Create State ADT Based Reducers

The typical Redux Reducer is function that takes in the previous state and an action and uses a switch case to determine how to transition the provided State. We can take advantage of the Action Names being Strings and replace the typical switch case with a JavaScript Object that pairs our State ADT reducers with their actions.

We can also take care of the case in which a reducer does not have an implementation for a given action, by reaching for the Maybe data type and updating our main Redux reducer to handle the case for us, by providing the previous state untouched. And all of this can be captured in a simple helper function we can use in all of our reducer files.