#14442: InstanceSigs fails -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: InstanceSigs 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 simonpj): Suppose you'd written the instance decl like this {{{ instance EQ Bool where eq = my_eq my_eq :: Sing (x :: Bool) -> Sing (y :: Bool) -> Maybe (x :~~: y) my_eq SFalse SFalse = Just HRefl }}} That works. Now remove the kind signature on `x :: Bool`. Fails. And indeed it should, because `my_eq`'s signature means {{{ my_eq :: forall k (x::k) (y::Bool). Sing x -> Sing (y :: Bool) -> Maybe (x :~~: y) }}} and indeed the code does not have this type. So I think it's behaving right. Can you suggest a concrete improvement to the user manual that would make that clearer? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14442#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler