Re: [apps-discuss] Review of: draft-yevstifeyev-abnf-separated-lists-02

Dave CROCKER <> Sat, 11 December 2010 16:08 UTC

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Date: Sat, 11 Dec 2010 08:10:06 -0800
From: Dave CROCKER <>
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Cc: Mykyta Yevstifeyev <>
Subject: Re: [apps-discuss] Review of: draft-yevstifeyev-abnf-separated-lists-02
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On 12/10/2010 12:38 PM, Dave CROCKER wrote:
> FWIW, I'm not fond of this notation. The parenthetical seems clunky, especially
> since it overloads the use of parens. I also don't like
> putting it in between the upper/lower bound.
> Out of curiosity, why ^ rather than re-use #?

I see that the new version of the notation is:

>      <n>^(<a>)^<m>element

Having the same character used twice invites some parsing errors, though perhaps 
I'm being a purist on this point.  But having the separator be buried within the 
repetition boundaries numbers this way still causes me some discomfort.

At this point I am wondering whether it would not be cleaner to have the 
notation be:


In other words, augment the existing repetition construct with a clean separator 
construct.  The up-arrow only specifies a separator, it does not also specify 



would be 1 to 10 tag-vals separated by colons, and

       *^" "words

would be zero or more words separated by a space.

I'm still not in love with the up-arrow, but can see an argument for not 
overloading #, which runs the risk that a reader won't know which definition of 
# is in force.

Also the issue of allowing LWS or the like around the separator might best be 
expressed within the separator construct rather than be implied.  (On 
reflection, I have a vague memory that one of the other concerns about # was 
that whitespace was implied.)


     1*3^(*LWSP "," *LWSP)

makes whitespace optional around the separator, whereas:

     1*3^("," LWSP)

requires exactly one whitespace character after each comma.


   Dave Crocker
   Brandenburg InternetWorking