iota clojure

iota.clj

(defn iota [t nxt stop y]
  (take-while stop (iterate #(t (nxt %)) y)))

(def upto
  (fn [start end]
    (iota identity inc #(< % end) start)))

(def downto
  (fn [start end]
    (iota identity dec #(> % end) start)))

(upto 1 10)
(downto 20 10)

(defn to 
  ([end]
     (to 1 end))
  ([start end]
     (if (<= start end)
        (upto start end)
        (downto start end))))

(to 10 20)
(to 20 10)
(to 5 -5)
(to 10)