I wonder how the "ladder languages" for PLC work though. These may be similar to interpreters
Those I have worked with are compilers.

I've met eeprom software for a '52 clone that allows tracing/debugging "step by step" of the user program using serial line. How do you think?
fairly simple to do (level interrupt with the pin permanently low) but totally worthless since execution time would be 1000 times slower.

There are so many schemes to make an "economical ICE substitute' but so there is to make a perpetuum mobile.

For 'economical emulation' the only choice today is SILabs, something is in the pipeline from Philips but not seen yet.

Erik