#14860: QuantifiedConstraints: Can't quantify constraint involving type family -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.5 checker) | Keywords: Resolution: | QuantifiedConstraints wipT2893 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 RyanGlScott): Replying to [comment:10 simonpj]:
Re comment:7 there are no type functions are there. It's the function in the constraint head that is the nub of the problem.
Again... so what? I'm trying to demonstrate why hypothetically allowing type families in quantified constraints would be no different than allowing type variables heading instances in quantified constraints. So far, the only rebuttal you've given me is "but we don't allow type families in instances", which is circular reasoning. So I'm still left wondering what exactly the substantive difference between these two scenarios is. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14860#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler