刚看到一段 scala程序：Merry Xmas
import annotation.tailrecabstract class Tree(val left: Tree) { def o = new Ball(this) def x = new Spike(this) def * = new Candle(this) def oxo = new BigBall(this) def oo = new DoubleBall(this) def *** = new ElectricCandle(this) def / = new LeftNeedle(this) def \ = new RightNeedle(this) def | = new Trunk(this)}class Top(star: Star) extends Tree(star)abstract class Needle(left: Tree) extends Tree(left)class LeftNeedle(left: Tree) extends Needle(left)class RightNeedle(left: Tree) extends Needle(left) { def |||() { |||(true) } @tailrec final def |||(sparkle: Boolean) { val f = (t: Tree) => t match { case _: LeftNeedle => "/" case _: RightNeedle => "\\" case _: Trunk => "|" case _: Ball => "o" case _: Spike => "x" case _: Candle => "*" case _: BigBall => "oxo" case _: DoubleBall => "oo" case _: ElectricCandle => "***" } def walk(t: Tree, depth: Int): List[String] = { def walkLevel(t: Tree, acc: String, f: (Tree) => String): (Tree, String) = { val fx = (t: Tree) => if (sparkle) f(t).toUpperCase else f(t) t match { case l: LeftNeedle => (l.left, fx(l) + "." + acc) case t: Tree => walkLevel(t.left, fx(t) + "." + acc, f) } } t match { case r: RightNeedle => val l = walkLevel(r, "", f) l._2 +: walk(l._1, depth + 1) case s: Star => List("-->*<-- ", "\\-/.") } } val tree = "||| " +: walk(this, 0) tree.reverse.foreach({l => val numSpaces = 30 - (l.length() / 2) val padding = " " * numSpaces print(padding) println(l) }) Thread.sleep(500) |||(!sparkle) }}class Trunk(parent: Tree) extends Tree(parent)abstract class Decoration(left: Tree) extends Tree(left)class Star extends Decoration(null)class Candle(left: Tree) extends Decoration(left)class Ball(left: Tree) extends Decoration(left)class Spike(left: Tree) extends Decoration(left)class BigBall(left: Tree) extends Decoration(left)class DoubleBall(left: Tree) extends Decoration(left)class ElectricCandle(left: Tree) extends Decoration(left)trait DecorationBuilder { def \-/ = new PartialDecoration}class PartialDecoration { def -->*<-- = new Star}object ChristmasTree extends DecorationBuilder { def main(args: Array[String]) { \-/. -->*<-- . /.\ ./.|.\. /.oxo.\ ./.*.|.x.\. /.oo.|.oo.\ ./.oxo.|.***.\. /.*.oo.|.*.oo.\. ||| }}