#clojure – 2008-06-23

2008-06-23

04:08	jmbr	hi
04:09	jgrant	hi
07:24	spacebat_	I think I'm missing something basic about clojure
07:24	spacebat_	(def x 1) says I've bound #'user/x
07:24	spacebat_	I can evaluate it with x
07:24	spacebat_	and get 1
07:24	drewr	spacebat_: You're in the user namespace by default.
07:25	spacebat_	yup
07:25	spacebat_	like common lisp
07:25	spacebat_	but there is no setf
07:25	drewr	:-)
07:25	spacebat_	(set! x 2) doesn't work
07:25	spacebat_	(set! user/x 2) doesn't work
07:26	drewr	Clojure doesn't let you set a value that easily.
07:26	drewr	It's a feature.
07:26	spacebat_	nor (set #'user/x 2) nor (var-set x 2)
07:26	drewr	x is a Var, which are immutable.
07:26	spacebat_	but in a few places they say that Vars are mutable (thread locally)
07:27	spacebat_	"While Vars ensure safe use of mutable mutable storage locations via thread isolation..." (http://clojure.org/refs)
07:28	drewr	You have to wrap it in a BINDING form, which is thread-local.
07:28	spacebat_	each time I update it?
07:28	spacebat_	but when I leave the binding that change is gone
07:29	drewr	What problem are you tring solve?
07:29	drewr	trying
07:29	spacebat_	I have a recursive function
07:29	spacebat_	I thought I could close over a variable to count the number of invokations
07:30	spacebat_	like I can in common lisp
07:30	drewr	There's an idiom for that in Clojure. Likely you'll want LOOP..RECUR.
07:31	drewr	Something like (loop [ct 0] ... (recur (inc ct))).
07:31	spacebat_	pjb3 mentioned that this morning, but I'm not getting far with the docs I'm afraid
07:31	spacebat_	it seems on the one hand I don't know enough lisp to understand some things
07:32	spacebat_	but I know enough common lisp to go about things the wrong way :)
07:32	drewr	You probably write imperative CL, which won't help.
07:32	drewr	You need to think more functionally (which Clojure forces you into).
07:33	spacebat_	yes I'm not used to being forced
07:33	spacebat_	so loop..recur operats on refs
07:34	drewr	They operate on whatever arguments you give them.
07:34	drewr	Not Ref-specific.
07:34	spacebat_	and can go anywhere - its not like a loop construct is like a foor or while in imperative languages
07:34	spacebat_	ok
07:34	drewr	Look through boot.clj to get some examples.
07:34	spacebat_	thanks drewr I will
07:35	spacebat_	looking at clojure I thought, I should learn some CL in order to 'get' it
07:35	spacebat_	but it seems clojure is different enough that I should just focus on it
07:37	drewr	I agree.
08:10	cgrand	spacebat_, can you paste your code? http://paste.lisp.org/new/clojure
08:13	lisppaste8	spacebat_ pasted "trivial recursive function" at http://paste.lisp.org/display/62714
08:15	spacebat_	the paste is of the function before I tried loop...recur
08:15	spacebat_	because I have no idea how to use it in a recursive context
08:16	cgrand	well loop...recur is here to work around the lack of TCO on the jvm. Since your function is not tail recursive you can't use loop...recur to write it
08:18	spacebat_	is there a way to count how many times fib is called?
08:19	cgrand	as said before, with binding and set!, let me annotate your paste
08:20	spacebat_	right, I couldn't see how to keep the value of the binding after I'd left the scope
08:20	spacebat_	or can the binding wrap the function...
08:23	lisppaste8	cgrand annotated #62714 with "counting fibs invocations" at http://paste.lisp.org/display/62714#1
08:25	spacebat_	right, so (def fib-count) is 'unbound' because there is no initial value, it looks up and finds the binding
08:26	cgrand	you can provide a default (root) value but you are unable to alter it with set!
08:26	spacebat_	I tried using def and set! but when I threw in binding as well, put it in the wrong place
08:26	spacebat_	ok
08:26	spacebat_	but binding allows it
08:27	spacebat_	so this is imperative style, but binding limits the scope
08:28	cgrand	and the only way to change the root value is to re-def. Yup, binding sets a value for the var and allows you to alter it
08:29	spacebat_	thanks a lot, that brings some pieces together
08:30	cgrand	yw
08:30	spacebat_	now to find out how to get command line args
08:30	spacebat_	someone posted a patch to the group but I assume its been integrated by now
08:31	cgrand	don't forget to put -- before your args
10:27	cgrand	rhickey: Hello, could clojure.lang.Numbers.compare be exposed? (as <=> or whatever please you) Without it an unsuspecting user (eg me) may write comparators using substraction and get overflows on the return value of the Comprator :-(
10:28	rhickey	ok
10:29	cgrand	thanks!
10:32	rhickey	Although I heard <=> referred to as the "spaceship operator" at a Java One talk and instantly developed an aversion to it...
10:35	cgrand	it reminds me of text-mode breakout games but it was the only one (with cmp) to come to my mind.
10:36	cgrand	signum ?
10:37	rhickey	ah
10:37	rhickey	but that is a unary op
10:38	cgrand	you're right :-(
10:38	rhickey	one I want to add
10:45	cgrand	or AFn.compare could be changed to not use intValue
10:57	rhickey	cgrand: what would that solve?
10:58	rhickey	compare is defined to return int in Comparator
11:11	StartsWithK	why there is no (char-array) and #^chars hint?
11:12	rhickey	StartsWithK: haven't gotten to it - first pass was for numerics
11:13	cgrand	rhickey: By changing AFn.compare to not use Number.intValue, I mean replacing the call to Number.intValue by something signum-like. It would make use of fns as comparators more foolproof: a comparator fn would then be able to return any number without caring whether it firs into an int or not.
11:13	cgrand	s/firs/fits/
11:14	rhickey	seems like double work
11:37	rhickey	ok - I've added compare, and based sorts on compare:
11:37	rhickey	user=> (sort [19 3M 9.0 2 7 nil 4])
11:37	rhickey	(nil 2 3M 4 7 9.0 19)
11:40	cgrand	thanks!
13:00	StartsWithK	how do i create array of bytes (not java.lang.Byte)?
13:01	rhickey	(make-array Byte/TYPE 100)
13:02	rhickey	or (make-array (. Byte TYPE) 100) if you are not on SVN
13:03	rhickey	the names of the classes corresponding to the primitives are static members of their respective boxed types, all called TYPE
13:04	StartsWithK	rhickey, this works perfectly, thanks
13:33	Lau_of_DK	rhickey: In the concurrency talk you mentioned some theory on log(n) calc times (or O(n)) and similar things, which were important in regards to obtaining near constant time. Do you have some links for some background reading on these issues?
14:49	abrooks	Chouser: What was the last version of Clojure SVN you had working with Enclojure?
14:49	rhickey	Lau_of_DK: you can find some info by googling bagwell hash tries
14:50	abrooks	Lau_of_DK: This wikipedia page has two good links: http://en.wikipedia.org/wiki/Hash_array_mapped_trie
14:55	Lau_of_DK	Thanks to both of you
16:25	arbscht	does clojure have trouble handling class names containing .? I can't access java.awt.geom.Point2D.Double for example (ClassNotFoundException)
16:26	rhickey	the real name of that nested class is: java.awt.geom.Point2D$Double
16:26	arbscht	I see
16:27	arbscht	thanks
16:27	rhickey	sure
16:37	jgrant	hey everyone, i have a question about var scope
16:38	jgrant	I've defined a global var x in a specific package 'mypackage
16:38	jgrant	now after calling the load-file function I'd like to access this variable and update it
16:39	jgrant	it seems the loaded file has it's own scope if i do a (def x) it seems to be a copy ?
16:40	rhickey	are you still in the same package?
16:40	rhickey	namespace
16:40	jgrant	yes
16:41	rhickey	what makes it feel like a copy?
16:44	jgrant	it doesn't have the value assigned in the parent file
16:45	jgrant	thanks for bearing with me i'm still figuring my way around clojure's idioms
16:45	rhickey	if in the defining file you say (def x 42), then after loading x should be 42, no?
16:45	jgrant	yea i agree it should i must be doing something wrong
16:46	rhickey	are you def'ing it again somewhere?
16:48	jgrant	yes in the loaded file
16:48	rhickey	2x in the same file?
16:48	jgrant	once
16:49	jgrant	once in the parent and once in the loaded file
16:49	rhickey	I don't understand what you mean by parent then
16:50	rhickey	foo.clj defs x and loads bar.clj that defs x?
16:50	jgrant	clojure loads file1 (which defs var x) which loads file2 (which also defs var x)
16:50	jgrant	yes
16:50	rhickey	both in same ns?
16:50	jgrant	yes
16:51	rhickey	they both have in-ns explicitly?
16:51	jgrant	bar.clj has same (in-ns ...) as foo.clj
16:51	jgrant	yes it's explicit
16:51	rhickey	last def should win
16:52	jgrant	should foo.clj see the update made to x by bar ?
16:53	rhickey	exprs happen in order, latter see former
16:54	jgrant	ok it's working now , not sure what i fixed
16:54	jgrant	another related question
16:54	jgrant	bar.clj will be updating x in a thread
16:54	rhickey	oh
16:54	jgrant	would (dosync (def serve-count (inc serve-count))) be valid ?
16:55	rhickey	updating by def?
16:55	jgrant	yea
16:55	rhickey	then x should be a ref and you shouldn't be re-def-ing it
16:55	rhickey	(def cnt (ref 0))
16:56	rhickey	(dosync (commute cnt inc))
16:56	jgrant	ah i see !
17:00	jgrant	I'm getting 'Unable to resolve symbol: x' when i try that ?
17:02	rhickey	are you launching your threads in bar prior to the def in foo?
17:02	jgrant	not at all
17:02	jgrant	(def cnt (ref 0))
17:02	jgrant	is one of the first lines in foo.clj
17:03	jgrant	uggh, you are right
17:03	jgrant	i was not !
17:06	jgrant	thx rich
17:06	rhickey	sure
17:21	jgrant	mmmm, (println x) doesn't seem to report the right value
17:21	rhickey	@x
17:22	jgrant	um yea that's what i mean
17:22	rhickey	you want the value in the ref, not the ref itself
17:22	jgrant	it seems to do with how many threads are trying to update x
17:22	jgrant	if i run a few at a time i see the value inc
17:22	jgrant	if i run a lot it seems to stay at 0
17:26	jgrant	aha
17:29	jgrant	calling (dosync (commute cnt inc))
17:29	jgrant	has to be in the enclosing function used by the thread
17:29	jgrant	if it's in another function called by the thread then it does not work
17:38	jgrant	(or maybe it requires the dosync to be in foo.clj)
17:39	jgrant	having it in bar.clj doesn't seem to work
17:52	jgrant	The dosync doesn't work if it's in a function that exists also in foo.clj
17:52	jgrant	seems like it needs to be in the same function
17:52	jgrant	that is used as the thread
18:00	jgrant	rich : nevermind another one of my own bugs, it works exactly as you described
23:33	jgrant	why does not work in clojure ?
23:34	jgrant	(map (fn [fname]
23:34	jgrant	(load-file (str (. (File. ".") getCanonicalPath) "/src/" fname))) '("file1.clj" "file2.clj" "file3.clj"))