Add a diff library.

I was hesitant to add a diff library, but it was surprisingly easy. A
straightforward application of dynamic programming.

1 files changed, 21 insertions, 2 deletions

diff --git a/csc/strings.csc b/csc/strings.csc
index 737c91b..0259697 100644
--- a/csc/strings.csc
+++ b/csc/strings.csc
@@ -1,14 +1,17 @@
 (define-library (csc strings)
   (export
+    contains
     find
     join
     not-found-error?
     prefix?
+    split
     str-quote)
   (import (scheme base)
           (only (scheme case-lambda) case-lambda)
           (only (scheme write) write)
-          (only (csc list) intercalate))
+          (only (csc list) intercalate)
+          (only (csc loop) loop))
   (begin
 
 
@@ -42,5 +45,21 @@
                  (else (loop (+ 1 i))))))))
 
 
+    (define (contains s substr)
+      (if (string=? "" substr)
+        #t
+        (guard (e ((not-found-error? e) #f))
+          (find substr s)
+          #t)))
+
+
     (define (join sep . strings)
-      (apply string-append (intercalate sep strings)))))
+      (apply string-append (intercalate sep strings)))
+
+
+    (define (split s sep)
+      (loop for s* = s then (string-copy s* (+ i (string-length sep)))
+            for i = (guard (e ((not-found-error? e) (string-length s*)))
+                      (find sep s*))
+            collect (substring s* 0 i)
+            while (< i (string-length s*))))))