[GHC] #12179: Incorrect parsing of a pattern synonym type

[GHC]

#12179: Incorrect parsing of a pattern synonym type
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           Reporter:  mpickering     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternSynonyms                    |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #12108
Differential Rev(s):                 |         Wiki Page:
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 The following definition is accepted by GHC.

 {{{
 pattern Q :: a -> forall. (Bool -> a)
 pattern Q v <- (($ True) -> v)
 }}}

 What does this type signature mean? Who knows. It should be rejected for
 being an invalid form.

 Maybe see #12108

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12179>
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