[mercury-users] typeclass constraints on types

[Julien Fischer]

On Wed, 30 May 2012, Michael Hendricks wrote:

> Imagine a Bloom filter module with this interface:
>
>    :- type filter(T).
>    :- func init = filter(T).
>    :- func from_list(list(T)) = filter(T) <= hashable(T).
>    :- func insert(T, filter(T)) = filter(T) <= hashable(T).
>    :- pred member(T::in, filter(T)::in) is semidet <= hashable(T).
>
> Each function and predicate declares the hashable(T) constraint.  Is there
> a way to factor out that constraint so that it's declared once on the type?

No, not in Mercury as it is currently defined.

Julien.
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