class Node(T)
    @val: T
    @next: Node(T)?

    def initialize(@val)
        @next = nil
    end

    property :val, :next
end

class LinkedList(T)
    @head: Node(T)?
    @tail: Node(T)?

    def push(val)
        node = Node(T).new val

        if @tail
            @tail.next = node
            @tail = node
        else
            @head = node
            @tail = node
        end
    end
end

ll = LinkedList(String).new
ll.push "Hello"
ll.push "World"