On Jun 22, 6:46 pm, "beatle...@gmail.com" <beatle...@gmail.com> wrote: > (take 10 (sort (for [x (range 1000000)] (rand))))) > > Now the problem is the memory usage, as it does not merely uses memory > space for 10 items, but it keeps a reference to the entire sequence. > If I leave out the sort its all ok, and done lazily.
Sort can't really be lazy without being unbelievably slow. I'm guessing what you want is for the long sequence produced by sort to be collectable garbage, aside from the ten items you take. Now the lazy nature of take 10 is biting you in the butt. If you make it eager with doall it *might* work. I'd instead do something like (vec (take 10 (sort ... ))) which constructs a whole new vector of ten items and drops any possible reference to the input. The GC should sweep away everything but the ten-element vector as soon as the memory is needed elsewhere. But this should not have been causing a stack overflow. If you're getting stack overflows, it's something else. Most likely you have very deep tail recursion and hoped it would be optimized like in Scheme. That won't work; you have to make tail recursion explicit in clojure using "(recur args)" instead of "(fn-name args)". You can also use "recur" together with "loop" to make a loop inside a function. It's "functional" in that, though the loop variables can be rebound each time around the loop, it's conceptually equivalent to defining and then calling a tail-recursive "letfn", and a lot less syntactically messy. Someone here recently wrote a macro, I forget its name, to make "lazy- seq" similarly less messy to use. Search the site for "lazy-seq". It's not as useful, because usually you've got something like "take" or "take-while" or "map" that can be used to make the lazy sequence you want, and rarely need to resort to "lazy-seq" itself. But for now, you probably just need to use "recur" at your tail calls to fix your stack overflows, unless you have multiple functions calling each other with circularities. That's messier to tail- optimize, unfortunately. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
