Function andThen

The curried version of the andThen method on the Parser interface.

const checkZipCode = (code: string): Parser<string> => {
  if (code.length === 5) {
    return succeed(code);
  } else {
    return problem("a U.S. zip code has exactly 5 digits");
  }
};

const zipCode: Parser<string> =
 andThen(checkZipCode)(chompWhile(Helpers.isDigit).getChompedString())