(a)
(define-syntax rotate
   (syntax-rules ()
      ((rotate a) (void)) ; i.e., do nothing
      ((rotate a b c ...) (begin
                            (swap a b)
                            (rotate b c ...)))))

(b)
(begin
   (swap n e)
   (rotate e s w))

(c) 
(begin
   (swap n e)
   (begin
      (swap e s)
      (rotate s w)))

(d)
(begin
   (swap n e)
   (begin
      (swap e s)
      (begin
         (swap s w)
         (void))))

Example 4: rotate macro.