#9858: Typeable instances should be kind-aware -------------------------------------+------------------------------------- Reporter: dreixel | Owner: dreixel Type: bug | Status: new Priority: highest | Milestone: 7.10.1 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: -------------------------------------+------------------------------------- Comment (by int-e): Replying to [comment:25 dreixel]:
How about just marking `Typeable` instances for polykinded type constructors as Unsafe (if that's possible)?
Given how notoriously hard it is to control exports of instances, that won't be enough. To make things worse, the offending instance used here (for {{{Proxy}}}) is derived in {{{Data.Typeable.Internal}}}, which is marked {{{Trustworthy}}}. So conscientious users of safe Haskell would not be able to trust the base package anymore, rendering safe Haskell all but useless. I guess the right way to leverage safe Haskell is to mark {{{Data.Typeable}}} as unsafe, and explain the situation in a big comment. It would still be a pain to track uses of {{{Data.Typeable}}} in {{{Trustworthy}}} modules of other libraries (say, lens and its dependencies). I'm afraid there is no good interim solution here. I favor spj's suggestion, but #9111 suggests that some people actually use {{{Typeable}}} for {{{Proxy}}}. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9858#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler