fun startHere() {
  var addResult = calculate(10, 3, { x, y ->
    x + y
  })

  var subtractResult = calculate(10, 3, { x, y ->
    x - y
  })
  ...
}

fun calculate(x: Int,
              y: Int,
              equation: (x: Int, y: Int) -> Int): Int {
  return equation(x, y)
}