dlist

dlist.hs

module DList where

import Prelude hiding (reverse)
import Prelude as P

{-
 - provide whatever list operation in O(1) time complexity ...
 - only toList do all the hard works.
 -}

type DList a = [a] -> [a]

addFirst :: a -> DList a -> DList a
addFirst a l = (a:) . l

addLast :: a -> DList a -> DList a
addLast a l = (++[a]) . l

remove :: Ord a => a -> DList a -> DList a
remove a l = filter (/=a) . l

reverse :: a -> DList a -> DList a
reverse a l = P.reverse . l

fromList :: [a] -> DList a
fromList = (++)

toList :: DList a -> [a]
toList dl = dl []