# File lib/iq_rdf/document.rb, line 140
    def to_turtle
      s = ""
      @namespaces.values.sort{ |n1, n2| n1.turtle_token <=> n2.turtle_token }.each do |namespace|
        s << "@prefix #{namespace.turtle_token}: <#{namespace.uri_prefix}>.\n"
      end
      s << "\n"
      @nodes.each do |node|
        pref = "#{node.to_s(@document_language)}"
        if node.rdf_type
          s << "#{pref} a #{node.rdf_type}"
          pref = ";\n" + "".ljust(node.to_s(@document_language).length)
        end
        node.nodes.each do |predicate|
          s << "#{pref} #{predicate.to_s} #{predicate.nodes.map{|o| o.to_s(predicate.lang || node.lang || @document_language)}.join(", ")}"
          pref = ";\n" + "".ljust(node.to_s(@document_language).length)
        end
        s << ".\n"
      end
      s
    end