diff -r 0bbb56867091 -r d7b2625c1193 src/Pure/General/scan.scala
--- a/src/Pure/General/scan.scala	Thu May 12 16:23:13 2011 +0200
+++ b/src/Pure/General/scan.scala	Thu May 12 16:28:46 2011 +0200
@@ -22,7 +22,7 @@
 
   object Lexicon
   {
-    private case class Tree(val branches: Map[Char, (String, Tree)])
+    protected case class Tree(val branches: Map[Char, (String, Tree)])
     private val empty_tree = Tree(Map())
 
     val empty: Lexicon = new Lexicon