require 'prettyprint' # for the p function

class Tree
  attr_accessor :name

  def initialize name
    @name = name
    @children = []
  end

  def visit visitor
    visitor.visit(self)
    for child in @children
      child.visit(visitor)
    end
    visitor.value
  end

  def << child
    @children << child
    self
  end
end

root = Tree.new("root") << (Tree.new("child") << Tree.new("grandkid") << Tree.new("grandkid2")) << Tree.new("child2")

class Visitor
  attr_accessor :value

  def initialize
    @value = []
  end

  def visit node
    @value << node.name.reverse
  end
end

p root.visit(Visitor.new)