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35 lines
1.3 KiB
Scheme
35 lines
1.3 KiB
Scheme
;;; srfi-31.scm --- special form for recursive evaluation
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;; Copyright (C) 2004, 2006 Free Software Foundation, Inc.
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;;
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;; This library is free software; you can redistribute it and/or
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;; modify it under the terms of the GNU Lesser General Public
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;; License as published by the Free Software Foundation; either
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;; version 2.1 of the License, or (at your option) any later version.
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;;
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;; This library is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;; Lesser General Public License for more details.
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;;
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;; You should have received a copy of the GNU Lesser General Public
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;; License along with this library; if not, write to the Free Software
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;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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;;; Original author: Rob Browning <rlb@defaultvalue.org>
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(define-module (srfi srfi-31)
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:export-syntax (rec))
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(define-macro (rec arg-form . body)
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(cond
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((and (symbol? arg-form) (= 1 (length body)))
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;; (rec S (cons 1 (delay S)))
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`(letrec ((,arg-form ,(car body)))
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,arg-form))
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;; (rec (f x) (+ x 1))
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((list? arg-form)
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`(letrec ((,(car arg-form) (lambda ,(cdr arg-form) ,@body)))
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,(car arg-form)))
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(else
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(error "syntax error in rec form" `(rec ,arg-form ,@body)))))
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