#10404: GHC panic when creating a monomorphised pattern synonym for GADT -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.1-rc1 Resolution: | Keywords: | PatternSynonyms Operating System: Linux | Architecture: x86 Type of failure: GHC rejects | Test Case: valid program | Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): The panic is bad but the original example fails to compile because there is a misunderstanding with the signature. The following program compiles. {{{ {-# LANGUAGE GADTs,PatternSynonyms #-} module Test where data Exp a where Fun :: (a -> b) -> (Exp a -> Exp b) pattern IntFun :: () => (a ~ Int) => (a -> b) -> (Exp a -> Exp b) pattern IntFun f x = Fun f x }}} Just giving one set of constraints correspond to provided constraints and an empty required constraints. In this case you want required constraints but empty provided constraints. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10404#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler