Hi,
Am 25.07.2011 um 23:58 schrieb Sam Aaron:
> Sorry, I should have been more specific. The callback-based watchers are
> cool, but I don't believe they specifically address my problem (which I don't
> believe I sufficiently explained from the outset).
>
> Hopefully this is a more succinct an
Hi again,
Am Dienstag, 26. Juli 2011 11:35:08 UTC+2 schrieb Meikel Brandmeyer:
> (defn update!
> [a f & args]
> (let [updated? (promise)
> watch (fn [k a o n] (remove-watch a k) (deliver updated? (not= o
> n)))]
> (add-watch a (Object.) watch)
> (apply swap! a f args)
> @
Hi Sam,
an another hardcore solution:
(defn update!
[a f & args]
(let [updated? (promise)
watch (fn [k a o n] (remove-watch a k) (deliver updated? (not= o
n)))]
(add-watch a (Object.) watch)
(apply swap! a f args)
@updated?))
But...
Am Dienstag, 26. Juli 2011 10:56:25 U
On Tue, Jul 26, 2011 at 4:56 AM, Sam Aaron wrote:
> Hey Ken,
>
> Thanks for this :-)
You're welcome.
> Actually I was just looking at compare-and-set! just now. This solution seems
> nicer than Nick's 'place changed/old-val in atom' but still not particularly
> clean as you have to enter a tig
Hey Ken,
On 26 Jul 2011, at 09:45, Ken Wesson wrote:
>
> This seems to have been left out:
>
> (defn swap-and-also-return-old! [^clojure.lang.Atom a f]
> (loop []
>(let [v @a
> nv (f v)]
> (if (compare-and-set! a v nv)
>[nv v]
>(recur)
>
> :)
Thanks for t
On Tue, Jul 26, 2011 at 4:00 AM, Sam Aaron wrote:
> However, it seems remarkably kludgy to encode the old value into the contract
> of the atom and *all* update fns when really this could be achieved in a much
> cleaner fashion with a version of swap! that returned a vec of new and old
> vals:
Hi Nick,
On 25 Jul 2011, at 23:55, cassiel wrote:
>
> Not very practical, but if you want a safe transaction-free operation
> on an atom which returns whether it was changed, you can perhaps hack
> it by embedding the change state into the atom itself:
>
> (def a (atom {:value 45 :changed? false
Of course, once posted, I realised the conditional could be
eliminated:
(defn update-and-check-whether-modified?
[update-fn]
(:changed?
(swap! a (fn [{v :value _ :changed?}]
(let [new-v (update-fn v)]
{:value new-v :changed? (not= v new-v)})
--
You receiv
Hi Sam,
A nice late night exercise...
Not very practical, but if you want a safe transaction-free operation
on an atom which returns whether it was changed, you can perhaps hack
it by embedding the change state into the atom itself:
(def a (atom {:value 45 :changed? false}))
(defn update-and-ch
Hi Meikel,
On 25 Jul 2011, at 22:46, Meikel Brandmeyer wrote:
> Am 25.07.2011 um 23:12 schrieb Sam Aaron:
>
> Since this is callback based, you can't return a value. Do you want more
> something like a polling solution? Then you'll have to roll your own with an
> atom and a clojure.lang.Persis
Hi,
Am 25.07.2011 um 23:12 schrieb Sam Aaron:
> So what if I would like #'update to return a boolean representing whether the
> state has changed rather than call #'changed-fn internally? (which is
> actually what i'm trying to do, I just refactored the example to be a lot
> simpler and hopefu
Hi Meikel,
On 25 Jul 2011, at 21:51, Meikel Brandmeyer wrote:
>
> you want a watch.
>
> (def a (atom 0))
> (add-watch a ::your-id (fn [_your-id _a old-val new-val] (when (not= old-val
> new-val) (println "New value:" new-val
> (swap! a inc)
> (reset! a 1)
> (swap! a inc)
>
That's cool to
Hi,
you want a watch.
(def a (atom 0))
(add-watch a ::your-id (fn [_your-id _a old-val new-val] (when (not= old-val
new-val) (println "New value:" new-val
(swap! a inc)
(reset! a 1)
(swap! a inc)
Sincerely
Meikel
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On 25 Jul 2011, at 21:45, Sam Aaron wrote:
>
> (defn update
> []
> (let [changed? (dosync
> (let [old-a @a
>new-a (ref-set a (new-val))]
>(= old-a new-a)))]
>(when changed? (changed-fn
Clearly I meant (not (= old-a new-a)) :-
Hi there,
I have some state which I'd like to set to some default value, A. I'd then like
to update A to a new value A' and then, if (not (= A A')) I'd like to fire off
a function - say print to stdout that A has changed. If (= A A') I'd like
nothing to happen at all. Additionally, I'd like to
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