Reasons for none

disjunction.scala

def noReasons(x: Int): Option[Int] = for {
  y <- Option(x).filter(_ > 0)
  z <- Option(y / 2).filter(_ > 1)
} yield z

(0 to 4) map noReasons
// scala.collection.immutable.IndexedSeq[Option[Int]] = Vector(None, None, None, None, Some(2))

import scalaz.\/
import scalaz.syntax.std.option._

def reasons(x: Int): String \/ Int = for {
  y <- Option(x).filter(_ > 0).toRightDisjunction("x was <= 0")
  z <- Option(y / 2).filter(_ > 1).toRightDisjunction("y / 2 was 1")
} yield z

(0 to 4) map reasons
// scala.collection.immutable.IndexedSeq[scalaz.\/[String,Int]] = Vector(-\/(x was <= 0), -\/(y / 2 was 1), -\/(y / 2 was 1), -\/(y / 2 was 1), \/-(2))