#14010: UndecidableSuperClasses - Could not deduce (Category d) -------------------------------------+------------------------------------- Reporter: int-index | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | UndecidableSuperClasses 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 int-index): To clarify, you say that given {{{ [G] Functor @(c,d) @* (f2 :: (c,d) -> *) }}} we have its superclasses: {{{ [G] Category (c,d) [G] Category * }}} and you claim we can't prove `[W] Category d` from this. But with the definition of `Functor` that does compile, the superclasses are: {{{ [G] Category ((c,d), *) }}} and GHC will want to extract `[W] Category (d, *)` from it. So GHC appears to do more work here! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14010#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler