We also bring the "existential" (provided) type variables into scope so
#16315: Pattern synonym implicit existential quantification -------------------------------------+------------------------------------- Reporter: int-index | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): In case it wasn't clear: Replying to [comment:1 RyanGlScott]: that if we find any occurrences of them in the pattern synonym body, //we can throw the relevant `APromotionErr` error//. (emphasis added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16315#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler