The What? and Why? of functional programming

Posted on 2017-09-15 Updated on 2017-10-17

When I talk to fellow programmers about functional programming it’s often about something specific, but occasionally that person will suddenly turn the conversation around and ask “So what actually is functional programming, anyway?”. I will talk about some specific features of FP but I will also cover something more general, a tagline or soundbite with which I could give people an instant sense of the philosophy behind functional programming and how it differs from object-oriented programming. As we will see, however, you can get a lot of the benefits of functional programming even if you don’t program in a function language.

Literally speaking, functional programming means that the basic units of your application (i.e. the bits that you compose together to make a complete program) are functions (as opposed to Object-Oriented Programming when they are classes). However, when it comes to the philosophies of the two, I think we can be a bit broader than that to contrast the two:

The main goal of a code unit in object-oriented / imperative programming is to perform actions

The main goal of a code unit in functional programming is to compute results

Why is this distinction important? It’s why functional programming values concepts such as immutability and purity (which have a whole host of benefits).

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