#11977: ghc doesn't agree with its own inferred pattern type -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: | PatternSynonyms 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 Iceland_jack): Just fooling around {{{#!hs pattern Mempty :: Monoid a => b -> forall x. a -> b pattern Mempty b <- (($ mempty) -> b) where Mempty b _ = b }}} {{{#!hs pattern Mempty :: b -> forall a. (Eq a, Monoid a) => a -> b pattern Mempty b <- (($ mempty @String) -> b) where Mempty b _ = b foo :: (forall a. (Eq a, Monoid a) => a -> b) -> b foo (Mempty x) = x }}} {{{ ghci> foo (== mempty) True ghci> :t Mempty 'a' Mempty 'a' :: forall {a}. (Monoid a, Eq a) => a -> Char ghci> :t foo (Mempty 'a') foo (Mempty 'a') :: Char ghci> foo (Mempty 'a') 'a' }}} or {{{#!hs type MEMPTY b = forall a. (Eq a, Monoid a) => a -> b pattern Mempty :: b -> MEMPTY b }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11977#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler