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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 | ||
7 | @page | |
8 | @node Procedures and Macros | |
9 | @section Procedures and Macros | |
10 | ||
11 | @menu | |
12 | * Lambda:: Basic procedure creation using lambda. | |
13 | * Primitive Procedures:: Procedures defined in C. | |
00ce5125 | 14 | * Compiled Procedures:: Scheme procedures can be compiled. |
07d83abe MV |
15 | * Optional Arguments:: Handling keyword, optional and rest arguments. |
16 | * Procedure Properties:: Procedure properties and meta-information. | |
17 | * Procedures with Setters:: Procedures with setters. | |
18 | * Macros:: Lisp style macro definitions. | |
19 | * Syntax Rules:: Support for R5RS @code{syntax-rules}. | |
20 | * Syntax Case:: Support for the @code{syntax-case} system. | |
21 | * Internal Macros:: Guile's internal representation. | |
22 | @end menu | |
23 | ||
24 | ||
25 | @node Lambda | |
26 | @subsection Lambda: Basic Procedure Creation | |
27 | @cindex lambda | |
28 | ||
29 | @c FIXME::martin: Review me! | |
30 | ||
31 | A @code{lambda} expression evaluates to a procedure. The environment | |
32 | which is in effect when a @code{lambda} expression is evaluated is | |
33 | enclosed in the newly created procedure, this is referred to as a | |
34 | @dfn{closure} (@pxref{About Closure}). | |
35 | ||
36 | When a procedure created by @code{lambda} is called with some actual | |
37 | arguments, the environment enclosed in the procedure is extended by | |
38 | binding the variables named in the formal argument list to new locations | |
39 | and storing the actual arguments into these locations. Then the body of | |
40 | the @code{lambda} expression is evaluation sequentially. The result of | |
41 | the last expression in the procedure body is then the result of the | |
42 | procedure invocation. | |
43 | ||
44 | The following examples will show how procedures can be created using | |
45 | @code{lambda}, and what you can do with these procedures. | |
46 | ||
47 | @lisp | |
48 | (lambda (x) (+ x x)) @result{} @r{a procedure} | |
49 | ((lambda (x) (+ x x)) 4) @result{} 8 | |
50 | @end lisp | |
51 | ||
52 | The fact that the environment in effect when creating a procedure is | |
53 | enclosed in the procedure is shown with this example: | |
54 | ||
55 | @lisp | |
56 | (define add4 | |
57 | (let ((x 4)) | |
58 | (lambda (y) (+ x y)))) | |
59 | (add4 6) @result{} 10 | |
60 | @end lisp | |
61 | ||
62 | ||
63 | @deffn syntax lambda formals body | |
64 | @var{formals} should be a formal argument list as described in the | |
65 | following table. | |
66 | ||
67 | @table @code | |
68 | @item (@var{variable1} @dots{}) | |
69 | The procedure takes a fixed number of arguments; when the procedure is | |
70 | called, the arguments will be stored into the newly created location for | |
71 | the formal variables. | |
72 | @item @var{variable} | |
73 | The procedure takes any number of arguments; when the procedure is | |
74 | called, the sequence of actual arguments will converted into a list and | |
75 | stored into the newly created location for the formal variable. | |
76 | @item (@var{variable1} @dots{} @var{variablen} . @var{variablen+1}) | |
77 | If a space-delimited period precedes the last variable, then the | |
78 | procedure takes @var{n} or more variables where @var{n} is the number | |
79 | of formal arguments before the period. There must be at least one | |
80 | argument before the period. The first @var{n} actual arguments will be | |
81 | stored into the newly allocated locations for the first @var{n} formal | |
82 | arguments and the sequence of the remaining actual arguments is | |
83 | converted into a list and the stored into the location for the last | |
84 | formal argument. If there are exactly @var{n} actual arguments, the | |
85 | empty list is stored into the location of the last formal argument. | |
86 | @end table | |
87 | ||
88 | The list in @var{variable} or @var{variablen+1} is always newly | |
89 | created and the procedure can modify it if desired. This is the case | |
90 | even when the procedure is invoked via @code{apply}, the required part | |
91 | of the list argument there will be copied (@pxref{Fly Evaluation,, | |
92 | Procedures for On the Fly Evaluation}). | |
93 | ||
94 | @var{body} is a sequence of Scheme expressions which are evaluated in | |
95 | order when the procedure is invoked. | |
96 | @end deffn | |
97 | ||
98 | @node Primitive Procedures | |
99 | @subsection Primitive Procedures | |
100 | @cindex primitives | |
101 | @cindex primitive procedures | |
102 | ||
103 | Procedures written in C can be registered for use from Scheme, | |
104 | provided they take only arguments of type @code{SCM} and return | |
105 | @code{SCM} values. @code{scm_c_define_gsubr} is likely to be the most | |
106 | useful mechanism, combining the process of registration | |
107 | (@code{scm_c_make_gsubr}) and definition (@code{scm_define}). | |
108 | ||
109 | @deftypefun SCM scm_c_make_gsubr (const char *name, int req, int opt, int rst, fcn) | |
110 | Register a C procedure @var{FCN} as a ``subr'' --- a primitive | |
111 | subroutine that can be called from Scheme. It will be associated with | |
112 | the given @var{name} but no environment binding will be created. The | |
113 | arguments @var{req}, @var{opt} and @var{rst} specify the number of | |
114 | required, optional and ``rest'' arguments respectively. The total | |
115 | number of these arguments should match the actual number of arguments | |
116 | to @var{fcn}. The number of rest arguments should be 0 or 1. | |
117 | @code{scm_c_make_gsubr} returns a value of type @code{SCM} which is a | |
118 | ``handle'' for the procedure. | |
119 | @end deftypefun | |
120 | ||
121 | @deftypefun SCM scm_c_define_gsubr (const char *name, int req, int opt, int rst, fcn) | |
122 | Register a C procedure @var{FCN}, as for @code{scm_c_make_gsubr} | |
123 | above, and additionally create a top-level Scheme binding for the | |
124 | procedure in the ``current environment'' using @code{scm_define}. | |
125 | @code{scm_c_define_gsubr} returns a handle for the procedure in the | |
126 | same way as @code{scm_c_make_gsubr}, which is usually not further | |
127 | required. | |
128 | @end deftypefun | |
129 | ||
130 | @code{scm_c_make_gsubr} and @code{scm_c_define_gsubr} automatically | |
131 | use @code{scm_c_make_subr} and also @code{scm_makcclo} if necessary. | |
132 | It is advisable to use the gsubr variants since they provide a | |
133 | slightly higher-level abstraction of the Guile implementation. | |
134 | ||
00ce5125 AW |
135 | @node Compiled Procedures |
136 | @subsection Compiled Procedures | |
137 | ||
138 | Procedures that were created when loading a compiled file are | |
139 | themselves compiled. (In contrast, procedures that are defined by | |
140 | loading a Scheme source file are interpreted, and often not as fast as | |
141 | compiled procedures.) | |
142 | ||
143 | Loading compiled files is the normal way that compiled procedures come | |
144 | to being, though procedures can be compiled at runtime as well. | |
145 | @xref{Read/Load/Eval/Compile}, for more information on runtime | |
146 | compilation. | |
147 | ||
5a069042 AW |
148 | Compiled procedures, also known as @dfn{programs}, respond all |
149 | procedures that operate on procedures. In addition, there are a few | |
46d666d4 | 150 | more accessors for low-level details on programs. |
5a069042 | 151 | |
46d666d4 AW |
152 | Most people won't need to use the routines described in this section, |
153 | but it's good to have them documented. You'll have to include the | |
154 | appropriate module first, though: | |
5a069042 AW |
155 | |
156 | @example | |
157 | (use-modules (system vm program)) | |
158 | @end example | |
159 | ||
46d666d4 AW |
160 | @deffn {Scheme Procedure} program? obj |
161 | @deffnx {C Function} scm_program_p (obj) | |
162 | Returns @code{#t} iff @var{obj} is a compiled procedure. | |
163 | @end deffn | |
164 | ||
5a069042 AW |
165 | @deffn {Scheme Procedure} program-bytecode program |
166 | @deffnx {C Function} scm_program_bytecode (program) | |
46d666d4 AW |
167 | Returns the object code associated with this program, as a |
168 | @code{u8vector}. | |
5a069042 AW |
169 | @end deffn |
170 | ||
46d666d4 AW |
171 | @deffn {Scheme Procedure} program-base program |
172 | @deffnx {C Function} scm_program_base (program) | |
173 | Returns the address in memory corresponding to the start of | |
174 | @var{program}'s object code, as an integer. This is useful mostly when | |
175 | you map the value of an instruction pointer from the VM to actual | |
176 | instructions. | |
177 | @end deffn | |
178 | ||
179 | @deffn {Scheme Procedure} program-objects program | |
180 | @deffnx {C Function} scm_program_objects (program) | |
181 | Returns the ``object table'' associated with this program, as a | |
182 | vector. @xref{VM Programs}, for more information. | |
5a069042 AW |
183 | @end deffn |
184 | ||
46d666d4 AW |
185 | @deffn {Scheme Procedure} program-module program |
186 | @deffnx {C Function} scm_program_module (program) | |
187 | Returns the module that was current when this program was created. | |
188 | Free variables in this program are looked up with respect to this | |
189 | module. | |
190 | @end deffn | |
191 | ||
192 | @deffn {Scheme Procedure} program-external program | |
193 | @deffnx {C Function} scm_program_external (program) | |
194 | Returns the set of heap-allocated variables that this program captures | |
195 | in its closure, as a list. If a closure is code with data, you can get | |
196 | the code from @code{program-bytecode}, and the data via | |
197 | @code{program-external}. | |
198 | ||
199 | Users must not modify the returned value unless they think they're | |
200 | really clever. | |
201 | @end deffn | |
202 | ||
203 | @deffn {Scheme Procedure} program-external-set! program external | |
204 | @deffnx {C Function} scm_program_external_set_x (program, external) | |
205 | Set @var{external} as the set of closure variables on @var{program}. | |
206 | ||
207 | The Guile maintainers will not be held responsible for side effects of | |
208 | calling this function, including but not limited to replacement of | |
209 | shampoo with hair dye, and a slight salty taste in tomorrow's dinner. | |
210 | @end deffn | |
211 | ||
212 | @deffn {Scheme Procedure} program-arity program | |
213 | @deffnx {C Function} scm_program_arity (program) | |
214 | @deffnx {Scheme Procedure} arity:nargs arity | |
5a069042 AW |
215 | @deffnx {Scheme Procedure} arity:nrest arity |
216 | @deffnx {Scheme Procedure} arity:nlocs arity | |
217 | @deffnx {Scheme Procedure} arity:nexts arity | |
46d666d4 | 218 | Accessors for a representation of the ``arity'' of a program. |
5a069042 AW |
219 | |
220 | @code{nargs} is the number of arguments to the procedure, and | |
221 | @code{nrest} will be non-zero if the last argument is a rest argument. | |
222 | ||
223 | The other two accessors determine the number of local and external | |
224 | (heap-allocated) variables that this procedure will need to have | |
225 | allocated. | |
226 | @end deffn | |
227 | ||
46d666d4 AW |
228 | @deffn {Scheme Procedure} program-meta program |
229 | @deffnx scm_program_meta (program) | |
230 | Return the metadata thunk of @var{program}, or @code{#f} if it has no | |
231 | metadata. | |
232 | ||
233 | When called, a metadata thunk returns a list of the following form: | |
234 | @code{(@var{bindings} @var{sources} . @var{properties})}. The format | |
235 | of each of these elements is discussed below. | |
236 | @end deffn | |
237 | ||
5a069042 AW |
238 | @deffn {Scheme Procedure} program-bindings program |
239 | @deffnx {Scheme Procedure} make-binding name extp index start end | |
240 | @deffnx {Scheme Procedure} binding:name binding | |
241 | @deffnx {Scheme Procedure} binding:extp binding | |
242 | @deffnx {Scheme Procedure} binding:index binding | |
243 | @deffnx {Scheme Procedure} binding:start binding | |
244 | @deffnx {Scheme Procedure} binding:end binding | |
245 | Bindings annotations for programs, along with their accessors. | |
246 | ||
247 | Bindings declare names and liveness extents for block-local variables. | |
248 | The best way to see what these are is to play around with them at a | |
249 | REPL. The only tricky bit is that @var{extp} is a boolean, declaring | |
250 | whether the binding is heap-allocated or not. @xref{VM Concepts}, for | |
251 | more information. | |
252 | ||
253 | Note that bindings information are stored in a program as part of its | |
254 | metadata thunk, so including them in the generated object code does | |
255 | not impose a runtime performance penalty. | |
256 | @end deffn | |
257 | ||
258 | @deffn {Scheme Procedure} program-sources program | |
259 | @deffnx {Scheme Procedure} source:addr source | |
260 | @deffnx {Scheme Procedure} source:line source | |
261 | @deffnx {Scheme Procedure} source:column source | |
262 | @deffnx {Scheme Procedure} source:file source | |
263 | Source location annotations for programs, along with their accessors. | |
264 | ||
46d666d4 AW |
265 | Source location information propagates through the compiler and ends |
266 | up being serialized to the program's metadata. This information is | |
267 | keyed by the offset of the instruction pointer within the object code | |
268 | of the program. Specifically, it is keyed on the @code{ip} @emph{just | |
269 | following} an instruction, so that backtraces can find the source | |
270 | location of a call that is in progress. | |
5a069042 AW |
271 | @end deffn |
272 | ||
273 | @deffn {Scheme Procedure} program-properties program | |
46d666d4 AW |
274 | Return the properties of a @code{program} as an association list, |
275 | keyed by property name (a symbol). | |
276 | ||
277 | Some interesting properties include: | |
278 | @itemize | |
279 | @item @code{name}, the name of the procedure | |
280 | @item @code{documentation}, the procedure's docstring | |
281 | @end itemize | |
282 | @end deffn | |
283 | ||
284 | @deffn {Scheme Procedure} program-property program name | |
285 | Access a program's property by name, returning @code{#f} if not found. | |
286 | @end deffn | |
287 | ||
288 | @deffn {Scheme Procedure} program-documentation program | |
5a069042 | 289 | @deffnx {Scheme Procedure} program-name program |
46d666d4 | 290 | Accessors for specific properties. |
5a069042 | 291 | @end deffn |
00ce5125 | 292 | |
07d83abe MV |
293 | @node Optional Arguments |
294 | @subsection Optional Arguments | |
295 | ||
296 | @c FIXME::martin: Review me! | |
297 | ||
298 | Scheme procedures, as defined in R5RS, can either handle a fixed number | |
299 | of actual arguments, or a fixed number of actual arguments followed by | |
300 | arbitrarily many additional arguments. Writing procedures of variable | |
301 | arity can be useful, but unfortunately, the syntactic means for handling | |
302 | argument lists of varying length is a bit inconvenient. It is possible | |
303 | to give names to the fixed number of argument, but the remaining | |
304 | (optional) arguments can be only referenced as a list of values | |
305 | (@pxref{Lambda}). | |
306 | ||
307 | Guile comes with the module @code{(ice-9 optargs)}, which makes using | |
308 | optional arguments much more convenient. In addition, this module | |
309 | provides syntax for handling keywords in argument lists | |
310 | (@pxref{Keywords}). | |
311 | ||
312 | Before using any of the procedures or macros defined in this section, | |
313 | you have to load the module @code{(ice-9 optargs)} with the statement: | |
314 | ||
315 | @cindex @code{optargs} | |
316 | @lisp | |
317 | (use-modules (ice-9 optargs)) | |
318 | @end lisp | |
319 | ||
320 | @menu | |
321 | * let-optional Reference:: Locally binding optional arguments. | |
322 | * let-keywords Reference:: Locally binding keywords arguments. | |
323 | * lambda* Reference:: Creating advanced argument handling procedures. | |
324 | * define* Reference:: Defining procedures and macros. | |
325 | @end menu | |
326 | ||
327 | ||
328 | @node let-optional Reference | |
329 | @subsubsection let-optional Reference | |
330 | ||
331 | @c FIXME::martin: Review me! | |
332 | ||
333 | The syntax @code{let-optional} and @code{let-optional*} are for | |
334 | destructuring rest argument lists and giving names to the various list | |
335 | elements. @code{let-optional} binds all variables simultaneously, while | |
336 | @code{let-optional*} binds them sequentially, consistent with @code{let} | |
337 | and @code{let*} (@pxref{Local Bindings}). | |
338 | ||
339 | @deffn {library syntax} let-optional rest-arg (binding @dots{}) expr @dots{} | |
340 | @deffnx {library syntax} let-optional* rest-arg (binding @dots{}) expr @dots{} | |
341 | These two macros give you an optional argument interface that is very | |
342 | @dfn{Schemey} and introduces no fancy syntax. They are compatible with | |
343 | the scsh macros of the same name, but are slightly extended. Each of | |
344 | @var{binding} may be of one of the forms @var{var} or @code{(@var{var} | |
345 | @var{default-value})}. @var{rest-arg} should be the rest-argument of the | |
346 | procedures these are used from. The items in @var{rest-arg} are | |
347 | sequentially bound to the variable names are given. When @var{rest-arg} | |
348 | runs out, the remaining vars are bound either to the default values or | |
349 | @code{#f} if no default value was specified. @var{rest-arg} remains | |
350 | bound to whatever may have been left of @var{rest-arg}. | |
351 | ||
352 | After binding the variables, the expressions @var{expr} @dots{} are | |
353 | evaluated in order. | |
354 | @end deffn | |
355 | ||
356 | ||
357 | @node let-keywords Reference | |
358 | @subsubsection let-keywords Reference | |
359 | ||
8e1973d9 KR |
360 | @code{let-keywords} and @code{let-keywords*} extract values from |
361 | keyword style argument lists, binding local variables to those values | |
362 | or to defaults. | |
363 | ||
364 | @deffn {library syntax} let-keywords args allow-other-keys? (binding @dots{}) body @dots{} | |
365 | @deffnx {library syntax} let-keywords* args allow-other-keys? (binding @dots{}) body @dots{} | |
366 | @var{args} is evaluated and should give a list of the form | |
367 | @code{(#:keyword1 value1 #:keyword2 value2 @dots{})}. The | |
368 | @var{binding}s are variables and default expressions, with the | |
369 | variables to be set (by name) from the keyword values. The @var{body} | |
370 | forms are then evaluated and the last is the result. An example will | |
371 | make the syntax clearest, | |
372 | ||
373 | @example | |
374 | (define args '(#:xyzzy "hello" #:foo "world")) | |
375 | ||
376 | (let-keywords args #t | |
377 | ((foo "default for foo") | |
378 | (bar (string-append "default" "for" "bar"))) | |
379 | (display foo) | |
380 | (display ", ") | |
381 | (display bar)) | |
382 | @print{} world, defaultforbar | |
383 | @end example | |
384 | ||
385 | The binding for @code{foo} comes from the @code{#:foo} keyword in | |
386 | @code{args}. But the binding for @code{bar} is the default in the | |
387 | @code{let-keywords}, since there's no @code{#:bar} in the args. | |
388 | ||
389 | @var{allow-other-keys?} is evaluated and controls whether unknown | |
390 | keywords are allowed in the @var{args} list. When true other keys are | |
391 | ignored (such as @code{#:xyzzy} in the example), when @code{#f} an | |
392 | error is thrown for anything unknown. | |
393 | ||
394 | @code{let-keywords} is like @code{let} (@pxref{Local Bindings}) in | |
395 | that all bindings are made at once, the defaults expressions are | |
396 | evaluated (if needed) outside the scope of the @code{let-keywords}. | |
397 | ||
398 | @code{let-keywords*} is like @code{let*}, each binding is made | |
399 | successively, and the default expressions see the bindings previously | |
400 | made. This is the style used by @code{lambda*} keywords | |
401 | (@pxref{lambda* Reference}). For example, | |
402 | ||
403 | @example | |
404 | (define args '(#:foo 3)) | |
405 | ||
406 | (let-keywords* args #f | |
407 | ((foo 99) | |
408 | (bar (+ foo 6))) | |
409 | (display bar)) | |
410 | @print{} 9 | |
411 | @end example | |
412 | ||
413 | The expression for each default is only evaluated if it's needed, | |
414 | ie. if the keyword doesn't appear in @var{args}. So one way to make a | |
415 | keyword mandatory is to throw an error of some sort as the default. | |
416 | ||
417 | @example | |
418 | (define args '(#:start 7 #:finish 13)) | |
419 | ||
420 | (let-keywords* args #t | |
421 | ((start 0) | |
422 | (stop (error "missing #:stop argument"))) | |
423 | ...) | |
424 | @result{} ERROR: missing #:stop argument | |
425 | @end example | |
07d83abe MV |
426 | @end deffn |
427 | ||
428 | ||
429 | @node lambda* Reference | |
430 | @subsubsection lambda* Reference | |
431 | ||
edcd3e83 KR |
432 | When using optional and keyword argument lists, @code{lambda} for |
433 | creating a procedure then @code{let-optional} or @code{let-keywords} | |
434 | is a bit lengthy. @code{lambda*} combines the features of those | |
435 | macros into a single convenient syntax. | |
07d83abe | 436 | |
edcd3e83 KR |
437 | @deffn {library syntax} lambda* ([var@dots{}] @* [#:optional vardef@dots{}] @* [#:key vardef@dots{} [#:allow-other-keys]] @* [#:rest var | . var]) @* body |
438 | @sp 1 | |
439 | Create a procedure which takes optional and/or keyword arguments | |
440 | specified with @code{#:optional} and @code{#:key}. For example, | |
07d83abe MV |
441 | |
442 | @lisp | |
443 | (lambda* (a b #:optional c d . e) '()) | |
444 | @end lisp | |
445 | ||
edcd3e83 KR |
446 | is a procedure with fixed arguments @var{a} and @var{b}, optional |
447 | arguments @var{c} and @var{d}, and rest argument @var{e}. If the | |
07d83abe MV |
448 | optional arguments are omitted in a call, the variables for them are |
449 | bound to @code{#f}. | |
450 | ||
edcd3e83 | 451 | @code{lambda*} can also take keyword arguments. For example, a procedure |
07d83abe MV |
452 | defined like this: |
453 | ||
454 | @lisp | |
455 | (lambda* (#:key xyzzy larch) '()) | |
456 | @end lisp | |
457 | ||
edcd3e83 KR |
458 | can be called with any of the argument lists @code{(#:xyzzy 11)}, |
459 | @code{(#:larch 13)}, @code{(#:larch 42 #:xyzzy 19)}, @code{()}. | |
460 | Whichever arguments are given as keywords are bound to values (and | |
461 | those not given are @code{#f}). | |
07d83abe | 462 | |
edcd3e83 KR |
463 | Optional and keyword arguments can also have default values to take |
464 | when not present in a call, by giving a two-element list of variable | |
465 | name and expression. For example in | |
07d83abe MV |
466 | |
467 | @lisp | |
468 | (lambda* (foo #:optional (bar 42) #:key (baz 73)) | |
469 | (list foo bar baz)) | |
470 | @end lisp | |
471 | ||
472 | @var{foo} is a fixed argument, @var{bar} is an optional argument with | |
473 | default value 42, and baz is a keyword argument with default value 73. | |
edcd3e83 KR |
474 | Default value expressions are not evaluated unless they are needed, |
475 | and until the procedure is called. | |
07d83abe | 476 | |
edcd3e83 KR |
477 | Normally it's an error if a call has keywords other than those |
478 | specified by @code{#:key}, but adding @code{#:allow-other-keys} to the | |
479 | definition (after the keyword argument declarations) will ignore | |
480 | unknown keywords. | |
07d83abe | 481 | |
edcd3e83 KR |
482 | If a call has a keyword given twice, the last value is used. For |
483 | example, | |
07d83abe MV |
484 | |
485 | @lisp | |
edcd3e83 KR |
486 | ((lambda* (#:key (heads 0) (tails 0)) |
487 | (display (list heads tails))) | |
488 | #:heads 37 #:tails 42 #:heads 99) | |
489 | @print{} (99 42) | |
07d83abe MV |
490 | @end lisp |
491 | ||
edcd3e83 KR |
492 | @code{#:rest} is a synonym for the dotted syntax rest argument. The |
493 | argument lists @code{(a . b)} and @code{(a #:rest b)} are equivalent | |
494 | in all respects. This is provided for more similarity to DSSSL, | |
495 | MIT-Scheme and Kawa among others, as well as for refugees from other | |
496 | Lisp dialects. | |
497 | ||
498 | When @code{#:key} is used together with a rest argument, the keyword | |
499 | parameters in a call all remain in the rest list. This is the same as | |
500 | Common Lisp. For example, | |
07d83abe | 501 | |
edcd3e83 KR |
502 | @lisp |
503 | ((lambda* (#:key (x 0) #:allow-other-keys #:rest r) | |
504 | (display r)) | |
505 | #:x 123 #:y 456) | |
506 | @print{} (#:x 123 #:y 456) | |
507 | @end lisp | |
508 | ||
509 | @code{#:optional} and @code{#:key} establish their bindings | |
510 | successively, from left to right, as per @code{let-optional*} and | |
511 | @code{let-keywords*}. This means default expressions can refer back | |
512 | to prior parameters, for example | |
513 | ||
514 | @lisp | |
515 | (lambda* (start #:optional (end (+ 10 start))) | |
516 | (do ((i start (1+ i))) | |
517 | ((> i end)) | |
518 | (display i))) | |
519 | @end lisp | |
07d83abe MV |
520 | @end deffn |
521 | ||
522 | ||
523 | @node define* Reference | |
524 | @subsubsection define* Reference | |
525 | ||
526 | @c FIXME::martin: Review me! | |
527 | ||
528 | Just like @code{define} has a shorthand notation for defining procedures | |
529 | (@pxref{Lambda Alternatives}), @code{define*} is provided as an | |
530 | abbreviation of the combination of @code{define} and @code{lambda*}. | |
531 | ||
532 | @code{define*-public} is the @code{lambda*} version of | |
533 | @code{define-public}; @code{defmacro*} and @code{defmacro*-public} exist | |
534 | for defining macros with the improved argument list handling | |
535 | possibilities. The @code{-public} versions not only define the | |
536 | procedures/macros, but also export them from the current module. | |
537 | ||
538 | @deffn {library syntax} define* formals body | |
539 | @deffnx {library syntax} define*-public formals body | |
540 | @code{define*} and @code{define*-public} support optional arguments with | |
541 | a similar syntax to @code{lambda*}. They also support arbitrary-depth | |
542 | currying, just like Guile's define. Some examples: | |
543 | ||
544 | @lisp | |
545 | (define* (x y #:optional a (z 3) #:key w . u) | |
546 | (display (list y z u))) | |
547 | @end lisp | |
548 | defines a procedure @code{x} with a fixed argument @var{y}, an optional | |
549 | argument @var{a}, another optional argument @var{z} with default value 3, | |
550 | a keyword argument @var{w}, and a rest argument @var{u}. | |
551 | ||
552 | @lisp | |
553 | (define-public* ((foo #:optional bar) #:optional baz) '()) | |
554 | @end lisp | |
555 | ||
556 | This illustrates currying. A procedure @code{foo} is defined, which, | |
557 | when called with an optional argument @var{bar}, returns a procedure | |
558 | that takes an optional argument @var{baz}. | |
559 | ||
560 | Of course, @code{define*[-public]} also supports @code{#:rest} and | |
561 | @code{#:allow-other-keys} in the same way as @code{lambda*}. | |
562 | @end deffn | |
563 | ||
564 | @deffn {library syntax} defmacro* name formals body | |
565 | @deffnx {library syntax} defmacro*-public name formals body | |
566 | These are just like @code{defmacro} and @code{defmacro-public} except that they | |
567 | take @code{lambda*}-style extended parameter lists, where @code{#:optional}, | |
568 | @code{#:key}, @code{#:allow-other-keys} and @code{#:rest} are allowed with the usual | |
569 | semantics. Here is an example of a macro with an optional argument: | |
570 | ||
571 | @lisp | |
572 | (defmacro* transmorgify (a #:optional b) | |
573 | (a 1)) | |
574 | @end lisp | |
575 | @end deffn | |
576 | ||
577 | ||
578 | @node Procedure Properties | |
579 | @subsection Procedure Properties and Meta-information | |
580 | ||
581 | @c FIXME::martin: Review me! | |
582 | ||
583 | Procedures always have attached the environment in which they were | |
584 | created and information about how to apply them to actual arguments. In | |
585 | addition to that, properties and meta-information can be stored with | |
586 | procedures. The procedures in this section can be used to test whether | |
587 | a given procedure satisfies a condition; and to access and set a | |
588 | procedure's property. | |
589 | ||
590 | The first group of procedures are predicates to test whether a Scheme | |
591 | object is a procedure, or a special procedure, respectively. | |
592 | @code{procedure?} is the most general predicates, it returns @code{#t} | |
593 | for any kind of procedure. @code{closure?} does not return @code{#t} | |
594 | for primitive procedures, and @code{thunk?} only returns @code{#t} for | |
595 | procedures which do not accept any arguments. | |
596 | ||
597 | @rnindex procedure? | |
598 | @deffn {Scheme Procedure} procedure? obj | |
599 | @deffnx {C Function} scm_procedure_p (obj) | |
600 | Return @code{#t} if @var{obj} is a procedure. | |
601 | @end deffn | |
602 | ||
603 | @deffn {Scheme Procedure} closure? obj | |
604 | @deffnx {C Function} scm_closure_p (obj) | |
605 | Return @code{#t} if @var{obj} is a closure. | |
606 | @end deffn | |
607 | ||
608 | @deffn {Scheme Procedure} thunk? obj | |
609 | @deffnx {C Function} scm_thunk_p (obj) | |
610 | Return @code{#t} if @var{obj} is a thunk. | |
611 | @end deffn | |
612 | ||
613 | @c FIXME::martin: Is that true? | |
614 | @cindex procedure properties | |
615 | Procedure properties are general properties to be attached to | |
616 | procedures. These can be the name of a procedure or other relevant | |
617 | information, such as debug hints. | |
618 | ||
619 | @deffn {Scheme Procedure} procedure-name proc | |
620 | @deffnx {C Function} scm_procedure_name (proc) | |
621 | Return the name of the procedure @var{proc} | |
622 | @end deffn | |
623 | ||
624 | @deffn {Scheme Procedure} procedure-source proc | |
625 | @deffnx {C Function} scm_procedure_source (proc) | |
626 | Return the source of the procedure @var{proc}. | |
627 | @end deffn | |
628 | ||
629 | @deffn {Scheme Procedure} procedure-environment proc | |
630 | @deffnx {C Function} scm_procedure_environment (proc) | |
631 | Return the environment of the procedure @var{proc}. | |
632 | @end deffn | |
633 | ||
634 | @deffn {Scheme Procedure} procedure-properties proc | |
635 | @deffnx {C Function} scm_procedure_properties (proc) | |
636 | Return @var{obj}'s property list. | |
637 | @end deffn | |
638 | ||
639 | @deffn {Scheme Procedure} procedure-property obj key | |
640 | @deffnx {C Function} scm_procedure_property (obj, key) | |
641 | Return the property of @var{obj} with name @var{key}. | |
642 | @end deffn | |
643 | ||
644 | @deffn {Scheme Procedure} set-procedure-properties! proc alist | |
645 | @deffnx {C Function} scm_set_procedure_properties_x (proc, alist) | |
646 | Set @var{obj}'s property list to @var{alist}. | |
647 | @end deffn | |
648 | ||
649 | @deffn {Scheme Procedure} set-procedure-property! obj key value | |
650 | @deffnx {C Function} scm_set_procedure_property_x (obj, key, value) | |
651 | In @var{obj}'s property list, set the property named @var{key} to | |
652 | @var{value}. | |
653 | @end deffn | |
654 | ||
655 | @cindex procedure documentation | |
656 | Documentation for a procedure can be accessed with the procedure | |
657 | @code{procedure-documentation}. | |
658 | ||
659 | @deffn {Scheme Procedure} procedure-documentation proc | |
660 | @deffnx {C Function} scm_procedure_documentation (proc) | |
661 | Return the documentation string associated with @code{proc}. By | |
662 | convention, if a procedure contains more than one expression and the | |
663 | first expression is a string constant, that string is assumed to contain | |
664 | documentation for that procedure. | |
665 | @end deffn | |
666 | ||
07d83abe MV |
667 | |
668 | @node Procedures with Setters | |
669 | @subsection Procedures with Setters | |
670 | ||
671 | @c FIXME::martin: Review me! | |
672 | ||
673 | @c FIXME::martin: Document `operator struct'. | |
674 | ||
675 | @cindex procedure with setter | |
676 | @cindex setter | |
677 | A @dfn{procedure with setter} is a special kind of procedure which | |
678 | normally behaves like any accessor procedure, that is a procedure which | |
679 | accesses a data structure. The difference is that this kind of | |
680 | procedure has a so-called @dfn{setter} attached, which is a procedure | |
681 | for storing something into a data structure. | |
682 | ||
683 | Procedures with setters are treated specially when the procedure appears | |
684 | in the special form @code{set!} (REFFIXME). How it works is best shown | |
685 | by example. | |
686 | ||
687 | Suppose we have a procedure called @code{foo-ref}, which accepts two | |
688 | arguments, a value of type @code{foo} and an integer. The procedure | |
689 | returns the value stored at the given index in the @code{foo} object. | |
690 | Let @code{f} be a variable containing such a @code{foo} data | |
691 | structure.@footnote{Working definitions would be: | |
692 | @lisp | |
693 | (define foo-ref vector-ref) | |
694 | (define foo-set! vector-set!) | |
695 | (define f (make-vector 2 #f)) | |
696 | @end lisp | |
697 | } | |
698 | ||
699 | @lisp | |
700 | (foo-ref f 0) @result{} bar | |
701 | (foo-ref f 1) @result{} braz | |
702 | @end lisp | |
703 | ||
704 | Also suppose that a corresponding setter procedure called | |
705 | @code{foo-set!} does exist. | |
706 | ||
707 | @lisp | |
708 | (foo-set! f 0 'bla) | |
709 | (foo-ref f 0) @result{} bla | |
710 | @end lisp | |
711 | ||
712 | Now we could create a new procedure called @code{foo}, which is a | |
713 | procedure with setter, by calling @code{make-procedure-with-setter} with | |
714 | the accessor and setter procedures @code{foo-ref} and @code{foo-set!}. | |
715 | Let us call this new procedure @code{foo}. | |
716 | ||
717 | @lisp | |
718 | (define foo (make-procedure-with-setter foo-ref foo-set!)) | |
719 | @end lisp | |
720 | ||
721 | @code{foo} can from now an be used to either read from the data | |
722 | structure stored in @code{f}, or to write into the structure. | |
723 | ||
724 | @lisp | |
725 | (set! (foo f 0) 'dum) | |
726 | (foo f 0) @result{} dum | |
727 | @end lisp | |
728 | ||
729 | @deffn {Scheme Procedure} make-procedure-with-setter procedure setter | |
730 | @deffnx {C Function} scm_make_procedure_with_setter (procedure, setter) | |
731 | Create a new procedure which behaves like @var{procedure}, but | |
732 | with the associated setter @var{setter}. | |
733 | @end deffn | |
734 | ||
735 | @deffn {Scheme Procedure} procedure-with-setter? obj | |
736 | @deffnx {C Function} scm_procedure_with_setter_p (obj) | |
737 | Return @code{#t} if @var{obj} is a procedure with an | |
738 | associated setter procedure. | |
739 | @end deffn | |
740 | ||
741 | @deffn {Scheme Procedure} procedure proc | |
742 | @deffnx {C Function} scm_procedure (proc) | |
743 | Return the procedure of @var{proc}, which must be either a | |
744 | procedure with setter, or an operator struct. | |
745 | @end deffn | |
746 | ||
747 | @deffn {Scheme Procedure} setter proc | |
748 | Return the setter of @var{proc}, which must be either a procedure with | |
749 | setter or an operator struct. | |
750 | @end deffn | |
751 | ||
752 | ||
753 | @node Macros | |
754 | @subsection Lisp Style Macro Definitions | |
755 | ||
756 | @cindex macros | |
757 | @cindex transformation | |
758 | Macros are objects which cause the expression that they appear in to be | |
759 | transformed in some way @emph{before} being evaluated. In expressions | |
760 | that are intended for macro transformation, the identifier that names | |
761 | the relevant macro must appear as the first element, like this: | |
762 | ||
763 | @lisp | |
764 | (@var{macro-name} @var{macro-args} @dots{}) | |
765 | @end lisp | |
766 | ||
767 | In Lisp-like languages, the traditional way to define macros is very | |
768 | similar to procedure definitions. The key differences are that the | |
769 | macro definition body should return a list that describes the | |
770 | transformed expression, and that the definition is marked as a macro | |
771 | definition (rather than a procedure definition) by the use of a | |
772 | different definition keyword: in Lisp, @code{defmacro} rather than | |
773 | @code{defun}, and in Scheme, @code{define-macro} rather than | |
774 | @code{define}. | |
775 | ||
776 | @fnindex defmacro | |
777 | @fnindex define-macro | |
778 | Guile supports this style of macro definition using both @code{defmacro} | |
779 | and @code{define-macro}. The only difference between them is how the | |
780 | macro name and arguments are grouped together in the definition: | |
781 | ||
782 | @lisp | |
783 | (defmacro @var{name} (@var{args} @dots{}) @var{body} @dots{}) | |
784 | @end lisp | |
785 | ||
786 | @noindent | |
787 | is the same as | |
788 | ||
789 | @lisp | |
790 | (define-macro (@var{name} @var{args} @dots{}) @var{body} @dots{}) | |
791 | @end lisp | |
792 | ||
793 | @noindent | |
794 | The difference is analogous to the corresponding difference between | |
795 | Lisp's @code{defun} and Scheme's @code{define}. | |
796 | ||
797 | @code{false-if-exception}, from the @file{boot-9.scm} file in the Guile | |
798 | distribution, is a good example of macro definition using | |
799 | @code{defmacro}: | |
800 | ||
801 | @lisp | |
802 | (defmacro false-if-exception (expr) | |
803 | `(catch #t | |
804 | (lambda () ,expr) | |
805 | (lambda args #f))) | |
806 | @end lisp | |
807 | ||
808 | @noindent | |
809 | The effect of this definition is that expressions beginning with the | |
810 | identifier @code{false-if-exception} are automatically transformed into | |
811 | a @code{catch} expression following the macro definition specification. | |
812 | For example: | |
813 | ||
814 | @lisp | |
815 | (false-if-exception (open-input-file "may-not-exist")) | |
816 | @equiv{} | |
817 | (catch #t | |
818 | (lambda () (open-input-file "may-not-exist")) | |
819 | (lambda args #f)) | |
820 | @end lisp | |
821 | ||
822 | ||
823 | @node Syntax Rules | |
824 | @subsection The R5RS @code{syntax-rules} System | |
825 | @cindex R5RS syntax-rules system | |
826 | ||
827 | R5RS defines an alternative system for macro and syntax transformations | |
828 | using the keywords @code{define-syntax}, @code{let-syntax}, | |
829 | @code{letrec-syntax} and @code{syntax-rules}. | |
830 | ||
831 | The main difference between the R5RS system and the traditional macros | |
832 | of the previous section is how the transformation is specified. In | |
833 | R5RS, rather than permitting a macro definition to return an arbitrary | |
834 | expression, the transformation is specified in a pattern language that | |
835 | ||
836 | @itemize @bullet | |
837 | @item | |
838 | does not require complicated quoting and extraction of components of the | |
839 | source expression using @code{caddr} etc. | |
840 | ||
841 | @item | |
842 | is designed such that the bindings associated with identifiers in the | |
843 | transformed expression are well defined, and such that it is impossible | |
844 | for the transformed expression to construct new identifiers. | |
845 | @end itemize | |
846 | ||
847 | @noindent | |
848 | The last point is commonly referred to as being @dfn{hygienic}: the R5RS | |
849 | @code{syntax-case} system provides @dfn{hygienic macros}. | |
850 | ||
851 | For example, the R5RS pattern language for the @code{false-if-exception} | |
852 | example of the previous section looks like this: | |
853 | ||
854 | @lisp | |
855 | (syntax-rules () | |
856 | ((_ expr) | |
857 | (catch #t | |
858 | (lambda () expr) | |
859 | (lambda args #f)))) | |
860 | @end lisp | |
861 | ||
862 | @cindex @code{syncase} | |
863 | In Guile, the @code{syntax-rules} system is provided by the @code{(ice-9 | |
864 | syncase)} module. To make these facilities available in your code, | |
865 | include the expression @code{(use-syntax (ice-9 syncase))} (@pxref{Using | |
866 | Guile Modules}) before the first usage of @code{define-syntax} etc. If | |
867 | you are writing a Scheme module, you can alternatively include the form | |
868 | @code{#:use-syntax (ice-9 syncase)} in your @code{define-module} | |
869 | declaration (@pxref{Creating Guile Modules}). | |
870 | ||
871 | @menu | |
872 | * Pattern Language:: The @code{syntax-rules} pattern language. | |
873 | * Define-Syntax:: Top level syntax definitions. | |
874 | * Let-Syntax:: Local syntax definitions. | |
875 | @end menu | |
876 | ||
877 | ||
878 | @node Pattern Language | |
879 | @subsubsection The @code{syntax-rules} Pattern Language | |
880 | ||
881 | ||
882 | @node Define-Syntax | |
883 | @subsubsection Top Level Syntax Definitions | |
884 | ||
885 | define-syntax: The gist is | |
886 | ||
887 | (define-syntax <keyword> <transformer-spec>) | |
888 | ||
889 | makes the <keyword> into a macro so that | |
890 | ||
891 | (<keyword> ...) | |
892 | ||
893 | expands at _compile_ or _read_ time (i.e. before any | |
894 | evaluation begins) into some expression that is | |
895 | given by the <transformer-spec>. | |
896 | ||
897 | ||
898 | @node Let-Syntax | |
899 | @subsubsection Local Syntax Definitions | |
900 | ||
901 | ||
902 | @node Syntax Case | |
903 | @subsection Support for the @code{syntax-case} System | |
904 | ||
905 | ||
906 | ||
907 | @node Internal Macros | |
908 | @subsection Internal Representation of Macros and Syntax | |
909 | ||
910 | Internally, Guile uses three different flavors of macros. The three | |
911 | flavors are called @dfn{acro} (or @dfn{syntax}), @dfn{macro} and | |
912 | @dfn{mmacro}. | |
913 | ||
914 | Given the expression | |
915 | ||
916 | @lisp | |
917 | (foo @dots{}) | |
918 | @end lisp | |
919 | ||
920 | @noindent | |
921 | with @code{foo} being some flavor of macro, one of the following things | |
922 | will happen when the expression is evaluated. | |
923 | ||
924 | @itemize @bullet | |
925 | @item | |
926 | When @code{foo} has been defined to be an @dfn{acro}, the procedure used | |
927 | in the acro definition of @code{foo} is passed the whole expression and | |
928 | the current lexical environment, and whatever that procedure returns is | |
929 | the value of evaluating the expression. You can think of this a | |
930 | procedure that receives its argument as an unevaluated expression. | |
931 | ||
932 | @item | |
933 | When @code{foo} has been defined to be a @dfn{macro}, the procedure used | |
934 | in the macro definition of @code{foo} is passed the whole expression and | |
935 | the current lexical environment, and whatever that procedure returns is | |
936 | evaluated again. That is, the procedure should return a valid Scheme | |
937 | expression. | |
938 | ||
939 | @item | |
940 | When @code{foo} has been defined to be a @dfn{mmacro}, the procedure | |
941 | used in the mmacro definition of `foo' is passed the whole expression | |
942 | and the current lexical environment, and whatever that procedure returns | |
943 | replaces the original expression. Evaluation then starts over from the | |
944 | new expression that has just been returned. | |
945 | @end itemize | |
946 | ||
947 | The key difference between a @dfn{macro} and a @dfn{mmacro} is that the | |
948 | expression returned by a @dfn{mmacro} procedure is remembered (or | |
949 | @dfn{memoized}) so that the expansion does not need to be done again | |
950 | next time the containing code is evaluated. | |
951 | ||
952 | The primitives @code{procedure->syntax}, @code{procedure->macro} and | |
953 | @code{procedure->memoizing-macro} are used to construct acros, macros | |
954 | and mmacros respectively. However, if you do not have a very special | |
955 | reason to use one of these primitives, you should avoid them: they are | |
956 | very specific to Guile's current implementation and therefore likely to | |
957 | change. Use @code{defmacro}, @code{define-macro} (@pxref{Macros}) or | |
958 | @code{define-syntax} (@pxref{Syntax Rules}) instead. (In low level | |
959 | terms, @code{defmacro}, @code{define-macro} and @code{define-syntax} are | |
960 | all implemented as mmacros.) | |
961 | ||
962 | @deffn {Scheme Procedure} procedure->syntax code | |
963 | @deffnx {C Function} scm_makacro (code) | |
964 | Return a macro which, when a symbol defined to this value appears as the | |
965 | first symbol in an expression, returns the result of applying @var{code} | |
966 | to the expression and the environment. | |
967 | @end deffn | |
968 | ||
969 | @deffn {Scheme Procedure} procedure->macro code | |
970 | @deffnx {C Function} scm_makmacro (code) | |
971 | Return a macro which, when a symbol defined to this value appears as the | |
972 | first symbol in an expression, evaluates the result of applying | |
973 | @var{code} to the expression and the environment. For example: | |
974 | ||
975 | @lisp | |
976 | (define trace | |
977 | (procedure->macro | |
978 | (lambda (x env) | |
979 | `(set! ,(cadr x) (tracef ,(cadr x) ',(cadr x)))))) | |
980 | ||
981 | (trace @i{foo}) | |
982 | @equiv{} | |
983 | (set! @i{foo} (tracef @i{foo} '@i{foo})). | |
984 | @end lisp | |
985 | @end deffn | |
986 | ||
987 | @deffn {Scheme Procedure} procedure->memoizing-macro code | |
988 | @deffnx {C Function} scm_makmmacro (code) | |
989 | Return a macro which, when a symbol defined to this value appears as the | |
990 | first symbol in an expression, evaluates the result of applying | |
991 | @var{code} to the expression and the environment. | |
992 | @code{procedure->memoizing-macro} is the same as | |
993 | @code{procedure->macro}, except that the expression returned by | |
994 | @var{code} replaces the original macro expression in the memoized form | |
995 | of the containing code. | |
996 | @end deffn | |
997 | ||
998 | In the following primitives, @dfn{acro} flavor macros are referred to | |
999 | as @dfn{syntax transformers}. | |
1000 | ||
1001 | @deffn {Scheme Procedure} macro? obj | |
1002 | @deffnx {C Function} scm_macro_p (obj) | |
1003 | Return @code{#t} if @var{obj} is a regular macro, a memoizing macro or a | |
1004 | syntax transformer. | |
1005 | @end deffn | |
1006 | ||
1007 | @deffn {Scheme Procedure} macro-type m | |
1008 | @deffnx {C Function} scm_macro_type (m) | |
1009 | Return one of the symbols @code{syntax}, @code{macro} or | |
1010 | @code{macro!}, depending on whether @var{m} is a syntax | |
1011 | transformer, a regular macro, or a memoizing macro, | |
1012 | respectively. If @var{m} is not a macro, @code{#f} is | |
1013 | returned. | |
1014 | @end deffn | |
1015 | ||
1016 | @deffn {Scheme Procedure} macro-name m | |
1017 | @deffnx {C Function} scm_macro_name (m) | |
1018 | Return the name of the macro @var{m}. | |
1019 | @end deffn | |
1020 | ||
1021 | @deffn {Scheme Procedure} macro-transformer m | |
1022 | @deffnx {C Function} scm_macro_transformer (m) | |
1023 | Return the transformer of the macro @var{m}. | |
1024 | @end deffn | |
1025 | ||
1026 | @deffn {Scheme Procedure} cons-source xorig x y | |
1027 | @deffnx {C Function} scm_cons_source (xorig, x, y) | |
1028 | Create and return a new pair whose car and cdr are @var{x} and @var{y}. | |
1029 | Any source properties associated with @var{xorig} are also associated | |
1030 | with the new pair. | |
1031 | @end deffn | |
1032 | ||
1033 | ||
1034 | @c Local Variables: | |
1035 | @c TeX-master: "guile.texi" | |
1036 | @c End: |