#12882: Unexpected constraint when using ExistentialQuantification -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: invalid | 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 danilo2): rwbarton: hmm, I dont know so deeply how GHC solves the things under the hood, but I imagine GHC could easily allow such code: {{{ class Foo a where foo :: a -> Int newtype ImplicitFoo a = Foo a => ImplicitFoo a getFoo :: ImplicitFoo a -> Int getFoo (ImplicitFoo a) = foo a }}} The constraint in the newtype just tells that if `ImplicitFoo` was ever constructed by somebody, the constraint was already met, so there is no need to check it again and pass along functions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12882#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler