single argument @var{n}, | |
3294 | which must be a positive integer, and returns the next uniformly | |
3295 | distributed random integer from the interval @{0, ..., @var{n}-1@} by | |
3296 | advancing the state of @var{source}. | |
3297 | ||
3298 | If an application obtains and uses several generators for the same | |
3299 | random source @var{source}, a call to any of these generators advances | |
3300 | the state of @var{source}. Hence, the generators do not produce the | |
3301 | same sequence of random integers each but rather share a state. This | |
3302 | also holds for all other types of generators derived from a fixed random | |
3303 | sources. | |
3304 | ||
3305 | While the SRFI text specifies that ``Implementations that support | |
3306 | concurrency make sure that the state of a generator is properly | |
3307 | advanced'', this is currently not the case in Guile's implementation of | |
3308 | SRFI-27, as it would cause a severe performance penalty. So in | |
3309 | multi-threaded programs, you either must perform locking on random | |
3310 | sources shared between threads yourself, or use different random sources | |
3311 | for multiple threads. | |
3312 | @end defun | |
3313 | ||
3314 | @defun random-source-make-reals source | |
3315 | @defunx random-source-make-reals source unit | |
3316 | Obtains a procedure to generate random real numbers @math{0 < x < 1} | |
3317 | using the random source @var{source}. The procedure rand is called | |
3318 | without arguments. | |
3319 | ||
3320 | The optional parameter @var{unit} determines the type of numbers being | |
3321 | produced by the returned procedure and the quantization of the output. | |
3322 | @var{unit} must be a number such that @math{0 < @var{unit} < 1}. The | |
3323 | numbers created by the returned procedure are of the same numerical type | |
3324 | as @var{unit} and the potential output values are spaced by at most | |
3325 | @var{unit}. One can imagine rand to create numbers as @var{x} * | |
3326 | @var{unit} where @var{x} is a random integer in @{1, ..., | |
3327 | floor(1/unit)-1@}. Note, however, that this need not be the way the | |
3328 | values are actually created and that the actual resolution of rand can | |
3329 | be much higher than unit. In case @var{unit} is absent it defaults to a | |
3330 | reasonably small value (related to the width of the mantissa of an | |
3331 | efficient number format). | |
3332 | @end defun | |
3333 | ||
620c8965 LC |
3334 | @node SRFI-30 |
3335 | @subsection SRFI-30 - Nested Multi-line Comments | |
3336 | @cindex SRFI-30 | |
3337 | ||
3338 | Starting from version 2.0, Guile's @code{read} supports SRFI-30/R6RS | |
3339 | nested multi-line comments by default, @ref{Block Comments}. | |
3340 | ||
8638c417 RB |
3341 | @node SRFI-31 |
3342 | @subsection SRFI-31 - A special form `rec' for recursive evaluation | |
3343 | @cindex SRFI-31 | |
7c2e18cd | 3344 | @cindex recursive expression |
8638c417 RB |
3345 | @findex rec |
3346 | ||
3347 | SRFI-31 defines a special form that can be used to create | |
3348 | self-referential expressions more conveniently. The syntax is as | |
3349 | follows: | |
3350 | ||
3351 | @example | |
3352 | @group | |
3353 | <rec expression> --> (rec <variable> <expression>) | |
3354 | <rec expression> --> (rec (<variable>+) <body>) | |
3355 | @end group | |
3356 | @end example | |
3357 | ||
3358 | The first syntax can be used to create self-referential expressions, | |
3359 | for example: | |
3360 | ||
3361 | @lisp | |
3362 | guile> (define tmp (rec ones (cons 1 (delay ones)))) | |
3363 | @end lisp | |
3364 | ||
3365 | The second syntax can be used to create anonymous recursive functions: | |
3366 | ||
3367 | @lisp | |
3368 | guile> (define tmp (rec (display-n item n) | |
3369 | (if (positive? n) | |
3370 | (begin (display n) (display-n (- n 1)))))) | |
3371 | guile> (tmp 42 3) | |
3372 | 424242 | |
3373 | guile> | |
3374 | @end lisp | |
12991fed | 3375 | |
eeadfda1 | 3376 | |
f50ca8da LC |
3377 | @node SRFI-34 |
3378 | @subsection SRFI-34 - Exception handling for programs | |
3379 | ||
3380 | @cindex SRFI-34 | |
3381 | Guile provides an implementation of | |
3382 | @uref{http://srfi.schemers.org/srfi-34/srfi-34.html, SRFI-34's exception | |
3383 | handling mechanisms} as an alternative to its own built-in mechanisms | |
3384 | (@pxref{Exceptions}). It can be made available as follows: | |
3385 | ||
3386 | @lisp | |
3387 | (use-modules (srfi srfi-34)) | |
3388 | @end lisp | |
3389 | ||
3390 | @c FIXME: Document it. | |
3391 | ||
3392 | ||
3393 | @node SRFI-35 | |
3394 | @subsection SRFI-35 - Conditions | |
3395 | ||
3396 | @cindex SRFI-35 | |
3397 | @cindex conditions | |
3398 | @cindex exceptions | |
3399 | ||
3400 | @uref{http://srfi.schemers.org/srfi-35/srfi-35.html, SRFI-35} implements | |
3401 | @dfn{conditions}, a data structure akin to records designed to convey | |
3402 | information about exceptional conditions between parts of a program. It | |
3403 | is normally used in conjunction with SRFI-34's @code{raise}: | |
3404 | ||
3405 | @lisp | |
3406 | (raise (condition (&message | |
3407 | (message "An error occurred")))) | |
3408 | @end lisp | |
3409 | ||
3410 | Users can define @dfn{condition types} containing arbitrary information. | |
3411 | Condition types may inherit from one another. This allows the part of | |
3412 | the program that handles (or ``catches'') conditions to get accurate | |
3413 | information about the exceptional condition that arose. | |
3414 | ||
3415 | SRFI-35 conditions are made available using: | |
3416 | ||
3417 | @lisp | |
3418 | (use-modules (srfi srfi-35)) | |
3419 | @end lisp | |
3420 | ||
3421 | The procedures available to manipulate condition types are the | |
3422 | following: | |
3423 | ||
3424 | @deffn {Scheme Procedure} make-condition-type id parent field-names | |
3425 | Return a new condition type named @var{id}, inheriting from | |
3426 | @var{parent}, and with the fields whose names are listed in | |
3427 | @var{field-names}. @var{field-names} must be a list of symbols and must | |
3428 | not contain names already used by @var{parent} or one of its supertypes. | |
3429 | @end deffn | |
3430 | ||
3431 | @deffn {Scheme Procedure} condition-type? obj | |
3432 | Return true if @var{obj} is a condition type. | |
3433 | @end deffn | |
3434 | ||
3435 | Conditions can be created and accessed with the following procedures: | |
3436 | ||
3437 | @deffn {Scheme Procedure} make-condition type . field+value | |
3438 | Return a new condition of type @var{type} with fields initialized as | |
3439 | specified by @var{field+value}, a sequence of field names (symbols) and | |
3440 | values as in the following example: | |
3441 | ||
3442 | @lisp | |
1317062f | 3443 | (let ((&ct (make-condition-type 'foo &condition '(a b c)))) |
f50ca8da LC |
3444 | (make-condition &ct 'a 1 'b 2 'c 3)) |
3445 | @end lisp | |
3446 | ||
3447 | Note that all fields of @var{type} and its supertypes must be specified. | |
3448 | @end deffn | |
3449 | ||
df0a1002 | 3450 | @deffn {Scheme Procedure} make-compound-condition condition1 condition2 @dots{} |
994d87be BT |
3451 | Return a new compound condition composed of @var{condition1} |
3452 | @var{condition2} @enddots{}. The returned condition has the type of | |
3453 | each condition of condition1 condition2 @dots{} (per | |
3454 | @code{condition-has-type?}). | |
f50ca8da LC |
3455 | @end deffn |
3456 | ||
3457 | @deffn {Scheme Procedure} condition-has-type? c type | |
3458 | Return true if condition @var{c} has type @var{type}. | |
3459 | @end deffn | |
3460 | ||
3461 | @deffn {Scheme Procedure} condition-ref c field-name | |
3462 | Return the value of the field named @var{field-name} from condition @var{c}. | |
3463 | ||
3464 | If @var{c} is a compound condition and several underlying condition | |
3465 | types contain a field named @var{field-name}, then the value of the | |
3466 | first such field is returned, using the order in which conditions were | |
64de6db5 | 3467 | passed to @code{make-compound-condition}. |
f50ca8da LC |
3468 | @end deffn |
3469 | ||
3470 | @deffn {Scheme Procedure} extract-condition c type | |
3471 | Return a condition of condition type @var{type} with the field values | |
3472 | specified by @var{c}. | |
3473 | ||
3474 | If @var{c} is a compound condition, extract the field values from the | |
3475 | subcondition belonging to @var{type} that appeared first in the call to | |
72b3aa56 | 3476 | @code{make-compound-condition} that created the condition. |
f50ca8da LC |
3477 | @end deffn |
3478 | ||
3479 | Convenience macros are also available to create condition types and | |
3480 | conditions. | |
3481 | ||
3482 | @deffn {library syntax} define-condition-type type supertype predicate field-spec... | |
3483 | Define a new condition type named @var{type} that inherits from | |
3484 | @var{supertype}. In addition, bind @var{predicate} to a type predicate | |
3485 | that returns true when passed a condition of type @var{type} or any of | |
3486 | its subtypes. @var{field-spec} must have the form @code{(field | |
3487 | accessor)} where @var{field} is the name of field of @var{type} and | |
3488 | @var{accessor} is the name of a procedure to access field @var{field} in | |
3489 | conditions of type @var{type}. | |
3490 | ||
3491 | The example below defines condition type @code{&foo}, inheriting from | |
3492 | @code{&condition} with fields @code{a}, @code{b} and @code{c}: | |
3493 | ||
3494 | @lisp | |
3495 | (define-condition-type &foo &condition | |
3496 | foo-condition? | |
3497 | (a foo-a) | |
3498 | (b foo-b) | |
3499 | (c foo-c)) | |
3500 | @end lisp | |
3501 | @end deffn | |
3502 | ||
df0a1002 BT |
3503 | @deffn {library syntax} condition type-field-binding1 type-field-binding2 @dots{} |
3504 | Return a new condition or compound condition, initialized according to | |
3505 | @var{type-field-binding1} @var{type-field-binding2} @enddots{}. Each | |
3506 | @var{type-field-binding} must have the form @code{(type | |
3507 | field-specs...)}, where @var{type} is the name of a variable bound to a | |
3508 | condition type; each @var{field-spec} must have the form | |
3509 | @code{(field-name value)} where @var{field-name} is a symbol denoting | |
3510 | the field being initialized to @var{value}. As for | |
f50ca8da LC |
3511 | @code{make-condition}, all fields must be specified. |
3512 | ||
3513 | The following example returns a simple condition: | |
3514 | ||
3515 | @lisp | |
3516 | (condition (&message (message "An error occurred"))) | |
3517 | @end lisp | |
3518 | ||
3519 | The one below returns a compound condition: | |
3520 | ||
3521 | @lisp | |
3522 | (condition (&message (message "An error occurred")) | |
3523 | (&serious)) | |
3524 | @end lisp | |
3525 | @end deffn | |
3526 | ||
3527 | Finally, SRFI-35 defines a several standard condition types. | |
3528 | ||
3529 | @defvar &condition | |
3530 | This condition type is the root of all condition types. It has no | |
3531 | fields. | |
3532 | @end defvar | |
3533 | ||
3534 | @defvar &message | |
3535 | A condition type that carries a message describing the nature of the | |
3536 | condition to humans. | |
3537 | @end defvar | |
3538 | ||
3539 | @deffn {Scheme Procedure} message-condition? c | |
3540 | Return true if @var{c} is of type @code{&message} or one of its | |
3541 | subtypes. | |
3542 | @end deffn | |
3543 | ||
3544 | @deffn {Scheme Procedure} condition-message c | |
3545 | Return the message associated with message condition @var{c}. | |
3546 | @end deffn | |
3547 | ||
3548 | @defvar &serious | |
3549 | This type describes conditions serious enough that they cannot safely be | |
3550 | ignored. It has no fields. | |
3551 | @end defvar | |
3552 | ||
3553 | @deffn {Scheme Procedure} serious-condition? c | |
3554 | Return true if @var{c} is of type @code{&serious} or one of its | |
3555 | subtypes. | |
3556 | @end deffn | |
3557 | ||
3558 | @defvar &error | |
3559 | This condition describes errors, typically caused by something that has | |
3560 | gone wrong in the interaction of the program with the external world or | |
3561 | the user. | |
3562 | @end defvar | |
3563 | ||
3564 | @deffn {Scheme Procedure} error? c | |
3565 | Return true if @var{c} is of type @code{&error} or one of its subtypes. | |
3566 | @end deffn | |
3567 | ||
d4c38221 LC |
3568 | @node SRFI-37 |
3569 | @subsection SRFI-37 - args-fold | |
3570 | @cindex SRFI-37 | |
3571 | ||
3572 | This is a processor for GNU @code{getopt_long}-style program | |
3573 | arguments. It provides an alternative, less declarative interface | |
3574 | than @code{getopt-long} in @code{(ice-9 getopt-long)} | |
3575 | (@pxref{getopt-long,,The (ice-9 getopt-long) Module}). Unlike | |
3576 | @code{getopt-long}, it supports repeated options and any number of | |
3577 | short and long names per option. Access it with: | |
3578 | ||
3579 | @lisp | |
3580 | (use-modules (srfi srfi-37)) | |
3581 | @end lisp | |
3582 | ||
3583 | @acronym{SRFI}-37 principally provides an @code{option} type and the | |
3584 | @code{args-fold} function. To use the library, create a set of | |
3585 | options with @code{option} and use it as a specification for invoking | |
3586 | @code{args-fold}. | |
3587 | ||
3588 | Here is an example of a simple argument processor for the typical | |
3589 | @samp{--version} and @samp{--help} options, which returns a backwards | |
3590 | list of files given on the command line: | |
3591 | ||
3592 | @lisp | |
3593 | (args-fold (cdr (program-arguments)) | |
3594 | (let ((display-and-exit-proc | |
3595 | (lambda (msg) | |
3596 | (lambda (opt name arg loads) | |
3597 | (display msg) (quit))))) | |
3598 | (list (option '(#\v "version") #f #f | |
3599 | (display-and-exit-proc "Foo version 42.0\n")) | |
3600 | (option '(#\h "help") #f #f | |
3601 | (display-and-exit-proc | |
3602 | "Usage: foo scheme-file ...")))) | |
3603 | (lambda (opt name arg loads) | |
3604 | (error "Unrecognized option `~A'" name)) | |
3605 | (lambda (op loads) (cons op loads)) | |
3606 | '()) | |
3607 | @end lisp | |
3608 | ||
3609 | @deffn {Scheme Procedure} option names required-arg? optional-arg? processor | |
3610 | Return an object that specifies a single kind of program option. | |
3611 | ||
3612 | @var{names} is a list of command-line option names, and should consist of | |
3613 | characters for traditional @code{getopt} short options and strings for | |
3614 | @code{getopt_long}-style long options. | |
3615 | ||
3616 | @var{required-arg?} and @var{optional-arg?} are mutually exclusive; | |
3617 | one or both must be @code{#f}. If @var{required-arg?}, the option | |
3618 | must be followed by an argument on the command line, such as | |
3619 | @samp{--opt=value} for long options, or an error will be signalled. | |
3620 | If @var{optional-arg?}, an argument will be taken if available. | |
3621 | ||
3622 | @var{processor} is a procedure that takes at least 3 arguments, called | |
3623 | when @code{args-fold} encounters the option: the containing option | |
3624 | object, the name used on the command line, and the argument given for | |
3625 | the option (or @code{#f} if none). The rest of the arguments are | |
3626 | @code{args-fold} ``seeds'', and the @var{processor} should return | |
3627 | seeds as well. | |
3628 | @end deffn | |
3629 | ||
3630 | @deffn {Scheme Procedure} option-names opt | |
3631 | @deffnx {Scheme Procedure} option-required-arg? opt | |
3632 | @deffnx {Scheme Procedure} option-optional-arg? opt | |
3633 | @deffnx {Scheme Procedure} option-processor opt | |
3634 | Return the specified field of @var{opt}, an option object, as | |
3635 | described above for @code{option}. | |
3636 | @end deffn | |
3637 | ||
df0a1002 BT |
3638 | @deffn {Scheme Procedure} args-fold args options unrecognized-option-proc operand-proc seed @dots{} |
3639 | Process @var{args}, a list of program arguments such as that returned by | |
3640 | @code{(cdr (program-arguments))}, in order against @var{options}, a list | |
3641 | of option objects as described above. All functions called take the | |
3642 | ``seeds'', or the last multiple-values as multiple arguments, starting | |
3643 | with @var{seed} @dots{}, and must return the new seeds. Return the | |
d4c38221 LC |
3644 | final seeds. |
3645 | ||
3646 | Call @code{unrecognized-option-proc}, which is like an option object's | |
3647 | processor, for any options not found in @var{options}. | |
3648 | ||
3649 | Call @code{operand-proc} with any items on the command line that are | |
3650 | not named options. This includes arguments after @samp{--}. It is | |
3651 | called with the argument in question, as well as the seeds. | |
3652 | @end deffn | |
3653 | ||
12708eeb AR |
3654 | @node SRFI-38 |
3655 | @subsection SRFI-38 - External Representation for Data With Shared Structure | |
3656 | @cindex SRFI-38 | |
3657 | ||
3658 | This subsection is based on | |
3659 | @uref{http://srfi.schemers.org/srfi-38/srfi-38.html, the specification | |
3660 | of SRFI-38} written by Ray Dillinger. | |
3661 | ||
3662 | @c Copyright (C) Ray Dillinger 2003. All Rights Reserved. | |
3663 | ||
3664 | @c Permission is hereby granted, free of charge, to any person obtaining a | |
3665 | @c copy of this software and associated documentation files (the | |
3666 | @c "Software"), to deal in the Software without restriction, including | |
3667 | @c without limitation the rights to use, copy, modify, merge, publish, | |
3668 | @c distribute, sublicense, and/or sell copies of the Software, and to | |
3669 | @c permit persons to whom the Software is furnished to do so, subject to | |
3670 | @c the following conditions: | |
3671 | ||
3672 | @c The above copyright notice and this permission notice shall be included | |
3673 | @c in all copies or substantial portions of the Software. | |
3674 | ||
3675 | @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS | |
3676 | @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF | |
3677 | @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | |
3678 | @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE | |
3679 | @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION | |
3680 | @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION | |
3681 | @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. | |
3682 | ||
3683 | This SRFI creates an alternative external representation for data | |
3684 | written and read using @code{write-with-shared-structure} and | |
3685 | @code{read-with-shared-structure}. It is identical to the grammar for | |
3686 | external representation for data written and read with @code{write} and | |
3687 | @code{read} given in section 7 of R5RS, except that the single | |
3688 | production | |
3689 | ||
3690 | @example | |
3691 | <datum> --> <simple datum> | <compound datum> | |
3692 | @end example | |
3693 | ||
3694 | is replaced by the following five productions: | |
3695 | ||
3696 | @example | |
3697 | <datum> --> <defining datum> | <nondefining datum> | <defined datum> | |
3698 | <defining datum> --> #<indexnum>=<nondefining datum> | |
3699 | <defined datum> --> #<indexnum># | |
3700 | <nondefining datum> --> <simple datum> | <compound datum> | |
3701 | <indexnum> --> <digit 10>+ | |
3702 | @end example | |
3703 | ||
3704 | @deffn {Scheme procedure} write-with-shared-structure obj | |
3705 | @deffnx {Scheme procedure} write-with-shared-structure obj port | |
3706 | @deffnx {Scheme procedure} write-with-shared-structure obj port optarg | |
3707 | ||
3708 | Writes an external representation of @var{obj} to the given port. | |
3709 | Strings that appear in the written representation are enclosed in | |
3710 | doublequotes, and within those strings backslash and doublequote | |
3711 | characters are escaped by backslashes. Character objects are written | |
3712 | using the @code{#\} notation. | |
3713 | ||
3714 | Objects which denote locations rather than values (cons cells, vectors, | |
3715 | and non-zero-length strings in R5RS scheme; also Guile's structs, | |
3716 | bytevectors and ports and hash-tables), if they appear at more than one | |
3717 | point in the data being written, are preceded by @samp{#@var{N}=} the | |
3718 | first time they are written and replaced by @samp{#@var{N}#} all | |
3719 | subsequent times they are written, where @var{N} is a natural number | |
3720 | used to identify that particular object. If objects which denote | |
3721 | locations occur only once in the structure, then | |
3722 | @code{write-with-shared-structure} must produce the same external | |
3723 | representation for those objects as @code{write}. | |
3724 | ||
3725 | @code{write-with-shared-structure} terminates in finite time and | |
3726 | produces a finite representation when writing finite data. | |
3727 | ||
3728 | @code{write-with-shared-structure} returns an unspecified value. The | |
3729 | @var{port} argument may be omitted, in which case it defaults to the | |
3730 | value returned by @code{(current-output-port)}. The @var{optarg} | |
3731 | argument may also be omitted. If present, its effects on the output and | |
3732 | return value are unspecified but @code{write-with-shared-structure} must | |
3733 | still write a representation that can be read by | |
3734 | @code{read-with-shared-structure}. Some implementations may wish to use | |
3735 | @var{optarg} to specify formatting conventions, numeric radixes, or | |
3736 | return values. Guile's implementation ignores @var{optarg}. | |
3737 | ||
3738 | For example, the code | |
3739 | ||
3740 | @lisp | |
3741 | (begin (define a (cons 'val1 'val2)) | |
3742 | (set-cdr! a a) | |
3743 | (write-with-shared-structure a)) | |
3744 | @end lisp | |
3745 | ||
3746 | should produce the output @code{#1=(val1 . #1#)}. This shows a cons | |
3747 | cell whose @code{cdr} contains itself. | |
3748 | ||
3749 | @end deffn | |
3750 | ||
3751 | @deffn {Scheme procedure} read-with-shared-structure | |
3752 | @deffnx {Scheme procedure} read-with-shared-structure port | |
3753 | ||
3754 | @code{read-with-shared-structure} converts the external representations | |
3755 | of Scheme objects produced by @code{write-with-shared-structure} into | |
3756 | Scheme objects. That is, it is a parser for the nonterminal | |
3757 | @samp{<datum>} in the augmented external representation grammar defined | |
3758 | above. @code{read-with-shared-structure} returns the next object | |
3759 | parsable from the given input port, updating @var{port} to point to the | |
3760 | first character past the end of the external representation of the | |
3761 | object. | |
3762 | ||
3763 | If an end-of-file is encountered in the input before any characters are | |
3764 | found that can begin an object, then an end-of-file object is returned. | |
3765 | The port remains open, and further attempts to read it (by | |
3766 | @code{read-with-shared-structure} or @code{read} will also return an | |
3767 | end-of-file object. If an end of file is encountered after the | |
3768 | beginning of an object's external representation, but the external | |
3769 | representation is incomplete and therefore not parsable, an error is | |
3770 | signalled. | |
3771 | ||
3772 | The @var{port} argument may be omitted, in which case it defaults to the | |
3773 | value returned by @code{(current-input-port)}. It is an error to read | |
3774 | from a closed port. | |
3775 | ||
3776 | @end deffn | |
d4c38221 | 3777 | |
eeadfda1 KR |
3778 | @node SRFI-39 |
3779 | @subsection SRFI-39 - Parameters | |
3780 | @cindex SRFI-39 | |
eeadfda1 | 3781 | |
99db1bc2 AW |
3782 | This SRFI adds support for dynamically-scoped parameters. SRFI 39 is |
3783 | implemented in the Guile core; there's no module needed to get SRFI-39 | |
3784 | itself. Parameters are documented in @ref{Parameters}. | |
eeadfda1 | 3785 | |
99db1bc2 AW |
3786 | This module does export one extra function: @code{with-parameters*}. |
3787 | This is a Guile-specific addition to the SRFI, similar to the core | |
3788 | @code{with-fluids*} (@pxref{Fluids and Dynamic States}). | |
eeadfda1 KR |
3789 | |
3790 | @defun with-parameters* param-list value-list thunk | |
3791 | Establish a new dynamic scope, as per @code{parameterize} above, | |
3792 | taking parameters from @var{param-list} and corresponding values from | |
64de6db5 | 3793 | @var{value-list}. A call @code{(@var{thunk})} is made in the new |
eeadfda1 KR |
3794 | scope and the result from that @var{thunk} is the return from |
3795 | @code{with-parameters*}. | |
eeadfda1 KR |
3796 | @end defun |
3797 | ||
50d08cd8 CJY |
3798 | @node SRFI-41 |
3799 | @subsection SRFI-41 - Streams | |
3800 | @cindex SRFI-41 | |
3801 | ||
80b809f1 MW |
3802 | This subsection is based on the |
3803 | @uref{http://srfi.schemers.org/srfi-41/srfi-41.html, specification of | |
3804 | SRFI-41} by Philip L.@: Bewig. | |
3805 | ||
3806 | @c The copyright notice and license text of the SRFI-41 specification is | |
3807 | @c reproduced below: | |
3808 | ||
3809 | @c Copyright (C) Philip L. Bewig (2007). All Rights Reserved. | |
3810 | ||
3811 | @c Permission is hereby granted, free of charge, to any person obtaining a | |
3812 | @c copy of this software and associated documentation files (the | |
3813 | @c "Software"), to deal in the Software without restriction, including | |
3814 | @c without limitation the rights to use, copy, modify, merge, publish, | |
3815 | @c distribute, sublicense, and/or sell copies of the Software, and to | |
3816 | @c permit persons to whom the Software is furnished to do so, subject to | |
3817 | @c the following conditions: | |
3818 | ||
3819 | @c The above copyright notice and this permission notice shall be included | |
3820 | @c in all copies or substantial portions of the Software. | |
3821 | ||
3822 | @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS | |
3823 | @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF | |
3824 | @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | |
3825 | @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE | |
3826 | @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION | |
3827 | @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION | |
3828 | @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. | |
3829 | ||
3830 | @noindent | |
3831 | This SRFI implements streams, sometimes called lazy lists, a sequential | |
3832 | data structure containing elements computed only on demand. A stream is | |
3833 | either null or is a pair with a stream in its cdr. Since elements of a | |
3834 | stream are computed only when accessed, streams can be infinite. Once | |
3835 | computed, the value of a stream element is cached in case it is needed | |
3836 | again. SRFI-41 can be made available with: | |
3837 | ||
3838 | @example | |
3839 | (use-modules (srfi srfi-41)) | |
3840 | @end example | |
3841 | ||
3842 | @menu | |
3843 | * SRFI-41 Stream Fundamentals:: | |
3844 | * SRFI-41 Stream Primitives:: | |
3845 | * SRFI-41 Stream Library:: | |
3846 | @end menu | |
3847 | ||
3848 | @node SRFI-41 Stream Fundamentals | |
3849 | @subsubsection SRFI-41 Stream Fundamentals | |
3850 | ||
3851 | SRFI-41 Streams are based on two mutually-recursive abstract data types: | |
3852 | An object of the @code{stream} abstract data type is a promise that, | |
0ddf484d | 3853 | when forced, is either @code{stream-null} or is an object of type |
80b809f1 MW |
3854 | @code{stream-pair}. An object of the @code{stream-pair} abstract data |
3855 | type contains a @code{stream-car} and a @code{stream-cdr}, which must be | |
3856 | a @code{stream}. The essential feature of streams is the systematic | |
3857 | suspensions of the recursive promises between the two data types. | |
3858 | ||
3859 | The object stored in the @code{stream-car} of a @code{stream-pair} is a | |
3860 | promise that is forced the first time the @code{stream-car} is accessed; | |
3861 | its value is cached in case it is needed again. The object may have any | |
3862 | type, and different stream elements may have different types. If the | |
3863 | @code{stream-car} is never accessed, the object stored there is never | |
3864 | evaluated. Likewise, the @code{stream-cdr} is a promise to return a | |
3865 | stream, and is only forced on demand. | |
3866 | ||
3867 | @node SRFI-41 Stream Primitives | |
3868 | @subsubsection SRFI-41 Stream Primitives | |
3869 | ||
3870 | This library provides eight operators: constructors for | |
0ddf484d | 3871 | @code{stream-null} and @code{stream-pair}s, type predicates for streams |
80b809f1 MW |
3872 | and the two kinds of streams, accessors for both fields of a |
3873 | @code{stream-pair}, and a lambda that creates procedures that return | |
3874 | streams. | |
3875 | ||
7bfbd293 | 3876 | @defvr {Scheme Variable} stream-null |
80b809f1 | 3877 | A promise that, when forced, is a single object, distinguishable from |
0ddf484d | 3878 | all other objects, that represents the null stream. @code{stream-null} |
80b809f1 | 3879 | is immutable and unique. |
7bfbd293 | 3880 | @end defvr |
80b809f1 MW |
3881 | |
3882 | @deffn {Scheme Syntax} stream-cons object-expr stream-expr | |
3883 | Creates a newly-allocated stream containing a promise that, when forced, | |
3884 | is a @code{stream-pair} with @var{object-expr} in its @code{stream-car} | |
3885 | and @var{stream-expr} in its @code{stream-cdr}. Neither | |
3886 | @var{object-expr} nor @var{stream-expr} is evaluated when | |
3887 | @code{stream-cons} is called. | |
3888 | ||
3889 | Once created, a @code{stream-pair} is immutable; there is no | |
3890 | @code{stream-set-car!} or @code{stream-set-cdr!} that modifies an | |
3891 | existing stream-pair. There is no dotted-pair or improper stream as | |
3892 | with lists. | |
3893 | @end deffn | |
3894 | ||
3895 | @deffn {Scheme Procedure} stream? object | |
3896 | Returns true if @var{object} is a stream, otherwise returns false. If | |
3897 | @var{object} is a stream, its promise will not be forced. If | |
3898 | @code{(stream? obj)} returns true, then one of @code{(stream-null? obj)} | |
3899 | or @code{(stream-pair? obj)} will return true and the other will return | |
3900 | false. | |
3901 | @end deffn | |
3902 | ||
3903 | @deffn {Scheme Procedure} stream-null? object | |
3904 | Returns true if @var{object} is the distinguished null stream, otherwise | |
3905 | returns false. If @var{object} is a stream, its promise will be forced. | |
3906 | @end deffn | |
3907 | ||
3908 | @deffn {Scheme Procedure} stream-pair? object | |
3909 | Returns true if @var{object} is a @code{stream-pair} constructed by | |
3910 | @code{stream-cons}, otherwise returns false. If @var{object} is a | |
3911 | stream, its promise will be forced. | |
3912 | @end deffn | |
3913 | ||
3914 | @deffn {Scheme Procedure} stream-car stream | |
3915 | Returns the object stored in the @code{stream-car} of @var{stream}. An | |
3916 | error is signalled if the argument is not a @code{stream-pair}. This | |
3917 | causes the @var{object-expr} passed to @code{stream-cons} to be | |
3918 | evaluated if it had not yet been; the value is cached in case it is | |
3919 | needed again. | |
3920 | @end deffn | |
3921 | ||
3922 | @deffn {Scheme Procedure} stream-cdr stream | |
3923 | Returns the stream stored in the @code{stream-cdr} of @var{stream}. An | |
3924 | error is signalled if the argument is not a @code{stream-pair}. | |
3925 | @end deffn | |
3926 | ||
3927 | @deffn {Scheme Syntax} stream-lambda formals body @dots{} | |
3928 | Creates a procedure that returns a promise to evaluate the @var{body} of | |
3929 | the procedure. The last @var{body} expression to be evaluated must | |
3930 | yield a stream. As with normal @code{lambda}, @var{formals} may be a | |
3931 | single variable name, in which case all the formal arguments are | |
3932 | collected into a single list, or a list of variable names, which may be | |
3933 | null if there are no arguments, proper if there are an exact number of | |
3934 | arguments, or dotted if a fixed number of arguments is to be followed by | |
3935 | zero or more arguments collected into a list. @var{Body} must contain | |
3936 | at least one expression, and may contain internal definitions preceding | |
3937 | any expressions to be evaluated. | |
3938 | @end deffn | |
3939 | ||
3940 | @example | |
3941 | (define strm123 | |
3942 | (stream-cons 1 | |
3943 | (stream-cons 2 | |
3944 | (stream-cons 3 | |
3945 | stream-null)))) | |
3946 | ||
3947 | (stream-car strm123) @result{} 1 | |
3948 | (stream-car (stream-cdr strm123) @result{} 2 | |
3949 | ||
3950 | (stream-pair? | |
3951 | (stream-cdr | |
3952 | (stream-cons (/ 1 0) stream-null))) @result{} #f | |
3953 | ||
3954 | (stream? (list 1 2 3)) @result{} #f | |
3955 | ||
3956 | (define iter | |
3957 | (stream-lambda (f x) | |
3958 | (stream-cons x (iter f (f x))))) | |
3959 | ||
3960 | (define nats (iter (lambda (x) (+ x 1)) 0)) | |
3961 | ||
3962 | (stream-car (stream-cdr nats)) @result{} 1 | |
3963 | ||
3964 | (define stream-add | |
3965 | (stream-lambda (s1 s2) | |
3966 | (stream-cons | |
3967 | (+ (stream-car s1) (stream-car s2)) | |
3968 | (stream-add (stream-cdr s1) | |
3969 | (stream-cdr s2))))) | |
3970 | ||
3971 | (define evens (stream-add nats nats)) | |
3972 | ||
3973 | (stream-car evens) @result{} 0 | |
3974 | (stream-car (stream-cdr evens)) @result{} 2 | |
3975 | (stream-car (stream-cdr (stream-cdr evens))) @result{} 4 | |
3976 | @end example | |
3977 | ||
3978 | @node SRFI-41 Stream Library | |
3979 | @subsubsection SRFI-41 Stream Library | |
3980 | ||
3981 | @deffn {Scheme Syntax} define-stream (name args @dots{}) body @dots{} | |
3982 | Creates a procedure that returns a stream, and may appear anywhere a | |
3983 | normal @code{define} may appear, including as an internal definition. | |
3984 | It may contain internal definitions of its own. The defined procedure | |
3985 | takes arguments in the same way as @code{stream-lambda}. | |
3986 | @code{define-stream} is syntactic sugar on @code{stream-lambda}; see | |
3987 | also @code{stream-let}, which is also a sugaring of | |
3988 | @code{stream-lambda}. | |
3989 | ||
3990 | A simple version of @code{stream-map} that takes only a single input | |
3991 | stream calls itself recursively: | |
3992 | ||
3993 | @example | |
3994 | (define-stream (stream-map proc strm) | |
3995 | (if (stream-null? strm) | |
3996 | stream-null | |
3997 | (stream-cons | |
3998 | (proc (stream-car strm)) | |
3999 | (stream-map proc (stream-cdr strm)))))) | |
4000 | @end example | |
4001 | @end deffn | |
4002 | ||
4003 | @deffn {Scheme Procedure} list->stream list | |
4004 | Returns a newly-allocated stream containing the elements from | |
4005 | @var{list}. | |
4006 | @end deffn | |
4007 | ||
4008 | @deffn {Scheme Procedure} port->stream [port] | |
4009 | Returns a newly-allocated stream containing in its elements the | |
4010 | characters on the port. If @var{port} is not given it defaults to the | |
4011 | current input port. The returned stream has finite length and is | |
0ddf484d | 4012 | terminated by @code{stream-null}. |
80b809f1 MW |
4013 | |
4014 | It looks like one use of @code{port->stream} would be this: | |
4015 | ||
4016 | @example | |
4017 | (define s ;wrong! | |
4018 | (with-input-from-file filename | |
4019 | (lambda () (port->stream)))) | |
4020 | @end example | |
4021 | ||
4022 | But that fails, because @code{with-input-from-file} is eager, and closes | |
4023 | the input port prematurely, before the first character is read. To read | |
4024 | a file into a stream, say: | |
4025 | ||
4026 | @example | |
4027 | (define-stream (file->stream filename) | |
4028 | (let ((p (open-input-file filename))) | |
4029 | (stream-let loop ((c (read-char p))) | |
4030 | (if (eof-object? c) | |
4031 | (begin (close-input-port p) | |
4032 | stream-null) | |
4033 | (stream-cons c | |
4034 | (loop (read-char p))))))) | |
4035 | @end example | |
4036 | @end deffn | |
4037 | ||
4038 | @deffn {Scheme Syntax} stream object-expr @dots{} | |
4039 | Creates a newly-allocated stream containing in its elements the objects, | |
4040 | in order. The @var{object-expr}s are evaluated when they are accessed, | |
4041 | not when the stream is created. If no objects are given, as in | |
4042 | (stream), the null stream is returned. See also @code{list->stream}. | |
4043 | ||
4044 | @example | |
4045 | (define strm123 (stream 1 2 3)) | |
4046 | ||
4047 | ; (/ 1 0) not evaluated when stream is created | |
4048 | (define s (stream 1 (/ 1 0) -1)) | |
4049 | @end example | |
4050 | @end deffn | |
4051 | ||
4052 | @deffn {Scheme Procedure} stream->list [n] stream | |
4053 | Returns a newly-allocated list containing in its elements the first | |
4054 | @var{n} items in @var{stream}. If @var{stream} has less than @var{n} | |
4055 | items, all the items in the stream will be included in the returned | |
4056 | list. If @var{n} is not given it defaults to infinity, which means that | |
4057 | unless @var{stream} is finite @code{stream->list} will never return. | |
4058 | ||
4059 | @example | |
4060 | (stream->list 10 | |
4061 | (stream-map (lambda (x) (* x x)) | |
4062 | (stream-from 0))) | |
4063 | @result{} (0 1 4 9 16 25 36 49 64 81) | |
4064 | @end example | |
4065 | @end deffn | |
4066 | ||
4067 | @deffn {Scheme Procedure} stream-append stream @dots{} | |
4068 | Returns a newly-allocated stream containing in its elements those | |
4069 | elements contained in its input @var{stream}s, in order of input. If | |
4070 | any of the input streams is infinite, no elements of any of the | |
4071 | succeeding input streams will appear in the output stream. See also | |
4072 | @code{stream-concat}. | |
4073 | @end deffn | |
4074 | ||
4075 | @deffn {Scheme Procedure} stream-concat stream | |
4076 | Takes a @var{stream} consisting of one or more streams and returns a | |
4077 | newly-allocated stream containing all the elements of the input streams. | |
4078 | If any of the streams in the input @var{stream} is infinite, any | |
4079 | remaining streams in the input stream will never appear in the output | |
4080 | stream. See also @code{stream-append}. | |
4081 | @end deffn | |
4082 | ||
4083 | @deffn {Scheme Procedure} stream-constant object @dots{} | |
4084 | Returns a newly-allocated stream containing in its elements the | |
4085 | @var{object}s, repeating in succession forever. | |
4086 | ||
4087 | @example | |
4088 | (stream-constant 1) @result{} 1 1 1 @dots{} | |
4089 | (stream-constant #t #f) @result{} #t #f #t #f #t #f @dots{} | |
4090 | @end example | |
4091 | @end deffn | |
4092 | ||
4093 | @deffn {Scheme Procedure} stream-drop n stream | |
4094 | Returns the suffix of the input @var{stream} that starts at the next | |
4095 | element after the first @var{n} elements. The output stream shares | |
4096 | structure with the input @var{stream}; thus, promises forced in one | |
4097 | instance of the stream are also forced in the other instance of the | |
4098 | stream. If the input @var{stream} has less than @var{n} elements, | |
4099 | @code{stream-drop} returns the null stream. See also | |
4100 | @code{stream-take}. | |
4101 | @end deffn | |
4102 | ||
4103 | @deffn {Scheme Procedure} stream-drop-while pred stream | |
4104 | Returns the suffix of the input @var{stream} that starts at the first | |
4105 | element @var{x} for which @code{(pred x)} returns false. The output | |
4106 | stream shares structure with the input @var{stream}. See also | |
4107 | @code{stream-take-while}. | |
4108 | @end deffn | |
4109 | ||
4110 | @deffn {Scheme Procedure} stream-filter pred stream | |
4111 | Returns a newly-allocated stream that contains only those elements | |
4112 | @var{x} of the input @var{stream} which satisfy the predicate | |
4113 | @code{pred}. | |
4114 | ||
4115 | @example | |
4116 | (stream-filter odd? (stream-from 0)) | |
4117 | @result{} 1 3 5 7 9 @dots{} | |
4118 | @end example | |
4119 | @end deffn | |
4120 | ||
4121 | @deffn {Scheme Procedure} stream-fold proc base stream | |
4122 | Applies a binary procedure @var{proc} to @var{base} and the first | |
4123 | element of @var{stream} to compute a new @var{base}, then applies the | |
4124 | procedure to the new @var{base} and the next element of @var{stream} to | |
4125 | compute a succeeding @var{base}, and so on, accumulating a value that is | |
4126 | finally returned as the value of @code{stream-fold} when the end of the | |
4127 | stream is reached. @var{stream} must be finite, or @code{stream-fold} | |
4128 | will enter an infinite loop. See also @code{stream-scan}, which is | |
4129 | similar to @code{stream-fold}, but useful for infinite streams. For | |
4130 | readers familiar with other functional languages, this is a left-fold; | |
4131 | there is no corresponding right-fold, since right-fold relies on finite | |
4132 | streams that are fully-evaluated, in which case they may as well be | |
4133 | converted to a list. | |
4134 | @end deffn | |
4135 | ||
4136 | @deffn {Scheme Procedure} stream-for-each proc stream @dots{} | |
4137 | Applies @var{proc} element-wise to corresponding elements of the input | |
4138 | @var{stream}s for side-effects; it returns nothing. | |
4139 | @code{stream-for-each} stops as soon as any of its input streams is | |
4140 | exhausted. | |
4141 | @end deffn | |
4142 | ||
4143 | @deffn {Scheme Procedure} stream-from first [step] | |
4144 | Creates a newly-allocated stream that contains @var{first} as its first | |
4145 | element and increments each succeeding element by @var{step}. If | |
4146 | @var{step} is not given it defaults to 1. @var{first} and @var{step} | |
4147 | may be of any numeric type. @code{stream-from} is frequently useful as | |
4148 | a generator in @code{stream-of} expressions. See also | |
4149 | @code{stream-range} for a similar procedure that creates finite streams. | |
4150 | @end deffn | |
4151 | ||
4152 | @deffn {Scheme Procedure} stream-iterate proc base | |
4153 | Creates a newly-allocated stream containing @var{base} in its first | |
4154 | element and applies @var{proc} to each element in turn to determine the | |
4155 | succeeding element. See also @code{stream-unfold} and | |
4156 | @code{stream-unfolds}. | |
4157 | @end deffn | |
4158 | ||
4159 | @deffn {Scheme Procedure} stream-length stream | |
4160 | Returns the number of elements in the @var{stream}; it does not evaluate | |
4161 | its elements. @code{stream-length} may only be used on finite streams; | |
4162 | it enters an infinite loop with infinite streams. | |
4163 | @end deffn | |
4164 | ||
4165 | @deffn {Scheme Syntax} stream-let tag ((var expr) @dots{}) body @dots{} | |
4166 | Creates a local scope that binds each variable to the value of its | |
4167 | corresponding expression. It additionally binds @var{tag} to a | |
4168 | procedure which takes the bound variables as arguments and @var{body} as | |
4169 | its defining expressions, binding the @var{tag} with | |
4170 | @code{stream-lambda}. @var{tag} is in scope within body, and may be | |
4171 | called recursively. When the expanded expression defined by the | |
4172 | @code{stream-let} is evaluated, @code{stream-let} evaluates the | |
4173 | expressions in its @var{body} in an environment containing the | |
4174 | newly-bound variables, returning the value of the last expression | |
4175 | evaluated, which must yield a stream. | |
4176 | ||
4177 | @code{stream-let} provides syntactic sugar on @code{stream-lambda}, in | |
4178 | the same manner as normal @code{let} provides syntactic sugar on normal | |
4179 | @code{lambda}. However, unlike normal @code{let}, the @var{tag} is | |
4180 | required, not optional, because unnamed @code{stream-let} is | |
4181 | meaningless. | |
4182 | ||
4183 | For example, @code{stream-member} returns the first @code{stream-pair} | |
4184 | of the input @var{strm} with a @code{stream-car} @var{x} that satisfies | |
4185 | @code{(eql? obj x)}, or the null stream if @var{x} is not present in | |
4186 | @var{strm}. | |
4187 | ||
4188 | @example | |
4189 | (define-stream (stream-member eql? obj strm) | |
4190 | (stream-let loop ((strm strm)) | |
4191 | (cond ((stream-null? strm) strm) | |
4192 | ((eql? obj (stream-car strm)) strm) | |
4193 | (else (loop (stream-cdr strm)))))) | |
4194 | @end example | |
4195 | @end deffn | |
4196 | ||
4197 | @deffn {Scheme Procedure} stream-map proc stream @dots{} | |
4198 | Applies @var{proc} element-wise to corresponding elements of the input | |
4199 | @var{stream}s, returning a newly-allocated stream containing elements | |
4200 | that are the results of those procedure applications. The output stream | |
4201 | has as many elements as the minimum-length input stream, and may be | |
4202 | infinite. | |
4203 | @end deffn | |
4204 | ||
4205 | @deffn {Scheme Syntax} stream-match stream clause @dots{} | |
4206 | Provides pattern-matching for streams. The input @var{stream} is an | |
4207 | expression that evaluates to a stream. Clauses are of the form | |
4208 | @code{(pattern [fender] expression)}, consisting of a @var{pattern} that | |
4209 | matches a stream of a particular shape, an optional @var{fender} that | |
4210 | must succeed if the pattern is to match, and an @var{expression} that is | |
4211 | evaluated if the pattern matches. There are four types of patterns: | |
4212 | ||
4213 | @itemize @bullet | |
4214 | @item | |
4215 | () matches the null stream. | |
4216 | ||
4217 | @item | |
4218 | (@var{pat0} @var{pat1} @dots{}) matches a finite stream with length | |
4219 | exactly equal to the number of pattern elements. | |
4220 | ||
4221 | @item | |
4222 | (@var{pat0} @var{pat1} @dots{} @code{.} @var{pat-rest}) matches an | |
4223 | infinite stream, or a finite stream with length at least as great as the | |
4224 | number of pattern elements before the literal dot. | |
4225 | ||
4226 | @item | |
4227 | @var{pat} matches an entire stream. Should always appear last in the | |
4228 | list of clauses; it's not an error to appear elsewhere, but subsequent | |
4229 | clauses could never match. | |
4230 | @end itemize | |
4231 | ||
4232 | Each pattern element may be either: | |
4233 | ||
4234 | @itemize @bullet | |
4235 | @item | |
4236 | An identifier, which matches any stream element. Additionally, the | |
4237 | value of the stream element is bound to the variable named by the | |
4238 | identifier, which is in scope in the @var{fender} and @var{expression} | |
4239 | of the corresponding @var{clause}. Each identifier in a single pattern | |
4240 | must be unique. | |
4241 | ||
4242 | @item | |
4243 | A literal underscore (@code{_}), which matches any stream element but | |
4244 | creates no bindings. | |
4245 | @end itemize | |
4246 | ||
4247 | The @var{pattern}s are tested in order, left-to-right, until a matching | |
4248 | pattern is found; if @var{fender} is present, it must evaluate to a true | |
4249 | value for the match to be successful. Pattern variables are bound in | |
4250 | the corresponding @var{fender} and @var{expression}. Once the matching | |
4251 | @var{pattern} is found, the corresponding @var{expression} is evaluated | |
4252 | and returned as the result of the match. An error is signaled if no | |
4253 | pattern matches the input @var{stream}. | |
4254 | ||
4255 | @code{stream-match} is often used to distinguish null streams from | |
4256 | non-null streams, binding @var{head} and @var{tail}: | |
4257 | ||
4258 | @example | |
4259 | (define (len strm) | |
4260 | (stream-match strm | |
4261 | (() 0) | |
4262 | ((head . tail) (+ 1 (len tail))))) | |
4263 | @end example | |
4264 | ||
4265 | Fenders can test the common case where two stream elements must be | |
4266 | identical; the @code{else} pattern is an identifier bound to the entire | |
4267 | stream, not a keyword as in @code{cond}. | |
4268 | ||
4269 | @example | |
4270 | (stream-match strm | |
4271 | ((x y . _) (equal? x y) 'ok) | |
4272 | (else 'error)) | |
4273 | @end example | |
4274 | ||
4275 | A more complex example uses two nested matchers to match two different | |
4276 | stream arguments; @code{(stream-merge lt? . strms)} stably merges two or | |
4277 | more streams ordered by the @code{lt?} predicate: | |
4278 | ||
4279 | @example | |
4280 | (define-stream (stream-merge lt? . strms) | |
4281 | (define-stream (merge xx yy) | |
4282 | (stream-match xx (() yy) ((x . xs) | |
4283 | (stream-match yy (() xx) ((y . ys) | |
4284 | (if (lt? y x) | |
4285 | (stream-cons y (merge xx ys)) | |
4286 | (stream-cons x (merge xs yy)))))))) | |
4287 | (stream-let loop ((strms strms)) | |
4288 | (cond ((null? strms) stream-null) | |
4289 | ((null? (cdr strms)) (car strms)) | |
4290 | (else (merge (car strms) | |
4291 | (apply stream-merge lt? | |
4292 | (cdr strms))))))) | |
4293 | @end example | |
4294 | @end deffn | |
4295 | ||
4296 | @deffn {Scheme Syntax} stream-of expr clause @dots{} | |
4297 | Provides the syntax of stream comprehensions, which generate streams by | |
4298 | means of looping expressions. The result is a stream of objects of the | |
4299 | type returned by @var{expr}. There are four types of clauses: | |
4300 | ||
4301 | @itemize @bullet | |
4302 | @item | |
4303 | (@var{var} @code{in} @var{stream-expr}) loops over the elements of | |
4304 | @var{stream-expr}, in order from the start of the stream, binding each | |
4305 | element of the stream in turn to @var{var}. @code{stream-from} and | |
4306 | @code{stream-range} are frequently useful as generators for | |
4307 | @var{stream-expr}. | |
4308 | ||
4309 | @item | |
4310 | (@var{var} @code{is} @var{expr}) binds @var{var} to the value obtained | |
4311 | by evaluating @var{expr}. | |
4312 | ||
4313 | @item | |
4314 | (@var{pred} @var{expr}) includes in the output stream only those | |
4315 | elements @var{x} which satisfy the predicate @var{pred}. | |
4316 | @end itemize | |
4317 | ||
4318 | The scope of variables bound in the stream comprehension is the clauses | |
4319 | to the right of the binding clause (but not the binding clause itself) | |
4320 | plus the result expression. | |
4321 | ||
4322 | When two or more generators are present, the loops are processed as if | |
4323 | they are nested from left to right; that is, the rightmost generator | |
4324 | varies fastest. A consequence of this is that only the first generator | |
4325 | may be infinite and all subsequent generators must be finite. If no | |
4326 | generators are present, the result of a stream comprehension is a stream | |
4327 | containing the result expression; thus, @samp{(stream-of 1)} produces a | |
4328 | finite stream containing only the element 1. | |
4329 | ||
4330 | @example | |
4331 | (stream-of (* x x) | |
4332 | (x in (stream-range 0 10)) | |
4333 | (even? x)) | |
4334 | @result{} 0 4 16 36 64 | |
4335 | ||
4336 | (stream-of (list a b) | |
4337 | (a in (stream-range 1 4)) | |
4338 | (b in (stream-range 1 3))) | |
4339 | @result{} (1 1) (1 2) (2 1) (2 2) (3 1) (3 2) | |
4340 | ||
4341 | (stream-of (list i j) | |
4342 | (i in (stream-range 1 5)) | |
4343 | (j in (stream-range (+ i 1) 5))) | |
4344 | @result{} (1 2) (1 3) (1 4) (2 3) (2 4) (3 4) | |
4345 | @end example | |
4346 | @end deffn | |
4347 | ||
4348 | @deffn {Scheme Procedure} stream-range first past [step] | |
4349 | Creates a newly-allocated stream that contains @var{first} as its first | |
4350 | element and increments each succeeding element by @var{step}. The | |
4351 | stream is finite and ends before @var{past}, which is not an element of | |
4352 | the stream. If @var{step} is not given it defaults to 1 if @var{first} | |
4353 | is less than past and -1 otherwise. @var{first}, @var{past} and | |
4354 | @var{step} may be of any real numeric type. @code{stream-range} is | |
4355 | frequently useful as a generator in @code{stream-of} expressions. See | |
4356 | also @code{stream-from} for a similar procedure that creates infinite | |
4357 | streams. | |
4358 | ||
4359 | @example | |
4360 | (stream-range 0 10) @result{} 0 1 2 3 4 5 6 7 8 9 | |
4361 | (stream-range 0 10 2) @result{} 0 2 4 6 8 | |
4362 | @end example | |
4363 | ||
4364 | Successive elements of the stream are calculated by adding @var{step} to | |
4365 | @var{first}, so if any of @var{first}, @var{past} or @var{step} are | |
4366 | inexact, the length of the output stream may differ from | |
4367 | @code{(ceiling (- (/ (- past first) step) 1)}. | |
4368 | @end deffn | |
4369 | ||
4370 | @deffn {Scheme Procedure} stream-ref stream n | |
4371 | Returns the @var{n}th element of stream, counting from zero. An error | |
4372 | is signaled if @var{n} is greater than or equal to the length of stream. | |
4373 | ||
4374 | @example | |
4375 | (define (fact n) | |
4376 | (stream-ref | |
4377 | (stream-scan * 1 (stream-from 1)) | |
4378 | n)) | |
4379 | @end example | |
4380 | @end deffn | |
4381 | ||
4382 | @deffn {Scheme Procedure} stream-reverse stream | |
4383 | Returns a newly-allocated stream containing the elements of the input | |
4384 | @var{stream} but in reverse order. @code{stream-reverse} may only be | |
4385 | used with finite streams; it enters an infinite loop with infinite | |
4386 | streams. @code{stream-reverse} does not force evaluation of the | |
4387 | elements of the stream. | |
4388 | @end deffn | |
4389 | ||
4390 | @deffn {Scheme Procedure} stream-scan proc base stream | |
4391 | Accumulates the partial folds of an input @var{stream} into a | |
4392 | newly-allocated output stream. The output stream is the @var{base} | |
4393 | followed by @code{(stream-fold proc base (stream-take i stream))} for | |
4394 | each of the first @var{i} elements of @var{stream}. | |
4395 | ||
4396 | @example | |
4397 | (stream-scan + 0 (stream-from 1)) | |
4398 | @result{} (stream 0 1 3 6 10 15 @dots{}) | |
4399 | ||
4400 | (stream-scan * 1 (stream-from 1)) | |
4401 | @result{} (stream 1 1 2 6 24 120 @dots{}) | |
4402 | @end example | |
4403 | @end deffn | |
4404 | ||
4405 | @deffn {Scheme Procedure} stream-take n stream | |
4406 | Returns a newly-allocated stream containing the first @var{n} elements | |
4407 | of the input @var{stream}. If the input @var{stream} has less than | |
4408 | @var{n} elements, so does the output stream. See also | |
4409 | @code{stream-drop}. | |
4410 | @end deffn | |
4411 | ||
4412 | @deffn {Scheme Procedure} stream-take-while pred stream | |
4413 | Takes a predicate and a @code{stream} and returns a newly-allocated | |
4414 | stream containing those elements @code{x} that form the maximal prefix | |
4415 | of the input stream which satisfy @var{pred}. See also | |
4416 | @code{stream-drop-while}. | |
4417 | @end deffn | |
4418 | ||
4419 | @deffn {Scheme Procedure} stream-unfold map pred gen base | |
4420 | The fundamental recursive stream constructor. It constructs a stream by | |
4421 | repeatedly applying @var{gen} to successive values of @var{base}, in the | |
4422 | manner of @code{stream-iterate}, then applying @var{map} to each of the | |
4423 | values so generated, appending each of the mapped values to the output | |
4424 | stream as long as @code{(pred? base)} returns a true value. See also | |
4425 | @code{stream-iterate} and @code{stream-unfolds}. | |
4426 | ||
4427 | The expression below creates the finite stream @samp{0 1 4 9 16 25 36 49 | |
4428 | 64 81}. Initially the @var{base} is 0, which is less than 10, so | |
4429 | @var{map} squares the @var{base} and the mapped value becomes the first | |
4430 | element of the output stream. Then @var{gen} increments the @var{base} | |
4431 | by 1, so it becomes 1; this is less than 10, so @var{map} squares the | |
4432 | new @var{base} and 1 becomes the second element of the output stream. | |
4433 | And so on, until the base becomes 10, when @var{pred} stops the | |
4434 | recursion and stream-null ends the output stream. | |
4435 | ||
4436 | @example | |
4437 | (stream-unfold | |
4438 | (lambda (x) (expt x 2)) ; map | |
4439 | (lambda (x) (< x 10)) ; pred? | |
4440 | (lambda (x) (+ x 1)) ; gen | |
4441 | 0) ; base | |
4442 | @end example | |
4443 | @end deffn | |
4444 | ||
4445 | @deffn {Scheme Procedure} stream-unfolds proc seed | |
4446 | Returns @var{n} newly-allocated streams containing those elements | |
4447 | produced by successive calls to the generator @var{proc}, which takes | |
4448 | the current @var{seed} as its argument and returns @var{n}+1 values | |
4449 | ||
4450 | (@var{proc} @var{seed}) @result{} @var{seed} @var{result_0} @dots{} @var{result_n-1} | |
4451 | ||
4452 | where the returned @var{seed} is the input @var{seed} to the next call | |
4453 | to the generator and @var{result_i} indicates how to produce the next | |
4454 | element of the @var{i}th result stream: | |
4455 | ||
4456 | @itemize @bullet | |
4457 | @item | |
4458 | (@var{value}): @var{value} is the next car of the result stream. | |
4459 | ||
4460 | @item | |
4461 | @code{#f}: no value produced by this iteration of the generator | |
4462 | @var{proc} for the result stream. | |
4463 | ||
4464 | @item | |
4465 | (): the end of the result stream. | |
4466 | @end itemize | |
4467 | ||
4468 | It may require multiple calls of @var{proc} to produce the next element | |
4469 | of any particular result stream. See also @code{stream-iterate} and | |
4470 | @code{stream-unfold}. | |
4471 | ||
4472 | @example | |
4473 | (define (stream-partition pred? strm) | |
4474 | (stream-unfolds | |
4475 | (lambda (s) | |
4476 | (if (stream-null? s) | |
4477 | (values s '() '()) | |
4478 | (let ((a (stream-car s)) | |
4479 | (d (stream-cdr s))) | |
4480 | (if (pred? a) | |
4481 | (values d (list a) #f) | |
4482 | (values d #f (list a)))))) | |
4483 | strm)) | |
4484 | ||
4485 | (call-with-values | |
4486 | (lambda () | |
4487 | (stream-partition odd? | |
4488 | (stream-range 1 6))) | |
4489 | (lambda (odds evens) | |
4490 | (list (stream->list odds) | |
4491 | (stream->list evens)))) | |
4492 | @result{} ((1 3 5) (2 4)) | |
4493 | @end example | |
4494 | @end deffn | |
4495 | ||
4496 | @deffn {Scheme Procedure} stream-zip stream @dots{} | |
4497 | Returns a newly-allocated stream in which each element is a list (not a | |
4498 | stream) of the corresponding elements of the input @var{stream}s. The | |
4499 | output stream is as long as the shortest input @var{stream}, if any of | |
4500 | the input @var{stream}s is finite, or is infinite if all the input | |
4501 | @var{stream}s are infinite. | |
4502 | @end deffn | |
50d08cd8 | 4503 | |
fdc8fd46 AR |
4504 | @node SRFI-42 |
4505 | @subsection SRFI-42 - Eager Comprehensions | |
4506 | @cindex SRFI-42 | |
4507 | ||
4508 | See @uref{http://srfi.schemers.org/srfi-42/srfi-42.html, the | |
4509 | specification of SRFI-42}. | |
eeadfda1 | 4510 | |
f16a2007 AR |
4511 | @node SRFI-45 |
4512 | @subsection SRFI-45 - Primitives for Expressing Iterative Lazy Algorithms | |
4513 | @cindex SRFI-45 | |
4514 | ||
4515 | This subsection is based on @uref{http://srfi.schemers.org/srfi-45/srfi-45.html, the | |
4516 | specification of SRFI-45} written by Andr@'e van Tonder. | |
4517 | ||
4518 | @c Copyright (C) André van Tonder (2003). All Rights Reserved. | |
4519 | ||
4520 | @c Permission is hereby granted, free of charge, to any person obtaining a | |
4521 | @c copy of this software and associated documentation files (the | |
4522 | @c "Software"), to deal in the Software without restriction, including | |
4523 | @c without limitation the rights to use, copy, modify, merge, publish, | |
4524 | @c distribute, sublicense, and/or sell copies of the Software, and to | |
4525 | @c permit persons to whom the Software is furnished to do so, subject to | |
4526 | @c the following conditions: | |
4527 | ||
4528 | @c The above copyright notice and this permission notice shall be included | |
4529 | @c in all copies or substantial portions of the Software. | |
4530 | ||
4531 | @c THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS | |
4532 | @c OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF | |
4533 | @c MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | |
4534 | @c NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE | |
4535 | @c LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION | |
4536 | @c OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION | |
4537 | @c WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. | |
4538 | ||
4539 | Lazy evaluation is traditionally simulated in Scheme using @code{delay} | |
4540 | and @code{force}. However, these primitives are not powerful enough to | |
4541 | express a large class of lazy algorithms that are iterative. Indeed, it | |
4542 | is folklore in the Scheme community that typical iterative lazy | |
4543 | algorithms written using delay and force will often require unbounded | |
4544 | memory. | |
4545 | ||
4546 | This SRFI provides set of three operations: @{@code{lazy}, @code{delay}, | |
4547 | @code{force}@}, which allow the programmer to succinctly express lazy | |
4548 | algorithms while retaining bounded space behavior in cases that are | |
4549 | properly tail-recursive. A general recipe for using these primitives is | |
4550 | provided. An additional procedure @code{eager} is provided for the | |
4551 | construction of eager promises in cases where efficiency is a concern. | |
4552 | ||
4553 | Although this SRFI redefines @code{delay} and @code{force}, the | |
4554 | extension is conservative in the sense that the semantics of the subset | |
4555 | @{@code{delay}, @code{force}@} in isolation (i.e., as long as the | |
4556 | program does not use @code{lazy}) agrees with that in R5RS. In other | |
4557 | words, no program that uses the R5RS definitions of delay and force will | |
4558 | break if those definition are replaced by the SRFI-45 definitions of | |
4559 | delay and force. | |
4560 | ||
d291d799 MW |
4561 | Guile also adds @code{promise?} to the list of exports, which is not |
4562 | part of the official SRFI-45. | |
4563 | ||
4564 | @deffn {Scheme Procedure} promise? obj | |
4565 | Return true if @var{obj} is an SRFI-45 promise, otherwise return false. | |
4566 | @end deffn | |
4567 | ||
f16a2007 | 4568 | @deffn {Scheme Syntax} delay expression |
65ad02b9 MW |
4569 | Takes an expression of arbitrary type @var{a} and returns a promise of |
4570 | type @code{(Promise @var{a})} which at some point in the future may be | |
4571 | asked (by the @code{force} procedure) to evaluate the expression and | |
4572 | deliver the resulting value. | |
f16a2007 AR |
4573 | @end deffn |
4574 | ||
4575 | @deffn {Scheme Syntax} lazy expression | |
65ad02b9 MW |
4576 | Takes an expression of type @code{(Promise @var{a})} and returns a |
4577 | promise of type @code{(Promise @var{a})} which at some point in the | |
4578 | future may be asked (by the @code{force} procedure) to evaluate the | |
4579 | expression and deliver the resulting promise. | |
f16a2007 AR |
4580 | @end deffn |
4581 | ||
65ad02b9 MW |
4582 | @deffn {Scheme Procedure} force expression |
4583 | Takes an argument of type @code{(Promise @var{a})} and returns a value | |
4584 | of type @var{a} as follows: If a value of type @var{a} has been computed | |
4585 | for the promise, this value is returned. Otherwise, the promise is | |
4586 | first evaluated, then overwritten by the obtained promise or value, and | |
4587 | then force is again applied (iteratively) to the promise. | |
f16a2007 AR |
4588 | @end deffn |
4589 | ||
65ad02b9 MW |
4590 | @deffn {Scheme Procedure} eager expression |
4591 | Takes an argument of type @var{a} and returns a value of type | |
4592 | @code{(Promise @var{a})}. As opposed to @code{delay}, the argument is | |
4593 | evaluated eagerly. Semantically, writing @code{(eager expression)} is | |
4594 | equivalent to writing | |
f16a2007 AR |
4595 | |
4596 | @lisp | |
4597 | (let ((value expression)) (delay value)). | |
4598 | @end lisp | |
4599 | ||
4600 | However, the former is more efficient since it does not require | |
65ad02b9 MW |
4601 | unnecessary creation and evaluation of thunks. We also have the |
4602 | equivalence | |
f16a2007 AR |
4603 | |
4604 | @lisp | |
4605 | (delay expression) = (lazy (eager expression)) | |
4606 | @end lisp | |
4607 | @end deffn | |
4608 | ||
4609 | The following reduction rules may be helpful for reasoning about these | |
4610 | primitives. However, they do not express the memoization and memory | |
4611 | usage semantics specified above: | |
4612 | ||
4613 | @lisp | |
4614 | (force (delay expression)) -> expression | |
4615 | (force (lazy expression)) -> (force expression) | |
65ad02b9 | 4616 | (force (eager value)) -> value |
f16a2007 AR |
4617 | @end lisp |
4618 | ||
4619 | @subsubheading Correct usage | |
4620 | ||
4621 | We now provide a general recipe for using the primitives @{@code{lazy}, | |
4622 | @code{delay}, @code{force}@} to express lazy algorithms in Scheme. The | |
4623 | transformation is best described by way of an example: Consider the | |
4624 | stream-filter algorithm, expressed in a hypothetical lazy language as | |
4625 | ||
4626 | @lisp | |
4627 | (define (stream-filter p? s) | |
4628 | (if (null? s) '() | |
4629 | (let ((h (car s)) | |
4630 | (t (cdr s))) | |
4631 | (if (p? h) | |
4632 | (cons h (stream-filter p? t)) | |
4633 | (stream-filter p? t))))) | |
4634 | @end lisp | |
4635 | ||
ecb87335 | 4636 | This algorithm can be expressed as follows in Scheme: |
f16a2007 AR |
4637 | |
4638 | @lisp | |
4639 | (define (stream-filter p? s) | |
4640 | (lazy | |
4641 | (if (null? (force s)) (delay '()) | |
4642 | (let ((h (car (force s))) | |
4643 | (t (cdr (force s)))) | |
4644 | (if (p? h) | |
4645 | (delay (cons h (stream-filter p? t))) | |
4646 | (stream-filter p? t)))))) | |
4647 | @end lisp | |
4648 | ||
4649 | In other words, we | |
4650 | ||
4651 | @itemize @bullet | |
4652 | @item | |
4653 | wrap all constructors (e.g., @code{'()}, @code{cons}) with @code{delay}, | |
4654 | @item | |
4655 | apply @code{force} to arguments of deconstructors (e.g., @code{car}, | |
4656 | @code{cdr} and @code{null?}), | |
4657 | @item | |
4658 | wrap procedure bodies with @code{(lazy ...)}. | |
4659 | @end itemize | |
4660 | ||
4ea9becb KR |
4661 | @node SRFI-55 |
4662 | @subsection SRFI-55 - Requiring Features | |
4663 | @cindex SRFI-55 | |
4664 | ||
4665 | SRFI-55 provides @code{require-extension} which is a portable | |
4666 | mechanism to load selected SRFI modules. This is implemented in the | |
4667 | Guile core, there's no module needed to get SRFI-55 itself. | |
4668 | ||
df0a1002 BT |
4669 | @deffn {library syntax} require-extension clause1 clause2 @dots{} |
4670 | Require the features of @var{clause1} @var{clause2} @dots{} , throwing | |
4671 | an error if any are unavailable. | |
4ea9becb KR |
4672 | |
4673 | A @var{clause} is of the form @code{(@var{identifier} arg...)}. The | |
4674 | only @var{identifier} currently supported is @code{srfi} and the | |
4675 | arguments are SRFI numbers. For example to get SRFI-1 and SRFI-6, | |
4676 | ||
4677 | @example | |
4678 | (require-extension (srfi 1 6)) | |
4679 | @end example | |
4680 | ||
4681 | @code{require-extension} can only be used at the top-level. | |
4682 | ||
4683 | A Guile-specific program can simply @code{use-modules} to load SRFIs | |
4684 | not already in the core, @code{require-extension} is for programs | |
4685 | designed to be portable to other Scheme implementations. | |
4686 | @end deffn | |
4687 | ||
4688 | ||
8503beb8 KR |
4689 | @node SRFI-60 |
4690 | @subsection SRFI-60 - Integers as Bits | |
4691 | @cindex SRFI-60 | |
4692 | @cindex integers as bits | |
4693 | @cindex bitwise logical | |
4694 | ||
4695 | This SRFI provides various functions for treating integers as bits and | |
4696 | for bitwise manipulations. These functions can be obtained with, | |
4697 | ||
4698 | @example | |
4699 | (use-modules (srfi srfi-60)) | |
4700 | @end example | |
4701 | ||
4702 | Integers are treated as infinite precision twos-complement, the same | |
4703 | as in the core logical functions (@pxref{Bitwise Operations}). And | |
4704 | likewise bit indexes start from 0 for the least significant bit. The | |
4705 | following functions in this SRFI are already in the Guile core, | |
4706 | ||
4707 | @quotation | |
4708 | @code{logand}, | |
4709 | @code{logior}, | |
4710 | @code{logxor}, | |
4711 | @code{lognot}, | |
4712 | @code{logtest}, | |
4713 | @code{logcount}, | |
4714 | @code{integer-length}, | |
4715 | @code{logbit?}, | |
4716 | @code{ash} | |
4717 | @end quotation | |
4718 | ||
4719 | @sp 1 | |
4720 | @defun bitwise-and n1 ... | |
4721 | @defunx bitwise-ior n1 ... | |
4722 | @defunx bitwise-xor n1 ... | |
4723 | @defunx bitwise-not n | |
4724 | @defunx any-bits-set? j k | |
4725 | @defunx bit-set? index n | |
4726 | @defunx arithmetic-shift n count | |
4727 | @defunx bit-field n start end | |
4728 | @defunx bit-count n | |
4729 | Aliases for @code{logand}, @code{logior}, @code{logxor}, | |
4730 | @code{lognot}, @code{logtest}, @code{logbit?}, @code{ash}, | |
4731 | @code{bit-extract} and @code{logcount} respectively. | |
4732 | ||
4733 | Note that the name @code{bit-count} conflicts with @code{bit-count} in | |
4734 | the core (@pxref{Bit Vectors}). | |
4735 | @end defun | |
4736 | ||
4737 | @defun bitwise-if mask n1 n0 | |
4738 | @defunx bitwise-merge mask n1 n0 | |
4739 | Return an integer with bits selected from @var{n1} and @var{n0} | |
4740 | according to @var{mask}. Those bits where @var{mask} has 1s are taken | |
4741 | from @var{n1}, and those where @var{mask} has 0s are taken from | |
4742 | @var{n0}. | |
4743 | ||
4744 | @example | |
4745 | (bitwise-if 3 #b0101 #b1010) @result{} 9 | |
4746 | @end example | |
4747 | @end defun | |
4748 | ||
4749 | @defun log2-binary-factors n | |
4750 | @defunx first-set-bit n | |
4751 | Return a count of how many factors of 2 are present in @var{n}. This | |
4752 | is also the bit index of the lowest 1 bit in @var{n}. If @var{n} is | |
4753 | 0, the return is @math{-1}. | |
4754 | ||
4755 | @example | |
4756 | (log2-binary-factors 6) @result{} 1 | |
4757 | (log2-binary-factors -8) @result{} 3 | |
4758 | @end example | |
4759 | @end defun | |
4760 | ||
4761 | @defun copy-bit index n newbit | |
4762 | Return @var{n} with the bit at @var{index} set according to | |
4763 | @var{newbit}. @var{newbit} should be @code{#t} to set the bit to 1, | |
4764 | or @code{#f} to set it to 0. Bits other than at @var{index} are | |
4765 | unchanged in the return. | |
4766 | ||
4767 | @example | |
4768 | (copy-bit 1 #b0101 #t) @result{} 7 | |
4769 | @end example | |
4770 | @end defun | |
4771 | ||
4772 | @defun copy-bit-field n newbits start end | |
4773 | Return @var{n} with the bits from @var{start} (inclusive) to @var{end} | |
4774 | (exclusive) changed to the value @var{newbits}. | |
4775 | ||
4776 | The least significant bit in @var{newbits} goes to @var{start}, the | |
4777 | next to @math{@var{start}+1}, etc. Anything in @var{newbits} past the | |
4778 | @var{end} given is ignored. | |
4779 | ||
4780 | @example | |
4781 | (copy-bit-field #b10000 #b11 1 3) @result{} #b10110 | |
4782 | @end example | |
4783 | @end defun | |
4784 | ||
4785 | @defun rotate-bit-field n count start end | |
4786 | Return @var{n} with the bit field from @var{start} (inclusive) to | |
4787 | @var{end} (exclusive) rotated upwards by @var{count} bits. | |
4788 | ||
4789 | @var{count} can be positive or negative, and it can be more than the | |
4790 | field width (it'll be reduced modulo the width). | |
4791 | ||
4792 | @example | |
4793 | (rotate-bit-field #b0110 2 1 4) @result{} #b1010 | |
4794 | @end example | |
4795 | @end defun | |
4796 | ||
4797 | @defun reverse-bit-field n start end | |
4798 | Return @var{n} with the bits from @var{start} (inclusive) to @var{end} | |
4799 | (exclusive) reversed. | |
4800 | ||
4801 | @example | |
4802 | (reverse-bit-field #b101001 2 4) @result{} #b100101 | |
4803 | @end example | |
4804 | @end defun | |
4805 | ||
4806 | @defun integer->list n [len] | |
4807 | Return bits from @var{n} in the form of a list of @code{#t} for 1 and | |
4808 | @code{#f} for 0. The least significant @var{len} bits are returned, | |
4809 | and the first list element is the most significant of those bits. If | |
4810 | @var{len} is not given, the default is @code{(integer-length @var{n})} | |
4811 | (@pxref{Bitwise Operations}). | |
4812 | ||
4813 | @example | |
4814 | (integer->list 6) @result{} (#t #t #f) | |
4815 | (integer->list 1 4) @result{} (#f #f #f #t) | |
4816 | @end example | |
4817 | @end defun | |
4818 | ||
4819 | @defun list->integer lst | |
4820 | @defunx booleans->integer bool@dots{} | |
4821 | Return an integer formed bitwise from the given @var{lst} list of | |
4822 | booleans, or for @code{booleans->integer} from the @var{bool} | |
4823 | arguments. | |
4824 | ||
4825 | Each boolean is @code{#t} for a 1 and @code{#f} for a 0. The first | |
4826 | element becomes the most significant bit in the return. | |
4827 | ||
4828 | @example | |
4829 | (list->integer '(#t #f #t #f)) @result{} 10 | |
4830 | @end example | |
4831 | @end defun | |
4832 | ||
4833 | ||
43ed3b69 MV |
4834 | @node SRFI-61 |
4835 | @subsection SRFI-61 - A more general @code{cond} clause | |
4836 | ||
4837 | This SRFI extends RnRS @code{cond} to support test expressions that | |
4838 | return multiple values, as well as arbitrary definitions of test | |
4839 | success. SRFI 61 is implemented in the Guile core; there's no module | |
4840 | needed to get SRFI-61 itself. Extended @code{cond} is documented in | |
9accf3d9 | 4841 | @ref{Conditionals,, Simple Conditional Evaluation}. |
43ed3b69 | 4842 | |
b306fae0 MW |
4843 | @node SRFI-62 |
4844 | @subsection SRFI-62 - S-expression comments. | |
4845 | @cindex SRFI-62 | |
4846 | ||
4847 | Starting from version 2.0, Guile's @code{read} supports SRFI-62/R7RS | |
4848 | S-expression comments by default. | |
4849 | ||
8175a07e AR |
4850 | @node SRFI-67 |
4851 | @subsection SRFI-67 - Compare procedures | |
4852 | @cindex SRFI-67 | |
4853 | ||
4854 | See @uref{http://srfi.schemers.org/srfi-67/srfi-67.html, the | |
4855 | specification of SRFI-67}. | |
43ed3b69 | 4856 | |
1317062f LC |
4857 | @node SRFI-69 |
4858 | @subsection SRFI-69 - Basic hash tables | |
4859 | @cindex SRFI-69 | |
4860 | ||
4861 | This is a portable wrapper around Guile's built-in hash table and weak | |
4862 | table support. @xref{Hash Tables}, for information on that built-in | |
4863 | support. Above that, this hash-table interface provides association | |
4864 | of equality and hash functions with tables at creation time, so | |
4865 | variants of each function are not required, as well as a procedure | |
4866 | that takes care of most uses for Guile hash table handles, which this | |
4867 | SRFI does not provide as such. | |
4868 | ||
4869 | Access it with: | |
4870 | ||
4871 | @lisp | |
4872 | (use-modules (srfi srfi-69)) | |
4873 | @end lisp | |
4874 | ||
4875 | @menu | |
4876 | * SRFI-69 Creating hash tables:: | |
4877 | * SRFI-69 Accessing table items:: | |
4878 | * SRFI-69 Table properties:: | |
4879 | * SRFI-69 Hash table algorithms:: | |
4880 | @end menu | |
4881 | ||
4882 | @node SRFI-69 Creating hash tables | |
4883 | @subsubsection Creating hash tables | |
4884 | ||
4885 | @deffn {Scheme Procedure} make-hash-table [equal-proc hash-proc #:weak weakness start-size] | |
4886 | Create and answer a new hash table with @var{equal-proc} as the | |
4887 | equality function and @var{hash-proc} as the hashing function. | |
4888 | ||
4889 | By default, @var{equal-proc} is @code{equal?}. It can be any | |
4890 | two-argument procedure, and should answer whether two keys are the | |
4891 | same for this table's purposes. | |
4892 | ||
4893 | My default @var{hash-proc} assumes that @code{equal-proc} is no | |
4894 | coarser than @code{equal?} unless it is literally @code{string-ci=?}. | |
4895 | If provided, @var{hash-proc} should be a two-argument procedure that | |
4896 | takes a key and the current table size, and answers a reasonably good | |
4897 | hash integer between 0 (inclusive) and the size (exclusive). | |
4898 | ||
4899 | @var{weakness} should be @code{#f} or a symbol indicating how ``weak'' | |
4900 | the hash table is: | |
4901 | ||
4902 | @table @code | |
4903 | @item #f | |
4904 | An ordinary non-weak hash table. This is the default. | |
4905 | ||
4906 | @item key | |
4907 | When the key has no more non-weak references at GC, remove that entry. | |
4908 | ||
4909 | @item value | |
4910 | When the value has no more non-weak references at GC, remove that | |
4911 | entry. | |
4912 | ||
4913 | @item key-or-value | |
4914 | When either has no more non-weak references at GC, remove the | |
4915 | association. | |
4916 | @end table | |
4917 | ||
4918 | As a legacy of the time when Guile couldn't grow hash tables, | |
4919 | @var{start-size} is an optional integer argument that specifies the | |
dfe8c13b LC |
4920 | approximate starting size for the hash table, which will be rounded to |
4921 | an algorithmically-sounder number. | |
1317062f LC |
4922 | @end deffn |
4923 | ||
dfe8c13b | 4924 | By @dfn{coarser} than @code{equal?}, we mean that for all @var{x} and |
1317062f LC |
4925 | @var{y} values where @code{(@var{equal-proc} @var{x} @var{y})}, |
4926 | @code{(equal? @var{x} @var{y})} as well. If that does not hold for | |
4927 | your @var{equal-proc}, you must provide a @var{hash-proc}. | |
4928 | ||
4929 | In the case of weak tables, remember that @dfn{references} above | |
4930 | always refers to @code{eq?}-wise references. Just because you have a | |
4931 | reference to some string @code{"foo"} doesn't mean that an association | |
4932 | with key @code{"foo"} in a weak-key table @emph{won't} be collected; | |
4933 | it only counts as a reference if the two @code{"foo"}s are @code{eq?}, | |
4934 | regardless of @var{equal-proc}. As such, it is usually only sensible | |
4935 | to use @code{eq?} and @code{hashq} as the equivalence and hash | |
4936 | functions for a weak table. @xref{Weak References}, for more | |
4937 | information on Guile's built-in weak table support. | |
4938 | ||
4939 | @deffn {Scheme Procedure} alist->hash-table alist [equal-proc hash-proc #:weak weakness start-size] | |
4940 | As with @code{make-hash-table}, but initialize it with the | |
4941 | associations in @var{alist}. Where keys are repeated in @var{alist}, | |
4942 | the leftmost association takes precedence. | |
4943 | @end deffn | |
4944 | ||
4945 | @node SRFI-69 Accessing table items | |
4946 | @subsubsection Accessing table items | |
4947 | ||
4948 | @deffn {Scheme Procedure} hash-table-ref table key [default-thunk] | |
4949 | @deffnx {Scheme Procedure} hash-table-ref/default table key default | |
4950 | Answer the value associated with @var{key} in @var{table}. If | |
4951 | @var{key} is not present, answer the result of invoking the thunk | |
4952 | @var{default-thunk}, which signals an error instead by default. | |
4953 | ||
4954 | @code{hash-table-ref/default} is a variant that requires a third | |
4955 | argument, @var{default}, and answers @var{default} itself instead of | |
4956 | invoking it. | |
4957 | @end deffn | |
4958 | ||
4959 | @deffn {Scheme Procedure} hash-table-set! table key new-value | |
4960 | Set @var{key} to @var{new-value} in @var{table}. | |
4961 | @end deffn | |
4962 | ||
4963 | @deffn {Scheme Procedure} hash-table-delete! table key | |
4964 | Remove the association of @var{key} in @var{table}, if present. If | |
4965 | absent, do nothing. | |
4966 | @end deffn | |
4967 | ||
4968 | @deffn {Scheme Procedure} hash-table-exists? table key | |
4969 | Answer whether @var{key} has an association in @var{table}. | |
4970 | @end deffn | |
4971 | ||
4972 | @deffn {Scheme Procedure} hash-table-update! table key modifier [default-thunk] | |
4973 | @deffnx {Scheme Procedure} hash-table-update!/default table key modifier default | |
4974 | Replace @var{key}'s associated value in @var{table} by invoking | |
4975 | @var{modifier} with one argument, the old value. | |
4976 | ||
4977 | If @var{key} is not present, and @var{default-thunk} is provided, | |
4978 | invoke it with no arguments to get the ``old value'' to be passed to | |
4979 | @var{modifier} as above. If @var{default-thunk} is not provided in | |
4980 | such a case, signal an error. | |
4981 | ||
4982 | @code{hash-table-update!/default} is a variant that requires the | |
4983 | fourth argument, which is used directly as the ``old value'' rather | |
4984 | than as a thunk to be invoked to retrieve the ``old value''. | |
4985 | @end deffn | |
4986 | ||
4987 | @node SRFI-69 Table properties | |
4988 | @subsubsection Table properties | |
4989 | ||
4990 | @deffn {Scheme Procedure} hash-table-size table | |
4991 | Answer the number of associations in @var{table}. This is guaranteed | |
4992 | to run in constant time for non-weak tables. | |
4993 | @end deffn | |
4994 | ||
4995 | @deffn {Scheme Procedure} hash-table-keys table | |
4996 | Answer an unordered list of the keys in @var{table}. | |
4997 | @end deffn | |
4998 | ||
4999 | @deffn {Scheme Procedure} hash-table-values table | |
5000 | Answer an unordered list of the values in @var{table}. | |
5001 | @end deffn | |
5002 | ||
5003 | @deffn {Scheme Procedure} hash-table-walk table proc | |
5004 | Invoke @var{proc} once for each association in @var{table}, passing | |
5005 | the key and value as arguments. | |
5006 | @end deffn | |
5007 | ||
5008 | @deffn {Scheme Procedure} hash-table-fold table proc init | |
5009 | Invoke @code{(@var{proc} @var{key} @var{value} @var{previous})} for | |
5010 | each @var{key} and @var{value} in @var{table}, where @var{previous} is | |
5011 | the result of the previous invocation, using @var{init} as the first | |
5012 | @var{previous} value. Answer the final @var{proc} result. | |
5013 | @end deffn | |
5014 | ||
5015 | @deffn {Scheme Procedure} hash-table->alist table | |
5016 | Answer an alist where each association in @var{table} is an | |
5017 | association in the result. | |
5018 | @end deffn | |
5019 | ||
5020 | @node SRFI-69 Hash table algorithms | |
5021 | @subsubsection Hash table algorithms | |
5022 | ||
5023 | Each hash table carries an @dfn{equivalence function} and a @dfn{hash | |
5024 | function}, used to implement key lookups. Beginning users should | |
5025 | follow the rules for consistency of the default @var{hash-proc} | |
5026 | specified above. Advanced users can use these to implement their own | |
5027 | equivalence and hash functions for specialized lookup semantics. | |
5028 | ||
5029 | @deffn {Scheme Procedure} hash-table-equivalence-function hash-table | |
5030 | @deffnx {Scheme Procedure} hash-table-hash-function hash-table | |
5031 | Answer the equivalence and hash function of @var{hash-table}, respectively. | |
5032 | @end deffn | |
5033 | ||
5034 | @deffn {Scheme Procedure} hash obj [size] | |
5035 | @deffnx {Scheme Procedure} string-hash obj [size] | |
5036 | @deffnx {Scheme Procedure} string-ci-hash obj [size] | |
5037 | @deffnx {Scheme Procedure} hash-by-identity obj [size] | |
5038 | Answer a hash value appropriate for equality predicate @code{equal?}, | |
5039 | @code{string=?}, @code{string-ci=?}, and @code{eq?}, respectively. | |
5040 | @end deffn | |
5041 | ||
5042 | @code{hash} is a backwards-compatible replacement for Guile's built-in | |
5043 | @code{hash}. | |
5044 | ||
da81e75d MW |
5045 | @node SRFI-87 |
5046 | @subsection SRFI-87 => in case clauses | |
5047 | @cindex SRFI-87 | |
5048 | ||
5049 | Starting from version 2.0.6, Guile's core @code{case} syntax supports | |
5050 | @code{=>} in clauses, as specified by SRFI-87/R7RS. | |
5051 | @xref{Conditionals}. | |
5052 | ||
189681f5 LC |
5053 | @node SRFI-88 |
5054 | @subsection SRFI-88 Keyword Objects | |
5055 | @cindex SRFI-88 | |
5056 | @cindex keyword objects | |
5057 | ||
e36280cb | 5058 | @uref{http://srfi.schemers.org/srfi-88/srfi-88.html, SRFI-88} provides |
189681f5 LC |
5059 | @dfn{keyword objects}, which are equivalent to Guile's keywords |
5060 | (@pxref{Keywords}). SRFI-88 keywords can be entered using the | |
5061 | @dfn{postfix keyword syntax}, which consists of an identifier followed | |
1518f649 | 5062 | by @code{:} (@pxref{Scheme Read, @code{postfix} keyword syntax}). |
189681f5 LC |
5063 | SRFI-88 can be made available with: |
5064 | ||
5065 | @example | |
5066 | (use-modules (srfi srfi-88)) | |
5067 | @end example | |
5068 | ||
5069 | Doing so installs the right reader option for keyword syntax, using | |
5070 | @code{(read-set! keywords 'postfix)}. It also provides the procedures | |
5071 | described below. | |
5072 | ||
5073 | @deffn {Scheme Procedure} keyword? obj | |
5074 | Return @code{#t} if @var{obj} is a keyword. This is the same procedure | |
5075 | as the same-named built-in procedure (@pxref{Keyword Procedures, | |
5076 | @code{keyword?}}). | |
5077 | ||
5078 | @example | |
5079 | (keyword? foo:) @result{} #t | |
5080 | (keyword? 'foo:) @result{} #t | |
5081 | (keyword? "foo") @result{} #f | |
5082 | @end example | |
5083 | @end deffn | |
5084 | ||
5085 | @deffn {Scheme Procedure} keyword->string kw | |
5086 | Return the name of @var{kw} as a string, i.e., without the trailing | |
5087 | colon. The returned string may not be modified, e.g., with | |
5088 | @code{string-set!}. | |
5089 | ||
5090 | @example | |
5091 | (keyword->string foo:) @result{} "foo" | |
5092 | @end example | |
5093 | @end deffn | |
5094 | ||
5095 | @deffn {Scheme Procedure} string->keyword str | |
5096 | Return the keyword object whose name is @var{str}. | |
5097 | ||
5098 | @example | |
5099 | (keyword->string (string->keyword "a b c")) @result{} "a b c" | |
5100 | @end example | |
5101 | @end deffn | |
5102 | ||
922d417b JG |
5103 | @node SRFI-98 |
5104 | @subsection SRFI-98 Accessing environment variables. | |
5105 | @cindex SRFI-98 | |
5106 | @cindex environment variables | |
5107 | ||
5108 | This is a portable wrapper around Guile's built-in support for | |
5109 | interacting with the current environment, @xref{Runtime Environment}. | |
5110 | ||
5111 | @deffn {Scheme Procedure} get-environment-variable name | |
5112 | Returns a string containing the value of the environment variable | |
5113 | given by the string @code{name}, or @code{#f} if the named | |
5114 | environment variable is not found. This is equivalent to | |
5115 | @code{(getenv name)}. | |
5116 | @end deffn | |
5117 | ||
5118 | @deffn {Scheme Procedure} get-environment-variables | |
5119 | Returns the names and values of all the environment variables as an | |
5120 | association list in which both the keys and the values are strings. | |
5121 | @end deffn | |
1317062f | 5122 | |
bf9eb54a MW |
5123 | @node SRFI-105 |
5124 | @subsection SRFI-105 Curly-infix expressions. | |
5125 | @cindex SRFI-105 | |
5126 | @cindex curly-infix | |
5127 | @cindex curly-infix-and-bracket-lists | |
5128 | ||
5129 | Guile's built-in reader includes support for SRFI-105 curly-infix | |
5130 | expressions. See @uref{http://srfi.schemers.org/srfi-105/srfi-105.html, | |
5131 | the specification of SRFI-105}. Some examples: | |
5132 | ||
5133 | @example | |
5134 | @{n <= 5@} @result{} (<= n 5) | |
5135 | @{a + b + c@} @result{} (+ a b c) | |
5136 | @{a * @{b + c@}@} @result{} (* a (+ b c)) | |
5137 | @{(- a) / b@} @result{} (/ (- a) b) | |
5138 | @{-(a) / b@} @result{} (/ (- a) b) as well | |
5139 | @{(f a b) + (g h)@} @result{} (+ (f a b) (g h)) | |
5140 | @{f(a b) + g(h)@} @result{} (+ (f a b) (g h)) as well | |
5141 | @{f[a b] + g(h)@} @result{} (+ ($bracket-apply$ f a b) (g h)) | |
5142 | '@{a + f(b) + x@} @result{} '(+ a (f b) x) | |
5143 | @{length(x) >= 6@} @result{} (>= (length x) 6) | |
5144 | @{n-1 + n-2@} @result{} (+ n-1 n-2) | |
5145 | @{n * factorial@{n - 1@}@} @result{} (* n (factorial (- n 1))) | |
5146 | @{@{a > 0@} and @{b >= 1@}@} @result{} (and (> a 0) (>= b 1)) | |
5147 | @{f@{n - 1@}(x)@} @result{} ((f (- n 1)) x) | |
5148 | @{a . z@} @result{} ($nfx$ a . z) | |
5149 | @{a + b - c@} @result{} ($nfx$ a + b - c) | |
5150 | @end example | |
5151 | ||
5152 | To enable curly-infix expressions within a file, place the reader | |
5153 | directive @code{#!curly-infix} before the first use of curly-infix | |
5154 | notation. To globally enable curly-infix expressions in Guile's reader, | |
5155 | set the @code{curly-infix} read option. | |
5156 | ||
5157 | Guile also implements the following non-standard extension to SRFI-105: | |
5158 | if @code{curly-infix} is enabled and there is no other meaning assigned | |
5159 | to square brackets (i.e. the @code{square-brackets} read option is | |
5160 | turned off), then lists within square brackets are read as normal lists | |
5161 | but with the special symbol @code{$bracket-list$} added to the front. | |
5162 | To enable this combination of read options within a file, use the reader | |
5163 | directive @code{#!curly-infix-and-bracket-lists}. For example: | |
5164 | ||
5165 | @example | |
5166 | [a b] @result{} ($bracket-list$ a b) | |
5167 | [a . b] @result{} ($bracket-list$ a . b) | |
5168 | @end example | |
5169 | ||
5170 | ||
5171 | For more information on reader options, @xref{Scheme Read}. | |
5172 | ||
12991fed | 5173 | @c srfi-modules.texi ends here |
193239f1 KR |
5174 | |
5175 | @c Local Variables: | |
5176 | @c TeX-master: "guile.texi" | |
5177 | @c End: |