#12473: Ambiguous type var with DefaultSignatures and FunctionalDependencies -------------------------------------+------------------------------------- Reporter: dylex | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): But we ''do'' call a function with the type given by the generic default signature! In effect the generic-default declaration gives rise to a definition {{{ $gdm_bar :: forall a b. (Bar a b, Foo a b) => b -> Int $gdm_bar b = foo (get b :: a) b }}} In an instance declaration where you do not give a declaration for `bar`, we fill in with this generic default method. That is {{{ instance blah => Bar t1 t2 where {} }}} becomes {{{ instance blah => Bar t1 t2 where bar = $gdm_bar }}} If the type of `$gdm_bar` was ambiguous, this really would be a problem. But in this case it isn't! I'll investigate -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12473#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler