module WG = MakeGroup (Name) (Request) defines a worker group all using the same
Event, etc. To instantiate a worker from a group, you must give the
WG.MakeWorker(Types). This defines a
Worker module of type
T. This last instantiation can be safely used as first class module.
The delayed application is there to prevent multiple side-effect executions in case of multiple instantiation. (Inner events trigger side effects.)