Kind classes and associated closed type families

[Ryan Scott]

...actually, nevermind, it's not a bug after all. It was just me being
boneheaded. Since Extract has a polymorphic return kind, there's no
way for GHCi to know what the kind of Extract 0 '(Int, Char) will be
unless there's a kind ascription. If you be more explicit, then GHCi
knows what to do:

    > :kind! (Extract 0 '(Int, Char) :: *)
    (Extract 0 '(Int, Char) :: *) :: *
    = Int
    > :kind! (Extract 0 '(Int, Char) :: * -> *)
    (Extract 0 '(Int, Char) :: * -> *) :: * -> *
    = (TypeError ...)

Thanks to Reid Barton for pointing this out to me.

Ryan S.
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[1] https://ghc.haskell.org/trac/ghc/ticket/10116