sketches VS eff

but free monads are an effect system and not an ergonomic one. I have a post on how one can do the same with constraints as with Hierarchical Free Monads, except with less boilerplate.

I have a post about pretty much exactly this problem. It has a good type families solution (no need to specify the arity of the zipping function) and an even better fundeps one.

Thirdly, composing arbitrary effects without losing state is really, really difficult. Things are fine when you limit yourself to State and Reader, sure, but once you start with nondeterminism you’ll discover it’s shockingly easy to produce behaviors that are baffling unless you’ve spent a preposterous amount of time thinking about this stuff. (I’ve been bitten in prod by silent state-dropping bugs, and rarely have I been more flummoxed.) Consider this example, which produces silent changes in the semantics of <|> depending on whether you use it inside or outside of a higher-order effect. Every single effect library (besides the still-unreleased eff) gets certain combinations of effects + nondeterminism wrong. You could make the argument that most people don’t use nondeterministic monads, but eDSLs really shine when you have access to them, as you can turn a concrete interpreter to an abstract one fairly easily.

I'm not a LISPer myself, but I've heard that each LISPer would have his/her own fundamentals that not composed to a common base to date. I wonder even though delimited continuations (as well as other devices leveraging the powerful S-expression) are composable, the semantics to be conveyed does not generally compose (so well). This feeling partially comes from Alexis King's eff documentary about effect semantics zoo, involving other Monad based effect libs.

It's actually the effect semantics doesn't compose (well), and you happen trying that via Monads. Check out: https://github.com/lexi-lambda/eff/blob/master/notes/semantics-zoo.md