gistfile1.txt

class RPNCalculator
  attr_accessor :stack
  
  def initialize
    self.stack = Array.new
  end

  def push(val)
    self.stack.push(val.to_f)
  end
  
  def plus
    eval(:+)
  end
  
  def minus
    eval(:-)
  end
  
  def times
    eval(:*)
  end
  
  def divide
    eval(:/)
  end
  
  def value
    self.stack.last
  end

  
  private
  
  def eval(operation)
#    raise "calculator is empty" unless self.stack.size >= 2

    op1 = self.stack.pop
    op2 = self.stack.pop
    
    case operation
    when :+
      val = op1 + op2
    when :-
      val = op2 - op1
    when :*
      val = op1 * op2
    when :/
      val = op2 / op1
    end
    
    self.stack << val
  end
end