reversePolishFunc.go

func reversePolish(arithmeticExpression string) int {
  //create regexp for matching against operators
	r := regexp.MustCompile("[+-/*]")
  //split input by spaces
	splitInput := strings.Split(arithmeticExpression, " ")
  //init Stack
	s := &Stack{}

	for _, char := range splitInput {
		if r.Match([]byte(char)) {
			int1 := s.pop()
			int2 := s.pop()
			expression := fmt.Sprintf("%v %v %v", int1, char, int2)

      //use the govaluate package to evalute the arithmetic expression
			eval, err := govaluate.NewEvaluableExpression(expression)
			if err != nil {
				fmt.Printf("There was an error building your expression: %v \n", expression)
				log.Fatal("The program is shutting down")
			}

			result, err := eval.Evaluate(nil)
			if err != nil {
				fmt.Printf("There was an error evaluating your expression: %v \n", expression)
				log.Fatal("The program is shutting down")
			}
			fmt.Printf("The expression being evaluated is %v = %v \n", expression, result)

			//govaluates returns an interface so we need to convert from interface to int
			intResult := int(result.(float64))
			s.push(intResult)

		} else {
      //if there isn't an operator, push the number onto the stack
			intVal, err := strconv.Atoi(char)
			if err != nil {
				fmt.Printf("%v is not a valid integer \n", char)
				log.Fatal("Please use valid characters for this program: 0-9 and *-/+")
			}
			s.push(intVal)
		}
	}
  //return the end result
	total := s.pop()

	fmt.Printf("The evaluation of %v yields %v \n", opts.UserInput, total)
	return total
}