14-222907.scala

def isSorted[A](as: Array[A], gt: (A,A) => Boolean): Boolean = {
  @annotation.tailrec
  def go(n: Int): Boolean =
    if (n >= as.length-1) true
    else if (gt(as(n), as(n+1))) false
    else go(n+1)

  go(0)
}

println(isSorted(Array(1,2,3), ((x: Int, y: Int) => x > y): ((Int, Int) => Boolean)))
println(isSorted(Array(1), ((x: Int, y: Int) => x > y): ((Int, Int) => Boolean)))

14-225248.scala

def isSorted[A](as: Array[A], gt: (A,A) => Boolean): Boolean = {
  as match {
    case as if as.length <= 1 => true
    case as if gt(as(0), as(1)) == false => isSorted(as.tail, gt)
    case _ => false
  }
}

println(isSorted(Array(1,2,3), ((x: Int, y: Int) => x > y): ((Int, Int) => Boolean)))

println(isSorted(Array(1), ((x: Int, y: Int) => x > y): ((Int, Int) => Boolean)))