document Rust-based builtins in lib/builtins.rs (#2030)

[mthom]

Document the remaining ISO built-ins implemented completely in Rust.

[bakaq]

Unfortunately, it seems that Doclog doesn't render the documentation if it's not immediately followed by a clause that is exported in the module, but I think Doclog itself could be altered to accept things like this (maybe with a different syntax) and I think it would be easier to implement than the extra files idea.

[mthom]

good thing I wanted to await @aarroyoc's feedback before merging this.

[aarroyoc]

Yes, @bakaq is right. DocLog only looks at publicly exported predicates. We could add some kind of meta-data inside comments to add predicates to the current file. It shouldn't be too hard, I'll try it soon.

Another option could be just analyze all the comments and join that result with the public exported list. It might be slower though

[aarroyoc]

I've updated DocLog (aarroyoc/doclog@b6c2f8c) and now it renders this kind of comments! (and should render the rest as before). Only problem is that they're not indexed in the search box yet.

[aarroyoc]

We should put just one predicate per comment. Right now it works because it's very lax in what it accepts but if in the future we want to derive more information it could be problematic. For example, this is going to be problematic for the search box if we want to index these fields too.

[triska]

This is not valid syntax, I have filed #2270 for this.

[triska]

It is valid to write it as @>(?X, ?Y) (with suitable prefix operator ?).