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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 |
a0e07ba4 NJ |
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 |
eeadfda1 | 40 | * SRFI-39:: Parameter objects |
a0e07ba4 NJ |
41 | @end menu |
42 | ||
43 | ||
44 | @node About SRFI Usage | |
3229f68b | 45 | @subsection About SRFI Usage |
a0e07ba4 NJ |
46 | |
47 | @c FIXME::martin: Review me! | |
48 | ||
49 | SRFI support in Guile is currently implemented partly in the core | |
50 | library, and partly as add-on modules. That means that some SRFIs are | |
51 | automatically available when the interpreter is started, whereas the | |
52 | other SRFIs require you to use the appropriate support module | |
12991fed | 53 | explicitly. |
a0e07ba4 NJ |
54 | |
55 | There are several reasons for this inconsistency. First, the feature | |
56 | checking syntactic form @code{cond-expand} (@pxref{SRFI-0}) must be | |
57 | available immediately, because it must be there when the user wants to | |
58 | check for the Scheme implementation, that is, before she can know that | |
59 | it is safe to use @code{use-modules} to load SRFI support modules. The | |
60 | second reason is that some features defined in SRFIs had been | |
61 | implemented in Guile before the developers started to add SRFI | |
62 | implementations as modules (for example SRFI-6 (@pxref{SRFI-6})). In | |
63 | the future, it is possible that SRFIs in the core library might be | |
64 | factored out into separate modules, requiring explicit module loading | |
65 | when they are needed. So you should be prepared to have to use | |
66 | @code{use-modules} someday in the future to access SRFI-6 bindings. If | |
67 | you want, you can do that already. We have included the module | |
68 | @code{(srfi srfi-6)} in the distribution, which currently does nothing, | |
69 | but ensures that you can write future-safe code. | |
70 | ||
71 | Generally, support for a specific SRFI is made available by using | |
72 | modules named @code{(srfi srfi-@var{number})}, where @var{number} is the | |
73 | number of the SRFI needed. Another possibility is to use the command | |
74 | line option @code{--use-srfi}, which will load the necessary modules | |
75 | automatically (@pxref{Invoking Guile}). | |
76 | ||
77 | ||
78 | @node SRFI-0 | |
3229f68b | 79 | @subsection SRFI-0 - cond-expand |
8742c48b | 80 | @cindex SRFI-0 |
a0e07ba4 | 81 | |
5eef0f61 KR |
82 | This SRFI lets a portable Scheme program test for the presence of |
83 | certain features, and adapt itself by using different blocks of code, | |
84 | or fail if the necessary features are not available. There's no | |
85 | module to load, this is in the Guile core. | |
a0e07ba4 | 86 | |
5eef0f61 KR |
87 | A program designed only for Guile will generally not need this |
88 | mechanism, such a program can of course directly use the various | |
89 | documented parts of Guile. | |
a0e07ba4 | 90 | |
5eef0f61 KR |
91 | @deffn syntax cond-expand (feature body@dots{}) @dots{} |
92 | Expand to the @var{body} of the first clause whose @var{feature} | |
93 | specification is satisfied. It is an error if no @var{feature} is | |
a0e07ba4 NJ |
94 | satisfied. |
95 | ||
5eef0f61 KR |
96 | Features are symbols such as @code{srfi-1}, and a feature |
97 | specification can use @code{and}, @code{or} and @code{not} forms to | |
98 | test combinations. The last clause can be an @code{else}, to be used | |
99 | if no other passes. | |
a0e07ba4 | 100 | |
5eef0f61 KR |
101 | For example, define a private version of @code{alist-cons} if SRFI-1 |
102 | is not available. | |
a0e07ba4 | 103 | |
5eef0f61 KR |
104 | @example |
105 | (cond-expand (srfi-1 | |
106 | ) | |
107 | (else | |
108 | (define (alist-cons key val alist) | |
109 | (cons (cons key val) alist)))) | |
110 | @end example | |
a0e07ba4 | 111 | |
5eef0f61 KR |
112 | Or demand a certain set of SRFIs (list operations, string ports, |
113 | @code{receive} and string operations), failing if they're not | |
114 | available. | |
a0e07ba4 | 115 | |
5eef0f61 KR |
116 | @example |
117 | (cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13) | |
118 | )) | |
119 | @end example | |
120 | @end deffn | |
a0e07ba4 | 121 | |
5eef0f61 KR |
122 | The Guile core provides features @code{guile}, @code{r5rs}, |
123 | @code{srfi-0} and @code{srfi-6} initially. Other SRFI feature symbols | |
124 | are defined once their code has been loaded with @code{use-modules}, | |
125 | since only then are their bindings available. | |
a0e07ba4 | 126 | |
5eef0f61 KR |
127 | The @samp{--use-srfi} command line option (@pxref{Invoking Guile}) is |
128 | a good way to load SRFIs to satisfy @code{cond-expand} when running a | |
129 | portable program. | |
a0e07ba4 | 130 | |
5eef0f61 KR |
131 | Testing the @code{guile} feature allows a program to adapt itself to |
132 | the Guile module system, but still run on other Scheme systems. For | |
133 | example the following demands SRFI-8 (@code{receive}), but also knows | |
134 | how to load it with the Guile mechanism. | |
a0e07ba4 NJ |
135 | |
136 | @example | |
5eef0f61 KR |
137 | (cond-expand (srfi-8 |
138 | ) | |
139 | (guile | |
140 | (use-modules (srfi srfi-8)))) | |
a0e07ba4 NJ |
141 | @end example |
142 | ||
5eef0f61 KR |
143 | It should be noted that @code{cond-expand} is separate from the |
144 | @code{*features*} mechanism (@pxref{Feature Tracking}), feature | |
145 | symbols in one are unrelated to those in the other. | |
a0e07ba4 NJ |
146 | |
147 | ||
148 | @node SRFI-1 | |
3229f68b | 149 | @subsection SRFI-1 - List library |
8742c48b | 150 | @cindex SRFI-1 |
7c2e18cd | 151 | @cindex list |
a0e07ba4 NJ |
152 | |
153 | @c FIXME::martin: Review me! | |
154 | ||
155 | The list library defined in SRFI-1 contains a lot of useful list | |
156 | processing procedures for construction, examining, destructuring and | |
157 | manipulating lists and pairs. | |
158 | ||
159 | Since SRFI-1 also defines some procedures which are already contained | |
160 | in R5RS and thus are supported by the Guile core library, some list | |
161 | and pair procedures which appear in the SRFI-1 document may not appear | |
162 | in this section. So when looking for a particular list/pair | |
163 | processing procedure, you should also have a look at the sections | |
164 | @ref{Lists} and @ref{Pairs}. | |
165 | ||
166 | @menu | |
167 | * SRFI-1 Constructors:: Constructing new lists. | |
168 | * SRFI-1 Predicates:: Testing list for specific properties. | |
169 | * SRFI-1 Selectors:: Selecting elements from lists. | |
170 | * SRFI-1 Length Append etc:: Length calculation and list appending. | |
171 | * SRFI-1 Fold and Map:: Higher-order list processing. | |
172 | * SRFI-1 Filtering and Partitioning:: Filter lists based on predicates. | |
85a9b4ed | 173 | * SRFI-1 Searching:: Search for elements. |
a0e07ba4 NJ |
174 | * SRFI-1 Deleting:: Delete elements from lists. |
175 | * SRFI-1 Association Lists:: Handle association lists. | |
176 | * SRFI-1 Set Operations:: Use lists for representing sets. | |
177 | @end menu | |
178 | ||
179 | @node SRFI-1 Constructors | |
3229f68b | 180 | @subsubsection Constructors |
7c2e18cd | 181 | @cindex list constructor |
a0e07ba4 NJ |
182 | |
183 | @c FIXME::martin: Review me! | |
184 | ||
185 | New lists can be constructed by calling one of the following | |
186 | procedures. | |
187 | ||
8f85c0c6 | 188 | @deffn {Scheme Procedure} xcons d a |
a0e07ba4 NJ |
189 | Like @code{cons}, but with interchanged arguments. Useful mostly when |
190 | passed to higher-order procedures. | |
191 | @end deffn | |
192 | ||
8f85c0c6 | 193 | @deffn {Scheme Procedure} list-tabulate n init-proc |
a0e07ba4 NJ |
194 | Return an @var{n}-element list, where each list element is produced by |
195 | applying the procedure @var{init-proc} to the corresponding list | |
196 | index. The order in which @var{init-proc} is applied to the indices | |
197 | is not specified. | |
198 | @end deffn | |
199 | ||
57066448 KR |
200 | @deffn {Scheme Procedure} list-copy lst |
201 | Return a new list containing the elements of the list @var{lst}. | |
202 | ||
203 | This function differs from the core @code{list-copy} (@pxref{List | |
204 | Constructors}) in accepting improper lists too. And if @var{lst} is | |
205 | not a pair at all then it's treated as the final tail of an improper | |
206 | list and simply returned. | |
207 | @end deffn | |
208 | ||
8f85c0c6 | 209 | @deffn {Scheme Procedure} circular-list elt1 elt2 @dots{} |
a0e07ba4 NJ |
210 | Return a circular list containing the given arguments @var{elt1} |
211 | @var{elt2} @dots{}. | |
212 | @end deffn | |
213 | ||
8f85c0c6 | 214 | @deffn {Scheme Procedure} iota count [start step] |
256853db KR |
215 | Return a list containing @var{count} numbers, starting from |
216 | @var{start} and adding @var{step} each time. The default @var{start} | |
217 | is 0, the default @var{step} is 1. For example, | |
a0e07ba4 | 218 | |
256853db KR |
219 | @example |
220 | (iota 6) @result{} (0 1 2 3 4 5) | |
221 | (iota 4 2.5 -2) @result{} (2.5 0.5 -1.5 -3.5) | |
222 | @end example | |
a0e07ba4 | 223 | |
256853db KR |
224 | This function takes its name from the corresponding primitive in the |
225 | APL language. | |
a0e07ba4 NJ |
226 | @end deffn |
227 | ||
228 | ||
229 | @node SRFI-1 Predicates | |
3229f68b | 230 | @subsubsection Predicates |
7c2e18cd | 231 | @cindex list predicate |
a0e07ba4 NJ |
232 | |
233 | @c FIXME::martin: Review me! | |
234 | ||
235 | The procedures in this section test specific properties of lists. | |
236 | ||
8f85c0c6 | 237 | @deffn {Scheme Procedure} proper-list? obj |
a0e07ba4 NJ |
238 | Return @code{#t} if @var{obj} is a proper list, that is a finite list, |
239 | terminated with the empty list. Otherwise, return @code{#f}. | |
240 | @end deffn | |
241 | ||
8f85c0c6 | 242 | @deffn {Scheme Procedure} circular-list? obj |
a0e07ba4 NJ |
243 | Return @code{#t} if @var{obj} is a circular list, otherwise return |
244 | @code{#f}. | |
245 | @end deffn | |
246 | ||
8f85c0c6 | 247 | @deffn {Scheme Procedure} dotted-list? obj |
a0e07ba4 NJ |
248 | Return @code{#t} if @var{obj} is a dotted list, return @code{#f} |
249 | otherwise. A dotted list is a finite list which is not terminated by | |
250 | the empty list, but some other value. | |
251 | @end deffn | |
252 | ||
8f85c0c6 | 253 | @deffn {Scheme Procedure} null-list? lst |
a0e07ba4 NJ |
254 | Return @code{#t} if @var{lst} is the empty list @code{()}, @code{#f} |
255 | otherwise. If something else than a proper or circular list is passed | |
85a9b4ed | 256 | as @var{lst}, an error is signalled. This procedure is recommended |
a0e07ba4 NJ |
257 | for checking for the end of a list in contexts where dotted lists are |
258 | not allowed. | |
259 | @end deffn | |
260 | ||
8f85c0c6 | 261 | @deffn {Scheme Procedure} not-pair? obj |
a0e07ba4 NJ |
262 | Return @code{#t} is @var{obj} is not a pair, @code{#f} otherwise. |
263 | This is shorthand notation @code{(not (pair? @var{obj}))} and is | |
264 | supposed to be used for end-of-list checking in contexts where dotted | |
265 | lists are allowed. | |
266 | @end deffn | |
267 | ||
8f85c0c6 | 268 | @deffn {Scheme Procedure} list= elt= list1 @dots{} |
a0e07ba4 NJ |
269 | Return @code{#t} if all argument lists are equal, @code{#f} otherwise. |
270 | List equality is determined by testing whether all lists have the same | |
271 | length and the corresponding elements are equal in the sense of the | |
272 | equality predicate @var{elt=}. If no or only one list is given, | |
273 | @code{#t} is returned. | |
274 | @end deffn | |
275 | ||
276 | ||
277 | @node SRFI-1 Selectors | |
3229f68b | 278 | @subsubsection Selectors |
7c2e18cd | 279 | @cindex list selector |
a0e07ba4 NJ |
280 | |
281 | @c FIXME::martin: Review me! | |
282 | ||
8f85c0c6 NJ |
283 | @deffn {Scheme Procedure} first pair |
284 | @deffnx {Scheme Procedure} second pair | |
285 | @deffnx {Scheme Procedure} third pair | |
286 | @deffnx {Scheme Procedure} fourth pair | |
287 | @deffnx {Scheme Procedure} fifth pair | |
288 | @deffnx {Scheme Procedure} sixth pair | |
289 | @deffnx {Scheme Procedure} seventh pair | |
290 | @deffnx {Scheme Procedure} eighth pair | |
291 | @deffnx {Scheme Procedure} ninth pair | |
292 | @deffnx {Scheme Procedure} tenth pair | |
a0e07ba4 NJ |
293 | These are synonyms for @code{car}, @code{cadr}, @code{caddr}, @dots{}. |
294 | @end deffn | |
295 | ||
8f85c0c6 | 296 | @deffn {Scheme Procedure} car+cdr pair |
a0e07ba4 NJ |
297 | Return two values, the @sc{car} and the @sc{cdr} of @var{pair}. |
298 | @end deffn | |
299 | ||
8f85c0c6 NJ |
300 | @deffn {Scheme Procedure} take lst i |
301 | @deffnx {Scheme Procedure} take! lst i | |
a0e07ba4 NJ |
302 | Return a list containing the first @var{i} elements of @var{lst}. |
303 | ||
304 | @code{take!} may modify the structure of the argument list @var{lst} | |
305 | in order to produce the result. | |
306 | @end deffn | |
307 | ||
8f85c0c6 | 308 | @deffn {Scheme Procedure} drop lst i |
a0e07ba4 NJ |
309 | Return a list containing all but the first @var{i} elements of |
310 | @var{lst}. | |
311 | @end deffn | |
312 | ||
8f85c0c6 | 313 | @deffn {Scheme Procedure} take-right lst i |
a0e07ba4 NJ |
314 | Return the a list containing the @var{i} last elements of @var{lst}. |
315 | @end deffn | |
316 | ||
8f85c0c6 NJ |
317 | @deffn {Scheme Procedure} drop-right lst i |
318 | @deffnx {Scheme Procedure} drop-right! lst i | |
a0e07ba4 NJ |
319 | Return the a list containing all but the @var{i} last elements of |
320 | @var{lst}. | |
321 | ||
322 | @code{drop-right!} may modify the structure of the argument list | |
323 | @var{lst} in order to produce the result. | |
324 | @end deffn | |
325 | ||
8f85c0c6 NJ |
326 | @deffn {Scheme Procedure} split-at lst i |
327 | @deffnx {Scheme Procedure} split-at! lst i | |
a0e07ba4 NJ |
328 | Return two values, a list containing the first @var{i} elements of the |
329 | list @var{lst} and a list containing the remaining elements. | |
330 | ||
331 | @code{split-at!} may modify the structure of the argument list | |
332 | @var{lst} in order to produce the result. | |
333 | @end deffn | |
334 | ||
8f85c0c6 | 335 | @deffn {Scheme Procedure} last lst |
a0e07ba4 NJ |
336 | Return the last element of the non-empty, finite list @var{lst}. |
337 | @end deffn | |
338 | ||
339 | ||
340 | @node SRFI-1 Length Append etc | |
3229f68b | 341 | @subsubsection Length, Append, Concatenate, etc. |
a0e07ba4 NJ |
342 | |
343 | @c FIXME::martin: Review me! | |
344 | ||
8f85c0c6 | 345 | @deffn {Scheme Procedure} length+ lst |
a0e07ba4 NJ |
346 | Return the length of the argument list @var{lst}. When @var{lst} is a |
347 | circular list, @code{#f} is returned. | |
348 | @end deffn | |
349 | ||
8f85c0c6 NJ |
350 | @deffn {Scheme Procedure} concatenate list-of-lists |
351 | @deffnx {Scheme Procedure} concatenate! list-of-lists | |
a0e07ba4 NJ |
352 | Construct a list by appending all lists in @var{list-of-lists}. |
353 | ||
354 | @code{concatenate!} may modify the structure of the given lists in | |
355 | order to produce the result. | |
a3e856f2 KR |
356 | |
357 | @code{concatenate} is the same as @code{(apply append | |
358 | @var{list-of-lists})}. It exists because some Scheme implementations | |
359 | have a limit on the number of arguments a function takes, which the | |
360 | @code{apply} might exceed. In Guile there is no such limit. | |
a0e07ba4 NJ |
361 | @end deffn |
362 | ||
8f85c0c6 NJ |
363 | @deffn {Scheme Procedure} append-reverse rev-head tail |
364 | @deffnx {Scheme Procedure} append-reverse! rev-head tail | |
a0e07ba4 NJ |
365 | Reverse @var{rev-head}, append @var{tail} and return the result. This |
366 | is equivalent to @code{(append (reverse @var{rev-head}) @var{tail})}, | |
367 | but more efficient. | |
368 | ||
369 | @code{append-reverse!} may modify @var{rev-head} in order to produce | |
370 | the result. | |
371 | @end deffn | |
372 | ||
8f85c0c6 | 373 | @deffn {Scheme Procedure} zip lst1 lst2 @dots{} |
a0e07ba4 NJ |
374 | Return a list as long as the shortest of the argument lists, where |
375 | each element is a list. The first list contains the first elements of | |
376 | the argument lists, the second list contains the second elements, and | |
377 | so on. | |
378 | @end deffn | |
379 | ||
8f85c0c6 NJ |
380 | @deffn {Scheme Procedure} unzip1 lst |
381 | @deffnx {Scheme Procedure} unzip2 lst | |
382 | @deffnx {Scheme Procedure} unzip3 lst | |
383 | @deffnx {Scheme Procedure} unzip4 lst | |
384 | @deffnx {Scheme Procedure} unzip5 lst | |
a0e07ba4 NJ |
385 | @code{unzip1} takes a list of lists, and returns a list containing the |
386 | first elements of each list, @code{unzip2} returns two lists, the | |
387 | first containing the first elements of each lists and the second | |
388 | containing the second elements of each lists, and so on. | |
389 | @end deffn | |
390 | ||
e508c863 KR |
391 | @deffn {Scheme Procedure} count pred lst1 @dots{} lstN |
392 | Return a count of the number of times @var{pred} returns true when | |
393 | called on elements from the given lists. | |
394 | ||
395 | @var{pred} is called with @var{N} parameters @code{(@var{pred} | |
396 | @var{elem1} @dots{} @var{elemN})}, each element being from the | |
397 | corresponding @var{lst1} @dots{} @var{lstN}. The first call is with | |
398 | the first element of each list, the second with the second element | |
399 | from each, and so on. | |
400 | ||
401 | Counting stops when the end of the shortest list is reached. At least | |
402 | one list must be non-circular. | |
403 | @end deffn | |
404 | ||
a0e07ba4 NJ |
405 | |
406 | @node SRFI-1 Fold and Map | |
3229f68b | 407 | @subsubsection Fold, Unfold & Map |
7c2e18cd KR |
408 | @cindex list fold |
409 | @cindex list map | |
a0e07ba4 NJ |
410 | |
411 | @c FIXME::martin: Review me! | |
412 | ||
8f85c0c6 | 413 | @deffn {Scheme Procedure} fold kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
414 | Fold the procedure @var{kons} across all elements of @var{lst1}, |
415 | @var{lst2}, @dots{}. Produce the result of | |
416 | ||
417 | @code{(@var{kons} @var{en1} @var{en2} @dots{} (@var{kons} @var{e21} | |
418 | @var{e22} (@var{kons} @var{e11} @var{e12} @var{knil})))}, | |
419 | ||
420 | if @var{enm} are the elements of the lists @var{lst1}, @var{lst2}, | |
421 | @dots{}. | |
422 | @end deffn | |
423 | ||
8f85c0c6 | 424 | @deffn {Scheme Procedure} fold-right kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
425 | Similar to @code{fold}, but applies @var{kons} in right-to-left order |
426 | to the list elements, that is: | |
427 | ||
428 | @code{(@var{kons} @var{e11} @var{e12}(@var{kons} @var{e21} | |
429 | @var{e22} @dots{} (@var{kons} @var{en1} @var{en2} @var{knil})))}, | |
430 | @end deffn | |
431 | ||
8f85c0c6 | 432 | @deffn {Scheme Procedure} pair-fold kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
433 | Like @code{fold}, but apply @var{kons} to the pairs of the list |
434 | instead of the list elements. | |
435 | @end deffn | |
436 | ||
8f85c0c6 | 437 | @deffn {Scheme Procedure} pair-fold-right kons knil lst1 lst2 @dots{} |
a0e07ba4 NJ |
438 | Like @code{fold-right}, but apply @var{kons} to the pairs of the list |
439 | instead of the list elements. | |
440 | @end deffn | |
441 | ||
8f85c0c6 | 442 | @deffn {Scheme Procedure} reduce f ridentity lst |
1ae7b878 KR |
443 | @code{reduce} is a variant of @code{fold}. If @var{lst} is |
444 | @code{()}, @var{ridentity} is returned. Otherwise, @code{(fold f (car | |
a0e07ba4 NJ |
445 | @var{lst}) (cdr @var{lst}))} is returned. |
446 | @end deffn | |
447 | ||
8f85c0c6 | 448 | @deffn {Scheme Procedure} reduce-right f ridentity lst |
b5aa0215 | 449 | This is the @code{fold-right} variant of @code{reduce}. |
a0e07ba4 NJ |
450 | @end deffn |
451 | ||
8f85c0c6 | 452 | @deffn {Scheme Procedure} unfold p f g seed [tail-gen] |
a0e07ba4 NJ |
453 | @code{unfold} is defined as follows: |
454 | ||
455 | @lisp | |
456 | (unfold p f g seed) = | |
457 | (if (p seed) (tail-gen seed) | |
458 | (cons (f seed) | |
459 | (unfold p f g (g seed)))) | |
460 | @end lisp | |
461 | ||
462 | @table @var | |
463 | @item p | |
464 | Determines when to stop unfolding. | |
465 | ||
466 | @item f | |
467 | Maps each seed value to the corresponding list element. | |
468 | ||
469 | @item g | |
470 | Maps each seed value to next seed valu. | |
471 | ||
472 | @item seed | |
473 | The state value for the unfold. | |
474 | ||
475 | @item tail-gen | |
476 | Creates the tail of the list; defaults to @code{(lambda (x) '())}. | |
477 | @end table | |
478 | ||
479 | @var{g} produces a series of seed values, which are mapped to list | |
480 | elements by @var{f}. These elements are put into a list in | |
481 | left-to-right order, and @var{p} tells when to stop unfolding. | |
482 | @end deffn | |
483 | ||
8f85c0c6 | 484 | @deffn {Scheme Procedure} unfold-right p f g seed [tail] |
a0e07ba4 NJ |
485 | Construct a list with the following loop. |
486 | ||
487 | @lisp | |
488 | (let lp ((seed seed) (lis tail)) | |
489 | (if (p seed) lis | |
490 | (lp (g seed) | |
491 | (cons (f seed) lis)))) | |
492 | @end lisp | |
493 | ||
494 | @table @var | |
495 | @item p | |
496 | Determines when to stop unfolding. | |
497 | ||
498 | @item f | |
499 | Maps each seed value to the corresponding list element. | |
500 | ||
501 | @item g | |
502 | Maps each seed value to next seed valu. | |
503 | ||
504 | @item seed | |
505 | The state value for the unfold. | |
506 | ||
507 | @item tail-gen | |
508 | Creates the tail of the list; defaults to @code{(lambda (x) '())}. | |
509 | @end table | |
510 | ||
511 | @end deffn | |
512 | ||
8f85c0c6 | 513 | @deffn {Scheme Procedure} map f lst1 lst2 @dots{} |
a0e07ba4 NJ |
514 | Map the procedure over the list(s) @var{lst1}, @var{lst2}, @dots{} and |
515 | return a list containing the results of the procedure applications. | |
516 | This procedure is extended with respect to R5RS, because the argument | |
517 | lists may have different lengths. The result list will have the same | |
518 | length as the shortest argument lists. The order in which @var{f} | |
519 | will be applied to the list element(s) is not specified. | |
520 | @end deffn | |
521 | ||
8f85c0c6 | 522 | @deffn {Scheme Procedure} for-each f lst1 lst2 @dots{} |
a0e07ba4 NJ |
523 | Apply the procedure @var{f} to each pair of corresponding elements of |
524 | the list(s) @var{lst1}, @var{lst2}, @dots{}. The return value is not | |
525 | specified. This procedure is extended with respect to R5RS, because | |
526 | the argument lists may have different lengths. The shortest argument | |
527 | list determines the number of times @var{f} is called. @var{f} will | |
85a9b4ed | 528 | be applied to the list elements in left-to-right order. |
a0e07ba4 NJ |
529 | |
530 | @end deffn | |
531 | ||
8f85c0c6 NJ |
532 | @deffn {Scheme Procedure} append-map f lst1 lst2 @dots{} |
533 | @deffnx {Scheme Procedure} append-map! f lst1 lst2 @dots{} | |
12991fed | 534 | Equivalent to |
a0e07ba4 NJ |
535 | |
536 | @lisp | |
12991fed | 537 | (apply append (map f clist1 clist2 ...)) |
a0e07ba4 NJ |
538 | @end lisp |
539 | ||
12991fed | 540 | and |
a0e07ba4 NJ |
541 | |
542 | @lisp | |
12991fed | 543 | (apply append! (map f clist1 clist2 ...)) |
a0e07ba4 NJ |
544 | @end lisp |
545 | ||
546 | Map @var{f} over the elements of the lists, just as in the @code{map} | |
547 | function. However, the results of the applications are appended | |
548 | together to make the final result. @code{append-map} uses | |
549 | @code{append} to append the results together; @code{append-map!} uses | |
550 | @code{append!}. | |
551 | ||
552 | The dynamic order in which the various applications of @var{f} are | |
553 | made is not specified. | |
554 | @end deffn | |
555 | ||
8f85c0c6 | 556 | @deffn {Scheme Procedure} map! f lst1 lst2 @dots{} |
a0e07ba4 NJ |
557 | Linear-update variant of @code{map} -- @code{map!} is allowed, but not |
558 | required, to alter the cons cells of @var{lst1} to construct the | |
559 | result list. | |
560 | ||
561 | The dynamic order in which the various applications of @var{f} are | |
562 | made is not specified. In the n-ary case, @var{lst2}, @var{lst3}, | |
563 | @dots{} must have at least as many elements as @var{lst1}. | |
564 | @end deffn | |
565 | ||
8f85c0c6 | 566 | @deffn {Scheme Procedure} pair-for-each f lst1 lst2 @dots{} |
a0e07ba4 NJ |
567 | Like @code{for-each}, but applies the procedure @var{f} to the pairs |
568 | from which the argument lists are constructed, instead of the list | |
569 | elements. The return value is not specified. | |
570 | @end deffn | |
571 | ||
8f85c0c6 | 572 | @deffn {Scheme Procedure} filter-map f lst1 lst2 @dots{} |
a0e07ba4 NJ |
573 | Like @code{map}, but only results from the applications of @var{f} |
574 | which are true are saved in the result list. | |
575 | @end deffn | |
576 | ||
577 | ||
578 | @node SRFI-1 Filtering and Partitioning | |
3229f68b | 579 | @subsubsection Filtering and Partitioning |
7c2e18cd KR |
580 | @cindex list filter |
581 | @cindex list partition | |
a0e07ba4 NJ |
582 | |
583 | @c FIXME::martin: Review me! | |
584 | ||
585 | Filtering means to collect all elements from a list which satisfy a | |
586 | specific condition. Partitioning a list means to make two groups of | |
587 | list elements, one which contains the elements satisfying a condition, | |
588 | and the other for the elements which don't. | |
589 | ||
60e25dc4 KR |
590 | The @code{filter} and @code{filter!} functions are implemented in the |
591 | Guile core, @xref{List Modification}. | |
a0e07ba4 | 592 | |
8f85c0c6 NJ |
593 | @deffn {Scheme Procedure} partition pred lst |
594 | @deffnx {Scheme Procedure} partition! pred lst | |
193239f1 KR |
595 | Split @var{lst} into those elements which do and don't satisfy the |
596 | predicate @var{pred}. | |
a0e07ba4 | 597 | |
193239f1 KR |
598 | The return is two values (@pxref{Multiple Values}), the first being a |
599 | list of all elements from @var{lst} which satisfy @var{pred}, the | |
600 | second a list of those which do not. | |
601 | ||
602 | The elements in the result lists are in the same order as in @var{lst} | |
603 | but the order in which the calls @code{(@var{pred} elem)} are made on | |
604 | the list elements is unspecified. | |
605 | ||
606 | @code{partition} does not change @var{lst}, but one of the returned | |
607 | lists may share a tail with it. @code{partition!} may modify | |
608 | @var{lst} to construct its return. | |
a0e07ba4 NJ |
609 | @end deffn |
610 | ||
8f85c0c6 NJ |
611 | @deffn {Scheme Procedure} remove pred lst |
612 | @deffnx {Scheme Procedure} remove! pred lst | |
a0e07ba4 NJ |
613 | Return a list containing all elements from @var{lst} which do not |
614 | satisfy the predicate @var{pred}. The elements in the result list | |
615 | have the same order as in @var{lst}. The order in which @var{pred} is | |
616 | applied to the list elements is not specified. | |
617 | ||
618 | @code{remove!} is allowed, but not required to modify the structure of | |
619 | the input list. | |
620 | @end deffn | |
621 | ||
622 | ||
623 | @node SRFI-1 Searching | |
3229f68b | 624 | @subsubsection Searching |
7c2e18cd | 625 | @cindex list search |
a0e07ba4 NJ |
626 | |
627 | @c FIXME::martin: Review me! | |
628 | ||
629 | The procedures for searching elements in lists either accept a | |
630 | predicate or a comparison object for determining which elements are to | |
631 | be searched. | |
632 | ||
8f85c0c6 | 633 | @deffn {Scheme Procedure} find pred lst |
a0e07ba4 NJ |
634 | Return the first element of @var{lst} which satisfies the predicate |
635 | @var{pred} and @code{#f} if no such element is found. | |
636 | @end deffn | |
637 | ||
8f85c0c6 | 638 | @deffn {Scheme Procedure} find-tail pred lst |
a0e07ba4 NJ |
639 | Return the first pair of @var{lst} whose @sc{car} satisfies the |
640 | predicate @var{pred} and @code{#f} if no such element is found. | |
641 | @end deffn | |
642 | ||
8f85c0c6 NJ |
643 | @deffn {Scheme Procedure} take-while pred lst |
644 | @deffnx {Scheme Procedure} take-while! pred lst | |
a0e07ba4 NJ |
645 | Return the longest initial prefix of @var{lst} whose elements all |
646 | satisfy the predicate @var{pred}. | |
647 | ||
648 | @code{take-while!} is allowed, but not required to modify the input | |
649 | list while producing the result. | |
650 | @end deffn | |
651 | ||
8f85c0c6 | 652 | @deffn {Scheme Procedure} drop-while pred lst |
a0e07ba4 NJ |
653 | Drop the longest initial prefix of @var{lst} whose elements all |
654 | satisfy the predicate @var{pred}. | |
655 | @end deffn | |
656 | ||
8f85c0c6 NJ |
657 | @deffn {Scheme Procedure} span pred lst |
658 | @deffnx {Scheme Procedure} span! pred lst | |
659 | @deffnx {Scheme Procedure} break pred lst | |
660 | @deffnx {Scheme Procedure} break! pred lst | |
a0e07ba4 NJ |
661 | @code{span} splits the list @var{lst} into the longest initial prefix |
662 | whose elements all satisfy the predicate @var{pred}, and the remaining | |
663 | tail. @code{break} inverts the sense of the predicate. | |
664 | ||
665 | @code{span!} and @code{break!} are allowed, but not required to modify | |
666 | the structure of the input list @var{lst} in order to produce the | |
667 | result. | |
3e73b6f9 KR |
668 | |
669 | Note that the name @code{break} conflicts with the @code{break} | |
670 | binding established by @code{while} (@pxref{while do}). Applications | |
671 | wanting to use @code{break} from within a @code{while} loop will need | |
672 | to make a new define under a different name. | |
a0e07ba4 NJ |
673 | @end deffn |
674 | ||
62705beb KR |
675 | @deffn {Scheme Procedure} any pred lst1 lst2 @dots{} lstN |
676 | Test whether any set of elements from @var{lst1} @dots{} lstN | |
677 | satisfies @var{pred}. If so the return value is the return from the | |
678 | successful @var{pred} call, or if not the return is @code{#f}. | |
679 | ||
680 | Each @var{pred} call is @code{(@var{pred} @var{elem1} @dots{} | |
681 | @var{elemN})} taking an element from each @var{lst}. The calls are | |
682 | made successively for the first, second, etc elements of the lists, | |
683 | stopping when @var{pred} returns non-@code{#f}, or when the end of the | |
684 | shortest list is reached. | |
685 | ||
686 | The @var{pred} call on the last set of elements (ie.@: when the end of | |
687 | the shortest list has been reached), if that point is reached, is a | |
688 | tail call. | |
689 | @end deffn | |
690 | ||
691 | @deffn {Scheme Procedure} every pred lst1 lst2 @dots{} lstN | |
692 | Test whether every set of elements from @var{lst1} @dots{} lstN | |
693 | satisfies @var{pred}. If so the return value is the return from the | |
694 | final @var{pred} call, or if not the return is @code{#f}. | |
695 | ||
696 | Each @var{pred} call is @code{(@var{pred} @var{elem1} @dots{} | |
697 | @var{elemN})} taking an element from each @var{lst}. The calls are | |
698 | made successively for the first, second, etc elements of the lists, | |
699 | stopping if @var{pred} returns @code{#f}, or when the end of any of | |
700 | the lists is reached. | |
701 | ||
702 | The @var{pred} call on the last set of elements (ie.@: when the end of | |
703 | the shortest list has been reached) is a tail call. | |
704 | ||
705 | If one of @var{lst1} @dots{} @var{lstN} is empty then no calls to | |
706 | @var{pred} are made, and the return is @code{#t}. | |
a0e07ba4 NJ |
707 | @end deffn |
708 | ||
8f85c0c6 | 709 | @deffn {Scheme Procedure} list-index pred lst1 lst2 @dots{} |
a0e07ba4 NJ |
710 | Return the index of the leftmost element that satisfies @var{pred}. |
711 | @end deffn | |
712 | ||
8f85c0c6 | 713 | @deffn {Scheme Procedure} member x lst [=] |
a0e07ba4 NJ |
714 | Return the first sublist of @var{lst} whose @sc{car} is equal to |
715 | @var{x}. If @var{x} does no appear in @var{lst}, return @code{#f}. | |
716 | Equality is determined by the equality predicate @var{=}, or | |
717 | @code{equal?} if @var{=} is not given. | |
ea6ea01b KR |
718 | |
719 | This function extends the core @code{member} by accepting an equality | |
720 | predicate. (@pxref{List Searching}) | |
a0e07ba4 NJ |
721 | @end deffn |
722 | ||
723 | ||
724 | @node SRFI-1 Deleting | |
3229f68b | 725 | @subsubsection Deleting |
7c2e18cd | 726 | @cindex list delete |
a0e07ba4 NJ |
727 | |
728 | @c FIXME::martin: Review me! | |
729 | ||
8f85c0c6 NJ |
730 | @deffn {Scheme Procedure} delete x lst [=] |
731 | @deffnx {Scheme Procedure} delete! x lst [=] | |
b6b9376a KR |
732 | Return a list containing the elements of @var{lst} but with those |
733 | equal to @var{x} deleted. The returned elements will be in the same | |
734 | order as they were in @var{lst}. | |
735 | ||
736 | Equality is determined by the @var{=} predicate, or @code{equal?} if | |
737 | not given. An equality call is made just once for each element, but | |
738 | the order in which the calls are made on the elements is unspecified. | |
a0e07ba4 | 739 | |
243bdb63 | 740 | The equality calls are always @code{(= x elem)}, ie.@: the given @var{x} |
b6b9376a KR |
741 | is first. This means for instance elements greater than 5 can be |
742 | deleted with @code{(delete 5 lst <)}. | |
743 | ||
744 | @code{delete} does not modify @var{lst}, but the return might share a | |
745 | common tail with @var{lst}. @code{delete!} may modify the structure | |
746 | of @var{lst} to construct its return. | |
ea6ea01b KR |
747 | |
748 | These functions extend the core @code{delete} and @code{delete!} in | |
749 | accepting an equality predicate. (@pxref{List Modification}) | |
a0e07ba4 NJ |
750 | @end deffn |
751 | ||
8f85c0c6 NJ |
752 | @deffn {Scheme Procedure} delete-duplicates lst [=] |
753 | @deffnx {Scheme Procedure} delete-duplicates! lst [=] | |
b6b9376a KR |
754 | Return a list containing the elements of @var{lst} but without |
755 | duplicates. | |
756 | ||
757 | When elements are equal, only the first in @var{lst} is retained. | |
758 | Equal elements can be anywhere in @var{lst}, they don't have to be | |
759 | adjacent. The returned list will have the retained elements in the | |
760 | same order as they were in @var{lst}. | |
761 | ||
762 | Equality is determined by the @var{=} predicate, or @code{equal?} if | |
763 | not given. Calls @code{(= x y)} are made with element @var{x} being | |
764 | before @var{y} in @var{lst}. A call is made at most once for each | |
765 | combination, but the sequence of the calls across the elements is | |
766 | unspecified. | |
767 | ||
768 | @code{delete-duplicates} does not modify @var{lst}, but the return | |
769 | might share a common tail with @var{lst}. @code{delete-duplicates!} | |
770 | may modify the structure of @var{lst} to construct its return. | |
771 | ||
772 | In the worst case, this is an @math{O(N^2)} algorithm because it must | |
773 | check each element against all those preceding it. For long lists it | |
774 | is more efficient to sort and then compare only adjacent elements. | |
a0e07ba4 NJ |
775 | @end deffn |
776 | ||
777 | ||
778 | @node SRFI-1 Association Lists | |
3229f68b | 779 | @subsubsection Association Lists |
7c2e18cd KR |
780 | @cindex association list |
781 | @cindex alist | |
a0e07ba4 NJ |
782 | |
783 | @c FIXME::martin: Review me! | |
784 | ||
785 | Association lists are described in detail in section @ref{Association | |
786 | Lists}. The present section only documents the additional procedures | |
787 | for dealing with association lists defined by SRFI-1. | |
788 | ||
8f85c0c6 | 789 | @deffn {Scheme Procedure} assoc key alist [=] |
a0e07ba4 NJ |
790 | Return the pair from @var{alist} which matches @var{key}. Equality is |
791 | determined by @var{=}, which defaults to @code{equal?} if not given. | |
792 | @var{alist} must be an association lists---a list of pairs. | |
ea6ea01b KR |
793 | |
794 | This function extends the core @code{assoc} by accepting an equality | |
795 | predicate. (@pxref{Association Lists}) | |
a0e07ba4 NJ |
796 | @end deffn |
797 | ||
8f85c0c6 | 798 | @deffn {Scheme Procedure} alist-cons key datum alist |
a0e07ba4 NJ |
799 | Equivalent to |
800 | ||
801 | @lisp | |
802 | (cons (cons @var{key} @var{datum}) @var{alist}) | |
803 | @end lisp | |
804 | ||
805 | This procedure is used to coons a new pair onto an existing | |
806 | association list. | |
807 | @end deffn | |
808 | ||
8f85c0c6 | 809 | @deffn {Scheme Procedure} alist-copy alist |
a0e07ba4 NJ |
810 | Return a newly allocated copy of @var{alist}, that means that the |
811 | spine of the list as well as the pairs are copied. | |
812 | @end deffn | |
813 | ||
8f85c0c6 NJ |
814 | @deffn {Scheme Procedure} alist-delete key alist [=] |
815 | @deffnx {Scheme Procedure} alist-delete! key alist [=] | |
bd35f1f0 KR |
816 | Return a list containing the elements of @var{alist} but with those |
817 | elements whose keys are equal to @var{key} deleted. The returned | |
818 | elements will be in the same order as they were in @var{alist}. | |
a0e07ba4 | 819 | |
bd35f1f0 KR |
820 | Equality is determined by the @var{=} predicate, or @code{equal?} if |
821 | not given. The order in which elements are tested is unspecified, but | |
822 | each equality call is made @code{(= key alistkey)}, ie. the given | |
823 | @var{key} parameter is first and the key from @var{alist} second. | |
824 | This means for instance all associations with a key greater than 5 can | |
825 | be removed with @code{(alist-delete 5 alist <)}. | |
826 | ||
827 | @code{alist-delete} does not modify @var{alist}, but the return might | |
828 | share a common tail with @var{alist}. @code{alist-delete!} may modify | |
829 | the list structure of @var{alist} to construct its return. | |
a0e07ba4 NJ |
830 | @end deffn |
831 | ||
832 | ||
833 | @node SRFI-1 Set Operations | |
3229f68b | 834 | @subsubsection Set Operations on Lists |
7c2e18cd | 835 | @cindex list set operation |
a0e07ba4 NJ |
836 | |
837 | @c FIXME::martin: Review me! | |
838 | ||
839 | Lists can be used for representing sets of objects. The procedures | |
840 | documented in this section can be used for such set representations. | |
85a9b4ed | 841 | Man combining several sets or adding elements, they make sure that no |
a0e07ba4 NJ |
842 | object is contained more than once in a given list. Please note that |
843 | lists are not a too efficient implementation method for sets, so if | |
844 | you need high performance, you should think about implementing a | |
845 | custom data structure for representing sets, such as trees, bitsets, | |
846 | hash tables or something similar. | |
847 | ||
848 | All these procedures accept an equality predicate as the first | |
849 | argument. This predicate is used for testing the objects in the list | |
850 | sets for sameness. | |
851 | ||
8f85c0c6 | 852 | @deffn {Scheme Procedure} lset<= = list1 @dots{} |
a0e07ba4 NJ |
853 | Return @code{#t} if every @var{listi} is a subset of @var{listi+1}, |
854 | otherwise return @code{#f}. Returns @code{#t} if called with less | |
855 | than two arguments. @var{=} is used for testing element equality. | |
856 | @end deffn | |
857 | ||
8f85c0c6 | 858 | @deffn {Scheme Procedure} lset= = list1 list2 @dots{} |
a0e07ba4 NJ |
859 | Return @code{#t} if all argument lists are equal. @var{=} is used for |
860 | testing element equality. | |
861 | @end deffn | |
862 | ||
8f85c0c6 NJ |
863 | @deffn {Scheme Procedure} lset-adjoin = list elt1 @dots{} |
864 | @deffnx {Scheme Procedure} lset-adjoin! = list elt1 @dots{} | |
a0e07ba4 NJ |
865 | Add all @var{elts} to the list @var{list}, suppressing duplicates and |
866 | return the resulting list. @code{lset-adjoin!} is allowed, but not | |
867 | required to modify its first argument. @var{=} is used for testing | |
868 | element equality. | |
869 | @end deffn | |
870 | ||
8f85c0c6 NJ |
871 | @deffn {Scheme Procedure} lset-union = list1 @dots{} |
872 | @deffnx {Scheme Procedure} lset-union! = list1 @dots{} | |
a0e07ba4 NJ |
873 | Return the union of all argument list sets. The union is the set of |
874 | all elements which appear in any of the argument sets. | |
875 | @code{lset-union!} is allowed, but not required to modify its first | |
876 | argument. @var{=} is used for testing element equality. | |
877 | @end deffn | |
878 | ||
8f85c0c6 NJ |
879 | @deffn {Scheme Procedure} lset-intersection = list1 list2 @dots{} |
880 | @deffnx {Scheme Procedure} lset-intersection! = list1 list2 @dots{} | |
a0e07ba4 NJ |
881 | Return the intersection of all argument list sets. The intersection |
882 | is the set containing all elements which appear in all argument sets. | |
883 | @code{lset-intersection!} is allowed, but not required to modify its | |
884 | first argument. @var{=} is used for testing element equality. | |
885 | @end deffn | |
886 | ||
8f85c0c6 NJ |
887 | @deffn {Scheme Procedure} lset-difference = list1 list2 @dots{} |
888 | @deffnx {Scheme Procedure} lset-difference! = list1 list2 @dots{} | |
a0e07ba4 NJ |
889 | Return the difference of all argument list sets. The difference is |
890 | the the set containing all elements of the first list which do not | |
891 | appear in the other lists. @code{lset-difference!} is allowed, but | |
892 | not required to modify its first argument. @var{=} is used for testing | |
893 | element equality. | |
894 | @end deffn | |
895 | ||
8f85c0c6 NJ |
896 | @deffn {Scheme Procedure} lset-xor = list1 @dots{} |
897 | @deffnx {Scheme Procedure} lset-xor! = list1 @dots{} | |
a0e07ba4 NJ |
898 | Return the set containing all elements which appear in the first |
899 | argument list set, but not in the second; or, more generally: which | |
900 | appear in an odd number of sets. @code{lset-xor!} is allowed, but | |
901 | not required to modify its first argument. @var{=} is used for testing | |
902 | element equality. | |
903 | @end deffn | |
904 | ||
8f85c0c6 NJ |
905 | @deffn {Scheme Procedure} lset-diff+intersection = list1 list2 @dots{} |
906 | @deffnx {Scheme Procedure} lset-diff+intersection! = list1 list2 @dots{} | |
a0e07ba4 NJ |
907 | Return two values, the difference and the intersection of the argument |
908 | list sets. This works like a combination of @code{lset-difference} and | |
909 | @code{lset-intersection}, but is more efficient. | |
910 | @code{lset-diff+intersection!} is allowed, but not required to modify | |
911 | its first argument. @var{=} is used for testing element equality. You | |
912 | have to use some means to deal with the multiple values these | |
913 | procedures return (@pxref{Multiple Values}). | |
914 | @end deffn | |
915 | ||
916 | ||
917 | @node SRFI-2 | |
3229f68b | 918 | @subsection SRFI-2 - and-let* |
8742c48b | 919 | @cindex SRFI-2 |
a0e07ba4 | 920 | |
4fd0db14 KR |
921 | @noindent |
922 | The following syntax can be obtained with | |
a0e07ba4 | 923 | |
4fd0db14 KR |
924 | @lisp |
925 | (use-modules (srfi srfi-2)) | |
926 | @end lisp | |
a0e07ba4 | 927 | |
4fd0db14 KR |
928 | @deffn {library syntax} and-let* (clause @dots{}) body @dots{} |
929 | A combination of @code{and} and @code{let*}. | |
930 | ||
931 | Each @var{clause} is evaluated in turn, and if @code{#f} is obtained | |
932 | then evaluation stops and @code{#f} is returned. If all are | |
933 | non-@code{#f} then @var{body} is evaluated and the last form gives the | |
6b1a6e4c KR |
934 | return value, or if @var{body} is empty then the result is @code{#t}. |
935 | Each @var{clause} should be one of the following, | |
4fd0db14 KR |
936 | |
937 | @table @code | |
938 | @item (symbol expr) | |
939 | Evaluate @var{expr}, check for @code{#f}, and bind it to @var{symbol}. | |
940 | Like @code{let*}, that binding is available to subsequent clauses. | |
941 | @item (expr) | |
942 | Evaluate @var{expr} and check for @code{#f}. | |
943 | @item symbol | |
944 | Get the value bound to @var{symbol} and check for @code{#f}. | |
945 | @end table | |
a0e07ba4 | 946 | |
4fd0db14 KR |
947 | Notice that @code{(expr)} has an ``extra'' pair of parentheses, for |
948 | instance @code{((eq? x y))}. One way to remember this is to imagine | |
949 | the @code{symbol} in @code{(symbol expr)} is omitted. | |
a0e07ba4 | 950 | |
4fd0db14 KR |
951 | @code{and-let*} is good for calculations where a @code{#f} value means |
952 | termination, but where a non-@code{#f} value is going to be needed in | |
953 | subsequent expressions. | |
954 | ||
955 | The following illustrates this, it returns text between brackets | |
956 | @samp{[...]} in a string, or @code{#f} if there are no such brackets | |
957 | (ie.@: either @code{string-index} gives @code{#f}). | |
958 | ||
959 | @example | |
960 | (define (extract-brackets str) | |
961 | (and-let* ((start (string-index str #\[)) | |
962 | (end (string-index str #\] start))) | |
963 | (substring str (1+ start) end))) | |
964 | @end example | |
965 | ||
966 | The following shows plain variables and expressions tested too. | |
967 | @code{diagnostic-levels} is taken to be an alist associating a | |
968 | diagnostic type with a level. @code{str} is printed only if the type | |
969 | is known and its level is high enough. | |
970 | ||
971 | @example | |
972 | (define (show-diagnostic type str) | |
973 | (and-let* (want-diagnostics | |
974 | (level (assq-ref diagnostic-levels type)) | |
975 | ((>= level current-diagnostic-level))) | |
976 | (display str))) | |
977 | @end example | |
978 | ||
979 | The advantage of @code{and-let*} is that an extended sequence of | |
980 | expressions and tests doesn't require lots of nesting as would arise | |
981 | from separate @code{and} and @code{let*}, or from @code{cond} with | |
982 | @code{=>}. | |
983 | ||
984 | @end deffn | |
a0e07ba4 NJ |
985 | |
986 | ||
987 | @node SRFI-4 | |
3229f68b | 988 | @subsection SRFI-4 - Homogeneous numeric vector datatypes |
8742c48b | 989 | @cindex SRFI-4 |
a0e07ba4 | 990 | |
e6b226b9 | 991 | The SRFI-4 procedures and data types are always available, @xref{Uniform |
3dd6e0cf | 992 | Numeric Vectors}. |
a0e07ba4 NJ |
993 | |
994 | @node SRFI-6 | |
3229f68b | 995 | @subsection SRFI-6 - Basic String Ports |
8742c48b | 996 | @cindex SRFI-6 |
a0e07ba4 NJ |
997 | |
998 | SRFI-6 defines the procedures @code{open-input-string}, | |
999 | @code{open-output-string} and @code{get-output-string}. These | |
1000 | procedures are included in the Guile core, so using this module does not | |
1001 | make any difference at the moment. But it is possible that support for | |
1002 | SRFI-6 will be factored out of the core library in the future, so using | |
1003 | this module does not hurt, after all. | |
1004 | ||
1005 | @node SRFI-8 | |
3229f68b | 1006 | @subsection SRFI-8 - receive |
8742c48b | 1007 | @cindex SRFI-8 |
a0e07ba4 NJ |
1008 | |
1009 | @code{receive} is a syntax for making the handling of multiple-value | |
1010 | procedures easier. It is documented in @xref{Multiple Values}. | |
1011 | ||
1012 | ||
1013 | @node SRFI-9 | |
3229f68b | 1014 | @subsection SRFI-9 - define-record-type |
8742c48b | 1015 | @cindex SRFI-9 |
7c2e18cd | 1016 | @cindex record |
a0e07ba4 | 1017 | |
6afe385d KR |
1018 | This SRFI is a syntax for defining new record types and creating |
1019 | predicate, constructor, and field getter and setter functions. In | |
1020 | Guile this is simply an alternate interface to the core record | |
1021 | functionality (@pxref{Records}). It can be used with, | |
a0e07ba4 | 1022 | |
6afe385d KR |
1023 | @example |
1024 | (use-modules (srfi srfi-9)) | |
1025 | @end example | |
1026 | ||
1027 | @deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{} | |
1028 | @sp 1 | |
1029 | Create a new record type, and make various @code{define}s for using | |
1030 | it. This syntax can only occur at the top-level, not nested within | |
1031 | some other form. | |
1032 | ||
1033 | @var{type} is bound to the record type, which is as per the return | |
1034 | from the core @code{make-record-type}. @var{type} also provides the | |
1035 | name for the record, as per @code{record-type-name}. | |
1036 | ||
1037 | @var{constructor} is bound to a function to be called as | |
1038 | @code{(@var{constructor} fieldval @dots{})} to create a new record of | |
1039 | this type. The arguments are initial values for the fields, one | |
1040 | argument for each field, in the order they appear in the | |
1041 | @code{define-record-type} form. | |
1042 | ||
1043 | The @var{fieldname}s provide the names for the record fields, as per | |
1044 | the core @code{record-type-fields} etc, and are referred to in the | |
1045 | subsequent accessor/modifier forms. | |
1046 | ||
1047 | @var{predictate} is bound to a function to be called as | |
1048 | @code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f} | |
1049 | according to whether @var{obj} is a record of this type. | |
1050 | ||
1051 | Each @var{accessor} is bound to a function to be called | |
1052 | @code{(@var{accessor} record)} to retrieve the respective field from a | |
1053 | @var{record}. Similarly each @var{modifier} is bound to a function to | |
1054 | be called @code{(@var{modifier} record val)} to set the respective | |
1055 | field in a @var{record}. | |
1056 | @end deffn | |
1057 | ||
1058 | @noindent | |
1059 | An example will illustrate typical usage, | |
a0e07ba4 NJ |
1060 | |
1061 | @example | |
6afe385d KR |
1062 | (define-record-type employee-type |
1063 | (make-employee name age salary) | |
1064 | employee? | |
1065 | (name get-employee-name) | |
1066 | (age get-employee-age set-employee-age) | |
1067 | (salary get-employee-salary set-employee-salary)) | |
a0e07ba4 NJ |
1068 | @end example |
1069 | ||
6afe385d KR |
1070 | This creates a new employee data type, with name, age and salary |
1071 | fields. Accessor functions are created for each field, but no | |
1072 | modifier function for the name (the intention in this example being | |
1073 | that it's established only when an employee object is created). These | |
1074 | can all then be used as for example, | |
a0e07ba4 NJ |
1075 | |
1076 | @example | |
6afe385d KR |
1077 | employee-type @result{} #<record-type employee-type> |
1078 | ||
1079 | (define fred (make-employee "Fred" 45 20000.00)) | |
1080 | ||
1081 | (employee? fred) @result{} #t | |
1082 | (get-employee-age fred) @result{} 45 | |
1083 | (set-employee-salary fred 25000.00) ;; pay rise | |
a0e07ba4 NJ |
1084 | @end example |
1085 | ||
6afe385d KR |
1086 | The functions created by @code{define-record-type} are ordinary |
1087 | top-level @code{define}s. They can be redefined or @code{set!} as | |
1088 | desired, exported from a module, etc. | |
1089 | ||
a0e07ba4 NJ |
1090 | |
1091 | @node SRFI-10 | |
3229f68b | 1092 | @subsection SRFI-10 - Hash-Comma Reader Extension |
8742c48b | 1093 | @cindex SRFI-10 |
a0e07ba4 NJ |
1094 | |
1095 | @cindex hash-comma | |
1096 | @cindex #,() | |
633acbe2 KR |
1097 | This SRFI implements a reader extension @code{#,()} called hash-comma. |
1098 | It allows the reader to give new kinds of objects, for use both in | |
1099 | data and as constants or literals in source code. This feature is | |
1100 | available with | |
a0e07ba4 | 1101 | |
633acbe2 KR |
1102 | @example |
1103 | (use-modules (srfi srfi-10)) | |
1104 | @end example | |
1105 | ||
1106 | @noindent | |
1107 | The new read syntax is of the form | |
a0e07ba4 NJ |
1108 | |
1109 | @example | |
633acbe2 | 1110 | #,(@var{tag} @var{arg}@dots{}) |
a0e07ba4 NJ |
1111 | @end example |
1112 | ||
633acbe2 KR |
1113 | @noindent |
1114 | where @var{tag} is a symbol and the @var{arg}s are objects taken as | |
1115 | parameters. @var{tag}s are registered with the following procedure. | |
a0e07ba4 | 1116 | |
633acbe2 KR |
1117 | @deffn {Scheme Procedure} define-reader-ctor tag proc |
1118 | Register @var{proc} as the constructor for a hash-comma read syntax | |
1119 | starting with symbol @var{tag}, ie. @nicode{#,(@var{tag} arg@dots{})}. | |
1120 | @var{proc} is called with the given arguments @code{(@var{proc} | |
1121 | arg@dots{})} and the object it returns is the result of the read. | |
1122 | @end deffn | |
a0e07ba4 | 1123 | |
633acbe2 KR |
1124 | @noindent |
1125 | For example, a syntax giving a list of @var{N} copies of an object. | |
1126 | ||
1127 | @example | |
1128 | (define-reader-ctor 'repeat | |
1129 | (lambda (obj reps) | |
1130 | (make-list reps obj))) | |
1131 | ||
1132 | (display '#,(repeat 99 3)) | |
1133 | @print{} (99 99 99) | |
1134 | @end example | |
1135 | ||
1136 | Notice the quote @nicode{'} when the @nicode{#,( )} is used. The | |
1137 | @code{repeat} handler returns a list and the program must quote to use | |
1138 | it literally, the same as any other list. Ie. | |
1139 | ||
1140 | @example | |
1141 | (display '#,(repeat 99 3)) | |
a0e07ba4 | 1142 | @result{} |
633acbe2 KR |
1143 | (display '(99 99 99)) |
1144 | @end example | |
a0e07ba4 | 1145 | |
633acbe2 KR |
1146 | When a handler returns an object which is self-evaluating, like a |
1147 | number or a string, then there's no need for quoting, just as there's | |
1148 | no need when giving those directly as literals. For example an | |
1149 | addition, | |
a0e07ba4 | 1150 | |
633acbe2 KR |
1151 | @example |
1152 | (define-reader-ctor 'sum | |
1153 | (lambda (x y) | |
1154 | (+ x y))) | |
1155 | (display #,(sum 123 456)) @print{} 579 | |
1156 | @end example | |
1157 | ||
1158 | A typical use for @nicode{#,()} is to get a read syntax for objects | |
1159 | which don't otherwise have one. For example, the following allows a | |
1160 | hash table to be given literally, with tags and values, ready for fast | |
1161 | lookup. | |
1162 | ||
1163 | @example | |
1164 | (define-reader-ctor 'hash | |
1165 | (lambda elems | |
1166 | (let ((table (make-hash-table))) | |
1167 | (for-each (lambda (elem) | |
1168 | (apply hash-set! table elem)) | |
1169 | elems) | |
1170 | table))) | |
1171 | ||
1172 | (define (animal->family animal) | |
1173 | (hash-ref '#,(hash ("tiger" "cat") | |
1174 | ("lion" "cat") | |
1175 | ("wolf" "dog")) | |
1176 | animal)) | |
1177 | ||
1178 | (animal->family "lion") @result{} "cat" | |
1179 | @end example | |
1180 | ||
1181 | Or for example the following is a syntax for a compiled regular | |
1182 | expression (@pxref{Regular Expressions}). | |
1183 | ||
1184 | @example | |
1185 | (use-modules (ice-9 regex)) | |
1186 | ||
1187 | (define-reader-ctor 'regexp make-regexp) | |
1188 | ||
1189 | (define (extract-angs str) | |
1190 | (let ((match (regexp-exec '#,(regexp "<([A-Z0-9]+)>") str))) | |
1191 | (and match | |
1192 | (match:substring match 1)))) | |
1193 | ||
1194 | (extract-angs "foo <BAR> quux") @result{} "BAR" | |
1195 | @end example | |
1196 | ||
1197 | @sp 1 | |
1198 | @nicode{#,()} is somewhat similar to @code{define-macro} | |
1199 | (@pxref{Macros}) in that handler code is run to produce a result, but | |
1200 | @nicode{#,()} operates at the read stage, so it can appear in data for | |
1201 | @code{read} (@pxref{Scheme Read}), not just in code to be executed. | |
1202 | ||
1203 | Because @nicode{#,()} is handled at read-time it has no direct access | |
1204 | to variables etc. A symbol in the arguments is just a symbol, not a | |
1205 | variable reference. The arguments are essentially constants, though | |
1206 | the handler procedure can use them in any complicated way it might | |
1207 | want. | |
1208 | ||
1209 | Once @code{(srfi srfi-10)} has loaded, @nicode{#,()} is available | |
1210 | globally, there's no need to use @code{(srfi srfi-10)} in later | |
1211 | modules. Similarly the tags registered are global and can be used | |
1212 | anywhere once registered. | |
1213 | ||
1214 | There's no attempt to record what previous @nicode{#,()} forms have | |
1215 | been seen, if two identical forms occur then two calls are made to the | |
1216 | handler procedure. The handler might like to maintain a cache or | |
1217 | similar to avoid making copies of large objects, depending on expected | |
1218 | usage. | |
1219 | ||
1220 | In code the best uses of @nicode{#,()} are generally when there's a | |
1221 | lot of objects of a particular kind as literals or constants. If | |
1222 | there's just a few then some local variables and initializers are | |
1223 | fine, but that becomes tedious and error prone when there's a lot, and | |
1224 | the anonymous and compact syntax of @nicode{#,()} is much better. | |
a0e07ba4 NJ |
1225 | |
1226 | ||
1227 | @node SRFI-11 | |
3229f68b | 1228 | @subsection SRFI-11 - let-values |
8742c48b | 1229 | @cindex SRFI-11 |
a0e07ba4 | 1230 | |
8742c48b KR |
1231 | @findex let-values |
1232 | @findex let-values* | |
a0e07ba4 NJ |
1233 | This module implements the binding forms for multiple values |
1234 | @code{let-values} and @code{let-values*}. These forms are similar to | |
1235 | @code{let} and @code{let*} (@pxref{Local Bindings}), but they support | |
1236 | binding of the values returned by multiple-valued expressions. | |
1237 | ||
1238 | Write @code{(use-modules (srfi srfi-11))} to make the bindings | |
1239 | available. | |
1240 | ||
1241 | @lisp | |
1242 | (let-values (((x y) (values 1 2)) | |
1243 | ((z f) (values 3 4))) | |
1244 | (+ x y z f)) | |
1245 | @result{} | |
1246 | 10 | |
1247 | @end lisp | |
1248 | ||
1249 | @code{let-values} performs all bindings simultaneously, which means that | |
1250 | no expression in the binding clauses may refer to variables bound in the | |
1251 | same clause list. @code{let-values*}, on the other hand, performs the | |
1252 | bindings sequentially, just like @code{let*} does for single-valued | |
1253 | expressions. | |
1254 | ||
1255 | ||
1256 | @node SRFI-13 | |
3229f68b | 1257 | @subsection SRFI-13 - String Library |
8742c48b | 1258 | @cindex SRFI-13 |
a0e07ba4 | 1259 | |
5676b4fa | 1260 | The SRFI-13 procedures are always available, @xref{Strings}. |
a0e07ba4 NJ |
1261 | |
1262 | @node SRFI-14 | |
3229f68b | 1263 | @subsection SRFI-14 - Character-set Library |
8742c48b | 1264 | @cindex SRFI-14 |
a0e07ba4 | 1265 | |
050ab45f MV |
1266 | The SRFI-14 data type and procedures are always available, |
1267 | @xref{Character Sets}. | |
a0e07ba4 NJ |
1268 | |
1269 | @node SRFI-16 | |
3229f68b | 1270 | @subsection SRFI-16 - case-lambda |
8742c48b | 1271 | @cindex SRFI-16 |
7c2e18cd KR |
1272 | @cindex variable arity |
1273 | @cindex arity, variable | |
a0e07ba4 NJ |
1274 | |
1275 | @c FIXME::martin: Review me! | |
1276 | ||
8742c48b | 1277 | @findex case-lambda |
a0e07ba4 NJ |
1278 | The syntactic form @code{case-lambda} creates procedures, just like |
1279 | @code{lambda}, but has syntactic extensions for writing procedures of | |
1280 | varying arity easier. | |
1281 | ||
1282 | The syntax of the @code{case-lambda} form is defined in the following | |
1283 | EBNF grammar. | |
1284 | ||
1285 | @example | |
1286 | @group | |
1287 | <case-lambda> | |
1288 | --> (case-lambda <case-lambda-clause>) | |
1289 | <case-lambda-clause> | |
1290 | --> (<formals> <definition-or-command>*) | |
1291 | <formals> | |
1292 | --> (<identifier>*) | |
1293 | | (<identifier>* . <identifier>) | |
1294 | | <identifier> | |
1295 | @end group | |
1296 | @end example | |
1297 | ||
1298 | The value returned by a @code{case-lambda} form is a procedure which | |
1299 | matches the number of actual arguments against the formals in the | |
1300 | various clauses, in order. @dfn{Formals} means a formal argument list | |
1301 | just like with @code{lambda} (@pxref{Lambda}). The first matching clause | |
1302 | is selected, the corresponding values from the actual parameter list are | |
1303 | bound to the variable names in the clauses and the body of the clause is | |
1304 | evaluated. If no clause matches, an error is signalled. | |
1305 | ||
1306 | The following (silly) definition creates a procedure @var{foo} which | |
1307 | acts differently, depending on the number of actual arguments. If one | |
1308 | argument is given, the constant @code{#t} is returned, two arguments are | |
1309 | added and if more arguments are passed, their product is calculated. | |
1310 | ||
1311 | @lisp | |
1312 | (define foo (case-lambda | |
1313 | ((x) #t) | |
1314 | ((x y) (+ x y)) | |
1315 | (z | |
1316 | (apply * z)))) | |
1317 | (foo 'bar) | |
1318 | @result{} | |
1319 | #t | |
1320 | (foo 2 4) | |
1321 | @result{} | |
1322 | 6 | |
1323 | (foo 3 3 3) | |
1324 | @result{} | |
1325 | 27 | |
1326 | (foo) | |
1327 | @result{} | |
1328 | 1 | |
1329 | @end lisp | |
1330 | ||
1331 | The last expression evaluates to 1 because the last clause is matched, | |
1332 | @var{z} is bound to the empty list and the following multiplication, | |
1333 | applied to zero arguments, yields 1. | |
1334 | ||
1335 | ||
1336 | @node SRFI-17 | |
3229f68b | 1337 | @subsection SRFI-17 - Generalized set! |
8742c48b | 1338 | @cindex SRFI-17 |
a0e07ba4 NJ |
1339 | |
1340 | This is an implementation of SRFI-17: Generalized set! | |
1341 | ||
8742c48b | 1342 | @findex getter-with-setter |
a0e07ba4 NJ |
1343 | It exports the Guile procedure @code{make-procedure-with-setter} under |
1344 | the SRFI name @code{getter-with-setter} and exports the standard | |
1345 | procedures @code{car}, @code{cdr}, @dots{}, @code{cdddr}, | |
1346 | @code{string-ref} and @code{vector-ref} as procedures with setters, as | |
1347 | required by the SRFI. | |
1348 | ||
1349 | SRFI-17 was heavily criticized during its discussion period but it was | |
1350 | finalized anyway. One issue was its concept of globally associating | |
1351 | setter @dfn{properties} with (procedure) values, which is non-Schemy. | |
1352 | For this reason, this implementation chooses not to provide a way to set | |
1353 | the setter of a procedure. In fact, @code{(set! (setter @var{proc}) | |
1354 | @var{setter})} signals an error. The only way to attach a setter to a | |
1355 | procedure is to create a new object (a @dfn{procedure with setter}) via | |
1356 | the @code{getter-with-setter} procedure. This procedure is also | |
1357 | specified in the SRFI. Using it avoids the described problems. | |
1358 | ||
12991fed TTN |
1359 | |
1360 | @node SRFI-19 | |
3229f68b | 1361 | @subsection SRFI-19 - Time/Date Library |
8742c48b | 1362 | @cindex SRFI-19 |
7c2e18cd KR |
1363 | @cindex time |
1364 | @cindex date | |
12991fed | 1365 | |
85600a0f KR |
1366 | This is an implementation of the SRFI-19 time/date library. The |
1367 | functions and variables described here are provided by | |
12991fed TTN |
1368 | |
1369 | @example | |
85600a0f | 1370 | (use-modules (srfi srfi-19)) |
12991fed TTN |
1371 | @end example |
1372 | ||
85600a0f KR |
1373 | @menu |
1374 | * SRFI-19 Introduction:: | |
1375 | * SRFI-19 Time:: | |
1376 | * SRFI-19 Date:: | |
1377 | * SRFI-19 Time/Date conversions:: | |
1378 | * SRFI-19 Date to string:: | |
1379 | * SRFI-19 String to date:: | |
1380 | @end menu | |
12991fed | 1381 | |
85600a0f | 1382 | @node SRFI-19 Introduction |
3229f68b | 1383 | @subsubsection SRFI-19 Introduction |
85600a0f KR |
1384 | |
1385 | @cindex universal time | |
1386 | @cindex atomic time | |
1387 | @cindex UTC | |
1388 | @cindex TAI | |
1389 | This module implements time and date representations and calculations, | |
1390 | in various time systems, including universal time (UTC) and atomic | |
1391 | time (TAI). | |
1392 | ||
1393 | For those not familiar with these time systems, TAI is based on a | |
1394 | fixed length second derived from oscillations of certain atoms. UTC | |
1395 | differs from TAI by an integral number of seconds, which is increased | |
1396 | or decreased at announced times to keep UTC aligned to a mean solar | |
1397 | day (the orbit and rotation of the earth are not quite constant). | |
1398 | ||
1399 | @cindex leap second | |
1400 | So far, only increases in the TAI | |
1401 | @tex | |
1402 | $\leftrightarrow$ | |
1403 | @end tex | |
1404 | @ifnottex | |
1405 | <-> | |
1406 | @end ifnottex | |
1407 | UTC difference have been needed. Such an increase is a ``leap | |
1408 | second'', an extra second of TAI introduced at the end of a UTC day. | |
1409 | When working entirely within UTC this is never seen, every day simply | |
1410 | has 86400 seconds. But when converting from TAI to a UTC date, an | |
1411 | extra 23:59:60 is present, where normally a day would end at 23:59:59. | |
1412 | Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI | |
1413 | seconds. | |
1414 | ||
1415 | @cindex system clock | |
1416 | In the current implementation, the system clock is assumed to be UTC, | |
1417 | and a table of leap seconds in the code converts to TAI. See comments | |
1418 | in @file{srfi-19.scm} for how to update this table. | |
1419 | ||
1420 | @cindex julian day | |
1421 | @cindex modified julian day | |
1422 | Also, for those not familiar with the terminology, a @dfn{Julian Day} | |
1423 | is a real number which is a count of days and fraction of a day, in | |
1424 | UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan | |
7c2e18cd KR |
1425 | 4713 B.C. A @dfn{Modified Julian Day} is the same, but starting from |
1426 | 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC. That time | |
1427 | is julian day 2400000.5. | |
85600a0f KR |
1428 | |
1429 | @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at | |
1430 | @c noon, UTC), but this is incorrect. It looks like it might have | |
1431 | @c arisen from the code incorrectly treating years a multiple of 100 | |
7c2e18cd | 1432 | @c but not 400 prior to 1582 as non-leap years, where instead the Julian |
85600a0f KR |
1433 | @c calendar should be used so all multiples of 4 before 1582 are leap |
1434 | @c years. | |
1435 | ||
1436 | ||
1437 | @node SRFI-19 Time | |
3229f68b | 1438 | @subsubsection SRFI-19 Time |
85600a0f KR |
1439 | @cindex time |
1440 | ||
1441 | A @dfn{time} object has type, seconds and nanoseconds fields | |
1442 | representing a point in time starting from some epoch. This is an | |
1443 | arbitrary point in time, not just a time of day. Although times are | |
1444 | represented in nanoseconds, the actual resolution may be lower. | |
1445 | ||
1446 | The following variables hold the possible time types. For instance | |
1447 | @code{(current-time time-process)} would give the current CPU process | |
1448 | time. | |
1449 | ||
1450 | @defvar time-utc | |
1451 | Universal Coordinated Time (UTC). | |
1452 | @cindex UTC | |
1453 | @end defvar | |
12991fed | 1454 | |
85600a0f KR |
1455 | @defvar time-tai |
1456 | International Atomic Time (TAI). | |
1457 | @cindex TAI | |
1458 | @end defvar | |
12991fed | 1459 | |
85600a0f KR |
1460 | @defvar time-monotonic |
1461 | Monotonic time, meaning a monotonically increasing time starting from | |
1462 | an unspecified epoch. | |
12991fed | 1463 | |
85600a0f KR |
1464 | Note that in the current implementation @code{time-monotonic} is the |
1465 | same as @code{time-tai}, and unfortunately is therefore affected by | |
1466 | adjustments to the system clock. Perhaps this will change in the | |
1467 | future. | |
1468 | @end defvar | |
12991fed | 1469 | |
85600a0f KR |
1470 | @defvar time-duration |
1471 | A duration, meaning simply a difference between two times. | |
1472 | @end defvar | |
12991fed | 1473 | |
85600a0f KR |
1474 | @defvar time-process |
1475 | CPU time spent in the current process, starting from when the process | |
1476 | began. | |
1477 | @cindex process time | |
1478 | @end defvar | |
12991fed | 1479 | |
85600a0f KR |
1480 | @defvar time-thread |
1481 | CPU time spent in the current thread. Not currently implemented. | |
1482 | @cindex thread time | |
1483 | @end defvar | |
12991fed | 1484 | |
85600a0f KR |
1485 | @sp 1 |
1486 | @defun time? obj | |
1487 | Return @code{#t} if @var{obj} is a time object, or @code{#f} if not. | |
1488 | @end defun | |
1489 | ||
1490 | @defun make-time type nanoseconds seconds | |
1491 | Create a time object with the given @var{type}, @var{seconds} and | |
1492 | @var{nanoseconds}. | |
1493 | @end defun | |
1494 | ||
1495 | @defun time-type time | |
1496 | @defunx time-nanosecond time | |
1497 | @defunx time-second time | |
1498 | @defunx set-time-type! time type | |
1499 | @defunx set-time-nanosecond! time nsec | |
1500 | @defunx set-time-second! time sec | |
1501 | Get or set the type, seconds or nanoseconds fields of a time object. | |
1502 | ||
1503 | @code{set-time-type!} merely changes the field, it doesn't convert the | |
1504 | time value. For conversions, see @ref{SRFI-19 Time/Date conversions}. | |
1505 | @end defun | |
1506 | ||
1507 | @defun copy-time time | |
1508 | Return a new time object, which is a copy of the given @var{time}. | |
1509 | @end defun | |
1510 | ||
1511 | @defun current-time [type] | |
1512 | Return the current time of the given @var{type}. The default | |
1513 | @var{type} is @code{time-utc}. | |
1514 | ||
1515 | Note that the name @code{current-time} conflicts with the Guile core | |
1516 | @code{current-time} function (@pxref{Time}). Applications wanting to | |
1517 | use both will need to use a different name for one of them. | |
1518 | @end defun | |
1519 | ||
1520 | @defun time-resolution [type] | |
1521 | Return the resolution, in nanoseconds, of the given time @var{type}. | |
1522 | The default @var{type} is @code{time-utc}. | |
1523 | @end defun | |
1524 | ||
1525 | @defun time<=? t1 t2 | |
1526 | @defunx time<? t1 t2 | |
1527 | @defunx time=? t1 t2 | |
1528 | @defunx time>=? t1 t2 | |
1529 | @defunx time>? t1 t2 | |
1530 | Return @code{#t} or @code{#f} according to the respective relation | |
1531 | between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2} | |
1532 | must be the same time type. | |
1533 | @end defun | |
1534 | ||
1535 | @defun time-difference t1 t2 | |
1536 | @defunx time-difference! t1 t2 | |
1537 | Return a time object of type @code{time-duration} representing the | |
1538 | period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be | |
1539 | the same time type. | |
1540 | ||
1541 | @code{time-difference} returns a new time object, | |
1542 | @code{time-difference!} may modify @var{t1} to form its return. | |
1543 | @end defun | |
1544 | ||
1545 | @defun add-duration time duration | |
1546 | @defunx add-duration! time duration | |
1547 | @defunx subtract-duration time duration | |
1548 | @defunx subtract-duration! time duration | |
1549 | Return a time object which is @var{time} with the given @var{duration} | |
1550 | added or subtracted. @var{duration} must be a time object of type | |
1551 | @code{time-duration}. | |
1552 | ||
1553 | @code{add-duration} and @code{subtract-duration} return a new time | |
1554 | object. @code{add-duration!} and @code{subtract-duration!} may modify | |
1555 | the given @var{time} to form their return. | |
1556 | @end defun | |
1557 | ||
1558 | ||
1559 | @node SRFI-19 Date | |
3229f68b | 1560 | @subsubsection SRFI-19 Date |
85600a0f KR |
1561 | @cindex date |
1562 | ||
1563 | A @dfn{date} object represents a date in the Gregorian calendar and a | |
1564 | time of day on that date in some timezone. | |
1565 | ||
1566 | The fields are year, month, day, hour, minute, second, nanoseconds and | |
1567 | timezone. A date object is immutable, its fields can be read but they | |
1568 | cannot be modified once the object is created. | |
1569 | ||
1570 | @defun date? obj | |
1571 | Return @code{#t} if @var{obj} is a date object, or @code{#f} if not. | |
1572 | @end defun | |
1573 | ||
1574 | @defun make-date nsecs seconds minutes hours date month year zone-offset | |
1575 | Create a new date object. | |
1576 | @c | |
1577 | @c FIXME: What can we say about the ranges of the values. The | |
1578 | @c current code looks it doesn't normalize, but expects then in their | |
1579 | @c usual range already. | |
1580 | @c | |
1581 | @end defun | |
1582 | ||
1583 | @defun date-nanosecond date | |
1584 | Nanoseconds, 0 to 999999999. | |
1585 | @end defun | |
1586 | ||
1587 | @defun date-second date | |
7c2e18cd KR |
1588 | Seconds, 0 to 59, or 60 for a leap second. 60 is never seen when working |
1589 | entirely within UTC, it's only when converting to or from TAI. | |
85600a0f KR |
1590 | @end defun |
1591 | ||
1592 | @defun date-minute date | |
1593 | Minutes, 0 to 59. | |
1594 | @end defun | |
1595 | ||
1596 | @defun date-hour date | |
1597 | Hour, 0 to 23. | |
1598 | @end defun | |
1599 | ||
1600 | @defun date-day date | |
1601 | Day of the month, 1 to 31 (or less, according to the month). | |
1602 | @end defun | |
1603 | ||
1604 | @defun date-month date | |
1605 | Month, 1 to 12. | |
1606 | @end defun | |
1607 | ||
1608 | @defun date-year date | |
7c2e18cd KR |
1609 | Year, eg.@: 2003. Dates B.C.@: are negative, eg.@: @math{-46} is 46 |
1610 | B.C. There is no year 0, year @math{-1} is followed by year 1. | |
85600a0f KR |
1611 | @end defun |
1612 | ||
1613 | @defun date-zone-offset date | |
1614 | Time zone, an integer number of seconds east of Greenwich. | |
1615 | @end defun | |
1616 | ||
1617 | @defun date-year-day date | |
1618 | Day of the year, starting from 1 for 1st January. | |
1619 | @end defun | |
1620 | ||
1621 | @defun date-week-day date | |
1622 | Day of the week, starting from 0 for Sunday. | |
1623 | @end defun | |
1624 | ||
1625 | @defun date-week-number date dstartw | |
1626 | Week of the year, ignoring a first partial week. @var{dstartw} is the | |
1627 | day of the week which is taken to start a week, 0 for Sunday, 1 for | |
1628 | Monday, etc. | |
1629 | @c | |
1630 | @c FIXME: The spec doesn't say whether numbering starts at 0 or 1. | |
1631 | @c The code looks like it's 0, if that's the correct intention. | |
1632 | @c | |
1633 | @end defun | |
1634 | ||
1635 | @c The SRFI text doesn't actually give the default for tz-offset, but | |
1636 | @c the reference implementation has the local timezone and the | |
1637 | @c conversions functions all specify that, so it should be ok to | |
1638 | @c document it here. | |
1639 | @c | |
1640 | @defun current-date [tz-offset] | |
7c2e18cd KR |
1641 | Return a date object representing the current date/time, in UTC offset |
1642 | by @var{tz-offset}. @var{tz-offset} is seconds east of Greenwich and | |
1643 | defaults to the local timezone. | |
85600a0f KR |
1644 | @end defun |
1645 | ||
1646 | @defun current-julian-day | |
1647 | @cindex julian day | |
1648 | Return the current Julian Day. | |
1649 | @end defun | |
1650 | ||
1651 | @defun current-modified-julian-day | |
1652 | @cindex modified julian day | |
1653 | Return the current Modified Julian Day. | |
1654 | @end defun | |
1655 | ||
1656 | ||
1657 | @node SRFI-19 Time/Date conversions | |
3229f68b | 1658 | @subsubsection SRFI-19 Time/Date conversions |
7c2e18cd KR |
1659 | @cindex time conversion |
1660 | @cindex date conversion | |
85600a0f KR |
1661 | |
1662 | @defun date->julian-day date | |
1663 | @defunx date->modified-julian-day date | |
1664 | @defunx date->time-monotonic date | |
1665 | @defunx date->time-tai date | |
1666 | @defunx date->time-utc date | |
1667 | @end defun | |
1668 | @defun julian-day->date jdn [tz-offset] | |
1669 | @defunx julian-day->time-monotonic jdn | |
1670 | @defunx julian-day->time-tai jdn | |
1671 | @defunx julian-day->time-utc jdn | |
1672 | @end defun | |
1673 | @defun modified-julian-day->date jdn [tz-offset] | |
1674 | @defunx modified-julian-day->time-monotonic jdn | |
1675 | @defunx modified-julian-day->time-tai jdn | |
1676 | @defunx modified-julian-day->time-utc jdn | |
1677 | @end defun | |
1678 | @defun time-monotonic->date time [tz-offset] | |
1679 | @defunx time-monotonic->time-tai time | |
1680 | @defunx time-monotonic->time-tai! time | |
1681 | @defunx time-monotonic->time-utc time | |
1682 | @defunx time-monotonic->time-utc! time | |
1683 | @end defun | |
1684 | @defun time-tai->date time [tz-offset] | |
1685 | @defunx time-tai->julian-day time | |
1686 | @defunx time-tai->modified-julian-day time | |
1687 | @defunx time-tai->time-monotonic time | |
1688 | @defunx time-tai->time-monotonic! time | |
1689 | @defunx time-tai->time-utc time | |
1690 | @defunx time-tai->time-utc! time | |
1691 | @end defun | |
1692 | @defun time-utc->date time [tz-offset] | |
1693 | @defunx time-utc->julian-day time | |
1694 | @defunx time-utc->modified-julian-day time | |
1695 | @defunx time-utc->time-monotonic time | |
1696 | @defunx time-utc->time-monotonic! time | |
1697 | @defunx time-utc->time-tai time | |
1698 | @defunx time-utc->time-tai! time | |
1699 | @sp 1 | |
1700 | Convert between dates, times and days of the respective types. For | |
1701 | instance @code{time-tai->time-utc} accepts a @var{time} object of type | |
1702 | @code{time-tai} and returns an object of type @code{time-utc}. | |
1703 | ||
1704 | For conversions to dates, @var{tz-offset} is seconds east of | |
7c2e18cd KR |
1705 | Greenwich. The default is the local timezone, at the given time, as |
1706 | provided by the system. | |
85600a0f KR |
1707 | |
1708 | The @code{!} variants may modify their @var{time} argument to form | |
1709 | their return. The plain functions create a new object. | |
1710 | @end defun | |
1711 | ||
1712 | @node SRFI-19 Date to string | |
3229f68b | 1713 | @subsubsection SRFI-19 Date to string |
85600a0f | 1714 | @cindex date to string |
7c2e18cd | 1715 | @cindex string, from date |
85600a0f KR |
1716 | |
1717 | @defun date->string date [format] | |
1718 | Convert a date to a string under the control of a format. | |
1719 | @var{format} should be a string containing @samp{~} escapes, which | |
1720 | will be expanded as per the following conversion table. The default | |
1721 | @var{format} is @samp{~c}, a locale-dependent date and time. | |
1722 | ||
1723 | Many of these conversion characters are the same as POSIX | |
1724 | @code{strftime} (@pxref{Time}), but there are some extras and some | |
1725 | variations. | |
1726 | ||
1727 | @multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM} | |
1728 | @item @nicode{~~} @tab literal ~ | |
1729 | @item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun} | |
1730 | @item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday} | |
1731 | @item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan} | |
1732 | @item @nicode{~B} @tab locale full month, eg.@: @samp{January} | |
1733 | @item @nicode{~c} @tab locale date and time, eg.@: @* | |
1734 | @samp{Fri Jul 14 20:28:42-0400 2000} | |
1735 | @item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31} | |
1736 | ||
1737 | @c Spec says d/m/y, reference implementation says m/d/y. | |
1738 | @c Apparently the reference code was the intention, but would like to | |
1739 | @c see an errata published for the spec before contradicting it here. | |
1740 | @c | |
1741 | @c @item @nicode{~D} @tab date @nicode{~d/~m/~y} | |
1742 | ||
1743 | @item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31} | |
1744 | @item @nicode{~f} @tab seconds and fractional seconds, | |
1745 | with locale decimal point, eg.@: @samp{5.2} | |
1746 | @item @nicode{~h} @tab same as @nicode{~b} | |
1747 | @item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23} | |
1748 | @item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12} | |
1749 | @item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366} | |
1750 | @item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23} | |
1751 | @item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12} | |
1752 | @item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12} | |
1753 | @item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59} | |
1754 | @item @nicode{~n} @tab newline | |
1755 | @item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999} | |
1756 | @item @nicode{~p} @tab locale AM or PM | |
1757 | @item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p} | |
1758 | @item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC | |
1759 | @item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @* | |
1760 | (usual limit is 59, 60 is a leap second) | |
1761 | @item @nicode{~t} @tab horizontal tab character | |
1762 | @item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S} | |
1763 | @item @nicode{~U} @tab week of year, Sunday first day of week, | |
1764 | @samp{00} to @samp{52} | |
1765 | @item @nicode{~V} @tab week of year, Monday first day of week, | |
1766 | @samp{01} to @samp{53} | |
1767 | @item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6} | |
1768 | @item @nicode{~W} @tab week of year, Monday first day of week, | |
1769 | @samp{00} to @samp{52} | |
1770 | ||
1771 | @c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale | |
1772 | @c date. The reference code has ~x as the locale date and ~X as a | |
1773 | @c locale time. The rule is apparently that the code should be | |
1774 | @c believed, but would like to see an errata for the spec before | |
1775 | @c contradicting it here. | |
1776 | @c | |
1777 | @c @item @nicode{~x} @tab week of year, Monday as first day of week, | |
1778 | @c @samp{00} to @samp{53} | |
1779 | @c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00} | |
1780 | ||
1781 | @item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99} | |
1782 | @item @nicode{~Y} @tab year, full, eg.@: @samp{2003} | |
1783 | @item @nicode{~z} @tab time zone, RFC-822 style | |
1784 | @item @nicode{~Z} @tab time zone symbol (not currently implemented) | |
1785 | @item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d} | |
1786 | @item @nicode{~2} @tab ISO-8601 time+zone, @samp{~k:~M:~S~z} | |
1787 | @item @nicode{~3} @tab ISO-8601 time, @samp{~k:~M:~S} | |
1788 | @item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~k:~M:~S~z} | |
1789 | @item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~k:~M:~S} | |
1790 | @end multitable | |
1791 | @end defun | |
1792 | ||
1793 | Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently | |
1794 | described here, since the specification and reference implementation | |
1795 | differ. | |
1796 | ||
1797 | Currently Guile doesn't implement any localizations for the above, all | |
1798 | outputs are in English, and the @samp{~c} conversion is POSIX | |
1799 | @code{ctime} style @samp{~a ~b ~d ~H:~M:~S~z ~Y}. This may change in | |
1800 | the future. | |
1801 | ||
1802 | ||
1803 | @node SRFI-19 String to date | |
3229f68b | 1804 | @subsubsection SRFI-19 String to date |
85600a0f | 1805 | @cindex string to date |
7c2e18cd | 1806 | @cindex date, from string |
85600a0f KR |
1807 | |
1808 | @c FIXME: Can we say what happens when an incomplete date is | |
1809 | @c converted? Ie. fields left as 0, or what? The spec seems to be | |
1810 | @c silent on this. | |
1811 | ||
1812 | @defun string->date input template | |
1813 | Convert an @var{input} string to a date under the control of a | |
1814 | @var{template} string. Return a newly created date object. | |
1815 | ||
1816 | Literal characters in @var{template} must match characters in | |
1817 | @var{input} and @samp{~} escapes must match the input forms described | |
1818 | in the table below. ``Skip to'' means characters up to one of the | |
1819 | given type are ignored, or ``no skip'' for no skipping. ``Read'' is | |
1820 | what's then read, and ``Set'' is the field affected in the date | |
1821 | object. | |
1822 | ||
1823 | For example @samp{~Y} skips input characters until a digit is reached, | |
1824 | at which point it expects a year and stores that to the year field of | |
1825 | the date. | |
1826 | ||
1827 | @multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}} | |
1828 | @item | |
1829 | @tab Skip to | |
1830 | @tab Read | |
1831 | @tab Set | |
1832 | ||
1833 | @item @nicode{~~} | |
1834 | @tab no skip | |
1835 | @tab literal ~ | |
1836 | @tab nothing | |
1837 | ||
1838 | @item @nicode{~a} | |
1839 | @tab @nicode{char-alphabetic?} | |
1840 | @tab locale abbreviated weekday name | |
1841 | @tab nothing | |
1842 | ||
1843 | @item @nicode{~A} | |
1844 | @tab @nicode{char-alphabetic?} | |
1845 | @tab locale full weekday name | |
1846 | @tab nothing | |
1847 | ||
1848 | @c Note that the SRFI spec says that ~b and ~B don't set anything, | |
1849 | @c but that looks like a mistake. The reference implementation sets | |
1850 | @c the month field, which seems sensible and is what we describe | |
1851 | @c here. | |
1852 | ||
1853 | @item @nicode{~b} | |
1854 | @tab @nicode{char-alphabetic?} | |
1855 | @tab locale abbreviated month name | |
1856 | @tab @nicode{date-month} | |
1857 | ||
1858 | @item @nicode{~B} | |
1859 | @tab @nicode{char-alphabetic?} | |
1860 | @tab locale full month name | |
1861 | @tab @nicode{date-month} | |
1862 | ||
1863 | @item @nicode{~d} | |
1864 | @tab @nicode{char-numeric?} | |
1865 | @tab day of month | |
1866 | @tab @nicode{date-day} | |
1867 | ||
1868 | @item @nicode{~e} | |
1869 | @tab no skip | |
1870 | @tab day of month, blank padded | |
1871 | @tab @nicode{date-day} | |
1872 | ||
1873 | @item @nicode{~h} | |
1874 | @tab same as @samp{~b} | |
1875 | ||
1876 | @item @nicode{~H} | |
1877 | @tab @nicode{char-numeric?} | |
1878 | @tab hour | |
1879 | @tab @nicode{date-hour} | |
1880 | ||
1881 | @item @nicode{~k} | |
1882 | @tab no skip | |
1883 | @tab hour, blank padded | |
1884 | @tab @nicode{date-hour} | |
1885 | ||
1886 | @item @nicode{~m} | |
1887 | @tab @nicode{char-numeric?} | |
1888 | @tab month | |
1889 | @tab @nicode{date-month} | |
1890 | ||
1891 | @item @nicode{~M} | |
1892 | @tab @nicode{char-numeric?} | |
1893 | @tab minute | |
1894 | @tab @nicode{date-minute} | |
1895 | ||
1896 | @item @nicode{~S} | |
1897 | @tab @nicode{char-numeric?} | |
1898 | @tab second | |
1899 | @tab @nicode{date-second} | |
1900 | ||
1901 | @item @nicode{~y} | |
1902 | @tab no skip | |
1903 | @tab 2-digit year | |
1904 | @tab @nicode{date-year} within 50 years | |
1905 | ||
1906 | @item @nicode{~Y} | |
1907 | @tab @nicode{char-numeric?} | |
1908 | @tab year | |
1909 | @tab @nicode{date-year} | |
1910 | ||
1911 | @item @nicode{~z} | |
1912 | @tab no skip | |
1913 | @tab time zone | |
1914 | @tab date-zone-offset | |
1915 | @end multitable | |
1916 | ||
1917 | Notice that the weekday matching forms don't affect the date object | |
1918 | returned, instead the weekday will be derived from the day, month and | |
1919 | year. | |
1920 | ||
1921 | Currently Guile doesn't implement any localizations for the above, | |
1922 | month and weekday names are always expected in English. This may | |
1923 | change in the future. | |
1924 | @end defun | |
12991fed | 1925 | |
1de8c1ae | 1926 | |
b0b55bd6 | 1927 | @node SRFI-26 |
3229f68b | 1928 | @subsection SRFI-26 - specializing parameters |
1de8c1ae | 1929 | @cindex SRFI-26 |
7c2e18cd KR |
1930 | @cindex parameter specialize |
1931 | @cindex argument specialize | |
1932 | @cindex specialize parameter | |
1de8c1ae KR |
1933 | |
1934 | This SRFI provides a syntax for conveniently specializing selected | |
1935 | parameters of a function. It can be used with, | |
1936 | ||
1937 | @example | |
1938 | (use-modules (srfi srfi-26)) | |
1939 | @end example | |
1940 | ||
1941 | @deffn {library syntax} cut slot @dots{} | |
1942 | @deffnx {library syntax} cute slot @dots{} | |
1943 | Return a new procedure which will make a call (@var{slot} @dots{}) but | |
1944 | with selected parameters specialized to given expressions. | |
1945 | ||
1946 | An example will illustrate the idea. The following is a | |
1947 | specialization of @code{write}, sending output to | |
1948 | @code{my-output-port}, | |
1949 | ||
1950 | @example | |
1951 | (cut write <> my-output-port) | |
1952 | @result{} | |
1953 | (lambda (obj) (write obj my-output-port)) | |
1954 | @end example | |
1955 | ||
1956 | The special symbol @code{<>} indicates a slot to be filled by an | |
1957 | argument to the new procedure. @code{my-output-port} on the other | |
1958 | hand is an expression to be evaluated and passed, ie.@: it specializes | |
1959 | the behaviour of @code{write}. | |
1960 | ||
1961 | @table @nicode | |
1962 | @item <> | |
1963 | A slot to be filled by an argument from the created procedure. | |
1964 | Arguments are assigned to @code{<>} slots in the order they appear in | |
1965 | the @code{cut} form, there's no way to re-arrange arguments. | |
1966 | ||
1967 | The first argument to @code{cut} is usually a procedure (or expression | |
1968 | giving a procedure), but @code{<>} is allowed there too. For example, | |
1969 | ||
1970 | @example | |
1971 | (cut <> 1 2 3) | |
1972 | @result{} | |
1973 | (lambda (proc) (proc 1 2 3)) | |
1974 | @end example | |
1975 | ||
1976 | @item <...> | |
1977 | A slot to be filled by all remaining arguments from the new procedure. | |
1978 | This can only occur at the end of a @code{cut} form. | |
1979 | ||
1980 | For example, a procedure taking a variable number of arguments like | |
1981 | @code{max} but in addition enforcing a lower bound, | |
1982 | ||
1983 | @example | |
1984 | (define my-lower-bound 123) | |
1985 | ||
1986 | (cut max my-lower-bound <...>) | |
1987 | @result{} | |
1988 | (lambda arglist (apply max my-lower-bound arglist)) | |
1989 | @end example | |
1990 | @end table | |
1991 | ||
1992 | For @code{cut} the specializing expressions are evaluated each time | |
1993 | the new procedure is called. For @code{cute} they're evaluated just | |
1994 | once, when the new procedure is created. The name @code{cute} stands | |
1995 | for ``@code{cut} with evaluated arguments''. In all cases the | |
1996 | evaluations take place in an unspecified order. | |
1997 | ||
1998 | The following illustrates the difference between @code{cut} and | |
1999 | @code{cute}, | |
2000 | ||
2001 | @example | |
2002 | (cut format <> "the time is ~s" (current-time)) | |
2003 | @result{} | |
2004 | (lambda (port) (format port "the time is ~s" (current-time))) | |
2005 | ||
2006 | (cute format <> "the time is ~s" (current-time)) | |
2007 | @result{} | |
2008 | (let ((val (current-time))) | |
2009 | (lambda (port) (format port "the time is ~s" val)) | |
2010 | @end example | |
2011 | ||
2012 | (There's no provision for a mixture of @code{cut} and @code{cute} | |
2013 | where some expressions would be evaluated every time but others | |
2014 | evaluated only once.) | |
2015 | ||
2016 | @code{cut} is really just a shorthand for the sort of @code{lambda} | |
2017 | forms shown in the above examples. But notice @code{cut} avoids the | |
2018 | need to name unspecialized parameters, and is more compact. Use in | |
2019 | functional programming style or just with @code{map}, @code{for-each} | |
2020 | or similar is typical. | |
2021 | ||
2022 | @example | |
2023 | (map (cut * 2 <>) '(1 2 3 4)) | |
2024 | ||
2025 | (for-each (cut write <> my-port) my-list) | |
2026 | @end example | |
2027 | @end deffn | |
b0b55bd6 | 2028 | |
8638c417 RB |
2029 | @node SRFI-31 |
2030 | @subsection SRFI-31 - A special form `rec' for recursive evaluation | |
2031 | @cindex SRFI-31 | |
7c2e18cd | 2032 | @cindex recursive expression |
8638c417 RB |
2033 | @findex rec |
2034 | ||
2035 | SRFI-31 defines a special form that can be used to create | |
2036 | self-referential expressions more conveniently. The syntax is as | |
2037 | follows: | |
2038 | ||
2039 | @example | |
2040 | @group | |
2041 | <rec expression> --> (rec <variable> <expression>) | |
2042 | <rec expression> --> (rec (<variable>+) <body>) | |
2043 | @end group | |
2044 | @end example | |
2045 | ||
2046 | The first syntax can be used to create self-referential expressions, | |
2047 | for example: | |
2048 | ||
2049 | @lisp | |
2050 | guile> (define tmp (rec ones (cons 1 (delay ones)))) | |
2051 | @end lisp | |
2052 | ||
2053 | The second syntax can be used to create anonymous recursive functions: | |
2054 | ||
2055 | @lisp | |
2056 | guile> (define tmp (rec (display-n item n) | |
2057 | (if (positive? n) | |
2058 | (begin (display n) (display-n (- n 1)))))) | |
2059 | guile> (tmp 42 3) | |
2060 | 424242 | |
2061 | guile> | |
2062 | @end lisp | |
12991fed | 2063 | |
eeadfda1 KR |
2064 | |
2065 | @node SRFI-39 | |
2066 | @subsection SRFI-39 - Parameters | |
2067 | @cindex SRFI-39 | |
2068 | @cindex parameter object | |
2069 | @tindex Parameter | |
2070 | ||
2071 | This SRFI provides parameter objects, which implement dynamically | |
2072 | bound locations for values. The functions below are available from | |
2073 | ||
2074 | @example | |
2075 | (use-modules (srfi srfi-39)) | |
2076 | @end example | |
2077 | ||
2078 | A parameter object is a procedure. Called with no arguments it | |
2079 | returns its value, called with one argument it sets the value. | |
2080 | ||
2081 | @example | |
2082 | (define my-param (make-parameter 123)) | |
2083 | (my-param) @result{} 123 | |
2084 | (my-param 456) | |
2085 | (my-param) @result{} 456 | |
2086 | @end example | |
2087 | ||
2088 | The @code{parameterize} special form establishes new locations for | |
2089 | parameters, those new locations having effect within the dynamic scope | |
2090 | of the @code{parameterize} body. Leaving restores the previous | |
2091 | locations, or re-entering through a saved continuation will again use | |
2092 | the new locations. | |
2093 | ||
2094 | @example | |
2095 | (parameterize ((my-param 789)) | |
2096 | (my-param) @result{} 789 | |
2097 | ) | |
2098 | (my-param) @result{} 456 | |
2099 | @end example | |
2100 | ||
2101 | Parameters are like dynamically bound variables in other Lisp dialets. | |
2102 | They allow an application to establish parameter settings (as the name | |
2103 | suggests) just for the execution of a particular bit of code, | |
2104 | restoring when done. Examples of such parameters might be | |
2105 | case-sensitivity for a search, or a prompt for user input. | |
2106 | ||
2107 | Global variables are not as good as parameter objects for this sort of | |
2108 | thing. Changes to them are visible to all threads, but in Guile | |
2109 | parameter object locations are per-thread, thereby truely limiting the | |
2110 | effect of @code{parameterize} to just its dynamic execution. | |
2111 | ||
2112 | Passing arguments to functions is thread-safe, but that soon becomes | |
2113 | tedious when there's more than a few or when they need to pass down | |
2114 | through several layers of calls before reaching the point they should | |
2115 | affect. And introducing a new setting to existing code is often | |
2116 | easier with a parameter object than adding arguments. | |
2117 | ||
2118 | ||
2119 | @sp 1 | |
2120 | @defun make-parameter init [converter] | |
2121 | Return a new parameter object, with initial value @var{init}. | |
2122 | ||
2123 | A parameter object is a procedure. When called @code{(param)} it | |
2124 | returns its value, or a call @code{(param val)} sets its value. For | |
2125 | example, | |
2126 | ||
2127 | @example | |
2128 | (define my-param (make-parameter 123)) | |
2129 | (my-param) @result{} 123 | |
2130 | ||
2131 | (my-param 456) | |
2132 | (my-param) @result{} 456 | |
2133 | @end example | |
2134 | ||
2135 | If a @var{converter} is given, then a call @code{(@var{converter} | |
2136 | val)} is made for each value set, its return is the value stored. | |
2137 | Such a call is made for the @var{init} initial value too. | |
2138 | ||
2139 | A @var{converter} allows values to be validated, or put into a | |
2140 | canonical form. For example, | |
2141 | ||
2142 | @example | |
2143 | (define my-param (make-parameter 123 | |
2144 | (lambda (val) | |
2145 | (if (not (number? val)) | |
2146 | (error "must be a number")) | |
2147 | (inexact->exact val)))) | |
2148 | (my-param 0.75) | |
2149 | (my-param) @result{} 3/4 | |
2150 | @end example | |
2151 | @end defun | |
2152 | ||
2153 | @deffn {library syntax} parameterize ((param value) @dots{}) body @dots{} | |
2154 | Establish a new dynamic scope with the given @var{param}s bound to new | |
2155 | locations and set to the given @var{value}s. @var{body} is evaluated | |
2156 | in that environment, the result is the return from the last form in | |
2157 | @var{body}. | |
2158 | ||
2159 | Each @var{param} is an expression which is evaluated to get the | |
2160 | parameter object. Often this will just be the name of a variable | |
2161 | holding the object, but it can be anything that evaluates to a | |
2162 | parameter. | |
2163 | ||
2164 | The @var{param} expressions and @var{value} expressions are all | |
2165 | evaluated before establishing the new dynamic bindings, and they're | |
2166 | evaluated in an unspecified order. | |
2167 | ||
2168 | For example, | |
2169 | ||
2170 | @example | |
2171 | (define prompt (make-parameter "Type something: ")) | |
2172 | (define (get-input) | |
2173 | (display (prompt)) | |
2174 | ...) | |
2175 | ||
2176 | (parameterize ((prompt "Type a number: ")) | |
2177 | (get-input) | |
2178 | ...) | |
2179 | @end example | |
2180 | @end deffn | |
2181 | ||
2182 | @deffn {Parameter object} current-input-port [new-port] | |
2183 | @deffnx {Parameter object} current-output-port [new-port] | |
2184 | @deffnx {Parameter object} current-error-port [new-port] | |
2185 | This SRFI extends the core @code{current-input-port} and | |
2186 | @code{current-output-port}, making them parameter objects. The | |
2187 | Guile-specific @code{current-error-port} is extended too, for | |
2188 | consistency. (@pxref{Default Ports}.) | |
2189 | ||
2190 | This is an upwardly compatible extension, a plain call like | |
2191 | @code{(current-input-port)} still returns the current input port, and | |
2192 | @code{set-current-input-port} can still be used. But the port can now | |
2193 | also be set with @code{(current-input-port my-port)} and bound | |
2194 | dynamically with @code{parameterize}. | |
2195 | @end deffn | |
2196 | ||
2197 | @defun with-parameters* param-list value-list thunk | |
2198 | Establish a new dynamic scope, as per @code{parameterize} above, | |
2199 | taking parameters from @var{param-list} and corresponding values from | |
2200 | @var{values-list}. A call @code{(@var{thunk})} is made in the new | |
2201 | scope and the result from that @var{thunk} is the return from | |
2202 | @code{with-parameters*}. | |
2203 | ||
2204 | This function is a Guile-specific addition to the SRFI, it's similar | |
2205 | to the core @code{with-fluids*} (@pxref{Fluids}). | |
2206 | @end defun | |
2207 | ||
2208 | ||
2209 | @sp 1 | |
2210 | Parameter objects are implemented using fluids (@pxref{Fluids}), so | |
2211 | each dynamic root has it's own parameter locations. That includes the | |
2212 | separate locations when outside any @code{parameterize} form. When a | |
2213 | parameter is created it gets a separate initial location in each | |
2214 | dynamic root, all initialized to the given @var{init} value. | |
2215 | ||
2216 | As alluded to above, because each thread is a separate dynamic root, | |
2217 | each thread has it's own locations behind parameter objects, and | |
2218 | changes in one thread are not visible to any other. When a new | |
2219 | dynamic root or thread is created, the values of parameters in the | |
2220 | originating context are copied, into new locations. | |
2221 | ||
2222 | SRFI-39 doesn't specify the interaction between parameter objects and | |
2223 | threads, so the threading behaviour described here should be regarded | |
2224 | as Guile-specific. | |
2225 | ||
2226 | ||
12991fed | 2227 | @c srfi-modules.texi ends here |
193239f1 KR |
2228 | |
2229 | @c Local Variables: | |
2230 | @c TeX-master: "guile.texi" | |
2231 | @c End: |