Dusa Programming Language (Finite-Choice Logic Programming)
dusa.rocks
dusa.rocks
Also potentially interesting to this crowd are the underlying editor, which I split out from the online Dusa editor and called "sketchzone" (https://github.com/robsimmons/sketchzone). Some of my motivations and hopes for sketchzone are blogged here: https://typesafety.net/rob/blog/endless-sketchzone
Also, I more-or-less did Advent of Code 2024 in Dusa: journal entries and links to solutions are at https://typesafety.net/rob/blog/advent-of-dusa-2024
Zig was also apparently partly developed whilst Andrew Kelley was there. Fun place.
Logic systems will be a key part of solving problems of hybrid data analysis (e.g. involving both social graphs, embedding spaces, and traditional relational data) - Cozo[1] sticks out as a great example.
[0] https://codeql.github.com/docs/ql-language-reference/about-t...
The Dusa implementation has a couple of ways to reason at a high level about the performance of programs. The academic paper that febin linked to elsethread spends a fair amount of time talking about this, and if you really want to dig in, I recommend searching the paper for the phrases "deduce, then choose" and "cost semantics".
There's work to do in helping non-academics who just want to use Dusa reason about program performance, so I appreciate your comment as encouragement to prioritize that work when I have the chance.
(The ArXiV preprint has the exact same content)
https://popl25.sigplan.org/attending/live-streams
I want to say that the cultural changes inside of the ACM to make historical research open access and to have excellent live streams of the conferences is just so damn wholesome and wonderful. Thank you ACM and the people inside the ACM that made this happen.
And in case someone from the ACM is reading this, the live streams are very useful for physical attendees. I was attending Splash! and there were a ton of talks where I would have needed to change rooms, wanted lots of desk space for notes and research. It was somewhat ironic attending half a day from a vacation rental. :)
The linked page suggests one intro if you have experience with Datalog, another intro if you have experience with Answer Set Programming (ASP), and a third for everyone else. That's because Datalog and ASP are the two logic programming things that are most like finite-choice logic programming. Finite-choice logic programming gives a completely new way of understanding what answer set programs mean. The Dusa implementation is able to solve some problems vastly more efficiently than state-of-the-art ASP solvers, and is able to easily solve other problems that mainstream ASP solvers are simply unable to handle because of something called the "grounding bottleneck." Right now it's not a strict win by any means: there are many problems that Dusa chokes on that state-of-the-art ASP solvers can easily handle, but we know how to solve at least some of those problems for implementations of finite-choice logic programming.
Regular Excel formulas are always terminating and therefore not computationally complete.
SQL without recursive CTEs is always terminating and therefore not computationally complete.
Simply typed lambda calculus is always terminating and therefore not computationally complete.
It's not the same, but restriction to terminating subsets gives very nice guarantees for a lot of program properties that would otherwise be undecidable.
Maybe it's obvious for the intended audience, given the mention of Datalog? But I suspect a lot of compsci people know of Prolog, and know about SAT(and similar) solvers, but don't really know how e.g Datalog places.
From the paper: "often people take “Datalog” to specifically refer to “function- free” logic programs where term constants have no arguments, a condition sufficient to ensure that every program has a finite model. We follow many theoretical developments and practical implementations of datalog in ignoring the function-free requirement." If every program has a finite model, the language cannot be Turing complete: the reverse is not necessarily true but in practice the reverse is usually true.
What is the reverse here? Sorry it's late and I can't calculate it.
Btw, what I know about ASP is that it is incomplete (in the sense of soundness and completeness). Turing completeness is a separate question.
If it is not possible to give every program a finite model, that doesn't imply that language IS Turing complete. However, in practice, a Datalog-family logic programming language where some programs have infinite models is likely, in my experience, to be Turing Complete.
(For what it's worth, I don't know what it means for ASP to be incomplete in the sense of soundness and completeness. Incomplete relative to what other thing?)
Thanks, yes, that makes sense. But I'm not convinced of arguments "in practice". In practice, why do we care about Turing completeness? It's not like anyone sells infinite tape. But "in practice" we end up having no idea what are the limits of this or that system, so some principled reasoning is sometimes useful... practically useful.
>> (For what it's worth, I don't know what it means for ASP to be incomplete in the sense of soundness and completeness. Incomplete relative to what other thing?)
Relative to proofs: a proof procedure is complete if, when there exists a proof of some formal statement, the procedure can always derive that proof. Consider Resolution; say A |= B; then there exists a Resolution-refutation of A ∧ ¬B (i.e. the derivation of the empty clause A ∪ ¬B ⊢ □) so Resolution is refutation-complete. As far as I understand it this is not the same as Turing completeness, which is about a system being able to compute every program a Universal Turing Machine can compute. E.g. the first order predicate calculus is Turing complete and its restriction to Horn clauses is also Turing complete, but that doesn't necessarily imply the existence of a complete proof procedure for Horn clauses- that has to be shown separately.
Or at least that's how I think about it. I might be dead wrong there so please correct me if you have a better understanding of this than me.
> Answer set programming is a way of writing Datalog-like programs to compute acceptable models (answer sets) that meet certain constraints. Whereas traditional datalog aims to compute just one solution, answer set programming introduces choices that let multiple possible solutions diverge.
Fascinating! I could see useful applications in litigation (e.g., narrowing potential claims; developing the theory of the case; finding impeaching lines of questioning).
Why not write it like it’s written in English? It could be one less thing to learn for people trying to adopt the language.
You can also think the same way about functions in typical languages: we don't write the body of the function first and then assign it to an identifier.
f(X) :- g(X), h(X).
f(a).
It's a reverse of the implication arrow and is meant to be read that way:
f(X) :- g(X), h(X).
From a principled point of view, the rule "a :- b, c" helps define what "a" means, and it seems, in practice, most helpful to be able to quickly visually identify the rules that define a certain relation. The list of premises tends to be of secondary importance (in addition to often being longer and more complicated).
From a practical point of view, we wrote Dusa as people familiar with existing Datalog and Answer Set Programming languages, which use the backwards ordering and ":-" notation, and some of the core target audience we hope to get interested in this project is people familiar with those languages, so we made some syntax choices to make things familiar to a specific target audience. (Same reason Java uses C-like syntax.)
if (want: edge Y X) { search for: edge X Y }
This is searching in reverse compared to a different if statement:
if (have: edge X Y) { assert: edge Y X }
No, what I want is a code example, front and center.
Even a month ago, I'd have asked "Where's the parallelism?" looking at any new language. AI has upended my world. My subscriptions are getting out of hand, they're starting to look like some peoples' sports channel cable bills. I'll be experimenting with the right specification prompt to get AI to write correct programs in three languages side by side, in either Cursor or Windsurf. Then ask it to write a better prompt, and go test that in the other editor. I'm not sleeping much, it's like buying my first Mac.
One constant debate I have with Claude is how much the choice of language affects AI reasoning ability. There's training corpus, but AI is even more appreciative of high level reasoning constructs than we are. AI doesn't need our idioms; when it taught itself the game Go it came up with its own.
So human documentation is nice, but who programs that way anymore? Where's the specification prompt that suffices for Claude to code whatever we want in Dusa?