#14331: Overzealous free-floating kind check causes deriving clause to be rejected -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: 8.2.2 Component: Compiler (Type | Version: 8.2.1 checker) | Resolution: | Keywords: deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | deriving/should_compile/T14331 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Ah yes, you're right. I was focusing on the `k`, but there's the `a` as well. But then I'd say that the error message is dead right. Let's put the implicit binders in: {{{ data D {k1} (a::k1) = D deriving (forall k. C (a :: k)) }}} Look at that! `a` has kind `k1`; but in the `deriving` clause we claim that the occurrence of `a` ahs type `k`. Boom. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14331#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler