#14070: Allow ‘unsafe’ deriving strategy, deriving code with ‘unsafeCoerce’ -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | QuantifiedContexts, deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Replying to [comment:7 RyanGlScott]:
My hunch is that just about every use case for this proposed `unsafe newtype` deriving strategy would be subsumed by the ability to have quantified contexts involving `Coercible`.
That's excellent and I hope that is indeed the case. A choice between `forall a. Coercible (m (M m a)) (m (m a))` and `forall a b. Coercible a b => Coercible (m a) (m b)` in the context is also interesting and makes me wonder if they differ in that example ---- Replying to [comment:11 RyanGlScott]:
Happily, writing instances the way `GeneralizedNewtypeDeriving` .. doesn't suffer from this problem.
ah! So this means we can also derive optic methods once `QuantifiedContexts` lands and (possibly / hopefully) that we can derive everything derivable? That would be huge for me and I would be fine with closing this ticket It does require `ImpredicativeTypes` written in the Haskell surface language, wasn't that removed in 8.2? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14070#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler