Zest: a programming language for malleable and legible systems
15 comments
·March 16, 2025ModernMech
one-more-minute
The author outlines a fair bit of the design thinking in this post [0].
What Datalog and co give you is the ability to do interesting program transformations. Mostly that's not because they are "declarative", if that means anything, but because they avoid all the little bits of non-determinism that imperative languages include. If you avoid those you're pretty much set. Coming from another angle, JAX [1] shows how you can do program transformations in Python with a relatively small set of semantic restrictions.
[0]: https://www.scattered-thoughts.net/writing/unexplanations-sq... [1]: https://github.com/jax-ml/jax
corysama
Oh crap. This is from the Eve folks? That was one of those projects where everyone got excited about how new and powerful it was. Then continued programming in PHP out of inertia.
ModernMech
It's from one of the Eve folks, Jamie Brandon.
noelwelsh
I could not tell if this is a hobby project, or the product of a research lab. Does anyone know? Very cool stuff. It would benefit from some institutional support.
returningfory2
The person behind Zest runs an interesting blog/work journal, I recommend subscribing [1]. I could be wrong, but my understanding is that they don't have a full-time job. Instead they do some amount of consulting, and then spend most of their time and intellectual energy working on their projects. Which is pretty cool I think.
flashgordon
Ah now that is an envious life! Not have to worry or be distracted by a full-time job that too by choice! Hope he gets to crank a lot more out!
TimorousBestie
Oh, that looks very interesting! Thanks for linking it.
Ohkay
The docs have test cases embedded in the markdown. This is a pretty cool use of markdown. I have started doing something similar with markdown in my project. I wonder if other programming languages have done this too.
returningfory2
Rust has this, and it just makes so much sense. Especially when you write a library in which the basic demo is also the basic unit test you want to make. Instead of writing a specific unit test that's hidden in source code, you just embed it in the docs and then you (a) don't have code duplication and (b) have verification your documentation's code samples are actually correct.
LoganDark
> and (b) have verification your documentation's code samples are actually correct.
I find a lot of libraries don't go through the effort to actually use doctests, and just stick `no_run` everywhere, which defeats a lot of the purpose.
jmholla
Python has doctests: https://docs.python.org/3/library/doctest.html
Calamitous
Elixir has this as well, IIRC.
oulipo
Well, it's what's called "literate programming"
null
Other programming languages this author has worked on:
Droplet: "Datalog in time and space" - https://github.com/jamii/droplet
Eve: "Datalog meets Smalltalk" - https://witheve.com
Imp: "An Eve for people who build Eves" - https://github.com/jamii/imp
These are some pretty "out there" languages with a high strangeness budget, so I'd expect the same of Zest.
I like the idea of exploring the interaction models that Eve provided but instead with a "well-trodden ground of a mostly-familiar imperative language", but I'm curious how that will work since the interactions in Eve were made possible due to the datalog-like language design. So my initial question is how "mostly-familiar" Zest really is; what imperative concessions does the language make to gain which interactions?
With Eve, a lot was gained just by keeping a database of compiler artefacts that would normally be thrown away. This allowed for a degree of "provenance" tracking, where you can ask the compiler how a runtime value came to be.
I think there's an interesting middle ground where maybe we can get a bunch of the things in Eve that were nice, but maybe tone down the weirdness budget to lower the learning curve. Maybe that's Zest? Will be interesting to follow this project.