Ugly and dumb solution for fucking run-length homework in PG's ACL.

run-length.lisp

(defun run-length (input)
  (let (l fin)
    (mapcar (lambda (x)
              (if (null x)
                  (setq x "nil"))
              (cond ((null l)
                     (setq fin (list (list 1 x)))
                     (setq l x))
                    ((equal x l)
                     (setq fin (cons (list (1+ (car (car fin))) x) (cdr fin))))
                    (t
                     (setq fin (cons (list 1 x) fin))
                     (setq l x))))
            input)
    (reverse
     (mapcar (lambda (x)
               (if (eq (car x) 1)
                   (cadr x)
                 x))
             fin))))

;; (run-length '(a a a b c c c c c d e e))
;; => ((3 a) b (5 c) d (2 e))