“Functional programming refers to the declarative evaluation of pure functions to create immutable. Learn to use PHP in ways you never knew you could. Functional Programming offers a fundamental shift in the way you design your. For more information, reference our Print and eBook Bulk Sales web page at . Why Not to Use PHP for Functional Programming .

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Challenge your procedural way of thinking with this article and learn the basic concepts of functional programming in PHP. It's not about OO against functional programming (FP), or to define which one is better. Due to the fact that PHP is a quite “classical” OO. The new hype in programming is all about functional programming paradigms. programming, be prepared to have great fun with this tutorial.

While based on very simple concepts, FP requires a shift in the way you think about a problem. As I mentioned before, you can implement a functional style using PHP 5. This is around the time that the Closure class was added to the language more on this later. However, there are good reasons for upgrading to PHP 7.

Aside from it being much faster, matching the runtime speed of Hack , and sometimes even better, the latest release adds strict typing and scalar type declarations. Type declarations allow you to qualify any function parameter with its proper class or scalar type boolean, integer, string, MyClass, etc. Being a dynamic language, PHP will always attempt to coerce values of the wrong type into the expected scalar type, if appropriate.

Sometimes we want this flexibility, but when we overdo it this can lead to very confusing and hard to read code.

Types checks also ensure your code is correct by enforcing type constraints on your function calls. Hello FP As I mentioned before, functional programming is not a framework or a tool, but a way of writing code; thinking functionally is radically different from thinking in object-oriented or imperative terms. So, how do you become functional?

How do you begin to think this way? Unlearning old habits is actually the hardest part and can be a huge paradigm shift for most people that come from a different background. In simple terms, FP is a software development style that places a major emphasis on the use of functions.

In this regard, you might consider it a procedural programming paradigm based on procedures, subroutines, or functions , and at its core it is, but with very different philosophies. Your goal will be to abstract entire control flows and operations on data with functions in order to avoid side effects and reduce mutation of state in your application.

Say you wanted to change the message contents or where it will be written to; you will need to rewrite this entire expression.

Functional Programming in PHP

Consider wrapping this code with a function and making these change-points parameters, so that you write it once and use it with any configuration. Suppose your requirements change and now you need to repeat this message twice. We need to make our code more extensible. Thinking functionally involves treating parameters as not just simple scalar values but also as functions themselves that provide additional functionality; it also involves using functions or callables as just pieces of data that can be passed around anywhere.

Returning functions from other functions? Let me fast-forward a bit more and show you how I can use this function in its current form.

Without a doubt, this looks radically different than the original. Also, notice how I was able to split the logic of IO from manipulating its contents.

We typically declare functions and invoke them directly. Above all, the important aspect about this code sample above is that it captures the process of decomposing a program into smaller pieces that are more reusable, reliable, and easier to understand; then they are combined to form an entire program that is easier to reason about as a whole. Thinking about each of these simple functions individually is very easy, and separating the concerns of business logic and file IO makes your programs easier to test.

Every functional program follows this fundamental principle.

Now I just introduced a new concept compose, itself a function, to invoke a series of other functions together. Behind the scenes, it basically links each function in a chain-like manner by passing the return value of one as input to the next. All you need to is make sure every function individually executes correctly.

Because PHP 7 ensures that all of the types match, you can be confident this program will yield the right results. This visual quality is not accidental. When comparing the functional to the non-functional solution, you may have noticed that there is a radical difference in style.

Both achieve the same purpose, yet look very different.

Declarative coding Functional programming is foremost a declarative programming paradigm. Chapter 3 shows you how to build these data flows using point-free coding.

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As you know, the more popular models used today in PHP are procedural and object-oriented, both imperative paradigms. For instance, sites built using older versions of Wordpress or Moodle are heavily procedural; whereas, sites built using Laravel are completely OOP. Imperative programming treats a computer program as merely a sequence of top-to-bottom statements that change the state of the system in order to compute a result. Suppose you need to square all of the numbers in an array.

This is the most common way of writing this code and most likely will be your first approach to tackling this problem. Declarative programming, on the other hand, separates program description from evaluation. It focuses on the use of expressions to describe what the logic of a program is or what output would look like without necessarily specifying its control flow or state changes.

Once you employ this vocabulary to concoct the instructions subroutines, functions, procedures, etc that make up your program, the PHP runtime translates this higher level of abstraction into regular PHP code: Shifting to a functional approach to tackle this same task, you only need to be concerned with applying the correct behavior at each element and cede control of looping to other parts of the system.

Notice a trend? Consider this example.

Understanding declarative programming We were taught to implement algorithm using basic coding blocks such as loops and conditionals when we started programming. This is called imperative programming, in which we describe each step a program must take to accomplish a task. For example, to convert array of string to uppercase in PHP, we would normally implement a loop as shown below: As opposite to imperative programming, we solve a problem by applying a set of functions to the problem set.

To solve the same problem above using declarative programming in PHP, we can do: Some key difference between imperative programming and declarative programming are: Imperative programming focuses on the algorithms whereas declarative programming focuses on input and output of a function.

No state changed in declarative programming whereas in imperative programming, state change is common. Understanding side-effects There is a long and detailed explanation for side-effects in programming on wikipedia. In our opinion, we can think of side-effects as implicitly changing something somewhere.

Implicitness is the nature of side-effects, in this case, there is no way other than looking into implementation of a piece of code to find out what it changes.

Let's demonstrate side-effects in code samples. It modifies the original array without us knowing it. A function that accepts an input and always return a predictable output is called pure function. GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again.

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PHP functional programming for beginner

Dismiss Join GitHub today GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software together. Sign up. Primitives for functional programming in PHP. Find File. Download ZIP. Sign in Sign up.

Launching GitHub DesktopFor example, side-effect-free functions lend well to parallel processing, but PHP scripts are not run in this manner. Type hints for PHPStorm Embrace immutability An object that cannot be changed after is creation is an immutable object.

So, from a practical standpoint, this object is predictable and constant. This is a very natural thing for us to do. In FP, your functions should abide by this motto:. This means that you can use the value 42 in place of any of these expressions.

The term lexical refers to the actual placement of the variable in the code.