Scryer Prolog as an integrated language in PostgreSQL

[tatut]

PostgreSQL supports many "procedural" languages you can make stored procedures with (including Rust).
I think a Prolog language would be a nice language to create database logic with, and thought of Scryer as a good candidate due to its implementation language.

I don't have knowledge about creating PostgreSQL extensions in Rust, but there seem to be many.
So I'm asking if anyone has guesses about how much work that would be?

[yrashk]

It's quite possible. I've done this for SWI Prolog here omnigres/omnigres#215 (just need to take this over the finish line).

It can be a considerable amount of work, but could be worthwhile to those who appreciate having Prolog.

I'd love to evolve the work I referenced above to support more than just SWI Prolog (or at least ensure that different implementations implement the same interfaces and predicates to accessing the database to make them portable).

[tatut]

Interesting, nice to see related work here.

SWI-Prolog has an interesting query interface CQL, that would be interesting to use in Prolog stored procedures.

[tatut]

I could do a proof of concept for this with pgrx, a basic consult+query looks like it would be relatively easy to do.

[tatut]

I'm working on a proof of concept, and it seems there is something weird happening to the .so file (on M1 mac).

If I have a postgres language handler that doesn't refer to scryer, it loads and executes in postgres, but as soon as I add this line

 let mut machine = machine::Machine::new_lib();

to my handler function to use scryer, it compiles but fails to load in PostgreSQL:

ERROR:  could not load library "/Users/tatutarvainen/.pgrx/13.14/pgrx-install/lib/postgresql/pgprolog.so": dlopen(/Users/tatutarvainen/.pgrx/13.14/pgrx-install/lib/postgresql/pgprolog.so, 0x000A): symbol not found in flat namespace '_ffi_call'

I'm a rust newbie, so any ideas about what could be the problem, are welcome.

[mthom]

Perhaps @aarroyoc has run into something similar with libffi? I'm not familiar with it myself but it looks as though part of the foreign function interface is missing

[tatut]

This seems to be an OS X issue, I spun up a Ubuntu machine on docker, and there it compiled and loaded ok.

[triska]

@tatut: I found a similar issue with a few suggestions, could you please take a look and see if it helps: ffi/ffi#946

[aarroyoc]

Unfortunately, I don't have access to a Mac to test this, which seems macOS-specific. I think macOS ships with a system libffi, so you could tune the Cargo.toml to use that. Change libffi = { version = "3.2.0", optional = true } to libffi = { version = "3.2.0", optional = true, features=["system"]}

[tatut]

Thanks, I'll try that.

[tatut]

https://github.com/tatut/pgprolog

Very preliminary proof of concept here. It only takes one TEXT parameter and returns TEXT, but it does consult the source and take the parameter from the function execution...