// returns minute ranges from 0 to 24*60
static L<IntRange> parseBusinessHours(S s) {
  LS parts = nempties(tok_splitAtComma(s));
  ret map(parts, part -> {
    LS l = splitAtMinus(part);
    IntRange r = intRange(
      parseHourAndOptionalMinutesToMinutes(first(l)),
      parseHourAndOptionalMinutesToMinutes(second(l)));
    if (r.end < r.start && r.start <= 12*60 && r.end < 12*60)
      r.end += 12*60;
    ret r;
  });
}