To return multiple things use values!
(defun average (&rest nums)
(let ((mean(/ (apply #'+ nums) (length nums)))
(median (nth (floor (/ (length nums) 2)) (sort nums #'<))))
(values mean median)))
;; => AVERAGE
(average 1.1 2 3 54 5 7 7 8)
;; => 10.8875
;; 7
return multiple values as a list
(multiple-value-list (values 1 2 4))
;; => (1 2 4)
(multiple-value-bind (a b c) (values 1 2 3)
(format nil "(a b c) - easy as ~a ~a ~a" a b c))
;; => "(a b c) - easy as 1 2 3"
multiple-value-bindcreates a lexical scope where the multiple values returned by a form are bound to variables you supply - kinda likelet.