func loop(ints ...int64) (<-chan int64, error) {
	var start, stop int64
	switch len(ints) {
	case 1:
		start, stop = 0, ints[0]
	case 2:
		start, stop = ints[0], ints[1]
	default:
		return nil, fmt.Errorf("loop: wrong number of arguments, expected 1 or 2"+
			", but got %d", len(ints))
	}

	ch := make(chan int64)

	go func() {
		for i := start; i < stop; i++ {
			ch <- i
		}
		close(ch)
	}()

	return ch, nil
}
func loop(ints ...int64) (<-chan int64, error) {
	var start, stop int64
	switch len(ints) {
	case 1:
		start, stop = 0, ints[0]
	case 2:
		start, stop = ints[0], ints[1]
	default:
		return nil, fmt.Errorf("loop: wrong number of arguments, expected 1 or 2"+
			", but got %d", len(ints))
	}

	ch := make(chan int64)

	go func() {
		for i := start; i < stop; i++ {
			ch <- i
		}
		close(ch)
	}()

	return ch, nil
}
// loop accepts varying parameters and differs its behavior. If given one
// parameter, loop will return a goroutine that begins at 0 and loops until the
// given int, increasing the index by 1 each iteration. If given two parameters,
// loop will return a goroutine that begins at the first parameter and loops
// up to but not including the second parameter.
//
//    // Prints 0 1 2 3 4
// 		for _, i := range loop(5) {
// 			print(i)
// 		}
//
//    // Prints 5 6 7
// 		for _, i := range loop(5, 8) {
// 			print(i)
// 		}
//