Clojure Transducer Meetup

(ns transducer-meetup.core)


(defn noop [xf]
  (clojure.pprint/pprint (type xf))
  (clojure.pprint/pprint xf)
  (fn
    ([] (xf))
    ([result] (xf result))
    ([result input] (xf result input))))

(defn debug
  ([]
   (debug ">" "<"))
  ([ident]
   (debug ident ">" "<"))
  ([in out]
   (fn debug-transducer [xf]
     (fn
       ([]
        (clojure.pprint/pprint "Arity 0")
        (xf))
       ([result]
        (clojure.pprint/pprint "Arity 1")
        (clojure.pprint/pprint result)
        (xf result))
       ([result input]
        (do
          (clojure.pprint/pprint (str in " " input))
          (let [output (xf result input)]
            (clojure.pprint/pprint (str out " " output))
            output))))))
  ([ident in out]
   (let [spaces (reduce str (repeat ident " "))]
     (debug (str spaces in) (str spaces out)))))

(defn slow-into [to xf from]
  (transduce xf conj to from))

; (defn beg [number]
;   (fn [xf]
;     (fn
;       ([] (xf))
;       ([result] (xf result))
;       ([result input]
;        (reduce xf result (repeat number input))))))

; From https://github.com/clojure/clojure/blob/clojure-1.9.0/src/clj/clojure/core.clj#L7532
(defn preserving-reduced [rf]
  (fn [a b]
    (let [ret (rf a b)]
     (if (reduced? ret)
       (reduced ret)
       ret))))

; Step 2
(defn beg [n]
  (fn [rf]
    (let [rrf (preserving-reduced rf)]
      (fn ([] (rf))
          ([result] (rf result))
          ([result input]
           (reduce rrf result (repeat n input)))))))

(def beg-data (list :may :i :beg :your :pardon :?))
(slow-into
  []
  (comp
    (debug 0)
    (beg 2)
    (debug 2)
    (take 3)
    (debug 4))
  beg-data)


; (transduce (debug "in" "out") + (range 3))

; (into [] noop (range 3))