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

fp15aug.tar.gz

php7.4

ch8-phonebook

php8.1

purescript

python-pytoolz

chapter5-challenge1

AMQP

eris-testing-lesson

AMQP-Challenge

eris-testing-challenge

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

# Overview

A **value object** is an abstract data type wherein each object represents an entity: the value. The grounds for a comparison of value objects is their value, *not* the identity of the object. The code below demonstrates this.

# Code example

<?php

class HttpMessage
{
  private int $code;

  private string $response;

  public function __construct(int $code, string $response)
  {
    $this->code     = $code;
    $this->response = $response;
  }

  public function verify(HttpMessage $message) : bool
  {
    return $this->response == $message->response &&
      $this->code == $message->code;
  }

  public function newMessage(int $code, string $response) : HttpMessage
  {
    $newMessage           = clone $this;
    $newMessage->code     = $code;
    $newMessage->response = $response;

    return $newMessage;
  }
}

$ok = new HttpMessage(200, 'OK');

$created = $ok->newMessage(201, 'OK');

echo $ok->verify($created) ?
  'Value objects are equal' :
  'Value objects are not equal';

The class above is instantiable as an HTTP message value object. It works in a domain where HTTP messages are representable as distinct `HttpMessage` objects—identifiable with a unique response code and HTTP message. Defined in the `HttpMessage` class are methods `verify` and `newMessage` that respectively perform equational reasoning on `HttpMessage` objects and create—via object cloning—new `HttpMessage` objects. **Equational reasoning,** as the name suggests, is a function application technique for proving expressions can be substituted for each other and is a means for ascertaining  referential transparency.

# Implications of value objects

Domain value validation checks and internal object duplication feature prominently in value objects. Complexities like the aforestated ideas are incredibly tedious to implement especially when the data domain of the value is something as simple as a set of positive decimal numbers. Value objects are best suited for situations that require interactions with multiple data primitives, and where needless repetitions are not common. It is, therefore, wise to assess the overall complexity associated with a translatable value domain (a set of data values) before attempting to code it to a value object. Like most things related to functional programming, value object methods should be precise in that their inputs and their outputs should also be clear and concise.

Learn about value objects and their implications.

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

Value Objects

Overview