Data structure to track changes over time

history.clj

(defn get-time
  []
  (.getTime (java.util.Date.)))

;; history-seq

(defn action
  "Attach keys and values to history stream"
  [hist & keyvals]
  (let [m (apply hash-map keyvals)
	base {:time (get-time)}]
    (conj hist (merge base m))))

(defn historic
  "Create a new history stream"
  [& keyvals]
  (apply action '() keyvals))

(defn history
  "Get built-up states of history stream over time"
  [hist]
  (reduce (fn
	    [states update]
	    (conj states (merge (last states) update)))
	  []
	  (sort-by :time hist)))

(defn current
  "Get current state of history stream"
  [hist]
  (last (history hist)))

(defn at
  "Get state of history stream at specific point in time"
  [hist time]
  (last (filter #(<= (or (:time %) 0) time) (history hist))))