[GHC] #11993: RFC, allow local bindings in pattern synonyms

[GHC]

#11993: RFC, allow local bindings in pattern synonyms
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           Reporter:  Iceland_jack   |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternSynonyms                    |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Code from #11992, allow users to write something like

 {{{#!hs
 pattern Suc :: Int -> Int
 pattern Suc n <- (hasSuc -> Just n)
   where Suc n = n + 1

         hasSuc :: Int -> Maybe Int
         hasSuc n = [ n - 1 | n > 0 ]
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11993>
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