#clojure – 2008-05-12

2008-05-12

12:05	abrooks	rhickey: I keep waiting for Yegge to realize that Clojure's the language he's looking for. I know he thinks the paren issue is too much for the genral population. I'm not quite sure. BTW, did you really post 15 minutes after Yegge posted his article?
12:24	rhickey	abrooks: Yegge seems most interested in JavaScript, having resigned himself to the language limits at Google. I've realized as people trot out the Lisp-has-had-its-day argument that I need to highlight how Clojure is, IMO, much cleaner looking and approachable than CL/Scheme, a combination of fewer parens in let et al and the vector and map literals.
12:25	rhickey	abrooks: I think I was much later than 15 minutes...
13:06	Chouser	I wonder if it'd be worth coding up a couple of relatively attrocious CL examples and show them with Clojure equivalents.
13:09	rhickey	Chouser: I think it's more important to go head-to-head with JRuby/Groovy/Jython, as those developers might not realize Lisp might not be the parens-infested nightmare they imagine. CL devs have already come to grips with parens, knowing the power of macros enabled by them...
13:11	Chouser	hm. ok. tougher sell, but ok. :-)
13:12	Chouser	I've got a friend who, after seeing some of your videos, has decided Clojure is the right way to go, if only he can create a C-like syntax on top of it.
13:12	rhickey	Oh no!!
13:13	rhickey	I attended many of the dynamic language sessions (Groovy/JRuby/Jython) at JavaOne. Clojure looks pretty decent by comparison, considering all the syntactic sugar they have, and is actually less complex due to the lack of it.
13:14	Chouser	I won't tell him you said that. I'm encouraging him to try, since the more closely you look at the problem (and spend time reading/writing s-expressions), the more better s-exprs look.
13:15	rhickey	Yeah, it's an inevitable part of learning Lisp...
13:17	Chouser	And for my part, I wouldn't mind if he succeeded. He's hardly the first to try, so I'm not too hopeful, but I'm sure there is a set of programmers who could be hooked if they had a more familiar syntax to start with.
13:24	rhickey	Clojure is no more different from Python than Python is from C/Java, syntactically, except no infix ops, say. Given the climate of people learning new language that exists today, I'm hopeful Clojure is directly approachable. Personally, Ruby/Scala etc syntax gives me a headache. The longer people avoid code-as-data the longer until they 'get' Clojure/Lisp.
13:26	mfredrickson	i think the statement vs. expression distinction is a larger impediment to Lisps than code vs data (though certainly an important concept)
13:27	rhickey	mfredrickson: interesting... Ruby is all expressions, Python too?
13:28	mfredrickson	rhickey: ruby (of which I am more familiar) skates a line between statemtents and expression
13:28	mfredrickson	for example, I can write a function like def foo; 3; end
13:28	mfredrickson	it evaluates to 3 and returns that value
13:29	mfredrickson	i can also write def foo; if something; return 12; end 3 end
13:29	rhickey	the return is needed?
13:29	mfredrickson	in the second foo, that first "if" is a statement (as in, no return value), but the 3 (if reached) is an expression
13:29	mfredrickson	not strictly
13:30	mfredrickson	thus the duality of the language
13:30	ozzilee	Hey all, is there a way to load in a .java file from the REPL? It's not in my classpath.
13:30	rhickey	yuck
13:30	rhickey	ozzilee: .java is source, do you mean .class?
13:30	mfredrickson	rhickey: yeah. it's weird. i'm writing some Rails code write now, and I keep switching back and forth between expression and statement style. I'm schizo
13:31	ozzilee	rhickey: No, actually .java. I'd be interested to hear of a way to do .class files as well though.
13:32	rhickey	General question for those that know Ruby/Python/Groovy - do you find Clojure to be simpler/smaller or more complex/larger?
13:33	rhickey	ozzilee: no, you must compile with javac and get the class file on the classpath, or use something like Janino from Clojure.
13:34	ozzilee	rhickey: So, in general, if I download a java library (be it a .java, .class, or .jar file), I'm going to need to restart my REPL before I can play with it?
13:35	rhickey	ozzilee: a Java library will most likely be in a .jar. I'm looking at adding support for dynamic loading of jars.
13:35	ozzilee	Ok, that would be cool.
13:36	ozzilee	mfredrickson: I might be wrong, but I'm pretty sure that "if" statement returns a value regardless. I haven't used ruby in a few months, though.
13:36	mfredrickson	ozzilee: it returns nil
13:37	mfredrickson	ozzilee: according to the IRB session i have open anyway
13:37	ozzilee	mfredrickson: Hrm you're right.
13:38	ozzilee	No, the repl just gets confused.
13:39	ozzilee	a = if 1; "foo"; end;
13:39	ozzilee	a is "foo"
13:39	ozzilee	It still returns a value.
13:41	mfredrickson	ozzilee: if the REPL is confused, how am I supposed to know what's going on? ;-)
13:42	ozzilee	Heh. Lines with colons in them just don't show their return values in the REPL, apparently.
13:42	ozzilee	1; 2; 3; // No return values.
13:42	Chouser	rhickey: I posted a pure-clojure hack for dynamic loading of .jars the other day.
13:42	mfredrickson	i would still argue that because of it favors the OO/mutal state model Ruby is more of a statement style language
13:43	mfredrickson	though I do appreciate using expressions in it
13:43	Chouser	python has distinction between statements and expressions (unlike ruby). ...and it hurts.
13:43	ozzilee	Chouser: Yeah, I think I found that.
13:44	ozzilee	http://paste.lisp.org/display/60512 ?
13:44	rhickey	Chouser: yes, thanks, just trying to avoid the setAccessible call
13:44	Chouser	rhickey: heh. yes. good idea.
13:45	Chouser	for example, python has "lambda", but only allows it to include a single expression. But "if" is a statement, so you can't use it in a lambda body.
13:45	rhickey	Chouser: looking at making DynamicClassLoader derive from URLClassLoader
13:46	mfredrickson	Chouser: my brain hurts already. and here I was thinking I should learn python to give significant whitespace a try
13:46	ozzilee	Chouser: Yeah, Python deliberately discourages anonymous funcitons. I believe I heard it said that he wanted to take lambda out all together.
13:46	ozzilee	(can't think of his name right now)
13:47	Chouser	mfredrickson: every language has warts, and Python certainly has merits.
13:47	rhickey	I'm trying to find the web page where the guy wrote Lisp code, then used progressively lighter fonts for the parens until it looked like Python, to demonstrate what happens after a while - the parens disappear for a Lisp programmer, but can't find it right now :(
13:47	mfredrickson	Chouser: I'm being dramatic. I'm sure I'd learn a thing or two from picking up python
13:48	Chouser	ozzilee: yeah, but Guido van Rossum's swimming up-stream. Python's picking up a lot of functional contructs -- to its benefit, I think.
13:48	ozzilee	Guido, that's his name :-)
13:49	ozzilee	I don't think he's anti-functional. Just anti-lambda.
13:49	rhickey	Chouser: I thought GVR was pro-iteration and against more functional style?
13:49	ozzilee	Are list comprehensions considered functional?
13:50	rhickey	not really, fancy iteration
13:50	rhickey	map/reduce/apply etc
13:50	ozzilee	Hmm. Well they're pretty slick, anyway.
13:50	ozzilee	Yeah, Python has those.
13:50	Chouser	well, but comprehensions generally accept a value and return a value without side-effects. ...more functional than many alternatives for the same functionality.
13:50	mfredrickson	rhickey: it's not the disappearing parens, but I've keeping my eye on "readable s-expression"
13:50	mfredrickson	http://www.dwheeler.com/readable/
13:51	mfredrickson	i keep meaning to write a little Lisp to try them out
13:51	Chouser	rhickey: That's my impression of GVR as well, but he has a community that he doesn't entirely ignore. :-)
13:52	rhickey	keeping lambda limited reduces the utility of map/reduce etc
13:52	ozzilee	Yeah, it sure does. Python's just got different goals, readability high on the list.
13:53	ozzilee	I'm certainly not saying it's better than lisp. It is pleasant, though.
13:53	rhickey	Anything Pythons list comprehensions do that Clojure's don't?
13:53	ozzilee	Heh I doubt it. No idea, though, haven't look at Clojure's.
13:56	Chouser	I don't think so. But the syntax is all backwards -- you start with the returning expression and then the bindings, and finally the test
13:57	rhickey	That's the Haskell way
13:58	rhickey	which makes somewhat more sense when your lists are built up using infix cons (::)
13:58	ozzilee	Speaking of list comprehensions, what's a good way to get a lazy infinite list of random values?
13:59	ozzilee	Or even a finite list.
13:59	ozzilee	I think I ended up on (for [x (range 10)] (rand)), but I don't really like that.
14:00	ozzilee	I'd like something like (take 10 (repeat (rand))); which obviously doesn't work.
14:01	rhickey	(defn randoms [] (lazy-cons (rand) (randoms)))
14:01	rhickey	(take 10 (randoms))
14:03	ozzilee	Blech :-)
14:03	rhickey	you don't like it?
14:03	ozzilee	How does fnseq work? (take 10 (fnseq (rand) rand)) doesn't do what I'd expect.
14:04	ozzilee	It's fine, I was just looking for something more general, like (take 10 (repeat-fn rand)) or something.
14:04	ozzilee	(which I'm I could write, but if it's built-in...)
14:05	rhickey	ozzilee: fnseq's second arg must be a fn that returns a seq
14:06	rhickey	ozzilee: yeah, I also occasionally want a repeatedly macro, (repeatedly (rand))
14:07	ozzilee	Yeah, that would work.
14:09	ozzilee	Sorry to sidetrack the conversation, just feeling my way around the language.
14:11	rhickey	(defmacro repeatedly [e]
14:11	rhickey	`((fn rec# []
14:11	rhickey	(lazy-cons ~e (rec#)))))
14:12	ozzilee	And there it is :-)
14:15	Chouser	I've got a new format for the #clojure logs up at: http://clojure-log.n01se.net/
14:15	Chouser	Let me know if it looks broken in your favorite browser.
14:16	rhickey	Chouser: looks fine here Camino OS/X 10.4.11
14:17	ozzilee	Chouser: Long usernames get screwed up on FF/Linux.
14:18	ozzilee	mfredrickson, for example.
14:18	ozzilee	By "screwed up" I mean cut off.
14:19	Chouser	hm. indeed -- text piling up.
14:20	ozzilee	Heh changing the margin-left on b elements fixes it, but that's not really a solution.
14:20	Chouser	yeah, because then you run into the timestamps.
14:21	Chouser	b { overflow: hidden } also solves it sorta-but-not-really.
14:24	mfredrickson	i win. I broke chouser's design.
14:24	Chouser	:-)
14:24	ozzilee	Heh.
14:26	ozzilee	Tables?
14:26	Chouser	Yeah, the old design used tables. http://n01se.net/chouser/clojure-log/2008-05-12.html
14:27	ozzilee	Yeah, I don't see any way around tables as long as you stick with that general layout.
14:28	ozzilee	Something like username<br>message could be done in css, but bleh.
14:28	Chouser	I don't mind clipping ridiculously long nicks (sorry, mfredrickson!) client-side if it looks good, but I'm not sure if it's worth the trouble.
14:28	ozzilee	Of course, that would stop really long usernames from shoving everything to the right...
14:29	Chouser	The benefit of no tables is it's easier for the browser to show the top of the page soon while still loading the bottom of the page.
14:29	Chouser	oh well. I can't work on it now anyway. I'll poke at it again some other time.
14:38	hoeck	chouser: long usernames look bad too on opera 9.02/linux
14:44	ozzilee	Is there anything set up to collect Clojure libraries? For example, if I were to write a JSON library...
14:46	Chouser	ozzilee: http://sourceforge.net/projects/clojure-contrib/
14:57	ozzilee	Chouser: Thanks.
15:21	abrooks	rhickey: Going back to this mornings context of Yegge's post -- Yes. My experience with Clojure is that it's really crossed a cleanliness / expressiveness barrier that other Lisps handn't been able to do (for me). I've sat down and gotten myself workably proficient with various CL implementationts four times in the past but never got to the point where I felt like the language was a natural way to express things. Clojure ...
15:21	abrooks	... crossed that barrier in the first hour of me using it. I've found myself very comfortable in Clojure and belive the small ammounts of additional map, set and vector literals and general expressiveness really bridge that gap for me.
15:21	abrooks	Chouser, rhickey: The friend who likes Clojure but doesn't like parens isn't looking for C syntax. It's more of a Pythonic indent based syntax that he's looing for.
15:22	abrooks	He gets annoyed at the duplicated expression of nesting (both in s-expressions and in indentation).
15:23	abrooks	Disappearing parens? I should read all of the backlog. I was in meetings and am just catching up now.
15:23	ozzilee	Does anything besides emacs do decent s-expr indentation? Eclipse?
15:23	ozzilee	abrooks: Have you tried Scheme, out of curiousity?
15:24	abrooks	rhickey: Are you talking about sweet-expressions?
15:24	abrooks	http://www.dwheeler.com/readable/retort-lisp-can-be-readable.html
15:24	abrooks	The parens bugged me too... up until Clojure. Then I just didn't care any more.
15:24	rhickey	no, not really disappearing, just an example of how they effectively disappear
15:25	rhickey	not in favor of sweet-expressions
15:26	abrooks	I'm not either. There was a time I thought that idea was nifty. Like I said, it doesn't bother me any more.
15:26	abrooks	I should really try to identify why it bugged me and why that
15:26	abrooks	I should really try to identify why it bugged me and why that's not an issue to me.
15:27	rhickey	right, the trick is to convey that effect to newcomers, since invariably anyone who sticks with it soon no longer cares
15:27	abrooks	rhickey: I do think one important thing that eventually happened over my previous Lisp forrays is learing to format Lisply instead of Cishly.
15:27	abrooks	Formatting properly is a big part of not having to read the parens.
15:27	rhickey	yes, indentation is as important as, well everywhere else
15:28	abrooks	Perhaps all intro to Lisp tutorials should start with a reformat your thinking about formatting.
15:29	abrooks	i.e. This is how you format and read code in Lisp (or in our case, Clojure).
15:31	ozzilee	What do you guys use for an editor?
15:31	abrooks	I'm using Vim for now. I want more out of it but its working well enough.
15:32	leadnose	I'm quite a newbie to lisp, but the parentheses never really bugged me because a proper editor should handle it just as easily as any else
15:32	leadnose	I've been using emacs with slime
15:33	ozzilee	Heh. Why is it that anytime the phrase "proper editor" comes up, it's emacs?
15:33	ozzilee	</rhetorical>
15:33	leadnose	I didn't say it is the only one :)
15:34	leadnose	but I think that the editor should handle most of the formatting in any language
15:34	leadnose	mostly indenting though
15:34	ozzilee	Yeah, it should, but a lot of editors don't deal with s-exprs very well. Textmate, for one. IDK about Eclipse, haven't tried it.
15:35	ozzilee	It's too bad about Clojure removing parens from cond. It doesn't indent properly without a special rule now...
15:35	Chouser	I'm working on getting jVi to work with enclojure in NetBeans. ...still don't have it right yet.
15:36	Chouser	I'm headed home. ...later...
15:36	ozzilee	later
15:37	abrooks	ozzilee: Didn't see your question until now -- no, I've never written Scheme though I've read chunks of SICP.
15:38	abrooks	Actually, I guess I did a really small amount of Guile.
15:38	abrooks	...And librep but that's neither here nor there.
15:39	ozzilee	abrooks: It's a lot cleaner than CL. I don't much like CL either.
15:40	ozzilee	Might be worth checking out. I think Clojure's going to end up being more practical for a lot of things.
15:40	ozzilee	I'd recommend Chicken Scheme myself.
15:41	ozzilee	er, "more practical for a lot of things, though."
15:50	rhickey	I've added repeatedly and add-classpath:
15:50	rhickey	(add-classpath "file:/Users/rich/dev/colt/lib/colt.jar")
15:51	rhickey	(take 10 (repeatedly rand))
15:52	ozzilee	rhickey: Wow, you're intense :-)
15:53	ozzilee	(repeatedly rand) or (repeatedly (rand)) ?
15:53	rhickey	note repeatedly is a function, not a macro like I showed before
15:53	ozzilee	Ok, that was my question :-)
15:53	rhickey	so (repeatedly rand)
15:55	ozzilee	Very cool, I'm going to have to switch to trunk for add-classpath, that will be nice.
15:56	ozzilee	Maybe just on my Mac at home though, I always feel like I'm working with boxing gloves on in Linux...
15:57	ozzilee	rhickey: Do you work on Clojure full-time?
16:00	rhickey	ozzilee: no
16:01	abrooks	It just might appear that way but Clojure has allowed rhickey to open a spacetime portal and have TWO full time jobs.
16:02	ozzilee	abrooks: I see. Is that macro in SVN trunk? I might have to upgrade for that...
16:03	abrooks	ozzilee: I've been trying to use it but I find it flaky. It must be something in rhickey's environment that I don't have. I wind up having half the time I had before I found Clojure. ;-)
16:04	ozzilee	heh
16:04	abrooks	Maybe I'm using the wrong JDK. Like one without quantum entanglement.
16:04	rhickey	abrooks: as long as you get twice as much done with the Clojure half...
16:06	abrooks	It's not quite there. I still have a lot of Java learning before I can just go in a straight line without zagging to check various Java resources. The clojure part is pretty smooth aside from the moments of confusion followed by epiphany. :)
16:06	ozzilee	abrooks: What languages are you coming from, if you don't mind me asking?
16:08	abrooks	C, C++, Python, Ruby, Haskell, et al.. I did some Java stuff ages ago but don't really count it.
16:09	abrooks	I mostly do C, Python and Bash at my current Job.
16:09	abrooks	The C is mostly Linux kernel. Most userspace is a mix of Bash and Python with some small parts in C.
16:11	ozzilee	Nice. So a decent mess of stuff :-)
16:11	abrooks	Oh, and GNU Make. =-O
16:11	abrooks	ozzilee: Yes, all the horrors of the programming language universe. :-)
16:12	abrooks	We actually use Lisp inhouse for our DMA engine compiler and some internal network analysis tools but that's not my domain.
16:12	abrooks	SBCL is the Lisp we use.
16:12	ozzilee	Interesting that Clojure seems to be pulling in a lot of people with no other interest in the JVM.
16:13	ozzilee	I don't think Scala or Groovy could say the same thing.
16:14	abrooks	Yes. I only had ill feelings for the Java universe. (I didn't mind the JVM so much as certain language misfeatures and the warped Sun mindset that Java is a self sufficient universe that doesn't need to acknowledge anything outside.)
16:15	abrooks	I think the things happening with GNU Classpath and IceTea are exciting. Hopefully opensource will truly come to JavaLand.
16:16	rhickey	One nice take-away from Java One was that the JVM is truly detached from Java - lots of support for non-Java langs etc.
16:16	abrooks	ozzilee: I do think it's interesting that the number of JVM languages appears to be growing. Java 7 has dynamic language support -- something that Sun would have never done 5 years ago as it does nothing for Java.
16:16	abrooks	rhickey: Exactly. --^
16:18	ozzilee	It will certainly be interesting to follow for the next few years.
16:19	rhickey	I think the JVM is going to see very much increased use
16:19	rhickey	So much free infrastructure
16:20	rhickey	great tech (HotSpot)
16:20	rhickey	open source
16:20	ozzilee	I'm curious to see if Apple changes their attitude on it. They seem pretty lukewarm towards it lately.
16:20	abrooks	Yep. And one thing I have been impressed with are the tools that Sun has provided for debuging and profiling.
16:21	rhickey	that was a stunning disconnect at the show. In the sessions I attended, Macs were used by 90% of the presenters...
16:21	rhickey	But some of the JavaFX stuff is still not supported on Mac, so they were running in VMs
16:21	rhickey	Sun and Apple have to get this together
16:24	ozzilee	They really do. Heh I just googled "iphone jvm" and found a bunch of articles talking about how the lack of Java was going to bury the iPhone. Not so much...
16:25	drewr	I'm not sure I understand how Java and the JVM can be disconnected. Could you write a language for hosting on the JVM in something other than Java?
16:26	abrooks	drewr: If you bootstrapped you could.
16:26	abrooks	I'm not sure you'd want to, I guess.
16:26	drewr	What's Java written in?
16:26	rhickey	You could write one today in Clojure
16:27	abrooks	Also, you'd lose all of the libraries if you were to entirely purge Java. I'm not sure you'd want that either.
16:27	abrooks	drewr: C++ IIRC.
16:28	rhickey	Java is really a good infrastructure language. I hope they stop changing it. But you need something like it, just not for all applications
16:28	drewr	So could you write a Scheme hosted on the JVM that's properly tail-recursive?
16:29	rhickey	the disconnection is that you don't need to program in Java in order to leverage it and the JVM
16:29	abrooks	drewr: Java sources, now that you distracted me. ;-) http://hg.openjdk.java.net/
16:29	ozzilee	drewr: Kawa is tail-recursive, I believe.
16:29	rhickey	only in a special slow mode
16:29	drewr	I guess I don't understand how VM architecture works (Gemstone, Hot Spot, et al).
16:30	abrooks	The bytecode instructions are stack based.
16:30	rhickey	an interpreter could be tail recursive, see SISC
16:30	drewr	Kawa and SISC are written in Java though, aren't they?
16:30	rhickey	and Sun could make the JVM native calling do TCO, in which case Clojure would immediately do the same
16:31	abrooks	It goes all the way down to the instructions but with the changes happening for dynamic languages in Java 7 I wonder if you could get an efficient tail recursion instruction set added.
16:31	rhickey	drewr: there is a spec for the bytecode, and many ways to generate that
16:31	drewr	Ah, OK.
16:31	rhickey	abrooks: TCO is not on the short list for JDK 7 AFAIK
16:32	abrooks	rhickey: No.
16:32	abrooks	rhickey: I meant theoretically the project might be ammenable to accepting it in a future release if you could demonstrate the demand.
16:32	rhickey	The JDK7 dynamic languages stuff benefits languages like JRuby and Jython more than Clojure
16:33	abrooks	Right. I've looked at the changes.
16:33	abrooks	They excite me but do nothing that I can tell for Clojure.
16:33	abrooks	Hm. Is there any benefit that Clojure could extract from the dynamic language changes?
16:33	abrooks	rhickey: --^
16:34	rhickey	abrooks: That emphasis (JRuby/Jython) is not a good one IMO. Trying to make ported interpreted languages without great semantics run well, vs languages written for the JVM (Clojure/Scala/Groovy)
16:34	rhickey	For Clojure I would like TCO and tagged references
16:35	abrooks	What would tagged references buy you?
16:35	rhickey	no boxed numbers
16:35	abrooks	boxed numbers?
16:36	rhickey	http://blogs.sun.com/jrose/entry/fixnums_in_the_vm
16:36	abrooks	Ah!
16:36	rhickey	would greatly speed up math and use of numbers
16:36	abrooks	Okay.
16:36	abrooks	Efficient "cut-through" objects without the objects, right?
16:37	rhickey	Other than that Clojure is pretty well satisfied by what currently exists, since type hints get rid of the need for all the reflection optimizations, and Clojure's native calling is very fast right now.
16:37	abrooks	I just didn't recognize the term.
16:38	rhickey	abrooks: no boxing means no allocations, no blowing cache to follow references to numbers in random memory locations etc
16:38	abrooks	Yep.
16:38	rhickey	It's my #1 feature request, but the importance of it is not recognized by some of the other dynamic lang devs
16:39	rhickey	http://groups.google.com/group/jvm-languages/browse_frm/thread/ac9308ae74da9b7e
16:40	rhickey	By building for the existing JVM, with a pragmatic approach, Clojure is doing quite well, vs langs that inherited a design they have to make work on the JVM, especially one that started out as an interpreter.
16:41	rhickey	off to my second full-time job :)
16:41	bpattison	has anyone had any problems using enclojure in netbeans 6.1 under windows? namely <alt-enter> doesn't seem to be committing my expression to REPL -- plus shift-ctl-L doesn't seem to work
17:09	ozzilee	What? Clojure doesn't have fold??
17:10	ozzilee	Oh, I guess I can just cons the starting value onto the front of the sequence and use reduce...
17:25	lisppaste8	ozzilee pasted "I love lisp." at http://paste.lisp.org/display/60648
18:58	esquesque_	what does a metadata map for a map look like?
18:59	esquesque_	is it just the type of the value?
19:00	esquesque_	#^String {:key "value"}
19:01	rhickey	no, metadata is an optional map that can be attached to some objects - collections and symbols. If you hadn't added metadata to a map there would be none:
19:01	rhickey	user=> (def m {:a 1 :b 2})
19:01	rhickey	#'user/m
19:01	rhickey	user=> (meta m)
19:01	rhickey	nil
19:02	esquesque_	you can't attach metadata to a map?
19:02	rhickey	yes you can
19:02	rhickey	there is no metadata unless you put some on it
19:04	esquesque_	erm... metadata for a function looks like #^Type (defn ...) because a function evaluates to only one value
19:04	esquesque_	but a map has two - key and value
19:04	esquesque_	i was wondering if the metadata for a map had a constraint for the key and value or just the value
19:05	rhickey	metadata is always a map, no matter what it is attached to
19:05	esquesque_	i'm talking about conveying types to the compiler
19:06	rhickey	there is read/print shorthand for metadata when the only entry in the map is :tag, in which case it prints like #^Tag
19:07	rhickey	when you convey types to the compiler you do so by attaching metadata to symbols usually. Metadata is also available for arbitrary program use
19:08	rhickey	user=> (def m #^{:x 1 :y 2} {:a 1 :b 2})
19:08	rhickey	#'user/m
19:08	rhickey	user=> m
19:08	rhickey	{:a 1, :b 2}
19:08	rhickey	user=> (meta m)
19:08	rhickey	{:x 1, :y 2}
19:11	esquesque_	okay, thanks
19:11	esquesque_	i was thinking you could apply :tag to maps