3.1 Higher Order Function - Gaoey/scala-diary GitHub Wiki

HOF is passing functions to functions

The first new idea is this:

functions are values.

And just like values of other types—such as integers, strings, and lists—functions can be assigned to variables, stored in data structures, and passed as arguments to functions.

When writing purely functional programs, we’ll often find it useful to write a function that accepts other functions as arguments. This is called a higher-order function (HOF)

from:

Functional Programming in Scala - By PAUL CHIUSANO, RÚNAR BJARNASON

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higher order function คือ การที่เราสามารถโยน function เข้าไปในฟังก์ชันได้, function เป็น argument ได้

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

    go(0)
  }
}

 Sort.isSorted(Array(1, 3, 5, 7), (x: Int, y: Int) => x > y) should be(true)
 Sort.isSorted(Array(7, 5, 1, 3), (x: Int, y: Int) => x < y) should be(false)