anchor.diff:   | Implicit_parameter_name
    ;
   
  -identifier_list : identifier (',' identifier_list)* ;
  +identifier_list : identifier (',' identifier)* ;
   
   fragment Identifier_head : [a-zA-Z]
    | '\u00A8' | '\u00AA' | '\u00AD' | '\u00AF' | [\u00B2-\u00B5] | [\u00B7-\u00BA]
  
positive.code: // GRAMMAR OF A PARENTHESIZED EXPRESSION
  
  parenthesized_expression : '(' expression_element_list? ')'  ;
  expression_element_list : expression_element (',' expression_element_list)* ;
  expression_element : expression | identifier ':' expression  ;
  
  // GRAMMAR OF A WILDCARD EXPRESSION
  
negative.code: 
  // GRAMMAR OF A FUNCTION DECLARATION
  // NOTE: Swift Grammar Spec indicates that a function_body is optional
  function_declaration
   : function_head function_name generic_parameter_clause? function_signature
     function_body?
   ;
  function_head : attributes? declaration_modifiers? 'func'  ;
  function_name : identifier |  operator  ;
  function_signature
   : parameter_clauses 'throws'? function_result?
   | parameter_clauses 'rethrows' function_result?
   ;
  function_result : arrow_operator attributes? type  ;
  