Luc Maranget a écrit :
>> You mean that if I write (I use OCaml syntax)
>>
>> match p, q with
>> | (true, true) -> A
>> | _ -> B
>>
>> Haskell will first check if (p is evaluated and false) or (q is evaluated and false)
>> and then, if it is not the case will evaluate p, and finally if p is true it will evaluate q ?
>>
>>     
>
> Haskell has left-to-right semantics for PM. Basically this is expressed
> by PM compilation.
>   
And this is not optimal (I was answering the sentence "Haskell does it
right"). In fact, there is no optimal
way of doing pattern matching in lazy languages (with deep pattern)
because the language can not
decide what is best to evaluate. Certainly left to right is a
reasonnable choice,
but letting the programmer choose (or even forcing him to choose has in
OCaml) is
a good choice (I think better).

-- 
Christophe Raffalli
Universite de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tel: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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