abstract-report.scala:1: error: class Unimplemented needs to be abstract, since:
it has 12 unimplemented members.
/** As seen from class Unimplemented, the missing signatures are as follows.
 *  For convenience, these are usable as stub implementations.
 */
  // Members declared in scala.collection.GenTraversableOnce
  def isTraversableAgain: Boolean = ???
  def toIterator: Iterator[String] = ???
  def toStream: Stream[String] = ???

  // Members declared in scala.collection.TraversableOnce
  def copyToArray[B >: String](xs: Array[B],start: Int,len: Int): Unit = ???
  def exists(p: String => Boolean): Boolean = ???
  def find(p: String => Boolean): Option[String] = ???
  def forall(p: String => Boolean): Boolean = ???
  def foreach[U](f: String => U): Unit = ???
  def hasDefiniteSize: Boolean = ???
  def isEmpty: Boolean = ???
  def seq: scala.collection.TraversableOnce[String] = ???
  def toTraversable: Traversable[String] = ???

class Unimplemented extends TraversableOnce[String] { }
      ^
one error found