refactor: Change annotation syntax to use @

[max-sixty]

This is not great code — likely needs some error handling, and maybe some changes to how it's implemented in Chumsky. But it works!

[snth]

Sorry, there's no linked issue so asking here: was there a discussion around #[...] vs @{...} syntax for annotations?

No preference from my side at this stage but just curious what the considerations would be.

[aljazerzen]

Makes sense. Annotations can now be arbitrary expressions - literals, function calls, tuples, lists.

And SQL backend expects only tuples.

[aljazerzen]

We mentioned here: #2694

[snth]

Some thoughts that came to me on this are that

• to the extent that the annotations are key-value pairs or tuples, it makes that we use our {} syntax for those, and
• if you think of them as ATtributes, then it makes sense to use the @ symbol as a useful mnemonic.

So @{...} seems like a great choice.

[eitsupi]

These changes are intentional?

[max-sixty]

No, I saw these too — I'm not sure why they happen...

[aljazerzen]

You've missed a few annotations.

https://github.com/PRQL/prql/pull/2729/files#diff-f6d964f7215b03bfdb696d81cf4258db7cf5686558bf44fa627d031f2f474c2eR100-R150

[max-sixty]

Ah sorry!

(I blame the comment syntax :D )

[max-sixty]

I cleaned up the code a bit, and merging.

I don't know why we're getting these extra parentheses at #2729 (comment) — I don't even see where it could be affecting this! Not super important so I won't spend time on it, lmk any dissent

[vanillajonathan]

In the future could there be other types of annotations?
Could custom annotations be declared?

Maybe @Binding{Strength=4} would be preferred over @{binding_strength=11} in that case.

The syntax is rather unorthodox, hence I think using square brackets instead of curly brackets would be preferred as it would be more familiar.

[aljazerzen]

Syntax for annotations is just:

Annotation :== '@' Expr

... where Expr can be any expression. We are just using a tuple here. You could use [] and have arrays.

In any case, this was added mostly as an internal detail. It is not documented and especially binding_strength is not part of the language, so it can be changed without notice. So there is no need to make it future proof.