anchor.diff:     ;
   
   assignment_statement
  -   : assignment_sub SEMI? 
  +   : assignment_sub SEMI?
      ;
   
   lvalue_sub
  
positive.code:    | (create_call_statement)
     | (destroy_call_statement)
     | (label_stat)
     | (identifier )
     | throw_stat
     | goto_stat
     | choose_statement
  
negative.code:    ;
  
  create_call_statement
     : create_call_sub
     ;
  
  destroy_call_sub
  