to_ical (Icalendar::RRule)

    # File lib/icalendar/parser.rb, line 47
        def to_ical
          result = ["FREQ=#{@frequency}"]
          result << ";UNTIL=#{@until.to_ical}" if @until
          result << ";COUNT=#{@count}" if @count
          result << ";INTERVAL=#{@interval}" if @interval
          @by_list.each do |key, value|
            result << ";#{key.to_s.upcase}=#{value}" if value
          end
          result << ";WKST=#{@wkst}" if @wkst
          result.join
        end