めも

scalaz04.scala

import scalaz._, Scalaz._

val f = (_: Int) + 1
val g = (_: Int) * 2

// Arrow
// ========
locally {
  // andThen
  assert((f >>> g)(1) === 4)
  // compose
  assert((f <<< g)(1) === 3)

  // 関数をあわせる
  assert((f *** g)(1, 1) === (2, 2))
  // 1つの引数でどっちの関数にも適用
  assert((f &&& g)(1) === (2, 2))
}

// Unapply
// 色々な型の組み替え方法
// TraverseOps[F[_],A]
// ========
locally {
  // traverse(f: A => G[B]): G[F[B]]
  assert(1.some.traverse[List, Int]((x: Int) => List(x)) === List(Option(1)))
  // sequence[G[_], B]: G[F[B]]
  assert(Option(List(1)).sequence[List, Int] === List(Option(1)))

  // 型を2つ以上とる場合はUnapplyを利用したtraverseUが使える
  val a = 1.some.traverse[({type λ[A]=Validation[String, A]})#λ, Int](_.success[String])
  val b = 1.some.traverseU(_.success[String])
  assert(a == b)

  // sequenceUも
  val c = Option(1.success[String]).sequence[({type λ[A]=Validation[String, A]})#λ, Int]
  val d = Option(1.success[String]).sequenceU
  assert(c == d)

  // traverseM[G[_], B](f: A => G[F[B]]): G[F[B]]
  val e = Option(List(1)).traverseM[List, String](_.map(_ + "!" some))
  assert(e === List(Option("1!")))
}