set-theory/cartesian-product

/**
 * Algorithm used by {@link product} to compute the product of one or more
 * iterables from pools of symbols.
 *
 * @example
 * // Ax Ay Bx By Cx Cy Dx Dy
 * _product(['xy', 'ABCD'], 0 , 2) ;
 *
 * @example
 * // 000 001 010 011 100 101 110 111
 * _product([[0,1],[0,1],[0,1]], 0 , 3) ;
 *
 * @param {Array<Iterable>} pools - The pools of symbols in reverse order.
 * @param {number} i - Index of the pool to draw the next symbol from
 * @param {number} n - Number of pools in total.
 * @returns {IterableIterator}
 */
export default function* _product(pools, i, n) {
    if (i === n) {
        yield [];
        return;
    }

    const iterable = pools[i];

    for (const buffer of _product(pools, i + 1, n)) {
        for (const item of iterable) {
            buffer.push(item);

            yield buffer;

            buffer.pop(item);
        }
    }
}