Imo, the advantage of "Haskell's approach" is that it's always obvious when you can and can't use imperative code, and the type system enforces it. I think this

Imo, the advantage of "Haskell's approach" is that it's always obvious when you can and can't use imperative code, and the type system enforces it. I think this is important in many contexts, like STM[1] or Facebook's React[0]. But there are plenty of disadvantages: * it's a bit more verbose. * you can accidentally implement a weaker interface than the one you'd want, e.g. by only implementing Functor and not Traversable for your data structure. * the flip side of the benefits is that adding I/O to a previously pure function changes its interface. I don't know how it'd compare to OCaml's algebraic effects proposal, though. [0]: https://reactjs.org/docs/hooks-effect.html https://reactjs.org/docs/hooks-effect.html [1]: http://joeduffyblog.com/2010/01/03/a-brief-retrospective-on-transactional-memory/ http://joeduffyblog.com/2010/01/03/a-brief-retrospective-on-...