package main// 参考文档：//     https://github.com/Unknwon/the-way-to-go_ZH_CN/blob/master/eBook/06.7.mdimport (    "fmt")func main () {    callback(1, Add)}func Add(a, b int) {    fmt.Printf("The sum of %d and %d is: %d\n", a, b, a+b);}func callback(y int, f func(int, int)) {    f(y, 2) // this becomes Add(1, 2)}