# Module Either_intf

    module Either_intf: sig .. end

Many functions in `Either` focus on just one constructor. The `Focused` signature abstracts over which constructor is the focus. To use these functions, use the `First` or `Second` modules in `S`.

    module type Focused = sig .. end

Many functions in `Either` focus on just one constructor.

    module type S = sig .. end

Many functions in `Either` focus on just one constructor. The `Focused` signature abstracts over which constructor is the focus. To use these functions, use the `First` or `Second` modules in `S`.
This type represents values with two possibilities. `Either` can be seen as a generic sum type, the dual of `Tuple`. `First` is neither more important nor less important than `Second`.
`first` and `second` are `First.return` and `Second.return`.