# 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