Colexicographic order in Clojure

colex.clj

(defn first-index [f coll]
  (->> (map-indexed vector coll)
       (filter (comp f second))
       (map first)
       (first)))

(defn first-incable [v]
  (or
    (first-index
      (fn [[a b]] (< (inc a) b))
      (map vector v (rest v)))
    (dec (count v))))

(defn colex-next [v]
  (let [i (first-incable v)]
    (->> (update (vec (drop i v)) 0 inc)
         (concat (take i (rest (range))))
         (vec))))

(defn colex-seq [v]
  (lazy-seq (cons v (colex-seq (colex-next v)))))

(defn colex-order [n]
  (colex-seq (vec (range 1 (inc n)))))

(assert
  (= (take 10 (colex-order 3))
     [[1 2 3]
      [1 2 4]
      [1 3 4]
      [2 3 4]
      [1 2 5]
      [1 3 5]
      [2 3 5]
      [1 4 5]
      [2 4 5]
      [3 4 5]]))