The biggest problem with monads that I am aware of is that they don't compose: if m1 and m2 are monads, then you can't automatically derive a new monad m3 where m1 (m2 a) and m3 a are equivalent.
Monad transformers are one solution to this. This lets you write the composition rules for m2 once, and then reuse them for every m1. A solution, but boilerplatey.
I don't understand algebraic effects quite as well, but my understanding is that they do simply compose.
Monad transformers are one solution to this. This lets you write the composition rules for m2 once, and then reuse them for every m1. A solution, but boilerplatey.
I don't understand algebraic effects quite as well, but my understanding is that they do simply compose.