For optimal speed, you should move as much code as possible outside the closures.

In particular, you should do the `switch op` at https://github.com/skx/simple-vm/blob/b3917aef0bd6c4178eed0c... outside the closure, and create a different, specialised closure for each case. Otherwise the "fast interpreter" may be almost as slow as a vanilla AST walker.

That's fair, thanks for taking the time to look and giving the feedback.