;нечитабельный вариант
(defun gen (x) (loop for i from 1 below (+ x 1) do (format t "~{~a~^-~}~%" (if (= (rem i 2) 0)  (reverse (loop for b from 1 below (+ i 1) append (list b))) (loop for b from 1 below (+ i 1) append (list b))))))

;читабельный вариант
CL-USER> (defun gen (x)
           (loop for i from 1 below (+ x 1) do
                (format t "~{~a~^-~}~%" (if (= (rem i 2) 0)
                    (reverse (loop for b from 1 below (+ i 1) append (list b)))
                        (loop for b from 1 below (+ i 1) append (list b))))))