There's another version of heterogeneous equality that takes its
arguments in the other order. I'm not sure if this is generally useful
enough to want to include.
-- (:~~:) :: forall j k. j -> k -> *
data OtherEquality :: forall j. j -> forall k. k -> Type where
OtherRefl :: OtherEquality a a
On Mon, Jul 10, 2017 at 11:24 AM, Ryan Scott
I also agree that we should keep HRefl a distinct name, and moreover, we should keep :~: and :~~: as distinct datatypes.
I'm also on-board with the idea that we should introduce a separate Data.Type.Equality.Hetero module that reexports :~~: and defines heterogeneous counterparts for sym, trans, etc. from Data.Type.Equality. I don't have a strong opinion on how they should be named (e.g., sym vs. hsym).
Ryan S.
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