Renamed object RedBlack to RedBlackTree.

This more clearly separates the new implementation from the now
deprecated abstract class RedBlack and avoids naming conflicts
for the member classes.

6 files changed, 690 insertions, 469 deletions

diff --git a/src/library/scala/collection/immutable/RedBlack.scala b/src/library/scala/collection/immutable/RedBlack.scala
index 37ff7a7f54..83eeaa45ee 100644
--- a/src/library/scala/collection/immutable/RedBlack.scala
+++ b/src/library/scala/collection/immutable/RedBlack.scala
@@ -11,412 +11,6 @@
 package scala.collection
 package immutable
 
-import annotation.tailrec
-import annotation.meta.getter
-
-/** An object containing the RedBlack tree implementation used by for `TreeMaps` and `TreeSets`.
- *
- *  Implementation note: since efficiency is important for data structures this implementation
- *  uses <code>null</code> to represent empty trees. This also means pattern matching cannot
- *  easily be used. The API represented by the RedBlack object tries to hide these optimizations
- *  behind a reasonably clean API.
- *
- *  @since 2.3
- */
-private[immutable]
-object RedBlack {
-
-  def isBlack(tree: Node[_, _]) = (tree eq null) || isBlackNode(tree)
-  def isRedNode(tree: Node[_, _]) = tree.isInstanceOf[RedNode[_, _]]
-  def isBlackNode(tree: Node[_, _]) = tree.isInstanceOf[BlackNode[_, _]]
-
-  def isEmpty(tree: Node[_, _]): Boolean = tree eq null
-
-  def contains[A](tree: Node[A, _], x: A)(implicit ordering: Ordering[A]): Boolean = lookup(tree, x) ne null
-  def get[A, B](tree: Node[A, B], x: A)(implicit ordering: Ordering[A]): Option[B] = lookup(tree, x) match {
-    case null => None
-    case tree => Some(tree.value)
-  }
-
-  @tailrec
-  def lookup[A, B](tree: Node[A, B], x: A)(implicit ordering: Ordering[A]): Node[A, B] = if (tree eq null) null else {
-    val cmp = ordering.compare(x, tree.key)
-    if (cmp < 0) lookup(tree.left, x)
-    else if (cmp > 0) lookup(tree.right, x)
-    else tree
-  }
-
-  def count(tree: Node[_, _]) = if (tree eq null) 0 else tree.count
-  def update[A, B, B1 >: B](tree: Node[A, B], k: A, v: B1)(implicit ordering: Ordering[A]): Node[A, B1] = blacken(upd(tree, k, v))
-  def delete[A, B](tree: Node[A, B], k: A)(implicit ordering: Ordering[A]): Node[A, B] = blacken(del(tree, k))
-  def range[A, B](tree: Node[A, B], from: Option[A], until: Option[A])(implicit ordering: Ordering[A]): Node[A, B] = blacken(rng(tree, from, until))
-
-  def smallest[A, B](tree: Node[A, B]): Node[A, B] = {
-    if (tree eq null) throw new NoSuchElementException("empty map")
-    var result = tree
-    while (result.left ne null) result = result.left
-    result
-  }
-  def greatest[A, B](tree: Node[A, B]): Node[A, B] = {
-    if (tree eq null) throw new NoSuchElementException("empty map")
-    var result = tree
-    while (result.right ne null) result = result.right
-    result
-  }
-
-  def foreach[A, B, U](tree: Node[A, B], f: ((A, B)) => U): Unit = if (tree ne null) {
-    if (tree.left ne null) foreach(tree.left, f)
-    f((tree.key, tree.value))
-    if (tree.right ne null) foreach(tree.right, f)
-  }
-  def foreachKey[A, U](tree: Node[A, _], f: A => U): Unit = if (tree ne null) {
-    if (tree.left ne null) foreachKey(tree.left, f)
-    f(tree.key)
-    if (tree.right ne null) foreachKey(tree.right, f)
-  }
-
-  def iterator[A, B](tree: Node[A, B]): Iterator[(A, B)] = new EntriesIterator(tree)
-  def keysIterator[A, _](tree: Node[A, _]): Iterator[A] = new KeysIterator(tree)
-  def valuesIterator[_, B](tree: Node[_, B]): Iterator[B] = new ValuesIterator(tree)
-
-  @tailrec
-  def nth[A, B](tree: Node[A, B], n: Int): Node[A, B] = {
-    val count = RedBlack.count(tree.left)
-    if (n < count) nth(tree.left, n)
-    else if (n > count) nth(tree.right, n - count - 1)
-    else tree
-  }
-
-  private def blacken[A, B](t: Node[A, B]): Node[A, B] = if (t eq null) null else t.black
-
-  private def mkNode[A, B](isBlack: Boolean, k: A, v: B, l: Node[A, B], r: Node[A, B]) =
-    if (isBlack) BlackNode(k, v, l, r) else RedNode(k, v, l, r)
-
-  private[this] def balanceLeft[A, B, B1 >: B](isBlack: Boolean, z: A, zv: B, l: Node[A, B1], d: Node[A, B1]): Node[A, B1] = {
-    if (isRedNode(l) && isRedNode(l.left))
-      RedNode(l.key, l.value, BlackNode(l.left.key, l.left.value, l.left.left, l.left.right), BlackNode(z, zv, l.right, d))
-    else if (isRedNode(l) && isRedNode(l.right))
-      RedNode(l.right.key, l.right.value, BlackNode(l.key, l.value, l.left, l.right.left), BlackNode(z, zv, l.right.right, d))
-    else
-      mkNode(isBlack, z, zv, l, d)
-  }
-  private[this] def balanceRight[A, B, B1 >: B](isBlack: Boolean, x: A, xv: B, a: Node[A, B1], r: Node[A, B1]): Node[A, B1] = {
-    if (isRedNode(r) && isRedNode(r.left))
-      RedNode(r.left.key, r.left.value, BlackNode(x, xv, a, r.left.left), BlackNode(r.key, r.value, r.left.right, r.right))
-    else if (isRedNode(r) && isRedNode(r.right))
-      RedNode(r.key, r.value, BlackNode(x, xv, a, r.left), BlackNode(r.right.key, r.right.value, r.right.left, r.right.right))
-    else
-      mkNode(isBlack, x, xv, a, r)
-  }
-  private[this] def upd[A, B, B1 >: B](tree: Node[A, B], k: A, v: B1)(implicit ordering: Ordering[A]): Node[A, B1] = if (tree eq null) {
-    RedNode(k, v, null, null)
-  } else {
-    val cmp = ordering.compare(k, tree.key)
-    if (cmp < 0) balanceLeft(tree.isBlack, tree.key, tree.value, upd(tree.left, k, v), tree.right)
-    else if (cmp > 0) balanceRight(tree.isBlack, tree.key, tree.value, tree.left, upd(tree.right, k, v))
-    else mkNode(tree.isBlack, k, v, tree.left, tree.right)
-  }
-
-    // Based on Stefan Kahrs' Haskell version of Okasaki's Red&Black Trees
-    // http://www.cse.unsw.edu.au/~dons/data/RedBlackNode.html
-  private[this] def del[A, B](tree: Node[A, B], k: A)(implicit ordering: Ordering[A]): Node[A, B] = if (tree eq null) null else {
-    def balance(x: A, xv: B, tl: Node[A, B], tr: Node[A, B]) = if (isRedNode(tl)) {
-      if (isRedNode(tr)) {
-        RedNode(x, xv, tl.black, tr.black)
-      } else if (isRedNode(tl.left)) {
-        RedNode(tl.key, tl.value, tl.left.black, BlackNode(x, xv, tl.right, tr))
-      } else if (isRedNode(tl.right)) {
-        RedNode(tl.right.key, tl.right.value, BlackNode(tl.key, tl.value, tl.left, tl.right.left), BlackNode(x, xv, tl.right.right, tr))
-      } else {
-        BlackNode(x, xv, tl, tr)
-      }
-    } else if (isRedNode(tr)) {
-      if (isRedNode(tr.right)) {
-        RedNode(tr.key, tr.value, BlackNode(x, xv, tl, tr.left), tr.right.black)
-      } else if (isRedNode(tr.left)) {
-        RedNode(tr.left.key, tr.left.value, BlackNode(x, xv, tl, tr.left.left), BlackNode(tr.key, tr.value, tr.left.right, tr.right))
-      } else {
-        BlackNode(x, xv, tl, tr)
-      }
-    } else {
-      BlackNode(x, xv, tl, tr)
-    }
-    def subl(t: Node[A, B]) =
-      if (t.isInstanceOf[BlackNode[_, _]]) t.red
-      else sys.error("Defect: invariance violation; expected black, got "+t)
-
-    def balLeft(x: A, xv: B, tl: Node[A, B], tr: Node[A, B]) = if (isRedNode(tl)) {
-      RedNode(x, xv, tl.black, tr)
-    } else if (isBlackNode(tr)) {
-      balance(x, xv, tl, tr.red)
-    } else if (isRedNode(tr) && isBlackNode(tr.left)) {
-      RedNode(tr.left.key, tr.left.value, BlackNode(x, xv, tl, tr.left.left), balance(tr.key, tr.value, tr.left.right, subl(tr.right)))
-    } else {
-      sys.error("Defect: invariance violation")
-    }
-    def balRight(x: A, xv: B, tl: Node[A, B], tr: Node[A, B]) = if (isRedNode(tr)) {
-      RedNode(x, xv, tl, tr.black)
-    } else if (isBlackNode(tl)) {
-      balance(x, xv, tl.red, tr)
-    } else if (isRedNode(tl) && isBlackNode(tl.right)) {
-      RedNode(tl.right.key, tl.right.value, balance(tl.key, tl.value, subl(tl.left), tl.right.left), BlackNode(x, xv, tl.right.right, tr))
-    } else {
-      sys.error("Defect: invariance violation")
-    }
-    def delLeft = if (isBlackNode(tree.left)) balLeft(tree.key, tree.value, del(tree.left, k), tree.right) else RedNode(tree.key, tree.value, del(tree.left, k), tree.right)
-    def delRight = if (isBlackNode(tree.right)) balRight(tree.key, tree.value, tree.left, del(tree.right, k)) else RedNode(tree.key, tree.value, tree.left, del(tree.right, k))
-    def append(tl: Node[A, B], tr: Node[A, B]): Node[A, B] = if (tl eq null) {
-      tr
-    } else if (tr eq null) {
-      tl
-    } else if (isRedNode(tl) && isRedNode(tr)) {
-      val bc = append(tl.right, tr.left)
-      if (isRedNode(bc)) {
-        RedNode(bc.key, bc.value, RedNode(tl.key, tl.value, tl.left, bc.left), RedNode(tr.key, tr.value, bc.right, tr.right))
-      } else {
-        RedNode(tl.key, tl.value, tl.left, RedNode(tr.key, tr.value, bc, tr.right))
-      }
-    } else if (isBlackNode(tl) && isBlackNode(tr)) {
-      val bc = append(tl.right, tr.left)
-      if (isRedNode(bc)) {
-        RedNode(bc.key, bc.value, BlackNode(tl.key, tl.value, tl.left, bc.left), BlackNode(tr.key, tr.value, bc.right, tr.right))
-      } else {
-        balLeft(tl.key, tl.value, tl.left, BlackNode(tr.key, tr.value, bc, tr.right))
-      }
-    } else if (isRedNode(tr)) {
-      RedNode(tr.key, tr.value, append(tl, tr.left), tr.right)
-    } else if (isRedNode(tl)) {
-      RedNode(tl.key, tl.value, tl.left, append(tl.right, tr))
-    } else {
-      sys.error("unmatched tree on append: " + tl + ", " + tr)
-    }
-
-    val cmp = ordering.compare(k, tree.key)
-    if (cmp < 0) delLeft
-    else if (cmp > 0) delRight
-    else append(tree.left, tree.right)
-  }
-
-  private[this] def rng[A, B](tree: Node[A, B], from: Option[A], until: Option[A])(implicit ordering: Ordering[A]): Node[A, B] = {
-    if (tree eq null) return null
-    if (from == None && until == None) return tree
-    if (from != None && ordering.lt(tree.key, from.get)) return rng(tree.right, from, until);
-    if (until != None && ordering.lteq(until.get, tree.key)) return rng(tree.left, from, until);
-    val newLeft = rng(tree.left, from, None)
-    val newRight = rng(tree.right, None, until)
-    if ((newLeft eq tree.left) && (newRight eq tree.right)) tree
-    else if (newLeft eq null) upd(newRight, tree.key, tree.value);
-    else if (newRight eq null) upd(newLeft, tree.key, tree.value);
-    else rebalance(tree, newLeft, newRight)
-  }
-
-  // The zipper returned might have been traversed left-most (always the left child)
-  // or right-most (always the right child). Left trees are traversed right-most,
-  // and right trees are traversed leftmost.
-
-  // Returns the zipper for the side with deepest black nodes depth, a flag
-  // indicating whether the trees were unbalanced at all, and a flag indicating
-  // whether the zipper was traversed left-most or right-most.
-
-  // If the trees were balanced, returns an empty zipper
-  private[this] def compareDepth[A, B](left: Node[A, B], right: Node[A, B]): (List[Node[A, B]], Boolean, Boolean, Int) = {
-    // Once a side is found to be deeper, unzip it to the bottom
-    def unzip(zipper: List[Node[A, B]], leftMost: Boolean): List[Node[A, B]] = {
-      val next = if (leftMost) zipper.head.left else zipper.head.right
-      next match {
-        case null => zipper
-        case node => unzip(node :: zipper, leftMost)
-      }
-    }
-
-    // Unzip left tree on the rightmost side and right tree on the leftmost side until one is
-    // found to be deeper, or the bottom is reached
-    def unzipBoth(left: Node[A, B],
-                  right: Node[A, B],
-                  leftZipper: List[Node[A, B]],
-                  rightZipper: List[Node[A, B]],
-                  smallerDepth: Int): (List[Node[A, B]], Boolean, Boolean, Int) = {
-      if (isBlackNode(left) && isBlackNode(right)) {
-        unzipBoth(left.right, right.left, left :: leftZipper, right :: rightZipper, smallerDepth + 1)
-      } else if (isRedNode(left) && isRedNode(right)) {
-        unzipBoth(left.right, right.left, left :: leftZipper, right :: rightZipper, smallerDepth)
-      } else if (isRedNode(right)) {
-        unzipBoth(left, right.left, leftZipper, right :: rightZipper, smallerDepth)
-      } else if (isRedNode(left)) {
-        unzipBoth(left.right, right, left :: leftZipper, rightZipper, smallerDepth)
-      } else if ((left eq null) && (right eq null)) {
-        (Nil, true, false, smallerDepth)
-      } else if ((left eq null) && isBlackNode(right)) {
-        val leftMost = true
-        (unzip(right :: rightZipper, leftMost), false, leftMost, smallerDepth)
-      } else if (isBlackNode(left) && (right eq null)) {
-        val leftMost = false
-        (unzip(left :: leftZipper, leftMost), false, leftMost, smallerDepth)
-      } else {
-        sys.error("unmatched trees in unzip: " + left + ", " + right)
-      }
-    }
-    unzipBoth(left, right, Nil, Nil, 0)
-  }
-  private[this] def rebalance[A, B](tree: Node[A, B], newLeft: Node[A, B], newRight: Node[A, B]) = {
-    // This is like drop(n-1), but only counting black nodes
-    def  findDepth(zipper: List[Node[A, B]], depth: Int): List[Node[A, B]] = zipper match {
-      case head :: tail if isBlackNode(head) =>
-        if (depth == 1) zipper else findDepth(tail, depth - 1)
-      case _ :: tail => findDepth(tail, depth)
-      case Nil => sys.error("Defect: unexpected empty zipper while computing range")
-    }
-
-    // Blackening the smaller tree avoids balancing problems on union;
-    // this can't be done later, though, or it would change the result of compareDepth
-    val blkNewLeft = blacken(newLeft)
-    val blkNewRight = blacken(newRight)
-    val (zipper, levelled, leftMost, smallerDepth) = compareDepth(blkNewLeft, blkNewRight)
-
-    if (levelled) {
-      BlackNode(tree.key, tree.value, blkNewLeft, blkNewRight)
-    } else {
-      val zipFrom = findDepth(zipper, smallerDepth)
-      val union = if (leftMost) {
-        RedNode(tree.key, tree.value, blkNewLeft, zipFrom.head)
-      } else {
-        RedNode(tree.key, tree.value, zipFrom.head, blkNewRight)
-      }
-      val zippedTree = zipFrom.tail.foldLeft(union: Node[A, B]) { (tree, node) =>
-        if (leftMost)
-          balanceLeft(node.isBlack, node.key, node.value, tree, node.right)
-        else
-          balanceRight(node.isBlack, node.key, node.value, node.left, tree)
-      }
-      zippedTree
-    }
-  }
-
-  /*
-   * Forcing direct fields access using the @inline annotation helps speed up
-   * various operations (especially smallest/greatest and update/delete).
-   *
-   * Unfortunately the direct field access is not guaranteed to work (but
-   * works on the current implementation of the Scala compiler).
-   *
-   * An alternative is to implement the these classes using plain old Java code...
-   */
-  sealed abstract class Node[A, +B](
-    @(inline @getter) final val key: A,
-    @(inline @getter) final val value: B,
-    @(inline @getter) final val left: Node[A, B],
-    @(inline @getter) final val right: Node[A, B])
-  extends Serializable {
-    final val count: Int = 1 + RedBlack.count(left) + RedBlack.count(right)
-    def isBlack: Boolean
-    def black: Node[A, B]
-    def red: Node[A, B]
-  }
-  final class RedNode[A, +B](key: A,
-                             value: B,
-                             left: Node[A, B],
-                             right: Node[A, B]) extends Node[A, B](key, value, left, right) {
-    override def isBlack = false
-    override def black = BlackNode(key, value, left, right)
-    override def red = this
-    override def toString = "RedNode(" + key + ", " + value + ", " + left + ", " + right + ")"
-  }
-  final class BlackNode[A, +B](key: A,
-                               value: B,
-                               left: Node[A, B],
-                               right: Node[A, B]) extends Node[A, B](key, value, left, right) {
-    override def isBlack = true
-    override def black = this
-    override def red = RedNode(key, value, left, right)
-    override def toString = "BlackNode(" + key + ", " + value + ", " + left + ", " + right + ")"
-  }
-
-  object RedNode {
-    @inline def apply[A, B](key: A, value: B, left: Node[A, B], right: Node[A, B]) = new RedNode(key, value, left, right)
-    def unapply[A, B](t: RedNode[A, B]) = Some((t.key, t.value, t.left, t.right))
-  }
-  object BlackNode {
-    @inline def apply[A, B](key: A, value: B, left: Node[A, B], right: Node[A, B]) = new BlackNode(key, value, left, right)
-    def unapply[A, B](t: BlackNode[A, B]) = Some((t.key, t.value, t.left, t.right))
-  }
-
-  private[this] abstract class TreeIterator[A, B, R](tree: Node[A, B]) extends Iterator[R] {
-    protected[this] def nextResult(tree: Node[A, B]): R
-
-    override def hasNext: Boolean = next ne null
-
-    override def next: R = next match {
-      case null =>
-        throw new NoSuchElementException("next on empty iterator")
-      case tree =>
-        next = findNext(tree.right)
-        nextResult(tree)
-    }
-
-    @tailrec
-    private[this] def findNext(tree: Node[A, B]): Node[A, B] = {
-      if (tree eq null) popPath()
-      else if (tree.left eq null) tree
-      else {
-        pushPath(tree)
-        findNext(tree.left)
-      }
-    }
-
-    private[this] def pushPath(tree: Node[A, B]) {
-      try {
-        path(index) = tree
-        index += 1
-      } catch {
-        case _: ArrayIndexOutOfBoundsException =>
-          /*
-           * Either the tree became unbalanced or we calculated the maximum height incorrectly.
-           * To avoid crashing the iterator we expand the path array. Obviously this should never
-           * happen...
-           *
-           * An exception handler is used instead of an if-condition to optimize the normal path.
-           * This makes a large difference in iteration speed!
-           */
-          assert(index >= path.length)
-          path :+= null
-          pushPath(tree)
-      }
-    }
-    private[this] def popPath(): Node[A, B] = if (index == 0) null else {
-      index -= 1
-      path(index)
-    }
-
-    private[this] var path = if (tree eq null) null else {
-      /*
-       * According to "Ralf Hinze. Constructing red-black trees" [http://www.cs.ox.ac.uk/ralf.hinze/publications/#P5]
-       * the maximum height of a red-black tree is 2*log_2(n + 2) - 2.
-       *
-       * According to {@see Integer#numberOfLeadingZeros} ceil(log_2(n)) = (32 - Integer.numberOfLeadingZeros(n - 1))
-       *
-       * We also don't store the deepest nodes in the path so the maximum path length is further reduced by one.
-       */
-      val maximumHeight = 2 * (32 - Integer.numberOfLeadingZeros(tree.count + 2 - 1)) - 2 - 1
-      new Array[Node[A, B]](maximumHeight)
-    }
-    private[this] var index = 0
-    private[this] var next: Node[A, B] = findNext(tree)
-  }
-
-  private[this] class EntriesIterator[A, B](tree: Node[A, B]) extends TreeIterator[A, B, (A, B)](tree) {
-    override def nextResult(tree: Node[A, B]) = (tree.key, tree.value)
-  }
-
-  private[this] class KeysIterator[A, B](tree: Node[A, B]) extends TreeIterator[A, B, A](tree) {
-    override def nextResult(tree: Node[A, B]) = tree.key
-  }
-
-  private[this] class ValuesIterator[A, B](tree: Node[A, B]) extends TreeIterator[A, B, B](tree) {
-    override def nextResult(tree: Node[A, B]) = tree.value
-  }
-}
-
-
 /** Old base class that was used by previous implementations of `TreeMaps` and `TreeSets`.
  *
  *  Deprecated due to various performance bugs (see [[https://issues.scala-lang.org/browse/SI-5331 SI-5331]] for more information).
diff --git a/src/library/scala/collection/immutable/RedBlackTree.scala b/src/library/scala/collection/immutable/RedBlackTree.scala
new file mode 100644
index 0000000000..ebd88ce3fe
--- /dev/null
+++ b/src/library/scala/collection/immutable/RedBlackTree.scala
@@ -0,0 +1,416 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2005-2011, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+
+
+package scala.collection
+package immutable
+
+import annotation.tailrec
+import annotation.meta.getter
+
+/** An object containing the RedBlack tree implementation used by for `TreeMaps` and `TreeSets`.
+ *
+ *  Implementation note: since efficiency is important for data structures this implementation
+ *  uses <code>null</code> to represent empty trees. This also means pattern matching cannot
+ *  easily be used. The API represented by the RedBlackTree object tries to hide these
+ *  optimizations behind a reasonably clean API.
+ *
+ *  @since 2.10
+ */
+private[immutable]
+object RedBlackTree {
+
+  def isEmpty(tree: Tree[_, _]): Boolean = tree eq null
+
+  def contains[A](tree: Tree[A, _], x: A)(implicit ordering: Ordering[A]): Boolean = lookup(tree, x) ne null
+  def get[A, B](tree: Tree[A, B], x: A)(implicit ordering: Ordering[A]): Option[B] = lookup(tree, x) match {
+    case null => None
+    case tree => Some(tree.value)
+  }
+
+  @tailrec
+  def lookup[A, B](tree: Tree[A, B], x: A)(implicit ordering: Ordering[A]): Tree[A, B] = if (tree eq null) null else {
+    val cmp = ordering.compare(x, tree.key)
+    if (cmp < 0) lookup(tree.left, x)
+    else if (cmp > 0) lookup(tree.right, x)
+    else tree
+  }
+
+  def count(tree: Tree[_, _]) = if (tree eq null) 0 else tree.count
+  def update[A, B, B1 >: B](tree: Tree[A, B], k: A, v: B1)(implicit ordering: Ordering[A]): Tree[A, B1] = blacken(upd(tree, k, v))
+  def delete[A, B](tree: Tree[A, B], k: A)(implicit ordering: Ordering[A]): Tree[A, B] = blacken(del(tree, k))
+  def range[A, B](tree: Tree[A, B], from: Option[A], until: Option[A])(implicit ordering: Ordering[A]): Tree[A, B] = blacken(rng(tree, from, until))
+
+  def smallest[A, B](tree: Tree[A, B]): Tree[A, B] = {
+    if (tree eq null) throw new NoSuchElementException("empty map")
+    var result = tree
+    while (result.left ne null) result = result.left
+    result
+  }
+  def greatest[A, B](tree: Tree[A, B]): Tree[A, B] = {
+    if (tree eq null) throw new NoSuchElementException("empty map")
+    var result = tree
+    while (result.right ne null) result = result.right
+    result
+  }
+
+  def foreach[A, B, U](tree: Tree[A, B], f: ((A, B)) => U): Unit = if (tree ne null) {
+    if (tree.left ne null) foreach(tree.left, f)
+    f((tree.key, tree.value))
+    if (tree.right ne null) foreach(tree.right, f)
+  }
+  def foreachKey[A, U](tree: Tree[A, _], f: A => U): Unit = if (tree ne null) {
+    if (tree.left ne null) foreachKey(tree.left, f)
+    f(tree.key)
+    if (tree.right ne null) foreachKey(tree.right, f)
+  }
+
+  def iterator[A, B](tree: Tree[A, B]): Iterator[(A, B)] = new EntriesIterator(tree)
+  def keysIterator[A, _](tree: Tree[A, _]): Iterator[A] = new KeysIterator(tree)
+  def valuesIterator[_, B](tree: Tree[_, B]): Iterator[B] = new ValuesIterator(tree)
+
+  @tailrec
+  def nth[A, B](tree: Tree[A, B], n: Int): Tree[A, B] = {
+    val count = RedBlackTree.count(tree.left)
+    if (n < count) nth(tree.left, n)
+    else if (n > count) nth(tree.right, n - count - 1)
+    else tree
+  }
+
+  def isBlack(tree: Tree[_, _]) = (tree eq null) || isBlackTree(tree)
+
+  private[this] def isRedTree(tree: Tree[_, _]) = tree.isInstanceOf[RedTree[_, _]]
+  private[this] def isBlackTree(tree: Tree[_, _]) = tree.isInstanceOf[BlackTree[_, _]]
+
+  private[this] def blacken[A, B](t: Tree[A, B]): Tree[A, B] = if (t eq null) null else t.black
+
+  private[this] def mkTree[A, B](isBlack: Boolean, k: A, v: B, l: Tree[A, B], r: Tree[A, B]) =
+    if (isBlack) BlackTree(k, v, l, r) else RedTree(k, v, l, r)
+
+  private[this] def balanceLeft[A, B, B1 >: B](isBlack: Boolean, z: A, zv: B, l: Tree[A, B1], d: Tree[A, B1]): Tree[A, B1] = {
+    if (isRedTree(l) && isRedTree(l.left))
+      RedTree(l.key, l.value, BlackTree(l.left.key, l.left.value, l.left.left, l.left.right), BlackTree(z, zv, l.right, d))
+    else if (isRedTree(l) && isRedTree(l.right))
+      RedTree(l.right.key, l.right.value, BlackTree(l.key, l.value, l.left, l.right.left), BlackTree(z, zv, l.right.right, d))
+    else
+      mkTree(isBlack, z, zv, l, d)
+  }
+  private[this] def balanceRight[A, B, B1 >: B](isBlack: Boolean, x: A, xv: B, a: Tree[A, B1], r: Tree[A, B1]): Tree[A, B1] = {
+    if (isRedTree(r) && isRedTree(r.left))
+      RedTree(r.left.key, r.left.value, BlackTree(x, xv, a, r.left.left), BlackTree(r.key, r.value, r.left.right, r.right))
+    else if (isRedTree(r) && isRedTree(r.right))
+      RedTree(r.key, r.value, BlackTree(x, xv, a, r.left), BlackTree(r.right.key, r.right.value, r.right.left, r.right.right))
+    else
+      mkTree(isBlack, x, xv, a, r)
+  }
+  private[this] def upd[A, B, B1 >: B](tree: Tree[A, B], k: A, v: B1)(implicit ordering: Ordering[A]): Tree[A, B1] = if (tree eq null) {
+    RedTree(k, v, null, null)
+  } else {
+    val cmp = ordering.compare(k, tree.key)
+    if (cmp < 0) balanceLeft(isBlackTree(tree), tree.key, tree.value, upd(tree.left, k, v), tree.right)
+    else if (cmp > 0) balanceRight(isBlackTree(tree), tree.key, tree.value, tree.left, upd(tree.right, k, v))
+    else mkTree(isBlackTree(tree), k, v, tree.left, tree.right)
+  }
+
+  // Based on Stefan Kahrs' Haskell version of Okasaki's Red&Black Trees
+  // http://www.cse.unsw.edu.au/~dons/data/RedBlackTree.html
+  private[this] def del[A, B](tree: Tree[A, B], k: A)(implicit ordering: Ordering[A]): Tree[A, B] = if (tree eq null) null else {
+    def balance(x: A, xv: B, tl: Tree[A, B], tr: Tree[A, B]) = if (isRedTree(tl)) {
+      if (isRedTree(tr)) {
+        RedTree(x, xv, tl.black, tr.black)
+      } else if (isRedTree(tl.left)) {
+        RedTree(tl.key, tl.value, tl.left.black, BlackTree(x, xv, tl.right, tr))
+      } else if (isRedTree(tl.right)) {
+        RedTree(tl.right.key, tl.right.value, BlackTree(tl.key, tl.value, tl.left, tl.right.left), BlackTree(x, xv, tl.right.right, tr))
+      } else {
+        BlackTree(x, xv, tl, tr)
+      }
+    } else if (isRedTree(tr)) {
+      if (isRedTree(tr.right)) {
+        RedTree(tr.key, tr.value, BlackTree(x, xv, tl, tr.left), tr.right.black)
+      } else if (isRedTree(tr.left)) {
+        RedTree(tr.left.key, tr.left.value, BlackTree(x, xv, tl, tr.left.left), BlackTree(tr.key, tr.value, tr.left.right, tr.right))
+      } else {
+        BlackTree(x, xv, tl, tr)
+      }
+    } else {
+      BlackTree(x, xv, tl, tr)
+    }
+    def subl(t: Tree[A, B]) =
+      if (t.isInstanceOf[BlackTree[_, _]]) t.red
+      else sys.error("Defect: invariance violation; expected black, got "+t)
+
+    def balLeft(x: A, xv: B, tl: Tree[A, B], tr: Tree[A, B]) = if (isRedTree(tl)) {
+      RedTree(x, xv, tl.black, tr)
+    } else if (isBlackTree(tr)) {
+      balance(x, xv, tl, tr.red)
+    } else if (isRedTree(tr) && isBlackTree(tr.left)) {
+      RedTree(tr.left.key, tr.left.value, BlackTree(x, xv, tl, tr.left.left), balance(tr.key, tr.value, tr.left.right, subl(tr.right)))
+    } else {
+      sys.error("Defect: invariance violation at ") // TODO
+    }
+    def balRight(x: A, xv: B, tl: Tree[A, B], tr: Tree[A, B]) = if (isRedTree(tr)) {
+      RedTree(x, xv, tl, tr.black)
+    } else if (isBlackTree(tl)) {
+      balance(x, xv, tl.red, tr)
+    } else if (isRedTree(tl) && isBlackTree(tl.right)) {
+      RedTree(tl.right.key, tl.right.value, balance(tl.key, tl.value, subl(tl.left), tl.right.left), BlackTree(x, xv, tl.right.right, tr))
+    } else {
+      sys.error("Defect: invariance violation at ") // TODO
+    }
+    def delLeft = if (isBlackTree(tree.left)) balLeft(tree.key, tree.value, del(tree.left, k), tree.right) else RedTree(tree.key, tree.value, del(tree.left, k), tree.right)
+    def delRight = if (isBlackTree(tree.right)) balRight(tree.key, tree.value, tree.left, del(tree.right, k)) else RedTree(tree.key, tree.value, tree.left, del(tree.right, k))
+    def append(tl: Tree[A, B], tr: Tree[A, B]): Tree[A, B] = if (tl eq null) {
+      tr
+    } else if (tr eq null) {
+      tl
+    } else if (isRedTree(tl) && isRedTree(tr)) {
+      val bc = append(tl.right, tr.left)
+      if (isRedTree(bc)) {
+        RedTree(bc.key, bc.value, RedTree(tl.key, tl.value, tl.left, bc.left), RedTree(tr.key, tr.value, bc.right, tr.right))
+      } else {
+        RedTree(tl.key, tl.value, tl.left, RedTree(tr.key, tr.value, bc, tr.right))
+      }
+    } else if (isBlackTree(tl) && isBlackTree(tr)) {
+      val bc = append(tl.right, tr.left)
+      if (isRedTree(bc)) {
+        RedTree(bc.key, bc.value, BlackTree(tl.key, tl.value, tl.left, bc.left), BlackTree(tr.key, tr.value, bc.right, tr.right))
+      } else {
+        balLeft(tl.key, tl.value, tl.left, BlackTree(tr.key, tr.value, bc, tr.right))
+      }
+    } else if (isRedTree(tr)) {
+      RedTree(tr.key, tr.value, append(tl, tr.left), tr.right)
+    } else if (isRedTree(tl)) {
+      RedTree(tl.key, tl.value, tl.left, append(tl.right, tr))
+    } else {
+      sys.error("unmatched tree on append: " + tl + ", " + tr)
+    }
+
+    val cmp = ordering.compare(k, tree.key)
+    if (cmp < 0) delLeft
+    else if (cmp > 0) delRight
+    else append(tree.left, tree.right)
+  }
+
+  private[this] def rng[A, B](tree: Tree[A, B], from: Option[A], until: Option[A])(implicit ordering: Ordering[A]): Tree[A, B] = {
+    if (tree eq null) return null
+    if (from == None && until == None) return tree
+    if (from != None && ordering.lt(tree.key, from.get)) return rng(tree.right, from, until);
+    if (until != None && ordering.lteq(until.get, tree.key)) return rng(tree.left, from, until);
+    val newLeft = rng(tree.left, from, None)
+    val newRight = rng(tree.right, None, until)
+    if ((newLeft eq tree.left) && (newRight eq tree.right)) tree
+    else if (newLeft eq null) upd(newRight, tree.key, tree.value);
+    else if (newRight eq null) upd(newLeft, tree.key, tree.value);
+    else rebalance(tree, newLeft, newRight)
+  }
+
+  // The zipper returned might have been traversed left-most (always the left child)
+  // or right-most (always the right child). Left trees are traversed right-most,
+  // and right trees are traversed leftmost.
+
+  // Returns the zipper for the side with deepest black nodes depth, a flag
+  // indicating whether the trees were unbalanced at all, and a flag indicating
+  // whether the zipper was traversed left-most or right-most.
+
+  // If the trees were balanced, returns an empty zipper
+  private[this] def compareDepth[A, B](left: Tree[A, B], right: Tree[A, B]): (List[Tree[A, B]], Boolean, Boolean, Int) = {
+    // Once a side is found to be deeper, unzip it to the bottom
+    def unzip(zipper: List[Tree[A, B]], leftMost: Boolean): List[Tree[A, B]] = {
+      val next = if (leftMost) zipper.head.left else zipper.head.right
+      next match {
+        case null => zipper
+        case node => unzip(node :: zipper, leftMost)
+      }
+    }
+
+    // Unzip left tree on the rightmost side and right tree on the leftmost side until one is
+    // found to be deeper, or the bottom is reached
+    def unzipBoth(left: Tree[A, B],
+                  right: Tree[A, B],
+                  leftZipper: List[Tree[A, B]],
+                  rightZipper: List[Tree[A, B]],
+                  smallerDepth: Int): (List[Tree[A, B]], Boolean, Boolean, Int) = {
+      if (isBlackTree(left) && isBlackTree(right)) {
+        unzipBoth(left.right, right.left, left :: leftZipper, right :: rightZipper, smallerDepth + 1)
+      } else if (isRedTree(left) && isRedTree(right)) {
+        unzipBoth(left.right, right.left, left :: leftZipper, right :: rightZipper, smallerDepth)
+      } else if (isRedTree(right)) {
+        unzipBoth(left, right.left, leftZipper, right :: rightZipper, smallerDepth)
+      } else if (isRedTree(left)) {
+        unzipBoth(left.right, right, left :: leftZipper, rightZipper, smallerDepth)
+      } else if ((left eq null) && (right eq null)) {
+        (Nil, true, false, smallerDepth)
+      } else if ((left eq null) && isBlackTree(right)) {
+        val leftMost = true
+        (unzip(right :: rightZipper, leftMost), false, leftMost, smallerDepth)
+      } else if (isBlackTree(left) && (right eq null)) {
+        val leftMost = false
+        (unzip(left :: leftZipper, leftMost), false, leftMost, smallerDepth)
+      } else {
+        sys.error("unmatched trees in unzip: " + left + ", " + right)
+      }
+    }
+    unzipBoth(left, right, Nil, Nil, 0)
+  }
+
+  private[this] def rebalance[A, B](tree: Tree[A, B], newLeft: Tree[A, B], newRight: Tree[A, B]) = {
+    // This is like drop(n-1), but only counting black nodes
+    def  findDepth(zipper: List[Tree[A, B]], depth: Int): List[Tree[A, B]] = zipper match {
+      case head :: tail if isBlackTree(head) =>
+        if (depth == 1) zipper else findDepth(tail, depth - 1)
+      case _ :: tail => findDepth(tail, depth)
+      case Nil => sys.error("Defect: unexpected empty zipper while computing range")
+    }
+
+    // Blackening the smaller tree avoids balancing problems on union;
+    // this can't be done later, though, or it would change the result of compareDepth
+    val blkNewLeft = blacken(newLeft)
+    val blkNewRight = blacken(newRight)
+    val (zipper, levelled, leftMost, smallerDepth) = compareDepth(blkNewLeft, blkNewRight)
+
+    if (levelled) {
+      BlackTree(tree.key, tree.value, blkNewLeft, blkNewRight)
+    } else {
+      val zipFrom = findDepth(zipper, smallerDepth)
+      val union = if (leftMost) {
+        RedTree(tree.key, tree.value, blkNewLeft, zipFrom.head)
+      } else {
+        RedTree(tree.key, tree.value, zipFrom.head, blkNewRight)
+      }
+      val zippedTree = zipFrom.tail.foldLeft(union: Tree[A, B]) { (tree, node) =>
+        if (leftMost)
+          balanceLeft(isBlackTree(node), node.key, node.value, tree, node.right)
+        else
+          balanceRight(isBlackTree(node), node.key, node.value, node.left, tree)
+      }
+      zippedTree
+    }
+  }
+
+  /*
+   * Forcing direct fields access using the @inline annotation helps speed up
+   * various operations (especially smallest/greatest and update/delete).
+   *
+   * Unfortunately the direct field access is not guaranteed to work (but
+   * works on the current implementation of the Scala compiler).
+   *
+   * An alternative is to implement the these classes using plain old Java code...
+   */
+  sealed abstract class Tree[A, +B](
+    @(inline @getter) final val key: A,
+    @(inline @getter) final val value: B,
+    @(inline @getter) final val left: Tree[A, B],
+    @(inline @getter) final val right: Tree[A, B])
+  extends Serializable {
+    final val count: Int = 1 + RedBlackTree.count(left) + RedBlackTree.count(right)
+    def black: Tree[A, B]
+    def red: Tree[A, B]
+  }
+  final class RedTree[A, +B](key: A,
+                             value: B,
+                             left: Tree[A, B],
+                             right: Tree[A, B]) extends Tree[A, B](key, value, left, right) {
+    override def black: Tree[A, B] = BlackTree(key, value, left, right)
+    override def red: Tree[A, B] = this
+    override def toString: String = "RedTree(" + key + ", " + value + ", " + left + ", " + right + ")"
+  }
+  final class BlackTree[A, +B](key: A,
+                               value: B,
+                               left: Tree[A, B],
+                               right: Tree[A, B]) extends Tree[A, B](key, value, left, right) {
+    override def black: Tree[A, B] = this
+    override def red: Tree[A, B] = RedTree(key, value, left, right)
+    override def toString: String = "BlackTree(" + key + ", " + value + ", " + left + ", " + right + ")"
+  }
+
+  object RedTree {
+    @inline def apply[A, B](key: A, value: B, left: Tree[A, B], right: Tree[A, B]) = new RedTree(key, value, left, right)
+    def unapply[A, B](t: RedTree[A, B]) = Some((t.key, t.value, t.left, t.right))
+  }
+  object BlackTree {
+    @inline def apply[A, B](key: A, value: B, left: Tree[A, B], right: Tree[A, B]) = new BlackTree(key, value, left, right)
+    def unapply[A, B](t: BlackTree[A, B]) = Some((t.key, t.value, t.left, t.right))
+  }
+
+  private[this] abstract class TreeIterator[A, B, R](tree: Tree[A, B]) extends Iterator[R] {
+    protected[this] def nextResult(tree: Tree[A, B]): R
+
+    override def hasNext: Boolean = next ne null
+
+    override def next: R = next match {
+      case null =>
+        throw new NoSuchElementException("next on empty iterator")
+      case tree =>
+        next = findNext(tree.right)
+        nextResult(tree)
+    }
+
+    @tailrec
+    private[this] def findNext(tree: Tree[A, B]): Tree[A, B] = {
+      if (tree eq null) popPath()
+      else if (tree.left eq null) tree
+      else {
+        pushPath(tree)
+        findNext(tree.left)
+      }
+    }
+
+    private[this] def pushPath(tree: Tree[A, B]) {
+      try {
+        path(index) = tree
+        index += 1
+      } catch {
+        case _: ArrayIndexOutOfBoundsException =>
+          /*
+           * Either the tree became unbalanced or we calculated the maximum height incorrectly.
+           * To avoid crashing the iterator we expand the path array. Obviously this should never
+           * happen...
+           *
+           * An exception handler is used instead of an if-condition to optimize the normal path.
+           * This makes a large difference in iteration speed!
+           */
+          assert(index >= path.length)
+          path :+= null
+          pushPath(tree)
+      }
+    }
+    private[this] def popPath(): Tree[A, B] = if (index == 0) null else {
+      index -= 1
+      path(index)
+    }
+
+    private[this] var path = if (tree eq null) null else {
+      /*
+       * According to "Ralf Hinze. Constructing red-black trees" [http://www.cs.ox.ac.uk/ralf.hinze/publications/#P5]
+       * the maximum height of a red-black tree is 2*log_2(n + 2) - 2.
+       *
+       * According to {@see Integer#numberOfLeadingZeros} ceil(log_2(n)) = (32 - Integer.numberOfLeadingZeros(n - 1))
+       *
+       * We also don't store the deepest nodes in the path so the maximum path length is further reduced by one.
+       */
+      val maximumHeight = 2 * (32 - Integer.numberOfLeadingZeros(tree.count + 2 - 1)) - 2 - 1
+      new Array[Tree[A, B]](maximumHeight)
+    }
+    private[this] var index = 0
+    private[this] var next: Tree[A, B] = findNext(tree)
+  }
+
+  private[this] class EntriesIterator[A, B](tree: Tree[A, B]) extends TreeIterator[A, B, (A, B)](tree) {
+    override def nextResult(tree: Tree[A, B]) = (tree.key, tree.value)
+  }
+
+  private[this] class KeysIterator[A, B](tree: Tree[A, B]) extends TreeIterator[A, B, A](tree) {
+    override def nextResult(tree: Tree[A, B]) = tree.key
+  }
+
+  private[this] class ValuesIterator[A, B](tree: Tree[A, B]) extends TreeIterator[A, B, B](tree) {
+    override def nextResult(tree: Tree[A, B]) = tree.value
+  }
+}
diff --git a/src/library/scala/collection/immutable/TreeMap.scala b/src/library/scala/collection/immutable/TreeMap.scala
index 50244ef21d..196c3a9d9d 100644
--- a/src/library/scala/collection/immutable/TreeMap.scala
+++ b/src/library/scala/collection/immutable/TreeMap.scala
@@ -12,6 +12,7 @@ package scala.collection
 package immutable
 
 import generic._
+import immutable.{RedBlackTree => RB}
 import mutable.Builder
 import annotation.bridge
 
@@ -45,14 +46,12 @@ object TreeMap extends ImmutableSortedMapFactory[TreeMap] {
  *  @define mayNotTerminateInf
  *  @define willNotTerminateInf
  */
-class TreeMap[A, +B] private (tree: RedBlack.Node[A, B])(implicit val ordering: Ordering[A])
+class TreeMap[A, +B] private (tree: RB.Tree[A, B])(implicit val ordering: Ordering[A])
   extends SortedMap[A, B]
      with SortedMapLike[A, B, TreeMap[A, B]]
      with MapLike[A, B, TreeMap[A, B]]
      with Serializable {
 
-  import immutable.{RedBlack => RB}
-
   @deprecated("use `ordering.lt` instead", "2.10")
   def isSmaller(x: A, y: A) = ordering.lt(x, y)
 
diff --git a/src/library/scala/collection/immutable/TreeSet.scala b/src/library/scala/collection/immutable/TreeSet.scala
index 899ef0e5eb..12e2197732 100644
--- a/src/library/scala/collection/immutable/TreeSet.scala
+++ b/src/library/scala/collection/immutable/TreeSet.scala
@@ -12,6 +12,7 @@ package scala.collection
 package immutable
 
 import generic._
+import immutable.{RedBlackTree => RB}
 import mutable.{ Builder, SetBuilder }
 
 /** $factoryInfo
@@ -47,11 +48,9 @@ object TreeSet extends ImmutableSortedSetFactory[TreeSet] {
  *  @define willNotTerminateInf
  */
 @SerialVersionUID(-5685982407650748405L)
-class TreeSet[A] private (tree: RedBlack.Node[A, Unit])(implicit val ordering: Ordering[A])
+class TreeSet[A] private (tree: RB.Tree[A, Unit])(implicit val ordering: Ordering[A])
   extends SortedSet[A] with SortedSetLike[A, TreeSet[A]] with Serializable {
 
-  import immutable.{RedBlack => RB}
-
   override def stringPrefix = "TreeSet"
 
   override def size = RB.count(tree)
@@ -105,7 +104,7 @@ class TreeSet[A] private (tree: RedBlack.Node[A, Unit])(implicit val ordering: O
 
   def this()(implicit ordering: Ordering[A]) = this(null)(ordering)
 
-  private def newSet(t: RedBlack.Node[A, Unit]) = new TreeSet[A](t)
+  private def newSet(t: RB.Tree[A, Unit]) = new TreeSet[A](t)
 
   /** A factory to create empty sets of the same type of keys.
    */
diff --git a/test/files/scalacheck/redblack.scala b/test/files/scalacheck/redblack.scala
index 83d3ca0c1f..bbc6504f58 100644
--- a/test/files/scalacheck/redblack.scala
+++ b/test/files/scalacheck/redblack.scala
@@ -1,4 +1,3 @@
-import collection.immutable._
 import org.scalacheck._
 import Prop._
 import Gen._
@@ -15,23 +14,26 @@ Both children of every red node are black.
 Every simple path from a given node to any of its descendant leaves contains the same number of black nodes.
 */
 
-package scala.collection.immutable {
 abstract class RedBlackTest extends Properties("RedBlack") {
   def minimumSize = 0
   def maximumSize = 5
 
-  import RedBlack._
+  object RedBlackTest extends scala.collection.immutable.RedBlack[String] {
+    def isSmaller(x: String, y: String) = x < y
+  }
+
+  import RedBlackTest._
 
-  def nodeAt[A](tree: Node[String, A], n: Int): Option[(String, A)] = if (n < iterator(tree).size && n >= 0)
-    Some(iterator(tree).drop(n).next)
+  def nodeAt[A](tree: Tree[A], n: Int): Option[(String, A)] = if (n < tree.iterator.size && n >= 0)
+    Some(tree.iterator.drop(n).next)
   else
     None
 
-  def treeContains[A](tree: Node[String, A], key: String) = iterator(tree).map(_._1) contains key
+  def treeContains[A](tree: Tree[A], key: String) = tree.iterator.map(_._1) contains key
 
-  def mkTree(level: Int, parentIsBlack: Boolean = false, label: String = ""): Gen[Node[String, Int]] =
+  def mkTree(level: Int, parentIsBlack: Boolean = false, label: String = ""): Gen[Tree[Int]] =
     if (level == 0) {
-      value(null)
+      value(Empty)
     } else {
       for {
         oddOrEven <- choose(0, 2)
@@ -42,9 +44,9 @@ abstract class RedBlackTest extends Properties("RedBlack") {
         right <- mkTree(nextLevel, !isRed, label + "R")
       } yield {
         if (isRed)
-          RedNode(label + "N", 0, left, right)
+          RedTree(label + "N", 0, left, right)
         else
-          BlackNode(label + "N", 0, left, right)
+          BlackTree(label + "N", 0, left, right)
       }
     }
 
@@ -54,10 +56,10 @@ abstract class RedBlackTest extends Properties("RedBlack") {
   } yield tree
 
   type ModifyParm
-  def genParm(tree: Node[String, Int]): Gen[ModifyParm]
-  def modify(tree: Node[String, Int], parm: ModifyParm): Node[String, Int]
+  def genParm(tree: Tree[Int]): Gen[ModifyParm]
+  def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int]
 
-  def genInput: Gen[(Node[String, Int], ModifyParm, Node[String, Int])] = for {
+  def genInput: Gen[(Tree[Int], ModifyParm, Tree[Int])] = for {
     tree <- genTree
     parm <- genParm(tree)
   } yield (tree, parm, modify(tree, parm))
@@ -66,30 +68,30 @@ abstract class RedBlackTest extends Properties("RedBlack") {
 trait RedBlackInvariants {
   self: RedBlackTest =>
 
-  import RedBlack._
+  import RedBlackTest._
 
-  def rootIsBlack[A](t: Node[String, A]) = isBlack(t)
+  def rootIsBlack[A](t: Tree[A]) = t.isBlack
 
-  def areAllLeavesBlack[A](t: Node[String, A]): Boolean = t match {
-    case null => isBlack(t)
-    case ne => List(ne.left, ne.right) forall areAllLeavesBlack
+  def areAllLeavesBlack[A](t: Tree[A]): Boolean = t match {
+    case Empty => t.isBlack
+    case ne: NonEmpty[_] => List(ne.left, ne.right) forall areAllLeavesBlack
   }
 
-  def areRedNodeChildrenBlack[A](t: Node[String, A]): Boolean = t match {
-    case RedNode(_, _, left, right) => List(left, right) forall (t => isBlack(t) && areRedNodeChildrenBlack(t))
-    case BlackNode(_, _, left, right) => List(left, right) forall areRedNodeChildrenBlack
-    case null => true
+  def areRedNodeChildrenBlack[A](t: Tree[A]): Boolean = t match {
+    case RedTree(_, _, left, right) => List(left, right) forall (t => t.isBlack && areRedNodeChildrenBlack(t))
+    case BlackTree(_, _, left, right) => List(left, right) forall areRedNodeChildrenBlack
+    case Empty => true
   }
 
-  def blackNodesToLeaves[A](t: Node[String, A]): List[Int] = t match {
-    case null => List(1)
-    case BlackNode(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves map (_ + 1)
-    case RedNode(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves
+  def blackNodesToLeaves[A](t: Tree[A]): List[Int] = t match {
+    case Empty => List(1)
+    case BlackTree(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves map (_ + 1)
+    case RedTree(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves
   }
 
-  def areBlackNodesToLeavesEqual[A](t: Node[String, A]): Boolean = t match {
-    case null => true
-    case ne =>
+  def areBlackNodesToLeavesEqual[A](t: Tree[A]): Boolean = t match {
+    case Empty => true
+    case ne: NonEmpty[_] =>
       (
         blackNodesToLeaves(ne).distinct.size == 1
         && areBlackNodesToLeavesEqual(ne.left)
@@ -97,10 +99,10 @@ trait RedBlackInvariants {
       )
   }
 
-  def orderIsPreserved[A](t: Node[String, A]): Boolean =
-    iterator(t) zip iterator(t).drop(1) forall { case (x, y) => x._1 < y._1 }
+  def orderIsPreserved[A](t: Tree[A]): Boolean =
+    t.iterator zip t.iterator.drop(1) forall { case (x, y) => isSmaller(x._1, y._1) }
 
-  def setup(invariant: Node[String, Int] => Boolean) = forAll(genInput) { case (tree, parm, newTree) =>
+  def setup(invariant: Tree[Int] => Boolean) = forAll(genInput) { case (tree, parm, newTree) =>
     invariant(newTree)
   }
 
@@ -112,13 +114,13 @@ trait RedBlackInvariants {
 }
 
 object TestInsert extends RedBlackTest with RedBlackInvariants {
-  import RedBlack._
+  import RedBlackTest._
 
   override type ModifyParm = Int
-  override def genParm(tree: Node[String, Int]): Gen[ModifyParm] = choose(0, iterator(tree).size + 1)
-  override def modify(tree: Node[String, Int], parm: ModifyParm): Node[String, Int] = update(tree, generateKey(tree, parm), 0)
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = choose(0, tree.iterator.size + 1)
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = tree update (generateKey(tree, parm), 0)
 
-  def generateKey(tree: Node[String, Int], parm: ModifyParm): String = nodeAt(tree, parm) match {
+  def generateKey(tree: Tree[Int], parm: ModifyParm): String = nodeAt(tree, parm) match {
     case Some((key, _)) => key.init.mkString + "MN"
     case None => nodeAt(tree, parm - 1) match {
       case Some((key, _)) => key.init.mkString + "RN"
@@ -132,31 +134,31 @@ object TestInsert extends RedBlackTest with RedBlackInvariants {
 }
 
 object TestModify extends RedBlackTest {
-  import RedBlack._
+  import RedBlackTest._
 
   def newValue = 1
   override def minimumSize = 1
   override type ModifyParm = Int
-  override def genParm(tree: Node[String, Int]): Gen[ModifyParm] = choose(0, iterator(tree).size)
-  override def modify(tree: Node[String, Int], parm: ModifyParm): Node[String, Int] = nodeAt(tree, parm) map {
-    case (key, _) => update(tree, key, newValue)
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = choose(0, tree.iterator.size)
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = nodeAt(tree, parm) map {
+    case (key, _) => tree update (key, newValue)
   } getOrElse tree
 
   property("update modifies values") = forAll(genInput) { case (tree, parm, newTree) =>
     nodeAt(tree,parm) forall { case (key, _) =>
-      iterator(newTree) contains (key, newValue)
+      newTree.iterator contains (key, newValue)
     }
   }
 }
 
 object TestDelete extends RedBlackTest with RedBlackInvariants  {
-  import RedBlack._
+  import RedBlackTest._
 
   override def minimumSize = 1
   override type ModifyParm = Int
-  override def genParm(tree: Node[String, Int]): Gen[ModifyParm] = choose(0, iterator(tree).size)
-  override def modify(tree: Node[String, Int], parm: ModifyParm): Node[String, Int] = nodeAt(tree, parm) map {
-    case (key, _) => delete(tree, key)
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = choose(0, tree.iterator.size)
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = nodeAt(tree, parm) map {
+    case (key, _) => tree delete key
   } getOrElse tree
 
   property("delete removes elements") = forAll(genInput) { case (tree, parm, newTree) =>
@@ -167,41 +169,40 @@ object TestDelete extends RedBlackTest with RedBlackInvariants  {
 }
 
 object TestRange extends RedBlackTest with RedBlackInvariants  {
-  import RedBlack._
+  import RedBlackTest._
 
   override type ModifyParm = (Option[Int], Option[Int])
-  override def genParm(tree: Node[String, Int]): Gen[ModifyParm] = for {
-    from <- choose(0, iterator(tree).size)
-    to <- choose(0, iterator(tree).size) suchThat (from <=)
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = for {
+    from <- choose(0, tree.iterator.size)
+    to <- choose(0, tree.iterator.size) suchThat (from <=)
     optionalFrom <- oneOf(Some(from), None, Some(from)) // Double Some(n) to get around a bug
     optionalTo <- oneOf(Some(to), None, Some(to)) // Double Some(n) to get around a bug
   } yield (optionalFrom, optionalTo)
 
-  override def modify(tree: Node[String, Int], parm: ModifyParm): Node[String, Int] = {
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = {
     val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
     val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
-    range(tree, from, to)
+    tree range (from, to)
   }
 
   property("range boundaries respected") = forAll(genInput) { case (tree, parm, newTree) =>
     val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
     val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
-    ("lower boundary" |: (from forall ( key => iterator(newTree).map(_._1) forall (key <=)))) &&
-    ("upper boundary" |: (to forall ( key => iterator(newTree).map(_._1) forall (key >))))
+    ("lower boundary" |: (from forall ( key => newTree.iterator.map(_._1) forall (key <=)))) &&
+    ("upper boundary" |: (to forall ( key => newTree.iterator.map(_._1) forall (key >))))
   }
 
   property("range returns all elements") = forAll(genInput) { case (tree, parm, newTree) =>
     val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
     val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
-    val filteredTree = (iterator(tree)
+    val filteredTree = (tree.iterator
       .map(_._1)
       .filter(key => from forall (key >=))
       .filter(key => to forall (key <))
       .toList)
-    filteredTree == iterator(newTree).map(_._1).toList
+    filteredTree == newTree.iterator.map(_._1).toList
   }
 }
-}
 
 object Test extends Properties("RedBlack") {
   include(TestInsert)
diff --git a/test/files/scalacheck/redblacktree.scala b/test/files/scalacheck/redblacktree.scala
new file mode 100644
index 0000000000..10f3f0fbbf
--- /dev/null
+++ b/test/files/scalacheck/redblacktree.scala
@@ -0,0 +1,212 @@
+import collection.immutable.{RedBlackTree => RB}
+import org.scalacheck._
+import Prop._
+import Gen._
+
+/*
+Properties of a Red & Black Tree:
+
+A node is either red or black.
+The root is black. (This rule is used in some definitions and not others. Since the
+root can always be changed from red to black but not necessarily vice-versa this
+rule has little effect on analysis.)
+All leaves are black.
+Both children of every red node are black.
+Every simple path from a given node to any of its descendant leaves contains the same number of black nodes.
+*/
+
+package scala.collection.immutable.redblacktree {
+  abstract class RedBlackTreeTest extends Properties("RedBlackTree") {
+    def minimumSize = 0
+    def maximumSize = 5
+
+    import RB._
+
+    def nodeAt[A](tree: Tree[String, A], n: Int): Option[(String, A)] = if (n < iterator(tree).size && n >= 0)
+      Some(iterator(tree).drop(n).next)
+    else
+      None
+
+    def treeContains[A](tree: Tree[String, A], key: String) = iterator(tree).map(_._1) contains key
+
+    def mkTree(level: Int, parentIsBlack: Boolean = false, label: String = ""): Gen[Tree[String, Int]] =
+      if (level == 0) {
+        value(null)
+      } else {
+        for {
+          oddOrEven <- choose(0, 2)
+          tryRed = oddOrEven.sample.get % 2 == 0 // work around arbitrary[Boolean] bug
+          isRed = parentIsBlack && tryRed
+          nextLevel = if (isRed) level else level - 1
+          left <- mkTree(nextLevel, !isRed, label + "L")
+          right <- mkTree(nextLevel, !isRed, label + "R")
+        } yield {
+          if (isRed)
+            RedTree(label + "N", 0, left, right)
+          else
+            BlackTree(label + "N", 0, left, right)
+        }
+      }
+
+    def genTree = for {
+      depth <- choose(minimumSize, maximumSize + 1)
+      tree <- mkTree(depth)
+    } yield tree
+
+    type ModifyParm
+    def genParm(tree: Tree[String, Int]): Gen[ModifyParm]
+    def modify(tree: Tree[String, Int], parm: ModifyParm): Tree[String, Int]
+
+    def genInput: Gen[(Tree[String, Int], ModifyParm, Tree[String, Int])] = for {
+      tree <- genTree
+      parm <- genParm(tree)
+    } yield (tree, parm, modify(tree, parm))
+  }
+
+  trait RedBlackTreeInvariants {
+    self: RedBlackTreeTest =>
+
+    import RB._
+
+    def rootIsBlack[A](t: Tree[String, A]) = isBlack(t)
+
+    def areAllLeavesBlack[A](t: Tree[String, A]): Boolean = t match {
+      case null => isBlack(t)
+      case ne => List(ne.left, ne.right) forall areAllLeavesBlack
+    }
+
+    def areRedNodeChildrenBlack[A](t: Tree[String, A]): Boolean = t match {
+      case RedTree(_, _, left, right) => List(left, right) forall (t => isBlack(t) && areRedNodeChildrenBlack(t))
+      case BlackTree(_, _, left, right) => List(left, right) forall areRedNodeChildrenBlack
+      case null => true
+    }
+
+    def blackNodesToLeaves[A](t: Tree[String, A]): List[Int] = t match {
+      case null => List(1)
+      case BlackTree(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves map (_ + 1)
+      case RedTree(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves
+    }
+
+    def areBlackNodesToLeavesEqual[A](t: Tree[String, A]): Boolean = t match {
+      case null => true
+      case ne =>
+        (
+          blackNodesToLeaves(ne).distinct.size == 1
+          && areBlackNodesToLeavesEqual(ne.left)
+          && areBlackNodesToLeavesEqual(ne.right)
+        )
+    }
+
+    def orderIsPreserved[A](t: Tree[String, A]): Boolean =
+      iterator(t) zip iterator(t).drop(1) forall { case (x, y) => x._1 < y._1 }
+
+    def setup(invariant: Tree[String, Int] => Boolean) = forAll(genInput) { case (tree, parm, newTree) =>
+      invariant(newTree)
+    }
+
+    property("root is black") = setup(rootIsBlack)
+    property("all leaves are black") = setup(areAllLeavesBlack)
+    property("children of red nodes are black") = setup(areRedNodeChildrenBlack)
+    property("black nodes are balanced") = setup(areBlackNodesToLeavesEqual)
+    property("ordering of keys is preserved") = setup(orderIsPreserved)
+  }
+
+  object TestInsert extends RedBlackTreeTest with RedBlackTreeInvariants {
+    import RB._
+
+    override type ModifyParm = Int
+    override def genParm(tree: Tree[String, Int]): Gen[ModifyParm] = choose(0, iterator(tree).size + 1)
+    override def modify(tree: Tree[String, Int], parm: ModifyParm): Tree[String, Int] = update(tree, generateKey(tree, parm), 0)
+
+    def generateKey(tree: Tree[String, Int], parm: ModifyParm): String = nodeAt(tree, parm) match {
+      case Some((key, _)) => key.init.mkString + "MN"
+      case None => nodeAt(tree, parm - 1) match {
+        case Some((key, _)) => key.init.mkString + "RN"
+        case None  => "N"
+      }
+    }
+
+    property("update adds elements") = forAll(genInput) { case (tree, parm, newTree) =>
+      treeContains(newTree, generateKey(tree, parm))
+    }
+  }
+
+  object TestModify extends RedBlackTreeTest {
+    import RB._
+
+    def newValue = 1
+    override def minimumSize = 1
+    override type ModifyParm = Int
+    override def genParm(tree: Tree[String, Int]): Gen[ModifyParm] = choose(0, iterator(tree).size)
+    override def modify(tree: Tree[String, Int], parm: ModifyParm): Tree[String, Int] = nodeAt(tree, parm) map {
+      case (key, _) => update(tree, key, newValue)
+    } getOrElse tree
+
+    property("update modifies values") = forAll(genInput) { case (tree, parm, newTree) =>
+      nodeAt(tree,parm) forall { case (key, _) =>
+        iterator(newTree) contains (key, newValue)
+      }
+    }
+  }
+
+  object TestDelete extends RedBlackTreeTest with RedBlackTreeInvariants  {
+    import RB._
+
+    override def minimumSize = 1
+    override type ModifyParm = Int
+    override def genParm(tree: Tree[String, Int]): Gen[ModifyParm] = choose(0, iterator(tree).size)
+    override def modify(tree: Tree[String, Int], parm: ModifyParm): Tree[String, Int] = nodeAt(tree, parm) map {
+      case (key, _) => delete(tree, key)
+    } getOrElse tree
+
+    property("delete removes elements") = forAll(genInput) { case (tree, parm, newTree) =>
+      nodeAt(tree, parm) forall { case (key, _) =>
+        !treeContains(newTree, key)
+      }
+    }
+  }
+
+  object TestRange extends RedBlackTreeTest with RedBlackTreeInvariants  {
+    import RB._
+
+    override type ModifyParm = (Option[Int], Option[Int])
+    override def genParm(tree: Tree[String, Int]): Gen[ModifyParm] = for {
+      from <- choose(0, iterator(tree).size)
+      to <- choose(0, iterator(tree).size) suchThat (from <=)
+      optionalFrom <- oneOf(Some(from), None, Some(from)) // Double Some(n) to get around a bug
+      optionalTo <- oneOf(Some(to), None, Some(to)) // Double Some(n) to get around a bug
+    } yield (optionalFrom, optionalTo)
+
+    override def modify(tree: Tree[String, Int], parm: ModifyParm): Tree[String, Int] = {
+      val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
+      val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
+      range(tree, from, to)
+    }
+
+    property("range boundaries respected") = forAll(genInput) { case (tree, parm, newTree) =>
+      val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
+      val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
+      ("lower boundary" |: (from forall ( key => iterator(newTree).map(_._1) forall (key <=)))) &&
+      ("upper boundary" |: (to forall ( key => iterator(newTree).map(_._1) forall (key >))))
+    }
+
+    property("range returns all elements") = forAll(genInput) { case (tree, parm, newTree) =>
+      val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
+      val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
+      val filteredTree = (iterator(tree)
+        .map(_._1)
+        .filter(key => from forall (key >=))
+        .filter(key => to forall (key <))
+        .toList)
+      filteredTree == iterator(newTree).map(_._1).toList
+    }
+  }
+}
+
+object Test extends Properties("RedBlackTree") {
+  import collection.immutable.redblacktree._
+  include(TestInsert)
+  include(TestModify)
+  include(TestDelete)
+  include(TestRange)
+}