From: Alain Frisch <Alain.Frisch@inria.fr>
To: Christophe Raffalli <christophe.raffalli@univ-savoie.fr>
Cc: caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] is this a bug ?
Date: Tue, 09 May 2006 15:47:59 +0200 [thread overview]
Message-ID: <44609D8F.4040100@inria.fr> (raw)
In-Reply-To: <44609473.6030004@univ-savoie.fr>
Christophe Raffalli wrote:
>
> hello,
>
> --------------------------------
> let f b l = match l with
> [] | [_] -> 1
> | [a;_] | [_;a] when a = b-> 2
> | _ -> 3
>
> let _ =
> print_int (f 1 [1;2]);
> print_int (f 1 [2;1]);
> print_newline ()
> --------------------------------
>
> Do you think this code should have a useless pattern warning and print
> "23" instead of "22" ?
Well, both happens, right? I don't see any problem.
The pattern [_;a] is useless because [a;_] matches the same values and
the first match (left-to-right) policy is specificed
(http://caml.inria.fr/pub/docs/manual-ocaml/manual014.html).
The guard is checked after the binding, and there is no backtracking.
This explains why the function returns 3 when b=1 l=[2;1].
-- Alain
next prev parent reply other threads:[~2006-05-09 13:49 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-09 13:09 Christophe Raffalli
2006-05-09 13:16 ` [Caml-list] " Remi Vanicat
2006-05-09 13:19 ` Samuel Mimram
2006-05-09 13:26 ` Christophe Raffalli
2006-05-09 13:33 ` Samuel Mimram
2006-05-09 13:30 ` Yoann Padioleau
2006-05-09 13:22 ` Christophe Raffalli
2006-05-09 13:33 ` Luc Maranget
2006-05-09 13:47 ` Arne Ehrlich
2006-05-09 18:24 ` Jonathan Roewen
2006-05-09 13:47 ` Alain Frisch [this message]
-- strict thread matches above, loose matches on Subject: below --
2007-05-01 12:59 Is this a bug? Thomas Fischbacher
2007-05-01 13:34 ` [Caml-list] " Eric Cooper
2007-05-02 0:25 ` Jacques Garrigue
2007-05-02 0:50 ` Thomas Fischbacher
2007-05-02 2:40 ` Jacques GARRIGUE
2002-07-08 19:53 [Caml-list] productivity improvement Oleg
2002-07-10 15:39 ` John Max Skaller
2002-07-12 12:16 ` [Caml-list] Is this a bug? John Max Skaller
2002-07-12 14:05 ` Xavier Leroy
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