Gain insights into functional programming in PHP. Learn about pure functions, immutable data, and monads. Explore error handling and apply principles through practical projects.

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Functional programming is a paradigm that emphasizes expressing program logic as compositions of pure functions. PHP is a good fit for functional programming as functions are first-class citizens in its userland.
 
This course introduces you to the core concepts of functional programming, like pure functions, immutable data structures, and referential transparency. From there, you'll explore ways to handle errors with default values and callbacks while also exploring sum types such as Either or Maybe. Next, you'll look at functors before diving deep into monads, including IO, State, Reader, and List.
 
By the end of this course, you'll have a keen understanding of how to apply these principles in practice through a worked-out project. Not only will you know another way to program, but you’ll also feel confident enough to apply these ideas to your projects in PHP.

Learn Functional Programming in PHP

# Functions in PHP

Functions are the heart of functional programming. Functions are relationships between inputs and outputs. The **arity** of a function is the number of arguments a function accepts, and the function **signature** specifies return types and argument types. Lastly, the **definition** of a function encapsulates the function logic. Here's a mathematically defined function:
 
$$f(x) = x + 1$$

It has an arity of one, and it increments the value of the parameter $x$ by 1. The parameter $x$ is effectively a placeholder for a general transformation given in the function definition using the addition operation: $x + 1$. Different results are obtained for different values of $x$ because the function offers localized computation. Each result is, therefore, unique to each input. For example:
$$f(2) = 3$$
$$f(3) = 4$$

Functions in PHP take on many forms. They're just as flexible as variables and have the following characteristics:

* The `function` keyword.

* Two sets of parentheses:
  * Round brackets `()` for the arguments.
  * Curly braces `{}` for the function definition.
* A return type (as of PHP version 7.0).

# Types of functions in PHP

The different types of functions in PHP are the following:

* Named functions
* Anonymous functions
* Closures
* Methods

## Named functions

**Named** functions in PHP, like the one below, are identical (apart from a few syntactic differences) to those defined in other programming languages. They typically have an arbitrary name sandwiched between a function keyword and an argument list followed by the function definition, that contains state transformation expressions.




Learn about functions in PHP and their types.

Getting Started

An Introduction to Functional Programming in PHP

Core Concepts: Functional Programming in PHP

Composition and Helper Functions

Error Handling in Functional Programming

Functors in PHP

Parallelization of Tasks in PHP

Recursion, Pattern Matching, and Property Testing

Phonebook Application — A Simple Project

Conclusion

Appendix

PHP Functions

Functions in PHP