Functional programming. Sure. I've been using functions for years. What's the catch? Indeed you have been using functions a lot, just not in this way. When you think of functions as merely a collection of statements grouped together as an executable, you're thinking procedural programming. The truth is, functional programming is not a tool or a framework, but fundamentally an approach to software development. Since PHP 5.3 you can take advantage of higher-order functions and closures to create code with an extremely high quality that is more robust, maintainable, extensible and bug free.
In this book, I provide a practical approach to functional programming and show how it compares to other programming paradigms (procedural and object-oriented). This book is filled with examples that showcase functional concepts and techniques, plus using PHP in a ways you've probably never though it could.
This book is for the professional PHP developer. There's no crazy academic nonsense or mathematical equations, just pure and practical hardcore use of functions with the most widespread web language today.