export function* zip<A, B>(a: Iterable<A>, b: Iterable<B>): Generator<[A, B], void, void> {
    const iter_a = a[Symbol.iterator](), iter_b = b[Symbol.iterator]();
    while (true) {
        const next_a = next(iter_a), next_b = next(iter_b);
        if (next_a === null || next_b === null) return;
        yield [next_a, next_b];
    }
}

export function next<T>(iterator: Iterator<T>) {
    const result = iterator.next().value;
    if (result === undefined) return null;
    else return result as T;
}

export function split_once(text: string, separator: string) {
    const cursor = text.indexOf(separator);
    if (cursor === -1) return [text, null] as const;
    const left = text.slice(0, cursor);
    const right = text.slice(cursor + separator.length);
    return [left, right] as const;
}