anchor.diff:     ;
   
   actual_parameter_list
  -   : actual_parameter
  -   | actual_parameter_list parameter_delimiter actual_parameter
  +   : actual_parameter (parameter_delimiter actual_parameter)*
      ;
   
   parameter_delimiter
      : ','
  -   | ')' letter_string ': ('
  +   | ')' letter_string ':' '('
      ;
   
   actual_parameter
  
positive.code:    ;
  
  designational_expression
     : simple_designational_expression
     | if_clause simple_designational_expression 'else' designational_expression
     ;
  
  simple_designational_expression
     : label
     | switch_designator
     | designational_expression
     ;
  
  switch_designator
     : switch_identifier  subscript_expression?
     ;
  
  procedure_statement
  
negative.code:    ;
  
  basic_statement
     : (label ':')* unlabelled_basic_statement?
     ;
  
  label
  