More than one signature

working.clj

(defn third
  ([lst]
   (third (seq lst) 0))
  ([lst currentIndex]
   (if (= (first lst) nil)
     0
     (if (= currentIndex 2)
       (first lst)
       (if (< currentIndex 2)
         (third (rest lst) (+ currentIndex 1)))))))

(defn nth-third [lst]
  (nth lst 2))

(defn loop-third [lst-in]
  (let [lst (seq lst-in)]
    (loop [item (first lst) remaining (rest lst) index 0]
      (if (= index 2)
        item
        (recur (first remaining) (rest remaining) (inc index))))))

(defn filter-third [lst-in]
  (let [lst (seq lst-in)]
    (first (keep last
                 (filter #(= (first %) 2)
                         (map vector (range) lst))))))