anchor.diff:     ;
   
   formal_arg
  -   : nil_or_D_list ':' type
  +   : nil_or_D_list ':' type_
      | nil_or_D ':' 'self' 'refopt' IDENTIFIER
      | nil_or_D ':' 'self' IDENTIFIER
      | '*'
  
positive.code:    : expression+
     ;
  
  type
     : data_type
     | function_type
     ;
  
negative.code:    ;
  
  declaration
     : identifier_list ':' type_ ';'
     | identifier_list ':' type_ ASSIGN expression ';'
     | identifier_list ':' 'con' expression ';'
     | identifier_list ':' 'import' IDENTIFIER ';'
     | identifier_list ':' 'type' type_ ';'
     | 'include' string_constant ';'
     ;
  
  