computational-problem-solving/sat

/**
 * _parse_int.
 *
 * @param {string} first_symbol
 * @param {Iterator<string>} iterator
 * @return {[boolean, number]}
 */
export default function _parse_int(first_symbol, iterator) {
    let i = 0;
    let s = 1;

    if (first_symbol === '-') s = -1;
    else i = Number(first_symbol);

    while (true) {
        const current = iterator.next();
        if (current.done) return [true, s * i];

        const c = current.value;

        if (c < '0' || c > '9') return [false, s * i];

        i *= 10;
        i += Number(c);
    }
}