#clojure – 2008-02-20

2008-02-20

00:10	Chouser	I guess you just can't use #( % ) in macros.
14:15	ctp	hi - sorry if this has already been covered, but I am currently doing some work in clojure with lwjgl, getting opengl going etc. All going well at the moment, but I have one question: lwjgl uses static methods on the 'GL11' class quite a lot, and im ending up with lots of similar lines like: (. GL11 (glColor3f 1 1 1)), followed by more beginning (. GL11 ...) - I have tried the '(doto ..)' macro, but this only seems to work for instances... i guess my question
14:19	rhickey	cut off?
14:19	ctp	cut off?
14:19	rhickey	your question is?
14:20	ctp	ahh - sorry - too much text :)
14:20	ctp	basically, am i missing something, or is there a 'doto' alike for static methods on a class?
14:21	ctp	if not, gives me a good reason for a new macro.
14:21	rhickey	the idea behind doto is that all of the methods will somehow side-effect the object, for statics I presume you'll want the return values?
14:23	ericthor	(defn GL [& body] ~(.. GL11 ~@body))
14:23	ericthor	this would work no?
14:23	ctp	maybe -
14:23	rhickey	defmacro?
14:24	ctp	effectively i am typing (. GL11 (glBegin (
14:24	ctp	(. GL11 (glEnd))
14:24	ctp	over and over - so, yes, defmacro
14:25	ctp	just devising one now - just wanted to check that i wasn't reinventing something in the core
14:25	ericthor	I have an expression that is returning a vector i want to pass into recur using an apply (apply recur my-vector)
14:25	ericthor	sorry did not mean to step on this thread
14:25	ericthor	i'll wait......
14:25	rhickey	ctp: no, but if you think this is something for which there is a general solution, I'll consider adding something
14:26	ctp	ericthor: np - think im done - macro writing.
14:26	hoeck	hi, mhhh, i found out that you cannot bound a static class to a variable in a let
14:26	ericthor	enjoy!
14:26	ctp	rhickey: thanks - let you know
14:27	hoeck	something like (let [a java.lang.Math) (. a (sin 1) does not work
14:27	rhickey	ericthor: can't apply recur - it's not a fn
14:27	ericthor	i know...
14:28	ericthor	i can rearrange...lots of options
14:28	rhickey	hoeck: dot (.) has special handling of its arguments, so not a function call
14:28	ericthor	but i wanted to call apply on recur :)
14:30	hoeck	ok
14:30	rhickey	Math is auto-imported, so no need for java.lang
14:31	hoeck	i have another question, are nested `sync' s a problem ?
14:31	rhickey	also check out tiny math lib: http://groups.google.com/group/clojure/browse_frm/thread/d07b93e26b2f0f06
14:32	rhickey	nested syncs belong to same (parent) transaction
14:35	hoeck	so they are just noise to the compiler?
14:35	hoeck	thanks, i already use math.clj :)
14:35	rhickey	which are noise, nested syncs?
14:36	hoeck	yes, are nested syncs ignored?
14:37	rhickey	I prefer to think that they participate in any enclosing transaction. While you may not write nested syncs in a lexical scope,
14:37	rhickey	you may end up with them when a larger transaction calls code that was written independently to be transactional
14:44	hoeck	okay, i was just thinking wether macros that use sync to wrap arbitrary code should care about syncs in that code
14:46	rhickey	they don't need to care, otherwise I think it would be unmanageable to compose code
14:50	hoeck	i was just expecting that, i asked just to be shure
14:50	rhickey	it should be fine
14:52	hoeck	btw, thank you for your work on clojure, i _really_ enjoy programming in/on clojure
14:52	rhickey	you're welcome!
14:57	ctp	rhickey: this macro seemed to do the work: (defmacro do-static [class & methods] `(do ~@(map (fn [m] (list '. class m)) methods)))
14:57	ctp	(lost formatting there... ;))
14:58	rhickey	so these static methods all have side effects?
14:59	ctp	yes - they are basically calling gl functions under the covers, afaik
14:59	ctp	for example, the lwjgl has a 'Display' class
15:00	ctp	on which you call 'Display.setFullscreen(false); Display.create()' etc...
15:00	ctp	which, in clojure, looks like: (. Display (setFullscreen false)) (. Display (create))
15:01	ctp	naturally, there are quite a few static methods - this seems to be the way it is implemented. only started playing with it today, so it is entirely possible i am wrong...
15:02	ctp	but clojure is very nice so far.
15:02	rhickey	I'm thinking it might be called in-scope
15:02	ctp	yes - seems like a better name
15:02	rhickey	but most imperative things begin with 'do'
15:02	ctp	i was thinking of Haskell's 'do', yes...
15:03	ctp	i'm not happy with 'do-static' - maybe 'do-with-scope' or alike?
15:03	ctp	its very close to 'doto' in implementation
15:04	rhickey	yes, Clojure has doto, dotimes, doseq, dorun, doall
15:04	rhickey	no dashes so far
15:04	rhickey	doscope?
15:04	ctp	sounds good to me
15:07	ctp	not sure how many java libraries use extensive statics, really. and 'doto' already exists for instances, so its probably of limited use.
15:07	rhickey	statics just for side-effects I think is rare
15:08	ctp	lots of cases of retrieving static symbols in lwjgl too: (. org.lwjgl.opengl.GL11 GL_QUADS)
15:08	ctp	im coming from GL in c/c++ - but the java lwjgl design does seem odd.
15:09	ctp	oh well - it was fun writing the macro! thanks for the help.
15:09	rhickey	sure
15:09	ctp	sure beats CFFI + SBCL so far...
15:10	rhickey	having java libs opens up a huge world
15:11	ctp	i'll continue my exploration. thanks again!
15:23	jgracin	when there are two threads that use "set" on the same ref, when does the restart of transaction happen? When the slower one tries to commit or as soon as it tries to set the ref?
15:25	rhickey	It's pretty complex. A thread will block a bit while another has the ref locked, but there are also timeouts, barging, and priorities for older transactions.
15:27	jgracin	thanks.
18:28	ericthor_	rich, given: (def data '[[a * b] + [c * d]])
18:28	ericthor_	(first data)
18:28	ericthor_	yields [a * b]
18:28	ericthor_	(rest data)
18:28	ericthor_	(+ [c * d])
18:28	ericthor_	why (seq? data)
18:28	ericthor_	false
18:29	rhickey	first and rest call seq on their argument
18:29	rhickey	(seq? (seq data)) will be true
18:29	ericthor_	very trickey
18:29	rhickey	but data is a vector, not a seq
18:31	rhickey	most sequence functions call seq on their arguments, which can be collections, arrays, strings etc, not just seqs
18:31	rhickey	you can use seq itself as a predicate, as is done often in boot.clj
18:32	rhickey	means there is stuff
18:32	rhickey	whereas seq? is a type test
18:32	ericthor_	so if I want to test if something is sequencable it should be (seq? (seq data))
18:32	rhickey	sequenceable?
18:33	rhickey	not sure what you mean
18:34	ericthor_	i guess it's just (not (atom? x)) I'm looking for...thx
18:35	rhickey	atom? is still tricky, I guess that's why I've avoided it. For instance strings support seq, but would usually be considered atoms
18:36	rhickey	but (instance? IPersistentCollection x) picks out the Clojure aggregates
18:48	hoeck	bye
20:52	pjb3	hey, there's a clojure chat room!
20:53	pjb3	I guess the link off the webpage should have given that away :)
20:53	pjb3	I've got some beginner questions about FP, anybody care to discuss?
21:06	Chouser	give it a shot. I might be a half-step ahead of you.
21:10	pjb3	Ok, so with FP you never create objects
21:10	pjb3	It's kind of the opposite of OOP in that way, right?
21:22	Chouser	heh. hm.
21:23	Chouser	That's kinda loaded.
21:23	pjb3	ok, well, clojure has no way of defining classes, right?
21:23	Chouser	There are languages that allow both FP and objects, but that's not really clojure I guess.
21:24	Chouser	pjb3: Essentially, I think you're correct. There's StructMap, but as the name suggests thats more of a struct thing than an object.
21:24	Chouser	You wouldn't usually put methods inside it.
21:25	pjb3	Ok, well having done mostly Java and Ruby, that's the part I'm having a hard time wrapping my mind around
21:25	pjb3	How do you build stuff without objects?
21:25	Chouser	so, yeah, normally in clojure you'll define functions at the top level of a given namespace, and pass data structures to those functions.
21:26	pjb3	how do you use namespaces?
21:28	Chouser	you can probably start off just using the default "user" namespace
21:28	Chouser	there's info at http://clojure.sourceforge.net/reference/namespaces.html on namespaces.
21:29	Chouser	I haven't done much with them, but you can use (in-ns 'foo) to switch into the foo namespace, then all your defn function declarations get added to the 'foo namespace.
21:31	pjb3	I see, and then you code that wants to use those functions has switch to that namespace to call them?
21:33	Chouser	you can call functions from a different namespace like: (foo/func ...)
21:34	pjb3	ahh
21:35	pjb3	Interesting, so I do a lot of web programming that deals with databases using libraries like Hibernate or Rails' ActiveRecord
21:35	pjb3	ORM frameworks
21:35	pjb3	not sure if you are familiar with that
21:35	Chouser	I've used ActiveRecord some
21:35	pjb3	Ok, cool
21:36	pjb3	so in AR if you have a users database table, you define a User class that subclasses ActiveRecord::Base
21:36	pjb3	then you can go User.find(:all)
21:36	pjb3	to get an array of user objects
21:36	pjb3	representing each row in your db table
21:37	pjb3	How do you think you would model something like that in a FP language like Clojure?
21:38	Chouser	heh, ok, let me take a couple swings at it...
21:41	Chouser	for simple cases, you could have a single find function that returns a list of StructMaps
21:42	Chouser	If you needed to specify some extra details that ActiveRecord might find in your subclass, you could pass those in as a separate data structure.
21:43	Chouser	If that separate data struct is stored in a var called User, then your example call above could be traslated to something like (db/find User :all)
21:44	Chouser	If you wanted more advanced features like callbacks or overriding of accessors or mutators, you should be able to do something with clojure's multimethods.
21:45	pjb3	Is StructMap differenct than the regular {} map?
21:45	Chouser	Anyway, that's a sketch of how I'd start, but I've done a lot more large-scale design in OO langs than non-OO, so .. this might not be the right approach. :-)
21:46	Chouser	only slightly. It's more efficient at storing a large number of maps with a common set of keys than regular map.
21:47	pjb3	what about creating a namespace for each object
21:47	pjb3	(User/find)
21:48	Chouser	probably the wrong approach, but I dunno it might work.
21:48	Chouser	You should probably try to dissect why you think you want objects or classes, like specifically which features.
21:49	Chouser	Clojure probably has support for each different feature, just packaged up in different ways.
21:49	Chouser	For example if it's polymorphism you want, multimethods are a more powerful way to do that.
21:50	pjb3	yeah, I was thinking about that
21:50	Chouser	If it's data hiding you want, you might be able to get what you want with nested functions (closures).
21:54	pjb3	does clojure have named params for functions?
21:58	pjb3	Chouser: got to go for now, thanks for your help
22:03	ericthor	rich: given (def r (ref 0))
22:03	ericthor	(sync nil (alter r (fn [y] y) 15))
22:04	ericthor	java.lang.reflect.InvocationTargetException
22:04	ericthor	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
22:05	ericthor	i'm sure it's right in front of me but i can't see what is wrong with my alter statement?
22:13	rhickey	are you trying to set r to 15?
22:18	rhickey	(sync nil (set r 15))
22:18	rhickey	alter if for functions that transform the value in a ref rather than replace it
22:18	rhickey	iis
22:18	rhickey	is
22:28	ericthor	what would be the example there?
22:28	ericthor	@r to 15