Data/Poset.hs

   1 {-
   2  - Copyright (C) 2009 Nick Bowler.
   3  -
   4  - License BSD2:  2-clause BSD license.  See LICENSE for full terms.
   5  - This is free software: you are free to change and redistribute it.
   6  - There is NO WARRANTY, to the extent permitted by law.
   7  -}
   8
   9 module Data.Poset (
  10     Poset(..), Sortable(..), Ordering(..),
  11     module Data.Poset
  12 ) where
  13
  14 import Prelude hiding (Ord(..), Ordering(..))
  15 import Data.Poset.Internal
  16
  17 import Data.Function
  18 import Data.Monoid
  19
  20 instance Poset a => Poset (Maybe a) where
  21     Just x  <= Just y = x <= y
  22     Nothing <= _      = True
  23     _       <= _      = False
  24
  25 instance Poset a => Poset [a] where
  26     compare = (mconcat .) . zipWith compare
  27
  28 -- | Sort a list using the default comparison function.
  29 sort :: Sortable a => [a] -> [a]
  30 sort = sortBy compare
  31
  32 -- | Apply a function to values before comparing.
  33 comparing :: Poset b => (a -> b) -> a -> a -> Ordering
  34 comparing = on compare