code: @Private Object word(String name) {
      Object p = words.apply(name);
      Checks.checkArgument(p != null, "token %s unavailable", name);
      return p;
    }
docs: Gets the token value identified by the token text. This text is the operator or the keyword.
  
  @param name the token text.
  @return the token object.
  @exception IllegalArgumentException if the token object does not exist.