I don't want to be excessively dismissive, but I'm curious if you have a more-precise explanation for why you think that Haskell's programming model "breaks down" at I/O? I'd say that one of Haskell's entire purposes as a research language has been exactly about modeling, reasoning about, and representing I/O and other sorts of effectful computation in the type system. Unless I've misunderstood you or there's something more subtle you're referring to, I don't follow what you're trying to say here.