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From: Pal-Kristian Engstad <engstad@naughtydog.com>
Organization: Naughty Dog, Inc.
To: Oleg <oleg_inconnu@myrealbox.com>, Pierre Weis <pierre.weis@inria.fr>,
        ijtrotts@ucdavis.edu (Issac Trotts)
Subject: Re: [Caml-list] function
Date: Thu, 5 Dec 2002 13:06:44 -0800
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References: <200212051000.LAA22469@pauillac.inria.fr> <200212051546.56416.oleg_inconnu@myrealbox.com>
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On Thursday 05 December 2002 12:46 pm, Oleg wrote:
> To help the original poster earn extra credit, I'll write the function =
in
> the three languages I [sort of] know:
>
> typedef std::list<char*> LS;
> typedef std::list<int> LI;
>
> void f(LS& input, LI& output) {
>     for(LS::iterator i =3D input.begin(); i !=3D input.end(); ++i)
>         for(char* p =3D *i; *p !=3D '\0'; ++p)
>             output.push_back(int(*p) - int('0'));
> }

Isn't there a foreach() algorithm in STL?

> let rec f_aux lst i acc =3D
>     match lst with
>
>     | [] -> acc
>     | x :: y when i =3D String.length x -> f_aux y 0 acc
>     | x :: y -> f_aux lst (i + 1) (digit x.[i] :: acc)
>
> let f lst =3D List.rev (f_aux lst 0 [])

Ah, the use of List.rev... :-) Of course, without it, it is hard. Here's =
my two=20
attempts:

let f4 strs =3D=20
  let to_ord c =3D int_of_char c - int_of_char '0' in
  let rec strings_to_list =3D function
    | [] -> []
    | str :: strs ->
	let rec to_list s k n =3D=20
	  if k =3D n then strings_to_list strs else to_ord s.[k] :: to_list s (k=
 + 1) n
	in
	  to_list str 0 (String.length str)=20
  in
    strings_to_list strs

This one is unfortunately not tail recursive, but it is neat in the sense=
 that it doesn't
use any library function except int_of_char.

let f5 strs =3D=20
  let to_ord c =3D int_of_char c - int_of_char '0' in
  let rec strings_to_list acc =3D function
    | [] -> acc
    | str :: strs ->
	let rec to_list acc s k n =3D
	  if k =3D n then strings_to_list acc strs else to_list (to_ord s.[k] ::=
 acc) s (k + 1) n
	in
	  to_list acc str 0 (String.length str)
  in
    List.rev(strings_to_list [] strs)

Equivalent to Oleg's I believe?

PKE.
--=20
  _      =20
  \`.       P=E5l-Kristian Engstad, Senior Software Engineer,
   \ `|     Naughty Dog, Inc., 1315 3rd Street Promenade,=20
  __\ |`.   Santa Monica, CA 90046, USA. (310) 752-1000 x799.=20
    /  /o   mailto:engstad@naughtydog.com http://www.naughtydog.com
   /  '~    mailto:mrengstad@yahoo.com    http://www.engstad.com
  / ,'      Hang-gliding Rulez!
  ~'

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