A type that 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
.
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
module type Either : sig ... end