Comment by carapace

I'm designing a such a system now, based on the pure functional Joy language with two additional data stores: a relational db system (Prolog (or maybe Datalog), not SQL) and what is effectively a git repo although I think of it as a "data oracle".

The role of the relational db system is explained in TFA. (Prolog makes a fine Relational Model DB (the "relations" in RMDBs are the same logical relations that Prolog "relations", um, are.) The language is cleaner and simpler and more powerful than stock SQL, there's an ISO standard and several solid implementations, and you can always back it up with SQLite or PostGRES or whatever if you need to.) The trick to integrating it with a purely functional system is to only use "pure and monotonic Prolog code" which you want to do anyway ( https://news.ycombinator.com/item?id=34936729