scratch.clj

(ns scratch
  (:require [clojure.core.reducers :as r]
            [clojure.core.protocols :as rp])
  (:refer-clojure :exclude [reductions]))

(defn reductions
  ;; curried, identity init
  ([reducef]
     (fn [coll] (reductions reducef coll)))
  ;; curried, arbitrary init
  ;; ...
  ;; uncurried, identity init
  ([reducef coll]
     (reductions reducef (reducef) coll))
  ;; uncurried, arbitrary init
  ([reducef val coll]
     (reify
       rp/CollReduce
       (coll-reduce [this f1]
         (rp/coll-reduce this f1 (f1)))
       (coll-reduce [_ f1 init]
         (let [acc (atom init)]
           (rp/coll-reduce coll
                           (fn [ret v]
                             (let [vret (reducef ret v)]
                               (swap! acc f1 vret)
                               vret))
                           val)
           @acc)))))


(comment
  (= (into [] (reductions + [1 2 3 4]))
     [1 3 6 10])
  true
  )