[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 goldfire):

 Replying to [comment:10 mpickering]:
 > That sounds right Richard but there is also another bug here that
 inlining the synonym changes the semantics. That shouldn't get lost
 either.

 Yes. We need to test that. But I think the problem is due to
 universal/existential confusion when implementing pattern synonyms, and
 that sorting it out will fix the original bug. This assumption could very
 well be wrong.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11224#comment:12>
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