[GHC] #12006: Can't infer constraint of pattern synonyms

[GHC]

#12006: Can't infer constraint of pattern synonyms
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Yes, I think in principle it should be possible to infer a type that works
 for both builder and matcher. I'm not quite sure how hard that would be;
 probably not terrible.

 Of course you can always work around the difficulty by providing a
 signature.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12006#comment:3>
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