According to Wikipedia, Functional Reactive Programming (FRP) is a programming paradigm for reactive programming, which uses the building blocks of functional programming. OK, that sounds fancy, but what does it mean? To understand the whole sentence we need to break it apart a bit. Let's try to define the following:

• A programming paradigm is an overarching theory, or way of working, centered around how a program should be organized and structured. Object-oriented programming and functional programming are examples of programming paradigms.
• Reactive programming, in short, is programming with asynchronous data streams. Asynchronous data streams are streams of data whose values can arrive at any point in time.
• Functional programming is a programming paradigm that takes a more mathematical approach, in that it sees a functional call as a mathematical computation and thereby avoids changing states or dealing with mutable data.

So, in short, our Wikipedia definition means we have a functional programming approach to values that might arrive at any point in time. That doesn't really mean much, but hopefully things will have been cleared up a bit by the end of this chapter.

In this chapter, we will learn about:

• The differences between declarative and imperative programming
• Asynchronous data streams
• How these streams can be manipulated