On Apr 18, 2010, at 9:21 AM, Yonov wrote:
> Hi,
> I am trying to implement memoize myself and have stucked on one place
> for a lot of time. This is the code:
>
> (defn mymemoize [func]
> (let [dict (ref (hash-map))
> inner #((let
> [val (@dict %)]
> (if (nil? val)
> (do (dosync (alter dict conj {% (func %)})) (println (class
> (@dict %))) (@dict %))
> val)))]
> inner))
>
>
> (defn gg [x]
> (if (= x 1) 1 2))
> (def ff (mymemoize gg))
> (ff 1)
>
> I am printing only for debuging purposes. Actually everything in the
> do-block is OK, but there is no return value. Why?
The body of your anonymous function literal (#()) has an extra level of
parentheses. Your code is coming up with the correct answer (the Integer 1) and
then trying to execute it with no arguments. That's what this exception:
java.lang.ClassCastException: java.lang.Integer cannot be cast to
clojure.lang.IFn (NO_SOURCE_FILE:0)
is trying to convey:
This works:
(defn mymemoize [func]
(let [dict (ref (hash-map))
inner #(let [val (@dict %)]
(if (nil? val)
(do (dosync (alter dict conj {% (func %)}))
(println (class (@dict %)))
(@dict %))
val))]
inner))
--Steve
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