Re: [GHC] #9858: Typeable instances should be kind-aware

#9858: Typeable instances should be kind-aware -------------------------------------+------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: new Priority: highest | Milestone: 7.10.2 Component: Compiler | Version: 7.9 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: Phab:D652 -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"7b042d5adabdb0fc06286db1a7f9cbf1e9fd1fbf/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="7b042d5adabdb0fc06286db1a7f9cbf1e9fd1fbf" Do not allow Typeable on constraints (Trac #9858) The astonishingly-ingenious trio of Shachaf Ben-Kiki, Ørjan Johansen and Nathan van Doorn managed to persuade GHC 7.10.1 to cough up unsafeCoerce. That is very bad. This patch fixes it by no allowing Typable on Constraint-kinded things. And that seems right, since it is, in effect, a form of impredicative polymorphism, which Typeable definitely doesn't support. We may want to creep back in the direction of allowing Typeable on constraints one day, but this is a good fix for now, and closes a terrible hole. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9858#comment:84 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler