#clojure – 2008-07-09

2008-07-09

00:50	Lau_of_DK	Top' of the morning Gents
00:55	hoeck	Lau_of_DK: good morning
01:32	Lau_of_DK	Gents, lets say I have an entire xml file loaded in zip/xml-zip format (trees with nested vectors I think) - How do I output this to an XML file in the easiet most fool-proof way ?
02:17	Lau_of_DK	Gents, lets say I have an entire xml file loaded in zip/xml-zip format (trees with nested vectors I think) - How do I output this to an XML file in the easiet most fool-proof way ?
02:47	hoeck	Lau_of_DK: (binding [out (new java.io.OutputStreamWriter (new java.io.FileOutputStream "my.xml"))] (xml/emit x))
02:51	Lau_of_DK	hoeck? Have you tried that approach? xml/emit here generates garbage output with data distortion and awful formatting
02:55	hoeck	yes, the formatting is bad, i have tested it on a very simple xml file
03:15	hoeck	Lau_of_DK: i forgot the (.close out)
03:17	lisppaste8	perspectivet pasted "loop-i-ness" at http://paste.lisp.org/display/63443
03:17	perspectivet	so I've been playing around with swt and clojure
03:19	perspectivet	I've been having some problems with the some of the basic functionality and I wondered if anyone had any ideas why my translation (pasted above) isn't working
03:21	perspectivet	(defn show-file ....
03:22	perspectivet	is supposed to be roughly a translation of the java snippet commented out above it
03:41	perspectivet	ah, boom
03:41	perspectivet	so if I do it simplistically it works
03:42	perspectivet	get rid of the doto's
03:42	perspectivet	just go up to a (. shell (open)) I get the expected result
03:43	perspectivet	oops
03:55	ktne	hello
03:55	ktne	does clojure have pattern matching?
03:57	perspectivet	in the haskell "case" sense of pattern matching?
03:57	ktne	i'm not familiar with haskell just with ocaml
03:57	ktne	match based on type and parameters
03:58	ktne	can you define for example multiple function bodies, one for each case?
03:58	ktne	*define
03:59	hoeck	ktne: no, it hasn't, it has only overloading on arity
03:59	ktne	ah
03:59	ktne	what about simple pattern matching, like a switch statement
03:59	ktne	does it have that?
04:01	hoeck	ktne: clojure has a `cond' clause, where one can check for several expressions
04:02	ktne	can you do something like this pseudocode: switch(shape) { case Rectangle(x1,y1,x2,y2): ; case Circle(x,y,radius): ; }?
04:04	hoeck	of course: (cond (rectangle? shape) (let [..] ) (circle? shape) ( ... ))
04:04	hoeck	but clojure has multimethods too
04:06	hoeck	with multimethods you are free to define you own dispatch functions
04:06	ktne	i'm reading about multimethods right now
04:07	hoeck	good :)
04:15	perspectivet	hoeck: found the problem I think
04:16	perspectivet	I'm a little unclear on let scope affects deallocation but I'm thinking that when the display goes out of the let scope it probably gets deallocated
04:17	hoeck	perspectivet: i tried your code, but nothing appears on my screen
04:17	ktne	how do i exit clojure repl? :)
04:17	perspectivet	Ctrl-d
04:17	ktne	thanks
04:17	perspectivet	since if I move display outside of defn I can at least get a window
04:17	perspectivet	hoeck: should i paste the new version?
04:18	hoeck	perspectivet: please
04:19	hoeck	perspectivet: i always read that one has to it own deallocation in swt
04:20	perspectivet	one has to do one's own deallocation?
04:21	lisppaste8	perspectivet pasted "less-loop-i-ness" at http://paste.lisp.org/display/63446
04:22	hoeck	oh, sorry, i mean the deallocation of the swt gui objects like buttons and so on
04:22	perspectivet	I'll have to read up on the top level containers like Display to see if that holds for them too
04:23	perspectivet	child objects of display are fine as long as display is not in a let
04:24	Lau_of_DK	hoeck: Even with (. close out) it still mangles the XML, like "Title" becomes " Title " with excessive whitespace and linebreaks
04:24	hoeck	perspectivet: i see, do you have prior experience with swt or are you trying it the first time?
04:25	perspectivet	1st time for both clojure and swt
04:25	perspectivet	how hard can it be? ;)
04:26	hoeck	^ ^
04:26	perspectivet	as in see above?
04:32	hoeck	Lau_of_DK: xml/emit looks very simple, e.g. it always inserts the `encoding=UTF-8' header as a plain string.
04:36	meredydd	Lau_of_DK: Are you using (println) and friends? They insert spaces.
04:36	meredydd	Eg: (println "I have" 1 "banana") --> "I have 1 banana"
04:36	meredydd	despite the fact that I didn't put spaces in there.
04:37	meredydd	whereas (str "I have" 1 "banana") --> "I have1banana"
04:39	hoeck	meredydd: emit uses (println (str ... ))
04:40	meredydd	Weird...
04:52	lisppaste8	perspectivet pasted "working-swt-snippet" at http://paste.lisp.org/display/63448
04:53	hoeck	perspectivet: your (second) sample works here!
04:53	perspectivet	it works somewhat, you still need the loop to be able to edit the text box
04:53	ktne	anyone here uses clojure with emacs?
04:53	hoeck	perspectivet: joy
04:53	ktne	i'm trying to use the clojure mode
04:53	perspectivet	ktne: I do
04:53	ktne	but it doesn't work
04:53	ktne	i've loaded clojure-mode.el
04:53	hoeck	ktne: me too
04:54	ktne	but the menu items are not bound to anything
04:54	perspectivet	menu items, what are those? ;)
04:54	perspectivet	no menus on my emacs...
04:55	ktne	hmm
04:55	ktne	it looks like i had to rename my clojure script to lisp
04:55	ktne	clojure-mode calls lisp command
04:55	ktne	it works now :)
05:07	lisppaste8	perspectivet pasted "more useful text swt snippet" at http://paste.lisp.org/display/63449
05:07	perspectivet	this one does multi-line
05:26	Lau_of_DK	meredydd Im using (str xxx) for passing new children when compiling the modified tree, and then I emit that tree in a (with-out-str) nest
05:32	hoeck	perspectivet: no window on my machine, something weird with scope is going on there
05:40	meredydd	Hey, this is a good one
05:40	meredydd	java.lang.VerifyError: (class: clojure/fns/verdi_router/handle_connection__27590, method: invoke signature: (Ljava/lang/Object;)Ljava/lang/Object;) Inconsistent stack height 0 != 1
05:40	meredydd	java.lang.VerifyError: (class: clojure/fns/verdi_router/handle_connection__27590, method: invoke signature: (Ljava/lang/Object;)Ljava/lang/Object;) Inconsistent stack height 0 != 1
05:40	meredydd	I think I may have stumbled upon a compiler bug.
08:35	Chouser	meredydd: example?
11:37	ktne	hello
11:37	Chouser	ktne: hi
11:37	ktne	anyone using the enclojure plugin for netbeans here?
11:38	ktne	hi Chouser
11:38	Chouser	there's an #enclojure channel
11:38	ktne	ah
11:38	Chouser	I've dabbled with enclojure, but probably not enough to answer any questions.
11:38	ktne	thanks
11:54	la_mer	ktne: I'm using it daily at this point
12:23	ktne	anyone here who can tell me how to create an enclojure project?
12:23	ktne	i already have a source file
15:19	rhickey	hi all
15:19	Chouser	rhickey: how's it going?
15:19	Chouser	rhickey: did you speak today?
15:19	rhickey	Good, except the connectivity at ECOOP is not that great, so I've been offline a lot
15:19	rhickey	I spoke Monday and yesterday - both went well
15:20	rhickey	wanted to thank every for carrying the ball here and on the group in my absence
15:20	rhickey	nice to see this community growing :)
15:21	Lau_of_DK	Hey rhickey, have you been out prepping new screencasts?
15:21	rhickey	I got one of the two, on the other the screencasting sw didn't capture
15:22	rhickey	but I'll probably hold off on that as I'm going to do a similar talk in Sept to the Boston Lisp Group
15:22	cemerick	There's a variety of new people here and there -- I personally know two developers that are using Clojure on small projects.
15:23	rhickey	cemerick: I'm definitely going to follow up on the gen-class load time issue when I get back
15:23	abrooks	rhickey: Oh, cool. When and where for the Boston talk?
15:23	Lau_of_DK	rhickey: ok sounds great
15:23	rhickey	Boston Sept 29th at MIT
15:23	abrooks	rhickey: I assume that's open to the public?
15:23	Lau_of_DK	Uuuuh MIT
15:23	Lau_of_DK	The pressure is on
15:23	cemerick	rhickey: you mean the "recursive" classname reference bit? That'd be great.
15:23	rhickey	abrooks: yes, probably pre-reg so you get dinner
15:24	cemerick	That would allow me to cut out a bunch of little workarounds in our build/test process.
15:24	Chouser	seems like we have a pretty deep bench, even if none of us have particularly intimate knowledge of things. A few people around to answer some questions, just about any time apparently.
15:24	abrooks	rhickey: Good to know, thanks!
15:24	rhickey	cemerick: that and the perf issue
15:24	rhickey	Chouser: yes, that's been fun to see
15:25	rhickey	Having seen some presentations here I can tell you all that in using Clojure you are on the forefront of the multi-core oriented future
15:25	cemerick	rhickey: Excellent. I'd love to hear what you think is going on with the initialization performance -- I'd worried that I was on a wild goose chase, there.
15:28	Lau_of_DK	Chouser: Did you see my posts about that xml/emit bug earlier today?
15:29	Chouser	Lau_of_DK: I did. I think you're right -- xml/parse and xml/emit both play a bit fast and loose with XML standards regarding whitespace
15:29	Lau_of_DK	oh okay, i'll just write a custom emitter then
15:30	Chouser	I don't how much code out there relies on current behavior, but I'll look at adding some options for my lazy-xml stuff to be a bit more strict.
15:30	Lau_of_DK	Just wanted to make sure, that it wasn't because I was using all 10 thumbs when writing the code
15:30	Chouser	I think if you just take a copy of emit but without any \n, you'll be ok.
15:31	Chouser	You'll have lost any whitespace on the parse side, but at least you won't include incorrect whitespace during emit.
15:31	Lau_of_DK	That would one step better than what I've got now. Internet Explorer reads the xml file just fine, but xml/parse doesnt even recognize it as xml
15:32	Chouser	huh.
15:33	Lau_of_DK	It doubles on \n in the output file, and "Title" becomes " Title "
15:54	perspectivet	so I've translated an swt snippet to clojure, but the loop section is kind of gross
15:54	perspectivet	any ideas on how to clean it up?
15:54	perspectivet	http://paste.lisp.org/display/63449
15:56	erochester	you could use (do ...) instead of (let [] ...)
15:56	perspectivet	ah, right
15:56	perspectivet	just read about do actually
15:57	Chouser	(when-not ...) instead of (if (not ...))
15:58	Chouser	you can drop a set of parens on each method call, either (.sleep d) or (. d sleep) for example
15:58	perspectivet	here let me paste the newest working version
15:58	Chouser	same for doto as well, I think: (doto s pack open)
15:59	perspectivet	yeah, you're right. don't know why I did it the way i did
16:03	lisppaste8	perspectivet pasted "cleaned-up-swt-translation" at http://paste.lisp.org/display/63468
16:04	perspectivet	much cleaner
16:06	Chouser	I'm sure there would be some torturous way to replace loop with take-while, map, etc... but I really don't think it would be clearer or better for what is an inherently non-functional API.
16:07	perspectivet	yeah, my thinking also
16:11	slava	when writing guis in a functional style you want to use something like the builder pattern...
16:12	slava	instead of passing the parent widget to the child's constructor, have the parent constructor take &rest args
16:13	slava	and replace setters with a map that you pass in
16:13	cemerick	We're biting the bullet and just using Netbeans/Java for our UI. It's decidedly "non-core", so we're going to do it wrong from the start. ;-)
16:14	Nafai	slava: Sounds nice.
16:15	slava	something shoes would work well in clojure i think: http://code.whytheluckystiff.net/shoes/
16:15	slava	especially since most of the hard work is done for you by swing
16:15	Nafai	Swing is painful at times :)
16:16	slava	or swt or whatever the flvaor of the month java gui is :)
16:16	Nafai	That's my day job right now, developing a Swing component
16:16	slava	msut be a big component if that's your entire job :)
16:17	Nafai	It's a fancy grid / table component
16:18	perspectivet	isn't swing performance still kind of lacking these days? at least compared to swt?
16:19	Nafai	I haven't found such; I used to use SWT at my last job.
16:20	perspectivet	how's the native look-n-feel these days? It was pretty bad last time I looked?
16:20	slava	from what i've seen lately, swing is starting to look more native than swt :)
16:20	slava	swt needs a big overhaul on os x to convert it from carbon to cocoa
16:21	perspectivet	that's underway though from what I've seen
16:21	perspectivet	Nafai: so you think swing is the way to go for a graphics heavy java app?
16:22	slava	what is swt's story when it comes to opengl?
16:22	slava	is it supported as well as swing?
16:22	perspectivet	with jogl panels and such
16:22	slava	good
16:22	perspectivet	http://www.eclipse.org/swt/opengl/
16:24	Nafai	perspectivet: I'm not sure how I feel. Both of the choices for SWT/Eclipse and Swing were handed down from up-above.
16:24	Nafai	An advantage of Swing is there are a lot more 3rd party things
16:27	perspectivet	You don't need to ship swt jars either
16:27	perspectivet	which is nice
16:46	jgrant	in the context of thread local variables...
16:46	jgrant	I've tried 2 approaches
16:47	jgrant	the first being (def x) (binding [x ...]) (set! x ...)
16:47	jgrant	this works but i know that this apparently not idiomatic of clojure
16:47	jgrant	winks about the exclamation in set!
16:48	jgrant	the other is (with-local-vars [x ...] (var-set x ...) (var-get x ...) )
16:48	jgrant	this second approach is very tedious
16:49	jgrant	and exceptions are thrown a local var is access but not yet set meaning even more exception handling code
16:49	jgrant	is there another less verbose way to handle thread local variables ?
16:50	Chouser	you want to mutate the variable, not just stack bindings I guess?
16:50	jgrant	i do not need to mutate the root var just looking for thread isolation
16:51	jgrant	(def x ...) is not thread-safe obviously from what i have seen
16:53	Chouser	I think your first form is actually correct.
16:54	Chouser	(set!) is documented for thread-local bindings: http://clojure.org/vars
16:54	Chouser	I think the exclamation is to signal mutation, which indeed is happening within the thread.
16:55	jgrant	yea it's much cleaner but i recall rich saying the set! should never be necessary in one of his talks but i'm not sure how else to do this ?
16:56	jgrant	doing var-get on everything is ugly and error prone
16:56	cemerick	Am I wrong in thinking that binding does exactly this?
16:56	cemerick	...exactly what you want, I mean. :-/
16:56	jgrant	does what ?
16:57	cemerick	"Bindings created with binding cannot be seen by any other thread." http://clojure.org/vars
16:57	jgrant	yes i set! works and it's cleaner but why would rich mark it with the exclamation ?
16:57	jgrant	yes bindings are thread local
16:58	jgrant	what is dangerous about set! if it's only modifying a thread local variable ?
16:58	cemerick	jgrant: Oh, because mutation like that is Bad (tm).
16:58	jgrant	why is it bad ?
16:58	erochester	jgrant: Chouser's right. The exclamation just signals that the function mutates something. It's a convention from scheme and other lisps.
16:59	erochester	i think bad = makes concurrency hard, and isn't a functional way of approaching a problem
16:59	cemerick	jgrant: It's a stylistic indication that if you're using set!, you're probably not taking advantage of other, cleaner primitives.
16:59	jgrant	cemerick : have you tried using (with-local-vars (var-set ...) (var-get)) in thread safe code ?
16:59	jgrant	what are those 'cleaner primitives' ? (I've asked a few times now)
17:00	cemerick	jgrant: I've not personally used with-local-vars, no.
17:00	jgrant	cemerick : (withlocal-vars) is hardly clean
17:00	jgrant	it turns my code into an eyesore
17:00	cemerick	an example of a cleaner primitive: set! is often used to manage state within a loop, etc. It's far better to use loop/recur in that scenario.
17:01	Chouser	set! will throw an exception when used without a thread-local binding. I think it's safe and valid.
17:01	jgrant	loop/recur has nothing to do with thread-local vars
17:01	Chouser	You shouldn't be doing any mutation at all if you can help it, but if you must, I think using set! within a thread isn't particularly bad.
17:01	jgrant	Chouser : i agree
17:02	cemerick	jgrant: strictly speaking, no, it has nothing to do with thread-locals, but in the case of iterative processing, loop/recur is way better than doseq/dotimes + set!.
17:02	Chouser	jgrant: you're sure you need to mutate, and can't use recursion or stacks of binding calls or anything?
17:02	jgrant	cemerick : how specifically is loop/recur better than doseq/dotimes + set! ?
17:02	jgrant	anyone care to define better ?
17:03	Chouser	no mutation.
17:03	Chouser	with loop/recur, a local gets it's value at the top of a block, and then doesn't change until the block is done
17:03	jgrant	if this was common lisp then i wouldn't be asking the question ;-)
17:03	erochester	common lisp isn't really a functional language :)
17:04	cemerick	jgrant: the same way using foreach over an enumerable is better than iterating through it manually with counters in C#/Java -- more idiomatic, and there's the small bonus of having no side-effects
17:04	jgrant	in real life no 100% pure functional language works
17:04	Chouser	with any kind of mutation (including set!) you have to scan through all depths of the code indentation, and possibly even within called functions to see who might be calling set!
17:04	jgrant	cemerick : your're assuming that what is being modifed needs to be looped over but in many cases it does not
17:05	cemerick	jgrant: Yes, I was citing one example.
17:05	Chouser	I don't think there's a real argument to be had here. set! is provided for thread-local bindings because it is needed sometimes.
17:05	jgrant	Chouser : thanks that's what i needed to know ;)
17:05	cemerick	Chouser: agreed, it's a handy backdoor for those very, very rare cases
17:05	Chouser	Often mutation (using set! or def) is done when it would be better not to.
17:06	erochester	it's handy for global parameters, like common lisp uses dynamic variables.
17:06	Chouser	Clojure provides one or two "backdoors" compared to a purely functional language, but it provides a whole pile of features to make it easy to avoid mutation entirely.
17:07	Chouser	jgrant: if you're willing, it'd be interesting to see your use case. Maybe somebody can come up with solution that is syntactically cleaner than set! or var-set, and also mutation-free.
17:51	ericthorsen	Is there a shortcut for (apply merge (;sequence of maps))? Similar to vec and vector?
17:53	ericthorsen	nevermind...(reduce conj maps)
18:29	jgrant	Chouser : the use case is really a thread that generates a string based on some variables (i.e. it looks up values in a hash map) so there really is no looping
18:31	jgrant	most important is that the variable that stores the string is thread local and that it can be modified over and over as the string is being generated and then finallly return
18:33	jgrant	using with-local-vars and var-set var-get turns this into very verbose code
18:37	slava	tomhickey_: are you related to rich? :)
18:38	tomhickey_	slava: yes, he's my brother
18:38	slava	cool
18:38	jgrant	tom : are you also involved in the clojure implementation ?
18:39	slava	will you guys start a company Hickey & Hickey LLP to commercialize Clojure? :)
18:40	tomhickey_	jgrant: no. but i do develop with it
18:41	tomhickey_	slava: =) that's all in Rich's hands
18:42	jgrant	tomhickey : cool, tom do you have any advice for me on my use case above ?
18:44	tomhickey_	jgrant: i wish. i think Chouser and cemerick provided much more help then i would be capable of
18:45	jgrant	tomhickey : thanks yea they did
18:47	StartsWithK	Why i can't get function medadata this way? (defn x [a] (println a)) (def get-meta [f] (meta (var f))) (get-meta x) But (meta (var x)) outside of a function works.
18:48	jgrant	slava : it's my understanding that rich will keep clojure open it's currently under the CPL v1.0
18:49	jgrant	http://www.opensource.org/licenses/cpl1.0.php
18:53	jgrant	looks like this has gone up recently --> http://clojure.org/state
18:53	jgrant	(i dont remember it being there before)
18:57	jgrant	the last sentence on that page says this : "In the local case, since Clojure does not have mutable local variables, instead of building up values in a mutating loop, you can instead do it functionally with recur or reduce."
18:57	jgrant	So the question is what if the mutation is not in a loop ?
19:04	Chouser	jgrant: you might consider using the StringBuilder class.
19:05	Chouser	But that's really just another form of the same "cheat", shoving the mutation down into a Java.
19:05	jgrant	yes that is something i'm considering
19:06	Chouser	So you're doing a lot of (set! foo (str foo "bar")) ?
19:07	jgrant	yes
19:08	Chouser	so you append "bar" and "alice" and "cindy". You might consider (str "bar" "alice" "cindy") instead.
19:08	Chouser	(yes, I realize this is a drastice over-simplification that might be hard to implement)
19:08	jgrant	and if there is logic between "bar" "alice" and "cindy" ;)
19:09	jgrant	Chouser : but thanks i see where you're going with this
19:10	jgrant	maybe i can convince rich to take the exclamation out of set! ;-)
19:10	Chouser	right. (str (let [...] ... (apply str (map ... "bar"))) "alice" (reduce ....))
19:10	jgrant	after all set! is for thread local variable modification it does not modify the root context
19:11	Chouser	I really think the ! just indicates mutation. The ruby standard library is full of methods differentiated by ! for whether they mutate their object or not.
19:11	jgrant	Chouser : you are right by those are methods on classes and set! is a function/macro
19:11	jgrant	so slightly different meaning
19:12	Chouser	well, if you say so. It seems to me they both indicate that the thing their operating on will return a different value afterward than they did before.
19:12	jgrant	Chouser : yes you're right
19:12	jgrant	but why dont we have def! or var-set!
19:12	jgrant	?
19:12	jgrant	(in clojure)
19:13	jgrant	;)
19:13	jgrant	even more of a reason for def! because it modifies variables that are not thread local
19:15	Chouser	indeed. but you're not supposed to use def anywhere much.
19:15	Chouser	bathtime for kiddos. bbl
19:16	jgrant	again it is necessary in apps that aren't threaded but have the same requirement as we've covered above with string building.
19:16	jgrant	Anyone raise your hands if you're ok with def or set! being removed from clojure ;-)
19:18	jgrant	yes we all agree imperative programming is 'evil' but a 99% functional 1% imperative language is still necessary for building real-world apps
19:26	jgrant	especially since clojure is built on java and takes advantage of existing libraries.
19:29	meredydd	jgrant is right, I think, about the exclamation point - it's intended as a "whoa...are you sure this is necessary?"
19:29	meredydd	I think you're dead wrong about state, though :)
19:30	jgrant	meredydd : how would you solve the problem described above with conditional string building ?
19:30	meredydd	looks
19:30	jgrant	(in a purely functional manner)
19:30	meredydd	What's the problem?
19:31	meredydd	(sorry, didn't grok what you were trying to say)
19:31	meredydd	could you state it again?
19:31	jgrant	sure...
19:31	jgrant	...a thread is generating a string stored in a thread local variable based on some conditions
19:32	meredydd	ah, and this is assumed?
19:32	jgrant	there's lots of concatenation going on
19:32	meredydd	Because if you're taking, as your starting assumption, that there is:
19:32	meredydd	a) a thread, operating sequentially
19:32	meredydd	b) storing its results in a thread-local variable
19:32	jgrant	ok lets use a real world example
19:32	jgrant	a web server
19:32	meredydd	...then yes, you're going to end up requiring imperative programming, because you've already assumed it :)
19:32	jgrant	we dont want to send all client the same payload right ?
19:33	jgrant	ok then do you have another solution ?
19:33	meredydd	Okay...what parts of a web server?
19:33	meredydd	Well, depends what the string generation is trying to do.
19:33	jgrant	servicing a request
19:33	jgrant	and returning a payload
19:33	jgrant	it's a dynamic payload based on params passed in to the server
19:33	meredydd	Uhh...so, to put it another way, the payload is a function of the request and its parameters? :)
19:33	jgrant	very simple
19:34	jgrant	yes
19:34	jgrant	ever used a function (in a mathematical sense) that modified a paramter ?
19:34	jgrant	it's very common
19:35	meredydd	So, generally speaking, you'll want to write a function which takes the request as a parameter, and returns the response.
19:35	meredydd	Really, jgrant? Give me an example.
19:35	jgrant	so everyone states i'm wrong (which i have no problem with) but no one has a solution yet ?
19:36	meredydd	It's difficult to have a discussion, when what you're essentially saying is "I need to do <procedural programming implementation technique>, so I need to use procedural programming!"
19:36	jgrant	is that what i'm saying ?
19:36	meredydd	My hunch is that whatever underlying problem you're solving can also be decomposed in a functional way.
19:37	jgrant	i'm open to any solution presented in fact i would love a purely functional solution instead
19:37	meredydd	For example, by the time you're thinking "servicing a request" = "generating a thread-local variable in another thread", then you've already committed yourself to a procedural approach.
19:37	meredydd	So, present the problem :)
19:37	jgrant	ok forget the thread-local variable
19:37	meredydd	What does this web-server need to do?
19:39	jgrant	commonly what you already described, i.e. serve a payload based on incoming parameters
19:39	jgrant	what most web servers do
19:39	meredydd	okay...in that case, I'd do something like:
19:39	jgrant	mereydydd : have you looked at web server implementations in functional langauges ?
19:39	meredydd	main loop:
19:40	meredydd	(loop [] (let [s (. my-server-socket (accept)] (new Thread #(handle-connection s))) (recur))
19:41	jgrant	yes that's not the problem though
19:41	jgrant	is generating the payload in the thread that's a problem
19:41	meredydd	(defn handle-connection [s] (.write s (generate-response (read-request s)))
19:42	meredydd	[note that I'm hideously mangling the ServerSocket API here - because of how Java works, there's a bunch of (.getOutputStream) and friends needed, but they don't affect the main point)
19:42	jgrant	now we're going somewhere, and what would generate-response implementation look like ;)
19:42	meredydd	okay, fudging the generation of a filesystem path from a request (which I think you'll agree is pretty easy to do as pure-functional):
19:43	jgrant	not concerened with any of that stuff
19:43	jgrant	it can all be handled purely functional
19:43	jgrant	it's generating the payload i.e. string concatenation
19:43	meredydd	(defn generate-response [file-path] (let [finp (new FileInputStream file-path my-response (read-all-from finp)] my-response))
19:43	jgrant	how would you do it without def or set! ?
19:44	meredydd	What kind of string concatenation are you after?
19:44	jgrant	aha !
19:44	jgrant	that would just load a static file form the filesystem
19:44	jgrant	i'm talking about generating a dynamic response
19:44	meredydd	yeah...you asked for "what a web-server normally does"
19:44	meredydd	All right...what do you want it to do?
19:45	jgrant	let's say you have a template
19:45	jgrant	and values that will be used to populate it ?
19:45	meredydd	(defn generate-response [request] (str "<html><body>Hello, " (:name request) "</body></html>")
19:45	meredydd	the "template" there is in S-expressions
19:45	jgrant	how would you make parts of the template conditional ?
19:46	meredydd	(defn generate-response [request] (str "<html><body>" (if (:name request) (str "Hello, " (:name request)) (str "Enter your name: <input name='name'...")) "</body></html>")
19:47	meredydd	That part's conditional on whether you specified a :name parameter (assumed to be grabbed from the HTTP params)
19:47	meredydd	If you wanted to load the template from a file, you could do something like:
19:48	jgrant	now what if the request needs to be 'cleaned' before being used ?
19:48	jgrant	where is that stored ?
19:48	meredydd	'cleaned' how? Shall we just say a functional cleaning?
19:49	jgrant	validation of incoming params
19:49	meredydd	(defn generate-response [dirty-request] (let [request (clean dirty-request)] ...code here...))
19:49	jgrant	decoding of values passed in
19:49	meredydd	Ah...and now I understand what you mean by "changing the arguments".
19:49	jgrant	and is let thread-safe ?
19:50	jgrant	from what i understand let is not
19:50	meredydd	"mu."
19:50	meredydd	(let)-bound variables are lexical, and never change value.
19:50	meredydd	*lexically-scoped.
19:50	meredydd	ahh...here's our confusion.
19:51	meredydd	My assumption here is that (clean) doesnt' modify the "request" object.
19:51	meredydd	because the request object is immutable.
19:51	meredydd	Instead, what it does is return a new "request" object, whose value is a cleaned-up version of its argument.
19:51	meredydd	This is how the Clojure collection functions work, as well. For example:
19:52	meredydd	(let [a {:name "meredydd} b (assoc a :name "jgrant")] (println "a:" a "b:" b))
19:52	jgrant	i see
19:52	meredydd	prints "a: {:name "meredydd"} b: {:name "jgrant"}"
19:53	meredydd	the value of "a" never changes - (assoc) just returns an immutable map which differs from the immutable map it was passed only in the value bound to the key :name.
19:53	jgrant	so we trade memory for going purely functional (which is what rich described on the state page of clojure.org)
19:54	jgrant	now in a large web server we end up using LOTS of memory the more clients we have connecting
19:54	meredydd	As a rule of thumb, when your procedural experience tells you "I need to change the value of this variable", The Functional Way is "I need to declare a new variable which is some function of the value I currently have"
19:54	meredydd	Aaah...yes. And this is where persistent collections come in.
19:54	meredydd	For example, if I did:
19:54	meredydd	(let [a {:name "meredydd" :data <lots-of-big-ugly-data>} b (assoc a :name "jgrant")] (println "a:" a "b:" b))
19:55	meredydd	the value of "b" shares its memory storage of <lots-of-big-ugly-data> with "a".
19:55	jgrant	'persistent' being a euphemism for imperative then ;)
19:55	meredydd	nope.
19:55	meredydd	so you've only allocated enough new memory for the new "name" value
19:55	jgrant	persistent objects are mutable correct ?
19:56	meredydd	Nope. Immutable.
19:56	meredydd	b is immutable, as is a.
19:56	jgrant	then they cannot be changed
19:56	meredydd	correct.
19:56	meredydd	But when you create b, using a as your argument to (assoc), you re-use as many bits of "a" as you can get away with.
19:57	jgrant	so we use more memory
19:57	meredydd	(and you can get away with a lot - because the value of "a" won't change, you can re-use all its data structures!)
19:57	joubert	well, if you want to store more information you need to use more memory, no?
19:57	jgrant	why when it's just a modified copy
19:58	jgrant	?
19:58	meredydd	jgrant: That's the point - you don't. You only allocate enough new memory to hold the new entry you just created (in this case, ":name --> 'jgrant'")
19:58	meredydd	It's not a "copy", like you're thinking of.
19:58	jgrant	if i have 32GB of data and use functional approach instead of the 'evil' imperative approach i could theoretically have to use 64GB instead
19:58	meredydd	Hold on one moment
19:58	jgrant	maybe not to the programmer but to the machine it is a copy
19:59	meredydd	Other way round, actually - the programmer can treat it as a copy
19:59	jgrant	or at least a modified copy
19:59	meredydd	(which is why I explained it to you that way)
19:59	meredydd	but to the machine it's much more efficient than that.
19:59	jgrant	the point is the functional approach requires significantly more memory
20:00	dudleyf	The machine only has to keep track of the "diffs" between the original structure and the new one
20:00	meredydd	Yes, and I'm arguing that that point is incorrect.
20:00	jgrant	dudleyf : thanks
20:00	jgrant	hadn't heard that yet
20:00	joubert	jgrant: that is exactly what meredydd was saying :-)
20:01	meredydd	http://www.skrbl.com/79556388
20:01	meredydd	jgrant: I'm going to draw you a diagram.
20:01	jgrant	meredydd : thanks
20:02	joubert	(btw, there's also a great presentation at http://clojure.blip.tv about persistent, immutable data structures)
20:02	dudleyf	Rich has some interesting diagrams on how the data structures actually work in one of his presentations
20:02	dudleyf	:-)
20:02	meredydd	oh, that'd be marvellous, dudleyf.
20:02	meredydd	Cause this interactive-whiteboard app is really killing me.
20:03	meredydd	jgrant: Have you opened that link?
20:06	jgrant	meredydd : yes looking at it now
20:06	meredydd	okay. You see the map value "A" on the left?
20:07	jgrant	yes
20:07	meredydd	It has two entries, ":name --> meredydd" and ":data --> big-chunk-of-data"
20:07	meredydd	it contains pointers to each entry
20:07	jgrant	right
20:07	meredydd	(and yes, I know how rich actually does this...this is a simplification, because the implementation details aren't important at this stage)
20:07	jgrant	sure
20:08	meredydd	Now, what that (assoc) function does is to make a new entry, for ":name --> jgrant"
20:09	jgrant	is see
20:09	meredydd	Now, it creates a map value "B", and puts in the pointers I'm drawing in red.
20:09	meredydd	So, A is still immutable - I haven't changed the value of any existing variable.
20:10	meredydd	But at the same time, what I have is a map that uses the same chunk of RAM to store our BIG_CHUNK_OF_DATA
20:10	jgrant	so A is updated with the existing values in A and the new ones in B ?
20:10	meredydd	but has a different value for the :name key.
20:10	meredydd	A isn't touched at all.
20:10	meredydd	There's no "updating">
20:10	jgrant	so how then is :name resolved correctly ?
20:10	meredydd	All I did was create a new map, with the pointers in red.
20:10	meredydd	Well...
20:11	Chouser	in the webserver example, A would be the uncleaned parameters, B might be the cleaned ones.
20:11	jgrant	ah i see
20:11	meredydd	If I look up :name in A, it'll look down the blue pointers and find the blue entry
20:11	Chouser	If you want the cleaned ones, you look them up in B instead of in A.
20:11	meredydd	thanks, Chouser.
20:11	Chouser	meredydd: using skrbl looks like a lot of work. ;-)
20:11	meredydd	Chouser: You don't say.
20:12	jgrant	but i have 2 refs now
20:12	meredydd	uhh...
20:12	meredydd	better use a different word - "ref" has a specific technical meaning in clojure.
20:12	meredydd	you have two bindings, yes.
20:13	Chouser	one other little point -- if you stop using the uncleaned params (A), the JVM reclaims that memory (the little bit where :name->"meredydd" was stored) and it gets used for something else.
20:13	meredydd	Chouser: I was just about to explain that :)
20:13	jgrant	so each time a modify something i have to deal with a new ref
20:13	jgrant	binding
20:13	jgrant	;)
20:13	meredydd	jgrant: Yes. As I say - when imperative stuff thinks "I need to change this value"
20:13	Chouser	jgrant: only if you want to. Do you want the cleaned ones? use those. The new object has new meaning.
20:14	meredydd	functional stuff thinks "I need to make a new variable, with a slightly-changed value"
20:14	jgrant	yea just thinking in my specific case
20:14	jgrant	if i modify something x number of times then i have x number of bindings
20:14	meredydd	yep.
20:14	jgrant	x1 x2 x3 x4 etc etc etc
20:15	jgrant	simply because i cannot rebind the new value to the existing symbol
20:15	meredydd	That's just a style thing. You actually don't need to do that many changes in sequence, under most circumstances.
20:15	Chouser	yes, but there are library of functions to make such multi-step "modifications" less necessary.
20:15	meredydd	If you find yourself doing that, you generally ought to look and see if you can do it more simply.
20:15	meredydd	(or, as Chouser says, use a library function)
20:15	Chouser	another detail is that if you really really want to, you can use the same name for the new object:
20:16	Chouser	(let [a 1, a (+ a 2), a (* a 5)] a) would return 15
20:16	meredydd	jgrant: Also note that if you're doing: (let [x1 (do-something x) x2 (something-else x1) x3 (and-again x2)] (...do something with x3))
20:17	meredydd	jgrant: ...in that case, the virtual machine will notice that you're not using x1 or x2 any more, and deallocate them
20:17	meredydd	(I'm drawing on the diagram, in green, what that would mean in our example)
20:18	jgrant	yea i get that
20:18	meredydd	jgrant: So, you don't use the extra memory.
20:19	jgrant	so how would you do conditional assignment of vars ?
20:19	jgrant	i.e. some vars are only set if others have certain values
20:20	meredydd	(let [x (if (sky-is-blue) "blue" "not blue")] ...do something with x...)
20:21	meredydd	If you're used to working in a language with a ?: operator, like Java or C, you'll be used to this kind of thing
20:21	jgrant	yes that makes sense
20:21	meredydd	(the Java equivalent is: { String x = sky_blue()?"blue":"not-blue"; })
20:22	meredydd	except that, this being a functional language, we have much more powerful tools than ?:
20:23	meredydd	We can use (cond), for example, which is like a turbo "if-elseif-elseif-elseif" version of ?:
20:24	jgrant	yea my main source of confusion has been using existing Java libraries (3rd party) and trying to convert the example code to idiomatic clojure code
20:26	meredydd	ah, yeah. That's definitely a problem.
20:26	meredydd	My personal advice would be to practice with pure clojure code
20:26	meredydd	Get your functional kung-fu up to scratch - get inside the mindset.
20:26	meredydd	Then, once you understand both sides of the fence, you can bridge it efficiently.
20:27	jgrant	i'd love to but i'm set on using clojure right now while i'm coming up to speed , i'm blown away at how productive it is even while learning
20:27	meredydd	Otherwise, if you only know one side, you'll end up trying to write Java in S-expressions
20:27	jgrant	very true
20:28	meredydd	(which is all right as far as it goes - as you say, it's still a massive leap over plain Java - but you'll be missing out on a lot of the fun stuff too if you do that)
20:28	jgrant	so when does the O'Reilly clojure in a nutshell come out ;) ?
20:28	meredydd	In that case, if you can, try to keep your Java interface code neatly segregated into a few functions.
20:29	jgrant	well what i find is that even the kludgey code i have to come back and re-write usually doesn't take very long once i discover the right way
20:29	meredydd	:) yep
20:29	meredydd	I recommend you make a religious point of never, ever using (set!), until you're really comfortable with it.
20:30	meredydd	(set!) is a way of bending the rules, and once you get a feeling for the functional mindset (it won't take long), you'll have a good idea when to break the rules, and when there's a perfectly good functional way of doing it.
20:30	jgrant	i know set works with (binding [...]) does it also work with let or does the binding have to be mutable ?
20:31	meredydd	It has to be a (binding).
20:31	jgrant	ok good
20:31	meredydd	As I can't think of anything I've done in my last ten thousand lines of code that would need a mutable binding, I'm inclined to recommend you forgo them altogether until you're used to working with (let)
20:31	jgrant	meredydd : thanks alot for explaining all this
20:31	meredydd	np.
20:32	meredydd	Chouser helped a lot, too - that "diff" comment was a one-line version of something I'd been trying to explain for ten minutes :)
20:32	jgrant	Chouser : yea thanks too !
20:37	meredydd	Right.
20:37	meredydd	Anything else I can help you with?
20:37	meredydd	cause I've just come back from London, and am in the mood for a good night's sleep :)
20:38	jgrant	meredydd : thanks, i'm sure i will have some more questions but get some sleep.
20:38	meredydd	Okies.
20:47	Chouser	"diff" was from dudleyf, but thanks anyway!
20:47	jgrant	Chouser : but yea i owe you anyway ;)
20:49	Chouser	it's a hard transistion to make, so it's great you're willing to put in the effort.
20:52	jgrant	Chouser : i've spent too much time with CL
20:52	jgrant	it's bridging the java libs with clojure idioms that's getting me
20:52	Chouser	yeah, Java and its libs definitely push you toward mutable state
20:52	jgrant	but i must say there is a great community around clojure
20:58	Chouser	I think so too. I wonder how that happens. Some languages and projects just don't -- you ask the wrong question and you're treated like some kind of idiot.
21:03	cemerick	Chouser: is the archive you maintain of #clojure kept by a bot, or is that just your personal transcript of the channel?
21:04	Chouser	It's collected from the connection I speaking over right now -- irssi, not a bot.
21:04	Chouser	It's converted to HTML by a clojure program.
21:05	wastrel	what sort of background is typical for someone picking up clojure?
21:06	cemerick	Lau got me thinking about throwing together a proper clojurebot.
21:06	wastrel	i know a lisp bot
21:07	cemerick	yeah, there's a lot of them out there. I think using a bot programmed in a different language is a cop-out. :-)
21:07	Chouser	cemerick: sure -- I'd be happy to hook the existing HTML generation into a bot instead.
21:07	cemerick	There's sure to be a java irc lib floating around, so it shouldn't be too hard.
21:08	cemerick	Chouser: We'll see what happens. I'm on deadline for next Friday, so it won't happen until after then.
21:08	Chouser	yep
21:08	cemerick	too many side projects, absolutely no time :-)
21:09	Chouser	yep :-)
21:09	Chouser	I started peeking at the Java security sandboxing stuff so we could allow the bot to eval expressions for us ... but then I got distracted by something else.
22:40	jgrant	is there an easy way to convert an IPersistentList to a java Array ?
22:48	Chouser	yes
22:50	Chouser	to-array to get an array of Object
22:50	Chouser	into-array to get a more specific type of array
22:54	jgrant	thanks !