diff -r 47a299e7010f -r 8d0af38389bc progs/token.scala
--- a/progs/token.scala	Sun Jul 28 01:00:41 2019 +0100
+++ b/progs/token.scala	Sun Jul 28 14:24:46 2019 +0100
@@ -1,4 +1,4 @@
-// Simple Tokenizer according to Sulzmann & Lu
+// A Simple Tokenizer according to Sulzmann & Lu
 
 import scala.language.implicitConversions    
 import scala.language.reflectiveCalls
@@ -48,7 +48,7 @@
 // A test for more conveninet syntax
 val re : Rexp = ("ab" | "a") ~ ("b" | ONE)
 
-// nullable function: tests whether the regular 
+// the nullable function: tests whether the regular 
 // expression can recognise the empty string
 def nullable (r: Rexp) : Boolean = r match {
   case ZERO => false
@@ -60,7 +60,7 @@
   case RECD(_, r1) => nullable(r1)
 }
 
-// derivative of a regular expression w.r.t. a character
+// the derivative of a regular expression w.r.t. a character
 def der (c: Char, r: Rexp) : Rexp = r match {
   case ZERO => ZERO
   case ONE => ZERO
@@ -73,7 +73,7 @@
   case RECD(_, r1) => der(c, r1)
 }
 
-// derivative w.r.t. a string (iterates der)
+// 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, der(c, r))
@@ -90,7 +90,7 @@
   case Rec(_, v) => flatten(v)
 }
 
-// extracts an environment from a value
+// extracts an environment from a value;
 // used for tokenise a string
 def env(v: Val) : List[(String, String)] = v match {
   case Empty => Nil
@@ -102,7 +102,10 @@
   case Rec(x, v) => (x, flatten(v))::env(v)
 }
 
-// injection part
+// The Injection Part of the Tokeniser
+
+// calculates a value for how a nullable regex 
+// matches the empty string 
 def mkeps(r: Rexp) : Val = r match {
   case ONE => Empty
   case ALT(r1, r2) => 
@@ -112,7 +115,7 @@
   case RECD(x, r) => Rec(x, mkeps(r))
 }
 
-
+// injects back a character into a value
 def inj(r: Rexp, c: Char, v: Val) : Val = (r, v) match {
   case (STAR(r), Sequ(v1, Stars(vs))) => Stars(inj(r, c, v1)::vs)
   case (SEQ(r1, r2), Sequ(v1, v2)) => Sequ(inj(r1, c, v1), v2)
@@ -124,7 +127,7 @@
   case (RECD(x, r1), _) => Rec(x, inj(r1, c, v))
 }
 
-// main lexing function (produces a value)
+// the main lexing function (produces a value)
 def lex(r: Rexp, s: List[Char]) : Val = s match {
   case Nil => if (nullable(r)) mkeps(r) 
               else throw new Exception("Not matched")
@@ -157,8 +160,8 @@
 }
 def F_ERROR(v: Val): Val = throw new Exception("error")
 
-// simplification of regular expressions returning also an
-// rectification function; no simplification under STAR 
+// simplification of regular expressions returns now also 
+// an rectification function; no simplification under STAR 
 def simp(r: Rexp): (Rexp, Val => Val) = r match {
   case ALT(r1, r2) => {
     val (r1s, f1s) = simp(r1)
@@ -188,6 +191,7 @@
   case r => (r, F_ID)
 }
 
+// lexing functions including simplification
 def lex_simp(r: Rexp, s: List[Char]) : Val = s match {
   case Nil => if (nullable(r)) mkeps(r) else throw new Exception("Not matched")
   case c::cs => {
@@ -200,7 +204,7 @@
 
 lexing_simp(("a" | "ab") ~ ("b" | ""), "ab")
 
-// Lexing Rules for a Small While Language
+// The Lexing Rules for a Small While Language
 
 def PLUS(r: Rexp) = r ~ r.%
 
@@ -285,7 +289,7 @@
 // some more timing tests with
 // i copies of the program
 
-for (i <- 1 to 21 by 10) {
+for (i <- 0 to 20 by 10) {
   print(i.toString + ":  ")
   time(lexing_simp(WHILE_REGS, prog2 * i))
 }