Proposal: export more from Data.Kind

[Richard Eisenberg]

I'm sympathetic to this proposal, but I don't have a well considered opinion. Instead, I'll present a few facts:

- TYPE, RuntimeRep, and Multiplicity should be allowed in Safe Haskell. You can't do anything untoward with these folks.

- That said, Safe should not imply that linear-types guarantees are in force. At least, not yet. Linear types features cannot cause seg-faults (or other violations of safety expectations).

- RuntimeRep has not yet stabilized. But it is a niche feature, and I wouldn't really expect stabilization here for some time.

Maybe a nice compromise is introducing GHC.Kind that is -XSafe and exports all of these?

Richard

> On Aug 3, 2020, at 6:49 AM, Carter Schonwald <carter.schonwald at gmail.com> wrote:
> 
> David makes a very good point here. That perhaps they should first stabilize a bit more before being exposed through there 
> 
> On Sun, Aug 2, 2020 at 12:12 PM David Feuer <david.feuer at gmail.com <mailto:david.feuer at gmail.com>> wrote:
> My impression is that RuntimeRep may not have stabilized all the way yet. There are things that work for LiftedRep and UnliftedRep that want to be polymorphic that way.
> 
> On Sun, Aug 2, 2020, 12:10 PM Krzysztof Gogolewski <krz.gogolewski at gmail.com <mailto:krz.gogolewski at gmail.com>> wrote:
> Hello,
> 
> I'd like to export TYPE, RuntimeRep(..), Multiplicity(..) from Data.Kind.
> (Multiplicity is the Linear Haskell type - One and Many.)
> 
> Currently you have to import GHC.Exts / GHC.Types which conflicts with
> Safe Haskell. I think both levity and linearity polymorphism
> should be available under Safe Haskell.
> 
> Data.Kind already contains Constraint and Type.
> 
> -Krzysztof
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