My implementation of a Scala speed test

ScalaNew.scala

package mathtree

object ScalaNew {

  sealed trait Term
  case class Number(value: Int) extends Term
  sealed trait Operator extends Term
  case object Add extends Operator
  case object Subtract extends Operator
  case object Multiply extends Operator
  case object Divide extends Operator

  sealed trait Expression
  case class SimpleExpr(value: Int) extends Expression
  case class ComplexExpr(op: Operator, op1: Expression, op2: Expression) extends Expression
  
  def main(args: Array[String]): Unit = {
    val start_time = System.nanoTime()
    var result : Int = 0
    for(i <- 1 to 2000) {
        result = calculate(make_expr(make_terms(args)))
    }
    val end_time = System.nanoTime()
    println("Scala new\ttime = " + (end_time - start_time)/1000000L + "\tresult = " + result)
  }

  def make_terms(args: Array[String]) : Array[Term] = {
    args.map {_ match {
      case "+" => Add
      case "-" => Subtract
      case "x" => Multiply
      case "/" => Divide
      case n => Number(n.toInt)
    }}
  }

  def make_expr(terms: Array[Term]): Expression = {
    val stack = new scala.collection.mutable.Stack[Expression]
    terms foreach { _ match {
      case op: Operator => stack.push(ComplexExpr(op, stack.pop(), stack.pop()))
      case n: Number => stack.push(SimpleExpr(n.value))
    }}
    stack.pop()
  }

  def calculate(expr: Expression): Int = expr match {
    case simple: SimpleExpr => simple.value
    case complex: ComplexExpr => complex.op match {
        case Add => calculate(complex.op2) + calculate(complex.op1)
        case Subtract => calculate(complex.op2) - calculate(complex.op1)
        case Multiply => calculate(complex.op2) * calculate(complex.op1)
        case Divide => calculate(complex.op2) / calculate(complex.op1)
    }
  }
}

You should have used case objects instead of case classes for operators.

Done! Thanks Daniel!

I noticed quite an improvement on performance. It now takes an average of 35ms instead of 40ms on my machine. (After several runs from within SBT)