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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Guile Reference Manual. | |
3 | @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004 | |
4 | @c Free Software Foundation, Inc. | |
5 | @c See the file guile.texi for copying conditions. | |
6 | ||
a0e07ba4 NJ |
7 | @page |
8 | @node SRFI Support | |
3229f68b | 9 | @section SRFI Support Modules |
8742c48b | 10 | @cindex SRFI |
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11 | |
12 | SRFI is an acronym for Scheme Request For Implementation. The SRFI | |
13 | documents define a lot of syntactic and procedure extensions to standard | |
14 | Scheme as defined in R5RS. | |
15 | ||
16 | Guile has support for a number of SRFIs. This chapter gives an overview | |
17 | over the available SRFIs and some usage hints. For complete | |
18 | documentation, design rationales and further examples, we advise you to | |
19 | get the relevant SRFI documents from the SRFI home page | |
20 | @url{http://srfi.schemers.org}. | |
21 | ||
22 | @menu | |
23 | * About SRFI Usage:: What to know about Guile's SRFI support. | |
24 | * SRFI-0:: cond-expand | |
25 | * SRFI-1:: List library. | |
26 | * SRFI-2:: and-let*. | |
27 | * SRFI-4:: Homogeneous numeric vector datatypes. | |
28 | * SRFI-6:: Basic String Ports. | |
29 | * SRFI-8:: receive. | |
30 | * SRFI-9:: define-record-type. | |
31 | * SRFI-10:: Hash-Comma Reader Extension. | |
32 | * SRFI-11:: let-values and let-values*. | |
33 | * SRFI-13:: String library. | |
34 | * SRFI-14:: Character-set library. | |
35 | * SRFI-16:: case-lambda | |
36 | * SRFI-17:: Generalized set! | |
bfc9c8e0 | 37 | * SRFI-19:: Time/Date library. |
1de8c1ae | 38 | * SRFI-26:: Specializing parameters |
8638c417 | 39 | * SRFI-31:: A special form `rec' for recursive evaluation |
a0e07ba4 NJ |
40 | @end menu |
41 | ||
42 | ||
43 | @node About SRFI Usage | |
3229f68b | 44 | @subsection About SRFI Usage |
a0e07ba4 NJ |
45 | |
46 | @c FIXME::martin: Review me! | |
47 | ||
48 | SRFI support in Guile is currently implemented partly in the core | |
49 | library, and partly as add-on modules. That means that some SRFIs are | |
50 | automatically available when the interpreter is started, whereas the | |
51 | other SRFIs require you to use the appropriate support module | |
12991fed | 52 | explicitly. |
a0e07ba4 NJ |
53 | |
54 | There are several reasons for this inconsistency. First, the feature | |
55 | checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be | |
56 | available immediately, because it must be there when the user wants to | |
57 | check for the Scheme implementation, that is, before she can know that | |
58 | it is safe to use @code{use-modules} to load SRFI support modules. The | |
59 | second reason is that some features defined in SRFIs had been | |
60 | implemented in Guile before the developers started to add SRFI | |
61 | implementations as modules (for example SRFI-6 (@pxref{SRFI-6})). In | |
62 | the future, it is possible that SRFIs in the core library might be | |
63 | factored out into separate modules, requiring explicit module loading | |
64 | when they are needed. So you should be prepared to have to use | |
65 | @code{use-modules} someday in the future to access SRFI-6 bindings. If | |
66 | you want, you can do that already. We have included the module | |
67 | @code{(srfi srfi-6)} in the distribution, which currently does nothing, | |
68 | but ensures that you can write future-safe code. | |
69 | ||
70 | Generally, support for a specific SRFI is made available by using | |
71 | modules named @code{(srfi srfi-@var{number})}, where @var{number} is the | |
72 | number of the SRFI needed. Another possibility is to use the command | |
73 | line option @code{--use-srfi}, which will load the necessary modules | |
74 | automatically (@pxref{Invoking Guile}). | |
75 | ||
76 | ||
77 | @node SRFI-0 | |
3229f68b | 78 | @subsection SRFI-0 - cond-expand |
8742c48b | 79 | @cindex SRFI-0 |
a0e07ba4 | 80 | |
5eef0f61 KR |
81 | This SRFI lets a portable Scheme program test for the presence of |
82 | certain features, and adapt itself by using different blocks of code, | |
83 | or fail if the necessary features are not available. There's no | |
84 | module to load, this is in the Guile core. | |
a0e07ba4 | 85 | |
5eef0f61 KR |
86 | A program designed only for Guile will generally not need this |
87 | mechanism, such a program can of course directly use the various | |
88 | documented parts of Guile. | |
a0e07ba4 | 89 | |
5eef0f61 KR |
90 | @deffn syntax cond-expand (feature body@dots{}) @dots{} |
91 | Expand to the @var{body} of the first clause whose @var{feature} | |
92 | specification is satisfied. It is an error if no @var{feature} is | |
a0e07ba4 NJ |
93 | satisfied. |
94 | ||
5eef0f61 KR |
95 | Features are symbols such as @code{srfi-1}, and a feature |
96 | specification can use @code{and}, @code{or} and @code{not} forms to | |
97 | test combinations. The last clause can be an @code{else}, to be used | |
98 | if no other passes. | |
a0e07ba4 | 99 | |
5eef0f61 KR |
100 | For example, define a private version of @code{alist-cons} if SRFI-1 |
101 | is not available. | |
a0e07ba4 | 102 | |
5eef0f61 KR |
103 | @example |
104 | (cond-expand (srfi-1 | |
105 | ) | |
106 | (else | |
107 | (define (alist-cons key val alist) | |
108 | (cons (cons key val) alist)))) | |
109 | @end example | |
a0e07ba4 | 110 | |
5eef0f61 KR |
111 | Or demand a certain set of SRFIs (list operations, string ports, |
112 | @code{receive} and string operations), failing if they're not | |
113 | available. | |
a0e07ba4 | 114 | |
5eef0f61 KR |
115 | @example |
116 | (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13) | |
117 | )) | |
118 | @end example | |
119 | @end deffn | |
a0e07ba4 | 120 | |
5eef0f61 KR |
121 | The Guile core provides features @code{guile}, @code{r5rs}, |
122 | @code{srfi-0} and @code{srfi-6} initially. Other SRFI feature symbols | |
123 | are defined once their code has been loaded with @code{use-modules}, | |
124 | since only then are their bindings available. | |
a0e07ba4 | 125 | |
5eef0f61 KR |
126 | The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is |
127 | a good way to load SRFIs to satisfy @code{cond-expand} when running a | |
128 | portable program. | |
a0e07ba4 | 129 | |
5eef0f61 KR |
130 | Testing the @code{guile} feature allows a program to adapt itself to |
131 | the Guile module system, but still run on other Scheme systems. For | |
132 | example the following demands SRFI-8 (@code{receive}), but also knows | |
133 | how to load it with the Guile mechanism. | |
a0e07ba4 NJ |
134 | |
135 | @example | |
5eef0f61 KR |
136 | (cond-expand (srfi-8 |
137 | ) | |
138 | (guile | |
139 | (use-modules (srfi srfi-8)))) | |
a0e07ba4 NJ |
140 | @end example |
141 | ||
5eef0f61 KR |
142 | It should be noted that @code{cond-expand} is separate from the |
143 | @code{*features*} mechanism (@pxref{Feature Tracking}), feature | |
144 | symbols in one are unrelated to those in the other. | |
a0e07ba4 NJ |
145 | |
146 | ||
147 | @node SRFI-1 | |
3229f68b | 148 | @subsection SRFI-1 - List library |
8742c48b | 149 | @cindex SRFI-1 |
a0e07ba4 NJ |
150 | |
151 | @c FIXME::martin: Review me! | |
152 | ||
153 | The list library defined in SRFI-1 contains a lot of useful list | |
154 | processing procedures for construction, examining, destructuring and | |
155 | manipulating lists and pairs. | |
156 | ||
157 | Since SRFI-1 also defines some procedures which are already contained | |
158 | in R5RS and thus are supported by the Guile core library, some list | |
159 | and pair procedures which appear in the SRFI-1 document may not appear | |
160 | in this section. So when looking for a particular list/pair | |
161 | processing procedure, you should also have a look at the sections | |
162 | @ref{Lists} and @ref{Pairs}. | |
163 | ||
164 | @menu | |
165 | * SRFI-1 Constructors:: Constructing new lists. | |
166 | * SRFI-1 Predicates:: Testing list for specific properties. | |
167 | * SRFI-1 Selectors:: Selecting elements from lists. | |
168 | * SRFI-1 Length Append etc:: Length calculation and list appending. | |
169 | * SRFI-1 Fold and Map:: Higher-order list processing. | |
170 | * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates. | |
85a9b4ed | 171 | * SRFI-1 Searching:: Search for elements. |
a0e07ba4 NJ |
172 | * SRFI-1 Deleting:: Delete elements from lists. |
173 | * SRFI-1 Association Lists:: Handle association lists. | |
174 | * SRFI-1 Set Operations:: Use lists for representing sets. | |
175 | @end menu | |
176 | ||
177 | @node SRFI-1 Constructors | |
3229f68b | 178 | @subsubsection Constructors |
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179 | |
180 | @c FIXME::martin: Review me! | |
181 | ||
182 | New lists can be constructed by calling one of the following | |
183 | procedures. | |
184 | ||
8f85c0c6 | 185 | @deffn {Scheme Procedure} xcons d a |
a0e07ba4 NJ |
186 | Like @code{cons}, but with interchanged arguments. Useful mostly when |
187 | passed to higher-order procedures. | |
188 | @end deffn | |
189 | ||
8f85c0c6 | 190 | @deffn {Scheme Procedure} list-tabulate n init-proc |
a0e07ba4 NJ |
191 | Return an @var{n}-element list, where each list element is produced by |
192 | applying the procedure @var{init-proc} to the corresponding list | |
193 | index. The order in which @var{init-proc} is applied to the indices | |
194 | is not specified. | |
195 | @end deffn | |
196 | ||
57066448 KR |
197 | @deffn {Scheme Procedure} list-copy lst |
198 | Return a new list containing the elements of the list @var{lst}. | |
199 | ||
200 | This function differs from the core @code{list-copy} (@pxref{List | |
201 | Constructors}) in accepting improper lists too. And if @var{lst} is | |
202 | not a pair at all then it's treated as the final tail of an improper | |
203 | list and simply returned. | |
204 | @end deffn | |
205 | ||
8f85c0c6 | 206 | @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{} |
a0e07ba4 NJ |
207 | Return a circular list containing the given arguments @var{elt1} |
208 | @var{elt2} @dots{}. | |
209 | @end deffn | |
210 | ||
8f85c0c6 | 211 | @deffn {Scheme Procedure} iota count [start step] |
256853db KR |
212 | Return a list containing @var{count} numbers, starting from |
213 | @var{start} and adding @var{step} each time. The default @var{start} | |
214 | is 0, the default @var{step} is 1. For example, | |
a0e07ba4 | 215 | |
256853db KR |
216 | @example |
217 | (iota 6) @result{} (0 1 2 3 4 5) | |
218 | (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5) | |
219 | @end example | |
a0e07ba4 | 220 | |
256853db KR |
221 | This function takes its name from the corresponding primitive in the |
222 | APL language. | |
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223 | @end deffn |
224 | ||
225 | ||
226 | @node SRFI-1 Predicates | |
3229f68b | 227 | @subsubsection Predicates |
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228 | |
229 | @c FIXME::martin: Review me! | |
230 | ||
231 | The procedures in this section test specific properties of lists. | |
232 | ||
8f85c0c6 | 233 | @deffn {Scheme Procedure} proper-list? obj |
a0e07ba4 NJ |
234 | Return @code{#t} if @var{obj} is a proper list, that is a finite list, |
235 | terminated with the empty list. Otherwise, return @code{#f}. | |
236 | @end deffn | |
237 | ||
8f85c0c6 | 238 | @deffn {Scheme Procedure} circular-list? obj |
a0e07ba4 NJ |
239 | Return @code{#t} if @var{obj} is a circular list, otherwise return |
240 | @code{#f}. | |
241 | @end deffn | |
242 | ||
8f85c0c6 | 243 | @deffn {Scheme Procedure} dotted-list? obj |
a0e07ba4 NJ |
244 | Return @code{#t} if @var{obj} is a dotted list, return @code{#f} |
245 | otherwise. A dotted list is a finite list which is not terminated by | |
246 | the empty list, but some other value. | |
247 | @end deffn | |
248 | ||
8f85c0c6 | 249 | @deffn {Scheme Procedure} null-list? lst |
a0e07ba4 NJ |
250 | Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f} |
251 | otherwise. If something else than a proper or circular list is passed | |
85a9b4ed | 252 | as @var{lst}, an error is signalled. This procedure is recommended |
a0e07ba4 NJ |
253 | for checking for the end of a list in contexts where dotted lists are |
254 | not allowed. | |
255 | @end deffn | |
256 | ||
8f85c0c6 | 257 | @deffn {Scheme Procedure} not-pair? obj |
a0e07ba4 NJ |
258 | Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise. |
259 | This is shorthand notation @code{(not (pair? @var{obj}))} and is | |
260 | supposed to be used for end-of-list checking in contexts where dotted | |
261 | lists are allowed. | |
262 | @end deffn | |
263 | ||
8f85c0c6 | 264 | @deffn {Scheme Procedure} list= elt= list1 @dots{} |
a0e07ba4 NJ |
265 | Return @code{#t} if all argument lists are equal, @code{#f} otherwise. |
266 | List equality is determined by testing whether all lists have the same | |
267 | length and the corresponding elements are equal in the sense of the | |
268 | equality predicate @var{elt=}. If no or only one list is given, | |
269 | @code{#t} is returned. | |
270 | @end deffn | |
271 | ||
272 | ||
273 | @node SRFI-1 Selectors | |
3229f68b | 274 | @subsubsection Selectors |
a0e07ba4 NJ |
275 | |
276 | @c FIXME::martin: Review me! | |
277 | ||
8f85c0c6 NJ |
278 | @deffn {Scheme Procedure} first pair |
279 | @deffnx {Scheme Procedure} second pair | |
280 | @deffnx {Scheme Procedure} third pair | |
281 | @deffnx {Scheme Procedure} fourth pair | |
282 | @deffnx {Scheme Procedure} fifth pair | |
283 | @deffnx {Scheme Procedure} sixth pair | |
284 | @deffnx {Scheme Procedure} seventh pair | |
285 | @deffnx {Scheme Procedure} eighth pair | |
286 | @deffnx {Scheme Procedure} ninth pair | |
287 | @deffnx {Scheme Procedure} tenth pair | |
a0e07ba4 NJ |
288 | These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}. |
289 | @end deffn | |
290 | ||
8f85c0c6 | 291 | @deffn {Scheme Procedure} car+cdr pair |
a0e07ba4 NJ |
292 | Return two values, the @sc{car} and the @sc{cdr} of @var{pair}. |
293 | @end deffn | |
294 | ||
8f85c0c6 NJ |
295 | @deffn {Scheme Procedure} take lst i |
296 | @deffnx {Scheme Procedure} take! lst i | |
a0e07ba4 NJ |
297 | Return a list containing the first @var{i} elements of @var{lst}. |
298 | ||
299 | @code{take!} may modify the structure of the argument list @var{lst} | |
300 | in order to produce the result. | |
301 | @end deffn | |
302 | ||
8f85c0c6 | 303 | @deffn {Scheme Procedure} drop lst i |
a0e07ba4 NJ |
304 | Return a list containing all but the first @var{i} elements of |
305 | @var{lst}. | |
306 | @end deffn | |
307 | ||
8f85c0c6 | 308 | @deffn {Scheme Procedure} take-right lst i |
a0e07ba4 NJ |
309 | Return the a list containing the @var{i} last elements of @var{lst}. |
310 | @end deffn | |
311 | ||
8f85c0c6 NJ |
312 | @deffn {Scheme Procedure} drop-right lst i |
313 | @deffnx {Scheme Procedure} drop-right! lst i | |
a0e07ba4 NJ |
314 | Return the a list containing all but the @var{i} last elements of |
315 | @var{lst}. | |
316 | ||
317 | @code{drop-right!} may modify the structure of the argument list | |
318 | @var{lst} in order to produce the result. | |
319 | @end deffn | |
320 | ||
8f85c0c6 NJ |
321 | @deffn {Scheme Procedure} split-at lst i |
322 | @deffnx {Scheme Procedure} split-at! lst i | |
a0e07ba4 NJ |
323 | Return two values, a list containing the first @var{i} elements of the |
324 | list @var{lst} and a list containing the remaining elements. | |
325 | ||
326 | @code{split-at!} may modify the structure of the argument list | |
327 | @var{lst} in order to produce the result. | |
328 | @end deffn | |
329 | ||
8f85c0c6 | 330 | @deffn {Scheme Procedure} last lst |
a0e07ba4 NJ |
331 | Return the last element of the non-empty, finite list @var{lst}. |
332 | @end deffn | |
333 | ||
334 | ||
335 | @node SRFI-1 Length Append etc | |
3229f68b | 336 | @subsubsection Length, Append, Concatenate, etc. |
a0e07ba4 NJ |
337 | |
338 | @c FIXME::martin: Review me! | |
339 | ||
8f85c0c6 | 340 | @deffn {Scheme Procedure} length+ lst |
a0e07ba4 NJ |
341 | Return the length of the argument list @var{lst}. When @var{lst} is a |
342 | circular list, @code{#f} is returned. | |
343 | @end deffn | |
344 | ||
8f85c0c6 NJ |
345 | @deffn {Scheme Procedure} concatenate list-of-lists |
346 | @deffnx {Scheme Procedure} concatenate! list-of-lists | |
a0e07ba4 NJ |
347 | Construct a list by appending all lists in @var{list-of-lists}. |
348 | ||
349 | @code{concatenate!} may modify the structure of the given lists in | |
350 | order to produce the result. | |
351 | @end deffn | |
352 | ||
8f85c0c6 NJ |
353 | @deffn {Scheme Procedure} append-reverse rev-head tail |
354 | @deffnx {Scheme Procedure} append-reverse! rev-head tail | |
a0e07ba4 NJ |
355 | Reverse @var{rev-head}, append @var{tail} and return the result. This |
356 | is equivalent to @code{(append (reverse @var{rev-head}) @var{tail})}, | |
357 | but more efficient. | |
358 | ||
359 | @code{append-reverse!} may modify @var{rev-head} in order to produce | |
360 | the result. | |
361 | @end deffn | |
362 | ||
8f85c0c6 | 363 | @deffn {Scheme Procedure} zip lst1 lst2 @dots{} |
a0e07ba4 NJ |
364 | Return a list as long as the shortest of the argument lists, where |
365 | each element is a list. The first list contains the first elements of | |
366 | the argument lists, the second list contains the second elements, and | |
367 | so on. | |
368 | @end deffn | |
369 | ||
8f85c0c6 NJ |
370 | @deffn {Scheme Procedure} unzip1 lst |
371 | @deffnx {Scheme Procedure} unzip2 lst | |
372 | @deffnx {Scheme Procedure} unzip3 lst | |
373 | @deffnx {Scheme Procedure} unzip4 lst | |
374 | @deffnx {Scheme Procedure} unzip5 lst | |
a0e07ba4 NJ |
375 | @code{unzip1} takes a list of lists, and returns a list containing the |
376 | first elements of each list, @code{unzip2} returns two lists, the | |
377 | first containing the first elements of each lists and the second | |
378 | containing the second elements of each lists, and so on. | |
379 | @end deffn | |
380 | ||
e508c863 KR |
381 | @deffn {Scheme Procedure} count pred lst1 @dots{} lstN |
382 | Return a count of the number of times @var{pred} returns true when | |
383 | called on elements from the given lists. | |
384 | ||
385 | @var{pred} is called with @var{N} parameters @code{(@var{pred} | |
386 | @var{elem1} @dots{} @var{elemN})}, each element being from the | |
387 | corresponding @var{lst1} @dots{} @var{lstN}. The first call is with | |
388 | the first element of each list, the second with the second element | |
389 | from each, and so on. | |
390 | ||
391 | Counting stops when the end of the shortest list is reached. At least | |
392 | one list must be non-circular. | |
393 | @end deffn | |
394 | ||
a0e07ba4 NJ |
395 | |
396 | @node SRFI-1 Fold and Map | |
3229f68b | 397 | @subsubsection Fold, Unfold & Map |
a0e07ba4 NJ |
398 | |
399 | @c FIXME::martin: Review me! | |
400 | ||
8f85c0c6 | 401 | @deffn {Scheme Procedure} fold kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
402 | Fold the procedure @var{kons} across all elements of @var{lst1}, |
403 | @var{lst2}, @dots{}. Produce the result of | |
404 | ||
405 | @code{(@var{kons} @var{en1} @var{en2} @dots{} (@var{kons} @var{e21} | |
406 | @var{e22} (@var{kons} @var{e11} @var{e12} @var{knil})))}, | |
407 | ||
408 | if @var{enm} are the elements of the lists @var{lst1}, @var{lst2}, | |
409 | @dots{}. | |
410 | @end deffn | |
411 | ||
8f85c0c6 | 412 | @deffn {Scheme Procedure} fold-right kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
413 | Similar to @code{fold}, but applies @var{kons} in right-to-left order |
414 | to the list elements, that is: | |
415 | ||
416 | @code{(@var{kons} @var{e11} @var{e12}(@var{kons} @var{e21} | |
417 | @var{e22} @dots{} (@var{kons} @var{en1} @var{en2} @var{knil})))}, | |
418 | @end deffn | |
419 | ||
8f85c0c6 | 420 | @deffn {Scheme Procedure} pair-fold kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
421 | Like @code{fold}, but apply @var{kons} to the pairs of the list |
422 | instead of the list elements. | |
423 | @end deffn | |
424 | ||
8f85c0c6 | 425 | @deffn {Scheme Procedure} pair-fold-right kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
426 | Like @code{fold-right}, but apply @var{kons} to the pairs of the list |
427 | instead of the list elements. | |
428 | @end deffn | |
429 | ||
8f85c0c6 | 430 | @deffn {Scheme Procedure} reduce f ridentity lst |
1ae7b878 KR |
431 | @code{reduce} is a variant of @code{fold}. If @var{lst} is |
432 | @code{()}, @var{ridentity} is returned. Otherwise, @code{(fold f (car | |
a0e07ba4 NJ |
433 | @var{lst}) (cdr @var{lst}))} is returned. |
434 | @end deffn | |
435 | ||
8f85c0c6 | 436 | @deffn {Scheme Procedure} reduce-right f ridentity lst |
b5aa0215 | 437 | This is the @code{fold-right} variant of @code{reduce}. |
a0e07ba4 NJ |
438 | @end deffn |
439 | ||
8f85c0c6 | 440 | @deffn {Scheme Procedure} unfold p f g seed [tail-gen] |
a0e07ba4 NJ |
441 | @code{unfold} is defined as follows: |
442 | ||
443 | @lisp | |
444 | (unfold p f g seed) = | |
445 | (if (p seed) (tail-gen seed) | |
446 | (cons (f seed) | |
447 | (unfold p f g (g seed)))) | |
448 | @end lisp | |
449 | ||
450 | @table @var | |
451 | @item p | |
452 | Determines when to stop unfolding. | |
453 | ||
454 | @item f | |
455 | Maps each seed value to the corresponding list element. | |
456 | ||
457 | @item g | |
458 | Maps each seed value to next seed valu. | |
459 | ||
460 | @item seed | |
461 | The state value for the unfold. | |
462 | ||
463 | @item tail-gen | |
464 | Creates the tail of the list; defaults to @code{(lambda (x) '())}. | |
465 | @end table | |
466 | ||
467 | @var{g} produces a series of seed values, which are mapped to list | |
468 | elements by @var{f}. These elements are put into a list in | |
469 | left-to-right order, and @var{p} tells when to stop unfolding. | |
470 | @end deffn | |
471 | ||
8f85c0c6 | 472 | @deffn {Scheme Procedure} unfold-right p f g seed [tail] |
a0e07ba4 NJ |
473 | Construct a list with the following loop. |
474 | ||
475 | @lisp | |
476 | (let lp ((seed seed) (lis tail)) | |
477 | (if (p seed) lis | |
478 | (lp (g seed) | |
479 | (cons (f seed) lis)))) | |
480 | @end lisp | |
481 | ||
482 | @table @var | |
483 | @item p | |
484 | Determines when to stop unfolding. | |
485 | ||
486 | @item f | |
487 | Maps each seed value to the corresponding list element. | |
488 | ||
489 | @item g | |
490 | Maps each seed value to next seed valu. | |
491 | ||
492 | @item seed | |
493 | The state value for the unfold. | |
494 | ||
495 | @item tail-gen | |
496 | Creates the tail of the list; defaults to @code{(lambda (x) '())}. | |
497 | @end table | |
498 | ||
499 | @end deffn | |
500 | ||
8f85c0c6 | 501 | @deffn {Scheme Procedure} map f lst1 lst2 @dots{} |
a0e07ba4 NJ |
502 | Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and |
503 | return a list containing the results of the procedure applications. | |
504 | This procedure is extended with respect to R5RS, because the argument | |
505 | lists may have different lengths. The result list will have the same | |
506 | length as the shortest argument lists. The order in which @var{f} | |
507 | will be applied to the list element(s) is not specified. | |
508 | @end deffn | |
509 | ||
8f85c0c6 | 510 | @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{} |
a0e07ba4 NJ |
511 | Apply the procedure @var{f} to each pair of corresponding elements of |
512 | the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not | |
513 | specified. This procedure is extended with respect to R5RS, because | |
514 | the argument lists may have different lengths. The shortest argument | |
515 | list determines the number of times @var{f} is called. @var{f} will | |
85a9b4ed | 516 | be applied to the list elements in left-to-right order. |
a0e07ba4 NJ |
517 | |
518 | @end deffn | |
519 | ||
8f85c0c6 NJ |
520 | @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{} |
521 | @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{} | |
12991fed | 522 | Equivalent to |
a0e07ba4 NJ |
523 | |
524 | @lisp | |
12991fed | 525 | (apply append (map f clist1 clist2 ...)) |
a0e07ba4 NJ |
526 | @end lisp |
527 | ||
12991fed | 528 | and |
a0e07ba4 NJ |
529 | |
530 | @lisp | |
12991fed | 531 | (apply append! (map f clist1 clist2 ...)) |
a0e07ba4 NJ |
532 | @end lisp |
533 | ||
534 | Map @var{f} over the elements of the lists, just as in the @code{map} | |
535 | function. However, the results of the applications are appended | |
536 | together to make the final result. @code{append-map} uses | |
537 | @code{append} to append the results together; @code{append-map!} uses | |
538 | @code{append!}. | |
539 | ||
540 | The dynamic order in which the various applications of @var{f} are | |
541 | made is not specified. | |
542 | @end deffn | |
543 | ||
8f85c0c6 | 544 | @deffn {Scheme Procedure} map! f lst1 lst2 @dots{} |
a0e07ba4 NJ |
545 | Linear-update variant of @code{map} -- @code{map!} is allowed, but not |
546 | required, to alter the cons cells of @var{lst1} to construct the | |
547 | result list. | |
548 | ||
549 | The dynamic order in which the various applications of @var{f} are | |
550 | made is not specified. In the n-ary case, @var{lst2}, @var{lst3}, | |
551 | @dots{} must have at least as many elements as @var{lst1}. | |
552 | @end deffn | |
553 | ||
8f85c0c6 | 554 | @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{} |
a0e07ba4 NJ |
555 | Like @code{for-each}, but applies the procedure @var{f} to the pairs |
556 | from which the argument lists are constructed, instead of the list | |
557 | elements. The return value is not specified. | |
558 | @end deffn | |
559 | ||
8f85c0c6 | 560 | @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{} |
a0e07ba4 NJ |
561 | Like @code{map}, but only results from the applications of @var{f} |
562 | which are true are saved in the result list. | |
563 | @end deffn | |
564 | ||
565 | ||
566 | @node SRFI-1 Filtering and Partitioning | |
3229f68b | 567 | @subsubsection Filtering and Partitioning |
a0e07ba4 NJ |
568 | |
569 | @c FIXME::martin: Review me! | |
570 | ||
571 | Filtering means to collect all elements from a list which satisfy a | |
572 | specific condition. Partitioning a list means to make two groups of | |
573 | list elements, one which contains the elements satisfying a condition, | |
574 | and the other for the elements which don't. | |
575 | ||
60e25dc4 KR |
576 | The @code{filter} and @code{filter!} functions are implemented in the |
577 | Guile core, @xref{List Modification}. | |
a0e07ba4 | 578 | |
8f85c0c6 NJ |
579 | @deffn {Scheme Procedure} partition pred lst |
580 | @deffnx {Scheme Procedure} partition! pred lst | |
193239f1 KR |
581 | Split @var{lst} into those elements which do and don't satisfy the |
582 | predicate @var{pred}. | |
a0e07ba4 | 583 | |
193239f1 KR |
584 | The return is two values (@pxref{Multiple Values}), the first being a |
585 | list of all elements from @var{lst} which satisfy @var{pred}, the | |
586 | second a list of those which do not. | |
587 | ||
588 | The elements in the result lists are in the same order as in @var{lst} | |
589 | but the order in which the calls @code{(@var{pred} elem)} are made on | |
590 | the list elements is unspecified. | |
591 | ||
592 | @code{partition} does not change @var{lst}, but one of the returned | |
593 | lists may share a tail with it. @code{partition!} may modify | |
594 | @var{lst} to construct its return. | |
a0e07ba4 NJ |
595 | @end deffn |
596 | ||
8f85c0c6 NJ |
597 | @deffn {Scheme Procedure} remove pred lst |
598 | @deffnx {Scheme Procedure} remove! pred lst | |
a0e07ba4 NJ |
599 | Return a list containing all elements from @var{lst} which do not |
600 | satisfy the predicate @var{pred}. The elements in the result list | |
601 | have the same order as in @var{lst}. The order in which @var{pred} is | |
602 | applied to the list elements is not specified. | |
603 | ||
604 | @code{remove!} is allowed, but not required to modify the structure of | |
605 | the input list. | |
606 | @end deffn | |
607 | ||
608 | ||
609 | @node SRFI-1 Searching | |
3229f68b | 610 | @subsubsection Searching |
a0e07ba4 NJ |
611 | |
612 | @c FIXME::martin: Review me! | |
613 | ||
614 | The procedures for searching elements in lists either accept a | |
615 | predicate or a comparison object for determining which elements are to | |
616 | be searched. | |
617 | ||
8f85c0c6 | 618 | @deffn {Scheme Procedure} find pred lst |
a0e07ba4 NJ |
619 | Return the first element of @var{lst} which satisfies the predicate |
620 | @var{pred} and @code{#f} if no such element is found. | |
621 | @end deffn | |
622 | ||
8f85c0c6 | 623 | @deffn {Scheme Procedure} find-tail pred lst |
a0e07ba4 NJ |
624 | Return the first pair of @var{lst} whose @sc{car} satisfies the |
625 | predicate @var{pred} and @code{#f} if no such element is found. | |
626 | @end deffn | |
627 | ||
8f85c0c6 NJ |
628 | @deffn {Scheme Procedure} take-while pred lst |
629 | @deffnx {Scheme Procedure} take-while! pred lst | |
a0e07ba4 NJ |
630 | Return the longest initial prefix of @var{lst} whose elements all |
631 | satisfy the predicate @var{pred}. | |
632 | ||
633 | @code{take-while!} is allowed, but not required to modify the input | |
634 | list while producing the result. | |
635 | @end deffn | |
636 | ||
8f85c0c6 | 637 | @deffn {Scheme Procedure} drop-while pred lst |
a0e07ba4 NJ |
638 | Drop the longest initial prefix of @var{lst} whose elements all |
639 | satisfy the predicate @var{pred}. | |
640 | @end deffn | |
641 | ||
8f85c0c6 NJ |
642 | @deffn {Scheme Procedure} span pred lst |
643 | @deffnx {Scheme Procedure} span! pred lst | |
644 | @deffnx {Scheme Procedure} break pred lst | |
645 | @deffnx {Scheme Procedure} break! pred lst | |
a0e07ba4 NJ |
646 | @code{span} splits the list @var{lst} into the longest initial prefix |
647 | whose elements all satisfy the predicate @var{pred}, and the remaining | |
648 | tail. @code{break} inverts the sense of the predicate. | |
649 | ||
650 | @code{span!} and @code{break!} are allowed, but not required to modify | |
651 | the structure of the input list @var{lst} in order to produce the | |
652 | result. | |
3e73b6f9 KR |
653 | |
654 | Note that the name @code{break} conflicts with the @code{break} | |
655 | binding established by @code{while} (@pxref{while do}). Applications | |
656 | wanting to use @code{break} from within a @code{while} loop will need | |
657 | to make a new define under a different name. | |
a0e07ba4 NJ |
658 | @end deffn |
659 | ||
8f85c0c6 | 660 | @deffn {Scheme Procedure} any pred lst1 lst2 @dots{} |
a0e07ba4 NJ |
661 | Apply @var{pred} across the lists and return a true value if the |
662 | predicate returns true for any of the list elements(s); return | |
663 | @code{#f} otherwise. The true value returned is always the result of | |
85a9b4ed | 664 | the first successful application of @var{pred}. |
a0e07ba4 NJ |
665 | @end deffn |
666 | ||
8f85c0c6 | 667 | @deffn {Scheme Procedure} every pred lst1 lst2 @dots{} |
a0e07ba4 NJ |
668 | Apply @var{pred} across the lists and return a true value if the |
669 | predicate returns true for every of the list elements(s); return | |
670 | @code{#f} otherwise. The true value returned is always the result of | |
85a9b4ed | 671 | the final successful application of @var{pred}. |
a0e07ba4 NJ |
672 | @end deffn |
673 | ||
8f85c0c6 | 674 | @deffn {Scheme Procedure} list-index pred lst1 lst2 @dots{} |
a0e07ba4 NJ |
675 | Return the index of the leftmost element that satisfies @var{pred}. |
676 | @end deffn | |
677 | ||
8f85c0c6 | 678 | @deffn {Scheme Procedure} member x lst [=] |
a0e07ba4 NJ |
679 | Return the first sublist of @var{lst} whose @sc{car} is equal to |
680 | @var{x}. If @var{x} does no appear in @var{lst}, return @code{#f}. | |
681 | Equality is determined by the equality predicate @var{=}, or | |
682 | @code{equal?} if @var{=} is not given. | |
ea6ea01b KR |
683 | |
684 | This function extends the core @code{member} by accepting an equality | |
685 | predicate. (@pxref{List Searching}) | |
a0e07ba4 NJ |
686 | @end deffn |
687 | ||
688 | ||
689 | @node SRFI-1 Deleting | |
3229f68b | 690 | @subsubsection Deleting |
a0e07ba4 NJ |
691 | |
692 | @c FIXME::martin: Review me! | |
693 | ||
8f85c0c6 NJ |
694 | @deffn {Scheme Procedure} delete x lst [=] |
695 | @deffnx {Scheme Procedure} delete! x lst [=] | |
b6b9376a KR |
696 | Return a list containing the elements of @var{lst} but with those |
697 | equal to @var{x} deleted. The returned elements will be in the same | |
698 | order as they were in @var{lst}. | |
699 | ||
700 | Equality is determined by the @var{=} predicate, or @code{equal?} if | |
701 | not given. An equality call is made just once for each element, but | |
702 | the order in which the calls are made on the elements is unspecified. | |
a0e07ba4 | 703 | |
243bdb63 | 704 | The equality calls are always @code{(= x elem)}, ie.@: the given @var{x} |
b6b9376a KR |
705 | is first. This means for instance elements greater than 5 can be |
706 | deleted with @code{(delete 5 lst <)}. | |
707 | ||
708 | @code{delete} does not modify @var{lst}, but the return might share a | |
709 | common tail with @var{lst}. @code{delete!} may modify the structure | |
710 | of @var{lst} to construct its return. | |
ea6ea01b KR |
711 | |
712 | These functions extend the core @code{delete} and @code{delete!} in | |
713 | accepting an equality predicate. (@pxref{List Modification}) | |
a0e07ba4 NJ |
714 | @end deffn |
715 | ||
8f85c0c6 NJ |
716 | @deffn {Scheme Procedure} delete-duplicates lst [=] |
717 | @deffnx {Scheme Procedure} delete-duplicates! lst [=] | |
b6b9376a KR |
718 | Return a list containing the elements of @var{lst} but without |
719 | duplicates. | |
720 | ||
721 | When elements are equal, only the first in @var{lst} is retained. | |
722 | Equal elements can be anywhere in @var{lst}, they don't have to be | |
723 | adjacent. The returned list will have the retained elements in the | |
724 | same order as they were in @var{lst}. | |
725 | ||
726 | Equality is determined by the @var{=} predicate, or @code{equal?} if | |
727 | not given. Calls @code{(= x y)} are made with element @var{x} being | |
728 | before @var{y} in @var{lst}. A call is made at most once for each | |
729 | combination, but the sequence of the calls across the elements is | |
730 | unspecified. | |
731 | ||
732 | @code{delete-duplicates} does not modify @var{lst}, but the return | |
733 | might share a common tail with @var{lst}. @code{delete-duplicates!} | |
734 | may modify the structure of @var{lst} to construct its return. | |
735 | ||
736 | In the worst case, this is an @math{O(N^2)} algorithm because it must | |
737 | check each element against all those preceding it. For long lists it | |
738 | is more efficient to sort and then compare only adjacent elements. | |
a0e07ba4 NJ |
739 | @end deffn |
740 | ||
741 | ||
742 | @node SRFI-1 Association Lists | |
3229f68b | 743 | @subsubsection Association Lists |
a0e07ba4 NJ |
744 | |
745 | @c FIXME::martin: Review me! | |
746 | ||
747 | Association lists are described in detail in section @ref{Association | |
748 | Lists}. The present section only documents the additional procedures | |
749 | for dealing with association lists defined by SRFI-1. | |
750 | ||
8f85c0c6 | 751 | @deffn {Scheme Procedure} assoc key alist [=] |
a0e07ba4 NJ |
752 | Return the pair from @var{alist} which matches @var{key}. Equality is |
753 | determined by @var{=}, which defaults to @code{equal?} if not given. | |
754 | @var{alist} must be an association lists---a list of pairs. | |
ea6ea01b KR |
755 | |
756 | This function extends the core @code{assoc} by accepting an equality | |
757 | predicate. (@pxref{Association Lists}) | |
a0e07ba4 NJ |
758 | @end deffn |
759 | ||
8f85c0c6 | 760 | @deffn {Scheme Procedure} alist-cons key datum alist |
a0e07ba4 NJ |
761 | Equivalent to |
762 | ||
763 | @lisp | |
764 | (cons (cons @var{key} @var{datum}) @var{alist}) | |
765 | @end lisp | |
766 | ||
767 | This procedure is used to coons a new pair onto an existing | |
768 | association list. | |
769 | @end deffn | |
770 | ||
8f85c0c6 | 771 | @deffn {Scheme Procedure} alist-copy alist |
a0e07ba4 NJ |
772 | Return a newly allocated copy of @var{alist}, that means that the |
773 | spine of the list as well as the pairs are copied. | |
774 | @end deffn | |
775 | ||
8f85c0c6 NJ |
776 | @deffn {Scheme Procedure} alist-delete key alist [=] |
777 | @deffnx {Scheme Procedure} alist-delete! key alist [=] | |
bd35f1f0 KR |
778 | Return a list containing the elements of @var{alist} but with those |
779 | elements whose keys are equal to @var{key} deleted. The returned | |
780 | elements will be in the same order as they were in @var{alist}. | |
a0e07ba4 | 781 | |
bd35f1f0 KR |
782 | Equality is determined by the @var{=} predicate, or @code{equal?} if |
783 | not given. The order in which elements are tested is unspecified, but | |
784 | each equality call is made @code{(= key alistkey)}, ie. the given | |
785 | @var{key} parameter is first and the key from @var{alist} second. | |
786 | This means for instance all associations with a key greater than 5 can | |
787 | be removed with @code{(alist-delete 5 alist <)}. | |
788 | ||
789 | @code{alist-delete} does not modify @var{alist}, but the return might | |
790 | share a common tail with @var{alist}. @code{alist-delete!} may modify | |
791 | the list structure of @var{alist} to construct its return. | |
a0e07ba4 NJ |
792 | @end deffn |
793 | ||
794 | ||
795 | @node SRFI-1 Set Operations | |
3229f68b | 796 | @subsubsection Set Operations on Lists |
a0e07ba4 NJ |
797 | |
798 | @c FIXME::martin: Review me! | |
799 | ||
800 | Lists can be used for representing sets of objects. The procedures | |
801 | documented in this section can be used for such set representations. | |
85a9b4ed | 802 | Man combining several sets or adding elements, they make sure that no |
a0e07ba4 NJ |
803 | object is contained more than once in a given list. Please note that |
804 | lists are not a too efficient implementation method for sets, so if | |
805 | you need high performance, you should think about implementing a | |
806 | custom data structure for representing sets, such as trees, bitsets, | |
807 | hash tables or something similar. | |
808 | ||
809 | All these procedures accept an equality predicate as the first | |
810 | argument. This predicate is used for testing the objects in the list | |
811 | sets for sameness. | |
812 | ||
8f85c0c6 | 813 | @deffn {Scheme Procedure} lset<= = list1 @dots{} |
a0e07ba4 NJ |
814 | Return @code{#t} if every @var{listi} is a subset of @var{listi+1}, |
815 | otherwise return @code{#f}. Returns @code{#t} if called with less | |
816 | than two arguments. @var{=} is used for testing element equality. | |
817 | @end deffn | |
818 | ||
8f85c0c6 | 819 | @deffn {Scheme Procedure} lset= = list1 list2 @dots{} |
a0e07ba4 NJ |
820 | Return @code{#t} if all argument lists are equal. @var{=} is used for |
821 | testing element equality. | |
822 | @end deffn | |
823 | ||
8f85c0c6 NJ |
824 | @deffn {Scheme Procedure} lset-adjoin = list elt1 @dots{} |
825 | @deffnx {Scheme Procedure} lset-adjoin! = list elt1 @dots{} | |
a0e07ba4 NJ |
826 | Add all @var{elts} to the list @var{list}, suppressing duplicates and |
827 | return the resulting list. @code{lset-adjoin!} is allowed, but not | |
828 | required to modify its first argument. @var{=} is used for testing | |
829 | element equality. | |
830 | @end deffn | |
831 | ||
8f85c0c6 NJ |
832 | @deffn {Scheme Procedure} lset-union = list1 @dots{} |
833 | @deffnx {Scheme Procedure} lset-union! = list1 @dots{} | |
a0e07ba4 NJ |
834 | Return the union of all argument list sets. The union is the set of |
835 | all elements which appear in any of the argument sets. | |
836 | @code{lset-union!} is allowed, but not required to modify its first | |
837 | argument. @var{=} is used for testing element equality. | |
838 | @end deffn | |
839 | ||
8f85c0c6 NJ |
840 | @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{} |
841 | @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{} | |
a0e07ba4 NJ |
842 | Return the intersection of all argument list sets. The intersection |
843 | is the set containing all elements which appear in all argument sets. | |
844 | @code{lset-intersection!} is allowed, but not required to modify its | |
845 | first argument. @var{=} is used for testing element equality. | |
846 | @end deffn | |
847 | ||
8f85c0c6 NJ |
848 | @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{} |
849 | @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{} | |
a0e07ba4 NJ |
850 | Return the difference of all argument list sets. The difference is |
851 | the the set containing all elements of the first list which do not | |
852 | appear in the other lists. @code{lset-difference!} is allowed, but | |
853 | not required to modify its first argument. @var{=} is used for testing | |
854 | element equality. | |
855 | @end deffn | |
856 | ||
8f85c0c6 NJ |
857 | @deffn {Scheme Procedure} lset-xor = list1 @dots{} |
858 | @deffnx {Scheme Procedure} lset-xor! = list1 @dots{} | |
a0e07ba4 NJ |
859 | Return the set containing all elements which appear in the first |
860 | argument list set, but not in the second; or, more generally: which | |
861 | appear in an odd number of sets. @code{lset-xor!} is allowed, but | |
862 | not required to modify its first argument. @var{=} is used for testing | |
863 | element equality. | |
864 | @end deffn | |
865 | ||
8f85c0c6 NJ |
866 | @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{} |
867 | @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{} | |
a0e07ba4 NJ |
868 | Return two values, the difference and the intersection of the argument |
869 | list sets. This works like a combination of @code{lset-difference} and | |
870 | @code{lset-intersection}, but is more efficient. | |
871 | @code{lset-diff+intersection!} is allowed, but not required to modify | |
872 | its first argument. @var{=} is used for testing element equality. You | |
873 | have to use some means to deal with the multiple values these | |
874 | procedures return (@pxref{Multiple Values}). | |
875 | @end deffn | |
876 | ||
877 | ||
878 | @node SRFI-2 | |
3229f68b | 879 | @subsection SRFI-2 - and-let* |
8742c48b | 880 | @cindex SRFI-2 |
a0e07ba4 | 881 | |
4fd0db14 KR |
882 | @noindent |
883 | The following syntax can be obtained with | |
a0e07ba4 | 884 | |
4fd0db14 KR |
885 | @lisp |
886 | (use-modules (srfi srfi-2)) | |
887 | @end lisp | |
a0e07ba4 | 888 | |
4fd0db14 KR |
889 | @deffn {library syntax} and-let* (clause @dots{}) body @dots{} |
890 | A combination of @code{and} and @code{let*}. | |
891 | ||
892 | Each @var{clause} is evaluated in turn, and if @code{#f} is obtained | |
893 | then evaluation stops and @code{#f} is returned. If all are | |
894 | non-@code{#f} then @var{body} is evaluated and the last form gives the | |
6b1a6e4c KR |
895 | return value, or if @var{body} is empty then the result is @code{#t}. |
896 | Each @var{clause} should be one of the following, | |
4fd0db14 KR |
897 | |
898 | @table @code | |
899 | @item (symbol expr) | |
900 | Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}. | |
901 | Like @code{let*}, that binding is available to subsequent clauses. | |
902 | @item (expr) | |
903 | Evaluate @var{expr} and check for @code{#f}. | |
904 | @item symbol | |
905 | Get the value bound to @var{symbol} and check for @code{#f}. | |
906 | @end table | |
a0e07ba4 | 907 | |
4fd0db14 KR |
908 | Notice that @code{(expr)} has an ``extra'' pair of parentheses, for |
909 | instance @code{((eq? x y))}. One way to remember this is to imagine | |
910 | the @code{symbol} in @code{(symbol expr)} is omitted. | |
a0e07ba4 | 911 | |
4fd0db14 KR |
912 | @code{and-let*} is good for calculations where a @code{#f} value means |
913 | termination, but where a non-@code{#f} value is going to be needed in | |
914 | subsequent expressions. | |
915 | ||
916 | The following illustrates this, it returns text between brackets | |
917 | @samp{[...]} in a string, or @code{#f} if there are no such brackets | |
918 | (ie.@: either @code{string-index} gives @code{#f}). | |
919 | ||
920 | @example | |
921 | (define (extract-brackets str) | |
922 | (and-let* ((start (string-index str #\[)) | |
923 | (end (string-index str #\] start))) | |
924 | (substring str (1+ start) end))) | |
925 | @end example | |
926 | ||
927 | The following shows plain variables and expressions tested too. | |
928 | @code{diagnostic-levels} is taken to be an alist associating a | |
929 | diagnostic type with a level. @code{str} is printed only if the type | |
930 | is known and its level is high enough. | |
931 | ||
932 | @example | |
933 | (define (show-diagnostic type str) | |
934 | (and-let* (want-diagnostics | |
935 | (level (assq-ref diagnostic-levels type)) | |
936 | ((>= level current-diagnostic-level))) | |
937 | (display str))) | |
938 | @end example | |
939 | ||
940 | The advantage of @code{and-let*} is that an extended sequence of | |
941 | expressions and tests doesn't require lots of nesting as would arise | |
942 | from separate @code{and} and @code{let*}, or from @code{cond} with | |
943 | @code{=>}. | |
944 | ||
945 | @end deffn | |
a0e07ba4 NJ |
946 | |
947 | ||
948 | @node SRFI-4 | |
3229f68b | 949 | @subsection SRFI-4 - Homogeneous numeric vector datatypes |
8742c48b | 950 | @cindex SRFI-4 |
a0e07ba4 NJ |
951 | |
952 | @c FIXME::martin: Review me! | |
953 | ||
f85f9591 KR |
954 | SRFI-4 defines a set of datatypes and functions for vectors whose |
955 | elements are numbers, all of the same numeric type. Vectors for | |
956 | signed and unsigned exact integers and inexact reals in several | |
957 | precisions are available. Being homogeneous means they require less | |
958 | memory than normal vectors. | |
a0e07ba4 | 959 | |
f85f9591 KR |
960 | The functions and the read syntax in this section are made available |
961 | with | |
a0e07ba4 | 962 | |
f85f9591 KR |
963 | @lisp |
964 | (use-modules (srfi srfi-4)) | |
965 | @end lisp | |
a0e07ba4 | 966 | |
f85f9591 KR |
967 | Procedures similar to the vector procedures (@pxref{Vectors}) are |
968 | provided for handling these homogeneous vectors, but they are distinct | |
969 | datatypes and the two cannot be inter-mixed. | |
a0e07ba4 NJ |
970 | |
971 | Ten vector data types are provided: Unsigned and signed integer values | |
972 | with 8, 16, 32 and 64 bits and floating point values with 32 and 64 | |
f85f9591 KR |
973 | bits. The type is indicated by a tag in the function names, |
974 | @code{u8}, @code{s8}, @code{u16}, @code{s16}, @code{u32}, @code{s32}, | |
975 | @code{u64}, @code{s64}, @code{f32}, @code{f64}. | |
a0e07ba4 | 976 | |
f85f9591 KR |
977 | The external representation (ie.@: read syntax) for these vectors is |
978 | similar to normal Scheme vectors, but with an additional tag | |
979 | indiciating the vector's type. For example, | |
a0e07ba4 NJ |
980 | |
981 | @lisp | |
982 | #u16(1 2 3) | |
a0e07ba4 NJ |
983 | #f64(3.1415 2.71) |
984 | @end lisp | |
985 | ||
f85f9591 KR |
986 | Note that the read syntax for floating-point here conflicts with |
987 | @code{#f} for false. In Standard Scheme one can write @code{(1 | |
988 | #f3)} for a three element list @code{(1 #f 3)}, but with the SRFI-4 | |
989 | module @code{(1 #f3)} is invalid. @code{(1 #f 3)} is almost certainly | |
990 | what one should write anyway to make the intention clear, so this is | |
991 | rarely a problem. | |
992 | ||
993 | @deffn {Scheme Procedure} u8vector? obj | |
994 | @deffnx {Scheme Procedure} s8vector? obj | |
995 | @deffnx {Scheme Procedure} u16vector? obj | |
996 | @deffnx {Scheme Procedure} s16vector? obj | |
997 | @deffnx {Scheme Procedure} u32vector? obj | |
998 | @deffnx {Scheme Procedure} s32vector? obj | |
999 | @deffnx {Scheme Procedure} u64vector? obj | |
1000 | @deffnx {Scheme Procedure} s64vector? obj | |
1001 | @deffnx {Scheme Procedure} f32vector? obj | |
1002 | @deffnx {Scheme Procedure} f64vector? obj | |
1003 | Return @code{#t} if @var{obj} is a homogeneous numeric vector of the | |
1004 | indicated type. | |
1005 | @end deffn | |
1006 | ||
1007 | @deffn {Scheme Procedure} make-u8vector n [value] | |
1008 | @deffnx {Scheme Procedure} make-s8vector n [value] | |
1009 | @deffnx {Scheme Procedure} make-u16vector n [value] | |
1010 | @deffnx {Scheme Procedure} make-s16vector n [value] | |
1011 | @deffnx {Scheme Procedure} make-u32vector n [value] | |
1012 | @deffnx {Scheme Procedure} make-s32vector n [value] | |
1013 | @deffnx {Scheme Procedure} make-u64vector n [value] | |
1014 | @deffnx {Scheme Procedure} make-s64vector n [value] | |
1015 | @deffnx {Scheme Procedure} make-f32vector n [value] | |
1016 | @deffnx {Scheme Procedure} make-f64vector n [value] | |
1017 | Return a newly allocated homogeneous numeric vector holding @var{n} | |
1018 | elements of the indicated type. If @var{value} is given, the vector | |
1019 | is initialized with that value, otherwise the contents are | |
1020 | unspecified. | |
a0e07ba4 NJ |
1021 | @end deffn |
1022 | ||
f85f9591 KR |
1023 | @deffn {Scheme Procedure} u8vector value @dots{} |
1024 | @deffnx {Scheme Procedure} s8vector value @dots{} | |
1025 | @deffnx {Scheme Procedure} u16vector value @dots{} | |
1026 | @deffnx {Scheme Procedure} s16vector value @dots{} | |
1027 | @deffnx {Scheme Procedure} u32vector value @dots{} | |
1028 | @deffnx {Scheme Procedure} s32vector value @dots{} | |
1029 | @deffnx {Scheme Procedure} u64vector value @dots{} | |
1030 | @deffnx {Scheme Procedure} s64vector value @dots{} | |
1031 | @deffnx {Scheme Procedure} f32vector value @dots{} | |
1032 | @deffnx {Scheme Procedure} f64vector value @dots{} | |
1033 | Return a newly allocated homogeneous numeric vector of the indicated | |
1034 | type, holding the given parameter @var{value}s. The vector length is | |
1035 | the number of parameters given. | |
1036 | @end deffn | |
1037 | ||
1038 | @deffn {Scheme Procedure} u8vector-length vec | |
1039 | @deffnx {Scheme Procedure} s8vector-length vec | |
1040 | @deffnx {Scheme Procedure} u16vector-length vec | |
1041 | @deffnx {Scheme Procedure} s16vector-length vec | |
1042 | @deffnx {Scheme Procedure} u32vector-length vec | |
1043 | @deffnx {Scheme Procedure} s32vector-length vec | |
1044 | @deffnx {Scheme Procedure} u64vector-length vec | |
1045 | @deffnx {Scheme Procedure} s64vector-length vec | |
1046 | @deffnx {Scheme Procedure} f32vector-length vec | |
1047 | @deffnx {Scheme Procedure} f64vector-length vec | |
1048 | Return the number of elements in @var{vec}. | |
1049 | @end deffn | |
1050 | ||
1051 | @deffn {Scheme Procedure} u8vector-ref vec i | |
1052 | @deffnx {Scheme Procedure} s8vector-ref vec i | |
1053 | @deffnx {Scheme Procedure} u16vector-ref vec i | |
1054 | @deffnx {Scheme Procedure} s16vector-ref vec i | |
1055 | @deffnx {Scheme Procedure} u32vector-ref vec i | |
1056 | @deffnx {Scheme Procedure} s32vector-ref vec i | |
1057 | @deffnx {Scheme Procedure} u64vector-ref vec i | |
1058 | @deffnx {Scheme Procedure} s64vector-ref vec i | |
1059 | @deffnx {Scheme Procedure} f32vector-ref vec i | |
1060 | @deffnx {Scheme Procedure} f64vector-ref vec i | |
1061 | Return the element at index @var{i} in @var{vec}. The first element | |
1062 | in @var{vec} is index 0. | |
1063 | @end deffn | |
1064 | ||
1065 | @deffn {Scheme Procedure} u8vector-ref vec i value | |
1066 | @deffnx {Scheme Procedure} s8vector-ref vec i value | |
1067 | @deffnx {Scheme Procedure} u16vector-ref vec i value | |
1068 | @deffnx {Scheme Procedure} s16vector-ref vec i value | |
1069 | @deffnx {Scheme Procedure} u32vector-ref vec i value | |
1070 | @deffnx {Scheme Procedure} s32vector-ref vec i value | |
1071 | @deffnx {Scheme Procedure} u64vector-ref vec i value | |
1072 | @deffnx {Scheme Procedure} s64vector-ref vec i value | |
1073 | @deffnx {Scheme Procedure} f32vector-ref vec i value | |
1074 | @deffnx {Scheme Procedure} f64vector-ref vec i value | |
1075 | Set the element at index @var{i} in @var{vec} to @var{value}. The | |
1076 | first element in @var{vec} is index 0. The return value is | |
1077 | unspecified. | |
a0e07ba4 NJ |
1078 | @end deffn |
1079 | ||
f85f9591 KR |
1080 | @deffn {Scheme Procedure} u8vector->list vec |
1081 | @deffnx {Scheme Procedure} s8vector->list vec | |
1082 | @deffnx {Scheme Procedure} u16vector->list vec | |
1083 | @deffnx {Scheme Procedure} s16vector->list vec | |
1084 | @deffnx {Scheme Procedure} u32vector->list vec | |
1085 | @deffnx {Scheme Procedure} s32vector->list vec | |
1086 | @deffnx {Scheme Procedure} u64vector->list vec | |
1087 | @deffnx {Scheme Procedure} s64vector->list vec | |
1088 | @deffnx {Scheme Procedure} f32vector->list vec | |
1089 | @deffnx {Scheme Procedure} f64vector->list vec | |
1090 | Return a newly allocated list holding all elements of @var{vec}. | |
1091 | @end deffn | |
1092 | ||
1093 | @deffn {Scheme Procedure} list->u8vector lst | |
1094 | @deffnx {Scheme Procedure} list->s8vector lst | |
1095 | @deffnx {Scheme Procedure} list->u16vector lst | |
1096 | @deffnx {Scheme Procedure} list->s16vector lst | |
1097 | @deffnx {Scheme Procedure} list->u32vector lst | |
1098 | @deffnx {Scheme Procedure} list->s32vector lst | |
1099 | @deffnx {Scheme Procedure} list->u64vector lst | |
1100 | @deffnx {Scheme Procedure} list->s64vector lst | |
1101 | @deffnx {Scheme Procedure} list->f32vector lst | |
1102 | @deffnx {Scheme Procedure} list->f64vector lst | |
1103 | Return a newly allocated homogeneous numeric vector of the indicated type, | |
a0e07ba4 NJ |
1104 | initialized with the elements of the list @var{lst}. |
1105 | @end deffn | |
1106 | ||
1107 | ||
1108 | @node SRFI-6 | |
3229f68b | 1109 | @subsection SRFI-6 - Basic String Ports |
8742c48b | 1110 | @cindex SRFI-6 |
a0e07ba4 NJ |
1111 | |
1112 | SRFI-6 defines the procedures @code{open-input-string}, | |
1113 | @code{open-output-string} and @code{get-output-string}. These | |
1114 | procedures are included in the Guile core, so using this module does not | |
1115 | make any difference at the moment. But it is possible that support for | |
1116 | SRFI-6 will be factored out of the core library in the future, so using | |
1117 | this module does not hurt, after all. | |
1118 | ||
1119 | @node SRFI-8 | |
3229f68b | 1120 | @subsection SRFI-8 - receive |
8742c48b | 1121 | @cindex SRFI-8 |
a0e07ba4 NJ |
1122 | |
1123 | @code{receive} is a syntax for making the handling of multiple-value | |
1124 | procedures easier. It is documented in @xref{Multiple Values}. | |
1125 | ||
1126 | ||
1127 | @node SRFI-9 | |
3229f68b | 1128 | @subsection SRFI-9 - define-record-type |
8742c48b | 1129 | @cindex SRFI-9 |
a0e07ba4 | 1130 | |
6afe385d KR |
1131 | This SRFI is a syntax for defining new record types and creating |
1132 | predicate, constructor, and field getter and setter functions. In | |
1133 | Guile this is simply an alternate interface to the core record | |
1134 | functionality (@pxref{Records}). It can be used with, | |
a0e07ba4 | 1135 | |
6afe385d KR |
1136 | @example |
1137 | (use-modules (srfi srfi-9)) | |
1138 | @end example | |
1139 | ||
1140 | @deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{} | |
1141 | @sp 1 | |
1142 | Create a new record type, and make various @code{define}s for using | |
1143 | it. This syntax can only occur at the top-level, not nested within | |
1144 | some other form. | |
1145 | ||
1146 | @var{type} is bound to the record type, which is as per the return | |
1147 | from the core @code{make-record-type}. @var{type} also provides the | |
1148 | name for the record, as per @code{record-type-name}. | |
1149 | ||
1150 | @var{constructor} is bound to a function to be called as | |
1151 | @code{(@var{constructor} fieldval @dots{})} to create a new record of | |
1152 | this type. The arguments are initial values for the fields, one | |
1153 | argument for each field, in the order they appear in the | |
1154 | @code{define-record-type} form. | |
1155 | ||
1156 | The @var{fieldname}s provide the names for the record fields, as per | |
1157 | the core @code{record-type-fields} etc, and are referred to in the | |
1158 | subsequent accessor/modifier forms. | |
1159 | ||
1160 | @var{predictate} is bound to a function to be called as | |
1161 | @code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f} | |
1162 | according to whether @var{obj} is a record of this type. | |
1163 | ||
1164 | Each @var{accessor} is bound to a function to be called | |
1165 | @code{(@var{accessor} record)} to retrieve the respective field from a | |
1166 | @var{record}. Similarly each @var{modifier} is bound to a function to | |
1167 | be called @code{(@var{modifier} record val)} to set the respective | |
1168 | field in a @var{record}. | |
1169 | @end deffn | |
1170 | ||
1171 | @noindent | |
1172 | An example will illustrate typical usage, | |
a0e07ba4 NJ |
1173 | |
1174 | @example | |
6afe385d KR |
1175 | (define-record-type employee-type |
1176 | (make-employee name age salary) | |
1177 | employee? | |
1178 | (name get-employee-name) | |
1179 | (age get-employee-age set-employee-age) | |
1180 | (salary get-employee-salary set-employee-salary)) | |
a0e07ba4 NJ |
1181 | @end example |
1182 | ||
6afe385d KR |
1183 | This creates a new employee data type, with name, age and salary |
1184 | fields. Accessor functions are created for each field, but no | |
1185 | modifier function for the name (the intention in this example being | |
1186 | that it's established only when an employee object is created). These | |
1187 | can all then be used as for example, | |
a0e07ba4 NJ |
1188 | |
1189 | @example | |
6afe385d KR |
1190 | employee-type @result{} #<record-type employee-type> |
1191 | ||
1192 | (define fred (make-employee "Fred" 45 20000.00)) | |
1193 | ||
1194 | (employee? fred) @result{} #t | |
1195 | (get-employee-age fred) @result{} 45 | |
1196 | (set-employee-salary fred 25000.00) ;; pay rise | |
a0e07ba4 NJ |
1197 | @end example |
1198 | ||
6afe385d KR |
1199 | The functions created by @code{define-record-type} are ordinary |
1200 | top-level @code{define}s. They can be redefined or @code{set!} as | |
1201 | desired, exported from a module, etc. | |
1202 | ||
a0e07ba4 NJ |
1203 | |
1204 | @node SRFI-10 | |
3229f68b | 1205 | @subsection SRFI-10 - Hash-Comma Reader Extension |
8742c48b | 1206 | @cindex SRFI-10 |
a0e07ba4 NJ |
1207 | |
1208 | @cindex hash-comma | |
1209 | @cindex #,() | |
1210 | The module @code{(srfi srfi-10)} implements the syntax extension | |
1211 | @code{#,()}, also called hash-comma, which is defined in SRFI-10. | |
1212 | ||
1213 | The support for SRFI-10 consists of the procedure | |
1214 | @code{define-reader-ctor} for defining new reader constructors and the | |
1215 | read syntax form | |
1216 | ||
1217 | @example | |
1218 | #,(@var{ctor} @var{datum} ...) | |
1219 | @end example | |
1220 | ||
1221 | where @var{ctor} must be a symbol for which a read constructor was | |
85a9b4ed | 1222 | defined previously, using @code{define-reader-ctor}. |
a0e07ba4 NJ |
1223 | |
1224 | Example: | |
1225 | ||
1226 | @lisp | |
4310df36 | 1227 | (use-modules (ice-9 rdelim)) ; for read-line |
a0e07ba4 NJ |
1228 | (define-reader-ctor 'file open-input-file) |
1229 | (define f '#,(file "/etc/passwd")) | |
1230 | (read-line f) | |
1231 | @result{} | |
1232 | "root:x:0:0:root:/root:/bin/bash" | |
1233 | @end lisp | |
1234 | ||
1235 | Please note the quote before the @code{#,(file ...)} expression. This | |
1236 | is necessary because ports are not self-evaluating in Guile. | |
1237 | ||
8f85c0c6 | 1238 | @deffn {Scheme Procedure} define-reader-ctor symbol proc |
a0e07ba4 NJ |
1239 | Define @var{proc} as the reader constructor for hash-comma forms with a |
1240 | tag @var{symbol}. @var{proc} will be applied to the datum(s) following | |
1241 | the tag in the hash-comma expression after the complete form has been | |
1242 | read in. The result of @var{proc} is returned by the Scheme reader. | |
1243 | @end deffn | |
1244 | ||
1245 | ||
1246 | @node SRFI-11 | |
3229f68b | 1247 | @subsection SRFI-11 - let-values |
8742c48b | 1248 | @cindex SRFI-11 |
a0e07ba4 | 1249 | |
8742c48b KR |
1250 | @findex let-values |
1251 | @findex let-values* | |
a0e07ba4 NJ |
1252 | This module implements the binding forms for multiple values |
1253 | @code{let-values} and @code{let-values*}. These forms are similar to | |
1254 | @code{let} and @code{let*} (@pxref{Local Bindings}), but they support | |
1255 | binding of the values returned by multiple-valued expressions. | |
1256 | ||
1257 | Write @code{(use-modules (srfi srfi-11))} to make the bindings | |
1258 | available. | |
1259 | ||
1260 | @lisp | |
1261 | (let-values (((x y) (values 1 2)) | |
1262 | ((z f) (values 3 4))) | |
1263 | (+ x y z f)) | |
1264 | @result{} | |
1265 | 10 | |
1266 | @end lisp | |
1267 | ||
1268 | @code{let-values} performs all bindings simultaneously, which means that | |
1269 | no expression in the binding clauses may refer to variables bound in the | |
1270 | same clause list. @code{let-values*}, on the other hand, performs the | |
1271 | bindings sequentially, just like @code{let*} does for single-valued | |
1272 | expressions. | |
1273 | ||
1274 | ||
1275 | @node SRFI-13 | |
3229f68b | 1276 | @subsection SRFI-13 - String Library |
8742c48b | 1277 | @cindex SRFI-13 |
a0e07ba4 | 1278 | |
5676b4fa | 1279 | The SRFI-13 procedures are always available, @xref{Strings}. |
a0e07ba4 NJ |
1280 | |
1281 | @node SRFI-14 | |
3229f68b | 1282 | @subsection SRFI-14 - Character-set Library |
8742c48b | 1283 | @cindex SRFI-14 |
a0e07ba4 | 1284 | |
050ab45f MV |
1285 | The SRFI-14 data type and procedures are always available, |
1286 | @xref{Character Sets}. | |
a0e07ba4 NJ |
1287 | |
1288 | @node SRFI-16 | |
3229f68b | 1289 | @subsection SRFI-16 - case-lambda |
8742c48b | 1290 | @cindex SRFI-16 |
a0e07ba4 NJ |
1291 | |
1292 | @c FIXME::martin: Review me! | |
1293 | ||
8742c48b | 1294 | @findex case-lambda |
a0e07ba4 NJ |
1295 | The syntactic form @code{case-lambda} creates procedures, just like |
1296 | @code{lambda}, but has syntactic extensions for writing procedures of | |
1297 | varying arity easier. | |
1298 | ||
1299 | The syntax of the @code{case-lambda} form is defined in the following | |
1300 | EBNF grammar. | |
1301 | ||
1302 | @example | |
1303 | @group | |
1304 | <case-lambda> | |
1305 | --> (case-lambda <case-lambda-clause>) | |
1306 | <case-lambda-clause> | |
1307 | --> (<formals> <definition-or-command>*) | |
1308 | <formals> | |
1309 | --> (<identifier>*) | |
1310 | | (<identifier>* . <identifier>) | |
1311 | | <identifier> | |
1312 | @end group | |
1313 | @end example | |
1314 | ||
1315 | The value returned by a @code{case-lambda} form is a procedure which | |
1316 | matches the number of actual arguments against the formals in the | |
1317 | various clauses, in order. @dfn{Formals} means a formal argument list | |
1318 | just like with @code{lambda} (@pxref{Lambda}). The first matching clause | |
1319 | is selected, the corresponding values from the actual parameter list are | |
1320 | bound to the variable names in the clauses and the body of the clause is | |
1321 | evaluated. If no clause matches, an error is signalled. | |
1322 | ||
1323 | The following (silly) definition creates a procedure @var{foo} which | |
1324 | acts differently, depending on the number of actual arguments. If one | |
1325 | argument is given, the constant @code{#t} is returned, two arguments are | |
1326 | added and if more arguments are passed, their product is calculated. | |
1327 | ||
1328 | @lisp | |
1329 | (define foo (case-lambda | |
1330 | ((x) #t) | |
1331 | ((x y) (+ x y)) | |
1332 | (z | |
1333 | (apply * z)))) | |
1334 | (foo 'bar) | |
1335 | @result{} | |
1336 | #t | |
1337 | (foo 2 4) | |
1338 | @result{} | |
1339 | 6 | |
1340 | (foo 3 3 3) | |
1341 | @result{} | |
1342 | 27 | |
1343 | (foo) | |
1344 | @result{} | |
1345 | 1 | |
1346 | @end lisp | |
1347 | ||
1348 | The last expression evaluates to 1 because the last clause is matched, | |
1349 | @var{z} is bound to the empty list and the following multiplication, | |
1350 | applied to zero arguments, yields 1. | |
1351 | ||
1352 | ||
1353 | @node SRFI-17 | |
3229f68b | 1354 | @subsection SRFI-17 - Generalized set! |
8742c48b | 1355 | @cindex SRFI-17 |
a0e07ba4 NJ |
1356 | |
1357 | This is an implementation of SRFI-17: Generalized set! | |
1358 | ||
8742c48b | 1359 | @findex getter-with-setter |
a0e07ba4 NJ |
1360 | It exports the Guile procedure @code{make-procedure-with-setter} under |
1361 | the SRFI name @code{getter-with-setter} and exports the standard | |
1362 | procedures @code{car}, @code{cdr}, @dots{}, @code{cdddr}, | |
1363 | @code{string-ref} and @code{vector-ref} as procedures with setters, as | |
1364 | required by the SRFI. | |
1365 | ||
1366 | SRFI-17 was heavily criticized during its discussion period but it was | |
1367 | finalized anyway. One issue was its concept of globally associating | |
1368 | setter @dfn{properties} with (procedure) values, which is non-Schemy. | |
1369 | For this reason, this implementation chooses not to provide a way to set | |
1370 | the setter of a procedure. In fact, @code{(set! (setter @var{proc}) | |
1371 | @var{setter})} signals an error. The only way to attach a setter to a | |
1372 | procedure is to create a new object (a @dfn{procedure with setter}) via | |
1373 | the @code{getter-with-setter} procedure. This procedure is also | |
1374 | specified in the SRFI. Using it avoids the described problems. | |
1375 | ||
12991fed TTN |
1376 | |
1377 | @node SRFI-19 | |
3229f68b | 1378 | @subsection SRFI-19 - Time/Date Library |
8742c48b | 1379 | @cindex SRFI-19 |
12991fed | 1380 | |
85600a0f KR |
1381 | This is an implementation of the SRFI-19 time/date library. The |
1382 | functions and variables described here are provided by | |
12991fed TTN |
1383 | |
1384 | @example | |
85600a0f | 1385 | (use-modules (srfi srfi-19)) |
12991fed TTN |
1386 | @end example |
1387 | ||
85600a0f KR |
1388 | @menu |
1389 | * SRFI-19 Introduction:: | |
1390 | * SRFI-19 Time:: | |
1391 | * SRFI-19 Date:: | |
1392 | * SRFI-19 Time/Date conversions:: | |
1393 | * SRFI-19 Date to string:: | |
1394 | * SRFI-19 String to date:: | |
1395 | @end menu | |
12991fed | 1396 | |
85600a0f | 1397 | @node SRFI-19 Introduction |
3229f68b | 1398 | @subsubsection SRFI-19 Introduction |
85600a0f KR |
1399 | |
1400 | @cindex universal time | |
1401 | @cindex atomic time | |
1402 | @cindex UTC | |
1403 | @cindex TAI | |
1404 | This module implements time and date representations and calculations, | |
1405 | in various time systems, including universal time (UTC) and atomic | |
1406 | time (TAI). | |
1407 | ||
1408 | For those not familiar with these time systems, TAI is based on a | |
1409 | fixed length second derived from oscillations of certain atoms. UTC | |
1410 | differs from TAI by an integral number of seconds, which is increased | |
1411 | or decreased at announced times to keep UTC aligned to a mean solar | |
1412 | day (the orbit and rotation of the earth are not quite constant). | |
1413 | ||
1414 | @cindex leap second | |
1415 | So far, only increases in the TAI | |
1416 | @tex | |
1417 | $\leftrightarrow$ | |
1418 | @end tex | |
1419 | @ifnottex | |
1420 | <-> | |
1421 | @end ifnottex | |
1422 | UTC difference have been needed. Such an increase is a ``leap | |
1423 | second'', an extra second of TAI introduced at the end of a UTC day. | |
1424 | When working entirely within UTC this is never seen, every day simply | |
1425 | has 86400 seconds. But when converting from TAI to a UTC date, an | |
1426 | extra 23:59:60 is present, where normally a day would end at 23:59:59. | |
1427 | Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI | |
1428 | seconds. | |
1429 | ||
1430 | @cindex system clock | |
1431 | In the current implementation, the system clock is assumed to be UTC, | |
1432 | and a table of leap seconds in the code converts to TAI. See comments | |
1433 | in @file{srfi-19.scm} for how to update this table. | |
1434 | ||
1435 | @cindex julian day | |
1436 | @cindex modified julian day | |
1437 | Also, for those not familiar with the terminology, a @dfn{Julian Day} | |
1438 | is a real number which is a count of days and fraction of a day, in | |
1439 | UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan | |
1440 | 4713 B.C. And a @dfn{Modified Julian Day} is the same, but starting | |
1441 | from 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. | |
1442 | ||
1443 | @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at | |
1444 | @c noon, UTC), but this is incorrect. It looks like it might have | |
1445 | @c arisen from the code incorrectly treating years a multiple of 100 | |
1446 | @c but not 400 prior to 1582 as leap years, where instead the Julian | |
1447 | @c calendar should be used so all multiples of 4 before 1582 are leap | |
1448 | @c years. | |
1449 | ||
1450 | ||
1451 | @node SRFI-19 Time | |
3229f68b | 1452 | @subsubsection SRFI-19 Time |
85600a0f KR |
1453 | @cindex time |
1454 | ||
1455 | A @dfn{time} object has type, seconds and nanoseconds fields | |
1456 | representing a point in time starting from some epoch. This is an | |
1457 | arbitrary point in time, not just a time of day. Although times are | |
1458 | represented in nanoseconds, the actual resolution may be lower. | |
1459 | ||
1460 | The following variables hold the possible time types. For instance | |
1461 | @code{(current-time time-process)} would give the current CPU process | |
1462 | time. | |
1463 | ||
1464 | @defvar time-utc | |
1465 | Universal Coordinated Time (UTC). | |
1466 | @cindex UTC | |
1467 | @end defvar | |
12991fed | 1468 | |
85600a0f KR |
1469 | @defvar time-tai |
1470 | International Atomic Time (TAI). | |
1471 | @cindex TAI | |
1472 | @end defvar | |
12991fed | 1473 | |
85600a0f KR |
1474 | @defvar time-monotonic |
1475 | Monotonic time, meaning a monotonically increasing time starting from | |
1476 | an unspecified epoch. | |
12991fed | 1477 | |
85600a0f KR |
1478 | Note that in the current implementation @code{time-monotonic} is the |
1479 | same as @code{time-tai}, and unfortunately is therefore affected by | |
1480 | adjustments to the system clock. Perhaps this will change in the | |
1481 | future. | |
1482 | @end defvar | |
12991fed | 1483 | |
85600a0f KR |
1484 | @defvar time-duration |
1485 | A duration, meaning simply a difference between two times. | |
1486 | @end defvar | |
12991fed | 1487 | |
85600a0f KR |
1488 | @defvar time-process |
1489 | CPU time spent in the current process, starting from when the process | |
1490 | began. | |
1491 | @cindex process time | |
1492 | @end defvar | |
12991fed | 1493 | |
85600a0f KR |
1494 | @defvar time-thread |
1495 | CPU time spent in the current thread. Not currently implemented. | |
1496 | @cindex thread time | |
1497 | @end defvar | |
12991fed | 1498 | |
85600a0f KR |
1499 | @sp 1 |
1500 | @defun time? obj | |
1501 | Return @code{#t} if @var{obj} is a time object, or @code{#f} if not. | |
1502 | @end defun | |
1503 | ||
1504 | @defun make-time type nanoseconds seconds | |
1505 | Create a time object with the given @var{type}, @var{seconds} and | |
1506 | @var{nanoseconds}. | |
1507 | @end defun | |
1508 | ||
1509 | @defun time-type time | |
1510 | @defunx time-nanosecond time | |
1511 | @defunx time-second time | |
1512 | @defunx set-time-type! time type | |
1513 | @defunx set-time-nanosecond! time nsec | |
1514 | @defunx set-time-second! time sec | |
1515 | Get or set the type, seconds or nanoseconds fields of a time object. | |
1516 | ||
1517 | @code{set-time-type!} merely changes the field, it doesn't convert the | |
1518 | time value. For conversions, see @ref{SRFI-19 Time/Date conversions}. | |
1519 | @end defun | |
1520 | ||
1521 | @defun copy-time time | |
1522 | Return a new time object, which is a copy of the given @var{time}. | |
1523 | @end defun | |
1524 | ||
1525 | @defun current-time [type] | |
1526 | Return the current time of the given @var{type}. The default | |
1527 | @var{type} is @code{time-utc}. | |
1528 | ||
1529 | Note that the name @code{current-time} conflicts with the Guile core | |
1530 | @code{current-time} function (@pxref{Time}). Applications wanting to | |
1531 | use both will need to use a different name for one of them. | |
1532 | @end defun | |
1533 | ||
1534 | @defun time-resolution [type] | |
1535 | Return the resolution, in nanoseconds, of the given time @var{type}. | |
1536 | The default @var{type} is @code{time-utc}. | |
1537 | @end defun | |
1538 | ||
1539 | @defun time<=? t1 t2 | |
1540 | @defunx time<? t1 t2 | |
1541 | @defunx time=? t1 t2 | |
1542 | @defunx time>=? t1 t2 | |
1543 | @defunx time>? t1 t2 | |
1544 | Return @code{#t} or @code{#f} according to the respective relation | |
1545 | between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2} | |
1546 | must be the same time type. | |
1547 | @end defun | |
1548 | ||
1549 | @defun time-difference t1 t2 | |
1550 | @defunx time-difference! t1 t2 | |
1551 | Return a time object of type @code{time-duration} representing the | |
1552 | period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be | |
1553 | the same time type. | |
1554 | ||
1555 | @code{time-difference} returns a new time object, | |
1556 | @code{time-difference!} may modify @var{t1} to form its return. | |
1557 | @end defun | |
1558 | ||
1559 | @defun add-duration time duration | |
1560 | @defunx add-duration! time duration | |
1561 | @defunx subtract-duration time duration | |
1562 | @defunx subtract-duration! time duration | |
1563 | Return a time object which is @var{time} with the given @var{duration} | |
1564 | added or subtracted. @var{duration} must be a time object of type | |
1565 | @code{time-duration}. | |
1566 | ||
1567 | @code{add-duration} and @code{subtract-duration} return a new time | |
1568 | object. @code{add-duration!} and @code{subtract-duration!} may modify | |
1569 | the given @var{time} to form their return. | |
1570 | @end defun | |
1571 | ||
1572 | ||
1573 | @node SRFI-19 Date | |
3229f68b | 1574 | @subsubsection SRFI-19 Date |
85600a0f KR |
1575 | @cindex date |
1576 | ||
1577 | A @dfn{date} object represents a date in the Gregorian calendar and a | |
1578 | time of day on that date in some timezone. | |
1579 | ||
1580 | The fields are year, month, day, hour, minute, second, nanoseconds and | |
1581 | timezone. A date object is immutable, its fields can be read but they | |
1582 | cannot be modified once the object is created. | |
1583 | ||
1584 | @defun date? obj | |
1585 | Return @code{#t} if @var{obj} is a date object, or @code{#f} if not. | |
1586 | @end defun | |
1587 | ||
1588 | @defun make-date nsecs seconds minutes hours date month year zone-offset | |
1589 | Create a new date object. | |
1590 | @c | |
1591 | @c FIXME: What can we say about the ranges of the values. The | |
1592 | @c current code looks it doesn't normalize, but expects then in their | |
1593 | @c usual range already. | |
1594 | @c | |
1595 | @end defun | |
1596 | ||
1597 | @defun date-nanosecond date | |
1598 | Nanoseconds, 0 to 999999999. | |
1599 | @end defun | |
1600 | ||
1601 | @defun date-second date | |
1602 | Seconds, 0 to 60. 0 to 59 is the usual range, 60 is for a leap second. | |
1603 | @end defun | |
1604 | ||
1605 | @defun date-minute date | |
1606 | Minutes, 0 to 59. | |
1607 | @end defun | |
1608 | ||
1609 | @defun date-hour date | |
1610 | Hour, 0 to 23. | |
1611 | @end defun | |
1612 | ||
1613 | @defun date-day date | |
1614 | Day of the month, 1 to 31 (or less, according to the month). | |
1615 | @end defun | |
1616 | ||
1617 | @defun date-month date | |
1618 | Month, 1 to 12. | |
1619 | @end defun | |
1620 | ||
1621 | @defun date-year date | |
1622 | Year, eg.@: 2003. | |
1623 | @end defun | |
1624 | ||
1625 | @defun date-zone-offset date | |
1626 | Time zone, an integer number of seconds east of Greenwich. | |
1627 | @end defun | |
1628 | ||
1629 | @defun date-year-day date | |
1630 | Day of the year, starting from 1 for 1st January. | |
1631 | @end defun | |
1632 | ||
1633 | @defun date-week-day date | |
1634 | Day of the week, starting from 0 for Sunday. | |
1635 | @end defun | |
1636 | ||
1637 | @defun date-week-number date dstartw | |
1638 | Week of the year, ignoring a first partial week. @var{dstartw} is the | |
1639 | day of the week which is taken to start a week, 0 for Sunday, 1 for | |
1640 | Monday, etc. | |
1641 | @c | |
1642 | @c FIXME: The spec doesn't say whether numbering starts at 0 or 1. | |
1643 | @c The code looks like it's 0, if that's the correct intention. | |
1644 | @c | |
1645 | @end defun | |
1646 | ||
1647 | @c The SRFI text doesn't actually give the default for tz-offset, but | |
1648 | @c the reference implementation has the local timezone and the | |
1649 | @c conversions functions all specify that, so it should be ok to | |
1650 | @c document it here. | |
1651 | @c | |
1652 | @defun current-date [tz-offset] | |
1653 | Return a date object representing the current date/time UTC. | |
1654 | @var{tz-offset} is seconds east of Greenwich, and defaults to the | |
1655 | local timezone. | |
1656 | @end defun | |
1657 | ||
1658 | @defun current-julian-day | |
1659 | @cindex julian day | |
1660 | Return the current Julian Day. | |
1661 | @end defun | |
1662 | ||
1663 | @defun current-modified-julian-day | |
1664 | @cindex modified julian day | |
1665 | Return the current Modified Julian Day. | |
1666 | @end defun | |
1667 | ||
1668 | ||
1669 | @node SRFI-19 Time/Date conversions | |
3229f68b | 1670 | @subsubsection SRFI-19 Time/Date conversions |
85600a0f KR |
1671 | |
1672 | @defun date->julian-day date | |
1673 | @defunx date->modified-julian-day date | |
1674 | @defunx date->time-monotonic date | |
1675 | @defunx date->time-tai date | |
1676 | @defunx date->time-utc date | |
1677 | @end defun | |
1678 | @defun julian-day->date jdn [tz-offset] | |
1679 | @defunx julian-day->time-monotonic jdn | |
1680 | @defunx julian-day->time-tai jdn | |
1681 | @defunx julian-day->time-utc jdn | |
1682 | @end defun | |
1683 | @defun modified-julian-day->date jdn [tz-offset] | |
1684 | @defunx modified-julian-day->time-monotonic jdn | |
1685 | @defunx modified-julian-day->time-tai jdn | |
1686 | @defunx modified-julian-day->time-utc jdn | |
1687 | @end defun | |
1688 | @defun time-monotonic->date time [tz-offset] | |
1689 | @defunx time-monotonic->time-tai time | |
1690 | @defunx time-monotonic->time-tai! time | |
1691 | @defunx time-monotonic->time-utc time | |
1692 | @defunx time-monotonic->time-utc! time | |
1693 | @end defun | |
1694 | @defun time-tai->date time [tz-offset] | |
1695 | @defunx time-tai->julian-day time | |
1696 | @defunx time-tai->modified-julian-day time | |
1697 | @defunx time-tai->time-monotonic time | |
1698 | @defunx time-tai->time-monotonic! time | |
1699 | @defunx time-tai->time-utc time | |
1700 | @defunx time-tai->time-utc! time | |
1701 | @end defun | |
1702 | @defun time-utc->date time [tz-offset] | |
1703 | @defunx time-utc->julian-day time | |
1704 | @defunx time-utc->modified-julian-day time | |
1705 | @defunx time-utc->time-monotonic time | |
1706 | @defunx time-utc->time-monotonic! time | |
1707 | @defunx time-utc->time-tai time | |
1708 | @defunx time-utc->time-tai! time | |
1709 | @sp 1 | |
1710 | Convert between dates, times and days of the respective types. For | |
1711 | instance @code{time-tai->time-utc} accepts a @var{time} object of type | |
1712 | @code{time-tai} and returns an object of type @code{time-utc}. | |
1713 | ||
1714 | For conversions to dates, @var{tz-offset} is seconds east of | |
1715 | Greenwich. The default is the local timezone. | |
1716 | ||
1717 | The @code{!} variants may modify their @var{time} argument to form | |
1718 | their return. The plain functions create a new object. | |
1719 | @end defun | |
1720 | ||
1721 | @node SRFI-19 Date to string | |
3229f68b | 1722 | @subsubsection SRFI-19 Date to string |
85600a0f KR |
1723 | @cindex date to string |
1724 | ||
1725 | @defun date->string date [format] | |
1726 | Convert a date to a string under the control of a format. | |
1727 | @var{format} should be a string containing @samp{~} escapes, which | |
1728 | will be expanded as per the following conversion table. The default | |
1729 | @var{format} is @samp{~c}, a locale-dependent date and time. | |
1730 | ||
1731 | Many of these conversion characters are the same as POSIX | |
1732 | @code{strftime} (@pxref{Time}), but there are some extras and some | |
1733 | variations. | |
1734 | ||
1735 | @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM} | |
1736 | @item @nicode{~~} @tab literal ~ | |
1737 | @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun} | |
1738 | @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday} | |
1739 | @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan} | |
1740 | @item @nicode{~B} @tab locale full month, eg.@: @samp{January} | |
1741 | @item @nicode{~c} @tab locale date and time, eg.@: @* | |
1742 | @samp{Fri Jul 14 20:28:42-0400 2000} | |
1743 | @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31} | |
1744 | ||
1745 | @c Spec says d/m/y, reference implementation says m/d/y. | |
1746 | @c Apparently the reference code was the intention, but would like to | |
1747 | @c see an errata published for the spec before contradicting it here. | |
1748 | @c | |
1749 | @c @item @nicode{~D} @tab date @nicode{~d/~m/~y} | |
1750 | ||
1751 | @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31} | |
1752 | @item @nicode{~f} @tab seconds and fractional seconds, | |
1753 | with locale decimal point, eg.@: @samp{5.2} | |
1754 | @item @nicode{~h} @tab same as @nicode{~b} | |
1755 | @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23} | |
1756 | @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12} | |
1757 | @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366} | |
1758 | @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23} | |
1759 | @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12} | |
1760 | @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12} | |
1761 | @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59} | |
1762 | @item @nicode{~n} @tab newline | |
1763 | @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999} | |
1764 | @item @nicode{~p} @tab locale AM or PM | |
1765 | @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p} | |
1766 | @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC | |
1767 | @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @* | |
1768 | (usual limit is 59, 60 is a leap second) | |
1769 | @item @nicode{~t} @tab horizontal tab character | |
1770 | @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S} | |
1771 | @item @nicode{~U} @tab week of year, Sunday first day of week, | |
1772 | @samp{00} to @samp{52} | |
1773 | @item @nicode{~V} @tab week of year, Monday first day of week, | |
1774 | @samp{01} to @samp{53} | |
1775 | @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6} | |
1776 | @item @nicode{~W} @tab week of year, Monday first day of week, | |
1777 | @samp{00} to @samp{52} | |
1778 | ||
1779 | @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale | |
1780 | @c date. The reference code has ~x as the locale date and ~X as a | |
1781 | @c locale time. The rule is apparently that the code should be | |
1782 | @c believed, but would like to see an errata for the spec before | |
1783 | @c contradicting it here. | |
1784 | @c | |
1785 | @c @item @nicode{~x} @tab week of year, Monday as first day of week, | |
1786 | @c @samp{00} to @samp{53} | |
1787 | @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00} | |
1788 | ||
1789 | @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99} | |
1790 | @item @nicode{~Y} @tab year, full, eg.@: @samp{2003} | |
1791 | @item @nicode{~z} @tab time zone, RFC-822 style | |
1792 | @item @nicode{~Z} @tab time zone symbol (not currently implemented) | |
1793 | @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d} | |
1794 | @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~k:~M:~S~z} | |
1795 | @item @nicode{~3} @tab ISO-8601 time, @samp{~k:~M:~S} | |
1796 | @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~k:~M:~S~z} | |
1797 | @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~k:~M:~S} | |
1798 | @end multitable | |
1799 | @end defun | |
1800 | ||
1801 | Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently | |
1802 | described here, since the specification and reference implementation | |
1803 | differ. | |
1804 | ||
1805 | Currently Guile doesn't implement any localizations for the above, all | |
1806 | outputs are in English, and the @samp{~c} conversion is POSIX | |
1807 | @code{ctime} style @samp{~a ~b ~d ~H:~M:~S~z ~Y}. This may change in | |
1808 | the future. | |
1809 | ||
1810 | ||
1811 | @node SRFI-19 String to date | |
3229f68b | 1812 | @subsubsection SRFI-19 String to date |
85600a0f KR |
1813 | @cindex string to date |
1814 | ||
1815 | @c FIXME: Can we say what happens when an incomplete date is | |
1816 | @c converted? Ie. fields left as 0, or what? The spec seems to be | |
1817 | @c silent on this. | |
1818 | ||
1819 | @defun string->date input template | |
1820 | Convert an @var{input} string to a date under the control of a | |
1821 | @var{template} string. Return a newly created date object. | |
1822 | ||
1823 | Literal characters in @var{template} must match characters in | |
1824 | @var{input} and @samp{~} escapes must match the input forms described | |
1825 | in the table below. ``Skip to'' means characters up to one of the | |
1826 | given type are ignored, or ``no skip'' for no skipping. ``Read'' is | |
1827 | what's then read, and ``Set'' is the field affected in the date | |
1828 | object. | |
1829 | ||
1830 | For example @samp{~Y} skips input characters until a digit is reached, | |
1831 | at which point it expects a year and stores that to the year field of | |
1832 | the date. | |
1833 | ||
1834 | @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}} | |
1835 | @item | |
1836 | @tab Skip to | |
1837 | @tab Read | |
1838 | @tab Set | |
1839 | ||
1840 | @item @nicode{~~} | |
1841 | @tab no skip | |
1842 | @tab literal ~ | |
1843 | @tab nothing | |
1844 | ||
1845 | @item @nicode{~a} | |
1846 | @tab @nicode{char-alphabetic?} | |
1847 | @tab locale abbreviated weekday name | |
1848 | @tab nothing | |
1849 | ||
1850 | @item @nicode{~A} | |
1851 | @tab @nicode{char-alphabetic?} | |
1852 | @tab locale full weekday name | |
1853 | @tab nothing | |
1854 | ||
1855 | @c Note that the SRFI spec says that ~b and ~B don't set anything, | |
1856 | @c but that looks like a mistake. The reference implementation sets | |
1857 | @c the month field, which seems sensible and is what we describe | |
1858 | @c here. | |
1859 | ||
1860 | @item @nicode{~b} | |
1861 | @tab @nicode{char-alphabetic?} | |
1862 | @tab locale abbreviated month name | |
1863 | @tab @nicode{date-month} | |
1864 | ||
1865 | @item @nicode{~B} | |
1866 | @tab @nicode{char-alphabetic?} | |
1867 | @tab locale full month name | |
1868 | @tab @nicode{date-month} | |
1869 | ||
1870 | @item @nicode{~d} | |
1871 | @tab @nicode{char-numeric?} | |
1872 | @tab day of month | |
1873 | @tab @nicode{date-day} | |
1874 | ||
1875 | @item @nicode{~e} | |
1876 | @tab no skip | |
1877 | @tab day of month, blank padded | |
1878 | @tab @nicode{date-day} | |
1879 | ||
1880 | @item @nicode{~h} | |
1881 | @tab same as @samp{~b} | |
1882 | ||
1883 | @item @nicode{~H} | |
1884 | @tab @nicode{char-numeric?} | |
1885 | @tab hour | |
1886 | @tab @nicode{date-hour} | |
1887 | ||
1888 | @item @nicode{~k} | |
1889 | @tab no skip | |
1890 | @tab hour, blank padded | |
1891 | @tab @nicode{date-hour} | |
1892 | ||
1893 | @item @nicode{~m} | |
1894 | @tab @nicode{char-numeric?} | |
1895 | @tab month | |
1896 | @tab @nicode{date-month} | |
1897 | ||
1898 | @item @nicode{~M} | |
1899 | @tab @nicode{char-numeric?} | |
1900 | @tab minute | |
1901 | @tab @nicode{date-minute} | |
1902 | ||
1903 | @item @nicode{~S} | |
1904 | @tab @nicode{char-numeric?} | |
1905 | @tab second | |
1906 | @tab @nicode{date-second} | |
1907 | ||
1908 | @item @nicode{~y} | |
1909 | @tab no skip | |
1910 | @tab 2-digit year | |
1911 | @tab @nicode{date-year} within 50 years | |
1912 | ||
1913 | @item @nicode{~Y} | |
1914 | @tab @nicode{char-numeric?} | |
1915 | @tab year | |
1916 | @tab @nicode{date-year} | |
1917 | ||
1918 | @item @nicode{~z} | |
1919 | @tab no skip | |
1920 | @tab time zone | |
1921 | @tab date-zone-offset | |
1922 | @end multitable | |
1923 | ||
1924 | Notice that the weekday matching forms don't affect the date object | |
1925 | returned, instead the weekday will be derived from the day, month and | |
1926 | year. | |
1927 | ||
1928 | Currently Guile doesn't implement any localizations for the above, | |
1929 | month and weekday names are always expected in English. This may | |
1930 | change in the future. | |
1931 | @end defun | |
12991fed | 1932 | |
1de8c1ae | 1933 | |
b0b55bd6 | 1934 | @node SRFI-26 |
3229f68b | 1935 | @subsection SRFI-26 - specializing parameters |
1de8c1ae KR |
1936 | @cindex SRFI-26 |
1937 | ||
1938 | This SRFI provides a syntax for conveniently specializing selected | |
1939 | parameters of a function. It can be used with, | |
1940 | ||
1941 | @example | |
1942 | (use-modules (srfi srfi-26)) | |
1943 | @end example | |
1944 | ||
1945 | @deffn {library syntax} cut slot @dots{} | |
1946 | @deffnx {library syntax} cute slot @dots{} | |
1947 | Return a new procedure which will make a call (@var{slot} @dots{}) but | |
1948 | with selected parameters specialized to given expressions. | |
1949 | ||
1950 | An example will illustrate the idea. The following is a | |
1951 | specialization of @code{write}, sending output to | |
1952 | @code{my-output-port}, | |
1953 | ||
1954 | @example | |
1955 | (cut write <> my-output-port) | |
1956 | @result{} | |
1957 | (lambda (obj) (write obj my-output-port)) | |
1958 | @end example | |
1959 | ||
1960 | The special symbol @code{<>} indicates a slot to be filled by an | |
1961 | argument to the new procedure. @code{my-output-port} on the other | |
1962 | hand is an expression to be evaluated and passed, ie.@: it specializes | |
1963 | the behaviour of @code{write}. | |
1964 | ||
1965 | @table @nicode | |
1966 | @item <> | |
1967 | A slot to be filled by an argument from the created procedure. | |
1968 | Arguments are assigned to @code{<>} slots in the order they appear in | |
1969 | the @code{cut} form, there's no way to re-arrange arguments. | |
1970 | ||
1971 | The first argument to @code{cut} is usually a procedure (or expression | |
1972 | giving a procedure), but @code{<>} is allowed there too. For example, | |
1973 | ||
1974 | @example | |
1975 | (cut <> 1 2 3) | |
1976 | @result{} | |
1977 | (lambda (proc) (proc 1 2 3)) | |
1978 | @end example | |
1979 | ||
1980 | @item <...> | |
1981 | A slot to be filled by all remaining arguments from the new procedure. | |
1982 | This can only occur at the end of a @code{cut} form. | |
1983 | ||
1984 | For example, a procedure taking a variable number of arguments like | |
1985 | @code{max} but in addition enforcing a lower bound, | |
1986 | ||
1987 | @example | |
1988 | (define my-lower-bound 123) | |
1989 | ||
1990 | (cut max my-lower-bound <...>) | |
1991 | @result{} | |
1992 | (lambda arglist (apply max my-lower-bound arglist)) | |
1993 | @end example | |
1994 | @end table | |
1995 | ||
1996 | For @code{cut} the specializing expressions are evaluated each time | |
1997 | the new procedure is called. For @code{cute} they're evaluated just | |
1998 | once, when the new procedure is created. The name @code{cute} stands | |
1999 | for ``@code{cut} with evaluated arguments''. In all cases the | |
2000 | evaluations take place in an unspecified order. | |
2001 | ||
2002 | The following illustrates the difference between @code{cut} and | |
2003 | @code{cute}, | |
2004 | ||
2005 | @example | |
2006 | (cut format <> "the time is ~s" (current-time)) | |
2007 | @result{} | |
2008 | (lambda (port) (format port "the time is ~s" (current-time))) | |
2009 | ||
2010 | (cute format <> "the time is ~s" (current-time)) | |
2011 | @result{} | |
2012 | (let ((val (current-time))) | |
2013 | (lambda (port) (format port "the time is ~s" val)) | |
2014 | @end example | |
2015 | ||
2016 | (There's no provision for a mixture of @code{cut} and @code{cute} | |
2017 | where some expressions would be evaluated every time but others | |
2018 | evaluated only once.) | |
2019 | ||
2020 | @code{cut} is really just a shorthand for the sort of @code{lambda} | |
2021 | forms shown in the above examples. But notice @code{cut} avoids the | |
2022 | need to name unspecialized parameters, and is more compact. Use in | |
2023 | functional programming style or just with @code{map}, @code{for-each} | |
2024 | or similar is typical. | |
2025 | ||
2026 | @example | |
2027 | (map (cut * 2 <>) '(1 2 3 4)) | |
2028 | ||
2029 | (for-each (cut write <> my-port) my-list) | |
2030 | @end example | |
2031 | @end deffn | |
b0b55bd6 | 2032 | |
8638c417 RB |
2033 | @node SRFI-31 |
2034 | @subsection SRFI-31 - A special form `rec' for recursive evaluation | |
2035 | @cindex SRFI-31 | |
2036 | @findex rec | |
2037 | ||
2038 | SRFI-31 defines a special form that can be used to create | |
2039 | self-referential expressions more conveniently. The syntax is as | |
2040 | follows: | |
2041 | ||
2042 | @example | |
2043 | @group | |
2044 | <rec expression> --> (rec <variable> <expression>) | |
2045 | <rec expression> --> (rec (<variable>+) <body>) | |
2046 | @end group | |
2047 | @end example | |
2048 | ||
2049 | The first syntax can be used to create self-referential expressions, | |
2050 | for example: | |
2051 | ||
2052 | @lisp | |
2053 | guile> (define tmp (rec ones (cons 1 (delay ones)))) | |
2054 | @end lisp | |
2055 | ||
2056 | The second syntax can be used to create anonymous recursive functions: | |
2057 | ||
2058 | @lisp | |
2059 | guile> (define tmp (rec (display-n item n) | |
2060 | (if (positive? n) | |
2061 | (begin (display n) (display-n (- n 1)))))) | |
2062 | guile> (tmp 42 3) | |
2063 | 424242 | |
2064 | guile> | |
2065 | @end lisp | |
12991fed TTN |
2066 | |
2067 | @c srfi-modules.texi ends here | |
193239f1 KR |
2068 | |
2069 | @c Local Variables: | |
2070 | @c TeX-master: "guile.texi" | |
2071 | @c End: |