anchor.diff:  /*
    * <arg_list>                   = <sap> | <sap>, <arg_list> | <named_arg_list>
    */
  -FSArgument _parseFSArguments(String s) {
  +_FSArgument _parseFSArguments(String s) {
     var sap = _parseFSScalarArrayProgram(s);
     if (sap != null) {
  -    return new FSArgument(sap);
  +    return new _FSArgument(sap);
     }
   
     var nal = _parseFSNamedArguments(s);
  
positive.code:     sign = -1;
    }
  
    FSNumScalar n = _firstNotNull([_parseFSInteger, _parseFSFloat])(s);
    if (n == null) {
      return null;
    }
  
negative.code: 
    var a = s.substring(first + 1, s.length - 1).trim();
    if (a.isEmpty) {
      return new _FSNoArgumentFunction(n);
    }
  
    var args = _parseFSArguments(s.substring(first + 1, s.length - 1).trim());
  