Certain programs no longer need QuantifiedConstraints to typecheck, even
#16140: Cannot create type synonym for quantified constraint without ImpredicativeTypes -------------------------------------+------------------------------------- Reporter: Ashley Yakeley | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Resolution: | Keywords: | QuantifiedConstraints, | ImpredicativeTypes Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): though they should Aha! That is easily dealt with. Now predicates have their own validity checker, `check_pred_ty`. So we can put the quantified-constraint check in the `ForAllPred` branch of the `classifyPredType` case analysis; and nowhere else. We don't need to monkey with the rank anymore! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16140#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler