Import guile-1.8 as multiple upstream tarball component

[lilypond.git] / guile18 / srfi / srfi-31.scm

diff --git a/guile18/srfi/srfi-31.scm b/guile18/srfi/srfi-31.scm
new file mode 100644 (file)
index 0000000..54c2f9f
--- /dev/null
+++ b/guile18/srfi/srfi-31.scm
@@ -0,0 +1,35 @@
+;;; srfi-31.scm --- special form for recursive evaluation
+
+;;     Copyright (C) 2004, 2006 Free Software Foundation, Inc.
+;;
+;; This library is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU Lesser General Public
+;; License as published by the Free Software Foundation; either
+;; version 2.1 of the License, or (at your option) any later version.
+;; 
+;; This library 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
+;; Lesser General Public License for more details.
+;; 
+;; You should have received a copy of the GNU Lesser General Public
+;; License along with this library; if not, write to the Free Software
+;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+;;; Original author: Rob Browning <rlb@defaultvalue.org>
+
+(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)))))