(collect (mapping (((a b c) (chunk 3 1 (scan-range :from 1 :upto 6)))) (list a b c)))

(collect (mapping (((&rest ns) (chunk 3 1 (scan-range :from 1 :upto 6)))) ns))

(defun pack (list len)
  (loop
    :until (null list)
    :collect (subseq list 0 len)
    :do (dotimes (i len list) (setf list (cdr list)))))

(let ((l (list 1 2 3 4 5 6 7 8 9)))
  (loop
    :for (a b c) :on l :by #'cdddr
    :collect (list a b c)))

(defun pack-2 (a b c &rest r)
    `((,a ,b ,c) ,@(if (null r) nil (apply #'pack-2 r))))

CL-USER> (pack-2 1 2 3 4 5 6 7 8 9)
((1 2 3) (4 5 6) (7 8 9))