#14070: Allow ‘unsafe’ deriving strategy, deriving code with ‘unsafeCoerce’ -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: duplicate | Keywords: | QuantifiedConstraints, deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #2893 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Replying to [comment:24 simonpj]:
Do we allow this?
Sadly, not without `ImpredicativeTypes` (which `GeneralizedNewtypeDeriving` enables under the hood).
(It's impredicative -- but in a benign way.)
Indeed. You had proposed a way to allow this without `ImpredicativeTypes` [https://mail.haskell.org/pipermail/ghc-devs/2016-September/012940.html here]—do you think you could create a GHC proposal about this? The details of this are far beyond my understanding, so it'd take someone with your level of expertise to get the details right in such a hypothetical proposal. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14070#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler