map for zipper

(defn map-zipper
  "apply f to every element of zipper z, return results as a lazy sequence"
  [f z]
  (lazy-seq
   #_(cl-format true "~&(F: ~a ~&Z: ~a~&" (f z) z)
   (if (z/end? z)
     nil ;;acc
     (cons (f z)
           (map-zipper f (z/next z))))))

(defn filter-zipper
  "return elements of zipper where (pred element) is true, as a lazy sequence"
  [pred z]
  (lazy-seq
   (if (z/end? z)
     nil
     (if (pred z)
       (cons z
             (filter-zipper pred (z/next z)))
       (filter-zipper pred (z/next z))))))