added patch of #1335

1 files changed, 12 insertions, 9 deletions

diff --git a/src/library/scala/Stream.scala b/src/library/scala/Stream.scala
index 6765ec1db8..1ddabae797 100644
--- a/src/library/scala/Stream.scala
+++ b/src/library/scala/Stream.scala
@@ -440,17 +440,20 @@ abstract class Stream[+A] extends Seq.Projection[A] {
    *           this stream is <code>[a<sub>0</sub>, ..., a<sub>n</sub>]</code>.
    */
   override def flatMap[B](f: A => Iterable[B]): Stream[B] = {
-    // optimization: drop A's for which f yields no B
-    val fstream = dropWhile(a => f(a) isEmpty)
-    if (fstream isEmpty) Stream.empty
-    else {
-      val s: Stream[B] = f(fstream.head) match {
-        case x: Stream[_] => x
-        case y: List[_]   => y.toStream
-        case z            => z.toList.toStream
+    // drops A's for which f yields an empty Iterable[B]
+    def loop(s: Stream[A]): Stream[B] = {
+      if (s.isEmpty)
+        Stream.empty
+      else {
+        val i = f(s.head)
+        if (i isEmpty)
+          loop(s.tail)
+        else
+          i.toStream append loop(s.tail)
       }
-      s append (fstream.tail flatMap f)
     }
+
+    loop(this)
   }
 
   override def toStream = this