[GHC] #12749: Typechecker regression involving RankNTypes

[GHC]

#12749: Typechecker regression involving RankNTypes
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by phadej):

 I wonder how and "Getting rid of -XImpredicativeTypes"
 https://mail.haskell.org/pipermail/ghc-devs/2016-September/012940.html
 comments are related.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12749#comment:1>
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