#clojure log - Sep 01 2008

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10:09 joubert: Hi, I have a question regarding the design of StructMaps

10:12 rhickey: joubert: ok

10:15 joubert: Hi Rich. One can serialize vectors via Java's ObjectOutputStream, but cannot do so with StructMaps

10:16 rhickey: joubert: I haven't done any work on serialization of Clojure's data structures

10:20 joubert: rhickey: right, I understand. It seems that persistence works (automagically) for some data structures, but not for seqs currently.

10:23 rhickey: joubert: I don't doubt that, but unless there's something trivial I can do to enable that, it remains part of the 'enable serialization of all data structures' todo item

10:24 joubert: rhickey: ok

12:10 blackdog_: if I use (load file "sql.clj") should i be able to say (ns :use [clojure.contrib.sql :as sql]) or something similar?

12:10 i.e. can the new libs work with the old system?

12:12 nevermind, it works

12:13 rhickey: blackdog_: it's best to get away from load-file ASAP, put your code in the classpath and use use/require or load-resource

12:14 blackdog_: yes, I'm doing that now, and am in a limbo state :)

14:22 achim_p: hi!

14:22 i must admit lazy seqs disturb me a little :)

14:22 any ideas why this throws a NullPointerException when taking more than 1 element ...:

14:22 (def lots-of-1s (lazy-cons 1 lots-of-1s))

14:23 while this doesn't?:

14:23 (def lots-of-1s (lazy-cons 1 (map identity lots-of-1s)))

14:34 jgracin: I'm not sure, but I think Clojure evals one value in advance

14:45 achim_p: jgracin: i think you're right, but while i see why taking the first element works in both cases, i don't see why it doesn't work for more than one with the first def. and i don't see why wrapping the seq in a map call makes a difference, as map yields a lazy sequence as well ...

14:47 i should probably get some haskell books ;)

15:24 rhickey: achim_p: that was a bug, now fixed (in rev 1014)

15:25 user=> (take 10 lots-of-1s)

15:25 (1 1 1 1 1 1 1 1 1 1)

16:45 jamii: how would i write a function that block until a given ref is not nil? is there a way to force the current transaction to retry, for example?

16:46 rhickey: I don't advocate tying workflow to transactions - you can use queues or latches from java.util.concurrent and save the transaction for when you have work to do

16:47 jamii: cheers, ill have a look at the java utils.

17:15 arohner: is pred.clj missing (map?)

17:15 it appears so

17:15 (defn map? [x] (instance? clojure.lang.IPersistentMap x))

17:18 duh. it's not in pred.clj because it's built in

17:41 achim_p: rhickey: okay, thanks!

18:10 lisppaste8: jamii pasted "qt-repl" at http://paste.lisp.org/display/66179

18:10 jamii: Could someone take a look at this? There must be a better way of doing this

18:19 arohner: how do you use set! on a java field?

18:19 (def r 22/7)

18:20 user=> (set! (. r numerator) 23)

18:20 (set! (. r numerator) 23)

18:20 java.lang.ClassCastException

18:20 java.lang.ClassCastException

18:20 at java.lang.Class.cast(Class.java:2951)

18:20 at clojure.lang.Reflector.boxArg(Reflector.java:330)

18:20 at clojure.lang.Reflector.setInstanceField(Reflector.java:235)

18:20 rhickey: numerator is final

18:20 why not make a new ratio?

18:21 arohner: yeah, that would work. I was more curious to see if I could do it

18:21 rhickey: you can for non-final fields - good luck finding one!

18:22 arohner: :-)

18:22 is there a way to create a ratio with a zero in the numerator or denominator?

18:23 what I'm trying to do is go through a list, and count up the number of items that match some predicates

18:23 and I want a percentage at the end, but it would be nice to say 0 out of X matched

18:53 achim_p: arohner: if you really want to do this - (clojure.lang.Ratio. (bigint 0) (bigint 0))

18:54 arohner: achim_p: thanks

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