#14968: QuantifiedConstraints: Can't be RHS of type family instances -------------------------------------+------------------------------------- Reporter: josef | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.5 checker) | Keywords: Resolution: | QuantifiedConstraints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9269 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Actually, I think the OP's use case should be OK. There is a big difference between the ''type'' `(forall x. x -> x, Int)` and the ''constraint'' `(forall x. A x => B x, Show x)`. The former is an impredicative use of the `(,)` constructor, while the second is not considered to be so. I think this is a simple case of updating the validity checker to allow the new thing. :) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14968#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler