> All Java programs "really" happen in the IO + Either monads

People say things like this all the time, and I think it's a vacuous assertion. While there is probably some very narrow view where returning early with an error, throwing an exception, and binding in Either are the same thing, such a view ignores a lot of important context (e.g. all of imperative programming). This is why you have to qualify it as "IO + Either", but that doesn't say anything at all because everything is possible in IO.