Ask HN: What do you code when learning a new language/framework?

My go-to projects have varied over time:

1. An implementation of Fisher's exact test for 2x2 tables. This adapts the algorithm from R's fisher.test() function, which was implemented with function closures for optimisation, which does not always map well to other languages.

2. A foreign function interface to the Rmath library. I have now done this for Standard ML (MLton, Poly/ML, Moscow ML, MLkit, SML/NJ, SML# and Manticore), OCaml, Ur/Web, Mercury and MonetDB. Code generation sometimes uses cpp, m4 or the language's tree and string facilities.

3. Discrete event simulation using message passing with an application to cost-effectiveness analysis. Someday, I'll get this published.

Usually I find whatever web framework the language supports. This usually tells you a lot about the language, like if it can hide some of the ugly details behind powerful features or if you get to see it all (nothing wrong with the Go approach of 0 magic), basically everyone can open a browser and see immediate feedback. I also like to see how responsive it is and all that.

It also lets you evaluate any database drivers, which are one of the top 10 things I want out of any language I use.

I'm a fullstack web developer. I know "some" devOps. I also develop for mobile but mostly via port frameworks like Capacitor.

I usually build something that'll be easy and can be built in a weekend. Like with Phoenix, I'm thinking of building a multiplayer app since that's the best usage for this specific framework.

socket programming

Depends on the language. Since this year I am getting up to speed with JavaScript and TypeScript, and there are a lot of different notions around to learn. It really clicked for me just recently when I implemented my own little unit testing tool (https://www.npmjs.com/package/instatest). This touched many aspects of the ecosystem I needed to know about, and was yet pretty simple to do.