Ticket #7586 (closed bug: fixed)
:kind command cannot show kind of type synonyms
The following illustrates the problem:
Prelude> type T a = Int Prelude> :k T <interactive>:1:1: Type synonym `T' should have 1 argument, but has been given none In a type in a GHCi command: T
Undoubtedly, T has a kind, and there's no reason to insist that the type given to the :kind command should be fully applied.