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[Q]: Mutable variant types in Caml Light 0.7
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Date: -- (:)
From: Andrew Conway <arc@l...>
Subject: Re: [Q]: Mutable variant types in Caml Light 0.7


Christian Boos wrote:
> ...
>Si ce raisonnement est correct, une amélioration pourrait alors être
>effectuée, permettant de cumuler efficacité et souplesse :
>  - soit une grosse refonte de la syntaxe des types, pour avoir des
>déclarations à la SML (mais plus expressives, en raison du 'mutable') :
>	
>	type t = A of { a:int; mutable b:float; c:string; }
>
>  - soit en faisant une modification sur la syntaxe de l'extension 3.6
>permettant d'avoir des types "union" mutables :
>
>	type t = A of int * (mutable float) * string

Moi aussi!

Why I would like it? Well, although I generally like strictness, 
sometimes lazy lists are useful. So I decided to make some lazy list
routines. I used the following type:

type 't lazylist =
          EndLL 
        | Element of 't llcont
        | Unconstructed of (unit -> 't lazylist)
and 't llcont = { value : 't ; mutable next : 't lazylist}
;;

The trouble is that takes 5 words per evaluated element, whereas 
with Christian's suggestion it could be done in 3 words like 
normal lists, as well as avoiding the ugliness in the above type
definition. Neither are huge things for me, but since it has already been
suggested, I second it.

( Incidentally, is there a nicer basic structure for lazy lists? )
			
Thanks again,

			Andrew.