[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):

 Replying to [comment:33 maeder]:
 > Replying to [comment:32 Iceland_jack]:
 > Surely, this is a lexical issue. No space is needed between symbols
 (like "\") and (unicode) letters (like x, y, or λ), although I recommend
 to always leave a space, i.e. "f  λ\ ..." would be parsed as "(f  λ)\
 ...".

 I was wondering if we could mimic the upper-case lambda `Λ` by using a
 lower-case `l` for lambda

 {{{#!hs
 ex' = l\ x -> l\ y -> x
 }}}

 `l\` look like a malformed lambda! (don't)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10843#comment:34>
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