Type for proving that an implicit parameter does
not exist in scope.
Code was copied from Shapeless,
authored by Miles Sabin.
Priority is a type class for prioritized implicit search.
This type class will attempt to provide an implicit instance of P
(the preferred type). If that type is not available it will
fallback to F (the fallback type). If neither type is available
then a Priority[P, F] instance will not be available.
This type can be useful for problems where multiple algorithms can
be used, depending on the type classes available.
Priority is a type copied from Algebra,
authored by Erik Osheim.