Woops. And of course there should be the check for bound in the update
functions of the lru and mu strategies...
(defn lru-cache-strategy
"Implements LRU cache strategy for memoize. At most bound number of
argument lists are kept in the cache. They are dropped in LRU
order."
[bound]
(let [values (ref {})]
[(fn lru-cache-strategy-lookup
[cache args]
(when-let [e (find cache args)]
(let [now (System/currentTimeMillis)]
(dosync (alter values assoc args now))
e)))
(fn lru-cache-strategy-update
[cache args]
(let [now (System/currentTimeMillis)]
(alter values assoc args now)
(if (> (co...@values) bound)
(let [k (min-key @values (keys @values))]
(alter values dissoc k)
(dissoc cache k))
cache))))]))
(defn most-used-cache-strategy
"Implements MU cache strategy for memoize. At most bound number of
argument lists are kept in the cache. They are dropped in LU order.
In case elements have the same usage count, the order of drop is
unspecified."
[bound]
(let [values (ref {})]
[(fn most-used-cache-strategy-lookup
[cache args]
(when-let [e (find cache args)]
(dosync (alter values update-in [args] inc))
e))
(fn most-used-cache-strategy-update
[cache args]
(alter values assoc args 1)
(if (> (count @values) bound)
(let [k (min-key @values (keys @values))]
(alter values dissoc k)
(dissoc cache k))
cache))]))
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