#9636: Function with type error accepted -------------------------------------+------------------------------------- Reporter: augustss | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:2 augustss]:
I don't think a warning is right, I think it's an error. I view closed type families as functions on types, and when you use a function you expect it to reduce to a normal form. With a warning you're saying that T x is sometimes equal to some other type and sometimes it's a new type. That makes no sense to me. It has nothing to do with being inhabited, uninhabited types are perfectly fine.
This is not a realm I know anything about, but I agree. `T Bool` is not an uninhabited type—it's simply not a type. The situation for data families is qualitatively different, and it would probably make sense to offer such a warning for those. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9636#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler