Add missing methods to GenTraversableLike.

src/library/scala/collection/GenIterableLike.scala

@@ -141,7 +141,4 @@ trait GenIterableLike[+A, +Repr] extends Any with GenTraversableLike[A, Repr] {
    */
   def zipAll[B, A1 >: A, That](that: GenIterable[B], thisElem: A1, thatElem: B)(implicit bf: CBF[Repr, (A1, B), That]): That
 
-  def isEmpty = iterator.isEmpty
-
-  def head = iterator.next
 }

src/library/scala/collection/GenTraversableLike.scala

@@ -59,24 +59,55 @@ trait GenTraversableLike[+A, +Repr] extends Any with GenTraversableOnce[A] with
 
   def size: Int
 
+  /** Selects the first element of this $coll.
+   *  $orderDependent
+   *  @return  the first element of this $coll.
+   *  @throws `NoSuchElementException` if the $coll is empty.
+   */
   def head: A
-
+
+  /** Optionally selects the first element.
+   *  $orderDependent
+   *  @return  the first element of this $coll if it is nonempty,
+   *           `None` if it is empty.
+   */
+  def headOption: Option[A]
+
   /** Tests whether this $coll can be repeatedly traversed.
    *  @return   `true`
    */
-  final def isTraversableAgain = true
+  def isTraversableAgain: Boolean
 
   /** Selects all elements except the first.
    *  $orderDependent
    *  @return  a $coll consisting of all elements of this $coll
    *           except the first one.
    *  @throws `UnsupportedOperationException` if the $coll is empty.
    */
-  def tail: Repr = {
-    if (isEmpty) throw new UnsupportedOperationException("empty.tail")
-    drop(1)
-  }
+  def tail: Repr
 
+  /** Selects the last element.
+    * $orderDependent
+    * @return The last element of this $coll.
+    * @throws NoSuchElementException If the $coll is empty.
+    */
+  def last: A
+
+  /** Optionally selects the last element.
+   *  $orderDependent
+   *  @return  the last element of this $coll$ if it is nonempty,
+   *           `None` if it is empty.
+   */
+  def lastOption: Option[A]
+
+  /** Selects all elements except the last.
+   *  $orderDependent
+   *  @return  a $coll consisting of all elements of this $coll
+   *           except the last one.
+   *  @throws `UnsupportedOperationException` if the $coll is empty.
+   */
+  def init: Repr
+
   /** Computes a prefix scan of the elements of the collection.
    *
    *  Note: The neutral element `z` may be applied more than once.

src/library/scala/collection/TraversableLike.scala

@@ -84,6 +84,8 @@ trait TraversableLike[+A, +Repr] extends Any
    */
   def repr: Repr = this.asInstanceOf[Repr]
 
+  final def isTraversableAgain: Boolean = true
+
   /** The underlying collection seen as an instance of `$Coll`.
    *  By default this is implemented as the current collection object itself,
    *  but this can be overridden.

src/library/scala/collection/parallel/ParIterableLike.scala

@@ -178,10 +178,30 @@ self: ParIterableLike[T, Repr, Sequential] =>
 
   def repr: Repr = this.asInstanceOf[Repr]
 
+  final def isTraversableAgain = true
+
   def hasDefiniteSize = true
 
+  def isEmpty = size == 0
+
   def nonEmpty = size != 0
-
+
+  def head = iterator.next
+
+  def headOption = if (nonEmpty) Some(head) else None
+
+  def tail = drop(1)
+
+  def last = {
+    var lst = head
+    for (x <- this.seq) lst = x
+    lst
+  }
+
+  def lastOption = if (nonEmpty) Some(last) else None
+
+  def init = take(size - 1)
+
   /** Creates a new parallel iterator used to traverse the elements of this parallel collection.
    *  This iterator is more specific than the iterator of the returned by `iterator`, and augmented
    *  with additional accessor and transformer methods.

test/files/pos/gen-traversable-methods.scala

@@ -0,0 +1,20 @@
+
+
+
+import collection._
+
+
+
+object Test {
+
+  def main(args: Array[String]) {
+    val gen: GenTraversable[Int] = List(1, 2, 3)
+    gen.head
+    gen.headOption
+    gen.tail
+    gen.last
+    gen.lastOption
+    gen.init
+  }
+
+}