Transformation demo

transformation-demo.clj

(defrecord BalanceSheet [liabilities equity])

(defn calc-assets
  [^BalanceSheet bs]
  (+ (:liabilities bs) (:equity bs)))

(defn replace-vals-with-assets
  "{:key1 BalanceSheet, ...} -> {:key1 (calc-assets BalanceSheet), ...}."
  [sheets]
  (reduce-kv (fn [m k v]
               (assoc m k (calc-assets v))) {} sheets))

(let [sheets {:1950 (->BalanceSheet 7000 15000)
              :1951 (->BalanceSheet 14000 100000)
              :1953 (->BalanceSheet 45000 350000)}]
  (-> sheets replace-vals-with-assets vals))

;; First, the call to (replace-vals-with-assets sheets) takes place and a new map is returned:
;; {:1950 22000, :1951 114000, :1953 395000}

;; Then a list of its values is made by calling (vals {:1950 22000, :1951 114000, :1953 395000}):
;; (22000 114000 395000).