[GHC] #11778: Preserve demandInfo on lambda binders in the simpifier

[GHC]

#11778: Preserve demandInfo on lambda binders in the simpifier
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        Reporter:  nomeata           |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Yes but it seem weirdly ad-hoc to zap if (a) the function is not
 saturated, but (b) it is applied to at least one argument.

 The approach I describe doesn't have this odd bump, AND it doesn't zap the
 binders on lambdas that aren't beta-reduced.

 So I prefer the suggestion I made.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11778#comment:2>
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