Scala Reactive Programming

What is a data stream or stream?

In Reactive programming, we write programs to work on a sequence of events. For instance, in a spreadsheet, we can observe the following events in a sequence:

1. The user enters a value 1 into cell A1. When the user inputs data into cell A1, the value in cell A3 is updated to 1.
2. The user enters a value 2 into cell A2. When the user inputs data to cell A2, A3 is updated to 3.

In the Reactive World, this sequence of events happening over time is known as a stream, events stream, or data stream. The following diagram shows how a sequence of events forms an events stream. It also shows how a Publisher sends events to an event stream and how a Subscriber receives events from that event stream: 

A stream or data ...