#clojure – 2008-07-03

2008-07-03

00:13	slava	Chouser: in the jvm, a 'try' block has zero cost if no exception is thrown
00:13	Chouser	slava: cool, thanks!
00:14	slava	i assume clojure compiles to intelligent bytecode for exception handling, then it won't be a performance issue at all
03:27	hoeck	cgrand: tried cryoPID on a clojured jvm, it somehow suspends and awakes, but it seems to close all file descriptors (at least the cryopid i built on my machine)
03:43	cgrand	hoeck: wow, I was kidding :-) Btw, I tried it myself yesterday and I ran into 2 pbs, one can easily be fixed (unlinking the file where hotspot stores runtime statistics so as to have cryopid embed this file in the snapshot), and the other one requires more work: cryopid works only on single threaded processes :-(
04:27	hoeck	cgrand: i was curious about that, it would be nice to suspend the jvm under certain conditions, but as my 'sessions' mostly include swing frames, it wouldn't be of great use for me.
04:36	cgrand	hoeck: there's other checkpointing solutions: https://lists.linux-foundation.org/pipermail/clusters_sig/attachments/20051025/88ed8b30/Comparison-CR-0001.pdf but restoring a swing app is certainly tricky
04:42	hoeck	i'm wondering that there is no suspend capability built into the jvm, that should be easier than suspending the whole jvm process
04:45	hoeck	BTW, i've got a laptop with working acpi-suspend-to-ram, so i can at least save one single clojure session :)
04:46	cgrand	:-)
05:37	Ycros	hoeck: if you're on linux you could try http://cryopid.berlios.de/
06:15	hoeck	ycros: yeah, cgrand already suggested it, and i tried it too, but it didn't work properly on my machine
10:18	cemerick	anyone planning to go to oopsla?
10:22	Chouser_	rhickey_: I'm in awe of drop-last's implementation. And thanks, I need it for lazy-xml.
10:33	Chouser_	If s is not itself a sequence, (seq s) will create a cache for the results as it walks along, right? Then won't the call to seq inside (drop n s) create its own separate cache?
10:37	rhickey_	a seq is a cursor, there isn't a lingering cache unless the interim seqs are held, but it will create 2 cursors unless you pass it a seq
10:38	rhickey_	I can add a (let [s (seq s)] ...
10:39	Chouser_	right, I was just trying to figure out if that would help anything or not
10:41	Chouser_	seems like it wouldn't really. You'd mainly want to make sure that if computing (rest s) takes any real work that it doesn't do it again just to track the offset. But if s was built with (lazy-cons) both calls to (seq) will just point to the original, so there wouldn't be a problem.
10:41	rhickey_	not if it's already a seq, then the drop seq is creating cache that the head will reuse
10:42	Chouser_	right
10:43	Chouser_	which leaves things like maps and vectors, where I assume advancing a seq is pretty lightweight.
10:43	rhickey_	Chouser_: yes, and you don't ever lose the advancing cost
10:44	Chouser_	and wouldn't be cached anyway ... right, ok.
10:45	rhickey_	one advantage of 2 cursors is you won't be holding onto n seqs in the interval, _unless_ you were passed a seq in the first place
10:49	Chouser_	I wrote a lazy-but-last a couple days ago and thought briefly about how much more code it would take to handle n>1; I was nowhere close to your implementation.
10:56	rhickey_	Chouser_: I constantly have to remind myself to try to use a higher-order fn, because lazy-cons is so easy
10:57	Chouser_	yeah, mine used destructuring to look ahead and lazy-cons to build the result. I thought I was all clever.
11:01	rhickey_	Chouser_: cgrand had the right idea earlier this week, just did work map already does: http://clj-me.blogspot.com/2008/07/lazy-butlast.html
11:04	rhickey_	Chouser_: I saw your case - one of the things Lisp cases do is take multiple test values that match to a single expr
11:07	Chouser_	I hadn't seen cgrand's blog. He did a lazy-in-another-thread too.
11:10	rhickey_	Chouser_: yeah, it's a one-ahead IIRC. I didn't see the need to go to Executors/Futures rather than use agents
11:11	Chouser_	yep, one-ahead. But it's interesting to me that he, I, and abrooks apparently all started thinking about that basic idea within the last week or so.
11:36	cemerick	rhickey_: Are there any plans to support overloads with the same arity but different signatures? (e.g. (defn foo ([#^String a] a) ([#^Integer a] a))
11:36	rhickey_	cemerick: no
11:36	rhickey_	multimethods?
11:37	cemerick	I'm thinking about that only in connection with proxy / gen-class.
11:37	rhickey_	proxy routes to a single handler, but gen-class can do that now
11:38	cemerick	right, right, param-types.
11:40	rhickey_	then independent handlers foo-String, foo-int
11:40	rhickey_	hmm... looks like that feature is not documented
12:31	rhickey_	lisppaste8: ?
12:32	Chouser_	rhickey_: are you opposed to an :else in case? Seems like it would be handy if the keyform is complex.
12:33	rhickey_	what if the keyform is :else ?
12:33	Chouser_	[:else]
12:33	Chouser_	same if you need to match a vector
12:33	rhickey_	what if the keyform is [:else] ?
12:34	Chouser_	[[:else]]
12:34	Chouser_	[1 2 3] will match 1 or 2 or 3
12:34	rhickey_	are you always requiring [] ?
12:35	Chouser_	no, any non-vector gets one vector wrapped around it
12:35	Chouser_	[[1 2 3] 4] will match [1 2 3] or 4
12:36	rhickey_	:a becomes [:a] in the expansion?
12:36	Chouser_	[:a :else 5] matches :a, :else, or 5; [:else] matches just [:else]; :else matches everything
12:37	Chouser_	[:a] and :a both become (or (= key :a))
12:38	rhickey_	hmm... maybe lists for grouping?
12:38	Chouser_	I guess requiring [] wouldn't hurt too bad, but I think not requiring it will be more helpful than confusing. I dunno, maybe I've got that backwards.
12:39	Chouser_	well, right now I'm evalling the keys so non-constants are allowed, so lists would require quoting.
12:40	rhickey_	most cases don't allow non-constants
12:40	Chouser_	between that and the fact that [] are visually different from the likely () used in the result expressions led me to use vectors.
12:41	lisppaste8	rhickey pasted "seque redux" at http://paste.lisp.org/display/63224
12:43	Chouser_	ah, sure
12:45	rhickey_	Chouser_: I'm not sure more configurability than pluggable queue is needed
12:46	Chouser_	ok
12:50	Chouser_	I figured out a way to put a finally clause back instead of catching and re-throwing the exception, but it only saves one line of code and puts the try block inside the loop. I didn't know if that was really better or not.
12:51	rhickey_	exception only has overhead when you have one, in which case efficiency isn't your problem :)
12:53	rhickey_	Thanks for your input on this. If no one sees any obvious deficiencies, I'll add that seque to Clojure
12:54	Chouser_	you're welcome, it's been fun.
12:55	Chouser_	I might yet take one more swing at a configurable fill to allow me my ugly enqueue thing. Maybe SAX parsers are the only thing that will ever need it, but I just wouldn't be surprised if some other Java interop could use it.
12:58	lisppaste8	Chouser annotated #63224 with "finally instead of catch/throw (if it matters)" at http://paste.lisp.org/display/63224#1
13:00	Chouser_	no, don't use that. If .offer throws something we'll be in bad shape
13:02	Lau_of_DK	Evening Gents
13:11	StartsWithK	Why do examples of gen-and-save-class (http://paste.lisp.org/display/63177 http://is.gd/Ljy) use (clojure/refere 'clojure) but when i do it i get a error saying that defs from clojure are allready in my ns http://pastebin.com/d3d640c0b
13:11	StartsWithK	i tried, but its just insane to prefix everything with clojure/
13:18	Lau_of_DK	I think its due to your initial (in-ns) , but its just a hunch
13:18	Lau_of_DK	does that ns refer clojure?
13:18	Chouser_	StartsWithK: yeah, you can also try using :exclude or :only in your (refer), but that also gets a bit painful.
13:19	StartsWithK	Lau_of_DK, how else will i implement functions that will map to class methods?
13:19	Chouser_	rhickey outlined a solution but I don't think he's started work on it yet.
13:19	Lau_of_DK	Does (com.paulbarry.HelloWorldServlet) refer Clojure ?
13:19	StartsWithK	Chouser, but ill have to exclude every function i use
13:20	StartsWithK	and not only that, but ill have to do it in every .clj file i have
13:20	StartsWithK	not only in that one..
13:22	Chouser_	well, just in your com.paulbarry.HelloWorldServlet ns, you would say (clojure/refer 'clojure :exclude '(print)) and such
13:22	Chouser_	you might have several more besides print, but you'd only need to do it in genclass namespaces, not all your other ones.
13:23	StartsWithK	but i then use (clojure/refer 'gl) or any other ns i have, and i get the same error for that file..
13:24	StartsWithK	i wouldn't like to put that :exclude in every file ill use
13:25	Chouser_	is 'gl a genclass namespace?
13:25	StartsWithK	no
13:25	Chouser_	but it defines a print function?
13:26	StartsWithK	no
13:26	StartsWithK	but it starts with (cojure/in-ns 'gl) (clojure/refer 'clojure)
13:27	Chouser_	and that gives you an error? what name is conflicting between 'gl and 'clojure?
13:28	StartsWithK	print
13:29	StartsWithK	but i guess thats just first conflict it finds so it stops there
13:30	Chouser_	ok, I'm still missing something. 'clojure defines print. if you have a conflict on (refer 'clojure) in 'gl, then 'gl must define print, either manually or via genclass
13:30	Chouser_	maybe you can paste a small standalone example of the failure?
13:36	StartsWithK	http://freehg.org/u/kresimir/neman/file/73d324443f70/ in examples directory is GearsApplet.clj and in neman subdirectory there is a gl.clj, error i get is http://pastebin.com/d3d640c0b
13:39	rhickey_	gen-class is going to create vars in your ns for _every_ non-private method in all superclasses/interfaces, so if one of your superclasses has print, that's all it takes
13:39	rhickey_	looks like java.awt.Container has print
13:41	StartsWithK	so ill have to exclude everything that some superclass implements when refering to clojure namespace?
13:41	rhickey_	or :only the things you use in the refer call, at least until I change this
14:41	cemerick	rhickey: any reason why delay is private?
14:43	rhickey	cemerick: I don't want to promise its continued existence - was an implementation helper at one point
14:46	Chouser_	hashes seem to return int keys in sorted order.
14:47	cemerick	it, or something similar is pretty necessary, IMO. A lazy companion is worthwhile, too (thinking here of the plt promise lib).
14:49	cemerick	I've got a delay-fn macro around here somewhere that expands into a delay that can take arguments, which can be handy.
14:53	rhickey_	I'm not opposed, I just don't want people reinventing lazy seqs...
14:54	rhickey_	when I first released Clojure I had to spend a lot of time explaining how and why it was different from Scheme
14:55	rhickey_	cemerick: isn't delay inherently lazy?
14:56	cemerick	rhickey_: Ah, no, I mean a function named "lazy" (or something like the scheme function of the same name). i.e. http://docs.plt-scheme.org/reference/Delayed_Evaluation.html
14:57	cemerick	I never liked the 'force' mechanic -- simply evaluating the thunk provided by delay or lazy always seemed more reasonable to me.
14:57	rhickey_	That's what delay does, just that it supports IFn, so the way to force it is to call it
14:57	cemerick	exactly -- much better 'usability', IMO
14:58	cemerick	I'm surprised you fielded questions about clojure w.r.t. scheme similarities/differences. There's plenty of variation out there, already.
14:59	rhickey_	(import '(clojure.lang Delay))
14:59	rhickey_	(def p (Delay. #(println "Hello")))
14:59	rhickey_	(p)
14:59	rhickey_	(p)
15:00	rhickey_	no TCO is the big difference from Scheme
15:00	cemerick	Yeah, I could do that. I'm using my own delay macro until I know clojure.lang.Delay is sticking around. :-)
15:00	rhickey_	many other superficial differences
15:01	rhickey_	cemerick: what does you delay macro use?
15:01	rhickey_	your
15:01	cemerick	Feh. (almost) pointless academic pissing matches, IMO.
15:11	Lau_of_DK	rhickey_: Isnt it about time, that you make (time ) produce some nicer output?
15:21	Chouser_	ah, such fun: (defn perm [r m p] (if (> m 0) (mapcat #(perm (disj r %) (dec m) (conj p %)) r) [p]))
15:22	Chouser_	(perm #{0 1 2} 3 []) => ([0 1 2] [0 2 1] [1 0 2] [1 2 0] [2 0 1] [2 1 0])
15:23	rhickey_	neart
15:23	rhickey_	neat
15:25	Chouser_	I can generate a million permutations of 10 digits in about 11 seconds.
15:26	rhickey_	cool
15:27	rhickey_	where's lazy-perm?
15:27	rhickey_	:)
15:27	Chouser_	hmph
15:28	Chouser_	I'll write it as soon as I can find lazy-mapcat in boot.clj
15:28	rhickey_	do you need that? won't it be lazy-cat .. map ...
15:29	Chouser_	hm, dunno, I just spoke without really thinking. hardly ever happens. ;-)
15:29	Chouser_	that is lazy, isn't it?
15:30	Chouser_	yeah, it is. I wrote lazy-perm already. leave me alone. I've got a database to resintall...
15:30	Chouser_	and a C++ app to recompile
15:33	lisppaste8	Chouser annotated #63135 with "case with vectors and :else" at http://paste.lisp.org/display/63135#1
15:37	cemerick	rhickey_: my delay macro isn't anything special. It just takes a function body, and then keeps a map in a ref that holds the thunk, and then the "forced" value after the fn that the macro generates is evaled.
15:38	rhickey_	how does it know it's been forced?
15:38	cemerick	It checks the map in the ref for a value in a :result slot.
15:39	cemerick	I have a "fancier" one that will accept arguments on the "force", but then it's a little weird in that it'll return the same forced value for any arguments provided afterwards. I thought it was such a good idea, until I didn't. ;-)
15:41	rhickey_	if your thunk has side effects or takes a long time, might be incompatible with the transaction running multiple times
15:42	cemerick	Yeah, it has the same dynamics as memoize (I think).
15:43	cemerick	I don't double-check the ref's map (like you double-check around the synchronize in clojure.lang.Delay), but it Works For Me (tm).
15:43	cemerick	I suppose I could add that shrug
15:44	rhickey_	if the delayed expression has side effects you can't use transactions for this
15:46	lisppaste8	cemerick pasted "delay macro" at http://paste.lisp.org/display/63238
15:46	Chouser_	shouldn't use anything with side effects in a transaction, right? Actually, I should stop talking, since I've been staring at the implementation of Delay and still don't get it.
15:47	cemerick	well, if you're trying to delay something you know has side effects, and you know you want those side effects to apply on every access of that delayed expression, then you're not using delay properly, right?
15:47	cemerick	by that I mean, all delay mechanisms have this problem, no?
15:48	cemerick	s/problem/"problem"
15:48	rhickey_	no, delay is run once, cache result
15:48	Chouser_	oh!
15:48	cemerick	ok
15:49	rhickey_	cemerick: this stuff is tricky
15:50	rhickey_	the macro has a few problems independent of the semantics of delay. You are doing several 'flying reads', i.e. outside the transaction, of values that matter to you in the transaction. Those reads should be in the transaction
15:51	cemerick	rhickey_: Yeah, I know. I just knocked it out last night when I saw that boot.clj's delay wasn't open for business.
15:52	cemerick	I wanted to check with you on its status/future before bullet-proofing it.
15:52	cemerick	"it" referring to two different things there, of course...
15:53	cemerick	rhickey_: are you concerned in general about people wandering into using delay inappropriately, etc?
16:08	rhickey_	I made it so the resulting object implements both IFn and IRef, so you can 'force/read' it with either (x) or @x
16:09	cemerick	ooooh, shiny :-)
16:10	Chouser_	like memoizing a function with no args
16:11	lisppaste8	cemerick annotated #63238 with "fixes to my delay macro, if anyone's interested" at http://paste.lisp.org/display/63238#1
16:13	rhickey_	cemerick: you would still want to check :fn before calling it
16:19	cemerick	ah, I see that now. 'twas my first usage of transactions. Thanks for the pointer.
16:33	Chouser_	with seque's fill now leaving the thread instead of blocking, it has diverged even further from what I need to wrap a SAX parser.
16:34	rhickey_	right, because seque is pull and SAX is push
16:34	Chouser_	What torments me is I'll still need the LBQ, the agent management, exception propagation, etc. So it'll still look really similar, but different enough to be unusable.
16:35	Chouser_	but I think I just need to get over myself.
16:35	rhickey_	I had the seque in 2 parts, as I had described, seq->queue, queue->seq, with the only connecting point being the weak-ref
16:36	rhickey_	then I got discouraged about the weak ref.
16:36	Chouser_	heh. yeah. :-/
16:36	rhickey_	you still have to solve the close problem
16:37	rhickey_	After ECOOP, I'm going to look hard at Closeable for LazySeq, and also for direct cde-gen for LazySeq, as it has become so important to Clojure
16:37	Chouser_	cool.
16:38	Chouser_	that starts week from now?
16:38	Chouser_	are you ready?
16:38	rhickey_	I give talks on Monday and Tuesday - working on my slides now
16:38	Chouser_	huh. I thought you were working on seque and delay. ;-)
17:02	jgracin	If I have a Clojure script in the classpath, is there a way to load it from REPL?
17:03	Chouser_	(.loadResourceScript RT "foo.clj")
17:03	Chouser_	(.loadResourceScript clojure.lang.RT "foo.clj")
17:04	jgracin	Chouser_: Beautiful! Thanks!
17:04	Chouser_	np
18:00	StartsWithK	hi
18:01	StartsWithK	i now have running gears demo as clojure applet at http://kreso.mooo.com/gears.html
18:01	StartsWithK	but, i had to copy all needed file in GearsApplet.clj..
18:03	bpattison	geospatial=> (defn f2 [ x y ] (pr "f2=" x y))
18:03	bpattison	#'geospatial/f2
18:03	bpattison	geospatial=> (defn f3 [x & more] (let [s (seq more)] (pr x) (f2 s) ) )
18:03	bpattison	#'geospatial/f3
18:03	bpattison	geospatial=> (f3 1 2 3)
18:03	bpattison	1java.lang.IllegalArgumentException: Wrong number of args passed to: f2
18:03	bpattison	I'm stuck trying to get the right number of arguments to f2 -- any ideas?
18:47	rhickey_	bpattison: if a function takes args and you want to use the contents of a seq as the args, you need to apply the function. If you just call it, the seq will be passed as a single arg:
18:47	rhickey_	(defn f3 [x & more] (let [s (seq more)] (pr x) (apply f2 s)))
20:14	bpattison	rhickey: thank you -- I was struggling with that for a while
23:40	arohner	hello. Is this a good place to ask newbie questions?
23:40	arohner	I have
23:40	rhickey_	sure
23:41	arohner	(def foo [a b c] (println a b c))
23:41	arohner	is there a way to pass a seq of length 3 as an argument to foo?
23:42	arohner	I believe that's called splatting in ruby
23:42	rhickey_	(apply foo [1 2 3])
23:42	arohner	ah, thanks
23:47	arohner	can you call apply on a java method?
23:50	rhickey_	no
23:52	arohner	ok, thanks
23:53	arohner	BTW, thanks for creating clojure. I've been really happy with it
23:56	rhickey_	you're welcome!