[GHC] #4517: Add Data.Functor.Backwards to transformers

[roconnor at theorem.ca]

#4517: Add Data.Functor.Backwards to transformers
---------------------------------+------------------------------------------
    Reporter:  r6                |       Owner:
        Type:  proposal          |      Status:  new
    Priority:  normal            |   Component:  libraries (other)
     Version:  7.0.1             |    Keywords:  backwards
    Testcase:                    |   Blockedby:
          Os:  Unknown/Multiple  |    Blocking:
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
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Data.Functor.Backwards is a wrapper for functors that allow Foldable,
Traversable, and Applicative functors to be operated backwards.  It is
similar to Dual for Monoids.  The Applicative instance runs effects in
reversed order.  The Foldable instance folds from right to left, The
Traversable instance traverses from right to left.

-- 
Russell O'Connor                                      <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''