#12708: RFC: Representation polymorphic Num -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 8.0.1 Resolution: | Keywords: 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 goldfire): Replying to [comment:3 Iceland_jack]:
Should this not be allowed when `minBound :: () -> a` is allowed?
Because `blah :: Int#` is not allowed? This would actually be OK, because methods -- even nullary ones, like `minBound` are actually functions that take dictionaries. So we're OK here. And to your question in comment:2: You won't be able to supply a default implementation of these functions because of the Golden Rule of Representation Polymorphism: You may never bind a variable whose type is representation polymorphic. Your default implementation violates this rule. I'm wondering if a `default` type signature can help, somehow, but I don't see how to write it: there's no way of saying `NotAVariable k` as a constraint. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12708#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler