[GHC] #8714: ExistentialQuantification plus DeriveDataTypeable leads to core lint error

[GHC]

#8714: ExistentialQuantification plus DeriveDataTypeable leads to core lint error
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        Reporter:  CoreyOConnor                  |            Owner:
            Type:  bug                           |           Status:  merge
        Priority:  highest                       |        Milestone:  7.8.1
       Component:  Compiler                      |          Version:
      Resolution:                                |  7.8.1-rc2
Operating System:  Unknown/Multiple              |         Keywords:
 Type of failure:  None/Unknown                  |     Architecture:
       Test Case:                                |  x86_64 (amd64)
  simplCore/should_compile/T8714                 |       Difficulty:
        Blocking:                                |  Unknown
                                                 |       Blocked By:
                                                 |  Related Tickets:
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Comment (by nomeata):

 Your commit does not validate:
 {{{
 compiler/simplCore/SetLevels.lhs:467:31:
     Not in scope: `expr'
     Perhaps you meant `exp' (imported from Prelude)
 }}}
 https://s3.amazonaws.com/archive.travis-ci.org/jobs/20523523/log.txt

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8714#comment:13>
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