[m-users.] Existential higher-order type

[Volker Wysk]

Hi!

Is it possible to retrieve a higher-order type from inside a data
constructor, which has an existentially quantified type variable?

I have this:

:- type checker(Arg)
    ---> some [T] ( 
       checker( pred(T::in) is det ) => argument(T) ).

How can you call the predicate that is stored inside, provided it has the
expected type? I want to do it inside a predicate that has a universally
quantified type variable T.

I have done something similar with a non-higher order type, and was able to
extract the value with private_builtin.typed_unify/2. (I've taken this from
the univ library.) This works, but you can't unify two higher-order terms.


Cheers,
Volker
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