bothGrandfathers.scala

def bothGrandfathersFlatMap(p: Person): Maybe[(Person, Person)] =
  p.mother flatMap { m =>
    m.father flatMap { fm =>
      p.father flatMap { f =>
        f.father flatMap { ff =>
          Just(fm, ff)
        }
      }
    }
  }

def bothGrandfathersNoFlatMap(p: Person): Maybe[(Person, Person)] =
  (p.mother, p.father) match {
    case (Just(m), Just(f)) =>
      (m.father, f.father) match {
        case (Just(fm), Just(ff)) => Just((fm, ff))
        case _ => MaybeNot
      }
    case _ => MaybeNot
  }

def assertBothGrandfathers(
  bothGrandfathers1: Person => Maybe[(Person, Person)],
  bothGrandfathers2: Person => Maybe[(Person, Person)]) =
  Person.persons foreach { p =>
    assert(bothGrandfathers1(p) == bothGrandfathers2(p))
  }

assertBothGrandfathers(bothGrandfathersFlatMap, bothGrandfathersNoFlatMap)