diff -r c82a45f48bfc -r 5365ef60707e progs/lexer/lexer.sc
--- a/progs/lexer/lexer.sc	Fri Oct 13 23:49:34 2023 +0100
+++ b/progs/lexer/lexer.sc	Sat Oct 21 09:09:09 2023 +0100
@@ -42,12 +42,6 @@
 implicit def string2rexp(s : String) : Rexp = 
   charlist2rexp(s.toList)
 
-extension (r: Rexp) {
-  def | (s: Rexp) = ALT(r, s)
-  def % = STAR(r)
-  def ~ (s: Rexp) = SEQ(r, s)
-}
-
 extension (s: String) {
   def | (r: Rexp) = ALT(s, r)
   def | (r: String) = ALT(s, r)
@@ -57,6 +51,17 @@
   def $ (r: Rexp) = RECD(s, r)
 }
 
+extension (r: Rexp) {
+  def | (s: Rexp) = ALT(r, s)
+  def % = STAR(r)
+  def ~ (s: Rexp) = SEQ(r, s)
+}
+
+
+
+val r : Rexp = ("a" | "b").% 
+println(r) 
+
 def nullable(r: Rexp) : Boolean = r match {
   case ZERO => false
   case ONE => true
@@ -79,6 +84,7 @@
   case RECD(_, r1) => der(c, r1)
 }
 
+println(der('a', ALT(STAR("a"), "b")))
 
 // extracts a string from a value
 def flatten(v: Val) : String = v match {
@@ -128,6 +134,8 @@
   case (RECD(x, r1), _) => Rec(x, inj(r1, c, v))
 }
 
+
+
 // some "rectification" functions for simplification
 def F_ID(v: Val): Val = v
 def F_RIGHT(f: Val => Val) = (v:Val) => Right(f(v))