[GHC] #9793: Some as-patterns could be accepted in pattern synonyms

[GHC]

#9793: Some as-patterns could be accepted in pattern synonyms
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        Reporter:  cactus            |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  7.8.3
  checker)                           |             Keywords:
      Resolution:                    |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1666
       Wiki Page:                    |
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Comment (by typedrat):

 I'm running up against this right now, and while the idea of contributing
 to GHC (especially with what may be a non-trivial first submitted change)
 is daunting, I'd be happy to at least try and do it if a design is decided
 on.

 Generally, my use case is trying to fake impredicative types in the
 specific application of GADT phantom types, and being able to just erase
 the existential wrapper from view and make it look like perfectly normal
 pattern matching when it's actually being taken apart would make it "feel"
 a lot nicer, in my opinion.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9793#comment:13>
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