[stutonk]

Well said. This is exactly my gripe with Haskell monads. There are too many places where the hierarchy isn't uniform and there are a bunch of special monads like IO and List. It leads to the same ambiguous "is a" problem of complicated OO hierarchies and is one of the reasons they don't compose well.

The ironic thing is that these algabraic effect systems have a feel/control flow pattern that's quite similar to exception handling from the OO languages or interrupt handlers in low-level code.

It's much easier to just say "this piece of code is impure, it may do X, Y, and Z and if so then ..." than to try and shove everything ad-hoc into the abstract math tree. But then you lose the purity of your language and it's really awkward in a language whose primary concern is purity. That may be a reason why algebraic effects seem a bit more natural in OCaml.