primitive-lenses.clj

(defn get-lens [k] (fn [m] (get m k)))

(defn get-in-lens
  [ks]
  (reduce
   (fn [f k]
     (fn [m]
       (let [lens (get-lens k)]
         (lens (f m)))))
   identity
   ks))

(comment
  ((get-in-lens [:a :b]) {:a {:b 1}}))

(defn assoc-lens [k v] (fn [m] (assoc m k v)))
(defn update-lens [k f] (fn [m] (update m k f)))

(defn assoc-in-lens
  [[k & ks] v]
  (if ks
    (update-lens k (assoc-in-lens ks v))
    (assoc-lens k v)))

((assoc-in-lens [:a :b :c] 1) {})

(defn update-in-lens
  [[k & ks] f]
  (if ks
    (update-lens k (update-in-lens ks f))
    (update-lens k f)))

(comment
  ((update-in-lens [:a :b :c] inc)
   ((assoc-in-lens [:a :b :c] 1) {})))

(defn dissoc-lens [k] (fn [m] (dissoc m k)))

(defn dissoc-in-lens
  [ks]
  (let [k (last ks)
        ks (butlast ks)]
    (update-in-lens ks (dissoc-lens k))))

(comment
  ((dissoc-in-lens [:a :b :c])
   ((assoc-in-lens [:a :b :c] 1) {})))