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Date: Tue, 18 Feb 2003 09:19:14 +0100
From: "sebastien FURIC" <sebastien.furic@tni-valiosys.com>
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To: OCaml List <caml-list@inria.fr>
Subject: Re: [Caml-list] Re: "ocaml_beginners"::[] string to list
References: <Pine.LNX.4.33.0302171704190.2037-100000@eagle.ancor.com> <3E516E75.3030703@ucdavis.edu>
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Issac Trotts a écrit :
> 
> Brian Hurt wrote:
> 
> >On Mon, 17 Feb 2003, Issac Trotts wrote:
> >
> >
> >
> >>Christian Schaller wrote:
> >>
> >>
> >>
> >>>Hi everyone!
> >>>
> >>>I'm trying to find a built in function for converting a string to a list of
> >>>characters, similar to SML's explode.  Is something like this available?
> >>>
> >>>Thank you!
> >>>
> >>>- Chris
> >>>
> >>>
> >>>
> >># let explode s =
> >>   let n = String.length s in
> >>   let rec aux k = if k = n then [] else s.[k] :: aux (k+1) in
> >>   aux 0;;
> >>      val explode : string -> char list = <fun>
> >># explode "foo";;
> >>- : char list = ['f'; 'o'; 'o']
> >>
> >>
> >>
> >
> >let explode s =
> >    let n = String.length s in
> >    let rec aux k accum = if k = n then (List.rev accum)
> >                          else aux (k+1) (s.[k] :: accum)
> >    in
> >    aux 0 []
> >;;
> >
> >See previous discussion.
> >
> Good point: we want it to be tail-recursive.
> Just to clean up, and make it more efficient...
> 
> let explode s =
>     let rec aux k accum = if k = -1 then accum
>                           else aux (k-1) (s.[k] :: accum)
>     in
>     aux (String.length s - 1) []
> ;;


 Sometimes the imperative version seems more clear:

let explode s =
  let res = ref [] in
  for i = String.length s - 1 downto 0 do
    res := s.[i] :: !res
  done;
  !res

 Sébastien.
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