Data.These

The These type represents values with two non-exclusive possibilities.

This can be useful to represent combinations of two values, where the combination is defined if either input is. Algebraically, the type These A B represents (A + B + AB), which doesn't factor easily into sums and products--a type like Either A (B, Maybe A) is unclear and awkward to use.

These has straightforward instances of Functor, Monad, &c., and behaves like a hybrid error/writer monad, as would be expected.

Case analysis for the These type.

Takes two default values and produces a tuple.

Coalesce with the provided operation.

BiMap and coalesce results with the provided operation.

A Traversal of the first half of a These, suitable for use with Control.Lens.

A Traversal of the second half of a These, suitable for use with Control.Lens.

Select all This constructors from a list.

Select all That constructors from a list.

Select all These constructors from a list.

Select each constructor and partition them into separate lists.

Bifunctor map.