#clojure – 2008-06-19

2008-06-19

07:12	asbjxrn	yrb, I don't think so. That is what rhickey suggested I use.
07:23	yrb	asbjxrn: I am divided if I like it or not, on onehand it makes it explict that I am using a nested class
07:50	asbjxrn	I guess there have to be some sort of separator anyway as clojure need to find thr class
08:37	cemerick	Chouser: Yesterday you wrote "(Math/pow 2 10)" -- which I assume is treating the Math class as a namespace, and all of its static functions as functions in that namespace. How is that set up (just evaling that sexp on my end yields an exception)?
08:37	blackdog	it's new in svn
08:38	cemerick	ah-ha
08:38	cemerick	blackdog: thanks
08:38	blackdog	there's no setup it just works :)
08:41	cemerick	Yeah -- Rich's checkin comment for r910 indicates that that feature is "experimental". Is there a discussion of it somewhere?
08:42	blackdog	yes http://groups.google.com/group/clojure/browse_thread/thread/bc005da4989468c7#
08:56	cemerick	feh, I don't know how I missed that.
09:34	cgrand	hmmm, good to know: sets can't be used to implement canonicalizing mappings
09:34	rhickey	cgrand: ?
09:35	cgrand	(meta (#{#^{:id "in set"} []} #^{:id "not in set"} [])) returns {:id "not in set"}
09:35	cgrand	(contrived one liner)
09:37	cgrand	I expectied taht a set would return the key and not the arg if found
09:42	rhickey	that's what I get for enabling get on sets, eh?
09:43	cgrand	?
09:44	rhickey	sets as functions of their keys
09:44	cgrand	yup
09:49	Chouser_	aren't you passing two args to a hash-set?
09:51	rhickey	cgrand: fixed
09:53	drewr	In general, does a NPE signify a bug in Clojure, or could I be doing something wrong to cause it?
09:54	rhickey	the only thing that is certainly a bug in Clojure is a verify error, for all else check your code first :)
09:55	drewr	Let me rephrase the question. Even if my code isn't correct, should Clojure be handing out NPEs?
09:56	drewr	Isn't that akin to my writing something in Python and getting a segfault?
09:56	rhickey	Chouser: that's a set with a metadata-tagged empty vector member being used as a function of another metadata-tagged vector, yielded arg (broken) rather than set member (fixed)
09:57	drewr	I'm willing to spend the time writing bug reports if clojure could handle the situation more gracefully.
09:57	rhickey	drewr: no, NPEs are often user bugs, and they are catchable by user code - what should Clojure do with them?
09:59	Chouser_	drewr: python libs don't hand out segfault. Java libs often throw NPEs.
10:00	drewr	Chouser_: Ah, I didn't know that was a common failure for Java libs.
10:01	cgrand1	rhickey: thanks for the fix
10:01	Chouser_	Well, that's my impression anyone. Someone that actually knows Java may correct me. :-)
10:01	Chouser_	s/anyone/anyway/
10:02	rhickey	So in Python you get a TypeError thrown - what's the real difference?
10:03	Chouser_	don't we get type errors in clojure too?
10:03	Chouser_	ok, thanks for the set explanation. I get it now. :-)
10:03	rhickey	you can get all sorts of errors, my point is they throw exceptions, you get stack traces etc, there's no magic to Python here
10:04	rhickey	neither dumps core
10:11	yrb	rhickey: have you got any plans to implement nested class access along the lines of the recent static member access?
10:17	yrb	and do you think it would be a good idea for import to load the nested classes into the namespace automatically?
10:33	rhickey	yrb: no, nested classes have composite names - why, don't like $ ?
10:37	cemerick	Train of consciousness: I've got an interface with methods foo and bar. My impulse is to use a map (or structmap) so I can do stuff like (:foo obj) rather than (. obj (foo)), and so that changes are easy and efficient. However, I then need a function that will pop off proxied instances that implement that interface so as to interoperate, and a function that will unpack instances coming in from Java into a map (or structmap). This basically sucks -- I a
10:37	cemerick	I guess this is getting back to the data-design topic. I'm probably making this harder on myself than it needs to be.
10:39	rhickey	cemerick: you can say (.foo obj)
10:39	rhickey	both Clojure and Java code create instances of this interface?
10:39	cemerick	Yeah, potentially.
10:40	cemerick	The nice thing about using simple maps is that changes are so efficient. Copying on changes is not something I want to do (although I guess that'd be required if I subclassed PStructMap).
10:42	cemerick	A bunch of multimethods would essentially give me everything I want, except it'd require more code than what seems reasonable for this case.
10:44	yrb	rhickey: it isn't the $, (I actually like the distinction) it is more not having to explictly import the nested classes of an class already imported
10:45	yrb	thought I am not sure if I would want that now...
10:47	yrb	I have mostly finished my awt/scene graph wrapper, and I don't think that style of java is very common outside the gui libs
10:48	rhickey	cemerick: so you want to use this interface functionally?
10:49	rhickey	Java implementations of the interface are unlikely to be functional
10:49	cemerick	rhickey: well, this particular interface is read-only, so that's something
10:49	rhickey	but you can implement an imperative interface with a ref to a map as its state
10:50	cemerick	Further, the interface is ours, so that helps, too :-)
10:51	rhickey	that's good, I guess my 2 cents is, don't hide/avoid/wrap the interface, use Clojure goodness in your implementation of it
10:51	cemerick	rhickey: Sure, and considering the general case, where we implement the interface and use a ref and map as a backing store -- it's obviously preferable to touch that ref and map when you're on the clojure side of things.
10:52	cemerick	The tricky part is being able to route and process instances that are implemented differently -- which brings me back to multimethods, I guess.
10:52	rhickey	caring about how they are implemented is a warning sign
10:53	cemerick	I know -- that's why I'm floundering a bit here :-)
10:54	cemerick	I could just not care how anything is implemented, and always copy on every mutation. Of course, that sucks -- perhaps an eager optimization, but perhaps not.
11:00	rhickey	ah, I see, your interface is read only and you'd like to treat instances persistently?
11:00	cemerick	indeed
11:01	rhickey	I'm running now, perhaps can follow up later...
11:01	cemerick	Yeah, we'll see how the rest of the morning goes. :-)
11:17	cemerick	This is (mostly) spurious, but shouldn't reduce take the initial value first, then the function and sequence? The way it is now, the (typically concise) initial val is in between two (potentially) verbose sexps.
11:22	cgrand1	cemerick: the current args order is mnemonic (at least for me :-) )
11:23	cemerick	cgrand1: it's just the opposite for me, but it's all moot now :-)
11:24	cemerick	does the literature generally use [fn, val, seq] order, or is that ordering typical from other lisps, or...?
11:24	Chouser_	the initial value is immediately before the seq that forms the rest of the values. it does make a kind of sense.
11:25	Chouser_	(reduce list 0 [1 2 3])
11:25	cemerick	Chouser: Yeah, I can see that. I always think of seed values as binding more to the fns that they travel with. A totally personal mental model sort of thing.
11:26	Chouser_	I admit I generally have to look it up.
11:27	cemerick	From a totally practical standpoint, if you've got a fn of any complexity, finding that lonely initial value that follows it requires a little squinting.
11:27	cemerick	At what point does a hash map tip over into a tree map?
11:27	Chouser_	never, I think.
11:28	Chouser_	PTreeMap is sorted, PHashMap is not, and I don't think there's any automatic conversion from one to the other.
11:29	cemerick	My apologies -- I forgot that PHashMap is a tree, internally.
11:31	Chouser_	I thought that might be it. I don't know how quickly it grows to what kinds of depths.
11:34	Chouser_	it'd be interesting to ask a particular hash what it's shape and depth is.
11:35	cemerick	One of Rich's screencasts goes into a couple of details about height and big-O guarantees.
11:39	cgrand	max depth: 6 (or 7, not sure of the details), 32 chlidren per node
11:40	Chouser_	but surely being a hash means the first node won't have a full 32 before it starts getting sub-nodes, right?
12:56	Chouser_	(double 2) is not equal to 4
12:57	drewr	Heh.
13:15	Chouser_	and so far I've had friends guess that it returns: 22, (2 2), and T
13:16	abrooks	2.0?
13:16	abrooks	:)
13:16	Chouser_	cheater.
13:17	abrooks	Not at all. I hadn't been in #noise yet. I just started here.
13:18	Chouser_	well, I guess I have to take your word for it, don't I? ;-)
13:18	abrooks	Indeed you do, unless you're snooping my gnu screen sessions.
13:19	abrooks	I did know that the unboxed numbers made their recent debut and you eliminated several alternatives above.
14:01	Chouser_	If I want to refer generically to a sequential collection, including things like Java array, Clojure vectors, Clojure lists, etc. what's the best word to use?
14:02	Chouser_	I would use "list" but that has specific meaning in Clojure.
14:03	rhickey	Chouser: 'sequential collection' ?
14:04	Chouser_	and so my variables can be named seqCollA, seqCollB. ;-)
14:04	rhickey	these are Java variables?
14:04	Chouser_	well, I was trying to use the same name in both. Maybe I shouldn't bother.
14:05	rhickey	fred/ethel/ricky/lucy works for me :)
14:05	Chouser_	yeah.
14:06	abrooks	littlericky gets a bit long though.
14:06	jmbr	hi
14:06	Chouser_	hi
14:22	cgrand	chouser_: about hashmap depth, I remembered I had a heap dump somewhere, so I ran some queries on it: hashmaps of ~400 elements seems to have nearly no (ie 1-3 per map) node of depth 4
14:22	Chouser_	cgrand: cool, thanks.
14:23	rhickey	if hashes are good, depth should be roughly log32N
14:23	rhickey	never more than 6
14:26	Chouser_	if two things hash the same, is there a linear bucket at the bottom of the tree?
14:26	rhickey	yes
14:26	Chouser_	I'm looking at the code and still can't tell. :-)
14:27	Chouser_	ok, thanks.
14:27	rhickey	sorry the persistent data structure code is lean and, well, mean
14:28	Chouser_	hm, but probably only if the hash is fully identical, right? You get more depth in the tree before you get the linear bucket?
14:28	rhickey	right, that's the 'trie' aspect
14:41	abrooks	This has bugged me since I came across JudyArrays long ago. Unfortunately, I'm not getting any traction. :-)
14:41	rhickey	yes, it's very annoying
14:42	Chouser_	can we also rename map or map, and perhaps double?
14:43	Chouser_	other sciences go and invent new latin-like words, don't they?
14:56	Lau_of_DK	Everything needs to stay exactly the way it is
14:57	Lau_of_DK	Ive had enough trouble learning Clojure, coming from Lisp
14:57	abrooks	:)
14:58	abrooks	Lau_of_DK: Perhaps we could use Danish terms instead of Latin?
15:07	Lau_of_DK	haha - you obviously dont know Danish
15:07	Lau_of_DK	Speaking 100% objectively: Its one of the most disgusting languages on earth
15:10	abrooks	Lau_of_DK: You are correct. My Danish vocabulary is (). :)
15:11	Lau_of_DK	user> (. Integer (toString 11121231230000))
15:11	Lau_of_DK	"1560900656"
15:11	Lau_of_DK	This is not what I expected...
15:12	Lau_of_DK	rhickey, is this your doing? Something is broke in the BigInt module?
15:15	Chouser_	Lau_of_DK: I think your BigInteger is being converted to an Integer in order to be passed to Integer/toString
15:15	Chouser_	Perhaps you wanted (.toString 11121231230000)
15:16	abrooks	Lau_of_DK: I thought English held the record for "Most Disgusting Language on Earth" (or maybe it was Klingon...).
15:16	Lau_of_DK	Chouser, ... Sure - so .toString is related to what.. if not Integer?
15:16	Lau_of_DK	abrooks, I think it might actually be Perl, then Danish :)
15:17	Chouser_	.toString is being called on whatever the actual type of its argument is -- in your example, BigInteger
15:17	rhickey	user=> (int 11121231230000)
15:17	rhickey	1560900656
15:17	Lau_of_DK	Aah I see
15:17	Lau_of_DK	So as I was just about to complain about Dynamic typing, its just because I dont really understand it, Clojure is a bit more clever than I had anticipated
15:19	rhickey	user=> (str 11121231230000)
15:19	rhickey	"11121231230000"
15:20	Lau_of_DK	thanks rhickey
15:41	Lau_of_DK	rhickey, would it be possible to compare the speeds of C, Python and Clojure for some computations? Have anything along those lines been done?
15:50	rsynnott	Lau_of_DK: there was a python/clojure one on reddit recently,I think
15:52	Lau_of_DK	Thanks rsynnott , I'll go look
15:57	cemerick	I think the data-design issues I was going on about earlier might be more general than I thought -- similar issues arise if one were to implement (for example) a tree data structure in Clojure whose interface is defined in Java, but should ideally have a richer interface in Clojure. This might just be the cost of doing business with Java callers and callees, I suppose.
16:00	lisppaste8	Lau_of_DK pasted "Java Heap...?" at http://paste.lisp.org/display/62507
16:00	Lau_of_DK	Gents- Simple task. Euler style. Find the first x that produces an x! that has 7^20 trailing zeroes... My code fries the Java Heap in about 5 - 7 minutes, so I assume Im doing something wrong ?
16:11	Lau_of_DK	(14 minutes actually)
16:13	Chouser_	thats a lot of zeros
16:13	Lau_of_DK	Yes ma'am
16:15	rhickey	cemerick: one option is to offer persistent 'mutation' in the interface, e.g. like IPersistentMap does
16:15	Lau_of_DK	Maybe its not supposed to be bruted though - There's a pretty clear pattern showing in the number of trailing zeroes
16:17	cemerick	rhickey: Yeah. Over time, we'll be doing exactly that for those interfaces we control and we can change in that way without freaking out our users.
16:20	cemerick	In the general case though (or simply when you don't have that option), it feels like there should be a relatively direct way to pass around proxied maps (for example), and when you get such an object back, be able to dereference the proxy to get a hold of the underlying map again. Totally doable with a couple of macros and multimethods (and probably an interface to allow the dereferencing bit). We'll see how motivated I get as I go along.
16:20	cemerick	rhickey: Any further suggestions you have are certainly welcome. :-)
16:21	rhickey	define and implement another interface for access to that implementation stuff
16:23	rhickey	(ah, you got that already, nevermind)
16:26	cemerick	rhickey: times like these, I wish clojure had a gen-and-save-interface ;-)
16:27	rhickey	I might consider that
16:28	cemerick	In a year or so, clojure will be the best interface to asm around.
16:36	Lau_of_DK	(gen-and-save) = (save-lisp-and-die) ?
16:38	drewr	Lau_of_DK: No. It's for created a (non-proxy) Java class.
16:39	Lau_of_DK	Ah ok
16:40	drewr	It's actually GEN-AND-SAVE-CLASS now.
16:41	drewr	The -SAVE part refers to the fact it actually writes the bytecode to a .class file.
16:41	drewr	Pretty cool. Check out genclass.clj.
16:42	drewr	The world would be a different place.
16:42	Lau_of_DK	drewr, did you know that rhickey is an alias for Skynet ver. 1.0 ?
16:44	drewr	Lau_of_DK: Surely he's at least r2 or r3.
16:55	cemerick	Is there a way to install a method by referring to an existing fn that I'm missing somewhere?
16:56	rhickey	cemerick: a proxy method?
16:57	cemerick	hrm, no -- for multimethods. So as to say (defmethod foo :bar some-fn)
16:58	cemerick	Just if I happen to have an appropriate fn floating around that is independent as well as useful as a multimethod.
16:58	rhickey	not right now, you'll have to forward to it
17:39	meredydd	Hey
17:39	meredydd	Who's responsible for the 'set namespace?
17:40	Chouser_	rhickey himself
17:40	meredydd	I just discovered it today, and it's The Shit.
17:40	meredydd	Ah.
17:40	meredydd	That...doesn't surprise me at all.
17:41	meredydd	It's that beautiful :)
17:41	Chouser_	:-) Gotta run.
17:42	meredydd	In any case, I'd like to beg rhickey to make more noise about that feature. It's really something.
18:55	shizzy0	I have a weird idea, that I'm trying to do. Can I make an anonymous macro? (mac [x] ...)
18:56	rhickey	shizzy0: no, how would it be called?
18:57	shizzy0	(let [m (mac [x] ...)] (m stuff...))
18:57	shizzy0	?
18:58	rhickey	ah, local macros like CL macrolet, and symbol-macrolet - nope, don't have those yet
18:59	shizzy0	(defmacro mac [parameters & body]
18:59	shizzy0	`(let [f# #^{:macro true}(fn ~parameters ~@body)]
18:59	shizzy0	(. (var f#) setMacro)
18:59	shizzy0	f#))
18:59	rhickey	it's not that simple
19:00	shizzy0	That's what I was playing with, but it doesn't like (var f#).
19:00	shizzy0	Right, it seems like a good opportunity to understand more of how things work.
19:01	rhickey	the compiler needs to participate in macroexpansion, right now there are no local macros
19:02	shizzy0	[nods] ok.
19:02	shizzy0	I'm just trying to stretch out in clojure, and see what I bump into.
19:02	rhickey	global vars can be tagged as macros, and their global definitions treated as macroexpanders, but local functions are not available to the compiler as macroexpanders
19:03	rhickey	It's something I would have to add, not something you can do with macros
19:04	rhickey	the concept is sound - I particularly miss symbol-macrolet
19:06	shizzy0	good to hear.
19:09	shizzy0	that the concept is sound. I hadn't used it in CL. :)
19:13	shizzy0	btw, rhickey, I really like what you've done. I haven't done anything with Java for a long time now, but I could see myself actually working in the JVM now.
19:14	rhickey	great!, thanks
19:22	meredydd	rhickey: By the way, I just discovered the 'set namespace, and am very impressed.
19:22	meredydd	Although I am somewhat confused by the (->) macro. The docstring is a bit, um, opaque.
19:22	rhickey	cool, I don't think anyone else has looked at it
19:23	meredydd	Yeah...I'm really hoping you'll change that - write it up as one of the pages in the sidebar, perhaps?
19:23	rhickey	-> threads the argument and successive returns as the first arg of subsequent forms
19:23	meredydd	I really think that having the relational algebra expressible natively is a really powerful thing
19:23	rhickey	yeah, I hope to do more with it
19:24	meredydd	(plus, it provides something I can point to and say - "Look! Native sets and maps in a Lisp is a beautiful thing"
19:25	rhickey	personally I think it is a shame that Lisp has been tied to lists for so long
19:26	shizzy0	ok, I don't know if this was intended, but I think this is pretty neat.
19:26	shizzy0	(map eval (map and '(true false) '(true true)))
19:26	meredydd	rhickey: right...so if I did (-> 1 (- 2) (+ 1)) it comes out as 3
19:27	shizzy0	The fact you can apply and map macros, and you'll get something weird out of them, but if you eval them, you get the actual results you'd naively expect.
19:27	meredydd	Oh, yeah...actually, that was something I wanted to say, too.
19:27	meredydd	I tried to do (map) with (and), and got some mighty funny results.
19:27	rhickey	meredydd: 0, no?
19:28	meredydd	Took me quite a while to figure out what went wrong. Any chance we could have a warning when some stupid programmer tries to do that kind of thing?
19:29	shizzy0	I got 0 for meredydd's expression.
19:29	meredydd	It's not always obvious which ops are macros and which are fns, and I could conceive of certain calls changing from one to another, say, between library releases
19:29	meredydd	(Yes, sorry. I meant 0, which is what the interp gave me)
19:29	rhickey	and is a macro, so can't be mapped, but you can do (map #(and %1 %2) ...)
19:29	rhickey	(map #(and %1 %2) [true true] [true false])
19:29	meredydd	I know - that's what I did. Trivial change, once I figured it out.
19:30	meredydd	But as it stands, if you try to use a macro as a fn value, it lets you
19:30	rhickey	I might be able to catch attempted use of macros as values...
19:30	meredydd	It just uses the macro's code-munging function instead
19:30	rhickey	right
19:31	meredydd	which caught me somewhat by surprise.
19:31	shizzy0	rhickey: but if you eval the expression you get from using a macro as a function, you get the right value it seems like. I actually kind of like that unification of macros and functions.
19:31	meredydd	Any chance of a molly-guard for the rest of us? I agree with shizzy0 that it might be cool to be able to throw macros around and do interesting things with them
19:32	rhickey	something being a macro or function is part of its interface
19:32	rhickey	in practice things don't toggle between
19:32	shizzy0	For instance, (apply and '(true false)) doesn't work but, (eval (apply and '(true false))) does.
19:32	rhickey	yes, as I said above, I might be able to flag it
19:32	meredydd	Perhaps like the reflection warnings - some explicit flag to say "I know what I'm doing, don't warn me about the fact that I'm taking this macro"
19:32	meredydd	That'd be great AFAIC.
19:33	meredydd	Oh, and one more, while I have you here. Looking at the doc for (->), I understand why I was so confused.
19:34	meredydd	...oh, no, scrub that. The doc's right, my brain's wrong. Ignore.