SICP Exercise 1.12 -- Pascal's triangle

gistfile1.el

;The following pattern of numbers is called Pascal's triangle
(defun pascal_x_y (x y)
  (if (or (= y 0) (= x y))
      1
    (+ (pascal_x_y (- x 1) (- y 1))
       (pascal_x_y (- x 1) y))))

(defun draw_line (n)
  (loop for idx from 0 to n do
        (prin1 (pascal_x_y n idx))
        (format t  " "))
  (format t "~%"))

(defun draw_pascal (n)
  (loop for line from 0 to n do
        (draw_line line)))

(draw_pascal 6)