Sum a tree using nil pointer receivers

main.go

package main

import "fmt"

type node struct {
	v int
	l *node
	r *node
}

func (n *node) sum() int {
	if n == nil {
		return 0
	}

	return n.v + n.l.sum() + n.r.sum()
}

//        n1
//     /      \
//    n2       n3
//   /  \        \
//  n4  n5        n6
// 	/  \      /
//    n7   n8   n9

func main() {

	n7 := node{3, nil, nil}
	n8 := node{5, nil, nil}

	n4 := node{v: 1, l: nil, r: nil}
	n5 := node{v: 4, l: &n7, r: &n8}
	n2 := node{v: 2, l: &n4, r: &n5}

	n9 := node{v: 8, l: nil, r: nil}
	n6 := node{v: 9, l: &n9, r: nil}
	n3 := node{v: 7, l: nil, r: &n6}

	n1 := node{v: 6, l: &n2, r: &n3}

	fmt.Println(n1.sum())
}