#9072: RankNTypes composition now requires ImpredicativeTypes -------------------------------------+------------------------------------- Reporter: gelisam | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: Unknown/Multiple | valid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- {{{ {-# LANGUAGE RankNTypes #-} instantiateId :: (forall a. a -> a) -> Int -> Int instantiateId f = f passes :: [Int] -> [Int] passes = map (instantiateId id) -- Couldn't match type ‘a0 -> a0’ with ‘forall a. a -> a’ fails :: [Int] -> [Int] fails = (map . instantiateId) id }}} works with ghc 7.6, fails with ghc 7.8, works with ghc 7.8 + `ImpredicativeTypes`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9072 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler