The resultant in a State ADT instance can be used as a means of communication between different stateful transactions. It can be used to read and transform a portion of our state into a form that another transaction is dependent on. This allows us to only keep what is needed state, without filling it with calculations that are only needed for one or few transactions.
We take can take advantage of this by pulling not only a random number using the seed from our state, but also pulling a list of card and filtering them, to randomly select one from our calculated state. Then we use the resultant to store the calculation before we save the result to state.