#14938: Pattern matching on GADT does not refine type family parameters -------------------------------------+------------------------------------- Reporter: kcsongor | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.2.2 checker) | Keywords: GADTs, Resolution: | TypeFamilies 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 goldfire): But if you have a type-level `Refl` here, then `x` and `y` really will be the same. The equation you want is `R x x Refl = Refl`, like in those other dependently typed languages. If you write a larger example, I can show you how the equation I suggest will work. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14938#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler