Reactive Programming

According to Wikipedia[1] "(...) reactive programming is a programming paradigm oriented around data flows and the propagation of change. This means that it should be possible to express static or dynamic data flows with ease in the programming languages used, and that the underlying execution model will automatically propagate changes through the data flow."

"For example, in an imperative programming setting, $a := b + c$ would mean that $a$ is being assigned the result of $b + c$ in the instant the expression is evaluated. Later, the values of $b$ and $c$ can be changed with no effect on the value of $a$."

"In reactive programming, the value of $a$ would be automatically updated based on the new values."

MS Excel is a reactive programming environment

Continuing from Wikipedia[2] "A modern spreadsheet program is an example of reactive programming. Spreadsheet cells can contain literal values, or formulas such as "=$B1+C1$" that are evaluated based on other cells. Whenever the value of the other cells change, the value of the formula is automatically updated."

Decoupling data from operations on data

To have a data flow between nodes it is necessary to decouple data from operations on data. Messages, tokens in dataflow parlance, are send from node to node. To have a more roubust design inherentely non-deterministic, the system should be assynchronous, using the Hollywood principle is stated as "don't call us, we'll call you."[3].