Several data-types like Either but with differing properties and type-class instances.
Library support is provided for those different representations, include
lens-related functions for converting between each and abstracting over their
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Validationdata type is isomorphic to
Either, but has an instance of
Applicativethat accumulates on the error side. That is to say, if two (or more) errors are encountered, they are appended using a
As a consequence of this
Applicativeinstance, there is no corresponding
Validationis an example of, "An applicative functor that is not a monad."