Transducing Reductions?

treductions.clj

(defn treductions [f]
  (fn [xf]
    (let [last-val (volatile! ::none)]
     (fn
       ([] (xf))
       ([result] (xf result))
       ([result input]
        (if (= ::none @last-val)
          (vreset! last-val input)
          (vreset! last-val (f @last-val input)))
        (xf result @last-val))))))


;;usage
(sequence (treductions +) (range 10))
;; output : (0 1 3 6 ...)

(sequence (treductions conj) (concat [[]] (range 10)))
;; output : ([] [0] [0 1] [0 1 2]...)