A gentle introduction to Category Theory for programmers used to OOP but interested in Functional Programming. No Haskell knowledge required. We will explain main concepts behind functional programming with many diagrams and simple metaphors and examples. Some code will clarify how to translate these ideas in programs. We will explain why Monoids and Monads are “mono”? What is the difference between a function and a functor? And what is a Category anyway? We believe that understanding the foundations of categories can help anyone to improve their programming skills. Finally we will look at some different possible strategies to apply these concept to real world programming and comparing them to classical OOP approach. Examples in Java and Kotlin with Vavr and Kategory libraries.
