In this case 'memoize' returns a memoized version of the function 'f', which
closes over 'mem'. Each time 'memoize' is called a new atom is created, not
each time the function it returns is called.
---
Joseph Smith
j...@uwcreations.com
On Nov 11, 2010, at 2:06 PM, Manoj wrote:
> I am a newbie to Clojure, so have some confusion around lexical
> scoping especially when "let" is used in a recursive function call. To
> be more precise, I am taking the example memoize() function used for
> explaining the concept of atom at clojure.org.
>
> Here is how it is explained:
>
> (defn memoize [f]
> (let [mem (atom {})]
> (fn [& args]
> (if-let [e (find @mem args)]
> (val e)
> (let [ret (apply f args)]
> (swap! mem assoc args ret)
> ret)))))
>
> (defn fib [n]
> (if (<= n 1)
> n
> (+ (fib (dec n)) (fib (- n 2)))))
>
> (time (fib 35))
> user=> "Elapsed time: 941.445 msecs"
>
> (def fib (memoize fib))
>
> (time (fib 35))
>
> user=> "Elapsed time: 0.044 msecs"
>
> My question is when "let" is used in this context, wouldn't it create
> a fresh binding to a new atom{}? Any explanation would be highly
> appreciated.
>
> Thanks.
>
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