#clojure – 2008-09-30

2008-09-30

00:02	arohner	is there any introspection that can be done on local variables that a macro creates?
00:03	arohner	I'm looking at a macro that does (let [foo (func-call)] (your-code))
00:03	arohner	aside from reading the macro source, is there any way to figure out where foo came from?
00:03	arohner	i.e. I can't do (meta (var foo)) because it's a local variable
01:04	abrooks	albino: Thanks for pointing out Nailgun. A couple of weeks ago I drew up plans to do a similar thing only using Unix domain sockets (on platforms that support it) instead of TCP sockets. Unix domain sockets have some neat features such as being able to actually verify uid/gid over the socket securely and the extra nifty ability to send file descriptors via the socket. (Unix domain sockets are only acessible on the same host.)
01:05	abrooks	With the ability to send file descriptors, the IO has zero overhead -- the "remote" process actually uses the same file descriptors directly.
01:07	abrooks	There are certain things (process niceness, capabilities (on Linux and others), process quotas, etc.) which cannot be sent across the socket but it's fairly reasonable that one can have near zero startup overhead and truly zero runtime overhead.
11:23	blackdog	http://blogs.azulsystems.com/cliff/2008/09/jvm-language-su.html
11:24	blackdog	some good comments from cc - "Clojure spits out bytecodes that look really nice. The purely functional data-structures also look really nice; and the STM scaled surprisingly well. I definitely need to do some coding with it."
11:25	rhickey	also: "I ran Clojure's STM Traveling Salesman Problem using 600 worker 'ants' to optimize the path. It ran straight-up without a hitch, no tweaks - and with great scaling"
11:27	blackdog	could be good for the front page of clojure.org
11:27	rhickey	he used that Clojure TSP program to demo his super-cool profiling tools - very neat to see Clojure bouncing 600 lines of his CPU meters
11:28	rhickey	It's still early days in testing STM at these scales, but Cliff's a great resource and very helpful
11:28	blackdog	a great start! not that i'll ever use a box like that :P
11:28	abrooks	rhickey: Glad to see you made it home safe! Sorry you were kept there so long. Did you get home before 1am?
11:29	rhickey	abrooks: just after - no problem driving, and was happy to stay and talk. Such a great audience!
11:30	abrooks	I brought five guests and they all loved it!
11:31	pjb3	Did anyone record the talk last night?
11:31	rhickey	Met Dan Weinreb. Gerald Sussman, Alan Bawden. Last week I had Guy Steele in the audience - fun to connect with these guys who started it all
11:32	rhickey	pjb3: I did a screen+audio capture and someone videotaped
11:32	pjb3	rhickey: cool
11:33	blackdog	did you have any awkward or standout questions last night ?
11:34	abrooks	rhickey: How did last night the group size rougly the same size audience as previous talks?
11:34	abrooks	er....
11:34	rhickey	I think the audience was genuinely interested in understanding Clojure rather than challenging it
11:34	abrooks	rhickey: How did last night's group size compare with the audience size from previous talks?
11:34	leafw	rhickey: because clojure is not just an incremental improvement over java.
11:34	walters	it seems pretty beyond challenge after looking at it for more than a few seconds, IMO
11:35	abrooks	leafw: Because Clojure's not an incremental improvement over Lisp...
11:35	blackdog	i noticed ola bini seemed to feel uncomforatable with clojure's new structures, which prompted my question if the 'old school' were cool
11:35	abrooks	leafw: This crowd knows that Lisp is an improvement over Java. ;-)
11:35	leafw	abrooks: libraries and legacy code, thye matter a lot.
11:36	abrooks	leafw: Certainly. One of the many great things about Clojure.
11:36	leafw	all of a sudden, we can have both.
11:36	leafw	(lisp and libraries)
11:37	rhickey	blackdog: I didn't get to finish my conversation with Ola about that, but I think if he saw how easy it is to handle the data structures uniformly in Clojure he might change his mind: e.g. (into (empty coll) (map f coll)) works for anything in Clojure
11:37	abrooks	leafw: CL has great libraries but they're have less relevance to the current universe.
11:40	rhickey	blackdog: I think the oldest of the old school were perhaps the most receptive - they remember Lisp before standardization when everyone had their own dialect and there was lots of variety and innovation
11:41	blackdog	fantastic, you hit a sweet spot for sure,
11:42	rhickey	I had so much fun - this was the audience best suited to 'getting' Clojure right away, as they already 'got' Lisp and I could presume that in my talk
11:45	Chouser	def-aset generates calls to Array static methods like setLong. Would it be acceptible for it to call RT.aset instead?
11:47	rhickey	abrooks: crowd was smaller than JVM languages summit, larger than the Java user group I did in June
11:48	abrooks	Oh, I wasn't really counting the JVM languages summit. Those folks weren't there just for Clojure. In 2010 they will be. :-)
11:49	rhickey	abrooks: It was the biggest user group so far
11:50	abrooks	Great. I heard it was over sixty. Thirty-five had registered.
11:51	walters	i wonder whether that large group that came in after 6pm was together in some way, like all from some class
11:57	danlarkin	oooo I can't wait for a new video
12:03	earthvssoup	here here
12:05	rhickey	It's over 3 hours...
12:06	rhickey	actually there were lots of good questions, if they came out in the audio it will be great
12:07	danlarkin	fantastic
12:16	earthvssoup	Heck, I'd watch 3-hours just to see the Emacs-Fu. ;)
12:20	leafw	[rhickey: I make it customary to repeat the questions, so everybody hears them through the microphone]
12:36	rhickey	leafw: yes, I keep telling myself to do that, but then forgetting...
12:47	Chouser	looks like JavaScript may be growing thread support after all: http://www.whatwg.org/specs/web-workers/current-work/
12:48	Chouser	message passing for inter-thread communication
12:48	rhickey	saw that
12:49	rhickey	I don't think they could support actual data sharing giving JS heritage, so offering an explicit API gets around that
12:49	Chouser	right
12:51	rhickey	A Boston Lisp Meeting report: http://xach.livejournal.com/#entry_191581
12:53	Chouser	I've been getting reports all morning from my half-dozen friends that were there.
12:53	Chouser	everyone enjoyed it
12:53	danlarkin	http://search.twitter.com/search?q=clojure lots of positive experiences on twitter too
12:54	earthvssoup	@Chouser. Thanks for the tips on my On Lisp -> Clojure project. Much appreciated.
12:54	baetis-fly	anyone know if a video exists of the boston lisp presentation on clojure exists?
12:54	Chouser	earthvssoup: sure, looks like a cool project.
12:55	earthvssoup	Thanks. That remains to be seen. ;)
12:55	Chouser	baetis-fly: nothing online yet, but there's hope.
12:56	rhickey	earthvssoup: yes, good project. You should try to stay functional when possible, rather than copying imperative things from CL, that will have the most value. Stuart Halloway has been doing the same (translating to FP style) in covering the PCL stuff, with much success
12:58	earthvssoup	rhickey: I am still trying to find my way out of my imperative nature. It's slow going for the first couple of chapters, but I'm confident that I'll come around.
13:02	danlarkin	earthvssoup: it's always helped me to think "what do I want" rather than "how do I get it"
13:55	earthvssoup	danlarkin: Thanks, I will keep that in mind.
17:08	StartsWithK	if i have macro like (doto x (something1 args) (something2 args)), i would like to (find-var something1) and (find-var something2) and if something exists and is macro, evoluate it in a same way (clojure/doto) evoluates first argument before it includes it in rest of the macro
17:08	StartsWithK	is something like this possible?
17:18	hoeck	StartsWithK: so you want a macro that treats other macros specially?
17:19	StartsWithK	something like that
17:19	hoeck	StartsWithK: or do you just want to expand nestet macros?
17:19	StartsWithK	hmm
17:19	StartsWithK	expand i think
17:19	StartsWithK	if that is right term
17:19	StartsWithK	ok, one 'example'
17:20	hoeck	the thing that `macroexpand' does
17:20	StartsWithK	(doto (JButton.) (on :action-performed (fn [e] (println "you clicked on button"))))
17:20	StartsWithK	this is what i will put on firs version
17:20	StartsWithK	where (on) is some sort of 'patch' multimetod that my doto macro will use
17:21	hoeck	ah, i see
17:21	StartsWithK	but what i wan is (doto (JButton.) (on :action-performed [e] (println "you clicked..")))
17:22	StartsWithK	so, on must be a macro in second example and it should expand to firs example before i use it in
17:22	StartsWithK	actualy :action-performed is defalut so it will be even shorter as (on [e] ...)
17:23	hoeck	so you want to roll your own doto macro?
17:23	StartsWithK	yes
17:24	StartsWithK	i mean, i have one now
17:24	StartsWithK	this is my idea of 'patch' system that i would like to include in it
17:24	Chouser	I think you could approach two ways -- either make "on" a global macro of its own, or have doto walk through its args looking for (on ...)
17:25	Chouser	actually, this first won't work. so you could try the second. ;-)
17:25	StartsWithK	Chouser: i was thinking i would lookup for var, and see does it have macro metadata on it
17:26	StartsWithK	or maybe on some metadata of my own like :dotoexpand true
17:27	Chouser	(meta (resolve foo)) where foo is a local that contains the symbol you're examining
17:27	StartsWithK	i pasted this yesterday http://pastebin.com/d3bb8978
17:27	StartsWithK	at the end is example of extended doto for now
17:28	StartsWithK	now what i want are two more things, first is that all (method args) are routed to (defmulti patch) that will first try to find multimethod for given class with given method name and execute it instead of classes method
17:29	StartsWithK	and second thing are the macros inside doto as i described them now
17:29	Chouser	I think "resolve" is what you're looking for to find the var for a symbol
17:30	Chouser	(:macro (meta (resolve f))), like you have (keyword? f)
17:31	StartsWithK	yes that is what i need
17:32	StartsWithK	but, how will i expand it
17:32	StartsWithK	that part bugs me even more
17:34	Chouser	you probably don't want to expand it yourself, but rather drop it into your output, where it can be expanded for you by the compiler
17:34	Chouser	if your macro produces (do .... (foo ...) ...), and foo is a macro, it'll get expanded for you
17:36	StartsWithK	when i process doto args, i will in the end transform (doto x (meth1 a) (meth2 b)) to something lik (. x meth1 a) (. x meth2 b)
17:36	StartsWithK	but if i don't expand on macro ill get (. x on ...)
17:37	Chouser	right, so don't do that.
17:37	Chouser	When you identify it as a macro, produce (on x ...) instead of (. x on ...)
17:37	StartsWithK	oh, i see
17:37	StartsWithK	yes
17:38	StartsWithK	i wasn't thinking i can just expand it in different way :)
17:39	Chouser	you know, I don't really like how doto has you specify methods without any .
17:39	Chouser	you could make a pretty simple macro that worked instead like (doto obj (.meth1 a) (.meth2 b))
17:40	Chouser	then you wouldn't have to do any special handling to get macros or even regular functions in there
17:40	Chouser	(doto obj (.meth1 a) (on foo) (.meth2 b))
17:40	Chouser	the doto macro would just insert obj as the 1st arg of each, and either get a method call, or a macro, or whatever.
17:41	Chouser	kinda like -> except for all applying to one thing instead of chaining.
17:42	StartsWithK	true, that would be much easyer way to do it
17:42	StartsWithK	but then i wouldn't be compatible with clojure/doto
17:43	Chouser	I actually think it'd be easier to read than clojure/doto
17:43	Chouser	yeah, good point. you might choose to name it differently
17:43	Chouser	or talk rhickey into accepting your syntax instead. :-)
17:43	StartsWithK	:)
17:44	StartsWithK	i will bug him when this monster is finished :)
17:45	StartsWithK	i would like at least something like (method+) syntax
17:45	StartsWithK	i find i do a lot of (addOption ..) (addOption ..) ...
17:48	Chouser	(with-arg foo (a) (b)) --> (do (a foo) (b foo))
17:48	Chouser	(with-cmd .foo (a) (b)) --> (do (.foo a) (.foo b))
17:49	Chouser	each would be simple and together would buy you doto and method+ functionality.
17:52	StartsWithK	let me sketch something bigger to demonstrate
17:53	H4ns	hi - i'm new to clozure. what is a [B@4a5afcb1 (something binary i guess) and how can i decode that into a string, possibly specifying the character set?
17:53	H4ns	clojure
17:54	danlarkin	H4ns: how did you get it?
17:54	H4ns	danlarkin: i got it from the http client.
17:54	rhickey	[B is a byte array
17:56	danlarkin	maybe run seq on it?
17:56	StartsWithK	Chouser: http://pastebin.com/d5b2bdf6e
17:56	rhickey	String has a ctor from byte array, so (String. ba)
17:56	rhickey	optional second arg is a string naming a charset
17:56	rhickey	(String. ba charset-name)
17:56	H4ns	rhickey: very cute, thanks! i've seen your talk yesterday, coming from cl.
17:57	rhickey	H4ns: cool - do you know Java?
17:58	H4ns	rhickey: only a tiny bit, i'm mostly common lisp, coming from perl, c++, c
17:58	rhickey	you might want to bookmark: http://java.sun.com/j2se/1.5.0/docs/api/ then
17:59	H4ns	rhickey: but i've written applets and small applications, so i'll find my way through. i'll just have to adopt to the notion that many primitive things are just java apis.
17:59	H4ns	rhickey: bookmarked, thanks
17:59	rhickey	H4ns: ok - I'm sure you'll get up to speed in no time, lots of helpful folks here and on the google group too
18:00	H4ns	rhickey: ok - thanks again for the warm welcome. yesterday morning i had no hope for lisp, that has changed a little now :)
18:02	H4ns	where do i find clojure.xml?
18:04	H4ns	ahj.
18:04	H4ns	never mind.
18:04	ppjt	Hi all; I'm playing with, & have aped successfully for use in macros, the `(let ~'[i 5] ...) form -- i.e. the ~', quote-unquote part -- but don't think I could explain it if I had to. I see that without it the variable, say, in the let binding above would be qualified with a namespace, but I'm still not exactly sure why.
18:05	ppjt	Does anyone mind explaining?
18:06	ppjt	[unquote-quote, that is]
18:08	H4ns	hm. (clojure.xml/parse "http://planet.lisp.org/rss20.xml") seems to end up in an unhandled exception when the server closes the connection. expected? better to slurp using the http client (which works) and then create a stream from that?
18:11	danlarkin	H4ns: (clojure.xml/parse "http://planet.lisp.org/rss20.xml") works for me
18:13	H4ns	danlarkin: i'm ending up in the slime debugger, (condition-case (error (slime-net-read ... - slime fairly recent, clojure from cvs, java 1.5 downloaded today
18:13	H4ns	i'll try without slime
18:13	ppjt	Me too; what's the exception you get, H4ns? A java.net.something-or-other?
18:14	H4ns	if i interpret the message correctly, it is actually slime that fails, no java in there, but a net-read-error. i'll try without first.
18:14	H4ns	yes, slime problem. is slime not really the way to go? what do others here use?
18:15	H4ns	might also be related to the fact that i'm using windows. if that is uncommon, i'll use something else.
18:16	ppjt	I'm not an emacser, but I believe someone has worked up a slime-like thing called swank-clojure. Just a sec...
18:16	H4ns	ppjt: that is what i use.
18:17	H4ns	ppjt: i've downloaded it fresh from git
18:17	fyuryu	I use clojure-mode for emacs, no problems so far
18:17	danlarkin	H4ns: slime is what rhickey uses too I believe
18:17	H4ns	fyuryu: how do you evaluate? just the bare repl in a inferior shell and copy and paste?
18:18	ppjt	Yeah, I think a lot of folks are having success w/ swank-clojure
18:18	fyuryu	H4ns: no, there are kb combos for that
18:18	fyuryu	H4ns: for sending code to the repl, that is
18:19	H4ns	okay, maybe windows is the culprit. i'll move to unix, thanks so far. the parsing and http clienting looks very nice, so i'll spend some time to get my environment straight :)
18:19	fyuryu	H4ns: i'm on windows too
18:20	danlarkin	could it be that code in H4ns' pull of swank-clojure has a bug and fyuryu's does not?
18:21	H4ns	danlarkin: could also be that my slime/emacs is not the right version.
18:21	fyuryu	danlarkin: I don't use swank-clojure, just clojure-mode
18:22	danlarkin	ah
18:29	H4ns	thanks so far. seems i need to tweak some more, bbl.
18:31	ppjt	Anyone familiar with the `(let ~'[i 5] i) -- i.e. the ~' part -- trick?
18:35	hoeck	ppjt: its to avoid the `i' becoming a namespace-qualified symbol
18:36	ppjt	hoeck: Do you know how it does that, exactly?
18:40	hoeck	it evaluates the quoted symbol and inserts that result into the macroexpansion
18:43	hoeck	the ~ means to evaluate the following expression
18:43	hoeck	and in case of `'foo, the following expr is 'foo
18:44	hoeck	evaluating to foo
18:44	ppjt	hoeck: why doesn't the resulting symbol, then, get namespace-qualified?
18:45	hoeck	cause its evalutated at the expansion time of the macro
18:45	ppjt	I think that's where I'm dropping out -- when does namespace-qualification happen in normal evaluation, & why wouldn't this symbol be subject to same?
18:46	hoeck	namespace-qualification happens only in backquote as far as i know
18:46	StartsWithK	hoeck, Chouser, thanks for help
18:47	ppjt	hoeck That makes sense, based on my REPL experiments...
18:48	hoeck	yeah, just try `(foo bar), `(foo ~'bar) and (let [bar [1 2]] `(foo ~bar))
18:49	ppjt	So, though everything inside a backquoted expression is _quoted_, the quote-unquote extra bit serves to avoid the ns-qualification stuff that comes as well w/ backquoting
18:51	hoeck	actually, its an unquote-quote :)
18:51	ppjt	Right!
18:53	ppjt	Though it makes more sense to think of the act of quoting, then unquoting that quote -- in right-to-left evaluation order that lisp works in...
18:53	ppjt	At least makes more sense to me
18:54	ppjt	hoeck: Do you know the utility of backquote's namespace-qualifying?
18:57	hoeck	when you define a macro in namespace a and expand it in namespace b, it avoids that the expanded expression does shadow symbols in namespace b
18:58	ppjt	Right -- makes good sense
18:59	hoeck	without this you would need to manually namespace-qualify each symbol
18:59	hoeck	or hope that no shadowing occurs
18:59	ppjt	Yeah -- would make for either tedious or bug-laden code
19:00	hoeck	right
19:00	ppjt	So is the quote-unquote (or vice-versa) technique the standard way to, say, set up let bindings inside of a backquoted expression in a macro?
19:00	ppjt	Or are there others?
19:01	hoeck	i guess its the only one
19:02	ppjt	I don't have time to look through boot.clj at the moment, but that'd be the place to investigate; I'll do so tonight...
19:02	hoeck	but you can build lists directly with (list 'let (vector 'i 5) ...)
19:03	ppjt	Oh yeah, good point
19:03	ppjt	Though, cause of lost readability there, I'd gladly take the ~' option
19:04	H4ns	can anyone here confirm that slime works on windows? i'd like to know that i'm not aiming for something too exotic
19:04	hoeck	backquote is basically an abbreviation, like quote '
19:05	ppjt	With the semantics of ', plus the ability to use ~, right?
19:06	hoeck	H4ns: i have a windows box at work, but I'm only using ilisp, not slime, could investigate tomorrow
19:06	H4ns	hoeck: so there is an ilisp backend? i would consider that, too.
19:08	hoeck	ppjt: yes, basically, + X times magic like doing namespace-qualif. in clojure and other things I don't know in cl
19:08	shoover	H4ns: yes, I use swank-clojure on a couple Windows machines. Make sure you have recent slime from CVS, at least from this month
19:09	H4ns	shoover: ah, thank you - any special emacs version, or stock windows emacs 22?
19:10	hoeck	H4ns: i build this one myself, but i want to use slime soon too, on windows and linux
19:11	H4ns	hoeck: ok - i'll first try an updated slime and then try ilisp if i fail. thanks!
19:11	ppjt	hoeck: An alternative to ~' in backquoted let expressions: `(let [i# 5] i#)
19:11	ppjt	Another bit of ` magic, it seems
19:11	shoover	H4ns: works with stock 22.2 and latest patched emacs 23 from http://ourcomments.org/cgi-bin/emacsw32-dl-latest.pl
19:16	H4ns	shoover: thanks, updating slime fixed my problem.
19:16	ppjt	hoeck: Gotta run -- thanks
19:16	hoeck	ppjt: np
19:44	H4ns	what ways to process xml are popular in clojure? i've looked at clojure.xml and cxml and there is java's facilities. i need something that lets me extracts elements out of a dom easily, preferably using an xpath/sxpath like syntax to specify what elements interest me
20:21	rhickey	H4ns: Chouser has an xpath-like library in clojure-contrib https://sourceforge.net/projects/clojure-contrib called zip-filter
20:22	rhickey	video from last night converting right now
20:23	H4ns	rhickey: i've also read what you wrote about 'xml is just data', trying to bend my head around that. i'll look at zip-filter, thanks.
20:33	H4ns	what is the proper way to quit clojure?
20:35	rhickey	H4ns: (System/exit 0)
20:36	H4ns	bow
21:13	danlarkin	rhickey: will you upload it to blip this evening?
21:23	rhickey	danlarkin: no, tomorrow, conversion to Flash takes over 8 hours
21:24	danlarkin	rhickey: I suppose I can wait that long...
22:05	acharlton	?
22:09	acharlton	Hi, all. Is there any reason why a piece of code would run differently in the repl than straight from the command line (ie. clojure.lang.Script)?
22:12	rhickey	acharlton: run differently in what way?
22:17	acharlton	I have a ref that is a map that holds other maps. As far as I can tell, when I run my program through clojure.lang.Script it adds an extra, duplicate map to that ref. This does not happen in the REPL.
22:22	acharlton	That's not really the whole story, since there are some functions manipulating the ref that seem to be creating the duplicate, but why would it only be happening with clojure.lang.Script?
22:26	Chouser	you run the same .clj file, the only difference being the class you name on the java command-line?
22:26	acharlton	That's right.
22:29	acharlton	Well, I suppose I haven't actually run the file through java command-line for the REPL instance. I've started the REPL and then (load-file "thesamefile.clj")
22:29	Chouser	hm.
22:34	acharlton	Huh. I just tried loading the file with the java clojure.lang.Repl, and the thing that happened with clojure.lang.Script happened again. It only seems to work properly (in the way I intended it - my code may very well be faulty) when I start the actual REPL and (load-file)
22:39	Chouser	you could paste your code, if you want.
22:54	acharlton	I'm not sure if it's worth the trouble. My code is actually broken (upon further inspection), and it's quite convoluted. I was just a little freaked out that it runs differently from inside the REPL.
23:12	acharlton	Alright. There was no mysterious map duplication. It was an accidental byproduct of a function. I'm still a little curious about why the results would differ inside and out of the REPL, though. Any insight?
23:13	acharlton	Or was it a freak of nature?
23:14	rhickey	there should be no difference, unless prior to load-file in the repl you manually set up some environment not present when run as a script
23:17	acharlton	I'm afraid not. (load-file) was the one and only command run in the repl.
23:19	rhickey	acharlton: Script just calls loadfile, so it shouldn't be different
23:20	acharlton	That's messed up, then.
23:20	rhickey	but if you can reproduce I'll chase it
23:33	acharlton	Well, it doesn't seem to affect me in any real way, and it does seem to be a weird fringe case. I'm not even sure if the ref itself was differet, I was just basing my assumptions off of the visual feedback of my program.
23:35	rhickey	if you see it again, grab it by the tail
23:36	acharlton	Heh. Alright.
23:36	acharlton	Thanks a lot for the help. Have a good night.