#clojure – 2008-05-25

2008-05-25

09:22	blackdog	am i correct in thinking that anything after the -- should be sent into command-line-args, in java -cp $CP clojure.lang.Script $comm.clj -- hello
09:24	blackdog	cos i'm getting java.lang.ClassCastException: clojure.lang.IteratorSeq cannot be cast to clojure.lang.IFn
09:55	rhickey	what are you doing with command-line-args? That's a sequence of args, not a function
09:55	rhickey	e.g. the script:
09:55	rhickey	(println command-line-args)
09:55	rhickey	(flush)
09:55	rhickey	prints: (hello)
10:27	blackdog	duh, thanks that works :)
10:27	rhickey	np
10:29	blackdog	rhickey, really enjoying clojure, just using it for scripting purposes right now while i learn lispish ways but i think you're onto a winner
10:29	rhickey	great
16:20	dabd	hi all
16:20	rhickey	hi
16:21	dabd	playing with clojure at the repl I found this behavior that I don't understand
16:21	dabd	(lazy-cons 1 (list))
16:22	dabd	returns (1 nil)
16:22	dabd	but (cons 1 (list)) returns (1)
16:23	dabd	I'm using clojure compiled from source boot.clj SVN 874
16:33	rhickey	the second arg to cons/lazy-cons must be a seq. Unfortunately, () and (list) are testing true for (seq? ) when they shouldn't. It should be (cons (seq (list))), just like it should be (cons (seq []))
16:34	rhickey	i.e. in clojure there's no such thing as a empty seq, either there is a seq with a first, or there is no seq - nil
16:34	abrooks	I thought a list was its own seq.
16:35	rhickey	except for (), I have to fix that
16:36	abrooks	Ah, I see.
16:36	rhickey	that is also an implementation detail, proper use of collections should call seq
16:36	rhickey	so you could swap a vector and it would still work
16:36	rhickey	list is not a privileged collection in Clojure
16:36	rhickey	just one of many
16:39	dabd	so in the examples I typed the compiler should issue an error?
16:45	rhickey	runtime error
17:04	dabd	thanks. I have one more question
17:05	rhickey	ok
17:05	dabd	I find the fibonacci example in the wiki book a little bit harder to understand than the classic haskell one liner
17:05	dabd	fiblist = 0 : 1 : (zipWith (+) fiblist (tail fiblist))
17:06	dabd	I tried to write a similar version in clojure but I couldn't
17:06	lisppaste8	dabd pasted "fib" at http://paste.lisp.org/display/61250
17:07	dabd	is it possible to write something similar in clojure with the lazy operators?
17:08	Chouser	dabd: looks ok to me
17:09	Chouser	(take 10 (fib)) ;==> (0 1 1 2 3 5 8 13 21 34)
17:10	dabd	ok I forgot to use 'take'
17:10	dabd	:-)
17:15	dabd	anyway my version is very inefficient
17:35	Chouser	(def fib (list* 0 1 ((fn step [a b] (lazy-cons (+ a b) (step b (+ a b)))) 0 1)))
17:36	Chouser	...because what we really need is more implementations of fib.
17:56	jbalint	Hi
17:56	Chouser	Hi
17:57	jbalint	i'm having a problem with the clojure emacs mode calling switch-to-lisp (when loading a file), but its opening the comint in the same window my file is in, but i already have it open it another window. any idea why this is happening or how to fix it?
17:57	Chouser	sorry, I've never tried clojure in emacs. Anyone else here have an idea?
17:57	jbalint	what do you use for editing
17:58	Chouser	usually just vim
17:58	jbalint	ah
17:58	Chouser	I've started trying to use enclojure in NetBeans, but it's not quite ready "enough" for me.
18:00	jbalint	whats kind of stuff are you working on with clojure
18:00	Chouser	http://clojure-log.n01se.net/ is generated by clojure code
18:01	jbalint	is it from your filesystem, or a bot?
18:02	Chouser	I also have a thing that pokes around on real estate sites and sends me an email summary of resent changes to properties that match my criteria.
18:02	dudleyf	jbalint: I've had better luck with the slime mode, even though it's pretty young
18:02	Chouser	for the irc log, it just reads a text file generated by irssi
18:02	jbalint	dudleyf: thanks, i'll give it a look
18:03	jbalint	Chouser: I see, cool
18:03	jbalint	is it possible to compile to a class file?
18:03	jbalint	the only thing i found was proxy , but its only sensible at runtime
18:03	Chouser	if you need to define a new class, you can use gen-and-save-class
18:04	jbalint	great, where is that documented?
18:04	Chouser	but that's really just for java interop. The implementation will still be in a .clj file.
18:04	Chouser	You can pack .clj's into a .jar and have the runtime find them there.
18:04	jbalint	is there a special classloader?
18:05	Chouser	gen-and-*-class is pretty new, not in the release. If you get the svn version, there are some docs and examples in the code.
18:05	jbalint	ok
18:07	Chouser	I belive Clojure uses it's own special classloader, yes. But I think that has more to do with how every expression is compiled on the spot and then loaded, more than anything to do with finding .clj files.
18:08	jbalint	but i need to be able to load classes, like java. so either i need a compiled classfile or a classloader that reads the cljs
18:09	Chouser	why do you need to load classes?
18:09	jbalint	i dont know? a thousand reasons. this is how java works
18:09	Chouser	I believe you, there are just different reasons with different solutions.
18:10	jbalint	the most obvious need would be using clj classes with some framework that you pass in a class name
18:10	jbalint	it would load the class, without needing some special "support" for clojure
18:10	Chouser	(gen-and-load-class) allows you to produce a new named class at runtime, which you can then pass to an extrnal framework.
18:11	dudleyf	But that just makes a "shell" object that uses Clojure functions as methods
18:11	jbalint	yes, thats fine
18:12	Chouser	I believe servlets need the path to a .class file. You can use (gen-and-save-class) to generate such a class file.
18:12	jbalint	see, there's another example :)
18:12	Chouser	If something needs you to pass in an instance of class derived from some specific base class, (proxy) may be all you need.
18:12	jbalint	yeah, i've been looking at that
18:13	jbalint	gen-and-save-class must be quite similar?
18:13	Chouser	So, as I said, it depends on what you actually need.
18:13	jbalint	besides the output of course
18:14	Chouser	no, gen-and-*-class are pretty different from proxy.
18:14	jbalint	well, i just need general classloading compatibility with java
18:14	Chouser	proxy is simpler, if you can get away with it.
18:14	jbalint	yes, sorry. i mean from the args point of view.
18:14	jbalint	although, what is the difference?
18:15	jbalint	proxy will need to generate a class, just goes into a classloade rinstead of a file
18:15	Chouser	proxy creates an anonymous class and an instance in-line. It's very easy to close around whatever data you need. And you can change your code and re-run it no problem.
18:16	jbalint	ah
18:16	Chouser	But gen-and-*-class create named final classes, so you can't change them once you load them.
18:16	Chouser	to reduce the pain that causes, they split of the class definition from the implementation, which makes them a bit more complicated to use.
18:17	jbalint	ok, sounds painful :p
18:18	Chouser	well, it's not too bad. But you still want to use proxy if you can.
18:19	Chouser	You can generally use proxy unless you need to call your super-class, or override something private or protected. There may be other restrictions I'm not thinking of.