Re: Proposal of Non-Sequential Group Notion in ABNF w/ a SIP case

eburger wrote:

Personally, I don't understand why we didn't just use YACC.

Exercise: write an RFC ?822 parse in yacc. It can be done, but not
easily, as the RFC ?822 grammar is not LALR(1).

I am really in favor of using a formal language for specifying grammar. As Munjo states, the ABNF is essentially documentation fluff - useless at best and wrong at worst.

As for this particular suggestion, I am ambivalent as to whether we hack ABNF, adopt YACC, or even adopt ASN.1.

One lesson from the DRUMS effort - rewrite an existing grammar at your
peril. Even if the old specification has errors, writing a new grammar
which verifiably recognizes exactly the same language as the old one
can be difficult. And even if you restrict the language that new
implementations can emit, you generally have to accept the old language
for compatibility's sake. So you end up with two grammars where one
was formerly (almost) good enough.

Keith

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