ABNF-based Grammar

[zkat]

I think it would be good to convert our current grammar to ABNF, even if we might need to make some notes about cuts/greediness.

It's gonna be a bit of a hassle, but I think it's going to be more in line with the expectations for RFCs. And tbh I don't entirely mind moving away from our fun little frankenstein, even if it'll be more verbose.

[zkat]

"let me solo her"

...unless y'all object.

[TheLostLambda]

It's not something I've done extensive research on just yet, but it would be interesting to compare a couple of different ABNF vs EBNF things perhaps?

In the past I've used the ISO standard EBNF to generate really nice documentation / interactive railroad diagrams with this tool: https://matthijsgroen.github.io/ebnf2railroad/try-yourself.html , but, that ISO standard also kinda sucks: https://dwheeler.com/essays/dont-use-iso-14977-ebnf.html

I know essentially nothing about ABNF, but I saw mention of some strange case insensitivity? https://stackoverflow.com/a/29875840 (Though now that I think about it, I suppose that won't matter for KDL itself — perhaps for the schema stuff?)

That's all to say that, personally, if I were rewriting the grammar, I'd pick the exact EBNF / ABNF version that is supported by the automated tools you want to use! :)

[zkat]

The advantage of ABNF is that it’s the primary grammar language for IETF RFCs (as defined in RFC 5234).

The main challenge with ABNF is that it’s going to be a bit more verbose in a few places because you can’t just do the - thing that we use a lot. We would need to have a lot of smaller productions and combine them piece by piece for the different cases instead. And yes, you can work around the case sensitivity pretty easily with the %s prefix.

The only things we do that ABNF does not have are the cut and the non-greedy parsing, but I think we can just use comments and/or prose to specify that. ABNF isn’t a regex engine, after all.

[TheLostLambda]

I think that's a really good argument for ABNF then! I'll have a look around for any tools that could play nicely with it in case we're ever interested :)