--- a/Fahad/Eclipse/ScalaProjects/bin/Handouts/Handout2.sc	Sun Nov 02 12:24:41 2014 +0000
+++ b/Fahad/Eclipse/ScalaProjects/bin/Handouts/Handout2.sc	Tue Nov 04 19:51:01 2014 +0000
@@ -16,14 +16,6 @@
 
   def OPT(r: Rexp) = ALT(r, EMPTY)                //> OPT: (r: Handouts.Handout2.Rexp)Handouts.Handout2.ALT
 
-  /*
-  def NTIMES(r: Rexp, n: Int): Rexp = n match {
-    case 0 => EMPTY
-    case 1 => r
-    case n => SEQ(r, NTIMES(r, n - 1))
-  }
-  */
-
   def nullable(r: Rexp): Boolean = r match {
     case NULL => false
     case EMPTY => true

--- a/Fahad/Eclipse/ScalaProjects/src/Handouts/Handout2.sc	Sun Nov 02 12:24:41 2014 +0000
+++ b/Fahad/Eclipse/ScalaProjects/src/Handouts/Handout2.sc	Tue Nov 04 19:51:01 2014 +0000
@@ -16,14 +16,6 @@
 
   def OPT(r: Rexp) = ALT(r, EMPTY)                //> OPT: (r: Handouts.Handout2.Rexp)Handouts.Handout2.ALT
 
-  /*
-  def NTIMES(r: Rexp, n: Int): Rexp = n match {
-    case 0 => EMPTY
-    case 1 => r
-    case n => SEQ(r, NTIMES(r, n - 1))
-  }
-  */
-
   def nullable(r: Rexp): Boolean = r match {
     case NULL => false
     case EMPTY => true

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Fahad/Eclipse/ScalaProjects/src/POSIX/PosixAlgo.sc	Tue Nov 04 19:51:01 2014 +0000
@@ -0,0 +1,44 @@
+package POSIX
+
+object PosixAlgo {
+
+  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 RECD(x: String, r: Rexp) extends Rexp
+
+	abstract class Val
+  case object Void extends Val
+  case class Chr(c: Char) extends Val
+  case class Sequ(v1: Val, v2: Val) extends Val
+  case class Left(v: Val) extends Val
+  case class Right(v: Val) extends Val
+  case class Stars(vs: List[Val]) extends Val
+  case class Rec(x: String, v: Val) extends Val
+
+	def nullable(r: Rexp): Boolean = r match {
+    case NULL => false
+    case EMPTY => true
+    case CHAR(_) => false
+    case ALT(r1, r2) => nullable(r1) || nullable(r2)
+    case SEQ(r1, r2) => nullable(r1) && nullable(r2)
+    case STAR(_) => true
+    case RECD(_, r1) => nullable(r1)
+  }                                               //> nullable: (r: POSIX.PosixAlgo.Rexp)Boolean
+  
+  def der(c: Char, r: Rexp): Rexp = r match {
+    case NULL => NULL
+    case EMPTY => NULL
+    case CHAR(d) => if (c == d) EMPTY else NULL
+    case ALT(r1, r2) => ALT(der(c, r1), der(c, r2))
+    case SEQ(r1, r2) =>
+      if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))
+      else SEQ(der(c, r1), r2)
+    case STAR(r) => SEQ(der(c, r), STAR(r))
+    case RECD(_, r1) => der(c, r1)
+  }                                               //> der: (c: Char, r: POSIX.PosixAlgo.Rexp)POSIX.PosixAlgo.Rexp
+}
\ No newline at end of file