Likely a good replacement for Python. If the ecosystem gets there, Ciro Santilli would gladly use it more.
Haskell by Ciro Santilli 40 Updated 2025-07-16
There are only two pre-requisites to using Haskell in 2020. You have to be an idealist. And you have to be a genius:
Java is good.
Its boilerplate requirement is a pain, but the design is otherwise very clean.
But its ecosystem sucks.
The development process is rather closed, the issue tracker obscure.
And above all, Google LLC v. Oracle America, Inc. killed everybody's trust in it once and for all. Thanks Oracle.
Video 1.
Java for the Haters in 100 Seconds by Fireship (2022)
Source.
JAVA_HOME by Ciro Santilli 40 Updated 2025-07-16
This ultimately determines which Java is used by a bunch of tools.
TODO is there a way to update it sanely in Ubuntu: askubuntu.com/questions/175514/how-to-set-java-home-for-java to always match the default java executable?
JavaScript by Ciro Santilli 40 Updated 2025-07-16
The language all browsers converted to as of 2019, and therefore the easiest one to distribute and most widely implemented programming language.
Hopefully will be killed by WebAssembly one day.
Because JavaScript is a relatively crap/ad-hoc language, it ended up some decent tooling to make up for that, e.g. stuff like linting via ESLint and reformatting through Prettier is much more widespread than in other languages.
JavaScript data structure are also quite a bit anemic, which makes libraries such as lodash incredibly popular. But most of that stuff should be in the stdlib.
Our JavaScript examples can be found at:
Twin paradox by Ciro Santilli 40 Updated 2025-07-16
The key question is: why is this not symmetrical?
One answer is: because one of the twin accelerates, and therefore changes inertial frames.
But the better answer is: understand what happens when the stationary twin sends light signals at constant time intervals to each other. When does the travelling twin receives them?
By doing that, we see that "all the extra aging happens immediately when the twin turns around":
  • on the out trip, both twins receive signals at constant intervals
  • when the moving twin turns around and starts to accelerate through different inertial frames, shit happens:
    • the moving twin suddenly notices that the rate of signals from the stationary twin increased. They are getting older faster than us!
    • the stationary twin suddenly notices that the rate of signals from the moving twin decreased. They are getting older slower than us!
  • then when the moving twin reaches the return velocity, both see constant signal rates once again
Figure 1.
Twin paradox illustration with twins sending light signals at regular intervals
. Source.
Another way of understanding it is: you have to make all calculations on a single inertial frame for the entire trip.
Supposing the sibling quickly accelerates out (or magically starts moving at constant speed), travels at constant speed, and quickly accelerates back, and travels at constant speed setup, there are three frames that seem reasonable:
  • the frame of the non-accelerating sibling
  • the outgoing trip of the accelerating sibling
  • the return trip of the accelerating sibling
If you do that, all three calculations give the exact same result, which is reassuring.
Another way to understand it is to do explicit integrations of the acceleration: physics.stackexchange.com/questions/242043/what-is-the-proper-way-to-explain-the-twin-paradox/242044#242044 This is the least insightful however :-)
Bibliography:
Phaser.js by Ciro Santilli 40 Updated 2025-07-16
Likely the best JavaScript 2D game engine as of 2023.Uses Matter.js as a physics engine if enabled. There's also an alternative (in-house?) "arcade" engine: photonstorm.github.io/phaser3-docs/Phaser.Physics.Arcade.ArcadePhysics.html but it appears to be simpler/less robust (but also possibly faster).
The examples are present under:
git clone https://github.com/photonstorm/phaser3-examples
but note that that repo is huge, about 4.5 GiB on local disk, as is has tons of assets.
The demos also include a Monaco-editor based sandbox mode where you can edit code directly on the web and see the game update which is a really sweet addition.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact