diff -r f824e1331fc6 -r bd5a8a6b3871 progs/cw1.scala
--- a/progs/cw1.scala	Wed Nov 27 08:49:51 2013 +0000
+++ b/progs/cw1.scala	Wed Nov 27 21:36:30 2013 +0000
@@ -95,6 +95,21 @@
   case OPT(_) => true
 }
 
+def zeroable (r: Rexp) : Boolean = r match {
+  case NULL => true
+  case EMPTY => false
+  case CHAR(_) => false
+  case ALT(r1, r2) => zeroable(r1) && zeroable(r2)
+  case SEQ(r1, r2) => zeroable(r1) || zeroable(r2)
+  case STAR(_) => false
+  case PLUS(r) => zeroable(r)
+  case NTIMES(r, i) => if (i == 0) false else zeroable(r)
+  case NUPTOM(r, i, j) => if (i == 0) false else zeroable(r)
+  case RANGE(_) => false
+  case NOT(r) => !(zeroable(r))
+  case OPT(_) => false
+}
+
 // derivative of a regular expression w.r.t. a character
 def der (c: Char, r: Rexp) : Rexp = r match {
   case NULL => NULL
@@ -212,3 +227,36 @@
 println(ders_simp("aaaaa".toList, test))
 println(ders_simp("aaaaaa".toList, test))
 println(ders_simp("aaaaaaa".toList, test))
+
+def TEST(s: String, r: Rexp) = {
+  println("Rexp |" + s + "|")
+  println("Derivative:\n" + ders_simp(s.toList, r))
+  println("Is Nullable: " + nullable(ders_simp(s.toList, r)))
+  println("Is Zeroable: " + zeroable(ders_simp(s.toList, r)))
+  Console.readLine
+}
+
+
+val ALL2 = "a" | "f"
+val COMMENT2 = ("/*" ~ NOT(ALL2.% ~ "*/" ~ ALL2.%) ~ "*/")
+
+println("1) TEST TEST")
+TEST("", COMMENT2)
+TEST("/", COMMENT2)
+TEST("/*", COMMENT2)
+TEST("/*f", COMMENT2)
+TEST("/*f*", COMMENT2)
+TEST("/*f*/", COMMENT2)
+TEST("/*f*/ ", COMMENT2)
+
+val ALL3 = "a" | "f"
+val COMMENT3 = ("/" ~ NOT(ALL3.% ~ "&" ~ ALL3.%) ~ "&")
+
+println("2) TEST TEST")
+TEST("", COMMENT3)
+TEST("/", COMMENT3)
+TEST("/", COMMENT3)
+TEST("/f", COMMENT3)
+TEST("/f&", COMMENT3)
+TEST("/f& ", COMMENT3)
+