[GHC] #4370: Bring back monad comprehensions

[GHC]

#4370: Bring back monad comprehensions
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        Reporter:  simonpj           |                Owner:
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler          |              Version:  6.12.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2247
       Wiki Page:                    |
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Comment (by rwbarton):

 bgamari, is this the right ticket?

 Also, I wish we wouldn't reopen issues with mega-threads like this one.
 Monad comprehensions were indeed added and you have to get to comment:62
 to find out what the open part of this ticket is. Much easier for
 posterity if the remaining piece is split out into its own ticket once the
 comment thread has become very long.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4370#comment:71>
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