#10524: PolyKinds doesn't interact well with DeriveFunctor -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #10561 | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): OK, so I fixed comment:7. But the original bug report remains {{{ newtype Compose f g a = Compose (f (g a)) deriving Functor }}} should be fine, but elicits {{{ T10524.hs:5:52: error: Couldn't match kind ‘k’ with ‘*’ arising from the first field of ‘Compose’ (type ‘f (g a)’) When deriving the instance for (Functor (Compose f g)) }}} After all, this explicit instance declaration typechecks fine {{{ instance (Functor f, Functor g) => Functor (Compose f g) where fmap fn (Compose x) = Compose (fmap (fmap fn) x) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10524#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler