Functional Programming in PHP: From Basics to Advanced Techniques

Most PHP developers are accustomed to writing imperative code: loops, mutable variables, side effects. But modern web development requires reliability, predictability, and ease of testing. The book "Functional Programming in PHP" is a practical guide that will show you how to apply the principles of FP (Functional Programming) in real PHP projects without abandoning your familiar toolkit.

What is this book about?

The book covers a full range of topics — from basic concepts to advanced techniques:

• Pure functions and data immutability — how to write code without side effects and why it simplifies debugging.
• Higher-order functions — map, filter, reduce and their implementation in PHP.
• Currying and partial application — creating flexible and reusable functions.
• Function composition — building complex logic from small building blocks.
• Monads — Maybe, Either, IO and working with nullable values without exceptions.
• Lazy evaluation and infinite sequences — saving resources in large projects.
• Functional error handling — moving away from try-catch in favor of Either and Option.
• Integration with OOP — how to combine functional and object-oriented styles.

Who is this book for?

• Junior and Middle level PHP developers who want to go beyond typical CRUD.
• Senior developers striving to improve the architecture of legacy projects.
• Tech leads and architects looking for ways to reduce bugs and simplify testing.
• Developers from other languages transitioning to PHP and wanting to bring best practices from Haskell, Scala, or Clojure.

What will you learn after reading?

• Write code that is easy to read, test, and maintain.
• Avoid "callback hell" and side effects.
• Use built-in PHP features (arrow functions, generators, closures) for a functional style.
• Implement functional programming patterns without external libraries.
• Apply monads for safe handling of null and exceptions.
• Refactor legacy code by gradually introducing FP approaches.

The book contains numerous code examples ready for use in real projects. Each chapter concludes with exercises to reinforce the material. You will learn to see PHP in a new light — as a full-fledged functional language.