higher-order-functions.clj

; me
(defn check-sum [sequence]
  (reduce + (map * (cycle [1 3]) sequence)))

; fp-oo
(def check-sum
     (fn [sequence]
       (apply + (map (fn [position digit]
                       (* digit (if (odd? position) 1 3)))
                     (range 1 (inc (count sequence)))
                     sequence))))