class Node
  def _init(val)
    self.val = val
    self.next = null
  end
  
  def _to_string()
    return "(${self.val})"
  end
end

class LinkedList
  def _init()
    self.head = null
  end
  
  def append(node)
    if self.head == null
      self.head = node
    else
      last = self.head
      while last.next
        last = last.next
      end
      last.next = node
    end
  end
  
  def reverse()
    curr = self.head
    prev = null; next = null
    while curr
      next = curr.next
      curr.next = prev
      prev = curr
      curr = next
    end
    self.head = prev
  end
  
  def _to_string()
    ret = ""
    next = self.head
    while next
      ret += next._to_string()
      ret += " --> "
      next = next.next
    end
    ret += "null"
    return ret
  end
end

ll = LinkedList()
ll.append(Node(4))
ll.append(Node(6))
ll.append(Node(3))
ll.append(Node(9))

## FIXME: No override supported at the moment.
print(ll._to_string())

ll.reverse()

print(ll._to_string())