diff -r 8178fcf377dc -r a697421eaa04 progs/display/thompson2.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/display/thompson2.scala	Fri Apr 28 11:01:25 2017 +0100
@@ -0,0 +1,44 @@
+// Thompson Construction (Part 2)
+
+// some more types abbreviations
+type NFAtrans = (TState, Char) :=> Set[TState]
+type eNFAtrans = (TState, Option[Char]) :=> Set[TState]
+
+
+// for composing an eNFA transition with a NFA transition
+implicit class RichPF(val f: eNFAtrans) extends AnyVal {
+  def +++(g: NFAtrans) : eNFAtrans = 
+  { case (q, None) =>  applyOrElse(f, (q, None)) 
+    case (q, Some(c)) => 
+      applyOrElse(f, (q, Some(c))) | applyOrElse(g, (q, c))  }
+}
+
+// sequence of two NFAs
+def NFA_SEQ(enfa1: NFAt, enfa2: NFAt) : NFAt = {
+  val new_delta : eNFAtrans = 
+    { case (q, None) if enfa1.fins(q) => enfa2.starts }
+  
+  eNFA(enfa1.starts, new_delta +++ enfa1.delta +++ enfa2.delta, 
+       enfa2.fins)
+}
+
+// alternative of two NFAs
+def NFA_ALT(enfa1: NFAt, enfa2: NFAt) : NFAt = {
+  val Q = TState()
+  val new_delta : eNFAtrans = 
+    { case (Q, None) => enfa1.starts | enfa2.starts }
+  val new_fins = (q: TState) => enfa1.fins(q) || enfa2.fins(q)
+
+  eNFA(Set(Q), new_delta +++ enfa1.delta +++ enfa2.delta, 
+       new_fins)
+}
+
+// star of a NFA
+def NFA_STAR(enfa: NFAt) : NFAt = {
+  val Q = TState()
+  val new_delta : eNFAtrans = 
+    { case (Q, None) => enfa.starts
+      case (q, None) if enfa.fins(q) => Set(Q) }
+
+  eNFA(Set(Q), new_delta +++ enfa.delta, Set(Q))
+}