RPNCalculator with Andrew... crushing it

RPNCalculator.rb

class RPNCalculator

  def initialize
    @rpn = []
  end

  def push(num)
    @rpn << num
  end

  def plus
    do_equation(:+)
  end

  def minus
    do_equation(:-)
  end

  def times
    do_equation(:*)
  end

  def divide
    do_equation(:/)
  end

  def value
    @rpn[-1]
  end
  
  def do_equation(op_symbol)
    operators = { :+ => lambda{ @rpn[-2] + @rpn[-1] },
                  :- => lambda{ @rpn[-2] - @rpn[-1] },
                  :* => lambda{ @rpn[-2] * @rpn[-1] },
                  :/ => lambda{ @rpn[-2].to_f / @rpn[-1] } } 
                                                           
    result = operators[op_symbol].call
    2.times { @rpn.slice!(-1) }
    @rpn << result
  end
end