Need kind annotations

In his blog post Edward Kmett finds that he needs kind annotations. In particular, he wants to be able to say this:

class Category (c :: k -> k -> *) where
  type Ob c :: k -> Constraint
  id :: Ob c a => c a a
  (.) :: (Ob c a, Ob c b, Ob c c) => c b c -> c a b -> c a c

Note that the kind of Ob must match the kind of c, so to declare its kind you need to mention the kind variable k, and that means k must be in scope.

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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