#clojure – 2008-05-13

2008-05-13

07:36	rhickey	esquesque: just saw you comment re: :tag on maps, you can apply :tag to maps, it's just not used by the compiler for any purpose:
07:37	rhickey	user=> (def m #^:Tag {:a 1 :b 2})
07:37	rhickey	#'user/m
07:37	rhickey	user=> (meta m)
07:37	rhickey	{:tag :Tag}
10:23	Chouser	ozzilee: clojure's reduce takes an optional "starting" value that may do what you want (for fold)
10:24	ozzilee	Chouser: I did not see that. Thank you.
10:24	ozzilee	That is indeed what I was looking for.
10:53	asbjxrn	I have some trouble creating a Ellipse2D.float object.
10:56	asbjxrn	I've (import '(java.awt.geom Ellipse2D))
10:56	esquesque_	is it a subclass?
10:56	asbjxrn	It's an inner class of Ellipse2D.
10:56	esquesque_	ech that is what i meant =P
10:56	esquesque_	maybe you would try:
10:57	esquesque_	(import '(java.awt.geom.Ellipse2D float))
10:58	asbjxrn	ClassNotFoundException.
10:58	esquesque_	hmmm, what does your (new ...) look like?
10:59	asbjxrn	I've tried (new Ellipse2D.Float).
10:59	asbjxrn	Doesn't work, though.
10:59	rhickey	java.awt.geom.Ellipse2D$Float
11:00	asbjxrn	Oh.
11:00	rhickey	That's the real Java name for a nested class
11:00	esquesque_	d'oh
11:01	asbjxrn	Seems to do the trick.
11:01	asbjxrn	thanks.
11:03	asbjxrn	Do you know the reason it's this way? (And the java doc only mentions Ellipse2D.Float as a constructor.)
11:03	esquesque_	they compile that way
11:04	rhickey	it's a jvm thing, nested classes aren't really nested, so there is some name munging that occurs
11:04	asbjxrn	Ah, so that is the name in the bytecode,
11:04	rhickey	and the class files
11:04	asbjxrn	Right. I must admit I don't know the difference :)
11:05	asbjxrn	Java -> parser -> class file -> compiler -> jar/bytecode ?
11:06	asbjxrn	Nah. The code goes through the compiler to transform into a class file, doesn't it?
11:06	rhickey	the class files contain bytecode, my point was that naming is used for the class files themselves, as well as for references within the bytecode
11:06	asbjxrn	Ah, I see.
11:06	rhickey	e.g. Ellipse2D$Float.class
11:07	esquesque_	i've done alot of work with bytecode
11:07	esquesque_	it's an irritating format
11:07	rhickey	did you use ASM?
11:07	esquesque_	asm and bcel
11:08	esquesque_	i don't like asm's visitor pattern too much
11:09	rhickey	I find ASM pretty easy, but ignore the visitor pattern (only doing code gen)
11:09	esquesque_	i made my own bc lib in java that never really got finished
11:09	esquesque_	so i know the format very well
11:09	esquesque_	the attribute model wasn't very well thought out
11:10	rhickey	it has its quirks, but you have to give them props for stability
11:10	asbjxrn	An agent can be a ref, but is that a good Idea?
11:13	asbjxrn	Since the agent is supposed to "guard" a place/state, but the ref is really a pointer to state?
11:13	rhickey	asbjxrn: you mean the state of an agent be a ref? I'd wonder why
11:13	rhickey	an agent's state can change - do you want to change it to a different ref at some point?
11:14	esquesque_	rhickey: when using proxy, is "super" bound?
11:14	rhickey	esquesque: no, there is no access to super from a proxy
11:14	asbjxrn	I've got a JPanel, and want to have some environment for it. Among other things, a list of functions that draws into the panel and a framerate.
11:15	rhickey	seems like a straight ref would work
11:15	esquesque_	is there any other function that gives me access to super?
11:16	asbjxrn	I was trying to put the JPanel in a closure, so when I trigger repaint, it can pass the environment to the render function. But for the framerate, the agent would need to know how long to sleep before retriggering.
11:16	rhickey	esquesque: the new gen-class stuff has more power to access the superclass
11:16	asbjxrn	And I want the functions in the functionlist to be able to change the framerate.
11:18	esquesque_	gen-class?
11:18	dudleyf	rhickey: gen-class? Is that something for creating Java classes from Lisp?
11:18	rhickey	asbjxrn: a ref will allow for coordinated access from multiple threads. That's orthogonal to how you might use scope to make it visible
11:19	rhickey	dudleyf: yes, relatively new in SVN. load genclass.clj and (doc gen-class)
11:19	asbjxrn	Yes, I don't think I need to access from more than one thread.
11:20	rhickey	asbjxrn: then you can use vars
11:20	asbjxrn	I'm struggling with this immutability-concept, and using a ref and rebinding it is the way I managed to keep state.
11:20	rhickey	asbjxrn: refs are fine
11:21	asbjxrn	alter works on refs, for var I would use set! ? (I haven't looked at vars yet...)
11:22	rhickey	yes, you'd set! a var
11:23	rhickey	asbjxrn: I don't advocate changing if you've got refs working
11:23	asbjxrn	It's not much code yet, and I'm just writing this code to learn... Don't worry.
11:24	asbjxrn	It's not a real project.
14:52	Chouser	hm, it's a pity I have to say (filter #(.isDirectory %) files) instead of just (filter .isDirectory files)
14:55	rhickey	yeah
14:57	Chouser	heh. does it bug you when people say things like that, implying that you ought to spend a few hours adding a feature so that I can save 5 keystrokes?
14:57	rhickey	:)
14:57	rhickey	first-class-izing is something I've thought a bit about
14:58	rhickey	as you might imagine
14:59	rhickey	there is memfn, which has the drawback of requiring args be explicit
15:00	rhickey	and now, not shorter than #()
15:00	Chouser	ah, hadn't seen memfn
15:01	rhickey	predates #()
15:01	Chouser	ok
15:16	rhickey	(defn jcall [obj name & args]
15:16	rhickey	(clojure.lang.Reflector.invokeInstanceMethod
15:16	rhickey	obj
15:16	rhickey	(str name)
15:16	rhickey	(if args (to-array args) (clojure.lang.RT.EMPTY_ARRAY))))
15:16	rhickey	(defn jfn [name]
15:16	rhickey	#(apply jcall %1 name %&))
15:16	rhickey	((jfn 'substring) "fred" 2 3)
15:16	rhickey	((jfn 'toupperCase) "fred")
15:17	rhickey	just a reader macro away from #.isDirectory => (jfn 'isDirectory)
15:34	Chouser	so would there be any reason to not have .foo always decome (jfn 'foo) ?
15:36	Chouser	s/decome/become/
15:37	rhickey	Right now .foo is a symbol. It gets macroexpanded in the operator position, but not otherwise. There are no symbol macros at this time
15:41	ozzilee	I have to say, coming from scheme, Clojure sure seems to have a lot of magic in it.
15:42	ozzilee	Of course, scheme doesn't interact with Java, either :-)
15:42	rhickey	exactly, most of the magic is there, and most of it is also based on standard reader/macro techniques
15:43	rhickey	at least standard CL techniques
15:43	rhickey	:)
15:43	rhickey	i.e. its not syntax, still data structures
15:44	rhickey	Clojure tends to be less verbose than the equivalent Scheme/CL
15:47	ozzilee	I think my clojure is outdated. Should (.count []) return zero?
15:48	ozzilee	(. [] (count)) works.
15:48	rhickey	(count [])
15:48	rhickey	?
15:49	ozzilee	Well, yeah, that. I mean calling java functions with the .foo syntax.
15:49	rhickey	ah, then yes, 0
15:50	ozzilee	Ok, mine freaks out. Must be old.
15:50	rhickey	yeah, (.member obj ...) is relatively new
15:51	ozzilee	It freaked me out the first time I saw it. I'm still not sure what I think of it. Looks funny to me.
15:51	ozzilee	The ... is the arglist?
15:52	rhickey	some consider it more Lispy, yes, args follow object
15:52	rhickey	(obj.member ...) also works
15:52	ozzilee	Oh, now that's way better, if you ask me.
15:52	ozzilee	So ([].count) would work?
15:54	rhickey	no, it's not syntax - obj.member is a single symbol that gets macroexpanded, [].count is a vector followed by the symbol .count
15:54	rhickey	Still sexprs
15:54	rhickey	just symbols containing '.' are macros, effectively
15:55	ozzilee	Ah.
15:55	ozzilee	Is there a nightly build, or should I checkout trunk and compile?
15:56	rhickey	just checkout trunk
15:56	rhickey	ant
15:56	rhickey	or maven
15:57	ozzilee	Ok. I'll play with that tonight maybe. I'm going to look at possibly writing a wrapper for prefuse.
16:13	Chouser	rhickey: I guess I was just thinking a reader macro for .foo instead of #.foo
16:13	Chouser	not all reader macros start with #, right?
16:14	rhickey	right, the thing would be, reader macros happen on read, so (.foo x) would read as ((jfn 'foo) x)
16:15	Chouser	right.
16:15	rhickey	while functionally equivalent, jfn is a lot slower - always reflective
16:16	rhickey	I wouldn't want that for (.foo x)
16:16	Chouser	ah, ok. That was the kind of reason I was looking for. ;-)
16:18	rhickey	so something would have to be 'special', either reinterpreting (jfn ...) when it appears in the operator position or .foo in a value context. I'd prefer the latter, but there is nothing else special like that, yet
16:18	ozzilee	Isn't .foo special like that, since it only gets interpreted when it's in the operator position?
16:18	rhickey	special things mean greater complexity
16:19	rhickey	.foo is a macro, people can see its effects using macroexpand
16:19	rhickey	user=> (macroexpand '(.foo x))
16:19	rhickey	(. x foo)
16:21	Chouser	I think as it stands is entirely reasonable. It's not like #(.foo %) is hard to say, and if I want to give a type hint I know just how to do it.
21:05	abrooks	rhickey: I'm creating a "Finding Clojure" group on Facebook, is it okay to use the Clojure Google Group logo for that? Who has rights on the logo? How is it licensed?
21:08	rhickey	I own the logo. You can use it to represent the Clojure language that I wrote.
21:08	rhickey	there's no fancy license
21:08	abrooks	rhickey: Thanks. :) Is there a larger source image that I should start from?
21:09	rhickey	how big will it end up?
21:09	abrooks	rhickey: Well, technically copyright exists whether we acknowledge it or not. :)
21:09	rhickey	I understand
21:09	abrooks	rhickey: 200x200 perhaps. It might be okay smaller but 200x200 would be better, I think.
21:11	rhickey	http://clojure.googlegroups.com/web/Clojure_300x300.png
21:12	abrooks	Ah, perfect. Thanks.
21:13	rhickey	is there a url for the FaceBook group?
21:16	abrooks	There is now: http://www.facebook.com/group.php?gid=13489774164
21:17	abrooks	I don't think it's visible outside of a Facebook login.
21:22	abrooks	drewr has apparently joined the group already. ;-)
21:27	abrooks	rhickey: I saw that you joined and added you as an admin.
21:28	rhickey	ok
21:36	drewr	abrooks: :-)
21:56	esquesque_	hi rhickey, how would i do load-file and keep all the bindings?
21:56	esquesque_	i do (load-file "genclass.clj") and gen-class is still unbound
21:57	rhickey	heading home now, maybe someone else can help, please?
21:57	esquesque_	i'm not picky :)
22:10	esquesque_	nevermind, i've got it sorted out
22:11	esquesque_	(in-ns 'clojure) gen-class