#clojure – 2008-04-21

2008-04-21

07:08	jteo	i keep getting stack overflows (trying to find a large prime).
09:43	vincenz	jteo: show me the code
09:44	jteo	lemme pastebin it. i think i don't quite grok lazy sequences.
09:45	jteo	i managed to solve it by using an iterative approach using loop.
09:45	rhickey_	paste.lisp.org has Clojure support: http://paste.lisp.org/new/clojure
09:49	vincenz	rhickey_: Hey if I roll my own language with some ideas of clojure (and obviously mention their origin) would you mind?
09:49	vincenz	s/of/from
09:49	lisppaste8	jteo pasted "primes" at http://paste.lisp.org/display/59467
09:49	rhickey_	what would you do differently?
09:50	vincenz	rhickey_: several things, some of which wouldn't be supported in your model
09:50	vincenz	Well, at least not by the jvm
09:50	vincenz	The fundamental thing I want are delimited-continuations in the presence of stm
09:50	vincenz	Since that requires me rolling a new lang, I'll prolly make some other changes as well, as well s keep some ideas
09:51	vincenz	rhickey_: place it somewhere between clojure, haskell and arc
09:51	vincenz	well mostly between clojure and haskell :)
09:51	vincenz	and scheme, cause of the dc's
09:52	vincenz	(The only neat thing from arc, though I think you support this as well are fun-callable data structures)
09:52	rhickey_	vincenz: well, few of the ideas in Clojure are novel, everyone borrows from the past - good luck!
09:52	vincenz	rhickey_: thanks :)
09:52	vincenz	Btw, you're welcome to join #oasis
09:52	vincenz	It's a bit of a social ltu for freenode
09:53	vincenz	Often silent, but we have bouts of interesting conversations, and a lot of smart people
09:54	jteo	ltu?
09:56	Chouser	http://lambda-the-ultimate.org/
09:57	Chouser	...where I go to remind myself how little I know about anything.
09:58	jteo	ah.
10:14	rhickey_	jteo: what's the problem with the primes you pasted?
10:15	jteo	rhickey_: stack overflow.
10:23	cgrand	rhickey, in Compiler.java:1790 shouldn't it be "Class classForName(String)" instead of "Class forName(String)"? (else I get MethodNotFound...)
11:51	cgrand	jteo: I think your code chains filters and, to get a new prime, it has to go through all the filters... and when there are too many filters your stack explodes.
11:52	jteo	cgrand: i guess so. I was trying to figure out how to iterate over a lazy seq.
11:54	jteo	ie. some way to skip forward to the nth item in the lazy-seq, without consuming large amounts of memory/cpu.
11:55	jteo	obviously loop is one way.
12:18	Modius	jteo: Depending on how the lazy sequence is implemented under the hood, looping through may not alter the CPU usage of any given stage of iteration, nor the memory footprint.
12:18	jteo	true.
12:19	Modius	jteo: What can lead to memory usage also are lazy sequences that make use of memoized links (some require these, e.g. certain self-referencing list solutions) - but the link back to the head (if you somehow keep one) causes all results to be preserved until the end of the computation, limiting how far you can traverse the sequence, or how many can be traversed in parallell with other actions that also use ram.
12:19	jteo	:)
12:20	Modius	jteo: The cliched haskell self-referencing fibonacci highlights this effect - AFAIK spking RAM proportional to N when obtaining the Nth item.
12:21	jteo	given that it's mostly run for small values of N..
12:21	jteo	(eg. in tutorials)
12:25	Modius	I believe Clojure has the raw tools required to solve these problems (macros + lambdas), and said solution would be inside its concurrency/STM model.
12:27	Modius	By "problem" I mean "ability to programmatically model solutions in this manner", not that it's a language problem per se
12:29	vincenz	Modius: Err..
12:29	vincenz	Modius: that's a lot of BS :)
12:29	Modius	vincenz: sorry
12:30	vincenz	1) recursive fibonacci in Haskell is just for tutorials
12:30	vincenz	2) if you do not want to keep it around, make it a function
12:30	vincenz	fib n = ...your memoized version !! n
12:31	vincenz	3) If you do not like to use space, then just write it recursively
12:31	vincenz	the whole point of the memoized version is to trade-off computation for storage
12:32	Modius	vincenz: Does writing it recursively partially memoize? Otherwise it'll become infinitely slow before the 30th element.
12:32	vincenz	Anywho, a bit weak to bash on $(LANGUAGE) if you do not intimately know said $(LANGUAGE) outside of the $(LANGUAGE) forum where noone is there to watch wat you say.
12:33	vincenz	Modius: just write it iteratively?
12:33	vincenz	uh?
12:33	Modius	vincenz: (On bashing) agreed, wasn't my intend, just to describe an effect. And I'd discussed it on #haskell by the way.
12:33	vincenz	s/uh/duh
12:33	Modius	vincehz: I did try to say "cliched haskell self-referencing fibonacci" - I wasn't indicting a language; but an expression form under memoization.
12:33	vincenz	let fib n = worker 0 1 1 where worker a b m = if m == n then b else worker b (a+b) (m+1)
12:34	vincenz	Modius: But the leakage-problem is acknowleged
12:34	vincenz	Modius: It's just a trade-off really, do you want to use CPU or do you want to use memory, and granted, if you're not careful you can leak more than you want to.
12:35	Modius	vincenz: I'm not going to hawk my own library in someone else's pond; but I have one where I was able to do both -self-referencing AND memoization; but memoization only between the links, not to the head.
12:36	vincenz	Modius: IIUC, you memoized the last two but not the whole thing?
12:36	Modius	vincenz: I don't consider the "leakage problem" that the cliched fibonacci highlights a haskell problem; but was trying to use it to describe an effect.
12:36	lisppaste8	cgrand pasted "a naive primes seq" at http://paste.lisp.org/display/59475
12:37	cgrand	jteo: I guess this is not what you look for?
12:45	jteo	cgrand: neat. now let me try to understand how it works. ;)
12:54	jteo	i'm having difficulty understanding why this one doesn't cause a stack overflow compared to the sieve implementation i tried.
13:05	cgrand	jteo: in yours, when you have already got 3, 5 and 7 to get the next prime, you ask to your seq (which filter out multiples of 7) for the next item, which asks to its parent seq (filter out 5x) which asks to its parent seq (filter out 3x) which asks to the odd numbers seq. In mine I just loop over the list of known primes (in prime?).
13:05	jteo	using "every?" you mean?
13:10	cgrand	yes, every? is just a loop
13:11	jteo	ah.
22:54	Chouser	does #(filter identity %) deserve its own built-in name?
22:56	Chouser	or maybe add an arity-one option to filter?