Functional OO Calculator

function_calc.rb

class StatefulCalculator
  def initialize(total)
    @total = total
  end
 
  def add(x)
    StatefulCalculator.new(@total + x)
  end
  
  def sub(x)
    StatefulCalculator.new(@total - x)
  end
  
  def mul(x)
    StatefulCalculator.new(@total * x)
  end
  
  def div(denom)
    StatefulCalculator.new(@total / x)
  end
  
  def result
    @total
  end
end