steam_with_skips.scala

import scala.annotation.tailrec

@tailrec
def nextStep(
    iter: Iterator[Int], someAcc: List[Int]): (Stream[Int], Iterator[Int], List[Int]) = {
  if (iter.hasNext) {
    val i = iter.next()
      // emulate some window function computation
      val newAcc = (i / 2) :: someAcc
      val windowValue = newAcc.sum

      // skip some items before a window function match some condition
      if (windowValue > 10000) {
        (Stream(i), iter, List.empty)
      } else {
        nextStep(iter, newAcc)
      }
  } else {
    (Stream.empty, iter, someAcc)
  }
}


def mkStream(seq: Iterator[Int], someAcc: List[Int]): Stream[Int] = {
  val (res, tail, newAcc) = nextStep(seq, someAcc)
  res append mkStream(tail, newAcc)
}

val iterator = (1 to 10000000).toIterator
println(mkStream(iterator, List.empty).take(100).toList.mkString(","))