Scalaz avoids variance in the sense of the Scala type parameter annotation, with its associated higher-kind implications, except where it has historically featured variance; even here, variance is vanishing as unsoundness in its released implementations is discovered. There is a deeply related concept in Scalaz’s typeclasses, though: covariant and contravariant functors. Functor is traditional shorthand for covariant functor, whereas Contravariant represents contravariant functors. These co...
