2010/8/5 Laurent PETIT <laurent.pe...@gmail.com>
> Hello,
>
> My "problem": the user types in the ccw's editor.
> Each time she types, there's an opportunity to reparse the editor's
> content.
> But the reparse is not always necessary, especially when the types a
> symbol.
>
> So I could use a delay to only force the repase "on-demand".
> On the other end, when the user stops typing for a while (say 500 ms), it
> could be interesting to automatically trigger a reparse, so that the next
> editor command implying a "fresh parsetree" seems to be instantaneous.
>
> So I could use a "delayed future". A future which would do nothing the
> first n milliseconds (eg n = 500 ms), and then do its job.
> But I can't use a "classic" future, 'cause I want the deref of this
> "delayed future" to bypass the pause.
>
> Is there an classical idiom for this ?
>
> Here is what I've come up in my head :
> * create a datastructure with 2 fields, one holding a future, one holding
> a delay. the future will "wait" for n millisecs, and then force the delay.
> * The datastructure will accept the future API and delegate all calls to
> the future,*except* for the deref call which will bypass the future and
> deref the delay instead
>
>
I had a first working version which implemented both clojure.lang.IDeref and
java.util.concurrent.Future, but as Meikel said, the less I'll depend on
several external interfaces, the better. And I also had the problem of not
knowing what to implement for certain methods of
java.util.concurrent.Future. e.g. what should the behaviour of (get [_
timeout _]) be ? timeout on what. This was silly.
So I wrote this final version which only implements IDeref (which I want
to), and also adds a cancel/isCancelled property a-la
java.util.concurrent.Future but not tied to the Future interface :
(ns delay.util)
(defprotocol Cancellable (isCancelled [this]) (cancel [this]))
(defn timed-delay [pause fun]
(let [d (delay (fun))
f (future (Thread/sleep pause) @d)]
(reify
clojure.lang.IDeref
(deref [_] @d)
delay.util.Cancellable
(isCancelled [_] (future-cancelled? f))
(cancel [_] (future-cancel f)))))
What about this ?
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