#clojure – 2008-05-26

2008-05-26

01:15	abrooks	Hrm. xml/emit-element does not properly escape XML entities.
01:53	abrooks	Has anyone use xml-stream-reader.clj?
01:53	abrooks	I'm properly steeped in Java to grok the context, I think.
01:53	abrooks	I'm looking for examples if anyone has them.
11:25	rapido	how hard would it be to allow meta-data for all types, not only for collections or symbols?
11:31	rhickey	impossible, as many types, like String are final
11:31	rhickey	and I don't want to require wrappers
11:32	rapido	can't you just keep a separate global map that maps any object to its meta data?
11:32	rapido	(i know global is evil)
11:32	rhickey	there is that
11:33	rhickey	plus, the original concept of metadata coincides with data as values - with-meta produces a new object
11:33	rhickey	any global cache would be identity-basec
11:33	rhickey	based
11:33	rhickey	metadata on Vars is an anomaly
11:34	rapido	still, i feel the concept can be pushed a lot further
11:35	rhickey	well, java.util.concurrent is there
11:36	rapido	does java.util.concurrent have something similar to meta-data?
11:37	rhickey	no, just the tools to build the global map you want
11:39	rhickey	actually, maybe not, as no concurrent identity map
11:41	rapido	i have been looking at PersistentHashMap which is nice, performance wise
11:41	rhickey	thanks
11:41	rapido	but i feel PersistentVector could be implemented similarly fast.
11:41	rapido	do you know about ropes?
11:42	rhickey	how is persistent vector not similarly fast?
11:42	rhickey	same data structure
11:42	rapido	is it possible to concatenate two vectors?
11:43	rapido	in O(log(n))?
11:44	rhickey	no, nothing that virtualizes concat for vector
11:45	rapido	i think you should do an implementation that's optimized for vectors
11:45	rhickey	of concat?
11:46	rapido	concat, head, tail, subvector etc. all the important operations
11:47	rhickey	I don't think vector concat is important
11:48	rhickey	head/tail/conj/subvector are all smoking, as is initialization with an existing array
11:48	rapido	let's say you have a sequence of chars
11:48	Chouser	rapido: wouldn't it be pretty easy to write an object that holds two (or more) vectors, and translates the operations you need to the underlying vectors?
11:49	rapido	fast concatenation of string would be nice not?
11:49	rapido	string<-strings
11:49	rhickey	There is fast concat, it just doesn't yield a vector
11:49	rapido	is it lazy?
11:49	rhickey	lazy-cat is
11:50	rapido	where can i find fast concat and what algorithm is used?
11:50	rhickey	um, the source for concat?
11:51	rhickey	boot.clj
11:51	rhickey	gotta run
11:53	rapido	but if you repeatedly concat n times you end up with a linear structure that resembles a linked list
11:54	rapido	but if the (lazy) structure would be balanced with using a tree balance algorithm you would still have good performance for all operations
11:54	rapido	chouser: does that answer your question?
11:55	rapido	chouser: that's how the ropes data structure works, see http://ahmadsoft.org/ropes/
11:56	rapido	replace strings(=sequence of chars) with any sequence of objects
11:58	Chouser	Yeah, I see your point.
11:58	Chouser	The Clojure data structures (vector, etc.) are written in Java. There's no reason you can't write your own if you have an application that needs a certain performance profile.
12:01	rapido	sure. it's the old 'library' versus 'build-in' debate :)
12:02	rapido	nevertheless, there are many more interesting immutable data structures
12:02	Chouser	yup.
12:03	Chouser	It'll be interesting to see how that debate plays out over time.
12:03	rapido	avl trees, alpha-beta trees, etc. etc.
12:03	Chouser	I think Rich wants to keep the core language pretty small, which seems like a good idea.
12:03	Chouser	We've got clojure-contrib as a semi-official place to offer general-purpose code.
12:04	rapido	i saw (one of) his presentations which are very good.
12:04	Chouser	I always liked how Python gives you such a large library be default. It'll be interesting to see where Clojure ends up.
12:05	rapido	i also very strongly believe that mutability is evil, but for more reasons than concurrency
12:06	rapido	still, keeping mutability out of all the frameworks will be difficult
12:07	Chouser	I'm not deeply familiar with this stuff, but in order to have complete immutability, don't you need monads? I think Clojure has chosen a more practical approach of carefully controlled mutability.
12:08	rapido	i've implementation my own (research) language that pushed immutability to the extreme
12:08	Chouser	ah
12:08	rapido	data, code, computations, environments are all immutable (without using monads)
12:09	rapido	i've done several implementations in java, factor, haskell and (finally) scala
12:10	rapido	haskell was nice but when i wanted to add io, the code turned into an ugly mess
12:10	rapido	chouser: do you know factor?
12:11	Chouser	nope
12:15	rapido	what i don't understand why slava, the factor developer, has moved away from the jvm
12:15	rapido	i think that was his biggest mistake
12:16	rapido	you can't beat the libraries and the cummulated thousands of man years of (compiler) research that went into the jvm
12:17	Chouser	yeah
12:17	rapido	i think rich made very a good choice there
12:21	rapido	chouser: so what's your take/interest on clojure
12:21	rapido	?
12:26	rapido	got to go... later..
13:59	leafw	I have just sent a feature proposal to the mailing list: embedding java code -like python weaver package. Would be great.
14:00	leafw	to have the best of both worlds ... convenience+power, and speed where it matters.
15:55	Chouser	rhickey: I'm poking at the code in the "embedded java" post to the group.
15:56	Chouser	ImageJ beat me up, so I'm using: (def pix (into-array (for [x (range 512) y (range 512)] (+ x y))))
15:57	Chouser	on my computer: (time (dotimes i 10 (/ (apply + pix) (count pix)))) ; 863.762673 msecs
15:58	Chouser	oh, nm -- I don't have anything interesting to say yet. Sorry.
16:05	Chouser	well, one thing is sort interesting: (reduce + pix) is pretty much the same speed as (reduce long/+ pix)