lisp-交換リストの2つの要素

* (defvar *mylist* (list 1 2 3 4))

*MYLIST*
*  (rotatef (nth 1 *mylist*) (nth 2 *mylist*))

NIL
* *mylist*

(1 3 2 4)

*  (defvar *mylist* `(223 44 99 -88))

*MYLIST*
* (rotatef (nth 1 *mylist*) (nth 2 *mylist*))  

NIL
* *mylist*  

(223 99 44 -88)
*