#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 rwbarton): Well there is no problem if you write `data` instead of `newtype`, above. But of course the `Foo a` dictionary must be stored within an `ImplicitFoo a`, so that it can provide the implementation of `foo` at runtime. You cannot think of the constraint `Foo a` as a box to be checked off to satisfy some bureaucratic type checker. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12882#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler