Commit | Line | Data |
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b2e72381 | 1 | ;;; srfi-31.scm --- special form for recursive evaluation |
e96f5a6e | 2 | |
1b09b607 | 3 | ;; Copyright (C) 2004, 2006 Free Software Foundation, Inc. |
e96f5a6e RB |
4 | ;; |
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. | |
9 | ;; | |
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. | |
14 | ;; | |
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 | |
92205699 | 17 | ;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
e96f5a6e RB |
18 | |
19 | ;;; Original author: Rob Browning <rlb@defaultvalue.org> | |
20 | ||
21 | (define-module (srfi srfi-31) | |
22 | :export-syntax (rec)) | |
23 | ||
24 | (define-macro (rec arg-form . body) | |
25 | (cond | |
26 | ((and (symbol? arg-form) (= 1 (length body))) | |
27 | ;; (rec S (cons 1 (delay S))) | |
28 | `(letrec ((,arg-form ,(car body))) | |
29 | ,arg-form)) | |
30 | ;; (rec (f x) (+ x 1)) | |
31 | ((list? arg-form) | |
32 | `(letrec ((,(car arg-form) (lambda ,(cdr arg-form) ,@body))) | |
33 | ,(car arg-form))) | |
cd184501 KR |
34 | (else |
35 | (error "syntax error in rec form" `(rec ,arg-form ,@body))))) |