static int fullPhraseCache_longestPhraseLength(FullPhraseCache cache, LS tok) {
  ret fullPhraseCache_longestPhraseLength(cache, tok, 1);
}

// returns index of C token in tok after longest match
static int fullPhraseCache_longestPhraseLength(FullPhraseCache cache, LS tok, int idx) {
  if (cache == null || tok == null) ret -1;
  int longest = -1;
  if (nempty(cache.phrases)) longest = idx;
  while (idx < l(tok)-1) {
    ifdef fullPhraseCache_longestPhraseLength_debug
      print("longest=" + longest + ", idx=" + idx + ", phrases=" + cache.phrases + ", next token= " + quote(tok.get(idx)));
    endifdef
    cache = mapGet(cache.byFirstWord, tok.get(idx));
    if (cache == null) break;
    idx += 2;
    if (nempty(cache.phrases)) longest = idx;
  }
  ret longest;
}

static int fullPhraseCache_longestPhraseLength(FullPhraseCache cache, S s) {
  if (cache == null || s == null) ret -1;
  ret fullPhraseCache_longestPhraseLength(cache, javaTokNPunctuation_cached(s));
}