// transformer can return null or input on no change

// will not call transformer on individual words

sS lambdaMapLike gazelle_deepTransform(IF1<S> transformer, S input, O... _) {

  if (transformer == null) ret input;

  // call transformer on whole input, return if change

  S transformed = transformer.get(input);

  if (transformed != null && transformed != input) ret transformed;

  // transformer didn't do anything, tokenize & go through parts

  O tokenizer = optPar tokenizer(_, f javaTokWithBrackets);

  LS tok = callTokenizer(tokenizer, input);

  bool changes;

  for ping (int i = 1; i < l(tok); i += 2) {

    S t = tok.get(i);

    if (tok_isRoundOrCurlyBracketed(t)) {

      S unBracketed = tok_deRoundOrCurlyBracket(t);

      transformed = gazelle_deepTransform(transformer, unBracketed, _);

      if (transformed != unBracketed) {

        if (!changes) tok = cloneList(tok); // in case a caching tokenizer was used

        // enclose in brackets & replace

        tok.set(i, startsWith(t, "(") ? roundOpt(transformed) : curlyOpt(transformed));

        set changes;

      }

    }

  }

  ret changes ? join(tok) : input;

}