Running/Debugging Scala programs within intellij on Mac

I have installed the scala and the scala application runner plugin sboth on my windows XP laptop and my Mac OSX (intel) desktop machine.
On the XP machine I am able to run and debug my scala code, but on my Mac, the only options I get are to compile and to run the scala console.
Is there some bit of configuration I missed, or does run/debug not work on the mac?
I have tested this by building  exactly the same single file program on both:

(adapted from Venkat Subramaniam's "programming Scala"

package Chapter4
/**
* User: charlesp
* Date: Aug 26, 2009
* Time: 4:28:36 PM
*/


trait Friend {
val name: String
def listen() = println("Your friend " + name + " is listening")
}

class Human(val name: String) extends Friend
class Man(override val name: String) extends Human(name)
class Woman(override val name: String) extends Human(name)

class Animal

class Dog(val name: String) extends Animal with Friend {
//optionally override method here.
override def listen = println(name + "'s listening quietly")
}

class Cat(val name: String) extends Animal


object TraitTest {
  val john = new Man("John")
  val sara = new Woman("Sara")
  val comet = new Dog("Comet")
  john.listen
  sara.listen
  comet.listen
  val mansBestFriend : Friend = comet
  mansBestFriend.listen

  val snowy = new Cat("Snowy") with Friend
   val friend : Friend = snowy
   friend.listen

   val snowbell: Friend = new Cat("Snowbell") with Friend
   snowbell.listen

  def main(args: Array[String]) {
  }
}