Iteratees

Iteratee is defined as a trait, Iteratee[E, +A], where E is the input type and A is the result type. The state of an Iteratee is represented by an instance of Step, which is defined as follows:

sealed trait Step[E, +A] {

  def it: Iteratee[E, A] = this match {
    case Step.Done(a, e) => Done(a, e)
    case Step.Cont(k) => Cont(k)
    case Step.Error(msg, e) => Error(msg, e)
  }

}

object Step {

  //done state of an iteratee
  case class Done[+A, E](a: A, remaining: Input[E]) extends Step[E, A]

  //continuing state of an iteratee.
  case class Cont[E, +A](k: Input[E] => Iteratee[E, A]) extends Step[E, A]

  //error state of an iteratee
  case class Error[E](msg: String, input: Input[E]) extends Step[E, Nothing]
}

The input used here represents an element of the data stream, which can be empty, an element, or an end of file indicator. Therefore, Input is defined as follows:

sealed trait Input[+E] {
  def map[U](f: (E => U)): Input[U] = this match {
    case Input...