class Sass::Script::Number

def compute_units(this, other, operation)
  case operation
  when :*
    [this.numerator_units + other.numerator_units, this.denominator_units + other.denominator_units]
  when :/
    [this.numerator_units + other.denominator_units, this.denominator_units + other.numerator_units]
  else  
    [this.numerator_units, this.denominator_units]
  end
end