// Thompson Construction (Part 1)
// (needs  :load dfa.scala
//         :load nfa.scala
//         :load enfa.scala)


// states for Thompson construction
case class TState(i: Int) extends State

object TState {
  var counter = 0
  
  def apply() : TState = {
    counter += 1;
    new TState(counter - 1)
  }
}


// a type abbreviation
type NFAt = NFA[TState, Char]


// a NFA that does not accept any string
def NFA_ZERO(): NFAt = {
  val Q = TState()
  NFA(Set(Q), { case _ => Set() }, Set())
}

// a NFA that accepts the empty string
def NFA_ONE() : NFAt = {
  val Q = TState()
  NFA(Set(Q), { case _ => Set() }, Set(Q))
}

// a NFA that accepts the string "c"
def NFA_CHAR(c: Char) : NFAt = {
  val Q1 = TState()
  val Q2 = TState()
  NFA(Set(Q1), { case (Q1, d) if (c == d) => Set(Q2) }, Set(Q2))
}