Add substring?

diff --git a/v7/src/runtime/string.scm b/v7/src/runtime/string.scm
index 46d4305bb851d74526917da267c5b814cdc9ddb3..aeb576a65a68b3879d911650aa82773dc20764af 100644 (file)
--- 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