Re: Fusion-ifying proto parse trees

Joel de Guzman wrote:
> Eric Niebler wrote:
> > What do you think? Zero-copy expression template construction and 
> > segmented iteration over the tree -- I think there's potential there.
>
> Or, simply use the raw view returned from push_back without doing
> a fusion::as_list call. That also amounts to zero-copy expression
> template construction.


Yes, sure but then the view returned by push_back will be, essentially, 
a proto parse tree. :-) And you'll want Fusion algorithms to work 
efficiently with them, so they should use a segmented iteration scheme. 
In other words, a Fusion join_view is a text-book example of a segmented 
data structure. If we add segmented algorithms to Fusion, they'll work 
better with your lazy views.


> Pardon my stubbornness. It's just that I always strive to arrive
> at the simplest solution. For Spirit-2, I'd like to adhere to the
> mantra that "less is more". Then here we are again adding complexity
> to tackle what I view as a simple need. I understand that you also wish
> to make proto "as simple as possible", but what we are doing seems
> more like moving the complexity somewhere else, and in the process,
> ultimately adding more complexity to address the need.


IMO, Fusion needs this extra complexity. Efficient evaluation of lazy 
sequences should be Fusion's bread and butter. Did you see how much 
faster segmented proto was over non-segmented proto? Today's join_views 
== non-segmented proto == the slow badness. Segmented join_views == mmm, 
tasty goodness. :-)

I'm also not sure how much complexity there really is. My impression is 
that making a non-segmented algorithm into a segmented one is a fairly 
mechanical translation. We may even get by with some Boost.PP magic to 
do it for us. I haven't tried making a segmented view, but I'm guessing 
that's fairly mechanical, as well. It's certainly worth looking into 
IMO, but I'm not trying to deceive you -- this would be a sea-change for 
Fusion.


> Ok... I'd really want to take a step back and meditate on this.
> I'd like to re-think the "flatness" requirement in hopes of
> eliminating it. If that is indeed possible, then we have a
> win-win situation.


OK, cool.


--
Eric Niebler
Boost Consulting
www.boost-consulting.com


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