#5462: Deriving clause for arbitrary classes -------------------------------------+------------------------------------- Reporter: simonpj | Owner: dreixel Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.2.1 Component: Compiler | Keywords: Generics Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: #7346 None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by sjoerd_visscher): From the wiki page: "We could try to figure this out in a clever way from the definition of the class being derived, but this is very hard in general." Why is this very hard in general? If I leave out the context in `instance MyClass (MyDatatype a)` then GHC will complain that it is missing `MyClass a`. So can't we use the type checker to give us the required context? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5462#comment:39 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler