Re: Trellis + expensive operations

On Wed, Nov 26, 2008 at 19:29, Phillip J. Eby <pje-Wh6+Hckhi6HFNGf7iClzIwC/[email protected]> wrote:
> At 10:50 AM 11/26/2008 +0200, Sergey Schetinin wrote:
>>
>> I think this can be accomplished by creating a cell type that when it
>> runs does not recompute itself  unless there are listeners. If there
>> are none it just sets some flag that indicates that it will need to
>> recompute on next access and preserves its dependencies. Its get_value
>> would check that flag and actually compute the value and cache it, it
>> would also need to make sure that dependencies are updated at this
>> point.
>
> I don't see how that's different from a @compute rule, except that @compute
> rules don't keep track of whether their value is dirty, and so are always
> recalculated "on next access" if there are no listeners.  However, as soon
> as that recalculation is done, if there's a listener, then it keeps track of
> dependencies and is not recalculated until they change.
>
> I actually considered implementing @compute as you describe, but found it to
> be over-complicated for the use case.

I believe what Christropher wants is to access it without creating a
listener, so I wasn't suggesting putting something like that into
Trellis, just how he should be able to get the behavior he described.