組み込み制御構造 while for if 例外処理 match

BuiltinControlStructure.scala

package PSSE.code

object BuitinControlStructures extends App {

  def gcdLoop(x: Long, y: Long): Long = {
    var a = x
    var b = y
    while (a != 0) {
      val temp = a
      a = b % a
      b = temp
    }
    b
  }

  println(gcdLoop(66, 42))

  def gcd(x: Long, y: Long): Long =
    if (y == 0) x else gcd(y, x % y)

  println(gcd(66, 42))

  //  var line = ""
  //  do {
  //    line = readLine()
  //    println("Read: "+ line)
  //  } while (line != "")

  val filesHere = (new java.io.File(".")).listFiles

  for (file <- filesHere)
    println(file)

  for (i <- 1 to 4)
    println("Iteration " + i)

  val filestmp = (new java.io.File("/tmp/scalaLesson/")).listFiles

  for (file <- filestmp if file.getName.endsWith(".scala"))
    println(file)

  // より防御的なコード
  for (
    file <- filestmp
    if file.isFile
    if file.getName.endsWith(".scala")
  ) println(file)

  def fileLines(file: java.io.File) =
    scala.io.Source.fromFile(file).getLines().toList

  //  def grep(pattern: String) =
  //    for (
  //      file <- filestmp
  //      if file.getName.endsWith(".scala");
  //      line <- fileLines(file)
  //      if line.trim.matches(pattern)
  //    ) println(file +": "+ line.trim)
  //
  //  grep(".*gcd.*")

  println("ループを二回まわす")

  def grep(pattern: String) =
    for {
      file <- filestmp
      if file.getName.endsWith(".scala")
      line <- fileLines(file)
      trimmed = line.trim
      if trimmed.matches(pattern)
    } println(file + ": " + trimmed)

  grep(".*gcd.*")

  // コレクションの生成
  def scalaFiles =
    for {
      file <- filestmp
      if file.getName.endsWith(".scala")
    } yield println(file)

  scalaFiles

  // for式でArray[File]からArray[Int]を生成する
  val forLineLengths =
    for {
      file <- filestmp
      if file.getName.endsWith(".scala")
      line <- fileLines(file)
      trimmed = line.trim
      if trimmed.matches(".*for.*")
    } yield println(trimmed)

  // 例外処理
  val n = 2
  val half =
    if (n % 2 == 0)
      n / 2
    else
      throw new RuntimeException("n must be even")

  import java.io.FileReader
  import java.io.FileNotFoundException
  import java.io.IOException

  try {
    val f = new FileReader("/tmp/scalaLesson/fooa.scala")
    // Use and close file
  } catch {
    case ex: FileNotFoundException => // Handle missing file
    case ex: IOException => // Handle other I/O error
  }

  val firstArg = "salt"

  firstArg match {
    case "salt" => println("pepper")
    case "chips" => println("salsa")
    case "eggs" => println("bacon")
    case _ => println("huh?")
  }

  // 再帰を使ったループコード　searchFrom(i + 1)　がcontinueの代わりとなる
  def searchFrom(i: Int): Int =
    if (i >= filestmp.length) -1
    else if (filestmp(i).getName.startsWith("-")) searchFrom(i + 1)
    else if (filestmp(i).getName.endsWith(".scala")) i
    else searchFrom(i + 1)

  val i = searchFrom(0)
  println(i)

  
  // 九九表を作成する
  def makeRowSeq(row: Int) =
    for (col <- 1 to 10) yield {
      val prod = (row * col).toString
      val padding = " " * (4 - prod.length)
      padding + prod
    }

  // Returns a row as a string
  def makeRow(row: Int) = makeRowSeq(row).mkString

  // Returns table as a string with one row per line
  def multiTable() = {

    val tableSeq = // a sequence of row strings
      for (row <- 1 to 10)
      yield makeRow(row)
    tableSeq.mkString("\n")
  }

  println(multiTable())
}