module List (
head,
ordNub,
sortOn,
list,
) where
import Data.List (sortBy)
import Data.Maybe (Maybe(..))
import Data.Ord (Ord, comparing)
import Data.Foldable (Foldable, foldr)
import Data.Function ((.))
import Data.Functor (fmap)
import Control.Monad (return)
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