// 1. Prints: A
retry(3, time.Second, func() error {
	fmt.Print("A")
	return nil
})

// 2. Prints: BB
var i int
retry(3, time.Second, func() error {
	i++
	fmt.Print("B")
	if i == 2 {
		return stop{errors.New("stop it")}
	}
	return errors.New("keep going")
})

// 3. Prints: CCC
retry(3, time.Second, func() error {
	fmt.Print("C")
	return errors.New("not today")
})