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Date: Wed, 02 Jan 2013 08:31:12 -0800
From: Dave Crocker <dcrocker@gmail.com>
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Cc: abnf-discuss@ietf.org, Paul Kyzivat <pkyzivat@alum.mit.edu>
Subject: Re: [abnf-discuss] Some thoughts about how to make ABNF more
 convenient to use
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On 1/2/2013 8:24 AM, Tony Finch wrote:
> Dave Crocker <dcrocker@gmail.com> wrote:
>> On 1/2/2013 7:57 AM, Tony Finch wrote:
>>> Dave Crocker <dcrocker@gmail.com> wrote:
>>>>
>>>> It would need to be able to distinguish among potentially
>>>> independent sets of rules, within a spec. We don't currently have a
>>>> way to indicate that.
>>>
>>> Has there ever been any need for it?
>>
>> Well, ummm, RFC822 had several parsers, such as for addresses versus dates
>> versus free-form like Subject.  Applications often need this, I believe.
>
> Hmm, well I would describe those as sub-languages whereas I thought we
> were talking about independent languages. But in both cases they can be
> defined / identified using the transitive closure from the starting rule,
> without revising ABNF.

I don't think so.  The parsing rules for a date field are quite 
different than for an an address field, in 822.  They share some lexical 
constructs, of course, but I don't find that very significant for the 
current topic.


> I can see that rule sets might be useful for importing collections of
> low-level rules, like the ABNF core rules.

The choice, here, is between a formally flat namespace versus one that 
is formally able to be partitioned.  Simplicity is the major benefit of 
the first, of course.  Rigor and the ability to enforce the package 
boundaries that are actually present are the benefits of the latter.


>> What I don't know is whether there will be the community will to pursue it --
>> will we see enough operational benefit?
>
> I think a formal import mechanism would be very useful and could be quite
> easy to deploy. Adding namespaces will be a lot of work.

ack.

Given the effort to make /any/ changes to a package like abnf, I thought 
it worth raising the additional issue, since it seemed to develop pretty 
naturally from the thread.  But again, I don't have any idea whether 
anyone else thinks it's worth pursuing...

d/
-- 
  Dave Crocker
  bbiw.net
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