// 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))

}