grammar Numerals
  rule percentage
    (decimal "%") {
      def to_f
        decimal.to_f / 100
      end
    }
  end

  rule decimal
    sign [0-9]+ '.' [0-9]* {
      def to_f
        text_value.to_f
      end
    }
  end

  rule sign
    ('+'/'-')? 
  end
end
