Support single argument to zip

[ghost]

Zip currently requires at least two arguments.

zip can be seen as "create tuples consisting of an element of every argument". So, if one argument is passed, zip can still operate by creating tuples of only one element.

This can be very handy in situations where the splat operator is used:

$itemsDynamicallyGenerated1 = [[1, 2]];
$itemsDynamicallyGenerated2 = [[1, 2], [3, 4]];

assert(zip(...$itemsDynamicallyGenerated1) === [[1], [2]]);
assert(zip(...$itemsDynamicallyGenerated2) === [[1, 3], [2, 4]]);

A real world use case is having some dynamically sized list of lists, where these nested lists need to be zipped together, after which you want to calculate the total (sum) contained in each element:

assert(map(partial(rpartial(reduce, 0), sum), zip(...[[1, 2]])) === [1, 2]);
assert(map(partial(rpartial(reduce, 0), sum), zip(...[[1, 2], [3, 4]])) === [4, 6]);

Currently this fails if your list happens to be only one element. By allowing this, you can still safely map and reduce your list, as you will still have tuples contained in them.