#clojure – 2008-05-19

2008-05-19

10:12	ozzilee	Is there a way to get a java.util.HashMap from a clojure.lang.PersistentHashMap ?
10:17	ozzilee	Alternately, has someone already created a json encoder for Clojure?
10:20	rhickey	Clojure maps do not yet implement java.util.Map, so you'd have to reduce:
10:20	rhickey	(reduce (fn [hm [k v]] (.put hm k v) hm) (HashMap. (count m)) m)
10:20	rhickey	json encoder should be trivial
10:22	ozzilee	That'll work.
10:22	ozzilee	Works with the json lib from couchdb4j anyway.
10:40	ozzilee	rhickey: Calling (next) when at the end of a zipper seems to block forever. Bug?
10:40	rhickey	code?
10:41	lisppaste8	ozzilee pasted "next blocks forever" at http://paste.lisp.org/display/60978
10:48	lisppaste8	ozzilee annotated #60978 with "end? doesn't work" at http://paste.lisp.org/display/60978#1
11:14	wabash	rhickey: Thanks for answering my questions last time. I was leading up to a question: Is it fundamentally impossible to do TCO on JVM due to current JVM lack of primitives to do so? Would TCO ever be possible on the JVM without a new JVM design?
11:19	rhickey	TCO is easy if you are an interpreter - see SISC Scheme. Using Java's call stack, the JVM would have to provide it. There are no fundamental technical difficulties, but potential issues for the security model, which uses the call stack to ensure privileges.
11:20	dudleyf	It won't need an entirely new JVM design, there are people at Sun working on modifications of the JVM to support languages other than Java
11:21	dudleyf	But nobody's pushing very hard for TCO right now
11:21	rhickey	I don't think TCO is a priority for them, as it's not a hot feature for JRuby or Groovy
11:22	dudleyf	rhickey: You could start pushing for it in the jvm-languages group
11:22	rhickey	Their focus is on "arguably popular" languages, so JRuby/Jython/Groovy
11:22	dudleyf	The JRuby and Groovy guys are just the most vocal
11:23	rhickey	I don't think it's that simple
11:24	dudleyf	Well, it's never that simple ;-)
11:24	rhickey	TCO is a pretty big change, JVM-wise
11:24	wabash	rhickey: dudleyf: thank you.
11:25	wabash	rhickey: SISC?
11:25	dudleyf	Bigger than continuations?
11:25	rhickey	but tail calls for loops will never be idiomatic JRuby/Jython/Groovy/Java
11:25	rhickey	wabash: http://www.google.com/search?q=sisc%20scheme&sourceid=mozilla2&ie=utf-8&oe=utf-8
11:26	rhickey	dudleyf: I don't know - I don't think they should add continuations in any case
11:26	dudleyf	Really?
11:26	dudleyf	Security concerns?
11:29	rhickey	I think continuations might be neat in theory, but not in practice
11:35	rhickey	Chouser: ozzilee's bug is due to the change in destructuring. Do you recall why, if given a nil as a map destructuring source, you changed it to a {} ? Some code in zip relies on :as binding of nil map to be nil, i.e. :as == what was supplied.
12:04	rhickey	ozzilee: fixed - thanks for the report
12:05	ozzilee	np, thanks for the fix
12:23	nsinghal	e
12:34	Chouser	rhickey: I'll look at it after lunch -- thanks for fixing it anyway. ;-)
13:24	Chouser	rhickey: yeah, you caught it. I used the map as a function instead of calling "get" so that sets would work, but then a nil input broke it.
15:56	ozzilee	Is it correct that keywords starting with a number are not allowed?
15:57	rhickey	yes, not allowed
15:58	ozzilee	Ok. Just saw the rules for symbols. Thanks.
16:16	ozzilee	Is there any way to break out of a function early? I'm trying to write a assert-exception macro, and I want to return in the (catch) block.
16:17	rhickey	no
16:17	ozzilee	Ok. I guess I can use with-local-vars to set a flag?
16:28	drewr	How true is this? "Beware of languages like Scala and Clojure that intend to be safer concurrently than Java - they still run on the JVM and integration with Java code. So by definition their safety only can go so far."
16:28	drewr	http://lnk.nu/patricklogan.blogspot.com/kpy.html
16:29	drewr	Haha, didn't get to the comments yet where rhickey already responded. :-)
16:29	lisppaste8	ozzilee pasted "illegal exception table range" at http://paste.lisp.org/display/60996
16:29	ozzilee	Not sure if the problem lies with me or Clojure, don't know what "illegal exception table range" means.
16:29	rhickey	drewr: my comment was submitted this morning - just got posted
16:37	ozzilee	rhickey: Can you give me any hints as to what's going wrong with the above paste?
17:18	lisppaste8	ozzilee annotated #60996 with "less noise" at http://paste.lisp.org/display/60996#1
17:45	lisppaste8	ozzilee annotated #60996 with "nested try is borked" at http://paste.lisp.org/display/60996#2
17:46	rhickey	please be patient, I'm looking into it
17:47	ozzilee	rhickey: That's all you had to say :-)
17:47	ozzilee	Just playing with it myself, not trying to needle you.
17:47	rhickey	it has to do with no-effect statements like 1 and nil
17:48	ozzilee	Huh, you're right.
17:48	rhickey	(try (try 1 (catch Exception e 2)) 3) has the problem but (try (try (prn 1) (catch Exception e 2)) 3) doesn't
17:50	ozzilee	Interesting.
17:51	rhickey	nil and 1 in non-tail positions don't make much sense
17:52	ozzilee	Not particularly, unless you're checking to see if an assert-exception macro works for non-exception-throwing-code :-)
17:53	ozzilee	I just stuck a (print) in there for now.
22:34	rhickey_	ozzilee: (try (try 1 ... is fixed
23:37	jonathan___	There's a really nice continuations example in the Expert F# book where it's, errr, used in a tree traversal I think (bit over my head, but at least it's not monads)