diff -r 115cf53a69d6 -r cd9e40280784 progs/scala/re-bit.scala
--- a/progs/scala/re-bit.scala	Fri Jun 24 12:35:16 2016 +0100
+++ b/progs/scala/re-bit.scala	Wed Jul 20 14:30:07 2016 +0100
@@ -151,6 +151,7 @@
   case c::cs => lex(der(c, r), cs)
 }
 
+def pre_lexing(r: Rexp, s: String) = lex(internalise(r), s.toList)
 def lexing(r: Rexp, s: String) : Val = decode(r, lex(internalise(r), s.toList))
 
 
@@ -212,9 +213,13 @@
 }
 
 
-
+val rf = ("a" | "ab") ~ ("ab" | "")
+println(pre_lexing(rf, "ab"))
+println(lexing(rf, "ab"))
+println(lexing_simp(rf, "ab"))
 
 val r0 = ("a" | "ab") ~ ("b" | "")
+println(pre_lexing(r0, "ab"))
 println(lexing(r0, "ab"))
 println(lexing_simp(r0, "ab"))