The birth of the @switch and @tailrec annotations.

They are located in package scala.annotation. Also in this patch:

 * numerous test cases for both annotations
 * addition of @tailrec and @switch in a few strategic locations
 * fixes for critical section NewScanners methods which were not being
   compiled into switches, immediately proving the value of @switch
 * tail recursive implementations for Iterator.{ dropWhile, drop}
   and List.dropWhile tagged with @tailrec, closing bug #1376

5 files changed, 67 insertions, 11 deletions

diff --git a/src/library/scala/Iterator.scala b/src/library/scala/Iterator.scala
index d04d32393a..b5092a2430 100644
--- a/src/library/scala/Iterator.scala
+++ b/src/library/scala/Iterator.scala
@@ -14,6 +14,7 @@ package scala
 
 import Predef._
 import collection.mutable.{Buffer, ListBuffer, ArrayBuffer}
+import annotation.tailrec
 
 /** The <code>Iterator</code> object provides various functions for
  *  creating specialized iterators.
@@ -248,8 +249,14 @@ trait Iterator[+A] {
    *  @param n the number of elements to drop
    *  @return  the new iterator
    */
-  def drop(n: Int): Iterator[A] =
-    if (n > 0 && hasNext) { next; drop(n - 1) } else this
+  def drop(n: Int): Iterator[A] = {
+    @tailrec
+    def loop(left: Int): Iterator[A] =
+      if (left > 0 && hasNext) { next; loop(left - 1) }
+      else this
+
+    loop(n)
+  }
 
   /** A sub-iterator of <code>until - from elements
    *  starting at index <code>from</code>
@@ -366,12 +373,18 @@ trait Iterator[+A] {
    *  @param p the predicate used to skip elements.
    *  @return  an iterator consisting of the remaining elements
    */
-  def dropWhile(p: A => Boolean): Iterator[A] =
-    if (hasNext) {
-      val x = next
-      if (p(x)) dropWhile(p)
-      else Iterator.single(x) append this
-    } else this
+  def dropWhile(p: A => Boolean): Iterator[A] = {
+    @tailrec
+    def loop(): Iterator[A] =
+      if (hasNext) {
+        val x = next
+        if (p(x)) loop()
+        else Iterator.single(x) append this
+      }
+      else this
+
+    loop()
+  }
 
   /** Return an iterator formed from this iterator and the specified iterator
    *  <code>that</code> by associating each element of the former with
diff --git a/src/library/scala/List.scala b/src/library/scala/List.scala
index eda39f9ec9..5482deabf4 100644
--- a/src/library/scala/List.scala
+++ b/src/library/scala/List.scala
@@ -12,6 +12,7 @@
 package scala
 
 import scala.collection.mutable.ListBuffer
+import annotation.tailrec
 import Predef._
 
 /** This object provides methods for creating specialized lists, and for
@@ -702,6 +703,7 @@ sealed abstract class List[+A] extends Seq[A] with Product {
    *  @return the suffix of length <code>n</code> of the list
    */
   def takeRight(n: Int): List[A] = {
+    @tailrec
     def loop(lead: List[A], lag: List[A]): List[A] = lead match {
       case Nil => lag
       case _ :: tail => loop(tail, lag.tail)
@@ -765,9 +767,14 @@ sealed abstract class List[+A] extends Seq[A] with Product {
    *  @return  the longest suffix of the list whose first element
    *           does not satisfy the predicate <code>p</code>.
    */
-  override def dropWhile(p: A => Boolean): List[A] =
-    if (isEmpty || !p(head)) this
-    else tail dropWhile p
+  override def dropWhile(p: A => Boolean): List[A] = {
+    @tailrec
+    def loop(xs: List[A]): List[A] =
+      if (xs.isEmpty || !p(xs.head)) xs
+      else loop(xs.tail)
+
+    loop(this)
+  }
 
   /** Returns the longest prefix of the list whose elements all satisfy
    *  the given predicate, and the rest of the list.
@@ -823,6 +830,7 @@ sealed abstract class List[+A] extends Seq[A] with Product {
    *  @return  the reversed list of results.
    */
   def reverseMap[B](f: A => B): List[B] = {
+    @tailrec
     def loop(l: List[A], res: List[B]): List[B] = l match {
       case Nil => res
       case head :: tail => loop(tail, f(head) :: res)
diff --git a/src/library/scala/annotation/switch.scala b/src/library/scala/annotation/switch.scala
new file mode 100644
index 0000000000..5ecbf73905
--- /dev/null
+++ b/src/library/scala/annotation/switch.scala
@@ -0,0 +1,17 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2002-2009, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+package scala.annotation
+
+/** <p>
+ *    An annotation to be applied to a match expression.  If present,
+ *    the compiler will verify that the match has been compiled to a
+ *    tableswitch or lookupswitch, and issue an error if it instead
+ *    compiles into a series of conditional expressions.
+ *  </p>
+ */
+final class switch extends StaticAnnotation
\ No newline at end of file
diff --git a/src/library/scala/annotation/tailrec.scala b/src/library/scala/annotation/tailrec.scala
new file mode 100644
index 0000000000..6ce23a92fa
--- /dev/null
+++ b/src/library/scala/annotation/tailrec.scala
@@ -0,0 +1,16 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2002-2009, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+package scala.annotation
+
+/** <p>
+ *    A method annotation which verifies that the method will be compiled
+ *    with tail call optimization.  If it is present, the compiler will
+ *    issue an error if the method cannot be optimized into a loop.
+ *  </p>
+ */
+final class tailrec extends StaticAnnotation
diff --git a/src/library/scalax/collection/immutable/Stream.scala b/src/library/scalax/collection/immutable/Stream.scala
index 036fefe70c..4055be40bc 100755
--- a/src/library/scalax/collection/immutable/Stream.scala
+++ b/src/library/scalax/collection/immutable/Stream.scala
@@ -14,6 +14,7 @@ package scalax.collection.immutable
 import mutable.ListBuffer
 import generic.{SequenceTemplate, SequenceFactory, EmptyIterableFactory, Builder, LazyBuilder}
 import annotation.unchecked.uncheckedVariance
+import annotation.tailrec
 
 /**
  * The object <code>Stream</code> provides helper functions
@@ -486,6 +487,7 @@ self =>
    *  @param sep   The separator string printed between consecutive elements.
    */
   def print(sep: String) {
+    @tailrec
     def loop(these: Stream[A], start: String) {
       Console.print(start)
       if (isEmpty) Console.print("empty")