[GHC] #13752: Odd pattern synonym type errors

[GHC]

#13752: Odd pattern synonym type errors
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.2.1-rc2
  checker)                           |             Keywords:
      Resolution:                    |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  patsyn/should_compile/T13752,
                                     |  T13752a
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 Wow, that was fast! Thanks! It may be a dark corner today. However, if my
 proposal to add type signatures to pattern synonym builders ends up going
 through with the committee-requested restriction to allow the signatures
 to vary only in constraints, I think we'll likely see more such code as
 people hack around the restriction.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13752#comment:4>
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