Document "fix" keyword

[dev-msp]

Hi, I've been enjoying reading up on the language, but I found when reading some of the examples in the main repo that the fix keyword seemingly isn't covered in the book.

There's also a construction that involves prefixing a Datalog program expression with ;, which seems related but I'm not too sure.

Thanks for the book, and for the lang itself!

[magnus-madsen]

Yes, you are right. We should document them.

We have a paper coming out soon that describes some of these features-- maybe we can port some of that text.

[magnus-madsen]

And thanks for the kind words :)

[magnus-madsen]

There is actually some information here:

https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2023.31

Section 6.