(defun print_triangle(height dir &optional (m height))
  (if (not (zerop height))
      (progn
        (if (zerop dir)
            (loop for i from 1 to (expt 2 (- height 1)) do (format t "@"))
            (loop for i from 1 to (expt 2 (abs(- height m))) do (format t "@")))
        (format t "~%")
        (print_triangle(- height 1) dir m))))