#clojure – 2008-07-23

2008-07-23

02:13	Chouser	I can't think of how to use any of the existing persistent structures as a queue efficiently.
02:14	Chouser	a subvec keeps a reference to the original vector, right? Otherwise it'd be perfect.
02:17	Chouser	Yep, SubVector has the original vector, a start index, and an end index.
02:19	Chouser	So how can I let dequeued items be GC'ed without mutating or copying the whole queue?
10:02	meredydd	Out of interest, is there a Clojure-idiomatic HTTP client library about the place, for playing with RESTish stuff?
10:22	cemerick	it seems that in-ns doesn't have any effect within a do block, i.e. (do (in-ns 'blah) (def name 5)) throws: java.lang.Exception: Name conflict, can't def name because namespace: user refers to:#'clojure/name
10:23	cemerick	The same thing happens if I use binding to set ns for the scope that the def is in. What am I missing here?
10:35	Chouser	cemerick: I wonder if the name is resolved compile time, such that you need to drop back up to the top level before any changes to ns take effect?
10:36	Chouser	It's not clear to me why you can't use fully-qualified names in def.
10:36	cemerick	Chouser: Yeah, that's what I figured.
10:37	cemerick	That would be nice.
10:40	cemerick	The big fallout from the way those names are resolved is that you can't fiddle with any other namespace, short of evaling defs, etc.
10:41	Chouser	maybe that's the point. still, it doesn't really protect much since any file can drop into any namespace and start def'ing
10:43	cemerick	yeah, it only limits certain macros
10:43	Chouser	oh, I see. yeah, good point.
10:45	cemerick	allowing fully-qualified names in def is the maximally-effective solution. There may well be an implementation detail that makes that undesirable.
10:47	Chouser	the errors you get appear to be very specific, as if rhickey considered that option and explicitly rejected it
10:47	Chouser	I don't think I've read an explanation anywhere though.
10:47	cemerick	we can tag-team him when he returns ;-)
12:11	cemerick	is this the only way to get a reference to the class for Object[] (for example): (. Class (forName "[Ljava.lang.Object;")) ?
12:44	Chouser	(class (to-array []))
12:44	Chouser	yours might be better, but there's another option anyway.
12:46	Chouser	(class (into-array [0])) ==> class [Ljava.lang.Integer;
13:22	nchubrich	Hi, has anyone encountered problems using JLine with clojure?
13:22	nchubrich	Specifically, I followed all the instructions on the group:
13:22	nchubrich	java -cp jline-0.9.94.jar:clojure.jar jline.ConsoleRunner clojure.lang.Repl
13:23	nchubrich	in the directory with both jars:
13:23	nchubrich	CPL.TXT changes.txt jline-0.9.94.jar readme.txt target
13:23	nchubrich	build.xml clojure.jar pom.xml src
13:24	nchubrich	and get:
13:24	nchubrich	Exception in thread "main" java.lang.ClassNotFoundException: clojure.lang.Repl
13:27	Chouser	nchubrich: sorry, I don't know. I use rlwrap instead of jline
13:28	Chouser	rhickey: have you explained somewhere why (def my-ns/foo) is disallowed?
13:29	nchubrich	Yes, rlwrap definitely works better; but for some reason JLine works better with Emacs
13:29	nchubrich	(I have a friend who got it on his system, but for some reason doesn't work on mine.)
13:32	fyuryu	nchubrich: you have svn version of Clojure?
13:33	rhickey	Chouser: there isn't a firm position there, mostly denied conservatively. One issue would be, locality of namespace definition - if anyone can inject into a namespace from any other it will be difficult for tools
13:33	nchubrich	I don't think so, but it's build 20080612
13:33	fyuryu	nchubrich: I remember having some problems with jline, but that was some time ago, it works now
13:34	Chouser	ok. cemerick was apparently trying to do something in a ns via a macro, but I'm not sure what.
13:34	nchubrich	fyuryu, do you think SVNing it would help for some reason?
13:35	fyuryu	nchubrich: yeah, that date sounds about right, try the svn version
13:35	nchubrich	I haven't put jline.jar in my system-wide extensions library; that seemed to cause problems so the group said.
13:36	rhickey	Chouser: you were looking for a queue? You could try clojure.lang.PerisistentQueue
13:37	fyuryu	nchubrich: I have jline in the same directory as clojure.jar. And use the scripts from the wiki
13:43	nchubrich	thanks for your help fyuryu, I'm going to try SVN....
13:49	cemerick	rhickey: what Chouser was referring to was a situation where a macro was looking to use gen-and-load-class, and also populate the necessary namespace that the gen-class'ed class would look in for method impls. Short of requiring the macro to be used from within the class namespace, the macro would either need to be able to def fully-qualified names, or be able to use in-ns in a try/finally so as to restore ns after populating the namespace.
13:52	rhickey	cemerick: you mean (bind [ns blah] ...) ?
13:56	cemerick	rhickey: I tried that; doesn't appear to work: (binding [ns (find-ns 'blah)] (def foo 5)) => #'user/foo
13:56	cemerick	maybe I'm missing something...?
13:57	Chouser	Is (conj (clojure.lang.PersistentQueue/EMPTY) ...) the Right Way to create one?
13:57	cemerick	(FWIW, namespace 'blah does already exist)
13:58	rhickey	you're not, that won't work because all the names involved are resolved at compile-time but the binding happens at run time, and is a common error
13:59	rhickey	gen-class et al are a good example of where one ns is defining another
14:00	cemerick	Yeah, I see why that doesn't work; I could eval all of the defs, but that's pretty irritating.
14:01	rhickey	cemerick: but aren't you in a macro?
14:02	cemerick	rhickey: yes; its forms are still subject to ns, though, right? Perhaps my macro-fu is weak.
14:02	rhickey	Chouser: yes, then you can use the conj/pop protocol
14:02	Chouser	rhickey: ok, thanks.
14:03	Chouser	it's count appears to including counting a seq -- not constant time?
14:03	Chouser	its
14:05	rhickey	Chouser: no, many seqs have constant-time count, including vector's
14:07	rhickey	cemerick: yeah being in a macro doesn't help
14:08	cemerick	rhickey: ok, glad I'm not losing it
14:09	cemerick	rhickey: FWIW, I've got a first pass of a 'defbean' macro working that does what we discussed last night, but it's less than ideal. Having to coordinate the namespaced impl. as well as ensure that the class in question isn't loaded twice makes for a hairy mess, really.
14:09	rhickey	cemerick: does defbean generate a bean on disk or immediately loaded?
14:10	cemerick	rhickey: right now, it's immediately loaded. We have a build process and such that coordinates where and when gen-class stuff is saved off, but I've been trying to not use that so defbean could be generally applicable.
14:11	rhickey	cemerick: who could consume the named members of such a bean (unless there is an interface defining them)?
14:12	cemerick	Looking back over our use-cases this morning, always having a Java interface for each entity we're interested in is common, so I may just downshift into using proxy to build the PSM subclass off of a given interface.
14:13	rhickey	cemerick: for dynamic beans that's all that makes sense to me
14:13	cemerick	rhickey: no one, unless we're saving the classes
14:15	cemerick	I'll have to go over our models and see whether simply referring to a concrete, gen-class'ed impl is something that would be beneficial. It's certainly irritating to have to have a pile of interfaces for every entity (compared to having the option of having them pop out concretely from clojure).
14:16	rhickey	cemerick: or do you want gen-interface?
14:16	cemerick	rhickey: I've always wanted gen-interface :-)
14:16	rhickey	cemerick: what were the loaded-twice issues?
14:17	cemerick	rhickey: Nothing super-complex -- the jvm would just throw a duplicate class def exception after a second eval of the defbean macro. Fixed with a check for the class that defbean emits via gen-class.
14:18	cemerick	rhickey: FWIW, what I really want is a gen-class that carries method impl's around with it, a la proxy.
14:18	cemerick	I know that opens up a whole other can of worms, tho.
14:19	rhickey	cemerick: but does defbean allow a change in signature, i.e. adding methods? if so people will expect it to be able to be run more than once
14:20	cemerick	rhickey: No. Another vote for either using proxy, or always saving the generated class.
14:22	rhickey	gen-and-load-class is very limited, because Java is limited in supporting static class names + dynamic signatures
14:24	rhickey	cemerick: as I said to Chouser, the prohibition on defs of explicitly-qualified names is conservatism on my part
14:25	Chouser	consider yourself tag-teamed.
14:25	cemerick	Chouser: :-P
14:26	rhickey	one issue is the fact that all of the names in any such definition will be resolved in ns, not the ns of the def'ed var
14:26	cemerick	rhickey: Given some of the example code I've seen on the group of late, I don't blame you at all. I do think there has to be some mechanism for safely def-ing fully-qualified names, though.
14:27	cemerick	maybe have a def-ns that we can bind, so that def-ed symbols are resolved there, but all others are resolved in ns?
14:28	rhickey	cemerick: still very confusing, for me too
14:28	cemerick	That feels over-complicated, though
14:31	Chouser	I would be very surprised if ns was 'user and (def foo/bar baz) was refering to any baz other than user/baz
14:31	rhickey	cemerick: want to past defbean so I can see what you are up against?
14:32	rhickey	Chouser: what about (def foo/bar bar) ?
14:33	Chouser	I really wouldn't expect any fully-qualified name to early in an expression to change the ns used by later symbols.
14:33	Chouser	now if it was (def-in-ns foo bar bar) ... then I would start to wonder.
14:34	rhickey	Chouser: (defn foo/bar [] .... (bar))
14:35	Chouser	yeah, I would expect to have to say (foo/bar), though I'm sure that would be a common mistake.
14:35	rhickey	Chouser: I'm not disagreeing, just highlighting what are likely to be the points of confusion
14:36	cemerick	rhickey: Yeah, I'll paste it in 5 min. It's a pretty ugly baby. :-)
14:36	Chouser	maybe not as common as forgetting to (refer 'clojure) after my (in-ns ...), but still common.
14:37	cemerick	IMO, def-ing a fully-qualified name is definitely an edge case -- I wouldn't expect it to be available by default. This is how I came to my def-ns suggestion.
14:40	Chouser	this would be a possible solution for the gen-class namespace pollution as well.
14:40	Chouser	as opposed to method function-name mangling.
14:40	rhickey	Chouser: how so?
14:42	Chouser	if I genclass namespace fooclass, instead of then wanting to do (in-ns 'fooclass) (refer 'clojure), I could stay in my 'user ns (or where-ever) and do (defn fooclass/methname1 ...)
14:43	Chouser	did that make any sense?
14:44	rhickey	Chouser: except it's not fooclass, it's com.company.package.Classname, and there's no ns in which to alias it!
14:45	Chouser	why couldn't I alias it? but even without that, I'd rather use a long name for each method def, than sprinkle clojure/ all through my code.
14:46	Chouser	granted mangling each method name with a leading . would be nicer than either. :-)
14:46	rhickey	Chouser: your straw man was function name mangling, which wouldn't require that
14:47	rhickey	Chouser: also, you'd have to qualify all helper fns etc
14:47	Chouser	I didn't mean to claim fully-qualified def was better than mangling, just that it could also solve the problem.
14:47	Chouser	indeed.
14:47	lisppaste8	cemerick pasted "defbean first cut" at http://paste.lisp.org/display/64107
14:49	cemerick	rhickey: so, it's a bit of a mess at the moment, but there are enough issues that I think it's worth not pursuing with the current state of things (in favor of an interface/proxy impl)
14:50	cemerick	(it's also possible that I've made a hash of it)
14:54	rhickey	cemerick: so it create a class with the same name as ns?
14:54	cemerick	rhickey: yes; it seemed like the only reasonable approach given the fully-qualified def issue
14:55	rhickey	right, just trying to understand
14:55	rhickey	you'd have preferred taking a class name too?
14:57	cemerick	well, that's not really settled yet -- I've seen a lot of code around that keeps all of the gen-class stuff in one file, in one namespace, and our approach is to put any gen-class in its own -gen.clj file (which makes the build process identify what generates classfiles, and what just needs to be loaded as a sanity check and to see about reflection warnings). Providing a classname to defbean certainly makes it clearer what's going on under the covers.
14:59	kotarak	is there a way to use apply with . besides (eval `(. ~obj foo ~@args))?
15:02	rhickey	kotarak: (defn jcall [obj name & args]
15:02	rhickey	(clojure.lang.Reflector.invokeInstanceMethod
15:02	rhickey	obj
15:02	rhickey	(str name)
15:02	rhickey	(if args (to-array args) (clojure.lang.RT.EMPTY_ARRAY))))
15:02	rhickey	(defn jfn [name]
15:02	rhickey	#(apply jcall %1 name %&))
15:03	kotarak	wow. thanks :)
15:44	rhickey	so who's gonna write the macro's to gen gxp? http://code.google.com/p/gxp/
15:49	cemerick	rhickey: since we have Class/field access (i.e. Math/PI), can we reclaim '.' so that it invokes methods on java.lang.Class? i.e. this doesn't work (.getMethods String)
15:55	Chouser	Compile-time type checking, lightweight runtime system -- is this a template or programming language?
16:17	rhickey	cemerick: (macroexpand '(Math/random))
16:18	rhickey	Chouser: it's your typical server pages thing except:
16:18	rhickey	it's functional
16:18	rhickey	it's compiled
16:19	rhickey	the resulting compiled classes can be consumed from Java/Clojure
16:19	cemerick	rhickey: OK, I deserved that :-)
16:21	cemerick	however, I'm confused in general. (.getName String) => Exception, and (.getName (class String)) => "java.lang.Class"
16:21	rhickey	cemerick: just wanted to show it is still not syntax, just a transformation. Making it first class could complicate code walkers etc, which for now can just call macroexpand and get the canonic form. I agree, (. classname static-member) is not otherwise preferable in any way to classname/static-member
16:22	rhickey	. has special evaluation rules, if its first argument looks like a classname, it's considered a static call
16:22	rhickey	(. String getName) - static call to getName method on String (doesn't exist, error)
16:23	rhickey	(. (class String) getName) -> the class of the String class object is Class
16:23	cemerick	heh, this works: (defn foo [c] (.getName c)) (foo String)
16:24	cemerick	yeah, I see what was going on there, I was just assuming that there was something more complicated going on
16:28	rhickey	(. classname member) predated class object literals, but the fundamental problem is Java's, which uses class names as scopes - I guess I could force everyone to use String.class to name the class object, like Java does
16:29	rhickey	(just kidding)
16:30	cemerick	but only a little, right? :-)
16:30	rhickey	cemerick: that's how it started out, no class literals, and (class String) meant String.class
16:31	cemerick	yeah, I was mostly winking towards the "it's Java's fault"
16:31	rhickey	now (class String) means (.getClass String) and String means String.class
16:31	rhickey	oh, it's definitely Java's fault
16:31	rhickey	:)
16:32	cemerick	:-)
16:32	cemerick	rhickey: I've been meaning to ask you about future generics plans (if any)...
16:34	rhickey	cemerick: my plan is to pray they never move away from type erasure for generics. Without it lots of Clojure's interop would be horribly type-burdened. This was a major factor for me in dropping .Net. Generics are bad for dynamic languages, after all, they are only about types.
16:38	cemerick	I've spent some not-inconsiderable amount of time in scala-land, so I'm not averse to types (and like them on occasion). I wouldn't mind eventually seeing a dynamic-friendly type system in clojure (perhaps implemented as a plugin for a future componentized clojure compiler). I'm obviously not asking you for this, though.
16:54	rhickey	cemerick: I'm not likely to settle for types - I just don't think they give the required benefits. If you look at something like the PLT contracts, Eiffel pre/post conditions, predicate dispatch, Qi's superimposable sequent-calculus based system etc, there are some cool ideas.
16:55	rhickey	I am in favor of programmers being able to assert things about their code and the compiler/runtime system assisting them.
20:24	rhickey	I've added validators for vars/refs/agents - an optional second arg for agent and ref, get/set-validator, also shutdown-agents