set-theory/powerset

import assert from 'assert';

import _increment from './_increment.js';

/**
 * _powerset.
 *
 * @param {Iterator} source
 * @return {IterableIterator<Array>}
 */
export default function* _powerset(source) {
    const bitset = [];
    const buffer = [];
    const stack = [];
    while (true) {
        yield stack;

        const i = _increment(bitset);

        if (i === buffer.length) {
            assert(stack.length === buffer.length);
            const {done, value} = source.next();
            if (done) return;
            buffer.push(value);
        }

        assert(i < buffer.length);
        for (let j = 0; j < i; ++j) stack.pop();
        stack.push(buffer[i]);
    }
}