漢数字パーサだよ

KanjiNumberParser.scala

import scalaz._
import Scalaz._
import scala.util.parsing.combinator._

object KanjiNumberParser extends RegexParsers {
  def one   = "一" ^^ { _ => 1L }
  def two   = "二" ^^ { _ => 2L }
  def three = "三" ^^ { _ => 3L }
  def four  = "四" ^^ { _ => 4L }
  def five  = "五" ^^ { _ => 5L }
  def six   = "六" ^^ { _ => 6L }
  def seven = "七" ^^ { _ => 7L }
  def eight = "八" ^^ { _ => 8L }
  def nine  = "九" ^^ { _ => 9L }

  def oneDigit =
    one | two | three | four | five | six | seven | eight | nine

  def ju    = opt(oneDigit) <~ "十" ^^ { n => (n | 1L) * 10L }
  def hyaku = opt(oneDigit) <~ "百" ^^ { n => (n | 1L) * 100L }
  def sen   = opt(oneDigit) <~ "千" ^^ { n => (n | 1L) * 1000L }

  def threeDigits = opt(sen) ~ opt(hyaku) ~ opt(ju) ~ opt(oneDigit) ^^ {
    case a ~ b ~ c ~ d => ~ (a |+| b |+| c |+| d)
  }

  def man = opt(threeDigits) <~ "万" ^^ { n => (n | 1L) * 10000L }
  def oku = opt(threeDigits) <~ "億" ^^ { n => (n | 1L) * 10000L * 10000L }
  def cho = opt(threeDigits) <~ "兆" ^^ { n => (n | 1L) * 10000L * 10000L * 10000L }

  def kanjiNumber = opt(cho) ~ opt(oku) ~ opt(man) ~ opt(threeDigits) ^^ {
    case a ~ b ~ c ~ d => ~ (a |+| b |+| c |+| d)
  }

  def parse(in: String) = parseAll(kanjiNumber, in)
}

object Main extends App {
  println(KanjiNumberParser.parse("千五百兆二千二億三千五百十九万百一"))
}
/*
 [info] Running Main
 [1.18] parsed: 1500200235190101
 */

Scalazだと

{ n => (n getOrElse 1L) * 10L }

が

{ n => (n | 1L) * 10L }

って書けるよ！

な、なんだってー！

あと

case a ~ b ~ c ~ d => (a |+| b |+| c |+| d) | 0L

は

case a ~ b ~ c ~ d => ~ (a |+| b |+| c |+| d)

って書けば、零元を明示的に書かなくて、短く書けて素敵！ってなるんじゃなイカ！？

https://github.com/scalaz/scalaz/blob/6.0.3/core/src/main/scala/scalaz/OptionW.scala#L80

短く書けて素敵！