#13105: Allow type families in RuntimeReps -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_fail/T13105 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Yes, the levity-polymorphism check sees the problem and reports a type of kind `TYPE (RepRep Int)` as levity-polymorphic. I will have a note in the manual about this. If the type checker didn't catch it, it would be a lint error, yes. I don't think it's as simple as a normalisation step in the type checker. For example: {{{ foo :: forall (a :: TYPE (RepRep Int)). a -> a foo x = x }}} In this code, `x` has type `a`. What's to normalise about that?? Now we could say that `x :: a |> co` where `co :: TYPE (RepRep Int) ~ TYPE IntRep`. But now `x`'s type has changed and that means we need to use casts wherever `x` has been used. And this is an easy case where the type checker can see the correct, normalised type from the get-go. In general, unification and type family reduction may be necessary before we can proceed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13105#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler