I know about effectful, but that doesn't use Reader (but provides one) but more or less directly IO (Ref) and "evidence passing", that's why it is faster than the other ones, the drawback is not being able to use non-deterministic effects and noo such thing as coroutines. But I talked about eff ("native" delimited continuations) should be more or less the same, maybe a bit faster, than effectful, but enable non-determinism and coroutines.