Using `Either` instead of `Option` would violate "Use the least complex approach that solves your problem".
If all you need is represent an optional value, why use `Either`, which needs a second type parameter representing the failure? If you don't care about what caused the failure (because there was no failure, an absence of value is a valid result), no need to represent it.
Besides, these two classes still represent fundamentally different concepts and they are not interchangeable at all.
My question was implicitly framed in the context of the "Error Handling" section of the paper. I agree that Option is an ideal choice for 0/1 cardinality situations and use if frequently for that purpose.
Sorry for any confusion I may have introduced when re-stating the question originally posed by "Joe Clueless" in the comments section.
If all you need is represent an optional value, why use `Either`, which needs a second type parameter representing the failure? If you don't care about what caused the failure (because there was no failure, an absence of value is a valid result), no need to represent it.
Besides, these two classes still represent fundamentally different concepts and they are not interchangeable at all.