[GHC] #12165: Multiple pattern type signatures accepted

[GHC]

#12165: Multiple pattern type signatures accepted
-------------------------------------+-------------------------------------
           Reporter:  goldfire       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternSynonyms                    |
       Architecture:                 |   Type of failure:  GHC accepts
  Unknown/Multiple                   |  invalid program
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This hogwash is accepted:

 {{{
 pattern P :: a -> b -> Maybe (a,b)
 pattern P :: foo => bar => blah -> urgh
 pattern P x y = Just (x, y)
 }}}

 A little experimentation shows that only the first pattern signature is
 examined. Others are accepted and ignored.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12165>
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