めも

scalaz01.scala

import scalaz._, Scalaz._

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

val h = for {
  x <- f
  y <- g
} yield {
  x + y
}
// (_ + 1) + (_ + 2)
// (1 + 1) + (1 + 2)
// 5
assert(h(1) === 5)

// 同上
val q = (f |@| g)(_ + _)
assert(q(1) === 5)

// f(1) : 2
val w = f <* g
assert(w(1) === 2)

// クライスリ
val kf = Kleisli[Option, Int, Int] { x: Int => Some(x + 1) }
val kg = Kleisli[Option, Int, Int] { x: Int => Some(x * 2) }
locally {
  // andThen
  val f = kf >=> kg
  assert(f(1) === 4.some)
  // compose
  val g = kf <=< kf
  assert(g(1) === 3.some)
  // andThen (kelisliでなく関数を受け取れる)
  val h = kf >==> ((x:Int) => x.some)
  assert(h(1) === 2.some)
}
locally {
  val h = for {
    f <- kf
    g <- kg
  } yield f + g // (1 + 1) + (1 * 2) = 4
  assert(h(1) === 4.some)
}