#clojure – 2008-04-22

2008-04-22

06:25	jteo	is someone working on a clojure tutorial already?
10:00	Chouser	jteo: not that I know of. sounds kinda fun, though. Are you starting one?
10:01	jteo	maybe, if i can get my head wrapped around this.
10:01	Chouser	"this"?
10:01	jteo	certain things are confusing in clojure to someone who just managed to get Common Lisp.
10:01	jteo	such as...immutables.
10:01	Chouser	heh. yeah.
10:02	Chouser	are you trying to do something in particular?
10:04	jteo	clojure is useful for me as a mental challenge.
10:04	jteo	anyway, i get bored with imperative languages.
10:06	jteo	plus clojure seems much more practical than Common Lisp. as in the library support.
10:09	Chouser	I agree.
10:11	drewr	jteo: We're in the same boat. I've been wanting to use CL, but it's hard to justify when I can get something done quickly in Python. Clojure's been scratching my Lisp itch but with the ability to solve real problems quickly.
10:11	jteo	precisely.
10:12	jteo	Practical Clojure would be an absolute gem. :)
10:12	drewr	I've been migrating some data for a client and they gave us part of it in a PDF. I used about 10 lines of Clojure with the PDFBox jar to extract the information.
10:13	drewr	It makes me enjoy Java. That's inconceivable.
10:13	drewr	Well, Java's libraries.
10:19	lisppaste8	drewr pasted "pwning a pdf" at http://paste.lisp.org/display/59535
10:24	Chouser	drewr: nice.
10:29	drewr	Obviously, you could make a fine PDF library with CL, but I'm guessing that problem is too uninteresting for a Lisper to solve (I wouldn't want to either) since I can't find CL-PDF. Clojure is like having an inexhaustible FFI for the Business Programmer.
10:31	jteo	precisely.
10:31	jteo	it's tiring to write libraries/glue from scratch.
13:58	Chouser	it seems like it would be common, when destructuring a map, to use the same names for the local formal args as the keys of the map.
13:59	rhickey	yes
13:59	Chouser	(let [{a :a b :b c :c} x] ...)
14:00	Chouser	would it be sensible to provide a shortcut?
14:00	rhickey	like?
14:00	Chouser	I have no idea what the syntax would be
14:00	rhickey	therein lies the rub
14:00	Chouser	(let [{{a b c}} x] ...)
14:00	rhickey	but a map is a valid binding form
14:01	Chouser	there might be something analegous on the calling side, such that a similar syntax could be used.
14:01	rhickey	e.g. (let [{{a b c} :abc } x] ...)
14:01	Chouser	when building a hash: (hashsyms a b c) ==> {:a a :b b :c c}
14:02	Chouser	right. {{ ... }} is a bad syntax.
14:02	Chouser	(let [(de-hash-syms a b c) x] ...) ?
14:02	rhickey	ugh
14:02	Chouser	I assume callable destruturing forms isn't a can of worms you want to open.
14:03	rhickey	it's something I want to save
14:03	Chouser	yeah, ok.
14:04	Chouser	but for destructuring maps, if a sane syntax could be found, you'd be open to something like this?
14:04	rhickey	yes, I've definitely thought about it
14:05	Chouser	#:{a b c} ==> {:a a :b b :c c} and (let [#:{a b c} x] ...)
14:05	rhickey	let's leave hashsyms out of it, much less common
14:06	Chouser	ok, fine by me. That's easy to write a macro for if I need it.
14:06	Chouser	I was bringing it up only for symmetry.
14:08	rhickey	maybe sets (let [#{:a :b :c} x] ...)
14:08	rhickey	uses name of key for local name
14:09	rhickey	will work with maps with keyword, symbol and string keys
14:09	Chouser	right. there's no other useful meaning for a set as a binding form?
14:09	rhickey	not right now
14:10	Chouser	the only thing I can think of would be to allow you to pluck out truth values from a passed-in set, but that doesn't seem terribly useful.
14:12	rhickey	no. but note you can't have what you want (let [#{a b c} x] ...)
14:12	rhickey	because you don't know the type of the keys
14:14	Chouser	I don't understand.
14:14	Chouser	I mean I'm content with #{:a :b :c} instead of #{a b c}...
14:14	rhickey	your first example presumed keyword keys
14:15	Chouser	oh! good point!
14:17	Chouser	(let [#{:a :b :c} x] ... ) would be fantastic.
14:18	Chouser	and if 'name' worked for strings, then you could get the formal param name for each key by calling 'name' on the given key.
14:21	rhickey	right, that would be added
15:07	Chouser	No way to use :as in a set.
15:08	rhickey	right
15:08	Chouser	are you working on this already?
15:08	rhickey	no
15:08	Chouser	ok
15:12	Modius	rhickey: Sent you a private message/question - uncertain if you have them filtered, or if you don't want to answer - if the former, just wanted to get feedback.
15:19	abrooks	Modius: Doesn't freenet filter private messages?
15:20	Modius	abrooks: Not for users registered with nickserv
15:20	abrooks	er... not freenet, freenode
15:21	abrooks	Modius: Ah, okay.
15:35	Chouser	rhickey: should symbol keys for sets be quoted or not? That is, should #{:a "b" 'c} work, or #{:a "b" c}, or both?
15:37	landonf	Howdy all. Anyone have a preferred unit testing framework?
15:47	landonf	Reading Kearsley Schieder-Wethy's work
15:50	rhickey	Chouser: in the macro, no. They are not evaluated, just as in the map case: {a :a b :b}
15:50	drewr	landonf: You could use jUnit.
15:51	drewr	But it would be more pedagogical to write your own.
15:58	Chouser	ok, so (let [#{a b c} x] ...) would work, it just wouldn't do what I originally suggested.
15:58	rhickey	right, that would match symbol keys only
15:59	rhickey	keywords: (let [#{:a :b :c} x] ...), strings: (let [#{"a" "b" "c"} x] ...)
15:59	Chouser	great. Well, I have those cases working.
16:00	rhickey	cool
16:01	Chouser	I'll post a patch in a minute, though I have no idea if the code is up to your standards. ;-)
16:02	rhickey	does it work when x is a set?
16:03	Chouser	nope, that gets you nils
16:03	rhickey	hmm...
16:04	Chouser	I'm using 'get'
16:05	Chouser	I could put the map in function position instead, and that ought to work.
16:05	rhickey	right
16:05	rhickey	but not with nil x
16:05	Chouser	indeed.
16:06	Chouser	I could put the key in function position, but of course that would only work for keywords. ;-)
16:06	rhickey	you'll need to special-case nil x
16:07	Chouser	I could wrap x in (or x #{})
16:07	rhickey	(and x (x k))
16:07	Chouser	would you prefer your special case on each binding, or mine on the first one?
16:08	rhickey	either
16:09	Chouser	done.
16:10	rhickey	the set stuff will be nice for boolean-flag style & keyword lists
16:22	Chouser	http://n01se.net/paste/SgX -- Destructure maps using sets
16:22	drewr	rhickey: What was that paper on tries you used to implement maps in Clojure?
16:22	drewr	(I'm giving you some props on reddit.)
16:23	rhickey	http://citeseer.ist.psu.edu/459691.html
16:29	rhickey	drewr: what reddit thread?
16:30	drewr	rhickey: http://reddit.com/r/programming/info/6gov3/comments/
16:31	drewr	I'm recommending Clojure in there, but I'm attempting to explain why it's compelling. :-)
16:34	drewr	Do I remember in the concurrency talk that your hash maps are near O(1)?
16:37	rhickey	They are log32N, so for a million items that's 3 hops, and for a billion, 6. IMO, that's small enough to ignore.
16:42	rhickey	right
16:52	nsinghal	Var fnptr = RT.var("nspace", "function"); returns a function - can i pass that variable to another clojure function in Invoke?
16:52	rhickey	sure
16:53	nsinghal	can i return a multimethod? so that the caller can call the method using the arity?
16:54	rhickey	an arity-overloaded function
16:54	rhickey	sure
16:56	nsinghal	how can i return that? I have written a multimethod. then when i will retunr that in a separate fn - wont it evaluate or something?
16:56	rhickey	?
16:56	rhickey	functions ar evalues like any other
16:56	rhickey	they don't get evaluated until called
16:57	nsinghal	sorry i was confused with multimethid and arity-overloaded fn - i think i understand now. thx
16:59	rhickey	all interested - here's an amortized O(1) persistent array design, but the constant factors are substantial, and the implementation very complex; http://citeseer.ist.psu.edu/328736.html
17:11	nsinghal	(defn multi-arity []
17:11	nsinghal	(fn ([] (this false))
17:11	nsinghal	([b]
17:11	nsinghal	(if b (str "hello") (str "bye bye")))))
17:12	nsinghal	what should i use where (this false) is? i want to call the same fn with a default argument
17:12	rhickey	ns: you can't have the [] after multi-arity
17:12	rhickey	nor the fn
17:13	nsinghal	i want to create a function which returns a function with different arity
17:13	rhickey	ah
17:14	rhickey	ok, what is this?
17:14	rhickey	'this'
17:15	nsinghal	i just used it - i didnt know how to call the same function with arg
17:15	rhickey	put the name after fn
17:15	nsinghal	ok let me try that
17:16	nsinghal	worked like a charm- great
17:30	Chouser	rhickey: I don't know if I quite love the set destructuring syntax. (of course I think of this after I'm done...)
17:30	Chouser	This is the first time you can bind to a symbol name without actually mentioning the name as a symbol.
17:31	Chouser	a naive text editor looking for "foo" may not find where it's bound using #{:foo} or #{"foo"}
17:31	rhickey	right, and no :as bothers me
17:32	rhickey	drewr: thanks for the mention: http://reddit.com/r/programming/info/6gov3/comments/
17:33	Chouser	(let [{_ :a _ :b} {:a 1 :b 2}] [a b]) ==> [1 2] ?
17:33	Chouser	(let [{* :a * :b} {:a 1 :b 2}] [a b]) ==> [1 2] ?
17:35	rhickey	that still doesn't have the name as a symbol
17:36	Chouser	oh. heh. right.
17:36	Chouser	well, it's going to be impossible to have the name as a symbol and allow for keyword/string/symbol keys.
17:37	Chouser	unless there's a completely different syntax for indicating which of the 3 it is.
17:37	rhickey	right, or marrying keywords
17:38	Chouser	{a :string b :keyword} <-- icky
17:38	rhickey	this is the thought process I went through and didn't find anything great
17:38	Chouser	hmph.
17:39	rhickey	:string and :keyword might be keys
17:41	rhickey	as could any other value
17:41	Chouser	yeah. But it only gets worse. {[:string a] * [:string b] *}
17:41	rhickey	nope, becaue maps can be binding forms and nested
17:41	Chouser	* could be a value
17:41	Chouser	and, right, nested vector form.
17:42	Chouser	did you borrow :as from somewhere?
17:43	rhickey	not specifically, but other pattern matchers have similar things
17:43	rhickey	the Clojure trick is that the binding forms are still data structures and non-conflicting with the things to which they bind
17:45	Chouser	there's no :as for vectors, though I guess & helps out.
17:46	rhickey	yes there is
17:46	Chouser	even just using sets to bind sets would cause problems for :as or & -- no order like & needs, and no value position like :as needs.
17:46	Chouser	oh, ok. It uses order then as well, like & does?
17:46	rhickey	?
17:47	Chouser	[a & b] works because [] has order and b comes after &
17:47	Chouser	#{a & b} can't mean anything about b specifically
17:48	rhickey	:as works in vectors because it is a keyword and thus can't be a bound name
17:48	rhickey	user=> (let [[a b c :as d] [1 2 3 4]] d)
17:48	rhickey	[1 2 3 4]
17:49	Chouser	right, and it's still relying on vectors having order. :as modifies the followind d -- meaningless in a set.
17:49	rhickey	ok, right
17:51	Chouser	I'm thinking that almost completely rules out sets as a robust binding form. If you were open to sets binding maps, would you be open to other mis-matches?
17:51	drewr	rhickey: You're welcome. Unfortunately, that lame link is getting down-modded so no one will see it. :-/
17:53	Chouser	I don't even know where that leads. Gah. I'm going home.
17:54	rhickey	(let [#{a b c :str/:key/:sym :anything-else-is-as} x] ...)
20:22	blbrown	hello
20:22	rhickey	hi
20:25	blbrown	rhickey, I am thinking of converting some swing/abcl code to clojure. it isn't much, but 6 months to a year from now, I think I will have made the right choice
20:25	rhickey	cool
20:40	Chouser	so (let [#{a b c :str} x]) would be the same as (let [{a "a", b "b", c "c"} x]) ?
20:40	rhickey	prefereably let [#{:str a b c} x])
20:40	rhickey	preferably
20:40	rhickey	yes
20:41	Chouser	and if unspecified it would default to :key, I hope?
20:41	Chouser	but what's :anything-else... ?
20:43	rhickey	only one of :str, :sym, :key can be supplied, if another keyword is supplied, it names the aggregate (i.e. fills the role of :as)
20:43	rhickey	(let [#{:str a b c :fred} x]) would be the same as (let [{a "a", b "b", c "c" :as fred} x])
20:57	Chouser	really? I guess that's better than what I've got, but will you be satisfied with it?
20:58	rhickey	I don't know, I wasn't thinking about it until you brought it up - just brainstorming
20:59	Chouser	ok
21:16	Chouser	{a :a, :keys [b c d], :strs [e f g], :as foo} = {a :a, b :b, c :c, d :d, e "e", f "f", g "g", :as foo}
21:19	rhickey	neat
21:28	Chouser	I guess anything that destructures maps can destructure sets just as well.
21:29	rhickey	yup
22:37	blbrown	thank god there is an ant script as opposed to mavent
22:38	blbrown	or not
23:05	rhickey	is it not working?
23:06	blbrown	no, I was just making a general comment.
23:13	Chouser	I build with ant all the time.
23:40	insectmessiah	Is anyone using webjure on a regular basis? Or is everyone basically rolling their own web frameworks right now?
23:41	insectmessiah	I need to stop being lazy and learn a Lisp, and no matter how many times I fire up SBCL, I keep coming back to wanting to pick up Clojure instead :D