[GHC] #10843: Allow do blocks without dollar signs as arguments

[GHC]

#10843: Allow do blocks without dollar signs as arguments
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        Reporter:  agibiansky        |                   Owner:  agibiansky
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.2
  (Parser)                           |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by agibiansky):

 I don't see a common usecase for `case`, `if`, and `let`, and think we
 should not include them. The motivation for this change is that `do` and
 lambdas are very commonly used in custom control structures (`when`,
 `unless`, `for`, `forM`, `with*`, and so on).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10843#comment:6>
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