#clojure – 2009-04-05

2009-04-05

14:25	AWizzArd	wb Chouser
14:25	hiredman	Chouser: welcome back
14:25	Chouser	AWizzArd: thanks!
14:26	clojurebot	Chouser might make night
14:26	hiredman	~botsnack
14:26	clojurebot	thanks; that was delicious. (nom nom nom)
14:26	Chouser	looks like my poor machine has been failing to log for a few days. :-(
14:26	AWizzArd	jsankey and hiredman: thanks for these introductions into jetty, tomcat, jboss, j2ee and java beans.
14:26	jsankey	np
14:27	jsankey	fwiw, i'm a happy Jetty user - I would recommend it if you need a servlet container
14:36	duck1123	can jetty be run as a service?
14:36	duck1123	that's why I use tomcat
14:36	jsankey	sure
14:36	jsankey	but any java program can using something like java service wrapper
14:37	jsankey	we embed jetty in our app so we use our own startup script which uses the service wrapper
14:38	duck1123	are you using jetty with clojure, or just plain java?
14:38	duck1123	I just updated my compojure app to the post-ring version, I think I'm liking it
14:38	jsankey	this is a java app i'm referring to, so java
14:39	dreish	,(- Integer/MIN_VALUE)
14:39	clojurebot	java.lang.ArithmeticException: integer overflow
14:39	dreish	,(#(- %) Integer/MIN_VALUE)
14:39	clojurebot	2147483648
14:39	Chouser	nice!
14:39	dreish	First one compiles to a call to static public int Numbers.minus(int x). Second one doesn't.
15:46	Sebboh	hey. Fix your damned bot.
15:46	Sebboh	Channel notices beep!
16:10	duck1123	does anyone know if it's possible to get compojure to output well-formed xhtml?
16:33	duck1123	or does anyone recommend a different library for easily creating xml
16:34	Chouser	there are many xml-emitting libs
16:35	duck1123	I need to do xforms, so good namespace support is important
16:35	Chouser	ah. well, that should help you narrow the field a bit
16:35	duck1123	clojure.xml is a little too verbose for my tastes
16:35	Chouser	possibly to zero. :-(
16:37	hiredman	yay!
16:42	danlarkin	How do I create a pattern with re-pattern that has the same escaping done on it that a #"" regex literal does?
16:43	replaca	danlarkin: ?, you mean on the source string? I don't think you do...
16:43	Chouser	,(re-pattern (str #"\woo" "bar"))
16:43	hiredman	I don't think you can
16:43	clojurebot	#"\woobar"
16:43	hiredman	heh
16:44	replaca	Chouser, FTW!
16:44	Chouser	danlarkin: is that what you meant?
16:44	Chouser	it's not terribly efficient, of course. One of the benefits of #"" is the Pattern is compiled at readtime, and the above example loses that benefit.
16:45	replaca	but if you're constructing patterns at run-time, what can you do?
16:45	replaca	regex's don't have sql-like prepared statements, do they?
16:45	danlarkin	well I have a series of complicated regexes that I kinda want to re-use in subsequent regexes
16:46	Chouser	danlarkin: I think the Right Solution for that kind of thing will be a clojure-sexp-based DSL for string processing.
16:47	Chouser	but until that exists, using #"" to build escaped Patterns, and then str to print them in a form that can be combinded, re-parsed, and re-compiled at runtime will have to do.
16:47	replaca	Chouser: I've heard you say that before (and I have also thought about it). Do you know if anyone has ever tried such a thing in Lisp?
16:48	Chouser	replaca: I haven't looked. Is there something that does for reading what cl-format does for writing?
16:48	hiredman	Chouser: I think it's called fnparse
16:48	Chouser	heh
16:48	Chouser	could be
16:48	hiredman	:P
16:48	hiredman	man
16:48	replaca	well, cl-format is kind of the inverse of regex
16:49	Chouser	right
16:49	hiredman	I completely forgot to get better at using fnparse
16:49	replaca	cryptic, but compact and powerful
16:49	Chouser	oh, I see what you mean. yeah, that's not what I'm talking about then, is it.
16:49	Chouser	but maybe it points to regex being a better alternative than I'm giving it credit for.
16:50	replaca	Chouser: yeah, of thought of the same thing for output - a real dsl for describing output
16:50	pstickne	is there a really simple way to tell if a list contains a given item?
16:50	Chouser	do people ever want to programmatically create cl-format directive strings like they want to with regexes?
16:50	pstickne	e.g. (list-contains :a [:a :b :c]) ?
16:50	replaca	the problem is that typically, you want to keep those things small to get them out of the way of your algorithm
16:51	hiredman	,(.contains [1 2 3] 2)
16:51	clojurebot	true
16:51	hiredman	,(.contains [1 2 3] 4)
16:51	clojurebot	false
16:51	Chouser	pstickne: maybe you want a set instead of a list?
16:51	replaca	Chouser: not so much, but they do complain about the write-only nature
16:51	pstickne	Chouser: a set is fine too, still with the .contains method?
16:51	hiredman	,(#{1 2 3} 2)
16:51	clojurebot	2
16:51	Chouser	pstickne: you can just "call" a set, like you would a function.
16:51	hiredman	,(#{1 2 3} 4)
16:51	clojurebot	nil
16:52	pstickne	ohh
16:52	pstickne	sweet
16:52	pstickne	like a map :p
16:52	hiredman	but sets also have .contains
16:52	pstickne	,([1 2 3] 0)
16:52	clojurebot	1
16:52	hiredman	.contains is part of the java collections api
16:52	pstickne	neat, thanks :)
16:53	Chouser	replaca: conversely, regexes sometimes are your algorithm.
16:55	hiredman	~literal [5] clojure
16:55	clojurebot	like life: you make trade-offs
16:55	hiredman	that uses regexs
17:15	slashus2	Is there an equivalent to prog1 in clojure?
17:16	cmvkk	what's the difference between prog1 and progn again?
17:16	slashus2	prog1 returns the first
17:17	cmvkk	there's nothing built in for that, to my knowledge. seems like it wouldn't be hard to make a macro for that though
18:17	replaca	Chouser: (sorry, I was eating & putting my kid to bed): Yes, you are right. My only point would be that once people learn to do regex, they seem uninterested in less compact ways of expressing the same thing
18:18	replaca	but I'd emphasize "seem" since I don't have any counter experience
18:21	gnuvince_	replaca: I know that some people I talk with think that regexes are better than other alternatives (such as having a real parser)
18:22	replaca	gnuvince_: one nice thing is that a regex is "in the form of" the data on which it's operating (i.e. a string)
18:23	danlarkin	parsers and regexes each have a legitimate domain
18:23	danlarkin	IMO
18:23	replaca	but there's obviously some crossover point where you've got the wrong hmmer for the nail
18:23	replaca	danlarkin: agree 100%, though there can be overlap
18:23	durka42	replaca: i don't know about that. simple regexes can look like their text, but they get unreadable really fast
18:23	replaca	esp, if the parser is really accessible, which usually isn't true
18:26	replaca	durka42: yeah, that's where you get into the grey area
18:26	replaca	but usually, bringing in a parser is really heavy artillery (think yacc/lex) so peopel will ride the regex train as far as they can
18:27	replaca	(mixed metaphors, our specialty)
18:29	Raynes-	The Twitter team has switched to Scala. They are now using Scala along with existing RoR code.
18:30	Raynes-	Would be moar awesome if it was Clojure, but it's a start.
18:36	replaca	THey were desparate for something that scaled and "Scala" sounds like it would, just from the name :-)
18:59	dakrone_hb	hi all, I'm attempting to get use a jar from Clojure and having some trouble importing it, the java line works as "import estraier.*;" and then a Database() object is available, however clojure won't let me do (import '(estraier Database)), even though estraier.jar is in the classpath
18:59	dakrone_hb	I apologize for the long question
18:59	dakrone_hb	I apologize for the long question
19:00	dakrone_hb	is this the right way to be importing from a 3rd-party jar?
19:00	hiredman	what happens when you try the import?
19:00	dakrone_hb	java.lang.ClassNotFoundException: estraier.Database (NO_SOURCE_FILE:0)
19:01	hiredman	are you sure it is on the classpath?
19:01	dakrone_hb	(import '(estraier)) returns nil, but I'm not sure that's the right way to import it
19:01	hiredman	(System/getProperty "java.class.path")
19:01	dakrone_hb	yea, command-line is java -cp /home/hinmanm/src/clojure/trunk/estraier.jar:/home/hinmanm/src/clojure/trunk/jline-0.9.94.jar:/home/hinmanm/src/clojure/trunk/clojure.jar jline.ConsoleRunner clojure.lang.Repl
19:01	hiredman	dakrone_hb: that is not
19:02	dakrone_hb	the getProperty command has the estraier.jar in it
19:02	hiredman	what is Database?
19:03	cmvkk	so does import estraier.Database; work from java?
19:03	dakrone_hb	http://hyperestraier.sourceforge.net/javanativeapi/
19:03	dakrone_hb	yep, an example of a short java file is here: http://hyperestraier.sourceforge.net/javanativeapi/
19:04	dakrone_hb	cmvkk, It's used as import estraier.*; in Java
19:04	cmvkk	right, but does it work to do estraier.Database; ?
19:04	cmvkk	because it ought to, right?
19:05	dakrone_hb	it should, I haven't tried it explicitly, should I?
19:05	cmvkk	I don't know...it can't hurt I guess
19:05	dakrone_hb	I'll give it a shot
19:05	cmvkk	your syntax is right, for clojure, there's no reason why your clojure code shouldn't work when the java code does. that's the only difference between them.
19:12	dakrone_hb	hmm...I think there might be a library installation problem.
19:13	dakrone_hb	but it's good that I know the clojure syntax is right, thanks cmvkk
19:13	cmvkk	i wonder what's wrong that .* would work but not .Database though
19:13	cmvkk	I am not very familiar with how packages and importing work in java
19:23	cp2	,'1/0
19:23	clojurebot	Divide by zero
19:23	cp2	lame
19:24	cmvkk	what do you want it to return?
19:24	hiredman	,'1/3
19:24	clojurebot	1/3
19:24	hiredman	,(class '1/3)
19:24	clojurebot	clojure.lang.Ratio
19:25	hiredman	go figure
19:25	cmvkk	what...what's surprising about that?
19:25	hiredman	,(symbol "1/3")
19:25	clojurebot	1/3
19:25	hiredman	,(class (symbol "1/3"))
19:25	clojurebot	clojure.lang.Symbol
19:27	cmvkk	because getting a ratio out of 1/3 is a reader trick.
19:27	cmvkk	,(namespace (symbol "1/3"))
19:27	clojurebot	"1"
19:50	slashus2	Hypothetically could clojure's STM be implemented in clojure?
19:51	hiredman	yes
19:51	hiredman	rhickey has talked about self hosting clojure somewhere post 1.0
19:51	hiredman	(which would imply the stm written in clojure)
19:52	slashus2	One would use the class generator?
19:53	hiredman	the stm is bascially a system of locks
19:54	slashus2	right
19:54	hiredman	and clojue has acess to locks
19:54	slashus2	(locking ?
19:54	hiredman	yeah
19:56	slashus2	To implement Ref Atom Agent etc. the class generator would have to be used?
19:56	hiredman	yeah, gen-interface at least
19:56	hiredman	I assume the asm library would not be rewritten in clojure
19:58	slashus2	hmm... I don't think it could if clojure was to self boot-strap.
19:58	slashus2	Unless you had a clojure implementation there to begin with.
19:58	slashus2	I guess that is how gcc works.
19:58	hiredman	the asm lib is some third party thing anyway
19:59	slashus2	It was first written in asm, compiled, then the compiler was written in C. The process is probably slightly different.
20:04	cmvkk	the thing about self-hosting clojure is that you wouldn't be able to just supply the source and expect people to build it
20:04	cmvkk	since you would need a compiled version of clojure to compile clojure
20:07	slashus2	cmvkk: Right.
20:08	slashus2	That was probably the problem with gcc to begin with too?
20:09	cmvkk	yeah. well all you need is one compiled C compiler, then after that, you just use the immediately previous version to compile the next version.
20:09	slashus2	yup
22:05	slashus2	In a transaction, if you both both an alter and a commute, what sort of retry behavior should be expected?
22:10	slashus2	I guess if the alter value changes, the whole transaction will retry, but it keeps it from retrying if the commute value changes.
22:12	cmvkk	the commute never goes through unless the transaction actually commits.
22:12	cmvkk	and then it goes through on commit, regardless of what else happened.
22:13	slashus2	So the alter value is the only thing holding it back.
22:13	slashus2	alter I should say
22:13	cmvkk	yeah, if you alter the ref inside a transaction, it will retry.
22:13	cmvkk	if something else alters it first, anyway
22:14	cmvkk	what i want to know is, if you commute a ref inside a transaction and then alter it, the actual behavior of the ref is reversed in the real world, from how it looks inside the ref
22:14	cmvkk	is that right?
22:16	slashus2	Well since the commute won't succeed unless the alter succeeds, I think it will fail if the ref is altered elsewhere. I don't think the world is touched until the transaction succeeds?
22:16	cmvkk	right, i mean if the transaction goes through.
22:16	cmvkk	inside the transaction, the ref is commuted then altered. but in the real world, the ref is altered first then commuted.
22:16	cmvkk	or so the commute docs seem to suggest.
22:17	slashus2	(dosync (commute r + 1) (ref-set r 20))
22:17	slashus2	If that succeeds I wouldn't the ref be commuted first?
22:18	cmvkk	interesting.
22:18	orero	hi. quick question: why do I need the quote before the map form in this (-> [1 2 3] '(map inc) first - dec (+ 3) (min 5)) ?
22:18	cmvkk	,(let [foo (ref 0)] (dosync (commute foo inc) (ref-set foo 20)))
22:18	clojurebot	java.lang.IllegalStateException: Can't set after commute
22:18	slashus2	ooo
22:18	slashus2	..
22:19	orero	anyone knows?
22:19	cmvkk	hold on
22:20	cmvkk	that's odd behavior, orero, but
22:21	orero	is that a bug or is it me?
22:21	cmvkk	based on the expected behavior of ->, that map form would be wrong...since it inserts the object as the first argument
22:21	cmvkk	i.e. #(map % inc), when what you want is #(map inc %)
22:21	orero	right.
22:21	cmvkk	using the quote somehow fixes that
22:21	cmvkk	apparently
22:21	orero	so how did it manage to work anyway?
22:22	cmvkk	oh wait.
22:22	cmvkk	,(-> [1 2 3] '(map inc))
22:22	slashus2	,(macroexpand '(-> [1 2 3] '(map inc) first - dec (+ 3) (min 5)))
22:22	clojurebot	[1 2 3]
22:22	clojurebot	(min (clojure.core/-> (clojure.core/-> (clojure.core/-> (clojure.core/-> (clojure.core/-> [1 2 3] (quote (map inc))) first) -) dec) (+ 3)) 5)
22:22	cmvkk	it doesn't do anything.
22:22	cmvkk	it puts the vector in as an argument to quote.
22:23	cmvkk	which returns it like normal.
22:23	cmvkk	so it doesn't give an error, but the answer isn't correct either.
22:23	orero	oh.
22:23	orero	got it. thanks, man.
22:24	slashus2	cmvkk: I am guessing that the alters and commutes are commited in order?
22:24	cmvkk	well, they are, but only because that order is enforced in-transaction.
22:25	slashus2	right
22:25	cmvkk	the commute docs say that the in-transaction value of the ref will be commuted when you call commute,
22:25	cmvkk	but the actual commute won't happen in the real world until the point of commit
22:25	cmvkk	which would be after the alter, if you did it that way.
22:25	slashus2	yeah
22:25	cmvkk	rather than having weird behavior, it seems it's just not allowed at all.
22:31	cmvkk	,(-> [1 2 3] (#(map inc %)))
22:31	clojurebot	(2 3 4)
22:31	cmvkk	is there a better way to do that i wonder
22:36	slashus2	,(let [a-fn (fn [x] (map inc x))] (-> [1 2 3] a-fn))
22:36	clojurebot	(2 3 4)