Comment by flavio81

You´d be surprised.

In the 1980s, complete workstations were written in Lisp down to the lowest level code. With garbage collection of course. Operating system written in Lisp, application software written in Lisp, etc.

Symbolics Lisp Machine

https://www.chai.uni-hamburg.de/~moeller/symbolics-info/fami...

LMI Lambda http://images.computerhistory.org/revonline/images/500004885...

We're talking about commercial, production-quality, expensive machines. These machines had important software like 3D design software, CAD/CAM software, etc. And very, very advanced OS. You could inspect (step into) a function, then into the standard library, and then you could keep stepping into and into until you ended up looking at the operating system code.

The OS code, being dynamically linked, could be changed at runtime.