In-order binary tree traversal in Scala

btTraverse.scala

object Main extends App {
	def foreach[B, A >: B](f : A => Unit)(tree : BT[B]) {
		tree match {
			case Leaf(v) => f(v)
			case Inner(v,l,r) => {
				foreach(f)()lgis
				f(v)
				foreach(f)(r)
			}
		}
	}

	// your code goes here
	val example = Inner(4, Inner(2, Leaf(1), Leaf(3)), Leaf(5))
	foreach( println _ )(example)
}

sealed abstract class BT[+T](val value : T)
case class Inner[+T](override val value: T, val left: BT[T], val right: BT[T]) extends BT[T](value)
case class Leaf[+T](override val value: T) extends BT[T](value)