#15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar" -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: | QuantifiedConstraints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: 9123, 14883 Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): The current behavior was introduced in b612da667fe8fa5277fc78e972a86d4b35f98364 That commit fixes some impredicativity bug but also rewrites GND to use type application. However, the change to GND also has it work with polytypes instead of its previous behavior, using monotypes. It sounds like we want to go to the previous behavior. As for Ryan's question: try passing both type arguments to `coerce`. As explained in the visible type application paper, type signatures on expressions are ''deeply skolemized'', which is causing havoc for you here. I think including the second type parameter to `coerce` will solve the problem. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15290#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler