#14880: GHC panic: updateRole -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.2.2 checker) | Resolution: | Keywords: Roles Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Even simpler {{{ data Foo (x :: Type) :: forall (a :: x). Proxy a -> Type data Bar :: Type -> Type where MkBar :: forall x arg. -- Commenting out the line below makes the issue go away Proxy (Foo arg) -> Bar x }}} The panic is caused because the existentials for `MkBar` are messed up; {{{ {- MkBar univ_tvs: (x :: *) ex_tvs: (a :: arg_aZv) (arg_XZx :: *) arg ty: Proxy @arg_XZx a result ty: Foo @arg_XZx a }}} Note the confusion of two `arg` variables. Ran out of time at that point. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14880#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler