stateful_memoization.clj

(defn- stateful-memoize
  [f #^java.util.Map map]
    (fn [& args]
      (if-let [e (find map args)]
        (val e)
        (let [ret (apply f args)]
          (.put map args ret)
          ret))))

(defn weak-memoize
  "Same as memoize, but uses a WeakHashMap for storing argument keys and result values.
   **Be aware of what this entails for persistence of values: lose your keys, and
   the associated value may get recalculated**"
  [f]
  (stateful-memoize f (java.util.WeakHashMap.)))

(defn lru-map
  [max-size]
  (proxy [java.util.LinkedHashMap] []
    (removeEldestEntry [entry]
      (> (.size #^java.util.Map this) max-size))))

(defn lru-memoize
  "Same as memoize, but uses a LinkedHashMap-based LRU cache to ensure that a maximum of
   max-size entries are held at any time."
  [f max-size]
  (stateful-memoize f (lru-map max-size)))