play around with a trivial trace transducer

trace-transducer.clj

;; play around with a trivial trace transducer
;; base on https://gist.github.com/ptaoussanis/e537bd8ffdc943bbbce7#file-transducers-clj

(defn trace-tran
  "print the new input on any iteration. 
   Combine with other transducers for tracing"
  [reducing-fn] 
  (fn new-reducing-fn
    ([] (reducing-fn))
    ([accumulation] (reducing-fn accumulation))
    ([accumulation new-input]
       (println (str "new-input: " new-input)) ;; side effect!
       (reducing-fn accumulation new-input))))

;; combine the new trace-tran with other transducers
;; notice the position of the trace-trans in the function composition
(def start-trans (comp trace-tran (map #(* % 2)) (map inc)))
(def mid-trans (comp (map #(* % 2)) trace-tran (map inc))) 
(def end-trans (comp (map #(* % 2)) (map inc) trace-tran))

(into [] start-trans (range 5))
(into [] mid-trans (range 5))
(into [] end-trans (range 5))