ll.clj

(definterface INode
  (getCar [])
  (getCdr [])
  (setCar [x])
  (setCdr [x])
  (valAt [i]))

(deftype Node [^:volatile-mutable car ^:volatile-mutable cdr]
  INode
  (getCar [_] car)
  (getCdr [_] cdr)
  (setCar [this x] (set! car x) this)
  (setCdr [this x] (set! cdr x) this)
  (valAt [this index] (loop [i index cursor this]
                         (if (zero? i)
                           cursor
                           (recur (dec i) (.cdr cursor)))))

  clojure.lang.Indexed
  (nth [this i] (.valAt this i))
  (nth [this i v] (if-let [n (nth this i)] (Node. v n)))

  clojure.lang.Seqable
  (seq [this] this)

  clojure.lang.ISeq
  (first [this] this)
  (more [this] (if-let [n (next this)] n ()))
  (next [this] (if-let [n (.getCdr this)] n)))

(defn new-node [car & [cdr]]
  (Node. car cdr))

(first (new-node "foo"))  ;; StackOverFlow