[GHC] #13065: Prohibit user-defined Generic and Generic1 instances

[GHC]

#13065: Prohibit user-defined Generic and Generic1 instances
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        Reporter:  dfeuer            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  Generics
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 Replying to [comment:8 RyanGlScott]:
 > About two weeks have passed since this was first proposed, and there
 doesn't seem to be any definite consensus. In fact, I'm not sure if you
 even want this to be implemented anymore, since you seem reticent to give
 up the ability to define custom `Generic` instances. If you do wish to
 pursue this further, I'd highly recommend creating a GHC proposal for it,
 since this seems to be a topic of contention.

 I am of two minds. I see very good reasons to make this change, and I see
 very good reasons to be wary of it. I'm not the main person pushing for
 it; I'm just the one who wrote it up.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13065#comment:9>
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