The Alternative typeclass represents the behavior of a monoid for types of kind * -> *. A typeclass for representing semigroups of kind * -> * is missing.
Currently, the Validation method or requires a monoid, while in theory a Semigroup would be enough. This is due to the fact that or is implemented on top of Alternative.
Following the Purescript typeclass hierarchy, we decide to introduce the Alt and the Plus typeclass.
We have now more possibilities when dealing with semigroups/monoids of kinds * -> *.
We can also implement Validation::or in terms of Alt, requiring a semigroup instead of a monoid.