Monads are not the same thing as effect types - the latter are most commonly modeled as Lawvere theories. They are at a different level of composability.

Regardless, this blogpost is about Rust which has yet to gain either feature, for well-known reasons (for one thing, monadic bind notation interacts badly w/ the multiple closure types in Rust). Talking about Haskell monads just does not seem all that relevant in this context.