Hello, author here! As the website says, the compiler itself is still in a very early state where basic things like functions, types, traits, inference, monomorphisation, and codegen are implemented. The fun stuff of algebraic effects, lifetime inference, and refinement types are not however. Though I can elaborate on implementation strategies of these for anyone curious. For example, algebraic effects in existing languages can be quite slow at runtime due to the use of continuations, the translation to a monad stack, and/or dynamically finding handlers at runtime. It is my plan to monomorphise them away and inline all these cases as in the following paper (1). With this, handlers are inlined into functions, continuations are normal closures, and continuations that aren't called multiple times are inlined.
(1) Zero-cost Effect Handlers by Staging: http://ps.informatik.uni-tuebingen.de/publications/schuster1...