Hi Mike,
This is interesting, thanks for writing it. I understand Refs better
than Agents, but even so, I'm thinking I was wrong when I first
suggested using Agents for Cells.
Pondering aloud here: The critical property of a Cell is that it is
completely finished updating before any of its dependent ("child")
cells are updated. Does this property still hold when using Agents
instead of Refs? I'm not sure it does, since an action on an Agent
occurs at an unspecified time in the future.
In the first examples I wrote, it probably doesn't matter. Here's a
more stressful example:
(def first-cell (cell 1))
(trace-cell first-cell)
(def bunch-of-cells
(doall
(take 5000
(iterate (fn [previous]
(cell (inc (cv previous))))
first-cell))))
(def last-cell (cell (inc (cv (last bunch-of-cells)))))
(trace-cell last-cell)
This works using cells.clj:
user=> (alter-cell first-cell 2)
first-cell changed from 1 to 2
last-cell changed from 5001 to 5002
But using acells.clj, you get an "Exception: Agent has errors" on (def
bunch-of-cells ...). The stack trace ends in a NullPointerException,
I think because new Cells are trying to dereference Cells that have
not yet been initialized. This is not to say definitively that Agents
won't work for Cells -- just that they may require more protections.
Incidentally, even with Refs, bunch-of-cells can't be much longer than
5000 without causing a StackOverflow. But I'm guessing a 5000+ chain
of serial dependencies is pretty rare.
-Stuart
On Sep 21, 7:29 pm, MikeM <[EMAIL PROTECTED]> wrote:
> Thanks for doing this. I've been curious about cells for a while, and
> wondered how it could be done in Clojure.
>
> Your comment (in the other thread) about using agents inspired me to
> see how this would work. I've uploaded acells.clj to the group, which
> is my attempt at converting your cells implementation to use agents in
> place of refs. Your examples work, but I haven't done anything with it
> beyond this. I'd like to hear your comments.
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