[Caml-list] String.(r)index_from

[Florent Monnier <monnier.florent@gmail.com>]

Hi,

Is this the expected behavior?

# let s = "012" ;;
val s : string = "012"

# String.index_from s 1 '1' ;;
- : int = 1
# String.index_from s 2 '2' ;;
- : int = 2
# String.index_from s 3 '3' ;;
Exception: Not_found.
# String.index_from s 4 '4' ;;
Exception: Invalid_argument "String.index_from".

(* ====================== *)

# String.rindex_from s 1 '1' ;;
- : int = 1
# String.rindex_from s 0 '0' ;;
- : int = 0
# String.rindex_from s (-1) '#' ;;
Exception: Not_found.
# String.rindex_from s (-2) '#' ;;
Exception: Invalid_argument "String.rindex_from".

(* ====================== *)

# String.contains_from s 2 '2' ;;
- : bool = true
# String.contains_from s 3 '2' ;;
- : bool = false
# String.contains_from s 4 '2' ;;
Exception: Invalid_argument "String.contains_from".

(* ====================== *)

If yes, please just ignore this email.

If no, here is a patch for the file "string.ml":
http://caml.inria.fr/cgi-bin/viewvc.cgi/ocaml/trunk/stdlib/string.ml?view=markup&pathrev=13748

### return exception Invalid_argument instead of false or Not_found
### when the index is out of bounds.
--- stdlib/string.ml.orig	2013-08-12 12:42:17.443013642 +0200
+++ stdlib/string.ml	2013-08-12 12:43:24.973014347 +0200
@@ -176,7 +176,7 @@

 let index_from s i c =
   let l = length s in
-  if i < 0 || i > l then invalid_arg "String.index_from" else
+  if i < 0 || i >= l then invalid_arg "String.index_from" else
   index_rec s l i c;;

 let rec rindex_rec s i c =
@@ -186,12 +186,12 @@
 let rindex s c = rindex_rec s (length s - 1) c;;

 let rindex_from s i c =
-  if i < -1 || i >= length s then invalid_arg "String.rindex_from" else
+  if i < 0 || i >= length s then invalid_arg "String.rindex_from" else
   rindex_rec s i c;;

 let contains_from s i c =
   let l = length s in
-  if i < 0 || i > l then invalid_arg "String.contains_from" else
+  if i < 0 || i >= l then invalid_arg "String.contains_from" else
   try ignore (index_rec s l i c); true with Not_found -> false;;

 let contains s c = contains_from s 0 c;;
(* ====================== *)


The behavior of these functions is then to raise
an Invalid_argument exception if the index is out of bounds:

# let s = "012" ;;
val s : string = "012"

# String.index_from s 3 '3' ;;
Exception: Invalid_argument "String.index_from".

# String.rindex_from s (-1) '#' ;;
Exception: Invalid_argument "String.rindex_from".

# String.contains_from s 3 '2' ;;
Exception: Invalid_argument "String.contains_from".

(* ====================== *)

-- 
Best regards
florent