IMHO, this is the right behavior. When walking over strings, it is often
practical to consider the position after the last character as legal
position. So far I see, this is consistent in the String module, e.g.
you can also do String.sub "abc" 3 0.

It's a bit like considering 0 as natural number.

Gerd

Am Montag, den 12.08.2013, 12:55 +0200 schrieb Florent Monnier:
> 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
> 

-- 
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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
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