ciao VS trealla-js

Some Prolog systems (like Ciao Prolog https://github.com/ciao-lang/ciao/blob/master/core/lib/forei...) implement bidirectional foreign interfaces. Once you have C bindings it is easy to write bindings from Rust, C++, or any other language (that can interoperate with C). I give here some details about Ciao because this is the system I know better but it should be similar for other popular Prolog implementations.

The tradeoffs depend on the complexity of the Prolog code and your needs for performance and features: pure LP, Prolog (search+unification+cut), garbage collection, dynamic database updates, constraint domains, etc. The Ciao Prolog engine is around 300-400KB. Adding a few libraries, compiler, etc. it goes to 2MB. Naive Prolog systems can be one order of magnitude smaller at the cost of sacrificing ISO compatibility, performance, etc. Note that "performance" can be very misleading. Some Prolog programs may run particularly fast in some Prolog system and very badly in others.

I think Prolog really shines as an embedded query engine (I know this is old and it's been removed since). It's perfect for declarative configuration, very easy to write powerful queries once you wrap your head around it.

The Yarn constraints plugin also used (Tau) Prolog, although it looks like it's in the process of being replaced with JS, which makes me a bit sad. The reasoning is here: https://github.com/yarnpkg/berry/issues/1276. Seems like the biggest issue is lack of a nice dev environment. I maintain the Trealla Prolog Wasm port (npm package 'trealla') and I hope some day to use it for a VSCode extension or LSP or something to provide a nice dev experience. Performance has also been cited as an issue[1] but Trealla is quite fast and I expect it could easily handle a complex Yarn workspace with tons of facts. If this sounds like something you'd be interested in helping me with, feel free to contact me or make an issue/discussion here: https://github.com/guregu/trealla-js

[1]: https://github.com/yarnpkg/berry/issues/4079#issuecomment-10...

port a C or Rust project to wasm and make a JS package for it (trealla-js is an example of such a package, porting a C Prolog interpreter to wasm)

Hey, this is mine. Thanks for submitting it. I'll answer some questions.

> Why?

I ported Trealla Prolog to WASM (WASI) and I was looking for something useful to test it against. I found Spin, which can run WASM+CGI, and landed on this. Making this project exposed a number of bugs in my port that have now been fixed, so consumers of more useful projects[1][2] benefit as well. Also, PHP style templates are just fun! There's something valuable to just being able to shove a little bit of code inside some HTML and get it up on the internet.

I started my webdev journey with PHP many many years ago, and it's nice to revisit it from a different perspective. I don't use the real (elephant) PHP anymore, but I've gained a newfound appreciation for how fun its quick & dirty development style is.

I hope this project can serve as an example of how to use Prolog for fun things. It does showcase some of the cooler dynamic aspects of the language, and the PHP parsing code is like 10 lines of DCG.

> Is it a joke?

Yes and no. The name is certainly a joke. I was pondering what 'Prolog on Rails' might be and thought calling it PHP would be funny. This led to the PHP-style templates which were quick to implement and pretty powerful. Despite the humorous presentation, it does actually work.

> Can you use Prolog for web services?

Yes! For example, SWI has a mature HTTP package: https://www.swi-prolog.org/pldoc/doc_for?object=section(%27p.... It's used to power SWISH, an online Prolog code sharing thing: https://swish.swi-prolog.org/

> Next steps?

I would like to support persistence somehow. I think it'd be really cool if you could use Prolog's dynamic database[3] as a persistent store. Spin has components for Postgres and Redis so it shouldn't be too hard to implement, but I lose the WASI compatibility if I do that... which means I can't use the binary from WAPM, etc.

I would also like to experiment with running Trealla on Cloudflare Workers. I have another project, worker-prolog[4], which uses Tau Prolog (a Prolog written in Javascript) on Workers.

On a somewhat related note, I've also been playing around with Cosmopolitan libc[5]. I got Trealla to compile to an APE executable but there's some issues with the embedded Prolog libraries getting garbled, so I need to improve my GDB skills and figure out what's going on there.

Finally, I'd like to say thanks to Andrew Davison (@infradig on GitHub), the author of Trealla Prolog, for letting me add WASM support to his project and helping me with lots of things. For example, PHP led to Andrew implementing improvements for using DCGs to parse Prolog terms, which is now super fast[6]!

[1]: https://github.com/guregu/trealla-js

[2]: https://github.com/trealla-prolog/go

[3]: https://www.swi-prolog.org/pldoc/man?predicate=assertz/1

[4]: https://github.com/guregu/worker-prolog

[5]: https://justine.lol/cosmopolitan/

[6]: https://github.com/trealla-prolog/trealla/issues/53

With trealla-prolog/go on the backend and trealla-js on the frontend, you can share the same validation code.

I found async generators to be handy while porting a C Prolog interpreter to WASM/JS. A `for await` loop is a natural way to iterate over query results, and as a bonus you can use `finally` within the iterator to automatically clean up resources (free memory). There are ways for determined users to leak (manually iterating and forgetting to call `.return()`) but I've found that setting a finalizer on a local variable inside of the generator seems to work :-). I can't say manual memory management is a common task in JS but it did the trick.

The generator in question, which is perhaps the gnarliest JS I've ever written: https://github.com/guregu/trealla-js/blob/887d200b8eecfca8ed...