arrow tutorial '5. kleisli arrows'

arrow_tutorial05.sc

import cats.arrow.Arrow
import cats.data.Kleisli

sealed case class SimpleFunc[A, B](runF: A => B)

import cats.syntax.arrow._
import cats.syntax.compose._

def arr[F[_, _]: Arrow, A, B](f: A => B): F[A, B] = Arrow[F] lift f
def split[F[_, _]: Arrow, A]: F[A, (A, A)] = arr(x => (x, x))
def unsplit[F[_, _]: Arrow, A, B, C](f: (A, B) => C): F[(A, B), C] =
  arr(f.tupled)
def liftA2[F[_, _], A, B, C, D](f: (B, C) => D, fb: F[A, B], fc: F[A, C])
  (implicit A: Arrow[F]): F[A, D] =
  (fb &&& fc) >>> unsplit(f)
//  split[F, A] >>> A.first(fb) >>> A.second(fc) >>> unsplit(f)

// Kleisli ------------------
type ListKleisli[A, B] = Kleisli[List, A, B]
def testKleisliArrow(n: Int)(implicit A0: Arrow[ListKleisli]) = {
  type Arr = ListKleisli[Int, Int]
  def plusMinus:Arr = Kleisli(x => x :: (-x) :: Nil)
  def double   :Arr = arr((_: Int) * 2)
  def h2       :Arr = liftA2((_: Int) + (_: Int), plusMinus, double)

  h2 run n
}
import cats.instances.list._
testKleisliArrow(8)