Re: [Caml-list] getting the type of a polymorphic data ?

[Diego Olivier Fernandez Pons <Diego.FERNANDEZ_PONS@etu.upmc.fr>]

    Bonjour,

> > Is it reasonable to admit that if Obj.is_int is true for x and y then
> > Hashtbl.hash is injective ?
>
> No.
>
> # type foo = A | B;;
> # let _ = Obj.is_int (Obj.repr 0);;
> - : bool = true
> # let _ = Obj.is_int (Obj.repr A);;
> - : bool = true
> # let _ = Hashtbl.hash A;;
> - : int = 0
> # let _ = Hashtbl.hash 0;;
> - : int = 0

I meant injective for a given (fixed) type. Obviously it won't in a
completely general case !

> The purpose of Hashtbl.hash is exactly no to be injective ! And
> hashing lists can't be injective.

That is why I said "isomorphic to a (finite) subset of (machine)
integers". And I said "isomorphic", not "in bijection" to be able to
add a few properties behind when needed and exclude the N x N ~ N
argument.

        Diego Olivier

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