Function optional

src/index.ts:153–158

(...potentials: Array<ParseYieldable | any>)

}

export function optional(...potentials: Array<ParseYieldable | any>): () => ParseGenerator<any> {
  return function* () {
    const result = yield [...potentials, ''];
    return result === '' ? undefined : result;
  };
}

export function lookAhead(regex: RegExp) {
  const lookAheadRegex = new RegExp(`^(?=${regex.source})`);