tail call comparision

flip-adjacent.lisp

(defun flip-adjacent (lst)
  (cond
    ((null lst) lst)
    ((null (cdr lst)) lst)
    (t (destructuring-bind (a b . r) lst
	 (cons b (cons a (flip-adjacent r)))))))

(defun flip-adjacent-2 (lst acc)
  (cond
    ((null lst) (reverse acc))
    ((null (cdr lst)) (reverse (cons (car lst) acc)))
    (t (flip-adjacent-2 (cddr lst) (cons (car lst)
					 (cons (cadr lst) acc))))))

;; The first implementation is almost as fast as the second for small inputs
;; I the only problem seems to be that stack is quickly run out of mem