From: Stephen Adams <edu/mit/csail/zurich/adams>
Date: Thu, 30 Sep 1993 17:08:17 +0000 (+0000)
Subject: Added fold-left and fold-right
X-Git-Tag: 20090517-FFI~7810
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=d5865675c1f128a43eafe444af70e456060d90a3;p=mit-scheme.git

Added fold-left and fold-right
---

diff --git a/v7/src/runtime/list.scm b/v7/src/runtime/list.scm
index 0d4f58b2c..199be9daa 100644
--- a/v7/src/runtime/list.scm
+++ b/v7/src/runtime/list.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Id: list.scm,v 14.17 1993/02/26 08:17:14 cph Exp $
+$Id: list.scm,v 14.18 1993/09/30 17:08:17 adams Exp $
 
 Copyright (c) 1988-93 Massachusetts Institute of Technology
 
@@ -489,6 +489,23 @@ MIT in each case. |#
 	(if (not (null? list))
 	    (error:wrong-type-argument list "list" 'REDUCE-RIGHT))
 	initial)))
+
+(define (fold-left procedure initial list)
+  (if (pair? list)
+      (fold-left procedure (procedure initial (car list)) (cdr list))
+      (begin
+	(if (not (null? list))
+	    (error:wrong-type-argument list "list" 'FOLD-LEFT))
+	initial)))
+
+(define (fold-right procedure initial list)
+  (if (pair? list)
+      (procedure (car list) (fold-right procedure initial (cdr list)))
+      (begin
+	(if (not (null? list))
+	    (error:wrong-type-argument list "list" 'FOLD-RIGHT))
+	initial)))
+
 
 ;;;; Generalized List Operations