#clojure – 2008-10-08

2008-10-08

02:41	schlarf	(defmacro assoc! [map_ k v]
02:41	schlarf	`(def ~map_ (assoc ~map_ ~k ~v)))
02:41	schlarf	that cant be done woth a defn right?
02:41	schlarf	and oh yeah, ima sinner babY!
02:41	Chouser	yeah it can, and you do sin.
02:41	Chouser	:-)
02:42	Chouser	oh, sorry, no you're right.
02:42	Chouser	because you're passing in the name, I think it has to be a macro.
02:43	Chouser	if you just used a ref instead, you could do it in a defn and it would play nice with STM and threads.
02:44	schlarf	ok ill look into refs. and anywa, im not planning to really use assoc!, just assoc...
03:13	schlarf	clojure/ <- why is thta coming into my macro?
03:23	hoeck	schlarf: to prevent aliasing
03:24	hoeck	to avoid it, use ~'foo in backquotes
04:12	lisppaste8	askl pasted "compress withr educe" at http://paste.lisp.org/display/68148
04:12	schlarf	^^ i posted a compress-function
04:13	schlarf	it it working using cond and recur but i want to use reduce
04:13	schlarf	but i cant get it to work
04:45	lisppaste8	yangsx annotated #68148 with "reduce is functional" at http://paste.lisp.org/display/68148#1
04:47	Lau_of_DK	Im making a Shortcut in Windows to launch a clojure script, but it requires a full path to start up properly, do you guys know of a %currendir% variable or something along those lines?
04:49	lisppaste8	hoeck annotated #68148 with "filter or reduce" at http://paste.lisp.org/display/68148#2
04:50	lisppaste8	tWip pasted "Latest Slime + swank-clojure does not start" at http://paste.lisp.org/display/68150
04:51	tWip	anyone experienced the same? clojure complains about symbol *1 in swank core.clj
04:57	yangsx	tWip: slime's using iso-latin-1-unix; you can try to use utf-8-unix
05:00	tWip	I'll try that.
05:09	hoeck	Lau_of_DK: `.' doesn't work?
05:10	Lau_of_DK	Unfortunately not
05:10	Lau_of_DK	%windir% works, but is not applicable :)
05:14	hoeck	Lau_of_DK: %cd% ?
05:27	Lau_of_DK	hoeck, %cd% works perfect, thanks alot
06:00	schlarf	is there no round function?
06:01	tWip	you can always use Math.round from Java
06:04	schlarf	i can import math but not round
06:04	schlarf	(import Math)
06:04	schlarf	(.Math.round 5.0)
06:04	schlarf	is the use right?
06:04	schlarf	not working...
06:05	tWip	it's in java.lang so no need to import
06:05	tWip	just (. Math (round 5.0))
06:15	hoeck	schlarf: its even a static method, so (Math/round 5.0) works too
06:15	tWip	oh I didn't know about that syntax
06:16	tWip	is that new? or newish
06:20	hoeck	rather newsish, maybe about 2-3 months old
06:20	tWip	ok
07:44	schlarf	slurp
07:44	schlarf	nice to see a language deisgner with a sense of humour
07:50	cemerick	rhickey: do fns capture all lexical bindings, or does it capture only those bindings that are used in the fn body? (I ask knowing that the latter might be pretty difficult in a dynamic setting....)
07:53	rhickey	cemerick: not exactly sure what you're getting at, can only capture those used
07:54	rhickey	is there a specific scenario you're thinking of?
07:55	cemerick	rhickey: My brain may not yet be working right. However, given (let [foo (some-really-large-obj)] #(blah (:key foo))), it would be nice to know that the returned fn isn't holding a reference to foo.
07:56	rhickey	how could it not?
07:56	rhickey	the returned fn calls :key on it every time it is called
07:57	cemerick	rhickey: right, see, I'm not thinking straight yet; I meant something more like (let [foo (large-obj) val (:key foo)] #(blah val))
07:58	rhickey	ok, in that case no reference to foo in the closure
07:58	cemerick	rhickey: OK, good to know. Thanks for your patience :-)
07:58	rhickey	np
08:28	gnuvince	Good morning
08:28	tWip	morning? surely not... it's time to go home soon.
08:30	H4ns	tWip: psst, he is in another time zone.
08:31	tWip	yes, I got that... just trying to make some (admittedly poor) humor
08:31	cemerick	nonsense, it's 8:28 everywhere :-)
08:32	H4ns	tWip: yeah, my remark was not really much better, apologies :)
08:32	cemerick	45 people in #clojure -- anyone have any ideas on where the influx is coming from?
08:32	cemerick	I suppose the steady trickle of clojure posts on proggit don't hurt.
08:32	rhickey	cemerick: we hit 63+ yesterday
08:32	blackdog	i think the boston meeting did it
08:32	cemerick	yeah, I saw that -- good to see it
08:33	schlarf	ceemrick: all my bots
08:33	cemerick	ah, so other lisp ex-pats, then?
08:33	rhickey	blackdog: yes, seemed to have connected with a good pool of people through that
08:33	H4ns	cemerick: i got two passports
08:34	rhickey	we're about to lap 600 on the group
08:34	tWip	I think Clojure really brings something to lispers in the JVM enterprise land
08:34	blackdog	also, the jvm summit got quite a few writeups on various influential blogs, and there were only good things to say
08:34	tWip	I was using jscheme before clojure, which was quite nice also, but nowhere near as good performance
08:34	cemerick	rhickey: BTW, I made some contact with business-side people at Sun last week, talked them up on Clojure. Certainly piqued their interest.
08:35	gnuvince	rhickey: do you use Clojure for your work?
08:35	rhickey	cemerick: cool
08:35	rhickey	gnuvince: yes
08:36	gnuvince	That's good
08:41	aking	hi donald - yup
08:41	aking	oppss
08:54	schlarf	how do i get parenthesis around < x 10: (list 'fn '[x] (hd xs) 'x (nth xs 1))
08:54	schlarf	(def xs '(< 10))
08:56	rhickey	schlarf: what are you trying to do?
08:56	schlarf	lol i posted it a few days ago but forgot
08:57	rhickey	#(< % 10)
08:57	rhickey	?
08:57	schlarf	yes
08:57	schlarf	where is the definition of #? its a macro right? in boot.clj?
08:58	rhickey	#() is reader syntax
08:58	schlarf	ok
09:01	schlarf	is clojure lazy throughout?
09:01	schlarf	everything is lazy?
09:01	rhickey	schlarf: no
09:01	schlarf	for some reason i dont get the same difficulty predicitng stuff as in haskell
09:01	schlarf	oh ok
09:01	rhickey	Clojure is strict, most of the sequence functions are lazy
09:02	schlarf	ah, strict by default, lazy where it makes sense
09:02	rhickey	and even there the notion of lazy is looser than Haskell's
09:03	schlarf	will you kill me if i post a message-passing-OO-system to comp.lang.clojure?
09:03	rhickey	i.e. args are still eagerly evaluated and the existence of a return seq is eagerly determined, but only as much of the consumed seqs are produced as are required
09:04	rhickey	schlarf: there is no comp.lang.clojure - you mean the google group?
09:05	schlarf	yes
09:05	rhickey	schlarf: I'm all for experimentation
09:06	schlarf	cool
09:15	schlarf	http://groups.google.de/group/comp.lang.lisp/browse_thread/thread/dbd4b63f41e11e40#
09:15	schlarf	^^clojure review
09:30	cemerick	schlarf: thanks for that, interesting stuff; here's an english link, btw: http://groups.google.com/group/comp.lang.lisp/browse_thread/thread/dbd4b63f41e11e40#
09:30	cemerick	The German UI labels were puzzling to me :-)
09:35	schlarf	why cant i list %
09:41	tWip	you mean? #(list %)?
10:26	Chouser	rhickey: I working on a response to your regex question, on the assumption that a breaking change doesn't completely rule out the proposal.
10:26	Chouser	s/I/I'm/
10:27	schlarf	(def inst (gensym)) ; (assoc inst "graph" 0) .> symbol cannot be cast to assoc
10:27	rhickey	Chouser: ok
10:28	Chouser	um, I mean -- does the fact that it will break some old regex literals completely rule out the proposal?
10:28	schlarf	i want a unique name for my hash-map, cant i get that?
10:29	schlarf	(def (gensym) (hash-map x y))
10:29	Chouser	schlarf: are you writing a macro?
10:29	schlarf	no but mayeb i should
10:29	rhickey	Chouser: I hope not, I just want to know what the story will be
10:29	Chouser	rhickey: ok, I'll keep working.
10:30	wwmorgan	schlarf: you can do (var-get (resolve symbol))
10:45	schlarf	is it impossible to modify a Map passed as an argument inside the function and have it keep it ouside?
10:46	wwmorgan	schlar: in general you want to return the changed map from the function
10:46	wwmorgan	*schlarf
10:46	schlarf	well imtrying to create an object-system with Maps
10:46	schlarf	using Maps
10:47	schlarf	and i want mutability for it
10:47	jgracin	schlarf: Clojure's map or Java's? In Clojure use refs
10:47	schlarf	not (def a = (update a))
10:47	schlarf	jgracin: ok
10:49	blackdog	you can just use alter on your ref of map to change the values
10:55	schlarf	but how do i use refs without any transactiosn going? i get that complaint when using alter ona ref
10:55	schlarf	and how do i get values from a ref?
10:55	blackdog	dosync round the alter
10:55	schlarf	(def a (ref (hash-map))); how can i change that map?
10:55	wwmorgan	schlarf: http://clojure.org/refs
10:55	blackdog	@a
10:55	schlarf	im reading there
10:56	blackdog	(dosync (alter a assoc :x 1))
10:56	schlarf	seems like im really not meant to do this in clojure? is it easier in other lisps?
10:56	rhickey	schlarf: an object system for Clojure should be either transactional (using refs) or async (using agents)
10:57	schlarf	ok
10:57	rhickey	the resulting OO system will be multicore ready, unlike almost all others
10:57	schlarf	cool
10:58	schlarf	very cool actually. so that would a huge problem for say, a python-program
10:58	schlarf	?
10:58	schlarf	to run it on mutliple cores
10:58	blackdog	probably as they have global interpreter lock which i guess is for one core??
10:58	schlarf	how do i get the value of ref?
10:58	blackdog	@a
10:59	schlarf	ah
11:04	schlarf	can i still use def? and it can satisfy transactionality or asynchronisity?
11:09	blackdog	yes, you can do (def x (ref (hash-map)))
11:10	blackdog	works just the same
11:11	rhickey	schlarf: but you wouldn't want an object system that required every object to have a global name, would you?
11:14	Chouser	hm, that sounds like a system I've used. This was the least of its problems.
11:14	schlarf	rhickey: and with def i force it to?
11:15	rhickey	schlarf: what languages do you know?
11:18	schlarf	python
11:23	rhickey	schlarf: when you create an instance of a class in Python that instance has no name, only the variable to which you assign it has a name
11:24	rhickey	so variables and objects are separate ideas
11:25	rhickey	def is about (global) variables, in which you can put anything, including instances of any objects you invent
11:25	rhickey	but you object system should be independent of def
11:27	schlarf	yes i see
11:34	schlarf	woot
11:34	schlarf	i think i just had a spark of enlightenment
11:34	schlarf	for programming in general
11:34	schlarf	ty clojure-channel
11:38	scottj	rhickey: on http://clojure.org/getting_started under Debugging it might be useful to mention where the -Xdebug flags should go in the java init command. I tried putting it at the end.
11:40	rhickey	scottj: doen
11:40	rhickey	done
12:17	fogus	Damn dirty lazy seqs! ;)
12:17	rhickey	You mean damn dirty side effects?
12:18	fogus	well, that too
12:19	Chouser	file closed too early?
12:20	fogus	Nah. My issue was that I was accumulating a "best
12:20	fogus	var from a seq
12:20	fogus	then trying to return the acculmulator
12:21	fogus	but it was always the 1st value
12:21	fogus	(of course)
12:21	Chouser	sure. what looping construct did you use? I would reach for "reduce" first, which is non-lazy.
12:21	rhickey	fogus: (doc max-key)
12:23	fogus	this was my first version http://pastebin.com/m2ae471a0
12:24	Chouser	very reasonable attempt! But yes, for is lazy, and you're trying to use it for side-effects.
12:24	fogus	(best > '(1 2 3 4 5)) => 5 in reality, but 1 with my defn
12:25	fogus	So then when it hit me that the for returned a lazy seq it became http://pastebin.com/d4832b6ee
12:27	fogus	But it still smells like a hack to me
12:27	Chouser	yep, I'd agree.
12:30	scottj	What is the idiom for looping while a condition is true, changing counter to rest of a list each time and collecting results? Example: http://pastebin.com/m250d5e94
12:31	gnuvince	scottj: not sure if Clojure has it, but take-while would be appropriate I think
12:34	scottj	gnuvince: but the predicate in take-while can only be a specific item in the list, not the rest of the list, right?
12:34	gnuvince	Right.
12:34	scottj	function of a specific item I mean
12:34	gnuvince	Hmmm
12:34	wwmorgan	scottj: is that one of the euler problems you're trying to solve?
12:35	scottj	wwmorgan: yep, solved it, but I was hoping there was a more concise, idiomatic way
12:35	wwmorgan	there is. Look at partition
12:36	rhickey	(defn best [f xs] (reduce #(if (f %1 %2) %1 %2) xs))
12:37	fogus	(humbled)
12:37	gnuvince	scottj: something in Haskell (don't have Clojure installed right now):
12:37	gnuvince	> takeWhile (\xs -> length xs == 5) (map (take 5) (tails [1..10]))
12:37	gnuvince	[[1,2,3,4,5],[2,3,4,5,6],[3,4,5,6,7],[4,5,6,7,8],[5,6,7,8,9],[6,7,8,9,10]]
12:38	wwmorgan	gnuvince: that's (partition 5 1 (range 1 10))
12:41	gnuvince	wwmorgan: nice
12:42	Chouser	Rich wrote a "tails" as well (for cases where you want the sort lists at the end, for example) ... but I always have trouble finding it.
12:44	scottj	thanks, partition definitely solves that problem much better
12:46	Chouser	oh, maybe it was "inits"
12:48	scottj	Is there a better way to convert an integer to a list of integers representing its digits than (map #(Integer/parseInt %) (map str (str n))) ?
12:48	schlarf	it would be possible to implement optional parameters with a macro right?
12:48	schlarf	because i dont want & rest
12:49	wwmorgan	schlarf: can you give an example of what you're looking for?
12:51	schlarf	(def-class [name &optional parent]...)
12:51	schlarf	i could ofc dp &rest and check if rest==nil
12:52	Chouser	schlarf: you can do destructuring on &rest: (let [[& [a b c]] [1 2]] (list a b c))
12:52	wwmorgan	right. Which in your case might look like (defmaco def-class [name & [parent & _]] ...)
13:15	schlarf	if using list in macro, should i then quote things i dont want to eval at compile time
13:16	schlarf	im getting: clojure.lang.LispReader$Unquote@af8b32 when macro-expanding
13:17	schlarf	instead of the should-be generated list
13:17	cemerick	rhickey: I don't remember if I suggested this in the past, but it would be nice to be able to determine whether a Delay has been forced yet. delayed? perhaps, with a corresponding public static fn on the Java side...
13:24	scottj	Is there a function that takes a series of collections (same size) and returns all possible combinations of the top level items in those collections?
13:36	Chouser	scottj: for does that
13:41	Chouser	schlarf: Unquote is generated by ~, which is meant to be used inside backticks: `(prn 1 2 ~(- 5 3))
13:41	aperotte	Is anyone having a problem with enclojure not recognizing certain names? The REPL in netbeans doesn't recognize "format" as a defined function.
13:42	schlarf	works with emacs
13:42	Chouser	aperotte: "format" is new-ish.
13:44	aperotte	oh ok, thanks
13:51	lisppaste8	schlarf pasted "dosync-macro" at http://paste.lisp.org/display/68176
13:52	lisppaste8	schlarf annotated #68176 with "what to geenerate" at http://paste.lisp.org/display/68176#1
13:52	schlarf	^^ can someone help me with that macro ^^
13:53	TommyOnMac	hi
13:53	schlarf	user=> (list 'dosync '(alter x assoc y z)) -> (dosync (alter x assoc y z)) is a start but how do i replace x y z with the params passed?
13:54	alec	schlarf: use list interpolation, don't build your own lists
13:54	alec	`(dosync (alter ~x assoc ~y ~z)) or something
13:54	Chouser	TommyOnMac: hi
13:56	schlarf	java.lang.ClassCastException: java.lang.Integer cannot be cast to clojure.lang.Ref
13:56	schlarf	when i use that alex
13:57	alec	schlarf: when I have trouble with macros, I run (macroexpand '(<code>)) and look at the output
14:01	schlarf	when i have troubales with macos macroexpand never works
14:01	schlarf	Caused by: java.lang.Exception: Unable to resolve symbol: macro-expand-1 in this context
14:02	Chouser	macroexpand-1 or macroexpand
14:03	schlarf	with both
14:04	schlarf	oh wait i used macro-expand
14:04	Chouser	heh, sorry, I mean "macro-expand-1" with two dashes is incorrect. please use either "macroexpand-1" or "macroexpand"
14:51	schlarf	if i want to (dosync (alter obj assoc :methods method_name)) but :methods is a vector and i wanto to conj to it
14:51	schlarf	i canr figure out how to write to it
14:56	Chouser	schlarf: you might want assoc-in
15:30	schlarf	assoc-in only seem to wor with numbers, not strings
15:32	schlarf	waitno
18:34	aperotte	Hello everyone. I was interested in adding the clojure-contrib files to my classpath, but it seems like I'm doing something wrong.
18:34	aperotte	I put the contents of the src folder from clojure-contrib into ~/clojure
18:35	aperotte	then I set the environment variable CLOJURE_CLASSPATH=~/clojure
18:36	aperotte	I then load clojure and try to run (use 'clojure.contrib.duck-streams)
18:36	aperotte	and errors fly
18:36	Chouser	clojure doesn't have it's own classpath
18:36	Chouser	you need to set java's classpath to include the clojure-contrib/src directory.
18:37	aperotte	ohh ok
18:37	Chouser	instead of copything that around I run clojure like this: java -cp ~/build/clojure/clojure.jar:/home/chouser/proj/clojure-contrib/src clojure.lang.Repl
18:38	aperotte	ok, I see
18:40	aperotte	Chouser: beautiful ... thank you
18:45	Chouser	np
19:38	gnuvince_	What would be a clear way to test if the elements of a collection are all equal?
19:40	gnuvince_	(every? #(= (first x) %) (rest x))
19:40	gnuvince_	Clear enough?
19:42	Chouser	(apply = x)
19:44	gnuvince_	...
19:45	Chouser	it's just an idea. There's probably a better way.
19:45	Chouser	ok, maybe not
19:46	gnuvince_	It's perfect.
22:09	ChibaPet	Hey, all. A quick question. I'm new to all this, but I'm wondering if the JVM does anything to distribute threads across multiple cores/CPUs, since Clojure uses Java threads... I'm looking at options for functional/concurrent programming, and was curious.
22:10	walters	java threads usually map to OS threads which the OS scheduler will distribute across cores
22:10	walters	unless you're using a broken VM or a broken OS it will Just Work
22:10	ChibaPet	hm, ok, cool
22:11	ChibaPet	Thank you.