From: Pierre Weis <pierre.weis@inria.fr>
To: luther@dpt-info.u-strasbg.fr (Sven Luther)
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Guards vs. conditionals
Date: Thu, 26 Dec 2002 17:36:06 +0100 (MET) [thread overview]
Message-ID: <200212261636.RAA01979@pauillac.inria.fr> (raw)
In-Reply-To: <20021226091303.GA803@iliana> from Sven Luther at "Dec 26, 102 10:13:03 am"
[...]
> > So, my question is, is there any objective reason to prefer the
> > pattern-match version over the conditional, or vice versa? Or is it just
> > a matter of coding style?
>
> It is just a matter of coding style. I think that the if version is
> maybe easier to do prooves on or something such,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
What do you mean ?
> and that guard version is easier to read and maybe better when there
> are more than one condition, but the compiler does not know when the
> guards cover all the cases, and may output a warning when non is
> needed :
>
> consider :
>
> let foo = function
> | i when i > 500 -> 1
> | i when i = 500 -> 2
> | i when i < 500 -> 3
>
> Which will output a warning.
>
> Friendly,
>
> Sven Luther
The guard version has the additional good property of allowing
sequences in the clauses with no need for parens or begin end:
| i when i > 500 -> print i; printe_newline ()
| i -> ...
Concerning the conjunction of guards and partial matches, the problem
is covered in large in the FAQ of the language, under the question
* Partial match with guards ?
Have a look to:
http://pauillac.inria.fr/caml/FAQ/FAQ_EXPERT-eng.html#gardes_partielles
In short, you just have to remember that the last clause does not need
a guard: use comments and the warning desapears :). For instance,
| i (* when i < 500 *) -> 3
Friendly,
Pierre Weis
INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/
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next prev parent reply other threads:[~2002-12-26 16:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-26 7:06 Matt Gushee
2002-12-26 9:13 ` Sven Luther
2002-12-26 16:36 ` Pierre Weis [this message]
2003-01-02 9:54 ` Xavier Leroy
[not found] <D4DBD8568F05D511A1C20002A55C008C11AC0404@uswaumsx03medge.med.ge.com>
2002-12-27 7:37 ` Matt Gushee
2002-12-27 9:15 ` Luc Maranget
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