Re: Fusion-ifying proto parse trees

Eric Niebler wrote:
> Joel de Guzman wrote:
> > The issue of flattening is based on extensive deliberations on
> > and off list that will take lots of effort for me to explain in
> > one post. The discussions go back years.
>
> It's crucial that I understand the context. Can you point me to the 
> discussions?

Oh jeez, that will require a bit of searching. I intend to do that
anyway when I rewrite the design strategies pages, but I'll have to
defer that work for later.

Anyway, one definite rationale is ease of transformation and
attribute processing. Given a>>b>>c>>d, the attribute is
tuple<RA,RB,RC,RD> where RA...RD are the attributes of a...d
that you can obtain through traits::attribute_of<P>::type.
It's definitely more convenient to process seq(a,b,c,d) than,
say, seq(seq(seq(a,b),c),d) and all its permutations (e.g.
seq(seq(a,b),seq(c,d)). It is a must for semantic handling too.
Imagine semantic actions receiving different permutations of
tuple A..D in various grouped forms.

Regards,
--
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net



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