#14111: strange error when using data families with levity polymorphism and unboxed sums and data families -------------------------------------+------------------------------------- Reporter: carter | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeFamilies 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 simonpj): I did mean "instantiate the head shape with unification variables". In our example, the head shape is `T a [a]`. So, when checking `T1`, I instantiate the head shape with unification varibles `T alpha [alpha]` and unify with the result of the data con `T Bool [Bool]`. Success, and the substitution for alpha tells me about the necessary equality constraints. The payoff is that the rigid bits of the head shape get to instantiate any kind-unification-variables floating around in the result type of the data constructor. So this has to be done before we kind-generalise the data constructor's type. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14111#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler