#clojure log - Feb 12 2008

The Joy of Clojure
Main Clojure site
Google Group
List of all logged dates

11:37 Chouser: I guess neither recur nor thisfn do what I want from inside a lazy-cons

11:38 rhickey: if you are on the latest SVN you can name your fn like this: (fn name [args]... (lazy-cons x (name ...

11:39 as described here: http://groups.google.com/group/clojure/msg/afb8809c741567bc

11:54 Chouser: ah, cool. Well, my function was already named via defn, so I could use its name.

11:54 I just thought recur would be more correct before I realized that it didn't really make sense for lazy-cons

11:55 rhickey: right, and thisfn didn't nest, so it had to go

11:55 Chouser: so then I tried thisfn, thinking that was still "more correct" than refering to my own function by name. That gave me a difficult to understand error.

11:55 wrong number of params.

11:56 I suppose thisfn was refering to a func built by the lazy-cons macro? Anyway, it took me a while to figure that out.

11:56 So now I'm back to the obvious solution that I had at first. ;-)

11:59 rhickey: that's good, sorry for the confusion

12:00 Chouser: no need to apologize. If I had any better idea how I thought it should work, I would suggest it. But I've got nothin'

12:00 Unless... hm, is there any way the "wrong number of args passed" error could give the name of the function you're actually calling?

12:01 ...if it's named.

12:01 or maybe the list of formal parameters? ...except of course there are many such lists for each fn.

12:01 Well, nm.

12:01 Like I said, I've got nothin'

12:02 rhickey: the name might be possible, I'll look into it

12:03 Chouser: It's very good to have the line number of the .clj file in the stack trace. Dunno how hard that was, but it sure helps a lot.

12:05 rhickey: Clojure emits real debug info - I wish more of the Java debuggers could deal with non-java files

12:06 Chouser: I think that's a problem with the whole IDE mentality... Giant stacks of code and tools all assuming some particular source language.

12:07 Maybe one day when we have the perfect language such effort will be justified. But for now I think it just helps lock people into old languages.

12:08 rhickey: but these days they know it could at least be JSP or Javascript, yet each gets special-cased...

12:08 Chouser: rhickey: have you looked at arc at all? I'm a bit curious what you think of its goals, syntax decisions, etc.

12:09 rhickey: I'm very envious of the attention it gets, but haven't looked at the language in detail. On the surface it seems to have a lot less going for it than Clojure ;)

12:11 Chouser: heh. yeah. If you'd published a couple popular books (and maybe made a million dollars) first, I bet clojure would get more attention.

12:11 rhickey: I'm working on it

12:11 Chouser: but I tend to agree. I wouldn't claim to know much about lisps, but I wrote a couple projecteuler solutions in arc, and was a bit disappointed.

12:12 I like some of the conventions that it has, but I can whip up a couple macros to give me that in clojure, and then I still get access to Java libs, namespaces, etc.

12:13 I like arc's (if) ... the power of (cond) with the simplicity of CL (if)

12:15 rhickey: I think other things are much more important - especially abstractions for the core data types

12:15 Chouser: yes, I agree.

12:16 like I said, if I want arc's (if) bad enough, I can write a pretty simple macro in clojure to get it (although any other clojure user might be annoyed while reading my code).

12:16 rhickey: Clojure cond is pretty lean already

12:17 Chouser: but trying to write macros in arc to get abstract data structures would be a *huge* pain, even if it were possible.

12:18 I played with scala a bit before picking up clojure, and the similarities and differences are interesting.

12:18 both have data structure abstractions, but scala is much more "classical" in it's OO.

12:19 I haven't done objects/classes/type tag stuff in clojure yet

12:20 rhickey: Clojure is much simpler than Scala

12:20 Chouser: Scala comes with the kitchen sink pre-installed.

12:21 But of course it also has static typing -- I'm not sure which I prefer on the front.

12:21 Scala has no macros, which is a big strike against it.

12:25 But I can't say I like lisp's lack of syntax. Clojure's [vectors] help a little, but I guess nobody willing to invest a bunch of time in creating a lisp is likely to see a need for more syntax.

12:37 oh! cond returns nil?

12:38 I guess its nested ifs for me.

12:47 rhickey: ? cond returns the value of the matching expr

12:48 takes an even number of args, this is not Arc :)

12:55 Chouser: http://clojure.sourceforge.net/reference/macros.html

12:55 "(cond) returns nil"

12:56 oh! And my problems was I was passing a list of lists of 2 items each.

13:02 rhickey: right - Clojure doesn't need those extra parens

13:06 Chouser: cool. What about that line in the docs? Did I misunderstand it, or is it incorrect?

13:08 rhickey: I thought you meant cond always returns nil. Yes (cond) returns nil.

13:12 Chouser: oh! ha. ok, so I misused the macro, and then misread the docs.

13:12 ericthor: there is a netbeans plugin and it's very easy to use

13:13 oops...wrong room

15:13 rhickey: insvn - compiled regex literals #"pattern" - #"[0-9]+"

15:14 (re-seq #"[0-9]+" "abs123def345ghi567") -> ("123" "345" "567")

15:15 la_mer: rhickey: oooh, very nice :-D

15:15 Does this mean reader macros are coming, or is this bolted into the runtime?

15:17 rhickey: It's a reader macro, but I still am not opening up the reader at this time

15:17 (let [[a b] (re-matches #"([-+]?[0-9]+)/([0-9]+)" "22/7")]

15:17 [a b])

15:17 -> ["22" "7"]

15:18 la_mer: FYI, I'm afraid that the eclipse plugin hasn't gotten much love over the past weeks. Work has been absolutely nuts.

15:18 rhickey: hopefully the namespace stuff will help

15:20 la_mer: That's also nice. I would think it'd be ideal if the regex literal yielded a fn that returned an easily destructurable vector when passed a string to match against.

15:20 Yeah, the namespaces will make everything a lot easier.

15:21 It's just a matter of getting a few spare hours over a couple of weekends to mash everything together (and unwind the eclipse API's along the way).

15:22 rhickey: I think hardwiring the vector might be limiting, useful sometimes but not others

15:22 e.g. the sequence case

15:33 Chouser: could #"" return a regex object that also implements IFn?

15:34 rhickey: The problem is it would no longer be a Pattern for use by the rest of the Java API, as it is now (Pattern is final)

15:34 Chouser: Ah. ok.

15:53 hash- and sorted-maps are immutable?

15:55 rhickey: yup

15:56 Chouser: so is there something better I should use for memoizing, where I'm going to be doing a lot of one-at-a-time inserts?

15:56 Or do they perform ok for that.

15:58 rhickey: they are very good, IMO. but java.util.concurrent.ConcurrentHashMap is still available - depends on the use case

15:58 The compiler uses the persistent collections extensively

15:59 and if you ever need to snapshot or branch, nothing can compete

16:00 Chouser: right, I (am beginning to) understand the huge value of immutable data and how to work with it, but I really need to have fast inserts.

16:00 I'll try with hash-map first and see how it goes.

16:02 rhickey: I benchmarked against the Java collections a good bit, the Clojure collections are within striking distance, and sometimes the lookup of the hash-map is faster. By all means try to use them and let me know if it becomes the bottleneck.

16:03 Chouser: it must not copy the entire data set for each insert?

16:04 rhickey: that's right

16:26 Chouser: turns out I only need a couple hundred inserts. plenty fast.

16:31 rhickey: (defn test-map [n]

16:31 (loop [m {} i 0]

16:31 (when (< i n)

16:31 (recur (assoc m i i) (inc i)))))

16:32 user=> (time (test-map 100000))

16:32 "Elapsed time: 322.976 msecs"

16:33 Chouser: :-)

16:33 now I just need to figure out why my algorithm is failing.

21:12 Could I use defmulti to define my own data structure that implements ISeq or whatever?

21:13 rhickey: look at bean in the latest boot.clj for an example of implementing IPersistentMap

21:14 lazy-cons implements ISeq pretty easily

21:14 Chouser: ok

21:14 rhickey: but multimethods don't map to Java methods

21:18 Chouser: (implement ...) huh, ok.

Logging service provided by n01se.net