Reverse Polish notation calculator

gistfile1.rb

class RPNCalculator
  def evaluate(values_and_operator)
    @array = (values_and_operator).split(' ')
      if @array.length == 1
        return @array.pop.to_i
      end

    while true
    @array.each_with_index do |element, i|
      if    element == "+"
        after_op  = @array.drop(i + 1)
        sum = (@array[i - 2]).to_i + (@array[i - 1]).to_i
        length_before_op = @array.length - (after_op.length + 3)
        before_op = @array.take(length_before_op)
        @array = [] << before_op << sum << after_op
        @array = @array.flatten!
        return sum if @array.length == 1
        break
      elsif element == "*"
        after_op  = @array.drop(i + 1)
        prod = (@array[i - 2]).to_i * (@array[i - 1]).to_i
        length_before_op = @array.length - (after_op.length + 3)
        before_op = @array.take(length_before_op)
        @array = [] << before_op << prod << after_op
        @array = @array.flatten!
        return prod if @array.length == 1
        break
      elsif element == "-"
        after_op  = @array.drop(i + 1)
        diff = (@array[i - 2]).to_i - (@array[i - 1]).to_i
        length_before_op = @array.length - (after_op.length + 3)
        before_op = @array.take(length_before_op)
        @array = [] << before_op << diff << after_op
        @array = @array.flatten!
        return diff if @array.length == 1
        break
      end # end for if
    end # end for do
    end # end for while
  end # end for def
end

just got it! Thanks!