#8745: GeneralizedNewtypeDeriving is still not Safe -------------------------------------------------+------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | 7.8.1-rc1 Operating System: Unknown/Multiple | Keywords: Safe Type of failure: None/Unknown | Architecture: Test Case: | Unknown/Multiple should_fail/TcCoercibleFailSafe | Difficulty: Blocking: | Unknown | Blocked By: | Related Tickets: -------------------------------------------------+------------------------- Comment (by nomeata):
One way forward here is to allow role annotations on classes only when we have IncoherentInstances. In fact, I rather like that solution -- a role annotation on a class quickly leads to the possibility of incoherence, and this solution also neatly prohibits such annotations in Safe Haskell. Thoughts?
That’s what I was about to propose as well. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8745#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler