either

An Access datatype represents an action, when evaluated, brings a value of type A into memory. The datatype needs to be monadic for the derivation mechanism to work.

The bifunctor package supports Access values that are bifunctors (covariant on both type parameters, i.e. not profunctors), but does not place any assumption on the meaning of the first type parameter.

aka traverse.

If you are implementing Access with your own datatype, and if you want batching/parallel behavior, please override this default behavior with a more efficient version that comes with your datatype.

See zquery or fetch modules for examples.