> Compiler was in OCaml

Not exactly a common language...

I don't have a math or computer science background so the more academic publications are almost always quite unreadable to me. I learn a lot by exploring the source code of existing virtual machines instead, and most are written in systems languages.

Sometimes much smarter people than I randomly decide to write articles that democratize access to very complex areas of programming language development. Examples:

https://journal.stuffwithstuff.com/2013/12/08/babys-first-ga...

https://www.wingolog.org/archives/2010/02/26/guile-and-delim...

It’s an extremely common language to write compilers in. The original Rust compiler was written in it for exemple.