#clojure – 2008-06-08

2008-06-08

14:50	Lau_of_DK	Any functional-p guru here, who can tell me if there's some neat way to do a prime factorization of x ?
15:26	slava	Lau_of_DK: asymtotically, all algorithms are exponential-time
15:26	slava	hi WardCunningham
15:27	WardCunningham	hello slava
15:27	slava	if you're _that_ WardCunningham, I spent much time browsing through the c2 wiki back in the day. it was quite educational when I was getting into the whole "languages other than Java" thing. :)
15:28	WardCunningham	Yes, that is my site. Thanks for the kind words.
15:29	WardCunningham	Are you a clojure geek now? Or just looking around like me?
15:29	slava	i think clojure is really neat. i don't see myself using it for projects any time soon, but it has a lot of good ideas and I like to learn new languages
15:30	WardCunningham	agree.
15:30	slava	in particular, its approach to immutability and concurrency strikes me as the Right Thing.
15:31	slava	you can still have mutable state, but the library gives you top-notch persistent collections.
15:31	WardCunningham	and stm.
15:31	slava	and as far as concurrency goes, you get STM and message passing.
15:32	slava	yup.
15:32	Lau_of_DK	slava, Cloure is the right thing, resistance is futile
15:33	slava	as far as collections go, persistent collections probably work fine in most cases. I think you still need mutable specialized arrays for numerics
15:34	slava	hmm. if the only mutable arrays are those specialized to hold a single numeric type, you avoid co-variance/contra-variance issues in the type system.
15:34	rhickey	Lau_of_DK: please no fighting or taunting here
15:34	Lau_of_DK	rhickey, dont worry, Im a man of peace
15:34	rhickey	Clojure has typed access to Java arrays of primitives
15:34	slava	does all the seq stuff work there?
15:35	rhickey	yup, but with boxing overhead
15:35	slava	how far are you going to go with compiler optimizations?
15:35	WardCunningham	slava: nice to meet you. I'm going back to just lurking ... saving my wrists for work.
15:35	rhickey	there's also higher-level but super-efficient whole-array transforming macros like amap and areduce
15:35	slava	if you implement some analysis you can avoid creating the iterator if its entirely consumed without being returned or used for its object identity
15:36	slava	rhickey: right; i'm suggesting that you can implemenet map, reduce etc gnerally using seqs and optimize the case where the seq is iterating over a known type
15:36	slava	depends on how much effort you want to put into the compiler, of course
15:36	rhickey	I might do that at some point, but there are lots of issues, as the 'mapped' function must be typed as well
15:37	rhickey	amap and areduce are functional
15:37	rhickey	i.e. return new arrays
15:37	slava	i don't think the mapped function must be typed; it doesn't see the iterator directly, does it?
15:37	rhickey	I'd like to avoid devolving into Java-like typing
15:38	rhickey	all fns take/return Objects
15:38	slava	i'm suggesting something more along the lines of inference, not declaration.
15:38	slava	if the fn is small, you can inline it and avoid the boxing at the procedure call boundary
15:39	rhickey	I understand, a lot of work
15:39	slava	yup :)
15:39	rhickey	Right now I'm getting terrific optimizations for free from HotSpot
15:39	slava	less work than writing a native compiler, though. once you get past the high-level optimizations, you get the rest from hotspot.
15:40	rhickey	right
15:40	rhickey	and they might do the boxing elimination for me at some point too
15:40	slava	might :)
15:41	slava	i think in general, boxing elimination is hard on the jvm unless you have specific knowledge
15:41	slava	there are too many ways to 'observe' the identity of an object
15:41	rhickey	I've added enough so that people who have to do number crunching don't have to leave Clojure. Other optimizations are premature for me right now.
15:42	slava	are you using/going to use clojure for commercial projects?
15:43	rhickey	starting to
15:43	slava	nice
15:44	slava	clojure seems really well designed. have you spent a lot of time working with scheme and cl in the past?
15:44	rhickey	CL
15:46	rhickey	In many ways Clojure is a challenge to Lisps to change
15:47	slava	yeah, CL is pretty stagnant. I worry that in 10 years, it will be mostly forgotten, which is a real shame because it has features you don't see in many languages (multiple dispatch, MOP, setf, procedural macros)
15:47	rhickey	it is a treasure-trove of ideas
15:47	slava	seeing your efficient persistent collections made me realize that the destructive list operations are mostly obsolete
15:48	slava	because in CL, you cannot assume they have side effets; they're purely for optimization
15:48	slava	and in general, why did you decide to keep cons cells around? is it because they map trivially to the seq protocol?
15:48	slava	it seems that in most cases persistent vectors can replace them
15:49	rhickey	consing at the front is useful, but yes, in practice vectors get a lot more use, at least in idiomatic Clojure code
15:49	rhickey	lists reserved mode for code
15:49	rhickey	more
15:50	slava	is it possible to make persistent vectors efficient for consing on the front? it seems like you could add a 'head' slot that works like 'tail', but i'm not sure if the tree rebalancing gets hairy
15:50	slava	i haven't thought about this before
15:50	rhickey	you could use the vectors backwards as lists
15:50	slava	ah, true
15:51	rhickey	both support a 'stack' protocol where you ignore the order
15:52	rhickey	using vectors for data and lists for code gives a nice separation vs Lisps where you use lists for both
15:52	slava	oh, i didn't find this in the code: how is append implemented on persistent vectors?
15:52	rhickey	conj adds to end of a vector
15:52	slava	i've found that having separate sequence types for code and data is nice too. it can catch mistakes and makes code easier to understand -- you know what the resulting sequence will be used for
15:52	slava	appending two persistent vectors, though
15:53	rhickey	not supported directly
15:53	rhickey	basically O(n) add one to the other
15:53	slava	i wonder if there's a way to do that more efficiently knowing the structure of persistent vectors
15:54	slava	it would still be o(n), just a constant speedup
15:54	rhickey	if the first was a multiple of 32 in size, easy
15:55	slava	yup
15:58	slava	i just realized that one can implement a persistent-vector with double ended consing as a pair of persistent vectors :)
15:59	rhickey	There's a PersistentQueue in the Clojure lib, not yet exposed in the API
16:03	slava	i see a potential problem there in that popped entries won't be GC'd until the entire queue is empty
16:04	slava	unless RT.seq(r) converts the vector to a cons list
16:12	rhickey	You can't do that and preserve persistency
16:12	rhickey	retention of the vector depends on push/pop patterns
16:13	slava	that's what i meant; if you don't hold on to the old version of the queue, the values might not be GC'd anyway
16:13	slava	not sure if that's a problem with the way this code is used
16:13	slava	if you expose it to the user it will be something to address though
16:15	rhickey	if someone allows n items to be pushed before consuming any, nothing implies they ought to be GC'ed prior to n pops
16:15	rhickey	There are dual-list based queues with amortized persistency
16:16	rhickey	My queue is not amortized since seq of the vector is O(1)
16:17	slava	yup
16:17	rhickey	variant on Okasaki's
16:17	rhickey	enabled by persistent vectors
16:23	Lau_of_DK	Ive never used VIM but I noticed that there's a clojure plugin for it on the wiki. Does it have the features that emacs have like repl interaction, autocomplete, all that stuff?
16:45	Lau_of_DK	Guess VIM doesn't have much of a user-core in here
16:46	rsynnott	is there an emacs repl for clojure?
16:47	Lau_of_DK	yea, you can connect to slime and get a REPL directly in emacs, if thats what you mean
16:53	rsynnott	ah, there's slime for clojure?
16:54	Lau_of_DK	Well, there's a swank-clojure package
16:54	rsynnott	(I havn't really used clojure as yet; I'm more of a CL persn. It looks interesting, though)
16:54	rsynnott	ah, cool, may give that a go
16:54	rsynnott	main thing putting me off was percieved lack of a proper ide
16:54	Lau_of_DK	Yea, want me to find a link for you ?
16:54	Lau_of_DK	Have you ever tried some of the Eulers ?
16:54	rsynnott	got it
16:56	Lau_of_DK	I re-did some of the Eulers in clojure, just to try and get that functional feel, it was fun - and most effective
16:57	Lau_of_DK	You can also check this out, just to see an easy little simulation with a GUI. http://ubuntuforums.org/showpost.php?p=5123892&postcount=16
16:57	Lau_of_DK	Rich did something similar, his is better, but also a little bit more complicated
17:25	Lau_of_DK	rhickey, are there any tools to help setup more complex GUIs, or does it have to be done manually ?
17:26	rhickey	Some people are using Netbeans' Matisse to build a GUI they drive with Clojure
17:28	Lau_of_DK	How do they import it, so as to drive it ?