just a place to keep deleted stuff to ease my sentiment (better than leaving commented out in the code)

UtilGraveyard.scala

implicit val decodeResultMonad: Monad[DR] = new Monad[DR] {
  override def flatMap[A, B](fa: DR[A])(f: A => DR[B]): DR[B] = fa.flatMap(f)
  override def tailRecM[A, B](a: A)(f: A => DR[Either[A, B]]): DR[B] = f(a) match {
    case DR.Value(Left(aa)) => tailRecM(aa)(f)
    case DR.Value(Right(b)) => DR.Value(b)
    case failedDecodeResult =>
      // scalastyle:off null
      failedDecodeResult.map(_.getOrElse(null.asInstanceOf[B])) // stays DR.failure - map is not applied
      // scalastyle:on null
  }
  override def pure[A](x: A): DR[A] = DR.Value(x)
}

def failFastFold[A, B, C, F[_]: Monad](coll: IterableOnce[A], z: C)
                                      (decd: A => F[B])
                                      (isok: F[C] => Boolean)
                                      (fold: (C, B) => C): F[C] = {
  val m = implicitly[Monad[F]]
  // scalastyle:off var.local
  var out: F[C] = m.pure(z)
  // scalastyle:on var.local
  val it = coll.iterator
  while(it.hasNext && isok(out)) {
    out = m.flatMap(decd(it.next())) { b =>
      m.map(out) { c =>
        fold(c, b)
      }
    }
  }
  out
}