I'm sorry if these are dumb questions, I'd be totally fine with some pointers in the right directions if you don't want to waste your time :)

I'm under the impression that the implementation is based on algebraic effects. Does that include extending the language in a way that lets users define their own effects & handlers?

Also, how's the performance? Last time I looked this stuff up (and played around with Eff), which was quite a while ago, I was told that regular usage of effects may impact performance quite noticeably.