[GHC] #9900: Support pattern synonyms in GHCi

[GHC]

#9900: Support pattern synonyms in GHCi
-------------------------------------+-------------------------------------
       Reporter:  cactus             |                   Owner:  cactus
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:  7.10.1
      Component:  GHCi               |                 Version:  7.8.3
       Keywords:  PatternSynonyms    |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:  8749, 7253         |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 Pattern synonyms are not parsed in GHCi:

 {{{
 λ» :set -XPatternSynonyms
 λ» pattern P x = x

 <interactive>:5:1: parse error on input ‘pattern’

 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9900>
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