Comment by howerj

I wrote a Forth interpreter for a SUBLEQ machine (https://github.com/howerj/subleq), and for a bit-serial machine (https://github.com/howerj/bit-serial), both of which do not have a function call stack which is a requirement of Forth. SUBLEQ also does not allow indirect loading and stores as well and requires self-modifying code to do anything non-trivial. The approach I took for both machines was to build a virtual machine that could do those things, along with cooperative multithreading. The heap, if required, is written in Forth, along with a floating point word-set (various MCUs not having instructions for floating point numbers is still fairly common, and can be implemented as calls to software functions that implement them instead).

I would imagine that other compilers took a similar approach which wasn't mentioned.

EDIT: There were some BASIC interpreters which did this as well, implementing a VM and then targetting that instead. P-Code is a similar thing.