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Re: [abnf-discuss] ABNF/RFC7405/ Update: EBNF syntactic exception

Carsten Bormann <cabo@tzi.org> Sat, 09 July 2022 01:54 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Sat, 09 Jul 2022 03:54:22 +0200
Cc: Paul Kyzivat <pkyzivat@alum.mit.edu>, "abnf-discuss@ietf.org" <abnf-discuss@ietf.org>
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To: Jacob Friedman <jfriedman@virgilsystems.com>
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Subject: Re: [abnf-discuss] ABNF/RFC7405/ Update: EBNF syntactic exception
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On 9. Jul 2022, at 02:57, Jacob Friedman <jfriedman@virgilsystems.com> wrote:
> 
> concatenation = repetition [ exception ] *(1*c-wsp repetition [ exception ] )
> 
> ; The previous repetition, *except* the repetition following the backslash.
> exception = *c-wsp “\” *c-wsp [ repetition ]

This grammar is ambiguous.

Why on earth is the repetition in the second production optional?

But as some of us said, getting the grammar right really is trivial; the impact on tools that no longer can use decades of knowledge about CFG (context-free grammars) is the significant part.

Grüße, Carsten

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