[GHC] #11216: RebindableSyntax with pattern guards needs `fail`

[GHC]

#11216: RebindableSyntax with pattern guards needs `fail`
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
                                     |  RebindableSyntax
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  T11216
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by cdsmith):

 This also applies to bindings in list comprehensions, and is still
 happening as of GHC 8.0.1.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11216#comment:4>
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