IO.scala

sealed trait IO[+A] {

  def unsafeRunSync(): A

  def flatMap[B](f: A => IO[B]): IO[B] = IO.FlatMap(this, f)
  def map[B](f: A => B): IO[B] = flatMap(f andThen IO.pure _)

  // -------------------- Sync Maniputation Methods ----------------------------
  def attempt: Either[Throwable, A] = scala.util.Try(unsafeRunSync()).toEither

  // -------------------- Async Maniputation Methods ---------------------------

}

object IO {

  // ---------------------------- Init ATDs ------------------------------------
  private case class Apply[A](f: () => A) extends IO[A] {
    override def unsafeRunSync(): A = f()
  }

  private case class Pure[A](f: () => A) extends IO[A] {
    override def unsafeRunSync(): A = f()
  }

  private case class Error[A](t: Throwable) extends IO[A] {
    override def unsafeRunSync(): A = throw t
  }

  // ------------------------ Manipulation ATDs --------------------------------
  private case class FlatMap[A, B](io: IO[A], f: A => IO[B]) extends IO[B] {
    override def unsafeRunSync(): B = f(io.unsafeRunSync()).unsafeRunSync()
  }

  // -------------------------- Init Method ------------------------------------
  def apply[A](a: => A): IO[A] = Apply(() => a)

  def pure[A](a: A): IO[A] = Pure(() => a)

  def error[A](t: Throwable): IO[A] = Error[A](t)

}