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

A code snippet is given below. It has an `authenticateUser` function that authenticates the provided `username` and `password` with the stored `username` and `password`. If authentication fails, the program throws an exception.

<?php
const USER_DATA = [
  'password' => '$2y$10$gaGFDPMaVRS61ONjnkGQAODo64voLOUJK1AlokiZY2HY3QiPE4zHq',
  'username' => 'kelly92',
  'admin' => false,
]; // valid password is trap_223

function authenticateUser(string $username, string $password): array
{
  if ($username !== USER_DATA['username']) {
    throw new Exception('Sorry, your username is invalid');
  }
  if (!password_verify($password, USER_DATA['password'])) {
    throw new Exception('Sorry, your password is invalid');
  }
  return USER_DATA;
}
 
authenticateUser('Some_User_Name','Some_Password');
?>

# Problem statement

Eliminate the exception in the snippet above by rewriting the `authenticateUser` as a two-track Either monad-based function. You have to perform the following tasks to complete the challenge:

1. If the provided `username` is not valid, then the string returned by the function must be

    `Sorry, your username is invalid`.

2. If the provided `password` is not valid, then the string returned by the function must be

    `Sorry, your password is invalid`.

3. If both—the provided `username` and `password`—are valid, then the function will perform the following tasks:

    * Add a new field with the name `role` in the `USER_DATA`, whose value is either `admin` or `customer` depending on the value of the `admin` key (`true` for the admin and `false` for the customer).

    * Remove the password from the resultant data.

 > **Note:** Unlike the first two constraints, you're not required to return a custom string for this one. The test cases for this challenge will automatically verify whether these two tasks are performed on `USER_DATA` or not.
    > - Actual username: `kelly92`
    > - Actual password: `trap_223`

# Sample inputs and outputs

## Sample input 1
```
Username = "kellys92"
Password = "trap_223"
```
## Expected output
```STRING
Sorry, your username is invalid
```

## Sample input 2
```
Username = "kelly92"
Password = "trap223"
```
## Expected output
```STRING
Sorry, your password is invalid
```

# Try it yourself


Test your knowledge by rewriting the given code without using any exceptions.

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

Challenge 1: Eliminate Exceptions Using the Either Monad

Problem