souffle VS swipl-devel

> In fact, we could have used Datalog to achieve our data goals — but that would mean we have to build our own Datalog implementation, backing data store, etc. We don’t want to do that.

Surprising that creating a whole new language made more sense then a backend. I wonder if they did a proof of concept with an existing logic system like Souffle¹ or Rel² first.

¹ https://github.com/souffle-lang/souffle

² https://relational.ai/blog/rel

Consider using Datalog (the incredible subset of Prolog) for this perfect use case. Compared to Prolog, you get:

1. Free de-duplication. No more debugging why a predicate is returning the same result more than once.

2. Commutativity. Order of predicates does not change the result. Finally, true logic programming!

3. Easy static analysis. There are many papers that describe how to do points-to analysis (and other similar techniques) with Datalog rules that fit on a single page :O

Souffle[0] is a mature Datalog that is highly performant and has many nice features. I highly recommend playing with it!

[0] https://souffle-lang.github.io

Still, there are many useful tools based on these ideas, used by programmers and mathematicians alike. What you describe sounds rather like Datalog (e.g. Soufflé Datalog), where you supply some rules and an initial fact, and the system repeatedly expands out the set of facts until nothing new can be derived. (This has to be finite, if you want to get anywhere.) In Prolog (e.g. SWI Prolog) you also supply a set of rules and facts, but instead of a fact as your starting point, you give a query containing some unknown variables, and the system tries to find an assignment of the variables that proves the query. And finally there is a rich array of theorem provers and proof assistants such as Agda, Coq, Lean, and Twelf, which can all be used to help check your reasoning or explore new ideas.

It's true that this SPARQL-inspired view of Datalog as a triplestore query language is quite a narrow interpretation compared to something closer to the academic Prolog roots like https://souffle-lang.github.io/ - what do you feel are the most important differences?

Very cool! I love the sqlite install everywhere model.

Could you compare use case with Souffle? https://souffle-lang.github.io/

I'd suggest putting the link to the docs more prominently on the github page

Is the "traditional" datalog `path(x,z) :- edge(x,y), path(y,z).` syntax not pleasant to the modern eye? I've grown to rather like it. Or is there something that syntax can't do?

I've been building a Datalog shim layer in python to bridge across a couple different datalog systems https://github.com/philzook58/snakelog (including a datalog built on top of the python sqlite bindings), so I should look into including yours

TerminusDB CTO here.

Echoing what triska said, CLP(ℤ) and friends are some of the most under-appreciated aspects of prolog implementations.

I'm amazed that programmers still don't have access to CLP when trying to do scheduling and planning solutions.

As an example in practice, what if you want to know about a transaction in which a number of entities transitively had holdings in one of the beneficiaries of the transaction at that particular time. The date window is not known, and the date windows are important in the ownership chain as well as the transactions that are being undertaken.

With CLP(FD) you can ask for a window of time, and the solution will zoom in on an appropriate time window which exists for the entire chain and match the time of the transaction.

Now try to do this query in SQL. It's almost impossibly hard.

I can't wait until I have the time to implement constraint variables for TerminusDB, but at the minute we are still working on more prosaic features.

Aside from that there are very interesting program correctness and optimisation systems which are based on prolog (usually a datalog). For instance Soufflé: https://souffle-lang.github.io

No problem :) What do you mean by voice control systems? Prolog has a bit of a learning curve and it's very difficult to write efficient code in. Although it did inspire Erlang, which is used in telecom and has some pretty interesting advantages not offered by other languages (reliance, multithreading, and updating without shutting down) Prolog is also pretty procedural, (the order you declare clauses in really really matters). There are other languages that use a much more pure for of logic Datalog: https://en.wikipedia.org/wiki/Datalog https://souffle-lang.github.io/

Still, there are many useful tools based on these ideas, used by programmers and mathematicians alike. What you describe sounds rather like Datalog (e.g. Soufflé Datalog), where you supply some rules and an initial fact, and the system repeatedly expands out the set of facts until nothing new can be derived. (This has to be finite, if you want to get anywhere.) In Prolog (e.g. SWI Prolog) you also supply a set of rules and facts, but instead of a fact as your starting point, you give a query containing some unknown variables, and the system tries to find an assignment of the variables that proves the query. And finally there is a rich array of theorem provers and proof assistants such as Agda, Coq, Lean, and Twelf, which can all be used to help check your reasoning or explore new ideas.

SWIProlog[1] has so far been my go to due to the extensive support system it has. However, I've been meaning to explore higher order logic a bit and Ciao[2] caught my attention there, with sugar for function-like notation and higher order programming including "lambda" style predicate expressions .... and it compiles down to executable. The function notation in this context is along the same lines as Mozart/Oz and can be convenient. Not explore the higher order aspects much though.

[1]: https://www.swi-prolog.org/

[2]: https://en.wikipedia.org/wiki/Ciao_(programming_language)

?- version(). Welcome to SWI-Prolog (threaded, 64 bits, version 9.0.0)SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details.For online help and background, visit https://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word). true. ?- del(a, L, [1,2,3]). L = [a, 1, 2, 3] ; L = [1, a, 2, 3] ; L = [1, 2, a, 3] ; L = [1, 2, 3, a] ; false.

$ swipl Welcome to SWI-Prolog (threaded, 64 bits, version 8.5.10) SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details. For online help and background, visit https://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word). ?- [fm2gp_primes]. true. ?- time( setup_call_cleanup(open('prolog-primes.txt', write, Out), with_output_to(Out, primes(500_000)), close(Out)) ). % 8,766,852 inferences, 1.055 CPU in 1.198 seconds (88% CPU, 8311018 Lips) Out = (0x600000648100).

The utilities in dgc/bacics.pl that you linked yourself are not too advanced, too quickly. Understanding those is exactly what you need in order to be able to write useful grammars for two reasons. They show how to approach many common issues with DCGs; and you know what building blocks you have at your disposal. I feel you discarded those too fast and strongly suggest you try to revisit them.

- And last but not least... the ability to convert authorization logic into SQL [4]. Which is done by having the language return constraints over any unbound (free) variables.

To me this is what makes logic programming exciting for authorization. It gives you this small kernel of declarative programming, and gives you a ton of freedom to build on top.

[1] https://www.swi-prolog.org/

(Btw. I'm using SWI Prolog.)

Welcome to SWI-Prolog (threaded, 64 bits, version 8.0.2) SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details. For online help and background, visit http://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word). ?- use_module(library(lists)). true. ?- clumped([a,a,a,b,b,c], Rs). ERROR: Undefined procedure: clumped/2 (DWIM could not correct goal) ?-

Many library predicates do the argument reordering to take advantage of this special case argument indexing as explained in the answer by u/mycl. For example library(apply) in SWI-Prolog. is full of those.