iterable helpers??

combinations.js

// @ts-check
/**
 * @template T
 * @param {Iterable<T>} iterable the collection of items for which to make combinations of
 * @param {number} size the size of each combination
 * @return {Iterable<Set<T>>} an iterable of sets for each combination
 */
function* combinations(iterable, size) {
	if (size < 1) return

	if (size === 1) {
		for (const item of iterable) {
			yield new Set([item])
		}
	}

	for (const [index, item] of entries(iterable)) {
		for (const rest of combinations(skip(iterable, index), size)) {
			const combination = new Set([item, ...rest])
			if (combination.size === size) yield combination
		}
	}
}

/**
 * @template T
 * @param {Iterable<T>} iterable
 * @return {Iterable<readonly [number, T]>}
 */
function* entries(iterable) {
	let i = 0
	for (const item of iterable) yield [i++, item]
}

/**
 * @template T
 * @param {Iterable<T>} iterable
 * @param {number} count
 * @return {Iterable<T>}
 */
function* skip(iterable, count) {
	for (const [index, item] of entries(iterable)) {
		if (index >= count) yield item
	}
}