isomorphism-transducer.clj

(defn depth [coll]
  (count (->> coll
              (tree-seq coll? identity)
              (filter coll?))))

(defn comp-times [n f]
  (reduce comp
          f
          (repeat (dec n) f)))
   
(let [coll [[[1 2 3]]]
      the-depth (dec (depth coll))
      xform (comp (comp-times the-depth cat)
                  (map inc))
      uncat (comp-times the-depth vector)
      rf (completing conj uncat)]
 (transduce xform rf coll))