[GHC] #10892: ApplicativeDo should use *> and <*

[GHC]

#10892: ApplicativeDo should use *> and <*
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        Reporter:  simonmar          |                Owner:  bollu
            Type:  task              |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:  ApplicativeDo
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:  12143
 Related Tickets:  #13309            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by AaronFriel):

 A user ElvishJerricco on Reddit posted an interesting test case
 ([[https://www.reddit.com/r/haskell/comments/6c7hen/applicativedo_overhaul_request_for_comments/dhw9po0/?context=3|my
 analysis here]]). There were two interesting things that popped out.
 Here's the reduced test case:

 {{{#!hs
 {-# LANGUAGE ApplicativeDo #-}

 foo :: Monad f => f () -> f ()
 foo f = f

 bar :: Monad f => f () -> f ()
 bar f = do
     _ <- f
     foo f
 }}}

 Clearly the two statements of `bar` are independent, and so we should use
 `*>` here too. The interesting thing to me is that this doesn't trigger
 the `ApplicativeDo` desugaring at all! The desugarer outputs: `bar = f >>=
 \_ -> foo f`. So this is another thing to make sure my revised rules
 cover.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10892#comment:27>
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