def sum(f: Int => Int)(a: Int)(b: Int): Int = {
 
  @annotation.tailrec
  def loop(n: Int, acc: Int): Int = {
   if (n > b) {
    println(s"n=${n},acc=${acc}")
    acc
   } else {
    println(s"n=${n},acc=${acc}")
    loop(n + 1, acc + f(n))
   }
  }
  loop(a, 0)
 }    
 sum(x => x)(1)(5)
 sum(x => x*x)(1)(5)
 //使用通配符
 val sumSqure = sum(x => x * x)_ 
 sumSqure(1)(5)