Re: [GHC] #14070: Allow ‘unsafe’ deriving strategy, deriving code with ‘unsafeCoerce’

[GHC]

#14070: Allow ‘unsafe’ deriving strategy, deriving code with ‘unsafeCoerce’
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        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:                    |
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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>
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