1 files changed, 10 insertions, 0 deletions
diff --git a/sources/scala/List.scala b/sources/scala/List.scala
index 8c7f8d0463..7acf1e7157 100644
--- a/sources/scala/List.scala
+++ b/sources/scala/List.scala
@@ -188,6 +188,16 @@ object List {
     sb.toString()
   }
 
+  /** Like (xs map f), but returns xs unchanged if the f maps all elements to themselves
+   */
+  def transform[a](xs: List[a])(f: a => a): List[a] = xs match {
+    case Nil => Nil
+    case head :: tail =>
+      val head1 = f(head);
+      val tail1 = transform(tail)(f);
+      if (head1 == head && tail1 == tail) xs else head1 :: tail1
+  }
+
   /** Returns the list resulting from applying the given function <code>f</code> to
    *  corresponding elements of the argument lists.
    *