I had read this article more as a "from-first-principles" example, but it's a good note for people who might be unfamiliar with practical Haskell. Using an effects system also promotes the domain DSL from an initial-tagless language (only the interpreter is extensible) to a tagless-final language (both the language and the interpreter are extensible).

It may be worth noting that effectful, polysemy, and the other "new kids" of effects systems are not the only option: record-of-functions, mtl, and type-class effects aren't cutting edge, but they're a little more approachable from an OOP dependency injection pattern.