jarpiain

(deftype Subvec [v n]
  clojure.lang.IPersistentVector
    (length [_] (quot (count v) n))
    (nth [_ i] (v (* i n)))
    (assocN [_ i val] (Subvec. (assoc v (* i n) val) n))
    (seq [_] (take-nth n (seq v))))

(Subvec. [1 2 3 4 5] 2)
; --> [1 3 5]

jarpiain

(defn prime? [n]
  (let [n (int n)
        q (int (Math/sqrt (double n)))]
    (loop [i 2]
      (if (> i q) true
        (if (zero? (unchecked-remainder n i)) false
          (recur (inc i)))))))

jarpiain

(defmacro currying-fn [args & body]
  `(fn
     (~args ~@body)
     ~@(for [i (next (range (count args)))]
         (let [[head tail] (split-at i args)]
           `(~(vec head) (currying-fn ~(vec tail) ~@body))))))

(def apply-if (currying-fn [p f x] (if (p x) (f x) x)))

(map (apply-if odd? inc) (range 10))