Re: [Cbor] cddl 0.8.17: Add .abnf (draft-ietf-cbor-cddl-control)

Paul Kyzivat <pkyzivat@alum.mit.edu> Sat, 27 February 2021 15:41 UTC

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To: Carsten Bormann <cabo@tzi.org>
Cc: cbor@ietf.org
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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Sat, 27 Feb 2021 10:41:40 -0500
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Archived-At: <https://mailarchive.ietf.org/arch/msg/cbor/CSmoqYrVGYEZTiI--FKPgDxMCmU>
Subject: Re: [Cbor] cddl 0.8.17: Add .abnf (draft-ietf-cbor-cddl-control)
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On 2/26/21 6:51 PM, Carsten Bormann wrote:
> Hi Paul,
> 
>> The obvious revision would be to simply change the syntax of rule to:
>>
>>      rule           =  WSP rulename defined-as elements c-nl
> 
> Well, a single WSP won’t cut it…
> 
>      rule           =  *WSP rulename defined-as elements c-nl
> 
>>
>> That seems unambiguous to me. But my formal parsing knowledge isn't sufficient to say if it is LL(1).
> 
> Once you allow white space before rulenames, it is most definitely not LL(1).
> 
> When you see…
> 
> A = B
>    C
> 
> …you need to look ahead one more to distinguish, say…
> 
> A = B
>    C = D
> (New rule)
> 
> …from…
> 
> A = B
>    C D
> (Still in same rule.)
> 
> I do think it is LL(2), but I didn’t formally check.

If there is no separate lexer, so that terminal symbols are all single 
bytes, then isn't the required effectively unbounded?

> Who else should we draw into this conversation?

We should restart the discussion on abnf-discuss.

	Thanks,
	Paul