Working on an RPN calculator

rpn

def rpn(expression) 

operands = [] 

	while expression.length > 0 
		token = expression.shift # puts first value of expression into variable "token"
		unless token =~ /^\d+$/ # Finding operators
			right = operands.pop 
			left = operands.pop
			token = eval "#{left} #{token} #{right}" #eval is really handy!
		end
		operands << token # push the evaluated value into the operands array
	end
operands.pop # returns last value from operands array 
end