functional-programming Loops by Recursive and Tail Recursive Functions tail recursive to optimize

Example

function sum(numbers) {
    return tail_sum(numbers, 0);
}

function tail_sum(numbers, acc) {
    if(numbers.length == 0) {
        return acc;
    }
    return tail_sum(numbers.slice(1), acc + numbers[0]);
}

in the tail recursive version, function return value does not need to wait till the end to do it its calculations, so there's no huge stack here; only two levels.

sum([10, 5, 6, 7]);

     tail_sum([10, 5, 6, 7], 0);

     tail_sum([5, 6, 7], 10);

     tail_sum([6, 7], 15);

     tail_sum([7], 21);

     tail_sum([], 28);

     28;