Re: [Caml-list] Weak array semantics with mutually recursive values.

[Christophe Raffalli <Christophe.Raffalli@univ-savoie.fr>]

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Le 22/01/11 18:56, Andrew a écrit :
>> let rec x = (1,y) and y = (2,x)

This was just a silly example, but -rectypes works in that case.

My real example is a type for hashconsed propositional formula
each formula pointing to its negation like this (ignoring hashconsing):

this is untested ...

type form =
Lit(bool * string*form)
| Conj(form*form*form)
| Disj(form*form*form)

let mkNot = function
  Lit(_,_,f) | Conj(_,_,f) | Disj(_,_,f) -> f

let mkLit v =
  let rec v1 = Lit(true,v,v2) and v2 = Lit(false,v,v1) in v1

let mkConj f1 f2 =
  let rec v1 = Conj(f1,f2,v2) and v2 = Disj(mkNot f1, mkNot f2, v1) in v1

So the real question is what is the best way to hashcons this ?

> Might be naïve curiosity, but how do you manage to build this? What's the
> type of x and y?
>
> My Ocaml toplevel returns 
>     # let rec x = (1,y) and y = (2,x);;
>     Characters 26-31:
>       let rec x = (1,y) and y = (2,x);;
>                                 ^^^^^
>     Error: This expression has type int * (int * (int * 'a))
>            but is here used with type int * 'a
>
> Andrew.
>
>


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

tel: (33) 4 79 75 81 03
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mail: Christophe.Raffalli@univ-savoie.fr
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