code: private AstParameter parseList() {
      eatChar('[');
      char nextChar = skipWS();
      AstParameter res = isQuote(nextChar)? parseStringList() : parseNumList();
      eatChar(']');
      return res;
    }
docs: Parse and return a list of tokens: either a list of strings, or a list of numbers.
  We do not support lists of mixed types, or lists containing variables (for now).