CollatzApp.scala

package org.kornel.collatz

object CollatzScala extends App {

  import StreamTakeWhileInclusive.StreamTWI

  val start = 15

  val collatz = Stream.iterate(15) {
    case n if n % 2 == 0 => n / 2
    case n => 3 * n + 1
  }

  collatz
    .takeWhileInc(_ != 1)
    .foreach(println)

}

object StreamTakeWhileInclusive {

  implicit class StreamTWI[A](s: Stream[A]) {
    def takeWhileInc(p: A => Boolean) = {
      val (left, right) = s.span(p)
      left :+ right.head
    }
  }

}