@tailrec注解与“蹦床”机制

import scala.util.control.TailCalls._
import scala.annotation._

object Sum extends App{
	//1
	def evenLength(xs:Seq[Int]):TailRec[Boolean]=
		if(xs.isEmpty) done(true) else tailcall(oddLength(xs.tail))
	def oddLength(xs:Seq[Int]): TailRec[Boolean]=
		if(xs.isEmpty) done(false) else tailcall(evenLength(xs.tail))
	println(evenLength(1 to 1000000).result)
	//2
	def sum1(xs:Seq[Int],partial:BigInt):TailRec[BigInt]=
		if(xs.isEmpty) done(partial) else tailcall(sum1(xs.tail,xs.head+partial))
	println(sum1(1 to 1000000,0).result)
	//3
	@tailrec def sum2(xs:Seq[Int],partial:BigInt):BigInt=
		if(xs.isEmpty) partial else sum2(xs.tail,xs.head+partial)
	println(sum2(1 to 1000000,0))
	//4
	def sum3(xs:Seq[Int]):BigInt=
		if(xs.isEmpty) 0 else xs.head+sum3(xs.tail)
	try{
		println(sum3(1 to 1000000))
	}catch{
		case _ => println("wrong")
	}
}