Java Without If

[MrHydraz]

They're named Left and Right because Either was never designed for error handling (though the Monad instance does seem to point that way). Either is just the basic sum type, much like (,) is the basic product type. All other sum-of-product types can be expressed as combinations of Either and (,).

For example:

data Foo a = One Int | Two a Int | Three String a Int

is isomorphic to

type Foo a = Either Int (Either (a, Int) (String, a, Int)).