[GHC] #14618: Higher rank typechecking is broken

[GHC]

#14618: Higher rank typechecking is broken
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        Reporter:  mniip             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mniip):

 Can't help but be curious about what caused this. Something related to
 broken instantiation before constraint solving, or overzealous
 generalization afterwards?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14618#comment:4>
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