[GHC] #10873: Bad error message for incorrect pattern synonym signature

[GHC]

#10873: Bad error message for incorrect pattern synonym signature
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        Reporter:  mpickering        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |
      Resolution:                    |             Keywords:  newcomer
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 mpickering):

 The error should now be triggered by switching around the constraints.

 {{{
 {-# LANGUAGE PatternSynonyms #-}

 pattern Pat :: () => Show a => a -> Maybe a
 pattern Pat a = Just a
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10873#comment:4>
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