#clojure – 2008-07-06

2008-07-06

00:22	Nafai	Yay, just wrote my first real working Clojure code
00:25	Nafai	http://paste.lisp.org/display/63330
00:26	Nafai	Any critiques would be welcome :)
00:48	Nafai	wa
00:48	Nafai	Whoops
01:11	slava	hey nafai
01:13	Nafai	Hi
01:14	slava	i heard you moved away from austin
01:14	Nafai	Yeah, moved back to Utah.
01:15	Nafai	Got a pretty good job and I have more friends here
01:55	arbscht	Nafai: fwiw: http://paste.lisp.org/display/63330#1
01:55	arbscht	Nafai: I make no assurance that it is in any way better, but maybe it gives you some ideas :)
01:58	Nafai	Thanks arbscht
02:01	Nafai	How do I assign a variable at the REPL?
02:01	Nafai	let won't work because the scope is over once you close the )
02:02	jgrant	(def varname value)
02:03	arbscht	the value is optional, too
02:07	Nafai	How do I find out what type objects in a seq are? I'm trying to print the sequence and I keep getting class-cast exceptions
02:12	Nafai	Ah, it's happening earlier
02:19	slava	Nafai: look who's here
02:19	Nafai	Hi erg
02:20	erg	hi Nafai
02:20	erg	how's the codez?
02:21	Nafai	Not bad
02:21	Nafai	Thought I'd pick a little Clojure to see if I like it
02:33	Nafai	Any ideas on how I would do this?
02:33	Nafai	I want to have a data file that has a vector per line
02:33	Nafai	Like: [1 2 3]
02:33	Nafai	I want to be able to use the reader and process each vector
02:34	Nafai	Maybe it's just I can't figure out the proper thing to do with loop and recur but I can't figure it out
02:51	arbscht	Nafai: if you wrap the contents of your file in [] you will get a vector of vectors when you (load-file)
02:53	Nafai	Oooo
08:48	ballzack3	l
08:49	ballzack3	hello
08:56	StartsWithK	how can i create instance of nested class?
08:56	blackdog	class$nested
08:58	StartsWithK	Unable to resolve classname: Ellipse2D$Float
08:58	StartsWithK	i have (import '(java.awt.geom Ellipse2D))
09:01	blackdog	try Ellipse2D$Float
09:01	blackdog	try import Ellipse2D$Float
09:05	StartsWithK	blackdog, that worked, thanks
09:06	blackdog	cool,
09:24	kotarak	Is it possible to have a lazy map like lazy-cons? ie. the value is only evaluated when I access the key.
11:23	Chouser	kotarak: I was just discussing that with abrooks.
11:24	Chouser	kotarak: I think you could use proxy to implement an IPersistenHash that has that behavior, but as far as I know there's no way as easy as lazy-cons
11:25	Chouser	...and unless you're going to assoc onto it, y really might just be talking about a memoized function.
11:28	kotarak	the use would be in the return type of a function, where certain things must be done lazily. One could of course return a lazy list, but the gets ugly when the return value changes
11:40	Chouser	you could return a memoized function, right? That would cover your use case?
11:42	kotarak	I would like to just get the value, w/o having to call a function.
11:43	kotarak	ie. the funcll would be transparw
11:43	kotarak	oops
11:43	kotarak	the funcall would be transparent to the program
11:45	ktne	hello
11:45	ktne	is clojure the best lisp for jvm?
11:48	kotarak	there is also a scheme, but don't remember the name.
11:49	ktne	is that a standard scheme?
11:50	kotarak	I think so, R5RS IIRC.
11:50	ktne	i see
11:50	ktne	i was thinking about something more experimental
11:50	ktne	not just a standard implementation
12:12	mac_	ktne: experimental in what way? clojure is made to easily support concurrent and functional programming
12:12	ktne	i mean, not just standard scheme implementation
12:14	mac_	It's definetly not a standard scheme. I'm pretty new to lisp and clojure myself so I can't tell you what the differences are exactly but it should be on the web page I think
12:15	mac_	there we go: http://clojure.org/lisps
12:15	ktne	thanks
12:18	Chouser	kotarak: if it were a hash, you'd still need to call something to get a value (get foo :key) or (foo :key) or (:key foo), right?
12:19	Chouser	if it's a memoized function called foo, you could call it with (foo :key) -- same syntax
12:19	kotarak	hmm... ok. That makes sense.
12:51	Chouser	hm, and there's a nice memoize already in clojure-contrib.
12:55	meredydd	Hey all.
12:55	Chouser	hi, meredydd.
12:55	meredydd	Is there an idiomatic way of modifying the value stored to a particular key in a map?
12:56	Chouser	can't modify anything. ;-)
12:56	meredydd	Chouser: Well, that's the problem. Because an in-place modify is fetch->modify
12:56	meredydd	whereas with immutability you have to do fetch->modify->writeback
12:56	meredydd	and 'fetch' and 'writeback' have quite a lot of redundancy.
12:56	Chouser	user=> (def m {:a 1 :b 2})
12:56	Chouser	#'user/m
12:56	Chouser	user=> (assoc m :a 9)
12:56	Chouser	{:b 2, :a 9}
12:57	Chouser	oh.
12:57	meredydd	I'm doing a lot of:
12:57	meredydd	(alter map-ref assoc key (do-something-complicated-to (@map-ref key))
12:58	meredydd	Was just going to knock up a macro to do the round-tripping for me (based on the "alter" idea - give it a map, a key, and a fn to apply to the value, and it'll give you the new map)
12:58	meredydd	but it strikes me as the kind of thing there might be something in the API fo
12:58	meredydd	r
13:00	kotarak	Maybe clojure wants you to do it differently? A lot of hassle is often a sign, that you work against the system.
13:00	meredydd	Indeed. Which is why I'm running it past here before doing that.
13:01	meredydd	On the other hand, I can't really think of another way around it - I need to store a set of Xs for each Y
13:02	kotarak	Maybe you should pass it on to a function instead of storing it somewhere?
13:02	meredydd	so unless you can think of a better option than an immutable map of Ys to immutable sets of Xs, you're going to have to do something
13:02	meredydd	kotarak: I'm familiar with the basics of functional programming. This is one of this program's three pieces of state.
13:06	meredydd	(In fact, one piece of state. But it needs to be looked up from several directions, so it ends up being in several maps.)
13:10	Chouser	meredydd: I think you're doing it right, although you if you think you can get away with commute instead of alter, that would be better.
13:11	Chouser	the pattern you described shows up a couple times in ants.clj
13:11	meredydd	Chouser: Commute would be good - unfortunately, there's some conditional logic in there and I think I'd be whacking a hornet's nest if I let multiple invocations on the same value of Y intersect.
13:11	meredydd	(defn alter-map-val
13:11	meredydd	[map-val key alter-fn & args]
13:11	meredydd	(assoc map-val key (apply alter-fn (get map-val key) args)))
13:12	Chouser	meredydd: yeah, ok, as long as you're thinking about it. I've not done enough different things with refs of hashes to think easily about when I would need alter vs. commute.
13:12	meredydd	Seems nice to me.
13:13	meredydd	Okay, that just made the whole statement fit on one line. That's promising.
13:14	Chouser	meredydd: can you paste an example usage?
13:14	Chouser	you'll use ref-set now instead of alter?
13:14	meredydd	{:test #(assert= (alter-value {:a 4 :b 5} :b #(+ %1 %2) 1) {:a 4 :b 6})}
13:15	meredydd	Usage goes:
13:15	meredydd	(alter user-roles-by-component (alter-map-val victim #(disj % [user, role])))
13:15	meredydd	(where the #(disj...) stuff is the application-specific stuff - removing something from taht set)
13:16	meredydd	aaand I have to go.
13:16	meredydd	bbl, might discuss this further if you're around, Ch
13:16	meredydd	*chouser
13:17	Chouser	Hm! I think it looks good!
14:53	Chouser	meredydd: I know you're not here, but that's not quite right
14:55	meredydd	?
14:56	meredydd	Chouser?
14:56	Chouser	oh, hi.
14:56	Chouser	alter's second arg is a fn, so either alter-map-val needs to return a fn, or something else needs to be different
15:08	Chouser	(defn alter-map-val [m key alter-fn & args] (alter m assoc key (alter-fn (@m key))))
15:08	Chouser	(dosync (alter-map-val victim :a #(disj % [user, role])))
15:11	Chouser	You could have a commute-map-val too, I suppose
15:58	Lau_of_DK	public class MyClass implements JButton {} -- How is this done in Clojure?
15:59	Chouser	gen-class or proxy
16:00	Lau_of_DK	got a brief example?
16:01	Chouser	(proxy [JButton] []) will create a new instance of a class derived from JButton.
16:02	Chouser	xml.clj includes an example of proxy
16:04	Lau_of_DK	Thanks, exactly what I needed to know
16:05	Lau_of_DK	Chouser - Maybe you should look through the documentation on Clojure.com? I find it somewhat lacking in a few various areas
16:06	Chouser	proxy is documented on the java-interop page
16:11	Chouser	scgilardi: I noticed your memoize in clojure-contrib today. Thanks for that!
16:12	scgilardi	you're welcome! I noticed the discussion earlier about alter. does memoize show how to do something similar more simply?
16:14	Chouser	I don't think so. There was a conversation about a lazy-cons for hashes, and I was saying that for some use cases, memoize might be sufficient (since we don't currently have a lazy-cons for hashes).
16:15	scgilardi	ok, I haven't worked through it all yet, but it seems like "assoc" when used in a "commute" fills the role of "alter-map-val". I've been pleased with how "conj" and "assoc" have been all I've needed when commuting.
16:16	Chouser	yeah, the alter stuff was an different topic.
16:16	scgilardi	"commute" -> "alter"
16:16	scgilardi	ok cool
16:17	Chouser	I don't think alter-map-val is necessary, but without it you often end up repeating the name of the map ref and the key -- once for the lookup and once for the assoc or conj.
16:17	Chouser	alter-map-val or something like it just reduces the repetition.
16:18	scgilardi	alter returns the new value. is it to try to capture the previous value?
16:18	scgilardi	(actually I haven't yet used alter... I'm familiar with commute)
16:19	Chouser	both alter and commut pass in the old value, but if your ref is of a hash you still need to look up the key you want to change.
16:20	Chouser	...and the thing you need to return from your alter or commute func is the whole hash, not just the new val. that's where alter-map-val would help.
16:22	scgilardi	interesting ok. I'll work through an example to understand it.
16:24	Chouser	(def m (ref {:a 1}))
16:25	Chouser	(dosync (commute m assoc :a (inc (m :a))))
16:25	Chouser	m and :a are each mentioned twice
16:26	Chouser	(dosync (alter-map-val m :a inc))
16:26	Chouser	with the alter-map-val I gave above, m and a are only mentioned once each.
16:27	scgilardi	ok I see now, thanks
16:28	Chouser	but as you said, commute would be good too, so maybe it would be useful to also have commute-map-val
16:28	scgilardi	or to make alter or commute an argument rather than part of the function name
16:28	Chouser	sure
17:37	meredydd	Yo, Chouser
17:37	meredydd	You said you had a bug in my map-alter fn
17:53	Chouser	yep -- did you actually try your version?
17:55	Chouser	meredydd: http://clojure-log.n01se.net/date/2008-07-06.html#14:56b
17:56	meredydd	Chouser: Not yet, tes
17:56	meredydd	*not yet
17:58	meredydd	Chouser: Hmm. Comp crashed, and I've lost that file. Hold on...
17:58	meredydd	Oh, yes, you're right.
17:58	meredydd	(alter user-roles-by-component (alter-map-val victim #(disj % [user, role]))) is wrong
17:59	meredydd	(alter user-roles-by-component alter-map-val victim #(disj % [user, role]))
17:59	meredydd	That's right.
18:06	Chouser	oh!
18:06	Chouser	very well then.. that way you can use commute without needed a commut-map-val
18:09	meredydd	Chouser: ha!
18:09	meredydd	I just read that log, and was about to make the same point.
18:09	meredydd	"alter" was the wrong name to give this fn.
18:09	meredydd	It should be "replace-map-val"
18:09	meredydd	(or, in fact, "replace-assoc-val", but that's really quite long)
18:10	meredydd	I named it after "alter" because I was thinking about how you can do this:
18:10	meredydd	(alter x + 1)
18:10	meredydd	or (alter x assoc :key :value)
18:11	meredydd	You can now thread this some distance:
18:11	meredydd	(alter user-roles-by-component alter-map-val victim disj [user, role])
18:12	Chouser	yikes
18:12	meredydd	(kinda a reverse "->")
18:13	meredydd	(which, again, is one of those things that first made me go "yikes", then after an hour of using it, made me appreciate rhickey even more than before)
18:14	Chouser	:-)
18:19	Chouser	well, it's very hard for me to think through how that works, but it's hard to argue with the brevity.
18:19	Chouser	I suppose it wouldn't take long to get used to the pattern.
21:46	arohner	has anyone here played with compojure?