Learning Functional Programming

Chapter 3. Category Theory and Patterns

In this chapter, I will introduce software patterns and describe how they work in FP. I will also introduce category theory and explain how it can be useful as a source of functional software patterns and also how it is the foundation from which FP comes.

A software pattern is a reusable solution to a commonly occurring problem within a given context in software design. Software patterns mean that we do not have to start from scratch every time we write code. A software pattern is a template for solving a type of problem. The more of these templates you know about, the better equipped you are to tackle a given development obstacle. Once these patterns become second nature and you no longer have to look them up, you will become a more proficient developer.

Note

A pattern is just a tool for helping you formulate your code. Most of the problems we attempt to solve in software creation have already been solved in a universal, efficient manner. A pattern describes one of these solutions.

Patterns were popularized by the Gang of Four software patterns book. This book put patterns on the map and they have since become a popular tool for programmers to use. Now, if you ask functional programmers about patterns, they may say that patterns are not particularly relevant in FP. When they say this, they are likely thinking of the traditional, OOP patterns found in the Gang of Four book. However, there is another set of structures commonly used by functional ...