> If you have that, the only thing that's left is being able to inject the compiled code into the running REPL process.

This is alike JIT, where you MMAP and the mark that as executable?

Now thinking a little, could be easier using DLLs/dynamic linking, but how model the API is something I can't yet figure.

P.D: I think TinyCC is able to compile on memory, but I'm using rust for my project and probably the gymnastics of this are too much for now.