anchor.diff:                                   `(if ,tail-var
                                         ,(if suppliedp-variable
                                              `(car ,tail-var)
  -                                           `(prog1 (car ,tail-var)
  -                                              (setf ,tail-var (cdr ,tail-var))))
  +                                           `(pop ,tail-var))
                                         ,initform)
                                    (if suppliedp-variable
  -                                     `(let ((,suppliedp-variable (prog1 (not (null ,tail-var))
  -                                                                   (setf ,tail-var (cdr ,tail-var)))))
  +                                     `(let ((,suppliedp-variable (not (null (pop ,tail-var)))))
                                           ,form)
                                        form)))))))
      section
  
positive.code:            (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)))))
                        ,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))))))
     section
     form))
  
  
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
  