Fast enough for this approach to work for small examples. For longer examples, I'm less confident: I've yet to implement a proper module system (other than a slightly more principled version of C's #include) so this currently means compiling the entire standard library on every REPL line. Thankfully, the compiler can still handle this within about 100 milliseconds on my machine. Perhaps when I have a more rugged module system I can look into this more, thanks for the suggestion!