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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Guile Reference Manual. | |
994d87be | 3 | @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007, 2008, 2009, 2010, 2011, 2012, 2013 |
07d83abe MV |
4 | @c Free Software Foundation, Inc. |
5 | @c See the file guile.texi for copying conditions. | |
6 | ||
07d83abe MV |
7 | @node Modules |
8 | @section Modules | |
9 | @cindex modules | |
10 | ||
11 | When programs become large, naming conflicts can occur when a function | |
12 | or global variable defined in one file has the same name as a function | |
13 | or global variable in another file. Even just a @emph{similarity} | |
14 | between function names can cause hard-to-find bugs, since a programmer | |
15 | might type the wrong function name. | |
16 | ||
17 | The approach used to tackle this problem is called @emph{information | |
18 | encapsulation}, which consists of packaging functional units into a | |
19 | given name space that is clearly separated from other name spaces. | |
20 | @cindex encapsulation | |
21 | @cindex information encapsulation | |
22 | @cindex name space | |
23 | ||
24 | The language features that allow this are usually called @emph{the | |
25 | module system} because programs are broken up into modules that are | |
26 | compiled separately (or loaded separately in an interpreter). | |
27 | ||
28 | Older languages, like C, have limited support for name space | |
29 | manipulation and protection. In C a variable or function is public by | |
30 | default, and can be made local to a module with the @code{static} | |
31 | keyword. But you cannot reference public variables and functions from | |
32 | another module with different names. | |
33 | ||
34 | More advanced module systems have become a common feature in recently | |
35 | designed languages: ML, Python, Perl, and Modula 3 all allow the | |
36 | @emph{renaming} of objects from a foreign module, so they will not | |
37 | clutter the global name space. | |
38 | @cindex name space - private | |
39 | ||
40 | In addition, Guile offers variables as first-class objects. They can | |
41 | be used for interacting with the module system. | |
42 | ||
07d83abe MV |
43 | @menu |
44 | * General Information about Modules:: Guile module basics. | |
45 | * Using Guile Modules:: How to use existing modules. | |
46 | * Creating Guile Modules:: How to package your code into modules. | |
992a3879 | 47 | * Modules and the File System:: Installing modules in the file system. |
dca14012 | 48 | * R6RS Version References:: Using version numbers with modules. |
71194485 | 49 | * R6RS Libraries:: The library and import forms. |
726b8ba3 | 50 | * Variables:: First-class variables. |
992a3879 AW |
51 | * Module System Reflection:: First-class modules. |
52 | * Accessing Modules from C:: How to work with modules with C code. | |
726b8ba3 AW |
53 | * provide and require:: The SLIB feature mechanism. |
54 | * Environments:: R5RS top-level environments. | |
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55 | @end menu |
56 | ||
57 | @node General Information about Modules | |
726b8ba3 | 58 | @subsection General Information about Modules |
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59 | |
60 | A Guile module can be thought of as a collection of named procedures, | |
61 | variables and macros. More precisely, it is a set of @dfn{bindings} | |
62 | of symbols (names) to Scheme objects. | |
63 | ||
07d83abe MV |
64 | Within a module, all bindings are visible. Certain bindings |
65 | can be declared @dfn{public}, in which case they are added to the | |
66 | module's so-called @dfn{export list}; this set of public bindings is | |
67 | called the module's @dfn{public interface} (@pxref{Creating Guile | |
68 | Modules}). | |
69 | ||
70 | A client module @dfn{uses} a providing module's bindings by either | |
71 | accessing the providing module's public interface, or by building a | |
72 | custom interface (and then accessing that). In a custom interface, the | |
73 | client module can @dfn{select} which bindings to access and can also | |
74 | algorithmically @dfn{rename} bindings. In contrast, when using the | |
75 | providing module's public interface, the entire export list is available | |
76 | without renaming (@pxref{Using Guile Modules}). | |
77 | ||
992a3879 AW |
78 | All Guile modules have a unique @dfn{module name}, for example |
79 | @code{(ice-9 popen)} or @code{(srfi srfi-11)}. Module names are lists | |
80 | of one or more symbols. | |
81 | ||
82 | When Guile goes to use an interface from a module, for example | |
83 | @code{(ice-9 popen)}, Guile first looks to see if it has loaded | |
84 | @code{(ice-9 popen)} for any reason. If the module has not been loaded | |
85 | yet, Guile searches a @dfn{load path} for a file that might define it, | |
86 | and loads that file. | |
07d83abe | 87 | |
992a3879 AW |
88 | The following subsections go into more detail on using, creating, |
89 | installing, and otherwise manipulating modules and the module system. | |
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90 | |
91 | @node Using Guile Modules | |
726b8ba3 | 92 | @subsection Using Guile Modules |
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93 | |
94 | To use a Guile module is to access either its public interface or a | |
95 | custom interface (@pxref{General Information about Modules}). Both | |
96 | types of access are handled by the syntactic form @code{use-modules}, | |
97 | which accepts one or more interface specifications and, upon evaluation, | |
98 | arranges for those interfaces to be available to the current module. | |
99 | This process may include locating and loading code for a given module if | |
0740cb49 AW |
100 | that code has not yet been loaded, following @code{%load-path} |
101 | (@pxref{Modules and the File System}). | |
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102 | |
103 | An @dfn{interface specification} has one of two forms. The first | |
104 | variation is simply to name the module, in which case its public | |
105 | interface is the one accessed. For example: | |
106 | ||
aba0dff5 | 107 | @lisp |
07d83abe | 108 | (use-modules (ice-9 popen)) |
aba0dff5 | 109 | @end lisp |
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110 | |
111 | Here, the interface specification is @code{(ice-9 popen)}, and the | |
112 | result is that the current module now has access to @code{open-pipe}, | |
254d313a | 113 | @code{close-pipe}, @code{open-input-pipe}, and so on (@pxref{Pipes}). |
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114 | |
115 | Note in the previous example that if the current module had already | |
116 | defined @code{open-pipe}, that definition would be overwritten by the | |
117 | definition in @code{(ice-9 popen)}. For this reason (and others), there | |
118 | is a second variation of interface specification that not only names a | |
119 | module to be accessed, but also selects bindings from it and renames | |
120 | them to suit the current module's needs. For example: | |
121 | ||
46bb559d | 122 | @cindex binding renamer |
aba0dff5 | 123 | @lisp |
07d83abe | 124 | (use-modules ((ice-9 popen) |
8d9cb14e NJ |
125 | #:select ((open-pipe . pipe-open) close-pipe) |
126 | #:renamer (symbol-prefix-proc 'unixy:))) | |
aba0dff5 | 127 | @end lisp |
07d83abe MV |
128 | |
129 | Here, the interface specification is more complex than before, and the | |
130 | result is that a custom interface with only two bindings is created and | |
131 | subsequently accessed by the current module. The mapping of old to new | |
132 | names is as follows: | |
133 | ||
134 | @c Use `smallexample' since `table' is ugly. --ttn | |
135 | @smallexample | |
136 | (ice-9 popen) sees: current module sees: | |
137 | open-pipe unixy:pipe-open | |
138 | close-pipe unixy:close-pipe | |
139 | @end smallexample | |
140 | ||
141 | This example also shows how to use the convenience procedure | |
142 | @code{symbol-prefix-proc}. | |
143 | ||
144 | You can also directly refer to bindings in a module by using the | |
145 | @code{@@} syntax. For example, instead of using the | |
146 | @code{use-modules} statement from above and writing | |
147 | @code{unixy:pipe-open} to refer to the @code{pipe-open} from the | |
148 | @code{(ice-9 popen)}, you could also write @code{(@@ (ice-9 popen) | |
149 | open-pipe)}. Thus an alternative to the complete @code{use-modules} | |
150 | statement would be | |
151 | ||
aba0dff5 | 152 | @lisp |
07d83abe MV |
153 | (define unixy:pipe-open (@@ (ice-9 popen) open-pipe)) |
154 | (define unixy:close-pipe (@@ (ice-9 popen) close-pipe)) | |
aba0dff5 | 155 | @end lisp |
07d83abe MV |
156 | |
157 | There is also @code{@@@@}, which can be used like @code{@@}, but does | |
158 | not check whether the variable that is being accessed is actually | |
159 | exported. Thus, @code{@@@@} can be thought of as the impolite version | |
160 | of @code{@@} and should only be used as a last resort or for | |
161 | debugging, for example. | |
162 | ||
163 | Note that just as with a @code{use-modules} statement, any module that | |
164 | has not yet been loaded yet will be loaded when referenced by a | |
165 | @code{@@} or @code{@@@@} form. | |
166 | ||
167 | You can also use the @code{@@} and @code{@@@@} syntaxes as the target | |
168 | of a @code{set!} when the binding refers to a variable. | |
169 | ||
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170 | @deffn {Scheme Procedure} symbol-prefix-proc prefix-sym |
171 | Return a procedure that prefixes its arg (a symbol) with | |
172 | @var{prefix-sym}. | |
07d83abe MV |
173 | @end deffn |
174 | ||
07d83abe MV |
175 | @deffn syntax use-modules spec @dots{} |
176 | Resolve each interface specification @var{spec} into an interface and | |
177 | arrange for these to be accessible by the current module. The return | |
178 | value is unspecified. | |
179 | ||
180 | @var{spec} can be a list of symbols, in which case it names a module | |
181 | whose public interface is found and used. | |
182 | ||
183 | @var{spec} can also be of the form: | |
184 | ||
46bb559d | 185 | @cindex binding renamer |
aba0dff5 | 186 | @lisp |
992a3879 | 187 | (MODULE-NAME [#:select SELECTION] [#:renamer RENAMER]) |
aba0dff5 | 188 | @end lisp |
07d83abe MV |
189 | |
190 | in which case a custom interface is newly created and used. | |
191 | @var{module-name} is a list of symbols, as above; @var{selection} is a | |
192 | list of selection-specs; and @var{renamer} is a procedure that takes a | |
193 | symbol and returns its new name. A selection-spec is either a symbol or | |
194 | a pair of symbols @code{(ORIG . SEEN)}, where @var{orig} is the name in | |
195 | the used module and @var{seen} is the name in the using module. Note | |
196 | that @var{seen} is also passed through @var{renamer}. | |
197 | ||
992a3879 AW |
198 | The @code{#:select} and @code{#:renamer} clauses are optional. If both are |
199 | omitted, the returned interface has no bindings. If the @code{#:select} | |
07d83abe MV |
200 | clause is omitted, @var{renamer} operates on the used module's public |
201 | interface. | |
202 | ||
992a3879 | 203 | In addition to the above, @var{spec} can also include a @code{#:version} |
dca14012 JG |
204 | clause, of the form: |
205 | ||
206 | @lisp | |
992a3879 | 207 | #:version VERSION-SPEC |
dca14012 JG |
208 | @end lisp |
209 | ||
992a3879 AW |
210 | where @var{version-spec} is an R6RS-compatible version reference. An |
211 | error will be signaled in the case in which a module with the same name | |
212 | has already been loaded, if that module specifies a version and that | |
213 | version is not compatible with @var{version-spec}. @xref{R6RS Version | |
214 | References}, for more on version references. | |
07d83abe | 215 | |
992a3879 AW |
216 | If the module name is not resolvable, @code{use-modules} will signal an |
217 | error. | |
07d83abe MV |
218 | @end deffn |
219 | ||
220 | @deffn syntax @@ module-name binding-name | |
221 | Refer to the binding named @var{binding-name} in module | |
222 | @var{module-name}. The binding must have been exported by the module. | |
223 | @end deffn | |
224 | ||
225 | @deffn syntax @@@@ module-name binding-name | |
226 | Refer to the binding named @var{binding-name} in module | |
227 | @var{module-name}. The binding must not have been exported by the | |
228 | module. This syntax is only intended for debugging purposes or as a | |
229 | last resort. | |
230 | @end deffn | |
231 | ||
232 | @node Creating Guile Modules | |
726b8ba3 | 233 | @subsection Creating Guile Modules |
07d83abe MV |
234 | |
235 | When you want to create your own modules, you have to take the following | |
236 | steps: | |
237 | ||
238 | @itemize @bullet | |
239 | @item | |
240 | Create a Scheme source file and add all variables and procedures you wish | |
241 | to export, or which are required by the exported procedures. | |
242 | ||
243 | @item | |
244 | Add a @code{define-module} form at the beginning. | |
245 | ||
246 | @item | |
247 | Export all bindings which should be in the public interface, either | |
248 | by using @code{define-public} or @code{export} (both documented below). | |
249 | @end itemize | |
250 | ||
df0a1002 | 251 | @deffn syntax define-module module-name option @dots{} |
992a3879 | 252 | @var{module-name} is a list of one or more symbols. |
07d83abe | 253 | |
aba0dff5 | 254 | @lisp |
07d83abe | 255 | (define-module (ice-9 popen)) |
aba0dff5 | 256 | @end lisp |
07d83abe MV |
257 | |
258 | @code{define-module} makes this module available to Guile programs under | |
259 | the given @var{module-name}. | |
260 | ||
df0a1002 BT |
261 | @var{option} @dots{} are keyword/value pairs which specify more about the |
262 | defined module. The recognized options and their meaning are shown in | |
07d83abe MV |
263 | the following table. |
264 | ||
07d83abe MV |
265 | @table @code |
266 | @item #:use-module @var{interface-specification} | |
267 | Equivalent to a @code{(use-modules @var{interface-specification})} | |
268 | (@pxref{Using Guile Modules}). | |
269 | ||
950f97ac | 270 | @item #:autoload @var{module} @var{symbol-list} |
65f1345f | 271 | @cindex autoload |
950f97ac KR |
272 | Load @var{module} when any of @var{symbol-list} are accessed. For |
273 | example, | |
274 | ||
275 | @example | |
276 | (define-module (my mod) | |
277 | #:autoload (srfi srfi-1) (partition delete-duplicates)) | |
278 | ... | |
279 | (if something | |
280 | (set! foo (delete-duplicates ...))) | |
281 | @end example | |
282 | ||
a236df75 | 283 | When a module is autoloaded, all its bindings become available. |
950f97ac KR |
284 | @var{symbol-list} is just those that will first trigger the load. |
285 | ||
286 | An autoload is a good way to put off loading a big module until it's | |
287 | really needed, for instance for faster startup or if it will only be | |
288 | needed in certain circumstances. | |
289 | ||
290 | @code{@@} can do a similar thing (@pxref{Using Guile Modules}), but in | |
291 | that case an @code{@@} form must be written every time a binding from | |
292 | the module is used. | |
07d83abe MV |
293 | |
294 | @item #:export @var{list} | |
65f1345f | 295 | @cindex export |
78c22f5e | 296 | Export all identifiers in @var{list} which must be a list of symbols |
992a3879 | 297 | or pairs of symbols. This is equivalent to @code{(export @var{list})} |
78c22f5e | 298 | in the module body. |
07d83abe | 299 | |
46bb559d KR |
300 | @item #:re-export @var{list} |
301 | @cindex re-export | |
302 | Re-export all identifiers in @var{list} which must be a list of | |
78c22f5e JG |
303 | symbols or pairs of symbols. The symbols in @var{list} must be |
304 | imported by the current module from other modules. This is equivalent | |
305 | to @code{re-export} below. | |
46bb559d | 306 | |
46bb559d KR |
307 | @item #:replace @var{list} |
308 | @cindex replace | |
309 | @cindex replacing binding | |
310 | @cindex overriding binding | |
311 | @cindex duplicate binding | |
78c22f5e JG |
312 | Export all identifiers in @var{list} (a list of symbols or pairs of |
313 | symbols) and mark them as @dfn{replacing bindings}. In the module | |
314 | user's name space, this will have the effect of replacing any binding | |
315 | with the same name that is not also ``replacing''. Normally a | |
316 | replacement results in an ``override'' warning message, | |
317 | @code{#:replace} avoids that. | |
46bb559d | 318 | |
d68a81e0 AW |
319 | In general, a module that exports a binding for which the @code{(guile)} |
320 | module already has a definition should use @code{#:replace} instead of | |
321 | @code{#:export}. @code{#:replace}, in a sense, lets Guile know that the | |
322 | module @emph{purposefully} replaces a core binding. It is important to | |
323 | note, however, that this binding replacement is confined to the name | |
324 | space of the module user. In other words, the value of the core binding | |
325 | in question remains unchanged for other modules. | |
326 | ||
327 | Note that although it is often a good idea for the replaced binding to | |
328 | remain compatible with a binding in @code{(guile)}, to avoid surprising | |
329 | the user, sometimes the bindings will be incompatible. For example, | |
330 | SRFI-19 exports its own version of @code{current-time} (@pxref{SRFI-19 | |
331 | Time}) which is not compatible with the core @code{current-time} | |
332 | function (@pxref{Time}). Guile assumes that a user importing a module | |
333 | knows what she is doing, and uses @code{#:replace} for this binding | |
334 | rather than @code{#:export}. | |
e724644d | 335 | |
992a3879 AW |
336 | A @code{#:replace} clause is equivalent to @code{(export! @var{list})} |
337 | in the module body. | |
338 | ||
e724644d MV |
339 | The @code{#:duplicates} (see below) provides fine-grain control about |
340 | duplicate binding handling on the module-user side. | |
46bb559d | 341 | |
dca14012 JG |
342 | @item #:version @var{list} |
343 | @cindex module version | |
344 | Specify a version for the module in the form of @var{list}, a list of | |
345 | zero or more exact, nonnegative integers. The corresponding | |
346 | @code{#:version} option in the @code{use-modules} form allows callers | |
347 | to restrict the value of this option in various ways. | |
348 | ||
46bb559d KR |
349 | @item #:duplicates @var{list} |
350 | @cindex duplicate binding handlers | |
351 | @cindex duplicate binding | |
352 | @cindex overriding binding | |
353 | Tell Guile to handle duplicate bindings for the bindings imported by | |
354 | the current module according to the policy defined by @var{list}, a | |
355 | list of symbols. @var{list} must contain symbols representing a | |
356 | duplicate binding handling policy chosen among the following: | |
357 | ||
358 | @table @code | |
359 | @item check | |
360 | Raises an error when a binding is imported from more than one place. | |
361 | @item warn | |
362 | Issue a warning when a binding is imported from more than one place | |
363 | and leave the responsibility of actually handling the duplication to | |
364 | the next duplicate binding handler. | |
365 | @item replace | |
366 | When a new binding is imported that has the same name as a previously | |
367 | imported binding, then do the following: | |
368 | ||
369 | @enumerate | |
370 | @item | |
371 | @cindex replacing binding | |
372 | If the old binding was said to be @dfn{replacing} (via the | |
373 | @code{#:replace} option above) and the new binding is not replacing, | |
374 | the keep the old binding. | |
375 | @item | |
376 | If the old binding was not said to be replacing and the new binding is | |
377 | replacing, then replace the old binding with the new one. | |
378 | @item | |
379 | If neither the old nor the new binding is replacing, then keep the old | |
380 | one. | |
381 | @end enumerate | |
382 | ||
383 | @item warn-override-core | |
384 | Issue a warning when a core binding is being overwritten and actually | |
385 | override the core binding with the new one. | |
386 | @item first | |
387 | In case of duplicate bindings, the firstly imported binding is always | |
388 | the one which is kept. | |
389 | @item last | |
390 | In case of duplicate bindings, the lastly imported binding is always | |
391 | the one which is kept. | |
392 | @item noop | |
393 | In case of duplicate bindings, leave the responsibility to the next | |
394 | duplicate handler. | |
395 | @end table | |
396 | ||
397 | If @var{list} contains more than one symbol, then the duplicate | |
398 | binding handlers which appear first will be used first when resolving | |
399 | a duplicate binding situation. As mentioned above, some resolution | |
400 | policies may explicitly leave the responsibility of handling the | |
401 | duplication to the next handler in @var{list}. | |
402 | ||
992a3879 AW |
403 | If GOOPS has been loaded before the @code{#:duplicates} clause is |
404 | processed, there are additional strategies available for dealing with | |
405 | generic functions. @xref{Merging Generics}, for more information. | |
406 | ||
46bb559d KR |
407 | @findex default-duplicate-binding-handler |
408 | The default duplicate binding resolution policy is given by the | |
409 | @code{default-duplicate-binding-handler} procedure, and is | |
410 | ||
aba0dff5 | 411 | @lisp |
46bb559d | 412 | (replace warn-override-core warn last) |
aba0dff5 | 413 | @end lisp |
46bb559d | 414 | |
07d83abe | 415 | @item #:pure |
65f1345f | 416 | @cindex pure module |
07d83abe MV |
417 | Create a @dfn{pure} module, that is a module which does not contain any |
418 | of the standard procedure bindings except for the syntax forms. This is | |
419 | useful if you want to create @dfn{safe} modules, that is modules which | |
420 | do not know anything about dangerous procedures. | |
421 | @end table | |
422 | ||
423 | @end deffn | |
07d83abe MV |
424 | |
425 | @deffn syntax export variable @dots{} | |
78c22f5e JG |
426 | Add all @var{variable}s (which must be symbols or pairs of symbols) to |
427 | the list of exported bindings of the current module. If @var{variable} | |
428 | is a pair, its @code{car} gives the name of the variable as seen by the | |
429 | current module and its @code{cdr} specifies a name for the binding in | |
430 | the current module's public interface. | |
07d83abe MV |
431 | @end deffn |
432 | ||
07d83abe MV |
433 | @deffn syntax define-public @dots{} |
434 | Equivalent to @code{(begin (define foo ...) (export foo))}. | |
435 | @end deffn | |
07d83abe | 436 | |
46bb559d | 437 | @deffn syntax re-export variable @dots{} |
78c22f5e JG |
438 | Add all @var{variable}s (which must be symbols or pairs of symbols) to |
439 | the list of re-exported bindings of the current module. Pairs of | |
440 | symbols are handled as in @code{export}. Re-exported bindings must be | |
441 | imported by the current module from some other module. | |
46bb559d KR |
442 | @end deffn |
443 | ||
992a3879 AW |
444 | @deffn syntax export! variable @dots{} |
445 | Like @code{export}, but marking the exported variables as replacing. | |
446 | Using a module with replacing bindings will cause any existing bindings | |
447 | to be replaced without issuing any warnings. See the discussion of | |
448 | @code{#:replace} above. | |
cdf1ad3b MV |
449 | @end deffn |
450 | ||
992a3879 AW |
451 | @node Modules and the File System |
452 | @subsection Modules and the File System | |
07d83abe | 453 | |
992a3879 AW |
454 | Typical programs only use a small subset of modules installed on a Guile |
455 | system. In order to keep startup time down, Guile only loads modules | |
456 | when a program uses them, on demand. | |
e376f9e5 | 457 | |
992a3879 AW |
458 | When a program evaluates @code{(use-modules (ice-9 popen))}, and the |
459 | module is not loaded, Guile searches for a conventionally-named file | |
460 | from in the @dfn{load path}. | |
07d83abe | 461 | |
992a3879 AW |
462 | In this case, loading @code{(ice-9 popen)} will eventually cause Guile |
463 | to run @code{(primitive-load-path "ice-9/popen")}. | |
464 | @code{primitive-load-path} will search for a file @file{ice-9/popen} in | |
0740cb49 | 465 | the @code{%load-path} (@pxref{Load Paths}). For each directory in |
992a3879 AW |
466 | @code{%load-path}, Guile will try to find the file name, concatenated |
467 | with the extensions from @code{%load-extensions}. By default, this will | |
468 | cause Guile to @code{stat} @file{ice-9/popen.scm}, and then | |
925172cf | 469 | @file{ice-9/popen}. @xref{Load Paths}, for more on |
992a3879 | 470 | @code{primitive-load-path}. |
e376f9e5 | 471 | |
992a3879 AW |
472 | If a corresponding compiled @file{.go} file is found in the |
473 | @code{%load-compiled-path} or in the fallback path, and is as fresh as | |
474 | the source file, it will be loaded instead of the source file. If no | |
475 | compiled file is found, Guile may try to compile the source file and | |
476 | cache away the resulting @file{.go} file. @xref{Compilation}, for more | |
477 | on compilation. | |
07d83abe | 478 | |
992a3879 AW |
479 | Once Guile finds a suitable source or compiled file is found, the file |
480 | will be loaded. If, after loading the file, the module under | |
481 | consideration is still not defined, Guile will signal an error. | |
e376f9e5 | 482 | |
992a3879 AW |
483 | For more information on where and how to install Scheme modules, |
484 | @xref{Installing Site Packages}. | |
07d83abe MV |
485 | |
486 | ||
dca14012 | 487 | @node R6RS Version References |
726b8ba3 | 488 | @subsection R6RS Version References |
dca14012 JG |
489 | |
490 | Guile's module system includes support for locating modules based on | |
491 | a declared version specifier of the same form as the one described in | |
492 | R6RS (@pxref{Library form, R6RS Library Form,, r6rs, The Revised^6 | |
493 | Report on the Algorithmic Language Scheme}). By using the | |
494 | @code{#:version} keyword in a @code{define-module} form, a module may | |
495 | specify a version as a list of zero or more exact, nonnegative integers. | |
496 | ||
497 | This version can then be used to locate the module during the module | |
498 | search process. Client modules and callers of the @code{use-modules} | |
499 | function may specify constraints on the versions of target modules by | |
500 | providing a @dfn{version reference}, which has one of the following | |
501 | forms: | |
502 | ||
503 | @lisp | |
504 | (@var{sub-version-reference} ...) | |
505 | (and @var{version-reference} ...) | |
506 | (or @var{version-reference} ...) | |
507 | (not @var{version-reference}) | |
508 | @end lisp | |
509 | ||
510 | in which @var{sub-version-reference} is in turn one of: | |
511 | ||
512 | @lisp | |
513 | (@var{sub-version}) | |
514 | (>= @var{sub-version}) | |
515 | (<= @var{sub-version}) | |
516 | (and @var{sub-version-reference} ...) | |
517 | (or @var{sub-version-reference} ...) | |
518 | (not @var{sub-version-reference}) | |
519 | @end lisp | |
520 | ||
521 | in which @var{sub-version} is an exact, nonnegative integer as above. A | |
522 | version reference matches a declared module version if each element of | |
523 | the version reference matches a corresponding element of the module | |
524 | version, according to the following rules: | |
525 | ||
526 | @itemize @bullet | |
527 | @item | |
528 | The @code{and} sub-form matches a version or version element if every | |
529 | element in the tail of the sub-form matches the specified version or | |
530 | version element. | |
531 | ||
532 | @item | |
533 | The @code{or} sub-form matches a version or version element if any | |
534 | element in the tail of the sub-form matches the specified version or | |
535 | version element. | |
536 | ||
537 | @item | |
538 | The @code{not} sub-form matches a version or version element if the tail | |
539 | of the sub-form does not match the version or version element. | |
540 | ||
541 | @item | |
542 | The @code{>=} sub-form matches a version element if the element is | |
543 | greater than or equal to the @var{sub-version} in the tail of the | |
544 | sub-form. | |
545 | ||
546 | @item | |
547 | The @code{<=} sub-form matches a version element if the version is less | |
548 | than or equal to the @var{sub-version} in the tail of the sub-form. | |
549 | ||
550 | @item | |
551 | A @var{sub-version} matches a version element if one is @var{eqv?} to | |
552 | the other. | |
553 | @end itemize | |
554 | ||
555 | For example, a module declared as: | |
556 | ||
557 | @lisp | |
558 | (define-module (mylib mymodule) #:version (1 2 0)) | |
559 | @end lisp | |
560 | ||
561 | would be successfully loaded by any of the following @code{use-modules} | |
562 | expressions: | |
563 | ||
564 | @lisp | |
565 | (use-modules ((mylib mymodule) #:version (1 2 (>= 0)))) | |
566 | (use-modules ((mylib mymodule) #:version (or (1 2 0) (1 2 1)))) | |
567 | (use-modules ((mylib mymodule) #:version ((and (>= 1) (not 2)) 2 0))) | |
568 | @end lisp | |
569 | ||
570 | ||
71194485 JG |
571 | @node R6RS Libraries |
572 | @subsection R6RS Libraries | |
573 | ||
574 | In addition to the API described in the previous sections, you also | |
43d6eb75 | 575 | have the option to create modules using the portable @code{library} form |
71194485 JG |
576 | described in R6RS (@pxref{Library form, R6RS Library Form,, r6rs, The |
577 | Revised^6 Report on the Algorithmic Language Scheme}), and to import | |
578 | libraries created in this format by other programmers. Guile's R6RS | |
43d6eb75 JG |
579 | library implementation takes advantage of the flexibility built into the |
580 | module system by expanding the R6RS library form into a corresponding | |
581 | Guile @code{define-module} form that specifies equivalent import and | |
582 | export requirements and includes the same body expressions. The library | |
583 | expression: | |
71194485 JG |
584 | |
585 | @lisp | |
586 | (library (mylib (1 2)) | |
587 | (import (otherlib (3))) | |
588 | (export mybinding)) | |
589 | @end lisp | |
590 | ||
591 | is equivalent to the module definition: | |
592 | ||
593 | @lisp | |
594 | (define-module (mylib) | |
595 | #:version (1 2) | |
596 | #:use-module ((otherlib) #:version (3)) | |
597 | #:export (mybinding)) | |
598 | @end lisp | |
599 | ||
600 | Central to the mechanics of R6RS libraries is the concept of import | |
43d6eb75 | 601 | and export @dfn{levels}, which control the visibility of bindings at |
71194485 JG |
602 | various phases of a library's lifecycle --- macros necessary to |
603 | expand forms in the library's body need to be available at expand | |
604 | time; variables used in the body of a procedure exported by the | |
605 | library must be available at runtime. R6RS specifies the optional | |
606 | @code{for} sub-form of an @emph{import set} specification (see below) | |
607 | as a mechanism by which a library author can indicate that a | |
608 | particular library import should take place at a particular phase | |
609 | with respect to the lifecycle of the importing library. | |
610 | ||
c8eb2797 | 611 | Guile's library implementation uses a technique called |
43d6eb75 JG |
612 | @dfn{implicit phasing} (first described by Abdulaziz Ghuloum and R. |
613 | Kent Dybvig), which allows the expander and compiler to automatically | |
614 | determine the necessary visibility of a binding imported from another | |
615 | library. As such, the @code{for} sub-form described below is ignored by | |
616 | Guile (but may be required by Schemes in which phasing is explicit). | |
71194485 | 617 | |
43d6eb75 | 618 | @deffn {Scheme Syntax} library name (export export-spec ...) (import import-spec ...) body ... |
71194485 JG |
619 | Defines a new library with the specified name, exports, and imports, |
620 | and evaluates the specified body expressions in this library's | |
621 | environment. | |
622 | ||
623 | The library @var{name} is a non-empty list of identifiers, optionally | |
624 | ending with a version specification of the form described above | |
625 | (@pxref{Creating Guile Modules}). | |
626 | ||
627 | Each @var{export-spec} is the name of a variable defined or imported | |
628 | by the library, or must take the form | |
629 | @code{(rename (internal-name external-name) ...)}, where the | |
630 | identifier @var{internal-name} names a variable defined or imported | |
631 | by the library and @var{external-name} is the name by which the | |
632 | variable is seen by importing libraries. | |
633 | ||
43d6eb75 | 634 | Each @var{import-spec} must be either an @dfn{import set} (see below) |
71194485 JG |
635 | or must be of the form @code{(for import-set import-level ...)}, |
636 | where each @var{import-level} is one of: | |
637 | ||
638 | @lisp | |
639 | run | |
640 | expand | |
641 | (meta @var{level}) | |
642 | @end lisp | |
643 | ||
644 | where @var{level} is an integer. Note that since Guile does not | |
645 | require explicit phase specification, any @var{import-set}s found | |
646 | inside of @code{for} sub-forms will be ``unwrapped'' during | |
647 | expansion and processed as if they had been specified directly. | |
648 | ||
649 | Import sets in turn take one of the following forms: | |
650 | ||
651 | @lisp | |
652 | @var{library-reference} | |
653 | (library @var{library-reference}) | |
654 | (only @var{import-set} @var{identifier} ...) | |
655 | (except @var{import-set} @var{identifier} ...) | |
656 | (prefix @var{import-set} @var{identifier}) | |
657 | (rename @var{import-set} (@var{internal-identifier} @var{external-identifier}) ...) | |
658 | @end lisp | |
659 | ||
660 | where @var{library-reference} is a non-empty list of identifiers | |
661 | ending with an optional version reference (@pxref{R6RS Version | |
662 | References}), and the other sub-forms have the following semantics, | |
663 | defined recursively on nested @var{import-set}s: | |
664 | ||
665 | @itemize @bullet | |
666 | ||
667 | @item | |
668 | The @code{library} sub-form is used to specify libraries for import | |
669 | whose names begin with the identifier ``library.'' | |
670 | ||
671 | @item | |
672 | The @code{only} sub-form imports only the specified @var{identifier}s | |
673 | from the given @var{import-set}. | |
674 | ||
675 | @item | |
676 | The @code{except} sub-form imports all of the bindings exported by | |
677 | @var{import-set} except for those that appear in the specified list | |
678 | of @var{identifier}s. | |
679 | ||
680 | @item | |
681 | The @code{prefix} sub-form imports all of the bindings exported | |
682 | by @var{import-set}, first prefixing them with the specified | |
683 | @var{identifier}. | |
684 | ||
685 | @item | |
686 | The @code{rename} sub-form imports all of the identifiers exported | |
687 | by @var{import-set}. The binding for each @var{internal-identifier} | |
688 | among these identifiers is made visible to the importing library as | |
689 | the corresponding @var{external-identifier}; all other bindings are | |
690 | imported using the names provided by @var{import-set}. | |
691 | ||
692 | @end itemize | |
693 | ||
694 | Note that because Guile translates R6RS libraries into module | |
695 | definitions, an import specification may be used to declare a | |
696 | dependency on a native Guile module --- although doing so may make | |
697 | your libraries less portable to other Schemes. | |
698 | ||
699 | @end deffn | |
700 | ||
43d6eb75 | 701 | @deffn {Scheme Syntax} import import-spec ... |
71194485 JG |
702 | Import into the current environment the libraries specified by the |
703 | given import specifications, where each @var{import-spec} takes the | |
43d6eb75 | 704 | same form as in the @code{library} form described above. |
71194485 JG |
705 | @end deffn |
706 | ||
707 | ||
992a3879 AW |
708 | @node Variables |
709 | @subsection Variables | |
710 | @tpindex Variables | |
711 | ||
712 | Each module has its own hash table, sometimes known as an @dfn{obarray}, | |
713 | that maps the names defined in that module to their corresponding | |
714 | variable objects. | |
715 | ||
716 | A variable is a box-like object that can hold any Scheme value. It is | |
717 | said to be @dfn{undefined} if its box holds a special Scheme value that | |
718 | denotes undefined-ness (which is different from all other Scheme values, | |
719 | including for example @code{#f}); otherwise the variable is | |
720 | @dfn{defined}. | |
721 | ||
722 | On its own, a variable object is anonymous. A variable is said to be | |
723 | @dfn{bound} when it is associated with a name in some way, usually a | |
724 | symbol in a module obarray. When this happens, the name is said to be | |
725 | bound to the variable, in that module. | |
726 | ||
727 | (That's the theory, anyway. In practice, defined-ness and bound-ness | |
728 | sometimes get confused, because Lisp and Scheme implementations have | |
729 | often conflated --- or deliberately drawn no distinction between --- a | |
730 | name that is unbound and a name that is bound to a variable whose value | |
731 | is undefined. We will try to be clear about the difference and explain | |
732 | any confusion where it is unavoidable.) | |
733 | ||
734 | Variables do not have a read syntax. Most commonly they are created and | |
735 | bound implicitly by @code{define} expressions: a top-level @code{define} | |
736 | expression of the form | |
737 | ||
738 | @lisp | |
739 | (define @var{name} @var{value}) | |
740 | @end lisp | |
741 | ||
742 | @noindent | |
743 | creates a variable with initial value @var{value} and binds it to the | |
744 | name @var{name} in the current module. But they can also be created | |
745 | dynamically by calling one of the constructor procedures | |
746 | @code{make-variable} and @code{make-undefined-variable}. | |
747 | ||
748 | @deffn {Scheme Procedure} make-undefined-variable | |
749 | @deffnx {C Function} scm_make_undefined_variable () | |
750 | Return a variable that is initially unbound. | |
751 | @end deffn | |
752 | ||
753 | @deffn {Scheme Procedure} make-variable init | |
754 | @deffnx {C Function} scm_make_variable (init) | |
755 | Return a variable initialized to value @var{init}. | |
756 | @end deffn | |
757 | ||
758 | @deffn {Scheme Procedure} variable-bound? var | |
759 | @deffnx {C Function} scm_variable_bound_p (var) | |
a4b4fbbd JE |
760 | Return @code{#t} if @var{var} is bound to a value, or @code{#f} |
761 | otherwise. Throws an error if @var{var} is not a variable object. | |
992a3879 AW |
762 | @end deffn |
763 | ||
764 | @deffn {Scheme Procedure} variable-ref var | |
765 | @deffnx {C Function} scm_variable_ref (var) | |
766 | Dereference @var{var} and return its value. | |
767 | @var{var} must be a variable object; see @code{make-variable} | |
768 | and @code{make-undefined-variable}. | |
769 | @end deffn | |
770 | ||
771 | @deffn {Scheme Procedure} variable-set! var val | |
772 | @deffnx {C Function} scm_variable_set_x (var, val) | |
773 | Set the value of the variable @var{var} to @var{val}. | |
774 | @var{var} must be a variable object, @var{val} can be any | |
775 | value. Return an unspecified value. | |
776 | @end deffn | |
777 | ||
778 | @deffn {Scheme Procedure} variable-unset! var | |
779 | @deffnx {C Function} scm_variable_unset_x (var) | |
780 | Unset the value of the variable @var{var}, leaving @var{var} unbound. | |
781 | @end deffn | |
782 | ||
783 | @deffn {Scheme Procedure} variable? obj | |
784 | @deffnx {C Function} scm_variable_p (obj) | |
a4b4fbbd JE |
785 | Return @code{#t} if @var{obj} is a variable object, else return |
786 | @code{#f}. | |
992a3879 AW |
787 | @end deffn |
788 | ||
789 | ||
790 | @node Module System Reflection | |
791 | @subsection Module System Reflection | |
792 | ||
793 | The previous sections have described a declarative view of the module | |
794 | system. You can also work with it programmatically by accessing and | |
795 | modifying various parts of the Scheme objects that Guile uses to | |
796 | implement the module system. | |
797 | ||
798 | At any time, there is a @dfn{current module}. This module is the one | |
799 | where a top-level @code{define} and similar syntax will add new | |
800 | bindings. You can find other module objects with @code{resolve-module}, | |
801 | for example. | |
802 | ||
803 | These module objects can be used as the second argument to @code{eval}. | |
804 | ||
805 | @deffn {Scheme Procedure} current-module | |
806 | @deffnx {C Function} scm_current_module () | |
807 | Return the current module object. | |
808 | @end deffn | |
809 | ||
810 | @deffn {Scheme Procedure} set-current-module module | |
811 | @deffnx {C Function} scm_set_current_module (module) | |
812 | Set the current module to @var{module} and return | |
813 | the previous current module. | |
814 | @end deffn | |
815 | ||
816 | @deffn {Scheme Procedure} save-module-excursion thunk | |
817 | Call @var{thunk} within a @code{dynamic-wind} such that the module that | |
818 | is current at invocation time is restored when @var{thunk}'s dynamic | |
819 | extent is left (@pxref{Dynamic Wind}). | |
820 | ||
821 | More precisely, if @var{thunk} escapes non-locally, the current module | |
822 | (at the time of escape) is saved, and the original current module (at | |
823 | the time @var{thunk}'s dynamic extent was last entered) is restored. If | |
824 | @var{thunk}'s dynamic extent is re-entered, then the current module is | |
825 | saved, and the previously saved inner module is set current again. | |
826 | @end deffn | |
827 | ||
994d87be BT |
828 | @deffn {Scheme Procedure} resolve-module name [autoload=#t] [version=#f] @ |
829 | [#:ensure=#t] | |
992a3879 AW |
830 | @deffnx {C Function} scm_resolve_module (name) |
831 | Find the module named @var{name} and return it. When it has not already | |
832 | been defined and @var{autoload} is true, try to auto-load it. When it | |
833 | can't be found that way either, create an empty module if @var{ensure} | |
834 | is true, otherwise return @code{#f}. If @var{version} is true, ensure | |
835 | that the resulting module is compatible with the given version reference | |
836 | (@pxref{R6RS Version References}). The name is a list of symbols. | |
837 | @end deffn | |
838 | ||
994d87be BT |
839 | @deffn {Scheme Procedure} resolve-interface name [#:select=#f] @ |
840 | [#:hide='()] [#:prefix=#f] @ | |
841 | [#:renamer=#f] [#:version=#f] | |
992a3879 AW |
842 | Find the module named @var{name} as with @code{resolve-module} and |
843 | return its interface. The interface of a module is also a module | |
844 | object, but it contains only the exported bindings. | |
845 | @end deffn | |
846 | ||
847 | @deffn {Scheme Procedure} module-uses module | |
848 | Return a list of the interfaces used by @var{module}. | |
849 | @end deffn | |
850 | ||
851 | @deffn {Scheme Procedure} module-use! module interface | |
852 | Add @var{interface} to the front of the use-list of @var{module}. Both | |
853 | arguments should be module objects, and @var{interface} should very | |
854 | likely be a module returned by @code{resolve-interface}. | |
855 | @end deffn | |
856 | ||
857 | @deffn {Scheme Procedure} reload-module module | |
858 | Revisit the source file that corresponds to @var{module}. Raises an | |
859 | error if no source file is associated with the given module. | |
860 | @end deffn | |
861 | ||
862 | As mentioned in the previous section, modules contain a mapping between | |
863 | identifiers (as symbols) and storage locations (as variables). Guile | |
864 | defines a number of procedures to allow access to this mapping. If you | |
865 | are programming in C, @ref{Accessing Modules from C}. | |
866 | ||
867 | @deffn {Scheme Procedure} module-variable module name | |
868 | Return the variable bound to @var{name} (a symbol) in @var{module}, or | |
869 | @code{#f} if @var{name} is unbound. | |
870 | @end deffn | |
871 | ||
872 | @deffn {Scheme Procedure} module-add! module name var | |
873 | Define a new binding between @var{name} (a symbol) and @var{var} (a | |
874 | variable) in @var{module}. | |
875 | @end deffn | |
876 | ||
877 | @deffn {Scheme Procedure} module-ref module name | |
878 | Look up the value bound to @var{name} in @var{module}. Like | |
879 | @code{module-variable}, but also does a @code{variable-ref} on the | |
880 | resulting variable, raising an error if @var{name} is unbound. | |
881 | @end deffn | |
882 | ||
883 | @deffn {Scheme Procedure} module-define! module name value | |
884 | Locally bind @var{name} to @var{value} in @var{module}. If @var{name} | |
885 | was already locally bound in @var{module}, i.e., defined locally and not | |
886 | by an imported module, the value stored in the existing variable will be | |
887 | updated. Otherwise, a new variable will be added to the module, via | |
888 | @code{module-add!}. | |
889 | @end deffn | |
890 | ||
891 | @deffn {Scheme Procedure} module-set! module name value | |
892 | Update the binding of @var{name} in @var{module} to @var{value}, raising | |
893 | an error if @var{name} is not already bound in @var{module}. | |
894 | @end deffn | |
895 | ||
896 | There are many other reflective procedures available in the default | |
897 | environment. If you find yourself using one of them, please contact the | |
898 | Guile developers so that we can commit to stability for that interface. | |
899 | ||
900 | ||
07d83abe | 901 | @node Accessing Modules from C |
726b8ba3 | 902 | @subsection Accessing Modules from C |
07d83abe MV |
903 | |
904 | The last sections have described how modules are used in Scheme code, | |
905 | which is the recommended way of creating and accessing modules. You | |
906 | can also work with modules from C, but it is more cumbersome. | |
907 | ||
908 | The following procedures are available. | |
909 | ||
7af1ba2f | 910 | @deftypefn {C Function} SCM scm_c_call_with_current_module (SCM @var{module}, SCM (*@var{func})(void *), void *@var{data}) |
07d83abe MV |
911 | Call @var{func} and make @var{module} the current module during the |
912 | call. The argument @var{data} is passed to @var{func}. The return | |
913 | value of @code{scm_c_call_with_current_module} is the return value of | |
914 | @var{func}. | |
915 | @end deftypefn | |
916 | ||
7af1ba2f LC |
917 | @deftypefn {C Function} SCM scm_public_variable (SCM @var{module_name}, SCM @var{name}) |
918 | @deftypefnx {C Function} SCM scm_c_public_variable ({const char *}@var{module_name}, {const char *}@var{name}) | |
831e6782 AW |
919 | Find a the variable bound to the symbol @var{name} in the public |
920 | interface of the module named @var{module_name}. | |
921 | ||
7af1ba2f | 922 | @var{module_name} should be a list of symbols, when represented as a |
831e6782 AW |
923 | Scheme object, or a space-separated string, in the @code{const char *} |
924 | case. See @code{scm_c_define_module} below, for more examples. | |
925 | ||
926 | Signals an error if no module was found with the given name. If | |
927 | @var{name} is not bound in the module, just returns @code{#f}. | |
928 | @end deftypefn | |
929 | ||
7af1ba2f LC |
930 | @deftypefn {C Function} SCM scm_private_variable (SCM @var{module_name}, SCM @var{name}) |
931 | @deftypefnx {C Function} SCM scm_c_private_variable ({const char *}@var{module_name}, {const char *}@var{name}) | |
831e6782 AW |
932 | Like @code{scm_public_variable}, but looks in the internals of the |
933 | module named @var{module_name} instead of the public interface. | |
934 | Logically, these procedures should only be called on modules you write. | |
935 | @end deftypefn | |
936 | ||
7af1ba2f LC |
937 | @deftypefn {C Function} SCM scm_public_lookup (SCM @var{module_name}, SCM @var{name}) |
938 | @deftypefnx {C Function} SCM scm_c_public_lookup ({const char *}@var{module_name}, {const char *}@var{name}) | |
939 | @deftypefnx {C Function} SCM scm_private_lookup (SCM @var{module_name}, SCM @var{name}) | |
940 | @deftypefnx {C Function} SCM scm_c_private_lookup ({const char *}@var{module_name}, {const char *}@var{name}) | |
831e6782 AW |
941 | Like @code{scm_public_variable} or @code{scm_private_variable}, but if |
942 | the @var{name} is not bound in the module, signals an error. Returns a | |
943 | variable, always. | |
944 | ||
945 | @example | |
f57ea23a | 946 | static SCM eval_string_var; |
831e6782 | 947 | |
f57ea23a MW |
948 | /* NOTE: It is important that the call to 'my_init' |
949 | happens-before all calls to 'my_eval_string'. */ | |
950 | void my_init (void) | |
951 | @{ | |
952 | eval_string_var = scm_c_public_lookup ("ice-9 eval-string", | |
953 | "eval-string"); | |
954 | @} | |
831e6782 | 955 | |
f57ea23a MW |
956 | SCM my_eval_string (SCM str) |
957 | @{ | |
831e6782 AW |
958 | return scm_call_1 (scm_variable_ref (eval_string_var), str); |
959 | @} | |
960 | @end example | |
961 | @end deftypefn | |
962 | ||
7af1ba2f LC |
963 | @deftypefn {C Function} SCM scm_public_ref (SCM @var{module_name}, SCM @var{name}) |
964 | @deftypefnx {C Function} SCM scm_c_public_ref ({const char *}@var{module_name}, {const char *}@var{name}) | |
965 | @deftypefnx {C Function} SCM scm_private_ref (SCM @var{module_name}, SCM @var{name}) | |
966 | @deftypefnx {C Function} SCM scm_c_private_ref ({const char *}@var{module_name}, {const char *}@var{name}) | |
831e6782 AW |
967 | Like @code{scm_public_lookup} or @code{scm_private_lookup}, but |
968 | additionally dereferences the variable. If the variable object is | |
969 | unbound, signals an error. Returns the value bound to @var{name} in | |
64de6db5 | 970 | @var{module_name}. |
831e6782 AW |
971 | @end deftypefn |
972 | ||
973 | In addition, there are a number of other lookup-related procedures. We | |
974 | suggest that you use the @code{scm_public_} and @code{scm_private_} | |
975 | family of procedures instead, if possible. | |
976 | ||
7af1ba2f | 977 | @deftypefn {C Function} SCM scm_c_lookup ({const char *}@var{name}) |
07d83abe MV |
978 | Return the variable bound to the symbol indicated by @var{name} in the |
979 | current module. If there is no such binding or the symbol is not | |
980 | bound to a variable, signal an error. | |
981 | @end deftypefn | |
982 | ||
7af1ba2f | 983 | @deftypefn {C Function} SCM scm_lookup (SCM @var{name}) |
07d83abe MV |
984 | Like @code{scm_c_lookup}, but the symbol is specified directly. |
985 | @end deftypefn | |
986 | ||
7af1ba2f LC |
987 | @deftypefn {C Function} SCM scm_c_module_lookup (SCM @var{module}, {const char *}@var{name}) |
988 | @deftypefnx {C Function} SCM scm_module_lookup (SCM @var{module}, SCM @var{name}) | |
07d83abe MV |
989 | Like @code{scm_c_lookup} and @code{scm_lookup}, but the specified |
990 | module is used instead of the current one. | |
991 | @end deftypefn | |
992 | ||
7af1ba2f | 993 | @deftypefn {C Function} SCM scm_module_variable (SCM @var{module}, SCM @var{name}) |
831e6782 AW |
994 | Like @code{scm_module_lookup}, but if the binding does not exist, just |
995 | returns @code{#f} instead of raising an error. | |
996 | @end deftypefn | |
997 | ||
998 | To define a value, use @code{scm_define}: | |
999 | ||
7af1ba2f | 1000 | @deftypefn {C Function} SCM scm_c_define ({const char *}@var{name}, SCM @var{val}) |
07d83abe MV |
1001 | Bind the symbol indicated by @var{name} to a variable in the current |
1002 | module and set that variable to @var{val}. When @var{name} is already | |
1003 | bound to a variable, use that. Else create a new variable. | |
1004 | @end deftypefn | |
1005 | ||
7af1ba2f | 1006 | @deftypefn {C Function} SCM scm_define (SCM @var{name}, SCM @var{val}) |
07d83abe MV |
1007 | Like @code{scm_c_define}, but the symbol is specified directly. |
1008 | @end deftypefn | |
1009 | ||
7af1ba2f LC |
1010 | @deftypefn {C Function} SCM scm_c_module_define (SCM @var{module}, {const char *}@var{name}, SCM @var{val}) |
1011 | @deftypefnx {C Function} SCM scm_module_define (SCM @var{module}, SCM @var{name}, SCM @var{val}) | |
07d83abe MV |
1012 | Like @code{scm_c_define} and @code{scm_define}, but the specified |
1013 | module is used instead of the current one. | |
1014 | @end deftypefn | |
1015 | ||
62e15979 AW |
1016 | In some rare cases, you may need to access the variable that |
1017 | @code{scm_module_define} would have accessed, without changing the | |
1018 | binding of the existing variable, if one is present. In that case, use | |
1019 | @code{scm_module_ensure_local_variable}: | |
1020 | ||
1021 | @deftypefn {C Function} SCM scm_module_ensure_local_variable (SCM @var{module}, SCM @var{sym}) | |
1022 | Like @code{scm_module_define}, but if the @var{sym} is already locally | |
1023 | bound in that module, the variable's existing binding is not reset. | |
1024 | Returns a variable. | |
1025 | @end deftypefn | |
1026 | ||
7af1ba2f | 1027 | @deftypefn {C Function} SCM scm_module_reverse_lookup (SCM @var{module}, SCM @var{variable}) |
64de6db5 | 1028 | Find the symbol that is bound to @var{variable} in @var{module}. When no such binding is found, return @code{#f}. |
07d83abe MV |
1029 | @end deftypefn |
1030 | ||
7af1ba2f | 1031 | @deftypefn {C Function} SCM scm_c_define_module ({const char *}@var{name}, void (*@var{init})(void *), void *@var{data}) |
07d83abe MV |
1032 | Define a new module named @var{name} and make it current while |
1033 | @var{init} is called, passing it @var{data}. Return the module. | |
1034 | ||
1035 | The parameter @var{name} is a string with the symbols that make up | |
1036 | the module name, separated by spaces. For example, @samp{"foo bar"} names | |
1037 | the module @samp{(foo bar)}. | |
1038 | ||
1039 | When there already exists a module named @var{name}, it is used | |
1040 | unchanged, otherwise, an empty module is created. | |
1041 | @end deftypefn | |
1042 | ||
7af1ba2f | 1043 | @deftypefn {C Function} SCM scm_c_resolve_module ({const char *}@var{name}) |
07d83abe MV |
1044 | Find the module name @var{name} and return it. When it has not |
1045 | already been defined, try to auto-load it. When it can't be found | |
1046 | that way either, create an empty module. The name is interpreted as | |
1047 | for @code{scm_c_define_module}. | |
1048 | @end deftypefn | |
1049 | ||
7af1ba2f | 1050 | @deftypefn {C Function} SCM scm_c_use_module ({const char *}@var{name}) |
07d83abe MV |
1051 | Add the module named @var{name} to the uses list of the current |
1052 | module, as with @code{(use-modules @var{name})}. The name is | |
1053 | interpreted as for @code{scm_c_define_module}. | |
1054 | @end deftypefn | |
1055 | ||
7af1ba2f | 1056 | @deftypefn {C Function} SCM scm_c_export ({const char *}@var{name}, ...) |
07d83abe MV |
1057 | Add the bindings designated by @var{name}, ... to the public interface |
1058 | of the current module. The list of names is terminated by | |
1059 | @code{NULL}. | |
1060 | @end deftypefn | |
1061 | ||
ef5f9163 | 1062 | |
726b8ba3 AW |
1063 | @node provide and require |
1064 | @subsection provide and require | |
1065 | ||
1066 | Aubrey Jaffer, mostly to support his portable Scheme library SLIB, | |
1067 | implemented a provide/require mechanism for many Scheme implementations. | |
1068 | Library files in SLIB @emph{provide} a feature, and when user programs | |
1069 | @emph{require} that feature, the library file is loaded in. | |
1070 | ||
1071 | For example, the file @file{random.scm} in the SLIB package contains the | |
1072 | line | |
1073 | ||
1074 | @lisp | |
1075 | (provide 'random) | |
1076 | @end lisp | |
1077 | ||
1078 | so to use its procedures, a user would type | |
1079 | ||
1080 | @lisp | |
1081 | (require 'random) | |
1082 | @end lisp | |
1083 | ||
1084 | and they would magically become available, @emph{but still have the same | |
1085 | names!} So this method is nice, but not as good as a full-featured | |
1086 | module system. | |
1087 | ||
1088 | When SLIB is used with Guile, provide and require can be used to access | |
1089 | its facilities. | |
1090 | ||
1091 | @node Environments | |
1092 | @subsection Environments | |
1093 | @cindex environment | |
1094 | ||
1095 | Scheme, as defined in R5RS, does @emph{not} have a full module system. | |
1096 | However it does define the concept of a top-level @dfn{environment}. | |
1097 | Such an environment maps identifiers (symbols) to Scheme objects such | |
1098 | as procedures and lists: @ref{About Closure}. In other words, it | |
1099 | implements a set of @dfn{bindings}. | |
1100 | ||
1101 | Environments in R5RS can be passed as the second argument to | |
1102 | @code{eval} (@pxref{Fly Evaluation}). Three procedures are defined to | |
1103 | return environments: @code{scheme-report-environment}, | |
1104 | @code{null-environment} and @code{interaction-environment} (@pxref{Fly | |
1105 | Evaluation}). | |
1106 | ||
1107 | In addition, in Guile any module can be used as an R5RS environment, | |
1108 | i.e., passed as the second argument to @code{eval}. | |
1109 | ||
1110 | Note: the following two procedures are available only when the | |
1111 | @code{(ice-9 r5rs)} module is loaded: | |
1112 | ||
1113 | @lisp | |
1114 | (use-modules (ice-9 r5rs)) | |
1115 | @end lisp | |
1116 | ||
1117 | @deffn {Scheme Procedure} scheme-report-environment version | |
1118 | @deffnx {Scheme Procedure} null-environment version | |
1119 | @var{version} must be the exact integer `5', corresponding to revision | |
1120 | 5 of the Scheme report (the Revised^5 Report on Scheme). | |
1121 | @code{scheme-report-environment} returns a specifier for an | |
1122 | environment that is empty except for all bindings defined in the | |
1123 | report that are either required or both optional and supported by the | |
1124 | implementation. @code{null-environment} returns a specifier for an | |
1125 | environment that is empty except for the (syntactic) bindings for all | |
1126 | syntactic keywords defined in the report that are either required or | |
1127 | both optional and supported by the implementation. | |
1128 | ||
1129 | Currently Guile does not support values of @var{version} for other | |
1130 | revisions of the report. | |
1131 | ||
1132 | The effect of assigning (through the use of @code{eval}) a variable | |
1133 | bound in a @code{scheme-report-environment} (for example @code{car}) | |
1134 | is unspecified. Currently the environments specified by | |
1135 | @code{scheme-report-environment} are not immutable in Guile. | |
1136 | @end deffn | |
1137 | ||
1138 | ||
1139 | ||
07d83abe MV |
1140 | @c Local Variables: |
1141 | @c TeX-master: "guile.texi" | |
1142 | @c End: |