#clojure – 2008-02-29

2008-02-29

00:13	Chouser	Well, that worked. Ugly as sin, but it worked. Bedtime.
00:45	ericthor	anyone having problems with meta data in the latest build?
00:46	ericthor	(def #^{:a "tag"} f 1)
00:46	ericthor	(meta f)
00:46	ericthor	yields nil
05:45	arbscht	is there a clever naming convention for clojure-relevant projects?
05:50	bgeron	something with a J in the middle maybe?
05:50	arbscht	j is worth 8 points in scrabble
05:50	arbscht	this is not easy to do
14:50	Chouser	clojure is just too much fun
15:05	hoeck_	what are you doing with clojure?
15:20	Chouser	Screen-scraping web pages to generate email notifications.
15:21	Chouser	But what makes it fun is the ease with which I can invent a task-specific mini-language and use it mixed in with regular clojure code.
15:22	Chouser	Once I've got the generic HTML/XML parsing and querying, URL parsing, and email functions all set up, the specific task at hand can be written in under 50 lines
15:23	Chouser	That's navigating through three pages, picking up context as I go, parsing the final page, generating a little report, and sending it off as email.
15:28	Chouser	anyway, fun.
15:28	Chouser	:-)
15:29	rhickey_	almost finished with proxies, which will let you derive from a concrete/abstract class
15:29	Chouser	rhickey_: cool! I'll be happy to banish my few lines of Java.
15:31	hoeck_	are there situations in clojure where one will need this?
15:31	Chouser	need to derive from an Java class?
15:31	rhickey_	it's forced by some library designs
15:31	hoeck_	yes
15:32	rhickey_	they fail to use interfaces
15:32	Chouser	I need it in order to use the javax.mail package. I don't think I would ever try to use it in the design of a clojure app.
15:34	hoeck_	oh, luckily, i never touched such a library where i need to subclass something
15:36	Chouser	heh, ew. Is there a better way to do this: (. mystr (replaceAll (str "[ " (char 160) "]+") " "))
15:37	Chouser	I've got these annoying char 160s I want to treat like whitespace. I think they're  s or something.
15:37	Chouser	Anyway, the regex \s doesn't match them.
15:54	hoeck_	chouser: you could use \u00A0 in the regex
15:54	nsinghal_	i want to see if m2 is subset of m1.
15:54	nsinghal_	(defn subset? [m1 m2]
15:54	nsinghal_	(= (select m1 (keys m2)) m2))
15:54	nsinghal_	I wanted this to work for any structure passed in, list, vector, maps
15:54	nsinghal_	I tried converting it to the sequences and then do the comparison.
15:54	nsinghal_	(defn subset? [m1 m2]
15:54	nsinghal_	(let [s1 (seq m1)
15:55	nsinghal_	s2 (seq m2)]
15:55	nsinghal_	(every? #(let [item = %] (some #(= item %) s2)) s1)))
15:55	nsinghal_	This function returns REPL:1749: Bad binding form, expected matched symbol expression pairs. What is wrong here?
15:55	rhickey_	item = % is bad syntax
15:56	nsinghal_	sorry let me try agina
15:56	Chouser	hoeck_: ok, that would be a bit better.
15:59	arbscht	\xA0 rather
16:09	nsinghal_	user=> (= {:a 1} {:a 1})
16:09	nsinghal_	true
16:09	nsinghal_	user=> (= (first s1) (first s2))
16:09	nsinghal_	false
16:09	nsinghal_	user=> (first s1)
16:09	nsinghal_	<:a 1>
16:09	nsinghal_	user=> (first s2)
16:09	nsinghal_	<:a 1>
16:09	nsinghal_	user=> (= (first {:a 1}) (first {:a 1}))
16:10	nsinghal_	true
16:10	nsinghal_	When i am comparing (= (first s1) (first s2)) it returns false
16:10	nsinghal_	(first s1) evaluates to <:a 1> and (first s2) evaluates to <:a 1>
16:17	hoeck_	nsinghal: i guess comparing "< >" is not implemented yet
16:17	Chouser	how are you setting s1 and s2? I used two separate defs, and (= (first s1) (first s2)) returns true for me.
16:18	hoeck_	chouser: i used two literal maps, it returned false
16:18	nsinghal_	(= (first (seq {:a 1})) (first (seq {:a 1})))
16:18	nsinghal_	this evaluates to true
16:18	nsinghal_	(= (first (seq {:a 1 :b 2})) (first (seq {:a 1 :b 2})))
16:18	nsinghal_	this evaluates to false
16:23	Chouser	ok, I see. Pretty squirrley.
16:23	Chouser	true: (= (first {:a 1}) (first {:a 1}))
16:23	Chouser	false: (= (first {:a 1 :b 2}) (first {:a 1 :b 2}))
16:28	rhickey	map entries don't have value semantics (yet)
16:29	rhickey	but you should always be careful with (first amap), unless it's a sorted map
16:30	Chouser	careful in what way?
16:30	nsinghal_	when we convert map to seq each seqeuence can have different order
16:30	rhickey	there's no guaranteed order
16:30	Chouser	I'm not comparing map entries, but I'm using first and rest to iterate
16:30	nsinghal_	but if we cache the seqeunce and perform the match - still returns false for comparison
16:30	nsinghal_	(def s1 {:a 1 :b 2})
16:30	nsinghal_	(def s2 {:a 1 :b 2})
16:30	nsinghal_	(= (first s1) (first s2)
16:30	nsinghal_	(= (first s1) (second s2))
16:30	nsinghal_	both returns flase
16:31	nsinghal_	but you answered that is is not value checking MapEntry
16:31	rhickey	right, not yet
16:31	nsinghal_	(defn subset? [m1 m2]
16:31	nsinghal_	(every? #(let [item %] (some #(= item %) (seq m1))) (seq m2)))
16:32	rhickey	I'm not happy with Map.Entry as a base - may switch map entries to pairs
16:32	rhickey	nsinghal_: nested #() forms is bad style - too hard to read
16:32	hoeck_	rhickey: and the '<>' sharp brackets? are they used for reading map entrys?
16:33	rhickey	no - there is no read syntax for map entries
16:33	rhickey	yet
16:33	nsinghal_	somehow it is fun to right hard code in Clojure but I will stay away from thius
16:33	nsinghal_	thx
16:34	rhickey	as I said, I think I'd rather switch to pairs than elevate map entries to first-class status
16:35	nsinghal_	that will be nice, map entries sound like part of a map while you can have list, sequence etc for pairs
16:35	rhickey	yeah, they aren;t more useful than [k v]
16:36	nsinghal_	thx
16:36	hoeck_	i was just puzzled by the output of (first {:a 1}) being <:a 1>
16:37	Chouser	Just today I wanted to use map to process both parts of a map entry.
16:37	rhickey	You can do destructuring of map entries already using [k v]
16:38	Chouser	ah, that's cool.
16:38	Chouser	oh! I can use that...
16:39	Chouser	ah, very nice.
16:41	hoeck_	destructuring in let and fn is really nice
16:41	rhickey	I still have to add it to loop
16:43	hoeck_	but i found out, while using clojure i am sticking more to the functional paradigms of lisp
16:44	Chouser	those immutable data strcutres are keeping you honest, aren't they.
16:44	rhickey	you pretty much have to
16:44	rhickey	:)
16:44	hoeck_	as opposed to common or emacs lisp where i loved (and love) the loop and iterate macros
16:44	rhickey	loop in Clojure is completely functional
16:45	Chouser	using scala broke me of needing looping structures. It's recursion or (map/reduce/filter) for me.
16:46	rhickey	Isn't Scala less functional than Clojure?
16:47	Chouser	eh. Scala allows some less functional code, but it too provides mainly immutable data, and fully supports tail recursion, map/reduce/filter, and for-comprehension.
16:47	Chouser	you can use while loops and Java mutable containers if you really want to.
16:48	rhickey	but Scala itself also has mutable variables and members, not just in the Java interop, right?
16:49	Chouser	yeah, you can declare a "var" instead of a "val", but that seems roughly like "def" instead of "let".
16:50	Chouser	Not sure about class data members -- didn't do much with that, but I think it's essentially the same-- pick an immutable "val" or a mutable "var".
16:50	rhickey	I don't think so - given a Scala object can you know that it is safe to treat it as a value, i.s. that it is immutable?
16:51	rhickey	If anywhere in the member chain there's a var, you can't
16:51	Chouser	Right, I'm not sure if that info is carried in the type system or not. I think probably not.
16:52	rhickey	mutable data scares me much more than lack of a 'type system"
16:52	Chouser	I haven't written anything big in Scala (or Clojure, for that matter) to become familiar with the interaction of more complex types.
16:53	Chouser	I'm still ambivalent about static types. I think what I want is optional static typing, but I'm not sure.
16:54	Chouser	Scala requires types, and I often found myself fighting to correctly declare what I new to be functionally correct code, or distorting my design to make up for static typing (or my lack of understanding of its type system).
16:54	Chouser	s/new/knew/
16:58	Chouser	what's the best way to test if x is empty, when x may be a map or a list of map entries?
16:58	rhickey	(seq x)
16:58	Chouser	(nil? (seq x)) works, but is it slow for a large x?
16:59	rhickey	no - seq is constant time for everything
16:59	Chouser	splendid, thank.
16:59	Chouser	thanks.
17:00	rhickey	(when-not (seq x)... better than (when (nil? (seq x)) ...
17:01	Chouser	for performance or readability?
17:01	rhickey	readability, more idiomatic, the return value of seq is directly testable by if, that's an important idiom
17:02	Chouser	ok
17:02	Chouser	I'm in a cond. I'll re-arrange...
17:02	rhickey	in a cond, ok
17:04	Chouser	I'm finding I like cond even when I could use if, just because I can mark the :else clause more clearly.
17:05	rhickey	interesting - pg took else out of cond and called it if in arc
17:05	Chouser	heh, yeha.
17:06	Chouser	is there a common idiom for where to put terminal case in recursion? First, last, doesn't matter?
17:07	rhickey	I usually follow the positive test - if there's stuff to do, do it, (else) return
17:08	Chouser	ok
17:13	ericthorsen	when passing java objects to clojure do i need to wrap them in something?
17:13	rhickey	nope
17:13	ericthorsen	just checking
17:13	rhickey	primitives will get boxed when passing to invoke as Object
17:14	rhickey	which is what Clojure expects to see
17:14	ericthorsen	just wanted to make sure clojureVarInJava.fn().invoke(new MyJava())
17:14	ericthorsen	was all i needed
17:15	rhickey	just use clojureVarInJava.invoke(...), don't use fn()
20:08	rhickey__	proxies are up! - you can now derive from concrete classes dynamically
20:16	albino	Is a concrete class a class written and compile in java?
20:16	rhickey__	It's a class that's not an interface
20:17	rhickey__	but yes, it must be named and therefore from Java-land
20:18	rhickey__	for instance you could derive a proxy from javax.mail.Authenticator
20:19	rhickey__	and override getPasswordAuthentication()
20:22	Chouser	hm, sounds familier...
20:28	Chouser	ha! just like that. worked perfectly first try.
20:28	rhickey__	great!
20:28	Chouser	thank you!
20:28	rhickey__	sure - it was the most frequently requested missing feature
20:28	Chouser	that code in proxy.clj's pretty scary.
20:29	rhickey__	Welcome to compiler writing
20:33	rhickey__	actually at ~200 lines of serious stuff, it's much more compact the kind of code that takes Compiler.java to 3500
20:40	albino	Is that an actual file Compiler.java?
20:41	rhickey__	yes, part of the Clojure source
20:41	albino	ahh, okay
20:41	albino	I thought you were referencing jdk7 source code or something
20:42	rhickey__	no, just me in Java vs me in Clojure
20:43	albino	yeah
20:43	albino	rhickey__: you pretty good with cL?
20:43	albino	err CL
20:43	rhickey__	ok
20:44	rhickey__	It was my first Lisp love...
20:44	albino	rhickey__: have you thought about porting clojure to CL?
20:44	rhickey__	clojure started in CL
20:44	albino	oh cool
20:44	albino	does that version still exist in some source control tool somwhere?
20:44	rhickey__	Originally it was CL that generated Java and C# source
20:45	rhickey__	Everything source-wise is on SF, all the design stuff is on my Macs
20:46	rhickey__	Clojure never targeted CL though
20:47	rhickey__	It has changed a bunch over the years, a lot of work preceded its release in October
20:48	Chouser	The first release was just in October?
20:48	rhickey__	yup
20:49	Chouser	How much have you written in Clojure, not counting parts of Clojure itself?
20:49	rhickey__	mostly Clojure
20:49	rhickey__	that's the bane of the compiler writer
20:50	Chouser	:-) yeah.
20:50	albino	rhickey__: so you've been working on it on your own for years, and just got around to releasing it recently?
20:50	rhickey__	I am very excited about using it for the rest of my work
20:51	Chouser	what is that other work?
20:51	Chouser	If I may ask.
20:51	rhickey__	yes, worked for years to solve the Lisp+Java/.Net problem - see jFli, Foil, Lisplets etc
20:52	rhickey__	My other work is audio research, cochlear modeling, scheduling systems etc
20:52	Chouser	huh! ok.
20:53	pjb3	Is there a way to have one clojure script load another clojure script?
20:54	rhickey__	load-file
20:54	albino	wow, never heard of jFli before, looks cool
20:57	Chouser	neither \xA0 nor \u00A0 work in my string literal
20:57	Chouser	So I guess I'll continue using (str (char 160))
21:27	pjb3	Is there something like load-path and require in clojure?
21:27	pjb3	where load-path is all of the places clojure looks for files to load
21:27	pjb3	and require loads them, making sure not to reload already loaded files
21:28	rhickey__	not yet, it has been suggested
21:29	pjb3	ok, it seems like that would be helpful for organizing larger projects, what do you think?
21:30	rhickey__	I think that loading and requiring are going to be separate
21:31	pjb3	what do you mean by that
21:32	rhickey__	that loading should not be a side-effect of requiring, requires can be analyzed to create a load system definition
21:38	pjb3	So would (require "foo") load foo.clj?
21:40	ericthor_	are you referring to parsing and finding all the refers for a set of files to determine a load order?
21:41	ericthor_	what about qualifier names? name-sapce/func-call
21:41	rhickey__	So would (require "foo") load foo.clj -> no
21:41	pjb3	then what does (require "foo") do ?
21:41	ericthor_	"requires can be analyzed to create a load system definition" ...how?
21:42	ericthor_	we were discussing this today and ran into the question on knowing about other namespaces not in the 'refers' calls
21:43	ericthor_	we were discussing this today and ran into the question on knowing about other namespaces not in the 'refers' calls
21:43	ericthor_	I'm ready to do it!
21:43	rhickey__	a program could be analyzed for refers and requires to determine the dependency graph and generate a loading plan
21:44	ericthor_	but it would need to analyze the use of qualified names as well...yes?
21:47	rhickey__	no - if you use qualified names without refer you will need a require
21:48	ericthor_	I cannot say n1/foo without a (require 'n1) ?
21:49	ericthor_	i know it works if n1/foo is loaded...is it not 'proper' clojure?
21:50	rhickey__	there is no such thing as require yet, we're just speculating, but the loading system will need it
21:51	ericthor_	that was my next question....
21:52	ericthor_	that would not be an unreasonable requirement IMHO and at least is something we can do and use now even if the requires is just used for a dependancy graph
21:52	ericthor_	i like it...it's simple