anchor.diff:          [ formal_list ]
           [ provisos_clause ]
           ( equal_value SEMICOLON
  -        | SEMICOLON
  -            [
  -                ( single_statement)+
  -                TOKENDFUNCTION [ COLON  function_name]
  -            ]
  +        | SEMICOLON [ ( single_statement)+ TOKENDFUNCTION [ COLON  function_name] ]
           )
   
       rule import_arg:
  
positive.code: 
      rule assign_rvalue:
          ( group_statement
          | case_statement
          | interface_declaration
          | TOKRULES [ COLON  VAR]
              ( rule_statement )*
  
negative.code:         | let_statement
          | TOKMATCH ( TOKTAGGED VAR dot_field_list | match_brace ) assign_opvalue SEMICOLON
          | TOKPAR statement_list TOKENDPAR
          | TOKRETURN assign_rvalue SEMICOLON
          | rule_statement
          | TOKWHILE paren_expression ( group_statement | VAR SEMICOLON)
  
  