higher_order.scala

def findFirst1(ss: Array[String], key: String): Int = {
  @annotation.tailrec
  def loop(n: Int): Int =
    if (n >= ss.length) -1
    else if (ss(n) == key) n
    else loop(n + 1)
  loop(0)
}

println(findFirst1(Array("a", "b", "c"), "a"))

def findFirst2[A](as: Array[A], p: A => Boolean): Int = {
  @annotation.tailrec
  def loop(n: Int): Int =
    if (n >= as.length) -1
    else if (p(as(n))) n
    else loop(n + 1)

  loop(0)
}

println(findFirst2(Array("a", "b", "c"), (x: String) => x == "a"))
println(findFirst2(Array(1, 2, 3), (x: Int) => x == 1))

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))