#11514: Impredicativity is still sneaking in -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is erroneously accepted: {{{ {-# LANGUAGE RankNTypes #-} module Bug where foo :: forall a. (Show a => a -> a) -> () foo = undefined }}} `undefined` is being instantiated at `(Show a => a -> a) -> ()`, which requires impredicativity. GHC does the right thing (reject!) if we try to instantiate with a type involving proper foralls. I imagine this is a simple missing check. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11514 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler