static Map<S, Int> parseEnglishMonthName_cache;

// returns 1-12 (or 0 if unknown)
static int parseEnglishMonthName(S s) {
  if (parseEnglishMonthName_cache == null)
    parseEnglishMonthName_cache = listIndexCI(englishMonthNames());
  ret or(parseEnglishMonthName_cache.get(s), -1)+1;
}