[GHC] #11224: Program doesn't preserve semantics after pattern synonym inlining.

[GHC]

#11224: Program doesn't preserve semantics after pattern synonym inlining.
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        Reporter:  anton.dubovik     |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
Operating System:  Windows           |         Architecture:  x86_64
 Type of failure:  Incorrect result  |  (amd64)
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11225            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 I think the solution you propose is very confusing to users. I think we
 should be able to do better inferring whether a type variable univ/ex
 especially as GHC already manages to infer the correct signature. Doing so
 would require looking at the pattern synonym itself but I don't think this
 is too bad?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11224#comment:13>
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