diff -r c7bdd7eac4cb -r 022e2cb1668d progs/dfa.scala
--- a/progs/dfa.scala	Sat Jul 04 16:58:12 2020 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,67 +0,0 @@
-// DFAs in Scala  using partial functions
-import scala.util.Try
-
-// a type abbreviation for partial functions
-type :=>[A, B] = PartialFunction[A, B]
-
-
-case class DFA[A, C](start: A,               // the starting state
-                     delta: (A, C) :=> A,    // transitions (partial fun)
-                     fins:  A => Boolean) {  // the final states
-
-  def deltas(q: A, s: List[C]) : A = s match {
-    case Nil => q
-    case c::cs => deltas(delta(q, c), cs)
-  }
-
-  def accepts(s: List[C]) : Boolean = 
-    Try(fins(deltas(start, s))) getOrElse false
-}
-
-// the example shown in the handout 
-abstract class State
-case object Q0 extends State
-case object Q1 extends State
-case object Q2 extends State
-case object Q3 extends State
-case object Q4 extends State
-
-val delta : (State, Char) :=> State = 
-  { case (Q0, 'a') => Q1
-    case (Q0, 'b') => Q2
-    case (Q1, 'a') => Q4
-    case (Q1, 'b') => Q2
-    case (Q2, 'a') => Q3
-    case (Q2, 'b') => Q2
-    case (Q3, 'a') => Q4
-    case (Q3, 'b') => Q0
-    case (Q4, 'a') => Q4
-    case (Q4, 'b') => Q4 }
-
-val dfa = DFA(Q0, delta, Set[State](Q4))
-dfa.accepts("aaabbb".toList) 
-
-dfa.accepts("bbabaab".toList)   // true
-dfa.accepts("baba".toList)      // false
-dfa.accepts("abc".toList)       // false
-
-// another DFA test with a Sink state
-abstract class S
-case object S0 extends S
-case object S1 extends S
-case object S2 extends S
-case object Sink extends S
-
-// a transition function with a sink state
-val sigma : (S, Char) :=> S = 
-  { case (S0, 'a') => S1
-    case (S1, 'a') => S2
-    case _ => Sink
-  }
-
-val dfa1a = DFA(S0, sigma, Set[S](S2))
-
-dfa1a.accepts("aa".toList)        // true
-dfa1a.accepts("".toList)          // false
-dfa1a.accepts("ab".toList)        // false
-