rirakkumya

モナドはリラックマだ

モナドはコンテナだ。リラックマもコンテナ(中身入ってるし)だ。
だったら、モナドはリラックマだ。

と言う訳で、リラックマでモナド則書いてみた。

まず、リラックマの実装。リラックマは、皮と中身がある。そもそもいない時もある。
まさにMaybeだ。なので、Optionにしてみる。
えぇ手抜きですとも。

rirakkumya

package controllers

import play.api._
import play.api.mvc._
import play.api.cache._
import play.api.Play.current

object Application extends Controller {
  import EA._
  def index(id:String) = EitherAction {req =>

rirakkumya

package controllers

import play.api._
import play.api.mvc._
import play.api.cache._
import play.api.Play.current

object EA {
  case class Bind[a1,a2](x:Either[a1,a2]) {
    def #>>[b](f:a2 => Either[a1,b]):Either[a1,b] = x.right flatMap f

rirakkumya

case class Sheep(name:String,father:Option[Sheep],mother:Option[Sheep])

object SampleBase {
  def father(sheep:Sheep):Option[Sheep] = sheep match {
    case Sheep(_, s, _) => s
    case _ => None
  }
  def mother(sheep:Sheep):Option[Sheep] = sheep match {
    case Sheep(_, _, s) => s
    case _ => None

rirakkumya

libraryDependencies += "com.github.scala-incubator.io" %% "scala-io-core" % "0.3.0"

libraryDependencies += "com.github.scala-incubator.io" %% "scala-io-file" % "0.3.0"

rirakkumya

def foo[A,B](in:Option[A])(valid:PartialFunction[Option[A],Either[B,A]])(invalid:PartialFunction[Option[A],Either[B,A]])(other: =>Either[B,A]) = {
  if(!valid.isDefinedAt(in) && !invalid.isDefinedAt(in)) {
    other
  }else{
    (valid orElse invalid)(in)
  }
}

def getFirstData(id:String) = {
  foo(Cache.get(id)){

rirakkumya

libraryDependencies += "com.github.scala-incubator.io" %% "scala-io-core" % "0.3.0"

libraryDependencies += "com.github.scala-incubator.io" %% "scala-io-file" % "0.3.0"

rirakkumya

scala> for{(x,y) <- Right((3,4)).right} yield (x,y)
<console>:10: error: constructor cannot be instantiated to expected type;
 found   : (T1, T2)
 required: Either[Nothing,(Int, Int)]
              for{(x,y) <- Right((3,4)).right} yield (x,y)

scala> Right((3,4)).right map {case (x,y) => (x,y)}
res118: Product with Either[Nothing,(Int, Int)] with Serializable = Right((3,4))

rirakkumya

def index(id:String) = Action {
  getFirstData(id)
}
private def getFirstData(id:String) = {
  Cache.get(id) match {
    case Some(id2) => getSecondData(id2)
    case None => NotFound
  }
}
private def getSecondData(id2:String) = {

rirakkumya

import scala.annotation.tailrec
def hexToStr(s:String):String = {
  @tailrec def r(target:String,result:String):String = {
    target splitAt 2 match {
      case (xx,xs) if !xx.isEmpty => r(xs,result + Integer.parseInt(xx,16).toChar)
      case _ => result
    }
  }
  r(s,"")
}