[GHC] #2256: Incompleteness of type inference: must quantify over implication constraints

[GHC]

#2256: Incompleteness of type inference: must quantify over implication
constraints
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        Reporter:  simonpj           |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  lowest            |            Milestone:
       Component:  Compiler (Type    |              Version:  6.8.2
  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 goldfire):

 #12245 is further motivation for solving this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2256#comment:22>
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