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From: Pierre Weis <pierre.weis@inria.fr>
Message-Id: <200212051000.LAA22469@pauillac.inria.fr>
Subject: Re: [Caml-list] function
In-Reply-To: <20021203232211.GC22545@beech> from Issac Trotts at "Dec 3, 102 03:22:11 pm"
To: ijtrotts@ucdavis.edu (Issac Trotts)
Date: Thu, 5 Dec 2002 11:00:50 +0100 (MET)
Cc: caml-list@inria.fr
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> On Mon, Dec 02, 2002 at 04:55:06PM +0100, altavillasalvatore@libero.it wrote:
> > Hi all,
> > I would want to know if a function exists that allows me to make this:
> > 
> > ["123";"45";"678"]  ->  [1;2;3;4;5;6;7;8;].
> 
> let f l = 
>   let ret = ref [] in
>   String.iter 
>     (fun c -> ret := ((int_of_char c) - (int_of_char '0')) :: !ret) 
>     (List.fold_left (^) "" l);
>   List.rev !ret;;
>   
> f ["123";"45";"678"];;
> 
> Cheers,
> Issac Trotts

If you like puzzles, here is an additional exercise:

00) List which parens are useless in this code, according to which
    rules given in the simple guide-lines and syntactic conventions of
    http://pauillac.inria.fr/caml/FAQ/qrg-eng.html#parens and
    http://pauillac.inria.fr/caml/FAQ/pgl-eng.html#parens.
0)  Rewrite this code to a more suitable form for a beginner,
    i.e. in a purely functional style with no side effect.
1)  Try to avoid the useless List.rev at the end.
2)  What is the complexity of your function f ?
3)  Explain why the List.fold_left application is not only over
    complex but also runtime over consuming.

Hope this helps.

Cheers,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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