The GetState is basically just a deferred way to get a state
of a ReduxStore stream at any given point in time.
So you have to call this method to get the state.
Reducer<A, S>= S Function(ScurrentState, AnewAction)
A simple type alias for a reducer function.
A Reducer takes a State and an Action as input and produces a state as output.
It is a function which takes a stream of actions and returns a stream of actions.
Actions in, actions out (concept borrowed from redux-observable.js.or - so called epics).