percival VS clingo

Souffle and Cozo mentioned below already implement the whole of "traditional" datalog.

Percival (https://github.com/ekzhang/percival) has some very nice examples showing how you can interactively write and test rules on top of a datalog interpreter.

Bud (http://bloom-lang.net/bud/) is Hellerstein's proof of concept playground. It has bit-rotted in the past few years, but the examples are readable even if you can't easily get it working.

The complexity can be quite good. You can syntactically determine when you've written linear recursion (equivalent to a for loop) vs not. Otherwise, the complexity is what you'd expect from incremental view maintenance in a normal SQL database. Which is to say O(n^k) with k being the number of relations joined, but usually much, much less with appropriate indexes and skew in the data. All the usual tricks concerning data normalization and indexes from databases apply.

I've worked on percival a bit, it compiles (transpiles?) the datalog ast into javascript code on demand and executes it to get the results, see [1]. Percival's creator, Eric, also submitted a 10m presentation about the project [2] to the HYTRADBOI 'virtual conference' earlier this year [2]. They also submitted a Show HN that received a couple comments [3]. The Have You Tried Rubbing A Database On It conference included several awesome presentations featuring datalog, which readers may find interesting [4].

[1]: https://github.com/ekzhang/percival/blob/main/crates/perciva...

[2]: https://www.hytradboi.com/2022/percival-a-reactive-language-...

[3]: https://news.ycombinator.com/item?id=29521975

[4]: https://www.hytradboi.com/

I haven't written a parser with Chumsky, bit I've played with a little one a bit if you wanna see an example syntax. The error reporting for this project is implemented with `ariadne` which is also really slick.

Parser: https://github.com/ekzhang/percival/blob/main/crates/perciva...

Error reporting: https://github.com/ekzhang/percival/blob/main/crates/perciva...

Datalog playground: https://percival.ink/

To see an error report, delete some punctuation from one of the Datalog code blocks then press shift-return.

One of the easiest to get started on Datalog in my opinion is really clingo https://potassco.org/clingo/ , which can be pip installed and has python bindings. Answer Set Programming goes beyond datalog, but it holds datalog semantics as a sublanguage. It is unfortunate this is not well advertised.

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Love this article and the push to build awareness of what modern SAT solvers can do.

The thing it misses, though, is that there are higher level abstractions that are far more accessible than SAT. If I were teaching a course on this, I would start with either Answer Set Programming or Satisfiability Modulo Theories (SMT). The most widely used solvers for those are clingo [0] and Z3 [1]:

With ASP, you write in a much clearer Prolog-like syntax that does not require nearly as much encoding effort as your typical SAT problem. Z3 is similar -- you can code up problems in a simple Python API, or write them in the smtlib language.

Both of these make it easy to add various types of optimization, constraints, etc. to your problem, and they're much better as modeling languages than straight SAT. Underneath, they have solvers that leverage all the modern CDCL tricks.

We wrote up a paper [2] on how to formulate a modern dependency solver in ASP; it's helped tremendously for adding new types of features like options, variants, and complex compiler/arch dependencies to Spack [3]. You could not get good solutions to some of these problems without a capable and expressive solver.

[0] https://github.com/potassco/clingo

Answer Set Programming is an incredibly powerful tool to declaratively solve combinatorial problems. Clingo is one of the best open source implementations in my opinion: https://github.com/potassco/clingo