On 20 July 2010 23:41, Moritz Ulrich <ulrich.mor...@googlemail.com> wrote: > I think the tour problem is the (def m-fib (memoize fib)). You create > a new memoized function m-fib, while fib will internally call the > non-memoized fib. You have to do something like: (binding [fib > (memoize fib)] (fib 42)). > However, this will break if you use recur instead of recursive calls to fib.
Actually self-calls don't go through Vars, so the binding changes nothing. Try this if you want to check it for yourself: user=> (defn foo [x] (Thread/sleep 100) (if (zero? x) :done (foo (dec x)))) #'user/foo user=> (binding [foo (memoize foo)] (println (foo 10)) (println (foo 10)) (println (foo 9))) :done ; after a delay :done ; immediately afterwards :done ; after another delay nil To force the self-call to go through the Var, you could use #'foo in place of foo: (defn foo [x] (Thread/sleep 100) (if (zero? x) :done (#'foo (dec x)))) If you try the above (binding ...) form with this version, you'll notice there's no delay before the final printout. This has a cost of its own and requires a change to the function's code, so might not always be a good idea. It's simpler than baking a local cache into the function itself, though; and if you've got a self-recursive function foo written in this fashion, you can do (alter-var-root #'foo memoize) to memoize it "in place". (If you need the original function, you could put it in the Var's metadata; and if at some point metadata on functions becomes officially supported -- as opposed to being an experimental feature -- maybe memoize could put the original function in the memoized function's metadata.) Sincerely, Michał -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
