Guix

A data-type like Either but with differing properties and type-class instances.

Library support is provided for this different representation, including lens-related functions for converting between each and abstracting over their similarities.

The Validation data type is isomorphic to Either, but has an instance of Applicative that accumulates on the error side. That is to say, if two (or more) errors are encountered, they are appended using a {Semigroup