Re: [Caml-list] String.(r)index_from

[Damien Doligez <damien.doligez@inria.fr>]

Hi,

Indeed, it was carefully designed this way. When you're doing
index_from s 3 '3', you're looking for the character 3 in the empty
string.

-- Damien



On 2013-08-12, at 14:58, Gerd Stolpmann wrote:

> 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
>> 
> 
> -- 
> ------------------------------------------------------------
> 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
> ------------------------------------------------------------
>