peek into transducing

core.clj

(ns transpeek.core
  (:gen-class)
  (:import (java.util ArrayList)))

(defn map-
  ([f]
   (fn [rf]
     (fn
       ([] (rf))
       ([result] (rf result))
       ([result input]
        (rf result (f input)))
       ([result input & inputs]
        (rf result (apply f input inputs)))))))

(defn peek-xform [xform]
  (let [list (ArrayList.)]
    [(fn [rf]
       (let [rf- (xform rf)]
         (fn
           ([] (rf-))
           ([result] (rf- result))
           ([result input]
            (let [res (rf- result input)]
              (.add list res)
              res))
           ([result input & inputs]
            (rf- result inputs)))))
     list]))

(def xform (map- inc))

#_(let [value (peek-xform xform)]
  (into [] (first value) [0 1 2 3 4])
  (clojure.pprint/pprint (last value)))

(let [value (peek-xform xform)]
  (transduce (first value) conj [0 1 2 3 4])
  (clojure.pprint/pprint (last value)))