1 files changed, 14 insertions, 1 deletions
diff --git a/src/dotty/tools/package.scala b/src/dotty/tools/package.scala
index 021e7360b..f23b62862 100644
--- a/src/dotty/tools/package.scala
+++ b/src/dotty/tools/package.scala
@@ -3,5 +3,18 @@ package dotty
 package object tools {
   type FatalError = scala.reflect.internal.FatalError
   val FatalError = scala.reflect.internal.FatalError
-  val ListOfNil = List(Nil)
+
+  val ListOfNil = Nil :: Nil
+
+  /** True if two lists have the same length.  Since calling length on linear sequences
+   *  is O(n), it is an inadvisable way to test length equality.
+   */
+  final def sameLength[T](xs: List[T], ys: List[T]): Boolean = xs match {
+    case _ :: xs1 =>
+      ys match {
+        case _ :: ys1 => sameLength(xs1, ys1)
+        case _ => false
+      }
+    case _ => ys.isEmpty
+  }
 }