#13430: Can't scope type variables when pattern matching on GADTs -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: 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 simonpj): BTW here is a workaround: {{{ bar :: Bar x -> String bar x@(MkBar _) = case x of (x :: Bar (a, b)) -> show (typeRep (Proxy :: Proxy b)) }}} Here, ''inside'' the pattern match for `MkBar` we make a new pattern-match on `x`, and give it a scoped type signature. Not beautiful but it works. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13430#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler