module

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.

Good ol' flatMap.

To traverse a relation graph edge by edge is sequential computation, so we require flatMap to be implemented on Access.

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.

Plain ol' map.

Can be implemented in terms of flatMap and succeed, but probably a bad idea considering what kinds of datatypes will be used to implement Access.

aka pure, point, ...