anchor.diff:          | (
                 (expression (COMMA expression)*
                 | TOKDEFAULT
  -              #| VAR
                 )
                 COLON (QUESTION SEMICOLON | function_body_statement)
             )*
  
positive.code:         | interface_declaration
          | typedef_declaration
          )+
  
      rule top_level_statement:
          package_statement_item
          | package_statement
          #| instance_statement
          #| method_declaration
          #| let_statement
          #| typeclass_statement
  
      rule package_statement_item:
          typedef_declaration
  
negative.code:         | group_statement
          | VAR SEMICOLON
          )
  
      rule function_body_statement:
          let_statement
  