validation-0.6.0: A data-type like Either but with an accumulating Applicative

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

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

• AccValidation

The AccValidation 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 operation.

As a consequence of this Applicative instance, there is no corresponding Bind or Monad instance. AccValidation is an example of, "An applicative functor that is not a monad."