#8745: GeneralizedNewtypeDeriving is still not Safe -------------------------------------+------------------------------------ Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1-rc1 Resolution: | Keywords: Safe Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by goldfire): The comments I've seen in relation to this are all in #5498. GND is now actually built on top of `coerce`, so I think it's a little incongruent to have one be Safe but not the other. To be fair, I'm not 100% sure that GND should be Safe, myself. While I am as confident as I can be about its type safety, it is very easy to imagine a library author omitting a key role annotation that would allow clients to (perhaps unwittingly) break class coherence or invariants. For example, if `base`'s `Set` doesn't have a role annotation, it would be very easy to cause the `Set` operations to misbehave. Simon PJ has advocated (see #5498) that GND should be Safe, on the other hand. My goal in creating this ticket is to make a reasoned decision on the matter, as opposed to letting inertia make the decision for us. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8745#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler