1 ;;;; optargs.scm -- support for optional arguments
3 ;;;; Copyright (C) 1997, 1998, 1999, 2001, 2002, 2004 Free Software Foundation, Inc.
5 ;;;; This library is free software; you can redistribute it and/or
6 ;;;; modify it under the terms of the GNU Lesser General Public
7 ;;;; License as published by the Free Software Foundation; either
8 ;;;; version 2.1 of the License, or (at your option) any later version.
10 ;;;; This library is distributed in the hope that it will be useful,
11 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
12 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 ;;;; Lesser General Public License for more details.
15 ;;;; You should have received a copy of the GNU Lesser General Public
16 ;;;; License along with this library; if not, write to the Free Software
17 ;;;; Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
19 ;;;; Contributed by Maciej Stachowiak <mstachow@alum.mit.edu>
25 ;;; {Optional Arguments}
27 ;;; The C interface for creating Guile procedures has a very handy
28 ;;; "optional argument" feature. This module attempts to provide
29 ;;; similar functionality for procedures defined in Scheme with
30 ;;; a convenient and attractive syntax.
32 ;;; exported macros are:
44 ;;; Summary of the lambda* extended parameter list syntax (brackets
45 ;;; are used to indicate grouping only):
47 ;;; ext-param-list ::= [identifier]* [#:optional [ext-var-decl]+]?
48 ;;; [#:key [ext-var-decl]+ [#:allow-other-keys]?]?
49 ;;; [[#:rest identifier]|[. identifier]]?
51 ;;; ext-var-decl ::= identifier | ( identifier expression )
53 ;;; The characters `*', `+' and `?' are not to be taken literally; they
54 ;;; mean respectively, zero or more occurences, one or more occurences,
55 ;;; and one or zero occurences.
60 (define-module (ice-9 optargs)
61 :export-syntax (let-optional
70 ;; let-optional rest-arg (binding ...) . body
71 ;; let-optional* rest-arg (binding ...) . body
72 ;; macros used to bind optional arguments
74 ;; These two macros give you an optional argument interface that is
75 ;; very "Schemey" and introduces no fancy syntax. They are compatible
76 ;; with the scsh macros of the same name, but are slightly
77 ;; extended. Each of binding may be of one of the forms <var> or
78 ;; (<var> <default-value>). rest-arg should be the rest-argument of
79 ;; the procedures these are used from. The items in rest-arg are
80 ;; sequentially bound to the variable namess are given. When rest-arg
81 ;; runs out, the remaining vars are bound either to the default values
82 ;; or to `#f' if no default value was specified. rest-arg remains
83 ;; bound to whatever may have been left of rest-arg.
86 (defmacro let-optional (REST-ARG BINDINGS . BODY)
87 (let-optional-template REST-ARG BINDINGS BODY 'let))
89 (defmacro let-optional* (REST-ARG BINDINGS . BODY)
90 (let-optional-template REST-ARG BINDINGS BODY 'let*))
94 ;; let-keywords rest-arg allow-other-keys? (binding ...) . body
95 ;; let-keywords* rest-arg allow-other-keys? (binding ...) . body
96 ;; macros used to bind keyword arguments
98 ;; These macros pick out keyword arguments from rest-arg, but do not
99 ;; modify it. This is consistent at least with Common Lisp, which
100 ;; duplicates keyword args in the rest arg. More explanation of what
101 ;; keyword arguments in a lambda list look like can be found below in
102 ;; the documentation for lambda*. Bindings can have the same form as
103 ;; for let-optional. If allow-other-keys? is false, an error will be
104 ;; thrown if anything that looks like a keyword argument but does not
105 ;; match a known keyword parameter will result in an error.
109 (defmacro let-keywords (REST-ARG ALLOW-OTHER-KEYS? BINDINGS . BODY)
110 (let-keywords-template REST-ARG ALLOW-OTHER-KEYS? BINDINGS BODY 'let))
112 (defmacro let-keywords* (REST-ARG ALLOW-OTHER-KEYS? BINDINGS . BODY)
113 (let-keywords-template REST-ARG ALLOW-OTHER-KEYS? BINDINGS BODY 'let*))
116 ;; some utility procedures for implementing the various let-forms.
118 (define (let-o-k-template REST-ARG BINDINGS BODY let-type proc)
119 (let ((bindings (map (lambda (x)
124 `(,let-type ,(map proc bindings) ,@BODY)))
126 (define (let-optional-template REST-ARG BINDINGS BODY let-type)
129 (let-o-k-template REST-ARG BINDINGS BODY let-type
133 ((not (null? ,REST-ARG))
134 (let ((result (car ,REST-ARG)))
135 ,(list 'set! REST-ARG
139 ,(cadr optional))))))))
141 (define (let-keywords-template REST-ARG ALLOW-OTHER-KEYS? BINDINGS BODY let-type)
144 (let* ((kb-list-gensym (gensym "kb:G"))
145 (bindfilter (lambda (key)
148 ((assq ',(car key) ,kb-list-gensym)
152 `(let* ((ra->kbl ,rest-arg->keyword-binding-list)
153 (,kb-list-gensym (ra->kbl ,REST-ARG ',(map
154 (lambda (x) (symbol->keyword (if (pair? x) (car x) x)))
156 ,ALLOW-OTHER-KEYS?)))
157 ,(let-o-k-template REST-ARG BINDINGS BODY let-type bindfilter)))))
160 (define (rest-arg->keyword-binding-list rest-arg keywords allow-other-keys?)
163 (let loop ((first (car rest-arg))
164 (rest (cdr rest-arg))
166 (let ((next (lambda (a)
167 (if (null? (cdr rest))
169 (loop (cadr rest) (cddr rest) a)))))
172 ((memq first keywords)
174 (error "Keyword argument has no value.")
175 (next (cons (cons (keyword->symbol first)
176 (car rest)) accum))))
177 ((not allow-other-keys?)
178 (error "Unknown keyword in arguments."))
179 (else (if (null? rest)
184 (loop (car rest) (cdr rest) accum)))))))
187 ;; lambda* args . body
188 ;; lambda extended for optional and keyword arguments
190 ;; lambda* creates a procedure that takes optional arguments. These
191 ;; are specified by putting them inside brackets at the end of the
192 ;; paramater list, but before any dotted rest argument. For example,
193 ;; (lambda* (a b #:optional c d . e) '())
194 ;; creates a procedure with fixed arguments a and b, optional arguments c
195 ;; and d, and rest argument e. If the optional arguments are omitted
196 ;; in a call, the variables for them are bound to `#f'.
198 ;; lambda* can also take keyword arguments. For example, a procedure
199 ;; defined like this:
200 ;; (lambda* (#:key xyzzy larch) '())
201 ;; can be called with any of the argument lists (#:xyzzy 11)
202 ;; (#:larch 13) (#:larch 42 #:xyzzy 19) (). Whichever arguments
203 ;; are given as keywords are bound to values.
205 ;; Optional and keyword arguments can also be given default values
206 ;; which they take on when they are not present in a call, by giving a
207 ;; two-item list in place of an optional argument, for example in:
208 ;; (lambda* (foo #:optional (bar 42) #:key (baz 73)) (list foo bar baz))
209 ;; foo is a fixed argument, bar is an optional argument with default
210 ;; value 42, and baz is a keyword argument with default value 73.
211 ;; Default value expressions are not evaluated unless they are needed
212 ;; and until the procedure is called.
214 ;; lambda* now supports two more special parameter list keywords.
216 ;; lambda*-defined procedures now throw an error by default if a
217 ;; keyword other than one of those specified is found in the actual
218 ;; passed arguments. However, specifying #:allow-other-keys
219 ;; immediately after the keyword argument declarations restores the
220 ;; previous behavior of ignoring unknown keywords. lambda* also now
221 ;; guarantees that if the same keyword is passed more than once, the
222 ;; last one passed is the one that takes effect. For example,
223 ;; ((lambda* (#:key (heads 0) (tails 0)) (display (list heads tails)))
224 ;; #:heads 37 #:tails 42 #:heads 99)
225 ;; would result in (99 47) being displayed.
227 ;; #:rest is also now provided as a synonym for the dotted syntax rest
228 ;; argument. The argument lists (a . b) and (a #:rest b) are equivalent in
229 ;; all respects to lambda*. This is provided for more similarity to DSSSL,
230 ;; MIT-Scheme and Kawa among others, as well as for refugees from other
234 (defmacro lambda* (ARGLIST . BODY)
237 (lambda (non-optional-args optionals keys aok? rest-arg)
238 ;; Check for syntax errors.
239 (if (not (every? symbol? non-optional-args))
240 (error "Syntax error in fixed argument declaration."))
241 (if (not (every? ext-decl? optionals))
242 (error "Syntax error in optional argument declaration."))
243 (if (not (every? ext-decl? keys))
244 (error "Syntax error in keyword argument declaration."))
245 (if (not (or (symbol? rest-arg) (eq? #f rest-arg)))
246 (error "Syntax error in rest argument declaration."))
247 ;; generate the code.
248 (let ((rest-gensym (or rest-arg (gensym "lambda*:G")))
249 (lambda-gensym (gensym "lambda*:L")))
250 (if (not (and (null? optionals) (null? keys)))
251 `(let ((,lambda-gensym
252 (lambda (,@non-optional-args . ,rest-gensym)
253 ;; Make sure that if the proc had a docstring, we put it
254 ;; here where it will be visible.
255 ,@(if (and (not (null? BODY))
256 (string? (car BODY)))
262 (let-keywords* ,rest-gensym
265 ,@(if (and (not rest-arg) (null? keys))
266 `((if (not (null? ,rest-gensym))
267 (error "Too many arguments.")))
271 (set-procedure-property! ,lambda-gensym 'arglist
278 `(lambda (,@non-optional-args . ,(if rest-arg rest-arg '()))
282 (define (every? pred lst)
284 (and (pred (car lst))
285 (every? pred (cdr lst)))))
287 (define (ext-decl? obj)
289 (and (list? obj) (= 2 (length obj)) (symbol? (car obj)))))
291 ;; XXX - not tail recursive
292 (define (improper-list-copy obj)
294 (cons (car obj) (improper-list-copy (cdr obj)))
297 (define (parse-arglist arglist cont)
298 (define (split-list-at val lst cont)
302 (if (memq val (cdr pos))
303 (error (with-output-to-string
306 " specified more than once in argument list.")))))
307 (cont (reverse (cdr (memq val (reverse lst)))) (cdr pos) #t))))
308 (else (cont lst '() #f))))
309 (define (parse-opt-and-fixed arglist keys aok? rest cont)
312 (lambda (before after split?)
313 (if (and split? (null? after))
314 (error "#:optional specified but no optional arguments declared.")
315 (cont before after keys aok? rest)))))
316 (define (parse-keys arglist rest cont)
318 #:allow-other-keys arglist
319 (lambda (aok-before aok-after aok-split?)
320 (if (and aok-split? (not (null? aok-after)))
321 (error "#:allow-other-keys not at end of keyword argument declarations.")
324 (lambda (key-before key-after key-split?)
326 ((and aok-split? (not key-split?))
327 (error "#:allow-other-keys specified but no keyword arguments declared."))
330 ((null? key-after) (error "#:key specified but no keyword arguments declared."))
331 ((memq #:optional key-after) (error "#:optional arguments declared after #:key arguments."))
332 (else (parse-opt-and-fixed key-before key-after aok-split? rest cont))))
333 (else (parse-opt-and-fixed arglist '() #f rest cont)))))))))
334 (define (parse-rest arglist cont)
336 ((null? arglist) (cont '() '() '() #f #f))
337 ((not (pair? arglist)) (cont '() '() '() #f arglist))
338 ((not (list? arglist))
339 (let* ((copy (improper-list-copy arglist))
340 (lp (last-pair copy))
343 (if (memq #:rest copy)
344 (error "Cannot specify both #:rest and dotted rest argument.")
345 (parse-keys copy ra cont))))
348 (lambda (before after split?)
351 ((0) (error "#:rest not followed by argument."))
352 ((1) (parse-keys before (car after) cont))
353 (else (error "#:rest argument must be declared last.")))
354 (parse-keys before #f cont)))))))
356 (parse-rest arglist cont))
360 ;; define* args . body
361 ;; define*-public args . body
362 ;; define and define-public extended for optional and keyword arguments
364 ;; define* and define*-public support optional arguments with
365 ;; a similar syntax to lambda*. They also support arbitrary-depth
366 ;; currying, just like Guile's define. Some examples:
367 ;; (define* (x y #:optional a (z 3) #:key w . u) (display (list y z u)))
368 ;; defines a procedure x with a fixed argument y, an optional agument
369 ;; a, another optional argument z with default value 3, a keyword argument w,
370 ;; and a rest argument u.
371 ;; (define-public* ((foo #:optional bar) #:optional baz) '())
372 ;; This illustrates currying. A procedure foo is defined, which,
373 ;; when called with an optional argument bar, returns a procedure that
374 ;; takes an optional argument baz.
376 ;; Of course, define*[-public] also supports #:rest and #:allow-other-keys
377 ;; in the same way as lambda*.
379 (defmacro define* (ARGLIST . BODY)
380 (define*-guts 'define ARGLIST BODY))
382 (defmacro define*-public (ARGLIST . BODY)
383 (define*-guts 'define-public ARGLIST BODY))
385 ;; The guts of define* and define*-public.
386 (define (define*-guts DT ARGLIST BODY)
387 (define (nest-lambda*s arglists)
390 `((lambda* ,(car arglists) ,@(nest-lambda*s (cdr arglists))))))
391 (define (define*-guts-helper ARGLIST arglists)
392 (let ((first (car ARGLIST))
393 (al (cons (cdr ARGLIST) arglists)))
395 `(,DT ,first ,@(nest-lambda*s al))
396 (define*-guts-helper first al))))
397 (if (symbol? ARGLIST)
398 `(,DT ,ARGLIST ,@BODY)
399 (define*-guts-helper ARGLIST '())))
403 ;; defmacro* name args . body
404 ;; defmacro*-public args . body
405 ;; defmacro and defmacro-public extended for optional and keyword arguments
407 ;; These are just like defmacro and defmacro-public except that they
408 ;; take lambda*-style extended paramter lists, where #:optional,
409 ;; #:key, #:allow-other-keys and #:rest are allowed with the usual
410 ;; semantics. Here is an example of a macro with an optional argument:
411 ;; (defmacro* transmorgify (a #:optional b)
413 (defmacro defmacro* (NAME ARGLIST . BODY)
414 (defmacro*-guts 'define NAME ARGLIST BODY))
416 (defmacro defmacro*-public (NAME ARGLIST . BODY)
417 (defmacro*-guts 'define-public NAME ARGLIST BODY))
419 ;; The guts of defmacro* and defmacro*-public
420 (define (defmacro*-guts DT NAME ARGLIST BODY)
422 (,(lambda (transformer) (defmacro:transformer transformer))
423 (lambda* ,ARGLIST ,@BODY))))
425 ;;; optargs.scm ends here