[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:  #11706            |  Differential Rev(s):  Phab:D1219
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Examples from EDSL
 [https://hackage.haskell.org/package/esqueleto-2.4.3/docs/Database-
 Esqueleto.html Esqueleto]:

 {{{#!hs
 -- select $
 -- from $ \p -> do
 -- where_ (p ^. PersonName ==. val "John")
 -- return p

 select do
   from \p -> do
     where_ (p ^. PersonName ==. val "John")
     return p
 }}}


 {{{#!hs
 -- select $
 -- from $ \person -> do
 -- where_ $ exists $
 --          from $ \post -> do
 --          where_ (post ^. BlogPostAuthorId ==. person ^. PersonId)
 -- return person

 select do
   from \person -> do
     where_ do
       exists do
         from \post ->
           where_ (post ^. BlogPostAuthorId ==. person ^. PersonId)
     return person
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10843#comment:18>
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