#clojure – 2008-02-13

2008-02-13

04:21	jgracin	guys, I have a Java class whose ctor is: public Conf(String... args). How can I call this from Clojure? The problem is the argument, which is an array of Strings.
15:41	jgracin	hi! I'm trying (meta vector), (meta clojure/vector), (meta 'clojure/test), (meta test) and other stuff in the HEAD and I'm getting nil's. How do I get the metadata?
15:42	rhickey	(meta (var vector)) or ^#'vector
15:43	jgracin	Oh, of course. Vars have meta-data. Thanks!
15:44	rhickey	sure
16:06	rhickey	Chouser: Thanks for the nice article on your blog
16:07	rhickey	http://n01senet.blogspot.com/2008/02/clojure-is-best-lisp-yet.html for those who haven't seen it
16:08	Chouser	rhickey: heh. sure! how'd you find that?
16:08	Chouser	oh, I bet a standing Google search for "clojure".
16:08	rhickey	yup
16:11	Chouser	well, you're quite welcome, though I'm not sure it's worth much. I'm not exactly an opinion leader. :-)
16:11	Chouser	I should be, but I'm not.
16:14	jgracin	Chouser: would you mind if I "reddit"-ed your blog? :-)
16:14	jgracin	I think Clojure needs advertising now.
16:15	Chouser	jgracin: I can't think of why I'd mind, so go right ahead.
16:16	Chouser	any obvious factual errors I should fix first? rhickey?
16:17	rhickey	no, I thought it was ok
16:21	jgracin	done.
16:22	rhickey	new release today, so good timing. Lots of updated docs on the site
16:25	Chouser	The "lisp worth talking about" from reddit a couple months ago is a better article. oh well.
16:27	jgracin	rhickey: yeah. I am amazed how things in and around Clojure keep fitting perfectly.
16:27	jgracin	you've struck gold. :-)
16:28	rhickey	:)
16:31	Chouser	I seem to pretty often want (filter (fn [x] x) (map A B)) for various A and B. Is there a better way to do that?
16:32	rhickey	identity == (fn [x] x)
17:45	Chouser	any handy way to go from '((1 2) (3 4) (5 6)) to '((1 3 5) (2 4 6)) ?
17:45	Chouser	some languages call this "zip"
17:52	Chouser	(defn zip [& args] (if (first args) (cons (map first args) (apply zip (map rest args))) nil))
17:58	Chouser	That's not what I wanted. This is closer: (defn zip [seq] (if (first seq) (cons (map first seq) (zip (map rest seq))) nil))
18:05	rhickey	neat. I think going that direction it's unzip
18:06	rhickey	hmmm, maybe they're the same once they are variadic...
18:07	Chouser	I have a tail-recursive version, but it has to call reverse at the end. Is that any better?
18:08	rhickey	I don't think there's anything wrong with the map version
18:10	Chouser	oh, this one still uses map, but it uses recur instead of creating a stack as deep as (count (first seq))
18:13	rhickey	(def zip (partial apply map list))
18:13	Chouser	http://n01se.net/paste/ijK
18:13	Chouser	whoa, what?
18:13	rhickey	try it
18:14	Chouser	I don't have partial. Is my clojure too old?
18:14	rhickey	yes, was appl then
18:15	Chouser	again, "whoa".
18:15	Chouser	Ok, I need to get food, but I'll have to look at that def.
18:24	rhickey	it's lazy: (take 5 (zip (list (iterate inc 1) (iterate inc 2) (iterate inc 3))))
18:24	rhickey	((1 2 3) (2 3 4) (3 4 5) (4 5 6) (5 6 7))
19:01	Chouser	I'm still not fully there. I don't yet understand what apply is doing with the 3rd arg.
19:17	rhickey	you mean mapping the list function?
19:18	rhickey	user=> (map list [1 2 3] [4 5 6] [7 8 9])
19:18	rhickey	((1 4 7) (2 5 8) (3 6 9))
19:19	rhickey	which is almost what you want, but your lists are in a sequence
19:19	rhickey	user=> (apply map list [[1 2 3] [4 5 6] [7 8 9]])
19:19	rhickey	((1 4 7) (2 5 8) (3 6 9))
19:47	Chouser	oh, it's the multiple sequences to map that's doing it.
19:54	Chouser	the multiple args to apply was throwing me as well, though.
19:56	Chouser	I didn't realize (apply + 1 2 '(3 4)) was like (apply + (list* 1 2 '(3 4)))
20:00	rhickey	right
20:23	Chouser	so between multi-param apply and multi-seq map, one hardly needs zip at all.
20:25	rhickey	right
23:11	Chouser	It's even better than that. I wanted zip so I could do this: (def prod (map (fn [seq] (apply * seq)) (zip fracs)))
23:12	Chouser	But of course I get the same result with: (def prod (apply map * fracs))
23:12	rhickey	fun
23:21	Chouser	any way to get the denominator of a RatioNum?
23:23	rhickey	for now: (. 22/7 denominator)
23:34	Chouser	thanks
23:36	albino	did the proggit article bring some newbies to the channel today?