lyricallogical

!SLIDE
sclaz7 の scalaz.Iteratee の紹介
================================

!SLIDE
発端
----

> @halcat0x15a: @lyrical_logical 7のiterateeが別物になってて読めないです・・・・ 11:38 PM - 14 Feb 12

lyricallogical

parseOpt(request.body) map { json =>
  (json \\ "events" \\ "message").values
} collect { case msg : Map[String, String] =>
  hoge
} getOrElse {
  huga
}

lyricallogical

Inductive even : nat -> Prop :=
| even_O : even 0
| even_S : forall n, odd n -> even (S n)
with odd : nat -> Prop :=
| odd_S : forall n, even n -> odd (S n).

Scheme even_mut := Induction for even Sort Prop
  with odd_mut := Induction for odd Sort Prop.

Theorem daigakuseinosuugakuryoku : forall n m,

lyricallogical

trait Abs { def f(): Int }
trait ConA extends Abs { def f() = 1 }
trait ConB extends Abs { abstract override def f() = super.f + 1 }

trait Delegate extends Abs {
  val abs: Abs
  def f() = abs.f
}

class A { this: Abs =>

lyricallogical

def withRight[A, B] = new { def apply[R](f: (Either[A, B] => Either.RightProjection[A, B]) => R) = f(_.right) }
def withLeft[A, B] = new { def apply[R](f: (Either[A, B] => Either.LeftProjection[A, B]) => R) = f(_.left) }

withRight[Int, Int] { implicit ev =>
  for {
    x <- Right(1)
    y <- Right(2)
  } yield x + y // => Right(3)
  for {
    x <- Right(1)

lyricallogical

trait Zero[A] { val zero: A }
implicit val IntZero = new Zero[Int] { val zero = 0 }

implicit def RightProjectionWithFilter[A, B](r: Either.RightProjection[A, B])(implicit azero: Zero[A]) = new {
  class WithFilter(p: B => Boolean) {
    def map[C](f: B => C): Either[A, C] = r.filter(p).getOrElse(Left(azero.zero)).right.map(f)
    def flatMap[AA >: A, C](f: B => Either[AA, C]): Either[AA, C] = r.filter(p).getOrElse(Left(azero.zero)).right.flatMap(f)
    def withFilter(p0: B => Boolean): WithFilter = new WithFilter(b => p(b) && p0(b))
  }
  def withFilter(p: B => Boolean): WithFilter = new WithFilter(p)

lyricallogical

type 'a node =
  | A: int -> int node
  | B: string -> string node

module type Exists = sig
  type t
  val ret: t node
end

module type PolyFun = sig

lyricallogical

lazy val fab: PartialFunction[Base, Int] = {
  case A(base) => 1 + fabc(base) // PartialFunction#apply の呼び出し。危ない！
  case B(left, right) => 1 + fabcd(left) + fabcd(right) // 同様
}

// 全域関数だと scala コンパイラにはわからない！
lazy val fabcd: PartialFunction[Base, Int] = fab orElse {
  case C => 1
  case D => 2
}

lyricallogical

!SLIDE
Play 2.0 の Action と BodyParser について学ぼう
----------------

!SLIDE
自己紹介
----------------
* 望月 慎也
* @lyrical_logical
* 株式会社レピダム

lyricallogical

imoprt Iteratee._

lazy val takeOdds = {
  val aux = for {
   one <- headOption[Byte[Array]] // ダサい
    _ <- headOption[Byte[Array]] // ダサい
  } yield one

  for {
    odds <- aux