Proto for Boost mailing list page: Re: [proto] Visitor Design Pattern

Subject: Re: [proto] Visitor Design Pattern
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2010-10-22 03:33:50

On Friday 22 October 2010 09:15:47 Eric Niebler wrote:
> On 10/21/2010 7:09 PM, Joel de Guzman wrote:
> > Check out the doc I sent (Annex A). It's really, to my mind,
> > generic languages -- abstraction of rules and templated grammars
> > through metanotions and hyper-rules.
> 
> Parameterized rules. Yes, I can understand that much. My understanding
> stops when I try to imagine how to build a parser that recognizes a
> grammar with parameterized rules.

And I can't understand how expression templates relate to parsing.

> > I have this strong feeling that
> > that's the intent of Thomas and your recent designs. Essentially,
> > making the phoenix language a metanotion in itself that can be
> > extended post-hoc through generic means.
> 
> I don't think that's what Thomas and I are doing. vW-grammars change the
> descriptive power of grammars. But we don't need more descriptive
> grammars. Thomas and I aren't changing the grammar of Phoenix at all.
> We're just plugging in different actions. The grammar is unchanged.

Exactly.
Though, I think this is the hard part to wrap the head around. We have a 
grammar, and this very same grammar is used to describe "visitation".