Reverseしても日付になる4桁の数値（社内研修用）

reversible_date.scala

import java.text._
import java.util.Date

object HelloWorld extends App {

  val d = { val d = new SimpleDateFormat("yyyyMMdd"); d.setLenient(false); d }

  def fmt = (x: Int) => { "%04d".format(x) }

  def parse(in: String): Option[Date] = try {
    Some(d.parse(s"2000$in"))
  } catch {
    case e: Exception => None
  }

  def compParse(num: String): Option[Date] = {
    (parse(num), parse(num.reverse)) match {
      case (Some(a), Some(b)) => Some(a)
      case _ => None
    }
  }

  Range(0, 9999).map(fmt(_)).filter(compParse(_).nonEmpty).foreach(println(_))
}