lean4 VS Lua

Recently replaced by Lean, though.

https://github.com/cedar-policy/cedar-spec

https://lean-lang.org

Nice read! Rust has pushed, and will continue to push, the limits of practical, bare metal, memory safe languages. And it's interesting to think about what's next, maybe eventually there will be some form of practical theorem proving "for the masses". Lean 4 looks great and has potential, but it's still mostly a language for mathematicians. There has been some research on AI constructed proofs, which could be the best of both worlds because then the type checker can verify that the AI generated code/proof is indeed correct. Tools like Kani are also a step forward in program correctness.

Yeah, I believe they said intend for it to be used as a general purpose programming language. I used it to complete Advent of Code last year.

There are some really interesting features for general purpose programming in there. For example: you can code updates to arrays in a functional style (change a value, get a new array back), but if the refcount is 1, it updates in place. This works for inductive types and structures, too. So I was able to efficiently use C-style arrays (O(1) update/lookup) while writing functional code. (paper: https://arxiv.org/abs/1908.05647 )

Another interesting feature is that the "do" blocks include mutable variables and for loops (with continue / break / return), that gets compiled down to monad operations. (paper: https://dl.acm.org/doi/10.1145/3547640 )

And I'm impressed that you can add to the syntax of the language, in the same way that the language is implemented, and then use that syntax in the next line of code. (paper: https://lmcs.episciences.org/9362/pdf ). There is an example in the source repository that adds and then uses a JSX-like syntax. (https://github.com/leanprover/lean4/blob/master/tests/playgr... )

My latest inspiration to use code to a) replace my video editor, b) learn the basics of EDM production and c) understand a few topics in higher maths. This might sound very strange given there are specialised tools for these jobs. There's iMovie / Adobe Premier for video, there's GarageBand and FL studio for music and old good pen and pencil for math proofs. But these tools have three big limitations. First they have a lot of idiosyncratic learning, you have to spend quite some time getting used to these tools and my experience is that this time is quite upsetting. In contrast, you only have to learn to code one, maybe spend a few hours getting used to the syntax of another language. I'm not sure if that's true for most people but it was true for me using the tools mentioned above and wanted a place to discuss and see other people ideas and experiments. The second issue is that all these custom-made tools, are not composing easily. I can't search for all math proofs that used a single theorem. I can't create a plugin for iMovie and apply it to all my videos. I can't pick easily pick a rhythm from the internet and build upon for fun. There's also the issue of costs and version control, all tools I'm using today are open source and my work is stored in my repositories. This way I can create branches and test my ideas and I'm also confident that I can work in these projects in years.

Dafny and Whiley are two examples with explicit verification support. Idris and other dependently typed languages should all be rich enough to express the required predicate but might not necessarily be able to accept a reasonable implementation as proof. Isabelle, Lean, Coq, and other theorem provers definitely can express the capability but aren't going to churn out much in the way of executable programs; they're more useful to guide an implementation in a more practical functional language but then the proof is separated from the implementation, and you could also use tools like TLA+.

https://dafny.org/

https://whiley.org/

https://www.idris-lang.org/

https://isabelle.in.tum.de/

https://leanprover.github.io/

https://coq.inria.fr/

http://lamport.azurewebsites.net/tla/tla.html

The EventSource uses the Lua language to search for any services with ports set to 80 or 443 in the ‘argocd’ namespace. More examples can be found here.

If you're new to the 12 in 24 series, I'm learning and building projects with a new programming language every month - this month, it's the Lua scripting language. You can find source code for the projects I build in the official GitHub repository (check it out, this week's folder contains code for both this and two other bonus projects!).

This month, we're talking about Lua. It's not always a first choice when it comes to programming, but I think there's a lot to enjoy about this little language. Heck, I'm a big game development fan myself - I would look into it even if that was the only reason to.

It’s Portuguese. It’s the same in the Lua codebase [1].

[1]: https://github.com/lua/lua

If we think we need more flexibility for processing records, we can write our own embedded filters using Lua language. Lua is a highly efficient programming language used mainly for embedded scripting.

Lua

➜ ~ brew info lua ==> lua: stable 5.4.6 (bottled) Powerful, lightweight programming language https://www.lua.org/ /opt/homebrew/Cellar/lua/5.4.6 (29 files, 788.7KB) * Poured from bottle using the formulae.brew.sh API on 2023-05-16 at 11:03:06 From: https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/l/lua.rb License: MIT ==> Caveats You may also want luarocks: brew install luarocks ==> Analytics install: 16,599 (30 days), 56,745 (90 days), 139,027 (365 days) install-on-request: 1,763 (30 days), 6,266 (90 days), 21,105 (365 days) build-error: 0 (30 days)

I think Lua is a good example of doing documentation well. The source code is commented only as much as needed, mainly with brief comments about things that might not be obvious and a small number of longer explanations of how the architecture works (mainly relevant to developers). It also has a super nice feature that's surprisingly rare: each file has a very short line at the top that describes what the file is, so you don't have to guess based on the filename alone. The API is documented in a single HTML file on the website that has both the high level descriptions of the language and architecture, as well as documentation for each public-facing function. The docs are maintained by hand, but the API is mostly stable, so the docs don't need to change very often.

This is using the Lua language and the Solar2d game framework