--- a/progs/matcher/re3.sc	Fri Sep 15 10:49:33 2023 +0100
+++ b/progs/matcher/re3.sc	Sun Sep 17 19:12:57 2023 +0100
@@ -1,4 +1,6 @@
-// A version with simplification of derivatives;
+// A version of the matcher with simplification 
+// of derivatives
+//
 // this keeps the regular expressions small, which
 // is good for the run-time
 // 
@@ -48,6 +50,7 @@
     if (i == 0) ZERO else SEQ(der(c, r), NTIMES(r, i - 1))
 }
 
+// simplification
 def simp(r: Rexp) : Rexp = r match {
   case ALT(r1, r2) => (simp(r1), simp(r2)) match {
     case (ZERO, r2s) => r2s
@@ -64,26 +67,23 @@
   case r => r
 }
 
-
-
 // the derivative w.r.t. a string (iterates der)
 def ders(s: List[Char], r: Rexp) : Rexp = s match {
   case Nil => r
   case c::s => ders(s, simp(der(c, r)))
 }
 
-
 // the main matcher function
 def matcher(r: Rexp, s: String) : Boolean = 
   nullable(ders(s.toList, r))
 
 
+// Test Cases
+//============
+
 // one or zero
 def OPT(r: Rexp) = ALT(r, ONE)
 
-
-// Test Cases
-
 // evil regular expressions: (a?){n} a{n}  and (a*)* b
 def EVIL1(n: Int) = SEQ(NTIMES(OPT(CHAR('a')), n), NTIMES(CHAR('a'), n))
 val EVIL2 = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))