mirror of
https://git.savannah.gnu.org/git/guile.git
synced 2025-04-30 03:40:34 +02:00
58 lines
2.5 KiB
Scheme
58 lines
2.5 KiB
Scheme
;;; srfi-31.scm --- special form for recursive evaluation
|
|
|
|
;; Copyright (C) 2004 Free Software Foundation, Inc.
|
|
;;
|
|
;; This program is free software; you can redistribute it and/or
|
|
;; modify it under the terms of the GNU General Public License as
|
|
;; published by the Free Software Foundation; either version 2, or
|
|
;; (at your option) any later version.
|
|
;;
|
|
;; This program is distributed in the hope that it will be useful,
|
|
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
;; General Public License for more details.
|
|
;;
|
|
;; You should have received a copy of the GNU General Public License
|
|
;; along with this software; see the file COPYING. If not, write to
|
|
;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
|
|
;; Boston, MA 02110-1301 USA
|
|
;;
|
|
;; As a special exception, the Free Software Foundation gives permission
|
|
;; for additional uses of the text contained in its release of GUILE.
|
|
;;
|
|
;; The exception is that, if you link the GUILE library with other files
|
|
;; to produce an executable, this does not by itself cause the
|
|
;; resulting executable to be covered by the GNU General Public License.
|
|
;; Your use of that executable is in no way restricted on account of
|
|
;; linking the GUILE library code into it.
|
|
;;
|
|
;; This exception does not however invalidate any other reasons why
|
|
;; the executable file might be covered by the GNU General Public License.
|
|
;;
|
|
;; This exception applies only to the code released by the
|
|
;; Free Software Foundation under the name GUILE. If you copy
|
|
;; code from other Free Software Foundation releases into a copy of
|
|
;; GUILE, as the General Public License permits, the exception does
|
|
;; not apply to the code that you add in this way. To avoid misleading
|
|
;; anyone as to the status of such modified files, you must delete
|
|
;; this exception notice from them.
|
|
;;
|
|
;; If you write modifications of your own for GUILE, it is your choice
|
|
;; whether to permit this exception to apply to your modifications.
|
|
;; If you do not wish that, delete this exception notice.
|
|
|
|
(define-module (srfi srfi-31)
|
|
:export-syntax (rec))
|
|
|
|
(define-macro (rec arg-form . body)
|
|
(cond
|
|
((and (symbol? arg-form) (= 1 (length body)))
|
|
;; (rec S (cons 1 (delay S)))
|
|
`(letrec ((,arg-form ,(car body)))
|
|
,arg-form))
|
|
;; (rec (f x) (+ x 1))
|
|
((list? arg-form)
|
|
`(letrec ((,(car arg-form) (lambda ,(cdr arg-form) ,@body)))
|
|
,(car arg-form)))
|
|
(else
|
|
(error "syntax error in rec form" `(rec ,arg-form ,@body)))))
|