[GHC] #2660: Add Down newtype wrapper for reversing orderings

[GHC]

#2660: Add Down newtype wrapper for reversing orderings
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    Reporter:  twanvl            |       Owner:                  
        Type:  proposal          |      Status:  new             
    Priority:  normal            |   Component:  libraries/base  
     Version:  6.8.3             |    Severity:  normal          
    Keywords:                    |    Testcase:                  
Architecture:  Unknown/Multiple  |          Os:  Unknown/Multiple
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 In the same spirit as the newtypes in Data.Monoid, we can also add a
 newtype for reversing the ordering of a type:
 {{{
 newtype Down a = Down { getDown :: a }

 instance Ord a => Ord (Down a) where
     Down x < Down y  =  y < x
     -- etc.
 }}}
 This newtype is especially useful in combination with `sortOn` (ticket
 #2629).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2660>
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