TIL sorting in reverse order in Haskell

Author: hdgarrood

haskell/sorting-in-reverse-order.md

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+# Sorting in reverse order
+
+`Data.Ord` contains a newtype, `Down`, which can wrap any type that has an
+`Ord` instance, in order to provide a reversed `Ord` instance for that type.
+
+For example:
+
+```hs
+Prelude> import Data.Ord (Down(..))
+Prelude Data.Ord> :info Down
+newtype Down a = Down a         -- Defined in ‘Data.Ord’
+instance Ord a => Ord (Down a)  -- Defined in ‘Data.Ord’
+Prelude Data.Ord> Down 3 > Down 4
+True
+```
+
+This can be very convenient for reversing sort order:
+
+```hs
+Prelude> import Data.Ord (Down(..), comparing)
+Prelude Data.Ord> import Data.List (sortBy)
+Prelude Data.Ord Data.List> sortBy (comparing Down) [1..10]
+[10,9,8,7,6,5,4,3,2,1]
+```