Thank you, that explains the failure of the lazy-cseq using top-level defs.
I really hope it gets fixed, Clojure is going to be a hard sell if I have to
explain things like this to my coworkers :(
Anyhow there is still the problem with nonlazy cseq blowing the heap.
(defn cseq [n]
(if (= 1 n)
[1]
(cons n (cseq (if (even? n)
(/ n 2)
(+ (* 3 n) 1 ))))))
(apply max-key count (map cseq (range 1 1000000)))
*BOOM*
2011/1/20 David Powell <[email protected]>
>
> This same problem was raised recently:
>
>
> https://groups.google.com/group/clojure/browse_thread/thread/df4ae16ab0952786?tvc=2&q=memory
>
> It isn't a GC problem, it is an issue in the Clojure compiler.
>
>
> The issue seems to only affect top-level defs. At the top-level:
>
> (reduce + (range 10000000))
>
> - runs quickly without using lots of memory
>
>
> (def x (#(reduce + (range 10000000))))
>
> - also runs quickly without using lots of memory
>
>
> (def x (reduce + (range 10000000)))
>
> - uses lots of memory due to the sequence getting forced
>
>
> The problem seems to be caused by the clojure compiler forcing the sequence
> when trying to figure out how to compile it, not
> by the compiled code retaining the sequence at runtime.
>
> It probably isn't a good idea to put expensive top-level defs in your code,
> because they get run when you just try to aot
> compile your code; but if you need to, a workaround at the moment is to
> wrap your value in a function and call it as above.
>
> I suspect that it is possible for us to fix the compiler not to force these
> sequences. I think it is happening in the
> InvokeExpr class.
>
> --
> Dave
>
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