anchor.diff:  
       rule if_statement:
           "if" LPAREN expression RPAREN
  -           if_item [ "else" if_item ]
  -
  -    rule function_header:
  -        FUNCTION Type_item_or_name [function_name]  argument_list
  +           function_body_statement [ "else" function_body_statement ]
   
       rule actionvalue_statement:
           "actionvalue"
           ( return_statement
  +        | let_statement
  +        | case_statement
           | expression SEMICOLON
           )*
           "endactionvalue"
  +
  +    rule function_header:
  +        FUNCTION Type_item_or_name [function_name]  argument_list
   
       rule function_statement:
           function_header
           ( EQUAL expression SEMICOLON
           | provisos
  -            (function_body_statement)*
  -            "endfunction" [ COLON  function_name]
  -        )
  -
  +            [ (function_body_statement)+
  +              "endfunction" [ COLON  function_name]
  +            ]
  +        )
   
   #    "parameter" parameter_name  EQUAL expression SEMICOLON
   #    "port" port_name  EQUAL expression SEMICOLON
  
positive.code:         | package_statement
          | typeclass_statement
          | define_statement
          | variable_declaration
          | ifdef_statement
  
  
negative.code:         )
  
      rule subinterface_declaration:
          "interface" Type_item_or_name [ VAR ] [ EQUAL expression ] SEMICOLON
  
      rule interface_arg:
          [ ["numeric"] "type" ] Type_name
  
      rule interface_declaration:
          "interface" VAR [VAR]
          ( SEMICOLON
              ( method_declaration
              | attribute_statement
              | subinterface_declaration
              )*
              "endinterface" [ COLON VAR ]
          | HASH LPAREN interface_arg ( COMMA interface_arg)* RPAREN SEMICOLON
              ( method_declaration
              | attribute_statement
              | subinterface_declaration
              )*
              "endinterface" [ COLON VAR ]
          | EQUAL expression SEMICOLON
          )
  
  