モナドとしての Option を for式 で連結

continual_random_sequence.scala

// お題：ランダム文字列
// <http://d.hatena.ne.jp/fumokmm/20110326/1301144291>
// に対する scala での答案（Iterator.continually編）by @akihiro4chawon

object Prob2 extends Application{
  def gen(nDigits: Int) = {
    val range = ('a' to 'z') ++ ('A' to 'Z') ++ ('0' to '9') :+ '_'
    Iterator.continually(range(Random.nextInt(range.size))) take nDigits mkString
  }

  println(gen(16))
  println(gen(16))
  println(gen(16))
}

jikoku_no_for.scala

// お題：時間帯重複チェック
// <http://d.hatena.ne.jp/fumokmm/20110326/1301146382>
// に対する scala での答案（for式とOption編）by @akihiro4chawon

// jikoku の for
object Prob1 extends Application {
  type Duration = (Int, Int, Int, Int)

  def timePointInMinutes(hour: Int, min: Int) =
    for {
      inMinutes <- Some(60 * hour + min)
      if inMinutes <= 60 * 24
      if 0 to 24 contains hour
      if 0 to 60 contains min
    } yield inMinutes

  val durationInMinutes = (d: Duration) => {
    val (h1, m1, h2, m2) = d
    for {
      t1 <- timePointInMinutes(h1, m1)
      t2 <- timePointInMinutes(h2, m2)
      if (t1 <= t2)
    } yield t1 until t2
  }

  // 問題への回答となる関数
  def timeDuplicationCheck(duration1: Duration, duration2: Duration) =
    for {
      d1 <- durationInMinutes(duration1)
      d2 <- durationInMinutes(duration2)
      intersection = d1 intersect d2
    } yield intersection.nonEmpty

  println(timeDuplicationCheck((1, 0, 5, 30), (9, 0, 23, 0))) // => Some(false) (重複なし)
  println(timeDuplicationCheck((1, 0, 2, 0), (2, 0, 3, 0)))   // => Some(false) (重複なし)
  println(timeDuplicationCheck((1, 0, 2, 1), (1, 59, 3, 0)))  // => Some(true) (重複あり)

  println(timeDuplicationCheck((1, 0, 5, 75), (9, 0, 23, 0))) // => None 範囲外の時刻
  println(timeDuplicationCheck((5, 30, 1, 5), (9, 0, 23, 0))) // => None 範囲外の時刻
}