diff -r 70c307641d05 -r 1e4da6d2490c progs/re2.scala
--- a/progs/re2.scala	Mon Sep 22 13:42:14 2014 +0100
+++ b/progs/re2.scala	Fri Sep 26 14:06:55 2014 +0100
@@ -1,26 +1,12 @@
-import scala.language.implicitConversions    
-    
 abstract class Rexp 
-
 case object NULL extends Rexp
 case object EMPTY extends Rexp
 case class CHAR(c: Char) extends Rexp
 case class ALT(r1: Rexp, r2: Rexp) extends Rexp 
 case class SEQ(r1: Rexp, r2: Rexp) extends Rexp 
 case class STAR(r: Rexp) extends Rexp 
-case class NTIMES(r: Rexp, n: Int) extends Rexp 
+case class NTIMES(r: Rexp, n: Int) extends Rexp //explicit constructor
 
-// some convenience for typing in regular expressions
-def charlist2rexp(s : List[Char]) : Rexp = s match {
-  case Nil => EMPTY
-  case c::Nil => CHAR(c)
-  case c::s => SEQ(CHAR(c), charlist2rexp(s))
-}
-implicit def string2rexp(s : String) : Rexp = charlist2rexp(s.toList)
-
-
-// nullable function: tests whether the regular 
-// expression can recognise the empty string
 def nullable (r: Rexp) : Boolean = r match {
   case NULL => false
   case EMPTY => true
@@ -31,7 +17,6 @@
   case NTIMES(r, i) => if (i == 0) true else nullable(r)
 }
 
-// derivative of a regular expression w.r.t. a character
 def der (c: Char, r: Rexp) : Rexp = r match {
   case NULL => NULL
   case EMPTY => NULL
@@ -45,20 +30,18 @@
     if (i == 0) NULL else SEQ(der(c, r), NTIMES(r, i - 1))
 }
 
-// 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, der(c, r))
 }
 
-// main matcher function
 def matcher(r: Rexp, s: String) : Boolean = nullable(ders(s.toList, r))
 
 
-//one or zero
+//optional: one or zero times
 def OPT(r: Rexp) = ALT(r, EMPTY)
 
-def EVIL(n: Int) = SEQ(NTIMES(OPT("a"), n), NTIMES("a", n))
+def EVIL(n: Int) = SEQ(NTIMES(OPT(CHAR('a')), n), NTIMES(CHAR('a'), n))
 
 def time_needed[T](i: Int, code: => T) = {
   val start = System.nanoTime()
@@ -71,7 +54,7 @@
   println(i + ": " + "%.5f".format(time_needed(1, matcher(EVIL(i), "a" * i))))
 }
 
-
+//a bit bolder test
 for (i <- 1 to 1000 by 50) {
   println(i + " " + "%.5f".format(time_needed(1, matcher(EVIL(i), "a" * i))))
 }