#9200: Milner-Mycroft failure at the kind level ----------------------------------------------+---------------------------- Reporter: ekmett | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by goldfire): Happily, I think everyone here has converged on (PARGEN) with the critical side condition that we do not unify a meta-variable with a kind containing a skolem. I realized yesterday that the side condition was necessary but didn't have the chance to write it up. In any case, I think we can end the design phase here and move onto the implementation phase. Most of (PARGEN) should be easy, as (PARGEN) is exactly what is implemented by `NonParametricKinds`, except for the side condition. To implement the side condition, I propose a new disjunct for `MetaInfo` named `NonSkolemTv` which is like `TauTv` but cannot unify with a type containing a skolem. The unifier, in !TcUnify, would just check this condition at the appropriate point. Sound reasonable? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9200#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler