OrdNub.hs

module OrdNub where

import qualified Data.Set as Set

ordNubOn :: Ord b => (a -> b) -> [a] -> [a]
ordNubOn f = go Set.empty
  where go _ [] = []
        go s (x:xs) | f_x `elem` s = go s xs
                    | otherwise    = x : go (Set.insert f_x s) xs
          where f_x = f x

ordNub :: Ord a => [a] -> [a]
ordNub = ordNubOn id