gistfile1.txt

def lazyFoldRight[A,B](as: List[A], z: B)(f: (A, =>B) => B): B =
as match {
  case Nil => z
  case x :: xs => f(x, lazyFoldRight(xs, z)(f))
}

def findWithPriority[T](xs: List[T], high: T => Boolean, low: T => Boolean): Option[T] = {
  val t = lazyFoldRight(xs,(None,None):(Option[T],Option[T]))((x,result)=>
      if(high(x)) (Some(x),None)
      else if(low(x)){
        if(result._1.isDefined) result  else (None,Some(x))
      }else
        result
  )
  t._1.orElse(t._2)
}

assert(findWithPriority(List(1, 3, 4, 2), (x: Int) => x > 3, (x: Int) => x > 2) == Some(4))
assert(findWithPriority(List(1, 4, 3, 2), (x: Int) => x > 2, (x: Int) => x > 3) == Some(4))
assert(findWithPriority(List(1, 3, 4, 2), (x: Int) => x > 3, (x: Int) => x > 4) == Some(4))
assert(findWithPriority(List(1, 3, 4, 2), (x: Int) => x > 4, (x: Int) => x > 3) == Some(4))
assert(findWithPriority(List(1, 3, 4, 2), (x: Int) => x > 4, (x: Int) => x > 4) == None)