7つの言語7つの世界 p24 Ruby

tree.rb

class Tree
  attr_accessor :children, :node_name

  def initialize(name, children={})
    @children = children
    @node_name = name
  end

  def visit_all(&block)
    visit &block
    children.each {|c| c.visit_all &block}
  end

  def visit(&block)
    block.call self
  end
end

ruby_tree = Tree.new("Ruby", [Tree.new("Reia"), Tree.new("MacRuby")])

puts "Visiting a node"
ruby_tree.visit {|node| puts node.node_name}
puts

puts "visiting entire tree"
ruby_tree.visit_all {|node| puts node.node_name}