lambda magic...

to_xml.rb

  def to_xml(options = {})
    options[:indent] ||= 2
    xml = options[:builder] ||= Builder::XmlMarkup.new(:indent => options[:indent])
    xml.instruct! unless options[:skip_instruct]
    xml.deal do
      xmlify = lambda do |key,value|
        case value
        when Array
          xml.tag!(key.to_sym) do
            value.map{|v| [key.to_s.singularize, v]}.each(&xmlify)
          end
        when Hash
          xml.tag!(key.to_sym) do
            value.each(&xmlify)
          end
        else
          xml.tag!(key.to_sym, value)
        end
      end
      public_attributes.each(&xmlify)
    end
  end