I fail to see how this is different. Say you have a function f1 returning an Either a b value then another method f2 which calls f1 but doesn't handle the erro

I fail to see how this is different. Say you have a function f1 returning an Either a b value then another method f2 which calls f1 but doesn't handle the error case will simply flatMap or bind or whatever the language of choice is calling it and return yet another Either a b value until at some point up the call hierarchy someone actually decides to unwrap and if necessary do something with the error case. The function signatures have the same problem as the parent comment mentioned. flatMapping over an Either and returning the result is no different than adding "throws SomeException". Then Option types (since they were mentioned as well somewhere) are a bit of a different story all together. They make sense for describing absence/presence if values/results and are definitely useful. However they don't compete with Exceptions in any real way since they don't really work for error handling beyond the most basic cases (i.e. where handling the error somewhere doesn't matter/need to happen).