#16114: strange "instance .. => .. => .. where ..." -------------------------------------+------------------------------------- Reporter: j.waldmann | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I don't understand what's happening here: {{{ GHCi, version 8.6.3: http://www.haskell.org/ghc/ :? for help Prelude> data T a Prelude> instance Eq a => Eq a => Eq (T a) where (==) = undefined <interactive>:2:10: error: • Class ‘Eq’ does not have a method ‘==’ • In the instance declaration for ‘Eq (T a)’ }}} Is that even syntactically correct? (ghc-8.4.4 says "malformed instance") If so, then I'd assume that `A => B => C` means `A && B => C`, that is, `(A,B) => C` in this case, but it does not, since this works: {{{ instance (Eq a, Eq a)=> Eq (T a) where (==) = undefined }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16114 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler