#14860: QuantifiedConstraints: Can't quantify constraint involving type family -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 8.5 checker) | Keywords: Resolution: wontfix | QuantifiedConstraints wipT2893 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 Iceland_jack): Replying to [comment:11 RyanGlScott]: I don't think you need quantified constraints (the ticket:14822#comment:3 trick does works to solve my previous comment), how about this: {{{#!hs instance Typeable f => Show (ExTyFam f) where show (MkExTyFam x) | Just HRefl <- typeRep @f `eqTypeRep` typeRep @(Proxy :: Type -> Type) = show x | otherwise = .. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14860#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler