In practice you use something like an exception monad, which makes this a lot more ergonomic since you don't need to carry a case distinction around for every unwrap: an exception monad essentially has an implicit passthrough that says "if it's a value, apply the function, if it's an exception just keep that". You only need to "catch" the exception if you actually need the value. I'm this case the exception monad is not that different from annotating a function with "throws": your calling function either needs it's own throws (=error monad wrapper) in which case exceptions just roll through, or you remove the throws, but now need to handle the exception explicitly (=unwrap the monad).