#clojure – 2008-09-12

2008-09-12

03:51	mhinchey	Hi. How do I get the namespace for a symbol? Shouldn't (namespace 'map) return something? It always returns nil.
03:55	hoeck_	mhinchey: hi
03:56	hoeck_	mhinchey: i think because 'map is not a namespace qualified symbol, if you try (namespace 'user/map) it will return "user"
04:02	mhinchey	oh, I was expecting it to return "clojure" since 'map is clojure/map. What I need is something to return the Namespace object of an existing symbol. Trying ...
04:05	hoeck_	well, you could try (resolve 'map), but this gives you only the var-object, not the namespace
04:09	mhinchey	thanks, this is what I need: (:ns ^(resolve 'map))
04:13	hoeck_	mhinchey: (ns-name (. (resolve 'map) ns))) would do the job
04:14	mhinchey	hoeck, thanks, this is what I need: (:ns ^(resolve 'map))
04:17	mhinchey	but that would work too
04:20	hoeck_	ahh, metadata, haven't thought of that, definitely better than poking around in clojure implementation-details :)
09:19	Chouser	(namespace `map)
09:21	rhickey	ok
09:22	Chouser	I'm glad you agree. ;-)
09:22	Chouser	Just answering a question from 4am, for the record.
09:24	rhickey	ah
09:39	Chouser	hoeck_: naw, looks like you got him to an answer.
10:28	Chouser	The structure I'm cobbling together for clojurescript could be mimicked to make a Clojure obfuscator.
10:29	Chouser	dunno how good it would be, but at least at first glance I imagine it would look pretty impenetrable.
10:31	rhickey	it's not obfuscated enough?
10:40	Chouser	oh, the JS is plenty obfuscated. I meant one could emit Clojure source again, but a bit scrambled.
10:42	rhickey	I think we should focus on clarity for a while :)
11:54	jamii	Is there a prefix form of the syntax-quote reader macro?
11:55	Chouser	(quote foo) ?
11:55	jamii	I'm after ` as opposed to '
11:55	jamii	Sorry - could have been clearer there
11:56	Chouser	oh! hm.
12:04	jamii	user=> ``a
12:04	jamii	(quote user/a)
12:04	jamii	Thats not a good sign - looks like ` might be special cased
12:04	Chouser	you're trying to generate this from a macro?
12:05	jamii	Yep - I want a macro that takes a form, does some processing and returns the form syntax-quoted
13:59	Chouser	I can't think of how to do looping inside a JS expression.
13:59	Chouser	(conj [] (loop [i 5] (if (pos? i) (recur (- i 2)) i))) ==> -1
13:59	Chouser	JS: conj( PersistentVector.EMPTY, do{..oops..}while() )
14:00	Chouser	will I have to turn all expressions inside out, assigning to temp vars along the way?
14:00	rhickey	the basic approach to this is, if you can't make an expression out of it, make a lambda and call it
14:01	rhickey	applies to loops, blocks, try/catch etc.
14:01	Chouser	hm... since this is a control structure point (unlike "let"), I guess a lambda would work fine.
14:02	rhickey	essentially you/ are translating an everything-is-an-expression lang into a statement/expr lang
14:02	Chouser	well, I was thinking that the comma operator would save me from some of this.
14:02	rhickey	some things work (i.e. if can be ?: expr), others don't
14:03	Chouser	and I guess it does some, but being unable to drop a do/while into the middle of it mucks things up a littl.e
14:03	rhickey	comma helps, I wished I had it when generating Java/C#
14:03	rhickey	the compiler tracks what 'context' you are in - expr/statement/return
14:03	rhickey	many emits have 2 flavors depending on context
14:04	rhickey	while as statement is easy, as expr needs to be lifted
14:04	rhickey	er, loop
14:04	Chouser	ok.
14:05	Chouser	I'm doing a lot of things the "simpler" way for now, as in what's simple to emit -- more work for JS at runtime.
14:05	Chouser	If the dumb thing actually works at all then we can clean it up.
14:11	rhickey	are you flowing context through tojs calls?
14:12	Chouser	yeah :-/
14:13	Chouser	clojure-contrib/clojurescript/tojs.clj
14:13	Chouser	I'm not passing along expr/statement/return yet, but I've got a hashmap that could hold that too if I need it.
14:14	Chouser	rhickey: jamii had a syntax-quite question I couldn't answer.
14:15	rhickey	jamii: syntax-quote is a reader thing, can't emit from compiler/macro
15:14	Chouser	should clojurescript provide something like vars? I guess it has to if we want metadata on them and things like the "var" builtin to work.
15:17	Chouser	which would make (def foo 5) translate to something like: foo = new Var(5) instead of foo = 5
15:19	Chouser	and later references to foo would have to be foo.get()
15:21	rhickey	Chouser: it depends on how rich/compatible you want clojurescript to be
15:22	rhickey	dynamic binding is the big var feature
15:23	Chouser	ah, push/pop. Hm.
15:24	Chouser	I guess there's still a little value in that, even when in single-threaded JS.
15:24	achim_p	hi! in case anyone's interested in a browser based doc ...well... browser, i made one today: http://launchpad.net/clojure-docbrowser/trunk/0.1/+download/docbrowser.tbz2
15:24	achim_p	it's a quick hack, very much unfinished. but perhaps it's useful to someone. jetty is required to run it. still needs lots of work - contributors welcome! :)
15:25	rhickey	Chouser: also indirection in referencing globals, defs go into vars, and you can pass the var around. If you use global js names, what would you pass around strings?, and how would you resolve - eval? hmm...
15:26	Chouser	achim_p: that's a pretty little servlet you've got there. nice.
15:27	Chouser	rhickey: well, I don't pass vars around much, but I suppose (var foo) needs to return something.
15:28	rhickey	Chouser: it doesn't necessarily, just thinking through the implications. Will there be symbols?
15:29	Chouser	I've punted so far on symbols and keywords, but I can't do that forever.
15:31	rhickey	your fiddling with js has made me think about cranking out AOT Java like I said the other day. That would give you a model, but doesn't solve the 'how much of a runtime' problem for you
15:38	Chouser	well, don't let me distract you from something people actually want. Like better error messages for example. ;-)
15:39	rhickey	better error messages is too generic to implement
15:41	cemerick	rhickey: I had no idea you were considering generating java source as a path to AOT. I would have thought that asm would give you the raw materials you needed to emit classfiles from scratch.
16:00	achim_p	Chouser: thanks for having a look! it's a bit paltry. i'd love to see some tool like this done properly, but am lacking both time and gui skills, i'm afraid
16:01	Chouser	I've got several little projects (mostly web-based) that I'd like to put together, but although they would be possible with Clojure as it is, I think it'll be more fun (for me!) to get more infrastructure in place first.
16:02	Chouser	things like clojurescript, gxp, and maybe some alternative to sql for on-disk storage.
16:07	ozzilee	rhickey: Out of curiosity, what do you mean by better error messages being too generic to implement?
16:09	rhickey	ozzilee: it's a generic request. Each scenario is different. I'd need examples: I typed this, it said that...
16:10	ozzilee	rhickey: Ah. Gotcha.
16:10	rhickey	but the general aversion to stack traces is something I don't relate to at all. The cause is now at the top, the rest is easy to ignore
16:11	rhickey	if there are common errors/patterns then that is something to go after
16:13	rhickey	the big-ticket items I'm interested in: datalog, AOT compilation, JavaScript generation, abstraction of queues/JMS
16:15	ozzilee	I hacked this together over my lunch break: http://pastie.org/271445
16:16	ozzilee	I think something like that would be helpful, where it would print out the actual forms that caused the error.
16:16	rhickey	I just don't see what's unclear about: Unable to resolve symbol: foo in this context
16:17	ozzilee	rhickey: Well, with just a single line on the Repl it's obvious, but more complicated stuff is... more complicated.
16:17	rhickey	but one thing is true, evaling right at the repl takes away line numbers, which would be present if code was loaded instead
16:17	ozzilee	rhickey: Yeah, the line numbers are nice for loaded code.
16:20	ozzilee	And honestly, the 20-odd lines of stack traces are pretty useless in this case, and I think most others as well.
16:20	rhickey	no one's forcing you to read it :)
16:21	rhickey	but it would be easy to have to repl store it away and print only the cause message, with the rest available on request
16:21	rhickey	patch welcome
16:21	ozzilee	Well, yeah, but it does force me to scroll up on the Repl to see what I was doing. Not a deal-breaker, just an annoyance.
16:21	ozzilee	rhickey: Yeah, I like that idea, I might dick around with it tonight.
16:22	Chouser	I wonder how easy/useful it would be to do the -----^ style ascii-art pointer.
16:22	ozzilee	Something like (print-stack-trace) you think? (print-last-stack-trace) ?
16:24	ozzilee	Chouser: I always thought lining up the sexps would be pretty, myself :-) http://pastie.org/271445
16:25	Chouser	heh. You'd have to teach me how to read that output.
16:26	ozzilee	Perhaps (.throw last-exception)... ho hum.
16:28	ozzilee	Chouser: Yeah, it'd probably make more sense reversed and cleaned up: http://pastie.org/271445.
16:28	ozzilee	Anyway. Back to work.
16:35	achim_p	i'd like every var defined in the repl to be annotated with its defining form as metadata. would i have to doctor clojure's internals to achieve this or is there an easier way i don't see right now?
16:35	achim_p	e.g.:
16:35	achim_p	(defn foo [x] "test")
16:35	achim_p	(:def ^#user/foo)
16:35	achim_p	=> (defn foo [x] "test")
16:37	Chouser	you could probably write your own def macro
16:48	achim_p	that would be an option ... but it won't work for the stuff in boot.clj, obviously, and i believe it wouldn't work for code that gets loaded into different namespaces either
16:49	rhickey	the file and line number are already in the metadata, you could just find the code
16:56	achim_p	the filenames are class-path-relative, right?
16:57	achim_p	wrong :)
18:39	defunkt	hey guys, clojure looks awesome
18:40	defunkt	i've never done any java - is that going to be a big problem as i try to learn it?
18:43	arbscht	not a big problem
18:43	arbscht	a small one, perhaps :)
18:43	defunkt	heh
18:44	arbscht	defunkt: what is your programming history?
18:45	defunkt	most recently a lot of lisp, objective-c, and ruby
18:46	arbscht	you should not have much difficulty, then
18:46	defunkt	excellent
18:52	fyuryu	defunkt: you'll probably need to learn something about classpath for java interop (but not only)
22:39	gnuvince_	How would I open an URL and download the entire content with Clojure? I don't know any Java.
22:40	arohner	gnuvince_: clojure would rely on the java libraries to do that
22:40	arohner	I don't know enough java to help you, I've only started to learn java because of clojure
22:41	gnuvince_	I found this URL class in java.net, but I can't seem to "finish the job"
22:46	arohner	lisppaste8: help
22:46	lisppaste8	To use the lisppaste bot, visit http://paste.lisp.org/new/clojure and enter your paste.
22:50	lisppaste8	arohner pasted "print-url" at http://paste.lisp.org/display/66740
22:50	arohner	try that
22:51	gnuvince_	arohner: very kind of you
22:51	arohner	btw, I stole the java example of this from http://www.devdaily.com/java/edu/pj/pj010011/pj010011.shtml
22:52	arohner	feel free to ask any questions about how it works or why I did it that way
22:53	gnuvince_	Only one question
22:53	gnuvince_	If I wanted to accumulate this into a string, how'd I do that?
22:56	lisppaste8	arohner pasted "str-url" at http://paste.lisp.org/display/66741
22:56	arohner	I'm not entirely sure about the performance of this, but it works
22:58	gnuvince_	arohner: doesn't matter, I'm currently more interested in exploring Clojure
22:59	arohner	do you understand how the code works?
23:00	gnuvince_	Yes
23:00	gnuvince_	I'm pretty familiar with Lisp and functional programming in general, but Java is a complete mystery to me.
23:00	arohner	yeah
23:01	arohner	I learned C & C++, then completely skipped java and learned python, ruby, lisp
23:01	arohner	now I find myself pushed to learn java because clojure is so nice
23:01	gnuvince_	I went the other way, Ruby, Python, Lisp, OCaml and then went to C.
23:03	albino	Ocaml even
23:03	gnuvince_	Right now, Clojure is at #2 on my list of interesting languages
23:04	arohner	what is #1?
23:04	albino	gnuvince_: do you have a bunch of sample programs you right code in to learn languages?
23:04	albino	s/right/write
23:04	albino	man it's been a long week
23:05	gnuvince_	arohner: Haskell. Crazy, crazy language :)
23:05	gnuvince_	albino: usually I start with the usual little stuff like fib and fact and stuff, I like to write a Cribbage point counter
23:06	gnuvince_	For clojure, I was thinking of porting my Python script to scrape a bunch of comic sites and generate an XML file
23:06	gnuvince_	I figured I'd see if I can make it concurrent
23:06	albino	first google hit even http://gnuvince.wordpress.com/2008/02/06/cribbage-point-counter-in-haskell/
23:06	gnuvince_	Though I'm probably gonna have to take a break from it, read a little more on clojure, and then come back to the problem
23:07	gnuvince_	albino: that's me.
23:07	albino	gnuvince_: I figured based on the subdomain
23:08	gnuvince_	Mind you, I got better code. Somebody showed me the Enum type class in Haskell which makes a couple functions pointless
23:09	arohner	man, I should learn haskell
23:10	arohner	I find it irritating that I can figure my way through most languages, but haskell is very hard to intuit
23:10	gnuvince_	arohner: it's a lot of fun and it completely obliterates the brain :)
23:10	gnuvince_	Oh yeah, me too
23:10	gnuvince_	I picked up quite a few languages since I started programming
23:10	gnuvince_	but I needed to try Haskell 4 times before it finally clicked
23:10	gnuvince_	It's one weird puppy
23:15	Chouser	FWIW, I like projecteuler.net for trying out a new language
23:20	albino	gnuvince_: ahh, python
23:20	gnuvince_	albino: yah, my main language
23:21	albino	gnuvince_: mine also