(defun pascal-next-row (a)
  (loop :for q :in a
        :and p = 0 :then q
        :as s = (list (+ p q))
        :nconc s :into a
        :finally (rplacd s (list 1))
                 (return a)))

(defun pascal (n)
   (loop :for a = (list 1) :then (pascal-next-row a)
         :repeat n
         :collect a))