D2038: [WIP] TysPrim: Generalize kind of (->)

[Ben Gamari]

Richard Eisenberg <rae at cs.brynmawr.edu> writes:

> I had another thought on my drive home: why do we need to sort out
> Constraint v Type for 8.2? I have the patch, and it's essentially all
> set. But it weakens equality in a way that's troublesome for D2038 and
> introduces heterogeneous axioms, which are strange, ill-understood
> beasts. And I don't think we need it.
>
> On the other hand, D2038 is essential for the new Typeable, because
> it's the only way we can give (->) a proper kind.
>
Snipped well-considered plan for proceeding.

> This route seems, to me, far preferable to monkeying around with roles
> and such in ways that we have no assurances are sound. (Remember,
> roles are there to keep the type system safe and sound. They were not
> added simply to annoy everyone, though they accomplish that goal quite
> nicely.)
>
:)

> What do we think? It's not ideal, but I think it's the best of
> suboptimal alternatives. And it's no worse than 8.0 w.r.t. Constraint
> v Type.
>
This sounds quite reasonable to me. I will need to fix up the remaining
issues in D2038 surrounding Constraint, but I think this shouldn't be so
difficult. The only reason I haven't tried already was my belief that
Constraint/Type would be resolved soon. I'll try to push another version
of D2038 tonight.

Cheers,

- Ben

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