Scala Calculator

Calculator.scala

import scala.collection.mutable

object Calculator {

  def main(args: Array[String]): Unit =
    if (args.length != 1) {
      throw new IllegalArgumentException("usage: Calculator <expression>")
    } else {
      val expression = args(0)
      val tokens = expression.split(" ")
      val stack = new mutable.Stack[Int]
      for (token <- tokens) {
        token match {
          case "+" =>
            val rhs = stack.pop()
            val lhs = stack.pop()
            stack.push(lhs + rhs)
          case "-" =>
            val rhs = stack.pop()
            val lhs = stack.pop()
            stack.push(lhs - rhs)
          case "*" =>
            val rhs = stack.pop()
            val lhs = stack.pop()
            stack.push(lhs * rhs)
          case "/" =>
            val rhs = stack.pop()
            val lhs = stack.pop()
            stack.push(lhs / rhs)
          case _ => try {
            stack.push(token.toInt)
          } catch {
            case _ => throw new IllegalArgumentException("invalid token " + token)
          }
        }
      }
      println(stack.pop())
    }
}