the-way-to-go_ZH_CN/eBook/examples/chapter_6/mut_recurs.go

// mut_recurs.go
package main

import (
	"fmt"
)

func main() {
	fmt.Printf("%d is even: is %t\n", 16, even(16)) // 16 is even: is true
	fmt.Printf("%d is odd: is %t\n", 17, odd(17))	// 17 is odd: is true
	fmt.Printf("%d is odd: is %t\n", 18, odd(18))	// 18 is odd: is false
}

func even(nr int) bool {
    if nr == 0 {return true}
    return odd(RevSign(nr)-1)
}

func odd(nr int) bool {
    if nr == 0 {return false}
    return even(RevSign(nr)-1)
}

func RevSign(nr int) int {
	if nr < 0 {return -nr}
	return nr
}