+let rec string_find s sub =
+ let len = String.length s in
+ let sublen = String.length sub in
+ let rec loop i =
+ if i <= len-sublen then (
+ let rec loop2 j =
+ if j < sublen then (
+ if s.[i+j] = sub.[j] then loop2 (j+1)
+ else -1
+ ) else
+ i (* found *)
+ in
+ let r = loop2 0 in
+ if r = -1 then loop (i+1) else r
+ ) else
+ -1 (* not found *)
+ in
+ loop 0
+