#10141: Kind inference regression in closed type families -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: highest | Milestone: 7.10.1 Component: Compiler | Version: 7.10.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by goldfire): Responding to comment:3: No, the return kind could well be `*`. I'll rewrite with explicit kinds: {{{ type family G (a :: k) :: * where G * Int = Bool G * Bool = Int G * a = a }}} This `G` doesn't really use its kind-polymorphism, but the definition kind checks. However, I think you're right about the suggestion for a CUSK, here and in other cases. And I think it's possible for GHC to have at least some heuristics for when a CUSK is the answer. Specifically, it could include a note about CUSKs in error messages that arise from kind mismatches in non- CUSK right-hand sides. And, yes, this would make for a decent test case. Thanks for the suggestion. I'm very unsure I can get to this by Friday (the next RC release), though! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10141#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler