#clojure – 2008-04-11

2008-04-11

11:13	drewr	Is there a built-in that tells me if an item in one sequence is in another?
11:13	drewr	In Python, "1 in [1, 2, 3] => True"
11:13	drewr	Sorry, ...if an item is in a sequence.
11:14	abrooks	(some? 1 '(1 2 3)) IIRC.
11:14	abrooks	Grr.
11:14	abrooks	That's not the right name.
11:14	abrooks	Hang on.
11:14	rhickey	drewr: no there isn't
11:15	drewr	OK, it's trivial to write; just thought I'd ask.
11:15	rhickey	Clojure still missing CL's sequential find/member etc
11:15	abrooks	(some #(= 1 %) '(1 2 3)) was what I wanted. (But not what drewr wanted apparently.)
11:16	Chouser	Arc's solution is to allow some high-order functions to take an object instead of a predicate, and assume you want the predicate to be equality.
11:16	Chouser	(some? 1 [1 2 3]) would act like (some? #(= % 1) [1 2 3])
11:16	abrooks	some is "some" not "some?" I was wrong.
11:16	rhickey	how do they distinguish 'objects' and predicates?
11:17	abrooks	A predicate is a function always, right?
11:17	rhickey	unless I'm looking for a function
11:17	Chouser	rhickey: I don't know how arc distiguishes. I can try to find out...
11:18	abrooks	Wrap a function in a list/vector as a single item?
11:18	Chouser	Wouldn't this suffice? (instance? Runnable x)
11:19	rhickey	Chouser: but what if I wanted to find a function, i.e. the value I'm looking for is a predicate?
11:19	Chouser	oh. excellent point.
11:19	rhickey	(some #{1} [1 2 3])
11:20	rhickey	seems easy enough
11:20	Chouser	oh, nice!
11:21	abrooks	Yeah, that's nifty.
11:21	Chouser	see, you have to tell people these things, rhickey. We're not smart enough to figure them out ourselves.
11:24	drewr	rhickey: So is nil the only false value?
11:25	Chouser	alsa 'false'
11:25	Chouser	er, 'false' is also false.
11:25	drewr	Ah, thanks.
11:25	abrooks	I knew they were there at one brief point in time.
11:26	cgrand	"false" is the false to use for java interop
11:26	Chouser	"nil and false representing the values of logical falsity in conditional tests - anything else is logical truth"
11:31	Chouser	Arc's 'some' converts its first argument using: (if (isa x 'fn) x [is _ x])
11:31	Chouser	I guess if you were looking for a function, you just can't use the shortcut.
11:32	rhickey	bleh
11:32	Chouser	heh
11:36	drewr	I can't figure out what I'm doing wrong here: http://paste.lisp.org/display/58981
11:36	Chouser	probably just extra parens after #
11:37	drewr	Chouser: Isn't #() synonomous with (fn [])?
11:38	Chouser	I think you want #(if (member? %2 b) (conj %1 %2) %1)
11:38	Chouser	That would be the same as (fn [x y] (if (member? y b) (conj x y) x))
11:39	drewr	Chouser: Ah! I totally missed that subtlety with the shortened syntax.
11:39	Chouser	yeah, I make that mistake a lot.
11:39	drewr	This is why I'm actually writing Clojure instead of reading it.
11:40	rhickey	(defn items-in-common [a b]
11:40	rhickey	(filter (set a) b))
11:41	drewr	...and that's much nicer.
11:42	rhickey	O(a + b) vs O(a*b)
11:42	Chouser	is that O(n log n) instead of O(n^2)?
11:42	Chouser	oh
11:43	Chouser	surely the lookups of b in (set a) take some time? log a?
11:43	drewr	;-)
11:45	Chouser	(set a) might be linear on a (is it really? not even log a?)
11:45	abrooks	A trie can naturally be accessed in order. I haven't looked at Riches implementations of sets but assume that they are tries.
11:46	Chouser	(filter * b) is linear on b * the set lookup operation, which can't be constant, can it?
11:47	abrooks	Chouser: If both sets are ordered, it's a staggered walk O(a+b).
11:47	abrooks	Actually, filter just uses conj doesn't it?
11:48	Chouser	filter uses lazy-cons (boot.clj)
11:48	abrooks	Oh, filter's in boot.clj
11:49	Chouser	but the set object built by (set a) isn't going to keep track of where it was last accessed, to allow a staggered walk, right? It'll have to do a fresh lookup from scratch for each item from b.
11:49	rhickey	set lookup is effectively constant
11:50	rhickey	ditto hashmaps
11:50	Chouser	because it's a hash and not a binary tree of some sort?
11:50	abrooks	rhickey: It's order of trie depth, right?
11:50	rhickey	the sorted versions are RB trees and thus logN
11:51	abrooks	rhickey: sort versions = sorted hashmap and what?
11:51	Chouser	abrooks: sorted-map
11:52	rhickey	trie depth is so small as to be ignorable 6 for 1 billion items, 3 for 1 million
11:52	Chouser	oh, and sorted-set
11:52	abrooks	Ah, sorted-set? Where is that? I only saw sorted-map (not hashmap I misspoke).
11:53	Chouser	abrooks: boot.clj. sorted-set is defined right after sorted-map
11:55	abrooks	Oh, it's just not on the Data Structures page.
11:55	abrooks	... because sets are not on the Data Structures page.
11:55	abrooks	:)
11:55	abrooks	No complaints. You're writing the language. We're all appreciative of that!
11:56	Chouser	rhickey: would you find it any easier to correct someone else's attempts at documenting things?
11:56	Chouser	or would you rather just do it yourself?
11:57	rhickey	does anyone else get the relational bits of set.clj without docs?
11:58	rhickey	e.g. that rels are sets of maps
11:58	Chouser	I think I understand it, but I haven't tried to use it, so I might be fooling myself.
12:01	rhickey	Chouser: probably wouldn't take less time to correct than to write, unless it was really solid coming in, at least for the reference docs...
12:02	rhickey	but the Wiki is a good place to take a crack at explaining it until I get around to it - if it's good I'll build on it
12:03	Chouser	rhickey: any reason there's no 'get' for sets?
12:03	rhickey	what's there to get?
12:04	Chouser	true or false, I suppose.
12:04	rhickey	they're not really associative
12:04	Chouser	ok. that's good enough. I mean, I don't really need get for hashes or vectors either, since I can use them as functions.
12:06	Chouser	I guess I would have assumed that (get foo x) would be the same as (foo x) for sets, just like it is for hash and vector. no biggie at all.
12:07	rhickey	It could be, but then it would return the key, not true/false. I'm not opposed
12:08	Chouser	right, I hadn't realized set returned the key. I'm not asking for a change, just pondering things.
12:08	Chouser	I hadn't ever used 'get', just collections-as-functions and 'nth'
12:25	Chouser	What would be the Clojure equiv of this java? new Signal2<QImage, Double>()
12:26	Chouser	(new QSignalEmitter$Signal2) says No matching ctor found.
12:26	rhickey	Just leave out the type params (new Signal2)
12:26	Chouser	hm.
12:26	rhickey	what is QSignalEmitter?
12:28	Chouser	I think what I'm trying to construct is actually com.trolltech.qt.QSignalEmitter$Signal2
12:29	Chouser	ah, I have source code. public final class Signal2<A, B> extends AbstractSignal
12:30	Chouser	ok, Signal2 is a class nested inside the class QSignalEmitter
12:31	Chouser	Signal2 definitely appears to have a constructor that takes no args.
12:37	Chouser	oh! A nested class constructor takes an instance of its containing class as its first argument?
12:38	Chouser	that seems to have worked, anyway.
13:48	ericthorsen	rich: question on java completion in the editor...
13:49	ericthorsen	In order for us to do the java completion in the editor we would have to have a clojure type hint or a compiled function.
13:50	ericthorsen	The compiled clojure is not practical (partially defeats the purpose od having completion) and the hints will cause people to have noise in the code
13:51	ericthorsen	We were thinking of making it part of the editor syntax where :
13:51	rhickey	et: I'm running now, can you email?
13:51	ericthorsen	If you use a clojure type hint, we would use that, else we would give you a way to give a type hint that would not wind up in the source....any thoughts?
13:51	ericthorsen	yes
14:02	Chouser	ericthorsen: what kind of completion are you trying to do?
14:03	ericthorsen	We are working on a NetBeans module for clojure....should have an alpha by the end of this month
14:03	ericthorsen	we have been using it in house
14:03	ericthorsen	integrated remote REPL, debugging, clojure and java completion, and the usual NetBeans language support stuff
14:03	Chouser	but completion of what? (str <tab> ...produces what?
14:04	Chouser	yeah, I saw the announcment. Sounds ambitious. ;-)
14:05	ericthorsen	whatever we can....we can do completion on namespaces and java types...there is also a code browser that lets you see all the current clojure bindings in your VM
14:05	ericthorsen	...and of course hippie completion
14:12	Chouser	ok, cool.
14:33	Chouser	how much of it have you been able to write in Clojure, or have you been trying?
14:34	ericthorsen	Most of it...the one issue we are up against is the nature of NetBeans using static Java classes to do their SPI/API mappings
14:35	Chouser	ok. I'm looking at NetBeans for the first time.
14:35	ericthorsen	We are close to having a static java wrapper for a clojure proxy...I'll put it up in the contrib when it's baked
14:35	ericthorsen	pretty amazing what comes out of the box
14:36	Chouser	If I can extend it (add key bindings, etc. ...simple stuff) in Clojure, then I'll be pretty interested.
14:37	ericthorsen	i'm sure is has a key binding mechanism in Netbeans but we have also made the REPL in a way that you can run commands locally (in the JVM that NetBeans is running)
14:38	ericthorsen	this is how we are writing the enclojure module...in clojure
14:39	Chouser	sounds great.
14:39	ericthorsen	It will be off by default, but you can set it in the preferences to enable a checkbox to execute commands in the local JVM or the remote REPL...it's a fun way to develop
14:39	ericthorsen	right now we are not adding any new features but just focusing on stability...something will be up before the end of April
14:40	Chouser	I've been a vimmer forever, and although the structure of emacs is interesting to me, its ancientness (and elisp) do not.
14:40	Chouser	I see there's a thing called jVi for NetBeans -- those plus clojure may be enough to move me off of vim.
14:40	ericthorsen	hard to get developers to move off their editors...:)
14:41	Chouser	yes, it is. I've tried really hard to use emacs, two or three times. Failed.
14:41	ericthorsen	I have high hopes of what I'm going to be able to do in my shop with clojure and NetBeans...very psyched
14:42	Chouser	is the idea of a "remote JVM" meant for like controlling a Java web server somewhere?
14:44	ericthorsen	that's a separate issue...part of the enclojure module is written in clojure but you do not want to execute you clojure commands within the JVM of your IDE.
14:44	ericthorsen	So the commands get sent to a remote JVM
14:45	Chouser	ok, so not "remote machine" just a JVM that's independant of the editor.
14:46	ericthorsen	we are thinking of allowing a remote REPL per NetBeans group so you can work against multiple running VMs for different groups but I'll want to get more feedbac from experienced NetBeans folks and users before moving ahead there
14:46	ericthorsen	that is correct
14:46	ericthorsen	although...it could be on a remote machine
14:47	Chouser	ok. Well, if I can get netbeans and jvi working happily enough, then I'll be very excited to try out enclojure. Keep it up!
14:48	ericthorsen	thx...u2