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1 | ;;;; srfi-16.scm --- `case-lambda' for Guile |
2 | ||
3 | ;;; Copyright (C) 2001 Free Software Foundation, Inc. | |
4 | ;;; | |
5 | ;;; This program is free software; you can redistribute it and/or | |
6 | ;;; modify it under the terms of the GNU General Public License as | |
7 | ;;; published by the Free Software Foundation; either version 2, or | |
8 | ;;; (at your option) any later version. | |
9 | ;;; | |
10 | ;;; This program 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 | ;;; General Public License for more details. | |
14 | ;;; | |
15 | ;;; You should have received a copy of the GNU General Public License | |
16 | ;;; along with this software; see the file COPYING. If not, write to | |
17 | ;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330, | |
18 | ;;; Boston, MA 02111-1307 USA | |
f480396b MV |
19 | ;;; |
20 | ;;; As a special exception, the Free Software Foundation gives permission | |
21 | ;;; for additional uses of the text contained in its release of GUILE. | |
22 | ;;; | |
23 | ;;; The exception is that, if you link the GUILE library with other files | |
24 | ;;; to produce an executable, this does not by itself cause the | |
25 | ;;; resulting executable to be covered by the GNU General Public License. | |
26 | ;;; Your use of that executable is in no way restricted on account of | |
27 | ;;; linking the GUILE library code into it. | |
28 | ;;; | |
29 | ;;; This exception does not however invalidate any other reasons why | |
30 | ;;; the executable file might be covered by the GNU General Public License. | |
31 | ;;; | |
32 | ;;; This exception applies only to the code released by the | |
33 | ;;; Free Software Foundation under the name GUILE. If you copy | |
34 | ;;; code from other Free Software Foundation releases into a copy of | |
35 | ;;; GUILE, as the General Public License permits, the exception does | |
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38 | ;;; this exception notice from them. | |
39 | ;;; | |
40 | ;;; If you write modifications of your own for GUILE, it is your choice | |
41 | ;;; whether to permit this exception to apply to your modifications. | |
42 | ;;; If you do not wish that, delete this exception notice. | |
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43 | |
44 | ;;; Commentary: | |
45 | ||
46 | ;;; Implementation of SRFI-16. `case-lambda' is a syntactic form | |
47 | ;;; which permits writing functions acting different according to the | |
48 | ;;; number of arguments passed. | |
49 | ;;; | |
50 | ;;; The syntax of the `case-lambda' form is defined in the following | |
51 | ;;; EBNF grammar. | |
52 | ;;; | |
53 | ;;; <case-lambda> | |
54 | ;;; --> (case-lambda <case-lambda-clause>) | |
55 | ;;; <case-lambda-clause> | |
56 | ;;; --> (<signature> <definition-or-command>*) | |
57 | ;;; <signature> | |
58 | ;;; --> (<identifier>*) | |
59 | ;;; | (<identifier>* . <identifier>) | |
60 | ;;; | <identifier> | |
61 | ;;; | |
62 | ;;; The value returned by a `case-lambda' form is a procedure which | |
63 | ;;; matches the number of actual arguments against the signatures in | |
64 | ;;; the various clauses, in order. The first matching clause is | |
65 | ;;; selected, the corresponding values from the actual parameter list | |
66 | ;;; are bound to the variable names in the clauses and the body of the | |
67 | ;;; clause is evaluated. | |
68 | ||
69 | ;;; Author: Martin Grabmueller | |
70 | ||
71 | ;;; Code: | |
1a179b03 MD |
72 | (define-module (srfi srfi-16) |
73 | :export-syntax (case-lambda)) | |
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75 | (cond-expand-provide (current-module) '(srfi-16)) |
76 | ||
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77 | (define-macro (case-lambda . clauses) |
78 | ||
79 | ;; Return the length of the list @var{l}, but allow dotted list. | |
80 | ;; | |
81 | (define (alength l) | |
82 | (cond ((null? l) 0) | |
83 | ((pair? l) (+ 1 (alength (cdr l)))) | |
84 | (else 0))) | |
85 | ||
86 | ;; Return @code{#t} if @var{l} is a dotted list, @code{#f} if it is | |
87 | ;; a normal list. | |
88 | ;; | |
89 | (define (dotted? l) | |
90 | (cond ((null? l) #f) | |
91 | ((pair? l) (dotted? (cdr l))) | |
92 | (else #t))) | |
93 | ||
94 | ;; Return the expression for accessing the @var{index}th element of | |
95 | ;; the list called @var{args-name}. If @var{tail?} is true, code | |
96 | ;; for accessing the list-tail is generated, otherwise for accessing | |
97 | ;; the list element itself. | |
98 | ;; | |
99 | (define (accessor args-name index tail?) | |
100 | (if tail? | |
101 | (case index | |
102 | ((0) `,args-name) | |
103 | ((1) `(cdr ,args-name)) | |
104 | ((2) `(cddr ,args-name)) | |
105 | ((3) `(cdddr ,args-name)) | |
106 | ((4) `(cddddr ,args-name)) | |
107 | (else `(list-tail ,args-name ,index))) | |
108 | (case index | |
109 | ((0) `(car ,args-name)) | |
110 | ((1) `(cadr ,args-name)) | |
111 | ((2) `(caddr ,args-name)) | |
112 | ((3) `(cadddr ,args-name)) | |
113 | (else `(list-ref ,args-name ,index))))) | |
114 | ||
115 | ;; Generate the binding lists of the variables of one case-lambda | |
116 | ;; clause. @var{vars} is the (possibly dotted) list of variables | |
117 | ;; and @var{args-name} is the generated name used for the argument | |
118 | ;; list. | |
119 | ;; | |
120 | (define (gen-temps vars args-name) | |
121 | (let lp ((v vars) (i 0)) | |
122 | (cond ((null? v) '()) | |
123 | ((pair? v) | |
124 | (cons `(,(car v) ,(accessor args-name i #f)) | |
125 | (lp (cdr v) (+ i 1)))) | |
126 | (else `((,v ,(accessor args-name i #t))))))) | |
127 | ||
128 | ;; Generate the cond clauses for each of the clauses of case-lambda, | |
129 | ;; including the parameter count check, binding of the parameters | |
130 | ;; and the code of the corresponding body. | |
131 | ;; | |
132 | (define (gen-clauses l length-name args-name) | |
133 | (cond ((null? l) (list '(else (error "too few arguments")))) | |
134 | (else | |
135 | (cons | |
136 | `((,(if (dotted? (caar l)) '>= '=) | |
137 | ,length-name ,(alength (caar l))) | |
138 | (let ,(gen-temps (caar l) args-name) | |
139 | ,@(cdar l))) | |
140 | (gen-clauses (cdr l) length-name args-name))))) | |
141 | ||
142 | (let ((args-name (gensym)) | |
143 | (length-name (gensym))) | |
144 | (let ((proc | |
145 | `(lambda ,args-name | |
146 | (let ((,length-name (length ,args-name))) | |
147 | (cond ,@(gen-clauses clauses length-name args-name)))))) | |
148 | proc))) |