scala进阶32-用for实现map、flattop、filter

object For_Advanced {  def map1[A, B](list: List[A], f: A => B): List[B] =    for(element <- list) yield f(element)  def flatMap1[A, B](list: List[A], f: A => List[B]): List[B] =    for(x <- list; y <- f(x)) yield y  def filter1[A](list: List[A], f: A => Boolean): List[A] =    for(elem <- list if f(elem)) yield elem  def main(args: Array[String]): Unit = {}}