#11399: Ill-kinded instance head involving -XTypeInType can invoke GHC panic -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): You don't even need `-XTypeInType`. I had this bite me earlier when I accidentally gave one too many type parameters to `K1`. {{{ class GEq1 t where gliftEq :: (a -> b -> Bool) -> t a -> t b -> Bool instance Eq c => GEq1 (K1 i c) where gliftEq _ (K1 c) (K1 d) = c == d }}} If you replace the instance with {{{ instance Eq c => GEq1 (K1 i c oops) where gliftEq _ (K1 c) (K1 d) = c == d }}} You get the same `fpProv falls into a hole` error. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11399#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler