anchor.diff:    ;
   
   indexed_function_call
  -  : name=ID LPAREN actual_parameter_list RPAREN call_result_index* ->
  -    ^(Call $name actual_parameter_list call_result_index*) ;
  +  : name=ID (LPAREN actual_parameter_list RPAREN)? call_result_index* ->
  +    ^(Call $name actual_parameter_list? call_result_index*) ;
   
   actual_parameter_list
  -  : actual_parameter (COMMA actual_parameter_list)?
  -    -> actual_parameter actual_parameter_list?
  -  |
  +  : actual_parameter (COMMA actual_parameter)*
  +    -> actual_parameter+
     ;
   
   actual_parameter
  
positive.code:   ;
  
  function_def
    : KW_FUNCTION name=ID LPAREN formal_parameter_list RPAREN
      LBRACE statement* RBRACE -> ^(KW_FUNCTION $name
        formal_parameter_list statement*)
    ;
  
  formal_parameter_list
    : formal_parameter (COMMA formal_parameter_list)?
        -> formal_parameter formal_parameter_list?
    ;
  
  formal_parameter
  
negative.code: 
  class_method_def
    : method_mod_list KW_FUNCTION is_ref name=ID
        (LPAREN formal_parameter_list RPAREN)? method_body
        -> ^(KW_FUNCTION $name method_mod_list is_ref
                          formal_parameter_list? method_body)
    ;
  
  method_mod_list
  