[GHC] #9761: A module can't usefully use both GeneralizedNewtypeDeriving and DeriveFoldable

[GHC]

#9761: A module can't usefully use both GeneralizedNewtypeDeriving and
DeriveFoldable
-------------------------------------+-------------------------------------
              Reporter:  dfeuer      |            Owner:  dfeuer
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Core        |          Version:  7.9
  Libraries                          |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  rejects valid program              |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by rwbarton):

 (To clarify, "this" = the fact that Foldable's parameter has type role
 nominal in HEAD, preventing GND. In 7.8 it has role representational, as
 it should.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9761#comment:3>
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