xuwei-k

パーザコンビネータマニアックス

Scala Advent Calendar jp 2011の記事です。12/07に割り振られていたことに気づいていませんでしたorz。申し訳ありません。 さて、ネタを後で考えるつもりだったので迷ったのですが、直近で面白かったネタということでパーザコンビネータのちょっと変わった 使い方について紹介したいと思います。

さて、いきなり話が飛びますが、皆様はRubyのヒアドキュメントについてご存知でしょうか？

puts <

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// Inversefizzbuzz
//  http://www.jasq.org/2/post/2012/05/inverse-fizzbuzz.html
//
// fork from https://gist.github.com/2699068
object InverseFizzbuzz extends App {

  def zzubzzif(pattern:Seq[String]) = {
    def fizzbuzz(n:Int) = (n%3, n%5) match{
      case (0,0) => "fizzbuzz"
      case (0,_) => "fizz"

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object RetryUtil {                                                                                      
                                                                                                        
  case class RetryException(throwables: List[Throwable]) extends Exception                              
                                                                                                        
  def retry[T](retryLimit: Int, retryInterval: Int, shouldCatch: Throwable => Boolean)(f: => T): T = {  
//    @annotation.tailrec                                                                               
    def _retry( errors: List[Throwable], f: => T):T = {                                                 
      try {                                                                                             
        f                                                                                               
      } catch {                                                                

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// コンストラクタをプライベートにし、コンパニオンオブジェクト経由でのみ生成させる。
class ClassName[A] private (val clazz: Class[A]) {
  // toString で、引数に指定されたクラスの名称を返す。
  override def toString(): String = {
    clazz.getName
  }
}

object ClassName {
  // Classを直接渡して生成する。

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  /*
  * http://projecteuler.net/problem=2
  * http://odz.sakura.ne.jp/projecteuler/index.php?cmd=read&page=Problem%202
  */
  val fib: List[Int] => List[Int] = {
    case Nil | _ :: Nil => throw new IllegalArgumentException
    case xs @ (a :: b :: tail) => {
      val nextNum = a + b
      if (nextNum >= 4000000) {
        xs

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{-# LANGUAGE NoImplicitPrelude, MultiParamTypeClasses, Rank2Types, TypeOperators #-}

newtype Id a =
  Id a

data a :\/ b =
  Left a
  | Right b

data a :/\ b =

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import scala.reflect.runtime.universe._
import scala.reflect._

object App{

  def main(args : Array[String]){

    val m = toMap(User("Kudo",2,false))
    println(m)
    //Map(admin_?  -> false, gender  -> 2, name  -> Kudo)

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package s

object Test {
  // Observe that x.companion is statically typed such that foo is callable
  def f1() = {
    val x = new Foo

    println(x)                // Foo instance
    println(x.companion)      // Foo companion
    println(x.companion.foo)  // I'm foo!

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import sbt._
import Keys._
import Build.data

object build extends Build {
  lazy val runAll = TaskKey[Unit]("run-all") 
  
  lazy val standardSettings = Seq(
    runAllIn(Compile)
  )

xuwei-k

The z in scalaz means this: it was early 2008 and I was working for a Java consultancy and so of course, I used the most appropriate tool for the job: scala. But it had *terrible* libraries, so I offered to fix those while also meeting my other objectives. Turns out that the Scala guys were extremely hostile to even half-decent libraries (and still are to this day). I still struggle to wrap my head around this sometimes.

Anyway, so I thought, well fuck it, I will just keep them to myself for now. My (awesome) employer had already agreed that we'd probably open-source such a thing, but I was concerned most about my primary goal. So then it came time to "name" this library. I had named it "scalax" simply so that I did not have the inclination to think of a proper name. Then I found out that such a library was being developed and with my internal name! Whatever, I thought.

So I looked at this scalax library, hoping that I could just abandon my efforts and jump on board with everyone else -- they too had figure