[GHC] #7888: Impredicativity flag needed more often

[GHC]

#7888: Impredicativity flag needed more often
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        Reporter:  monoidal          |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.6.3
  checker)                           |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Incorrect         |            Test Case:
  warning at compile-time            |  typecheck/should_compile/T7888
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 This is at odds with #11431. I'm going with #11431 as that's more
 consistent, as discussed on that ticket.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7888#comment:3>
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