[GHC] #12423: Panic with DeriveAnyClass

[GHC]

#12423: Panic with DeriveAnyClass
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        Reporter:  knrafto           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  Generics
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12144            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 I apologize, comment:3 is wrong in stating that you can't derive an `Eq1`
 instance for `Foo`. It is most certainly possible to–after all, you can
 create the following instance!

 {{{#!hs
 instance Eq1 Foo
 }}}

 That eta-reduction stuff was me confusing the details of `DeriveAnyClass`
 with other deriving mechanisms, like `GeneralizedNewtypeDeriving` and
 `DeriveFunctor`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12423#comment:5>
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