data Set e = Set [e] deriving Show
    
mySet :: Set Int
mySet = Set [1, 2, 3, 4, 5]
    
setLength :: Set e -> Int
setLength (Set s) = length s
    
empty :: Set e -> Bool
empty (Set s) = if null s then True else False
    
insert :: Set e -> e -> Set e
insert (Set s) value = Set $ value : s

main = print $ insert mySet 4