module List
( head
, ordNub
, sortOn
, list
) where
import Control.Monad (return)
import Data.Foldable (Foldable, foldr)
import Data.Function ((.))
import Data.Functor (fmap)
import Data.List (sortBy)
import Data.Maybe (Maybe (..))
import Data.Ord (Ord, comparing)
import qualified Data.Set as Set
head :: (Foldable f) => f a -> Maybe a
head = foldr (\x _ -> return x) Nothing
sortOn :: (Ord o) => (a -> o) -> [a] -> [a]
sortOn = sortBy . comparing
ordNub :: (Ord a) => [a] -> [a]
ordNub l = go Set.empty l
where
go _ [] = []
go s (x:xs) =
if x `Set.member` s
then go s xs
else x : go (Set.insert x s) xs
list :: [b] -> (a -> b) -> [a] -> [b]
list def f xs = case xs of
[] -> def
_ -> fmap f xs