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(defmacro unless (test :rest body)
`(if (not ,test) (progn ,@body)))
(defmacro assert (test)
`(unless ,test
(error "assert: value is false." ',test)))
(defun sum (sequence)
(let ((res 0))
(for ((xs sequence (cdr xs)))
((null xs) res)
(setq res (+ res (car xs))))))
(defun average-of-absolutes (values)
(the <list> values)
;; requires non-null list
(assert (> (length values) 0))
(let ((res (quotient (sum values) (length values))))
;; must ensure positive result
(assert (>= res 0))
(the <fixnum> res)))
;; (average-of-absolutes '(1 3))
;; (average-of-absolutes '())
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