#13546: Kind error with type equality -------------------------------------+------------------------------------- Reporter: int-index | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by int-index): I did not realize that `k` is a parameter, now the error is clear to me. However, than the definition of `UnT` should be rejected, no? {{{#!hs type family UnT (a :: Type) :: k where UnT (T (t :: k')) = t }}} `UnT` has kind `forall k. Type -> k`, but in the clause `UnT (T t) = t` it returns something of the kind `k'`. There's no guarantee that `k ~ k'`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13546#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler