gistfile1.clj

(defn compact-to-ranges [xs]
  (reverse
   (reduce (fn [rs x]
             (if (empty? rs)
               (list [x x])
               (let [[l u] (first rs)]
                 (if (= (inc u) x)
                   (cons [l x] (rest rs))
                   (cons [x x] rs)))))
           (list)
           xs)))
(assert (= (compact-to-ranges [1 2 3 4 6 7 9 10 11 15 16])) ([1 4] [6 7] [9 11] [15 16]))