#clojure – 2011-02-27

2011-02-27

02:59	amalloy	TimMc: apropos of the discussion like six hours ago: yes, if you only use reduce with named defns, you're probably not using reduce enough :)
03:41	amalloy	TimMc, Sgeo: god, that stanford paper is heavy reading. i got through the first few pages a couple months ago, and since picking it up again i'm on page nine and struggling :P
10:32	markskilbeck	Hi, all. Is it possible to have clojurebox auto close pairs (quotes, parens, etc)?
10:33	markskilbeck	Oh. Is clojurebox just emacs?
10:34	eckroth	markskilbeck: turn on paredit mode?
10:38	markskilbeck	eckroth: I can't find how to do so.
10:43	markskilbeck	Nevermind. I see.
10:48	eckroth	markskilbeck: ok good; I assume you typed M-x paredit-mode :)
10:52	Sgeo	amalloy_, the only reason I linked to it was to see clojurebot's reaction >.>
11:02	bmh	I'd like to guarantee that I'm using unsigned 64-bit values in a particular function -- any suggestions for accomplishing this?
11:03	Chousuke	the jvm doesn't even have unsigned types :/
11:04	bmh	that's too bad. I'm implementing a particular RNG
11:05	Chousuke	you can always pretend longs are unsigned of course but it complicates the logic somewhat.
11:05	bmh	That should be fine, as long as overflow from multiplication behaves sanely it shouldn't complicate anything
11:06	Chousuke	overflow behaviour was changed in 1.3 wasn't it? You should get an exception on overflow unless you're using unsafe ops or autopromoting types.
11:10	bmh	I can probably get by with unchecked ops
11:12	bmh	(Gosling really dropped the ball on that one)
11:39	TimMc	sritchie: Are you using count to force a lazy seq?
11:46	tscheibl	hey there
11:49	tscheibl	is it a common clojure idiom to put the whole source into a (let ...) to get the equivalent to private symbols?
11:49	tscheibl	or should I use (blabla ^{private: true} ...) ?
11:50	tscheibl	which feels clumsy
11:50	Dranik	tscheibl, if you mean the incapsulation via lexical closures -- then yes, its idiomatical
11:50	tscheibl	i mean (def blabla ^{private: true} ...)
11:51	Dranik	tscheibl, actually you may glance at SICP; there is a special chapter about incapsulation in lexical closures
11:52	tscheibl	(let [x 41] (def y (* x 2)) ?
11:52	Dranik	what's that?
11:52	tscheibl	is it still idiomatic if I do defs inside the let?
11:53	Dranik	well, may be I am not the person whom you should listen, but I bet it's a bad style
11:53	clojurebot	style is http://mumble.net/~campbell/scheme/style.txt
11:53	tscheibl	(let [x 41] (def y (* x 2)))
11:56	tscheibl	the other way would be: (def ^{:private true} x 42) (def y (* x 2))
11:56	tscheibl	which feels at least as clumsy
11:56	Dranik	tscheibl, it's ok to incapsulate x in let
11:57	Dranik	but it's a bit weird to me when you define a global variable there
11:57	tscheibl	but I've never seen it the clojure code of common libs
11:57	TimMc	tscheibl: Pretty sure that a def in a let is still global.
11:58	tscheibl	yeah it is... I know... but will anybody sue me when I do that ? ;)
11:59	Dranik	tscheibl, you should write such code under a pillow, AOT-compile it and never show the source :-)
12:00	tscheibl	you know ... nowadays people get sued for far less... at least in Sweden ;)
12:00	Dranik	:-)
12:00	Dranik	are you from Sweden?
12:01	tscheibl	happily not.. but some are :)
12:02	Dranik	never thought that it's so dangerous there.... :-)
12:19	tscheibl	hmm.. I've actually found a problem that arises when I put 'def' inside the 'let' body
12:19	clojurebot	"There is no problem in computer programming which cannot be solved by an added level of indirection." -- Dr Maurice Wilkes
12:21	tscheibl	... when I redef the symbol in the repl it wouldn't be redefined in the same 'let closure'
12:22	tscheibl	which makes interactive testing impossible
12:22	Dranik	tscheibl, try to use binding instead of def
12:23	tscheibl	hmm
12:23	Dranik	it is pretty much alike the let but it does not create the lexical closure around everything
12:23	pdk	binding lets you override the definition of an existing symbol thread-locally
12:23	Dranik	you may redefine your (def y ...)
12:23	pdk	the rub is if you create more threads within the binding scope they aren't aware of the new bindings themselves
12:25	tscheibl	I may also redefine y when it was defined inside the let body... but I wouldn't have access to the lexical clojure which it was defined in originally
12:26	tscheibl	that's bad for interactive development in the repl
12:27	tscheibl	I would have to reload the whole let form every time
12:28	tscheibl	so I'm probably better of with (def {:private true} x 42) (def y (* x 2))
12:29	tscheibl	,(def ^{:private true} x 42) (def y (* x 2))
12:29	clojurebot	DENIED
12:30	tscheibl	ha.. clojurbot won't let me def something
12:30	tscheibl	&(def ^{:private true} x 42) (def y (* x 2))
12:30	sexpbot	java.lang.SecurityException: You tripped the alarm! def is bad!
12:30	tscheibl	zed's dead, baby... zed's dead ;)
14:27	bamalut	what ide you all using? ive tried netbeans enclojure but it seems that debug is not working - i really loved drscheme when i programmed with scheme - is there equivalance?
14:28	Scriptor	vim :p
14:28	Scriptor	well, it's not like drscheme
14:28	TimMc	Emacs, finally.
14:28	Vinzent	emacs+slime probably most powerful ide for clojure
14:28	TimMc	What exactly is slime, anyway?
14:29	TimMc	I'm sill using Emacs as just a sexpr-aware editor.
14:29	bamalut	i tried clujure-box which its emacs + slime but didnt fully understand how to use it - any tutorial?
14:29	TimMc	I know slime has soemthing to do with a repl, but that's it.
14:29	Scriptor	it's a way to integrate the repl into emacs, afaik
14:29	Scriptor	you use swank as a server for the repl itself, and slime is the client
14:29	TimMc	got it
14:31	Vinzent	bamalut, there is handy slime cheat sheet soomewhere in the internet
14:32	bamalut	i will google it and try to use it again - thanks
14:32	devn	'lo all
14:32	Scriptor	hey devn
14:32	devn	TimMc: I thought I got you up to speed on using SLIME last week, no?
14:33	TimMc	devn: Nah, I only got as far as Emacs itself.
14:33	Vinzent	bamalut, alsotake a look at https://github.com/technomancy/durendal
14:33	devn	oh, well, it's not too hard to get SLIME working, most of the instructions should be pretty obvious and easy
14:33	TimMc	I have the lein plugin for swank though now.
14:34	devn	lein swank in your project directory, M-x slime-connect [RET],[RET],[RET], ta-da!
14:35	TimMc	Quick question: How to I add new .emacs settings without restarting emacs?
14:35	bamalut	Vinzent, i am looking at it now - thanks!
14:35	Vinzent	TimMc, eval .emacs buffer
14:35	TimMc	hrm
14:36	TimMc	So if I have .emacs in a buffer, I can safely re-eval the whole thing? There are some items that ask not to be run multiple times.
14:36	lelf	TimMc: or C-x C-e after that particular sexp
14:36	Vinzent	devn, btw i think lein-swank function which runs lein swank and connects to it with one keystroke is more convenient
14:36	TimMc	lelf: OK, cool.
14:37	Raynes	Scriptor: It does quite a bit more than that. You don't need SLIME for just an REPL, you can use inferior-lisp for that.
14:37	__name__	is clojurebot broken?
14:37	__name__	$source every?
14:37	sexpbot	every? is http://is.gd/yARZ9e
14:37	__name__	ah, it was sexpbot :)
14:37	Scriptor	Raynes: true, that's just the basic idea :)
14:37	Scriptor	I guess
14:37	Raynes	__name__: sexpbot that was broken or sexpbot?
14:38	Raynes	Or sexpbot that had the command you were looking for?
14:38	Scriptor	hmm
14:38	Raynes	I believe clojurebot has that same command.
14:38	Raynes	~source every?
14:38	__name__	I messaged clojurebot in query.
14:38	Scriptor	$source persistenthashmap
14:38	sexpbot	Source not found.
14:38	Scriptor	screw you sexpbot
14:38	Raynes	Scriptor: It isn't that clever. ;)
14:38	__name__	and it did a random url for $source every?
14:39	TimMc	clojurebot's every? link has a bad URL fragment
14:39	TimMc	Should be L2026 instead of LID2026
14:45	__name__	$source defn
14:45	sexpbot	defn is http://is.gd/LofGS4
14:50	Cozey	Good morning
14:51	Cozey	I'm not sure if my setup is incorrect, or am I doing something wrong: when I try to 'eval in frame' something during slime break, I get an exception: clojure.lang.Symbol cannot be cast to clojure.lang.Var
14:52	Cozey	I use the slime-repl 20100404 snaptshot (I believe the one from technomancy repo) and swank 1.2.1
14:57	__name__	any comments on https://gist.github.com/846470 are very appreciated
15:12	amalloy	TimMc: slime is zomg amazing
15:13	amalloy	gives you autocomplete, documentation, jump-to-definition...
15:21	tomoj	__name__: minor comment: prefer (zero? x) to (= x 0)
15:21	amalloy	tomoj: damn, that was the only comment i had written down so far :P
15:22	amalloy	so i'll nitpick instead: "dividable" should be either "divides" or "divisble"
15:22	amalloy	er, divisible
15:22	__name__	amalloy: i already fixed that
15:22	__name__	:-)
15:23	__name__	but thank you very much
15:23	spewn	tomoj: What if there are (= 1 x) and (= 2 x) nearby? Any reason to not use (= 0 x) instead of (zero? x), since the former is easier to read in that context, in my opinion.
15:24	__name__	amalloy: tomoj: other than that? did I split the code into functions in a idiomatic way?
15:25	tomoj	if it's called 'divisible?' it seems like the arglist should be [x n], not [n x]
15:25	__name__	tomoj: [n x] makes sense for the partial …
15:25	amalloy	__name__: then call it divides
15:25	__name__	Ah
15:25	__name__	fair enough :)
15:26	amalloy	__name__: yes, more or less. i wouldn't split things up into so many small functions, but it's reasonable to do so while you're getting the hang of things
15:26	amalloy	and it's a style question anyway
15:27	tomoj	spewn: sure
15:28	__name__	amalloy: I had a big blob in the beginning
15:28	gfrlog	can clojure.test be used to test macros?
15:28	__name__	I did not like it
15:29	amalloy	gfrlog: i don't see why not
15:30	gfrlog	amalloy: I would think so too. My issues are probably from something else. Am keep looking...
15:32	__name__	is (defn partial-last [f & args] (fn [ & iargs] (apply f (concat iargs args)))) a good idea?
15:33	gfrlog	ah I think I know. Must be careful in macro not to emit list in place of vector
15:33	gfrlog	__name__: I've often wondered that myself
15:36	gfrlog	I feel like with (is) being a macro this test is getting muddled...
15:37	gfrlog	Does (is (= '(normal-fn arg1 arg2) (macroexpand-1 '(my-macro arg3)))) look right?
15:39	amalloy	depends. if your macro is recursive it won't capture the eventual output of the last call, just the first one
15:39	gfrlog	not recursive
15:40	amalloy	have you tried macroexpanding that outside of clojure.test to see whether the issue is with your macro or your use of clojure.test?
15:40	gfrlog	nope
15:40	gfrlog	But that's what I'll check out next
15:41	gfrlog	my normal tests that use the macro are passing now, so I bet it's my use of clojure.test
15:41	amalloy	huh
15:42	amalloy	(macroexpand-1 '(blah)) returns what you expect it to?L
15:42	gfrlog	yep
15:42	gfrlog	just did that as well
15:42	gfrlog	exactly matches the other half of my (is) statement
15:42	gfrlog	gimme a second and I'll show the failure message
15:43	amalloy	wait, even with namespace resolution? the macroexpanded version probably has (foo.core/somefn ...)
15:43	gfrlog	it doesn't I didn't use backquote at all
15:43	gfrlog	my macro just ends in (list 'fn-name ...)
15:45	gfrlog	http://pastie.org/1614319
15:45	amalloy	can you gist the macro as well as the error message? debugging-by-guessing is fun but hard
15:46	gfrlog	that's the error message, with real values replaced with simple ones. If we can't figure it out from that I'll bring in the real code
15:46	amalloy	gfrlog: hm. maybe (is) is quoting things too much
15:46	gfrlog	yeah I feel like I'm in some kind of swirly macro soup
15:46	amalloy	&(macroexpand-1 ''(a macro thingy))
15:46	sexpbot	⟹ (quote (a macro thingy))
15:48	gfrlog	the macro is just a testing helper, and I figured out what was wrong with it already, so it's not imperative that I actually make a working test-helper-test
15:50	gfrlog	I'm trying (let [expected ..., actual ...] (is (= expected actual)))
15:50	gfrlog	to see if pulling them out of (is) fixes it
15:51	gfrlog	dangit deftest is a macro too
15:51	gfrlog	I'm pulling it out of those as well :-\|
15:54	gfrlog	And it worked that way
15:55	gfrlog	the lesson here, as always, is don't write macros
15:56	devn	i dont know if the lesson is always not to write a macro
15:56	devn	i think it's more that you need to be more careful when writing them
15:58	gfrlog	devn: the lesson is that you can always conclude with an absolute statement
16:00	amalloy	gfrlog: you're always better off shouting your absolute statements!
16:03	gfrlog	amalloy: CAN I ASK A QUESTION IN ALL-CAPS?
16:14	zippy314	Emacs clojure-test-mode question: On my emacs if a test fails after doing C-c C-, it doesn't high-light the offending test. An thoughts on what I need to do to get that working?
16:14	gfrlog	so require looks for something on the class path even if the associated namespace has already been loaded through (load-string)?
18:06	gfrlog	I can't believe I only just discovered clojure.core/complement
18:07	tscheibl	,(doc clojure.core/complemen)
18:07	clojurebot	Titim gan éirí ort.
18:07	tscheibl	,(doc clojure.core/complement)
18:07	clojurebot	"([f]); Takes a fn f and returns a fn that takes the same arguments as f, has the same effects, if any, and returns the opposite truth value."
18:14	tscheibl	every time I am surprised how easy and comprehensible I can solve problems with Clojure that would have needed tons of voodoo magic in OOP (e.g. adapter classes, AOP, etc...) to get realized.. and nobody would understand how to use it
18:15	tscheibl	.. no rhickey didn't pay me for posting that ;)
18:25	joshua__	tscheibl, I felt the same way yesterday while goofing around with graphics. I'm still not sure whether it is that I've improved or if it has to do with the language.
18:37	tscheibl	joshua__: must be the language.. I fiddled around with C++ for about 20 years but never had a comparable feeling... not even with STL and Boost which really help a lot
18:40	tscheibl	... and Spring with Java was the pure horror... without tons of Eclipse plugins you wouldn't even had a chance of grasping what was going on in all that AOP insanity
18:42	tscheibl	..Scala felt a bit better though... but still too clumsy
18:42	tscheibl	ok.. I go to bed, bye
19:35	Arelius\|laptop	Why is it that I can never (require ...) on a package that (requires clojure.contrib.string), even if both are imported :as ...
20:49	joshua__	amalloy, would this work as a non-blocking server for the link processing we were talking about last week? Finally got around to writing it, I was busy with school and the like: https://gist.github.com/2f783f6c5c4478ed53e1
20:49	joshua__	blocking rather
20:52	joshua__	Someone else can answer too. I want to make sure I don't have to do anything special to get a blocking server-socket..
20:52	amalloy	hm
20:52	amalloy	well, it's close
20:53	joshua__	amalloy, 5 is close to 4 but it doesn't make it good answer to 2+2.. how close are we talking?
20:53	amalloy	your server socket is (correctly) spawning a new thread for each incoming request, but those threads read forever, as though the connection will never close
20:53	amalloy	so read-links should handle end-of-stream
20:55	amalloy	and you're let'ing out-writer but never using it
20:55	joshua__	amalloy, good point.. I made a mini app to test with and forgot to remove the extra code
20:57	amalloy	i didn't know about c.c.server-socket, though, so that's handy
21:05	joshua__	Does this fix the problem? https://gist.github.com/2f783f6c5c4478ed53e1
21:05	joshua__	Or do I have to call close on all of the streams for them to close?
21:06	joshua__	I know in C++ leaving scope will call close for me.. not sure about java.
21:07	joshua__	Nevermind.. It is working how I hoped it would at least.
21:09	joshua__	Thanks for all the help =).
21:11	Apage43	joshua__: for things that need to be closed you can use with-ope
21:12	Apage43	*with-open
21:12	joshua__	,(doc with-open)
21:12	clojurebot	"([bindings & body]); bindings => [name init ...] Evaluates body in a try expression with names bound to the values of the inits, and a finally clause that calls (.close name) on each name in reverse...
21:12	zippy314	,(doc map)
21:12	clojurebot	"([f coll] [f c1 c2] [f c1 c2 c3] [f c1 c2 c3 & colls]); Returns a lazy sequence consisting of the result of applying f to the set of first items of each coll, followed by applying f to the set of se...
21:17	amalloy	joshua__: the updated gist looks good as long as you don't mind opening a new socket for each link you want to process
21:18	amalloy	though closing the streams is definitely a good idea, with or without with-open :P
21:18	joshua__	So you have to do it manually>
21:18	joshua__	?
21:18	joshua__	It doesn't implicitly call close on itself when garbage collected?
21:19	brehaut	joshua__: when is it garbage collected?
21:20	joshua__	brehaut, I thought when it was no longer in scope it would no longer be referenced and that when it was no longer referenced it would be garbage collected
21:20	joshua__	brehaut, am I mistaken?
21:20	amalloy	joshua__: that's when it will become eligible for gc
21:20	brehaut	joshua__: that makes it eligible for garbage collection
21:20	amalloy	brehaut: ninja'd!
21:20	brehaut	its entirely up to the runtime/vm when it is actually collected
21:20	brehaut	hah
21:20	joshua__	Is there a big difference?
21:20	amalloy	huge
21:20	brehaut	joshua__: if you are eligible to vote
21:21	brehaut	have you actually voted?
21:21	joshua__	brehaut, .. how did you know..
21:21	joshua__	brehaut, alright adding some (.closes
21:21	amalloy	lol
21:22	amalloy	living in new zealand comes with psychic powers
21:22	brehaut	its all the fine quality coffee we drink
21:24	brehaut	joshua__: if you are used to a reference counted* language like python, garbage collection typically occurs as soon as the reference count drops (* caveats etc) to 0. with more sophisticated schemes such as the ones employed by the openjvm, collection is often postponed till later events
21:24	brehaut	the result is that in python say, if you are sloppy with closing your resources, you are less likely to be bitten by the bug than you are with a more sophisticated system
21:25	brehaut	joshua__: its absolutely worth your time doing some reading into the basics of the major GC models
21:26	joshua__	brehaut, alright. And it sounds like python is more sophisticated from my perspective ;p makes things easier on me haha
21:26	brehaut	haha it comes with a cost
21:26	joshua__	brehaut, have a good link?
21:26	brehaut	joshua__: i'll have a look, but not on hand
21:27	brehaut	joshua__: because of the granularity of pythons collector (small frequent runs), you trade some performance cost for a simpler algorithm and a (from certain perspectives) a more predictable* memory profile (* caveats!!)
21:28	brehaut	the jvm has a bunch of collectors and collector profiles
21:28	brehaut	so you cant just say 'its this'
21:29	brehaut	but if you were to make such an imprecise statement, you say something about it being mark and sweep and generations
21:30	brehaut	mark and sweep being the other major concept from reference counting, where the collector runs periodically and marks all the objects to determine if they are alive
21:30	brehaut	generational means that the runtime tracks how old an object is; young objects are checked for gc eligiblity more fruqently than old objects.
21:31	brehaut	and im failing to find a good resource to link you
21:32	ttmrichter	brehaut: You're missing copying collectors.
21:32	ttmrichter	In serious garbage collection nobody uses reference counting anymore because of its many problems.
21:32	brehaut	ttmrichter: im missing a bunch of stuff
21:33	ttmrichter	But copying collectors are a major family.
21:33	ttmrichter	The three major families are counting, mark/sweep and copying.
21:33	ttmrichter	Everything else (that I'm aware of) is some variation or combination of these three.
21:34	joshua__	The moment when the garbage is actually collected can be unpredictable, resulting in stalls scattered throughout a session. Unpredictable stalls can be unacceptable in real-time environments such as device drivers, in transaction processing, or in interactive programs. This unpredictability also means that techniques such as RAII, which allows for automatic cleaning up of resources (e.g. closing file handles, deleting tempora
21:34	joshua__	ry files, etc.), cannot be used, since the cleanup might happen too late. See the Determinism section for a detailed discussion.
21:34	joshua__	from wikipedia
21:35	ttmrichter	joshua__: There are real-time capable garbage collectors.
21:35	ttmrichter	Baker's treadmill, for example.
21:36	brehaut	that wikipedia summary is from the same school as my brief blather above: kinda useful from a high level and basicly completely wrong in practise ;)
21:37	ttmrichter	There is a book, sadly long out of print to my knowledge, called simply Garbage Collection that is a good "this is the state of the art" looking-over of the technology.
21:37	ttmrichter	Well, it was state of the art back in the late '90s anyway.
21:37	ttmrichter	Nowadays I just hunt down research papers. :(
21:39	ttmrichter	Here's a good starting point, though, for people curious about the topic: http://www.cs.kent.ac.uk/people/staff/rej/gc.html
21:40	ttmrichter	The bibliography is a killer there.
21:44	ttmrichter	And here's an example of a real-time garbage collector (generational in this case): http://citeseer.ist.psu.edu/viewdoc/download?doi=10.1.1.42.7791&rep=rep1&type=pdf
21:45	joshua__	ttmrichter, that guy is extremely comprehensive. He even covers garbage the band.
21:59	ttmrichter	joshua__: Yeah. He used to also point to civil sanitation resources as well. He's a bit of a jokester. :)
22:00	ttmrichter	And I just found out the book isn't out of print any more.
22:00	ttmrichter	I need to get myself another copy. (I misplaced my old one. By which I mean someone "borrowed" it and didn't return it.)
22:13	amalloy	python is reference-counted, really? doesn't that mean any circular references will never be collected?
22:14	ttmrichter	amalloy: Python is reference-counted with a backup mark/sweep.
22:14	ttmrichter	That backup mark/sweep was a later addition when Guido finally admitted that reference counting was a problem for real-world code.
22:15	amalloy	ah. so mark-sweep for correctness, ref-counting for some kind of optimization
22:15	ttmrichter	Where "optimization" is in quotes because ref-counting is actually less efficient in overall system performance than is even naive mark-sweep.
22:15	amalloy	sure sure
22:15	amalloy	it optimizes for something
22:15	amalloy	whether that something is desirable, i can't comment on
22:15	ttmrichter	Ease of implementation. New Jersey school of design. :D
22:17	pdk	for the record
22:18	pdk	consider that new jersey design philosophy is what brought us c++
22:18	pdk	:)
22:19	amalloy	pdk: something you don't like about c++? </troll>
22:23	ttmrichter	pdk: You make that sound like a bad thing. :)
22:27	zippy314	is there a way to specify what kind of map a defrecord should be based on, i.e. if you want it to be a sorted-map rather than a hash-map?
22:29	amalloy	zippy314: i'm pretty sure that doesn't make sense, as a thing to want
22:30	amalloy	the only reason to have a map sorted is so you can iterate through its keys in sorted order; the (main) reason to have a defrecord is so that you can access its fields quickly by name
22:33	zippy314	Hmm. I'm using defrecord as way of implementing protocols, i.e. as a way of doing pseudo inheritance, and it does seem to make sense that some versions of the protocol might want to behave as sorted maps and others not.
22:41	amalloy	i'm having a hard time imagining your use case
23:25	joshua__	,(doc create-server)
23:25	clojurebot	excusez-moi