f.clj

(def spy #(do (println "DEBUG:" %) %))

(def items [{:steps 5 :date :ereyesterday}
            {:steps 4 :date :yesterday}
            {:steps 6 :date :today}
            {:steps 7 :date :tomorrow}
            {:steps 3 :date :overmorrow}])

(def items-noreach [{:steps 1 :date :ereyesterday}
                    {:steps 1 :date :yesterday}
                    {:steps 1 :date :today}
                    {:steps 1 :date :tomorrow}
                    {:steps 1 :date :overmorrow}])

(defn goal-reached? [n] (>= n 10))

(defn f-normales-reduce [items]
  (let [reductor     (fn [{:keys [steps-total] :as acc}
                          {:keys [steps date]}]
                       (if (goal-reached? steps-total)
                         acc
                         {:steps-total (+ steps-total steps)
                          :date        date}))
        intermediate (reduce reductor {:steps-total 0 :date nil} items)]

    (cond-> intermediate
      (not (goal-reached? (:steps-total intermediate))) (assoc :date nil))))

(defn f-anderer-ansatz-aber-komplexer-und-sackgasse [items]
  (let [reductor (fn [{:keys [steps-total]}
                      {:keys [steps date]}]
                   (let [new-steps-total (+ steps-total steps)]
                     {:steps-total new-steps-total
                      :date        (when (goal-reached? new-steps-total) date)}))]
    (->> items
         (reductions reductor {:steps-total 0 :date nil})
         spy
         (filter #(goal-reached? (:steps-total %)))
         spy
         first)))

(defn f-funktioniert-aber-viel-noise-im-code [items]
  (let [reductor (fn [{:keys [steps-total]}
                      {:keys [steps date]}]
                   (let [new-steps-total (+ steps-total steps)]
                     (if (goal-reached? new-steps-total)
                       (reduced {:steps-total new-steps-total :date date})
                       {:steps-total new-steps-total :date nil})))]
    (reduce reductor {:steps-total 0 :date nil} items)))

(defn f-funktioniert-fast-aber-weniger-noise [items]
  (let [reductor (fn [steps-total
                      {:keys [steps date]}]
                   (let [new-steps-total (+ steps-total steps)]
                     (if (goal-reached? new-steps-total)
                       (reduced {:steps-total new-steps-total :date date})
                       new-steps-total)))]
    (reduce reductor 0 items)))

(f-normales-reduce items)
(f-normales-reduce items-noreach)
(f-anderer-ansatz-aber-komplexer-und-sackgasse items)
(f-anderer-ansatz-aber-komplexer-und-sackgasse items-noreach)
(f-funktioniert-aber-viel-noise-im-code items)
(f-funktioniert-aber-viel-noise-im-code items-noreach)
(f-funktioniert-fast-aber-weniger-noise items)
(f-funktioniert-fast-aber-weniger-noise items-noreach)