ifclass ListAndIndex
static int tokenToCharIndex(ListAndIndex<S> ptr) {
  ret ptr == null ? -1 : tokenToCharIndex(ptr.list(), ptr.idx());
}
endif

static int tokenToCharIndex(LS tok, int tokenIndex) {
  if (tokenIndex < 0) ret -1;
  int idx = 0;
  tokenIndex = min(tokenIndex, l(tok));
  for i to tokenIndex: idx += l(tok.get(i));
  ret idx;
}