Scala equivalent of Haskell first and second

firstSecond.scala

import scalaz._, Scalaz._

object Main extends App {
  // Scala equivalent of Haskell first and second
  // http://stackoverflow.com/questions/39457088/scala-equivalent-of-haskell-first-and-second

  type T2 = Tuple2[Int, Int]
  val f = (n: Int) => n + 1
  val g = (n: Int) => n * 100

  def stdFirst[A, B, X](fn: A => X)(pair: (A, B)): (X, B) = (fn(pair._1), pair._2)
  def stdSecond[A, B, X](fn: B => X)(pair: (A, B)): (A, X) = (pair._1, fn(pair._2))

  assert { (stdFirst(f)((1, 2))) == ((2, 2): T2) }
  assert { (stdSecond(g)((1, 2))) == ((1, 200): T2) }

  //----------------------------------------------------------------------

  // first[A, B, C](fa: =>:[A, B]): =>:[(A, C), (B, C)]
  // second[A, B, C](f: =>:[A, B]): =>:[(C, A), (C, B)]
  assert { f.first((1, 2)) === ((2, 2): T2) }
  assert { g.second((1, 2)) === ((1, 200): T2) }

  assert { (f *** g)((1, 2)) === ((2, 200): T2) }
}