def enter_node( tree_node )
      str = ''
      (0...@depth).step {
        str << ' |-'
      }

      if @depth == 0
        puts str + tree_node.name.to_s
      else
        puts str + tree_node.name.to_s
      end
      @depth += 1
    end
def enter_node( tree_node )
      str = ''
      (0...@depth).step {
        str << ' |-'
      }

      if @depth == 0
        puts str + tree_node.name.to_s
      else
        puts str + tree_node.name.to_s
      end
      @depth += 1
    end
< BasicTreeNodeVisitor