ryoppy

Genericを使った型クラスインスタンスの導出

@ryoppy516

---

アジェンダ

1. HListについて
2. Genericについて

ryoppy

class Bench {
  @Benchmark
  def set2seq(): Unit = (1 to 100).combinations(2).toList.flatten.toSet.toSeq

  @Benchmark
  def distinct(): Unit = (1 to 100).combinations(2).toList.flatten.distinct
}

ryoppy

// stream
// ======
locally {
  val a: Stream[Int] = unfold(10) { x => if (x == 0) none else (x, x - 1).some }
  assert(a.toList === List(10,9,8,7,6,5,4,3,2,1))
}

// Memo
// メモ化
// ======

ryoppy

import scalaz._, Scalaz._

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

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

ryoppy

scala> val size = "300x250"
size: String = 300x250

scala> val Array(w, h) = size split "x" map (_.toInt)
w: Int = 300
h: Int = 250

scala> val Array(w, h, z) = size split "x" map (_.toInt)
scala.MatchError: [I@606d6d2c (of class [I)
  ... 33 elided

ryoppy

import scalaz._, Scalaz._

// Tree
// Tree構造。TreeLocを使うとDOMのように多彩なアクセスができる。
// ==================
locally {
  val tree = 'A'.node(
    'B'.node(
      'C'.leaf
    ),

ryoppy

import scalaz._, Scalaz._

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

val h = for {
  x <- f
  y <- g
} yield {
  x + y

ryoppy

implicit class RichFunction1[A, B](val f: A => B) extends AnyVal {
  def |>[C](g: B => C) = f andThen g
  def <|[C](g: C => A) = f compose g
}

val plus = (_: Int) + 1
val minus = (_: Int) - 1
val suffix = (_: Int) + "!"

val f = plus |> minus |> suffix

ryoppy

scala> def s[A: ({type λ[A] = A => Ordered[A]})#λ](xs: List[A]): List[A] = xs.sorted
s: [A](xs: List[A])(implicit evidence$1: A => scala.math.Ordered[A])List[A]

ryoppy

scala> def fid[F[_], A](a: F[A]): F[A] = a
warning: there was one feature warning; re-run with -feature for details
fid: [F[_], A](a: F[A])F[A]

scala> fid(List(1))
res0: List[Int] = List(1)

scala> fid(Option(1))
res1: Option[Int] = Some(1)