From 48cc8408cfd0b57f46746162b8d4c184f7a3ed5c Mon Sep 17 00:00:00 2001
From: Paul Phillips <paulp@improving.org>
Date: Wed, 26 Aug 2009 04:53:25 +0000
Subject: Tail recursive foldLeft for Stream.

---
 src/library/scala/collection/immutable/Stream.scala | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/library/scala/collection/immutable/Stream.scala b/src/library/scala/collection/immutable/Stream.scala
index 2841beea14..e6f3d3c47c 100644
--- a/src/library/scala/collection/immutable/Stream.scala
+++ b/src/library/scala/collection/immutable/Stream.scala
@@ -13,6 +13,7 @@ package scala.collection.immutable
 
 import scala.collection.mutable.ListBuffer
 import scala.collection.generic._
+import scala.annotation.tailrec
 
 /**
  * <p>The class <code>Stream</code> implements lazy lists where elements
@@ -180,6 +181,7 @@ self =>
    *         for allowing the GC to collect the underlying stream as elements are
    *         consumed.
    */
+  @tailrec
   override final def foreach[B](f: A => B) {
     if (!this.isEmpty) {
       f(head)
@@ -187,6 +189,15 @@ self =>
     }
   }
 
+  /** Stream specialization of foldLeft which allows GC to collect
+   *  along the way.
+   */
+  @tailrec
+  override final def foldLeft[B](z: B)(op: (B, A) => B): B = {
+    if (this.isEmpty) z
+    else tail.foldLeft(op(z, head))(op)
+  }
+
   /** Returns all the elements of this stream that satisfy the
    *  predicate <code>p</code>. The order of the elements is preserved.
    *
-- 
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