From 9ca7c9580a3eaf2225113ede7351b2fcaf8f6971 Mon Sep 17 00:00:00 2001
From: "Guillermo J. Rozas" <edu/mit/csail/zurich/gjr>
Date: Fri, 28 Aug 1992 16:05:58 +0000
Subject: [PATCH] Add substring?

---
 v7/src/runtime/string.scm | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/v7/src/runtime/string.scm b/v7/src/runtime/string.scm
index 46d4305bb..aeb576a65 100644
--- a/v7/src/runtime/string.scm
+++ b/v7/src/runtime/string.scm
@@ -1,8 +1,8 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/string.scm,v 14.4 1992/02/13 20:00:15 cph Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/string.scm,v 14.5 1992/08/28 16:05:58 jinx Exp $
 
-Copyright (c) 1988-92 Massachusetts Institute of Technology
+Copyright (c) 1988-1992 Massachusetts Institute of Technology
 
 This material was developed by the Scheme project at the Massachusetts
 Institute of Technology, Department of Electrical Engineering and
@@ -447,4 +447,21 @@ MIT in each case. |#
 		(let ((char (if (default-object? char) #\space char)))
 		  (substring-fill! result 0 i char))
 		(substring-move-right! string 0 length result i)))
-	  result))))
\ No newline at end of file
+	  result))))
+
+(define (substring? substring string)
+  ;; Returns starting-position or #f if not true.
+  (if (string-null? substring)
+      0
+      (let ((len (string-length substring))
+	    (end (string-length string))
+	    (char (string-ref substring 0)))
+	(let loop ((posn -1))
+	  (let ((posn* (substring-find-next-char string (1+ posn) end char)))
+	    (and posn*
+		 (let ((end* (+ posn* len)))
+		   (and (<= end* end)
+			(if (substring=? substring 0 len
+					 string posn* end*)
+			    posn*
+			    (loop posn*))))))))))
\ No newline at end of file
-- 
2.25.1