Proposal: Introduce GHC.TypeNats module with natVal :: forall n proxy. KnownNat n => proxy n -> Natural

[Ben Gamari]

Oleg Grenrus <oleg.grenrus at iki.fi> writes:

> Currently we have in the GHC.TypeLits module
>
> natVal :: forall n proxy. KnowNat n => proxy n -> Integer
>
> However, the result integer is never negative. Numeric.Natural module is
> in base since base-4.8.0.0.
>
This sounds quite reasonable to me and given how many much larger
8.2 changes are still not in the tree, I think it is in-scope for the
release. I agree with David that it would make sense if the evidence
itself were a Natural.

I'm not terribly concerned about compatibility in the face of
unsafeCoerce. We should be certain to clearly document the change
though.

Cheers,

- Ben
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