anchor.diff:             (var-or-lambda-list (variable parameter)))
          (etypecase var-or-lambda-list
            (symbol (let ((variable var-or-lambda-list))
  -                   `(let ((,variable (prog1 (car ,tail-var)
  -                                       (setf ,tail-var (cdr ,tail-var)))))
  +                   `(let ((,variable (pop ,tail-var)))
                         ,form)))
            (fcll:lambda-list (let ((lambda-list var-or-lambda-list))
  -                             (%expand-lambda-list lambda-list
  -                                                  `(prog1 (car ,tail-var)
  -                                                     (setf ,tail-var (cdr ,tail-var)))
  -                                                  form))))))
  +                             (%expand-lambda-list lambda-list `(pop ,tail-var) form))))))
      section
      form))
   
  
positive.code:                                  `(if ,tail-var
                                        ,(if suppliedp-variable
                                             `(car ,tail-var)
                                             `(prog1 (car ,tail-var)
                                                (setf ,tail-var (cdr ,tail-var))))
                                        ,initform)
                                   (if suppliedp-variable
                                       `(let ((,suppliedp-variable (prog1 (not (null ,tail-var))
                                                                     (setf ,tail-var (cdr ,tail-var)))))
                                          ,form)
                                       form)))))))
     section
  
negative.code:                    `(let (,@(when suppliedp-variable
                                    (list `(,suppliedp-variable (not (null ,tail-var)))))
                            (,variable (if ,tail-var
                                           (pop ,tail-var)
                                           ,initform)))
                        ,form)))
           (fcll:lambda-list
  