[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 akio):

 Replying to [comment:23 rwbarton]:
 > I don't think parsing `f a b {-# SCC #-} d e` as `f a b ({-# SCC #-} d
 e)` is even an option, really, since these pragmas must be ignorable by
 compilers that don't understand them.

 Agreed.

 > Also, I think/hope this proposal does not change the parsing of any
 program that currently parses, right?

 I believe this is the case, although I don't have a proof. My rough
 argument is:

 1. This extension doesn't introduce any new conflict in the parser
 (shift/reduce or reduce/reduce)
 2. By chasing the new grammar you can see that `do`, lambda, etc. continue
 to parse as a `lexp`.

 So if there is any change in the parsing of any currently-valid program,
 then it must be a result of somehow triggering an existing ambiguity in
 the grammar, but this seems unlikely.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10843#comment:25>
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