#clojure – 2008-03-13

2008-03-13

07:14	hoeck	rhickey: thanks for fixing!!!
07:36	rhickey	you're welcome
09:16	MarkJP	what am I doing wrong: (ns-interns 'clojure)
09:17	rhickey	'clojure is a symbol, ns- fns take namespaces: (ns-interns (find-ns 'clojure))
09:18	rhickey	I hope to change most of these to take a ns 'designator', i.e. either the ns itself or its (symbol) name
09:18	rhickey	in my spare time...
09:21	bgeron	(because you could set up a rule on how to make a ns out of a symbol
09:22	rhickey	ew
09:22	bgeron	not nice?
09:22	rhickey	user-defined conversions ruin static typing
09:22	bgeron	depends on how it's implemented
09:22	rhickey	because you can;t control when they are used
09:25	rhickey	not worth it - every feature like that adds more complexity than it reduces
09:26	rhickey	see Scala
09:30	Chouser	bgeron: yeah, Scala has a complete set of features for auto-converting from types to other types.
09:31	rhickey	I meant more generally - see Scala for an example of exponential complexity of interacting features
09:31	bgeron	ah
09:33	la_mer	bgeron: we use Scala for a real product (which stuns people sometimes) -- it's definitely got a 45-piece Craftsman set of tools, but one often finds that the set is missing simple screwdrivers, etc.
09:33	la_mer	when its features map well to your problem, it's very nice, though
09:33	bgeron	but then I also think that CL's &optional shouldn't have been hardcoded
09:33	bgeron	then maybe its features are too hardcoded :)
09:34	bgeron	PG's (opt x) syntax looks nice
09:36	rhickey	(opt x) ?
09:36	la_mer	this is arc, yes?
09:36	bgeron	(fn (a b (opt c)) ..)
09:36	bgeron	no, it was a plan for arc
09:36	bgeron	well, maybe it is real arc
09:36	bgeron	but if it's real arc, it's probably hardcoded :(
09:37	bgeron	down? ;)
09:37	la_mer	I hadn't thought that far.
09:37	Chouser	I think arc has optional args without using an "opt" keyword.
09:38	Chouser	...And I think I prefer clojure's mechanism for different arities on the same function.
09:39	bgeron	what's the difference?
09:40	bgeron	(not meaning to imply "there is no difference")
09:40	Chouser	The difference in how clojure does it?
09:40	bgeron	yes
09:41	Chouser	I think boot.clj's "reduce" function is a good example.
09:41	Chouser	It takes 2 or 3 args: either [f coll] or [f val coll]
09:41	bgeron	blegh, arc does optional args with (o arg [default])
09:41	rhickey	fyi Clojure used to have full CL &optional &keys and &rest
09:42	bgeron	casing on different lengths is nice :)
09:42	rhickey	and each fn was a single entry point, which dealt with that stuff
09:43	la_mer	rhickey: that was dropped to align more closely with java's function call mechanics, yes?
09:43	Chouser	So val is optional, but its in the middle. To do that with a single list of formal args (like CL, JavaScript, arc, etc.) you'd have to use something like [f coll-or-val (optional coll)] and then monkey around in the function body to get the correct coll
09:43	rhickey	now each entry point is distinct - IFn has 20+ overloads
09:44	rhickey	doing it this way is very much faster - esp when & comes into play
09:44	Chouser	I've started peeking at the Clojure Java code. I'm so glad rhickey wrote that kind of painful code so I don't have to. ;-)
09:44	rhickey	compare to other JVM langs which pack args into Object[]
09:44	rhickey	Clojure uses real stack
09:46	rhickey	Chouser's example is good too, real overloading is not the same as optional
09:47	Chouser	I must admit I have to beat down an occasional yearning for type-based overloading.
09:47	rhickey	multimethods
09:48	Chouser	oh!
09:48	Chouser	hm, how did I forget about those.
10:06	Chouser	aww... why's that?
10:06	bgeron	pretty pricey
10:06	Chouser	I bet.
10:07	bgeron	and I'm supposed to become the treasurer of an association this evening :p
10:07	bgeron	(because if there would be no new board, the association would get disbanded)
10:08	bgeron	maybe secretary would have been a better position for me
12:07	nsinghal	(def aa (fn [] :ns))
12:07	nsinghal	(aa) returns :ns
12:07	nsinghal	(def bb #(:ns))
12:07	nsinghal	(bb) throws Arity error
12:09	rhickey	#(...) => (fn [args] (...)) so #(:ns) => (fn [] (:ns))
12:09	nsinghal	(def cc #(:ns %))
12:10	rhickey	in the latest version error would be:
12:10	rhickey	java.lang.IllegalArgumentException: Wrong number of args passed to keyword: :ns
12:11	nsinghal	thanks that explains it
12:13	Chouser	rhickey: great update to the error message, by the way. Bound to be helpful.
12:14	rhickey	:)
12:26	Chouser	what do you think of: (defn coll? [x] (or (seq? x) (vector? x) (map? x) (set? x)))
12:27	rhickey	(instance? IPersistentCollection x)
12:29	Chouser	hm! Well, I can't be sure, but I suspect that when people are asking for something that says if an object is "seq-able" (and you rightly point out that (seq "foo") works and isn't what they want) ... what they may really want is coll?
12:30	rhickey	sometimes - that fact that it includes maps may not be what they intend - There's also Sequential
12:31	rhickey	but I can add predicates for all the marker interfaces
12:31	rhickey	IPersistentCollection, Sequential, Reversible, Associative etc
12:32	Chouser	you may be right -- it's hard to tell. Most place where I'm doing something like seq? I mainly want to know if I should recurse into it or not. So true for maps and other collections, false for strings, keywords, symbols.
12:32	Chouser	Are those names currently documented anywhere?
12:32	Chouser	Docs may be sufficient, and then you don't have to clutter up the clojure namespace with a bunch of new predicates.
12:33	rhickey	unfortunately I still haven't gotten around to documenting the Java side - which is quite extensive
12:33	Chouser	ok
12:43	MarkJP	what is the equivalent of instanceof in clojure
12:44	Chouser	instance
12:44	MarkJP	thx
12:44	Chouser	(instance? Classname obj)
12:44	Chouser	sorry, I forgot the question mark
12:44	MarkJP	cool
12:46	MarkJP	so lets say I proxy class Foo
12:47	MarkJP	(proxy [Foo] [] (method1 [] ... ) (method2 []...))
12:48	MarkJP	the resultant object doesnt seem to pass the (instance? Foo o) test
12:49	MarkJP	actually sorry, Foo is an interface in this case
12:50	Chouser	Well, you've just surpassed my knowledge. :-/ sorry.
12:52	MarkJP	np, I'll wait for Rich, he seems to know Clojure pretty well
12:54	MarkJP	interesting, it passes the instance? test for another proxy i did
12:54	MarkJP	I'm doing something wrong
13:00	rhickey	proxy should pass instance? for all of its supers
13:01	MarkJP	oh man
13:01	MarkJP	it works now
13:01	rhickey	gremlins
13:02	MarkJP	wow... don't do this:
13:02	MarkJP	(import '(clojure.lang.RT) '(clojure.lang.Var)) in clojure
13:02	MarkJP	:p
13:02	MarkJP	proxy wasnt working
13:03	MarkJP	I was able to make up methods within proxy without complaint
13:04	MarkJP	those imports where not intentional, cut and paste from java code
13:06	Chouser	extensive? really? http://n01se.net/paste/hV0
13:06	Chouser	that's a quick pass. probably a little buggy.
13:06	Chouser	not to mention ugly.
13:06	MarkJP	cool, how did you generate that?
13:07	Chouser	heh. well...
13:08	Chouser	a little perl, a little bash, and graphviz's "dot" command: http://n01se.net/paste/o9V
13:09	MarkJP	cool
13:09	Chouser	I think the word you're looking for is "gross", but I'll take "cool". ;-)
13:11	MarkJP	nah, definitely a neat one liner
13:34	rhickey	Chouser: wow - what a fun graph!
13:35	rhickey	have to put it up on my wall so I can remember my design :)
13:40	rhickey	missing a few things, though
14:18	Chouser	oh, is it? well, I think a hand-created one will look better anyway.
14:18	Chouser	What's missing?
14:19	rhickey	IPersistentVector extends Associative, Sequential, IPersistentStack, Reversible
14:20	rhickey	IPersistentMap extends Iterable, Associative
14:20	rhickey	etc, all like that
14:21	rhickey	the nice thing about a generated one is you don't have to maintain it
14:21	rhickey	just regen
14:22	Chouser	yeah, but it's ugly.
14:22	Chouser	I have long wished for some tool that combines the best of both, but I don't know of any such beast.
14:23	rhickey	as long as you can follow the paths, it has great utility even if not beautiful
14:23	Chouser	Like have a script generate SVG. Then edit the SVG in inkscape. Then have the script read new graph data and the SVG and make minimal changes to update any edges and nodes that have changed
14:24	Chouser	hm. Well, maybe I'll try to refine the autogen process a bit then.
14:24	Chouser	dot can be a little prettier, I think.
14:24	rhickey	I have OmniGraffle - if you can get it into a form it can import, it can make it pretty
14:25	Chouser	I've not seen OmniGraffle. Looks pretty. The front page says it has Graphviz built in... and it import dot scripts?
14:25	Chouser	er, "can it import"...?
14:26	rhickey	got me, looking now
14:26	rhickey	says a subset
14:27	Chouser	hm.
16:05	MarkJP	how do I do (new Foo.SubFoo ...)
16:05	MarkJP	?
16:06	rhickey	nested classes are separated by $ from their parents (a JVM thing): Foo$SubFoo
16:07	MarkJP	thx
16:20	Chouser	any easy way to convert a String to a java byte array?
16:21	rhickey	(. s (getBytes))
16:21	Chouser	oh. :-) right, thanks.
16:47	Chouser	this works: (new javax.swing.ImageIcon "/tmp/tmp.png")
16:47	Chouser	this doesn't: (new javax.swing.ImageIcon (. (slurp "/tmp/tmp.png") (getBytes)))
16:48	Chouser	An ImageIcon object is created, but it doesn't display anything.
17:00	Chouser	(int (first (slurp "/tmp/tmp.png"))) ==> 65533 ...but how could the first byte be larger than 255?
17:05	hoeck	unicode?
17:06	hoeck	(slurp ) returns a string
17:08	Chouser	yeah. I thought of that, but that doesn't seem to be it.
17:08	Chouser	oh!
17:09	Chouser	well, it's not 2-byte unicode. Maybe it thinks it's utf-8 or something.
17:12	Chouser	UTF8 it is.
17:14	Chouser	drat. forcing US-ASCII isn't helping.
17:15	Chouser	Oh, that's 7-bit. ISO-8859-1 does it.
17:23	hoeck	maybe it needs the magic number from the beginning of the image be stripped off?
17:24	hoeck	or the actual image-data begins at an certain offset in the image file
17:27	Chouser	no, you were right. It was just unicode.
17:27	hoeck	oh, ok
17:28	Chouser	If I create the InputStreamReader with ISO-8859-1, and write the bytes into ByteArrayOutputStream, I can do toByteArray and the icon works fine.
17:31	hoeck	mhh, i'm wondering wether one could directly read data from /dev/video using this method
17:49	hoeck	bye
19:59	Chouser	generate dot script from Clojure Java source: http://n01se.net/paste/yW2
20:02	Chouser	resulting dot script: http://n01se.net/paste/WL7S
20:07	Chouser	resulting png (updated): http://n01se.net/paste/yVa