How to get the currently evaluated items in a Stream in Scala

EvaluatedStream.scala

import annotation.tailrec
import collection.immutable.List
import collection.immutable.Stream.{Empty,Cons}

object EvaluatedStream {

  def evaluatedItems[T](stream: => Stream[T]): List[T] = {
    @tailrec
    def inner(s: => Stream[T], acc: List[T]): List[T] = s match {
      case Empty => acc
      case c: Cons[T] => if (c.tailDefined) {
        inner(c.tail, acc ++ List(c.head))
      } else { acc }
    }
    inner(stream, List())
  }

  def main(args: Array[String]) {
    val s = Stream.iterate(1) { _ + 1 }
    s takeWhile { _ < 10} force
    val list: List[Int] = evaluatedItems(s)
    assert(list == List(1, 2, 3, 4, 5, 6, 7, 8, 9))
  }

}