[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:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
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):

 Oh dear. This example illustrates that I, for one, don't have a grasp on
 pattern synonym signatures. I had assumed that the universals were
 precisely those variables mentioned in the result. But that's not true
 here, because `a` really is a universal, not an existential. So I'm
 clearly confused. And that sad state of affairs isn't going to be fixed at
 11pm at night, so perhaps I'll return to this tomorrow.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11224#comment:7>
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