In-depth PHP functional programming: Exploring Transducers

You may have heard of functional programming and advanced functions, but do you know Transducers? This article will take you to explore this powerful data conversion tool.

Core points:

• Transducers originated from Clojure and ported to PHP by Michael Dowling, is a powerful way to build reusable algorithm transformations. They are functions that accept one reduction function and return another reduction function.
• PHP's Transducers package allows data to be converted in a variety of ways, such as capitalizing the initials of names or removing minors from user lists. Transformations can be combined into a single Transducer for reuse.
• The reduction function in Transducer receives a value as a parameter and returns an array of reduction functions containing three elements: "init" (init), "result" (final result), and "step" (reduce) logic).
• The advantage of Transducers is that it separates the data conversion process from the actual data source, making the code more modular and easier to maintain. They allow the creation of reusable software components that can be used in any data source. However, due to their functional programming roots, they may be more complex than traditional PHP functions.

Transducers definition

To understand Transducers, you first need to understand Reducers. Quoting Rich Hickey:

A reduction function is exactly the type of function you pass to reduce - it receives the result so far and a new input and returns the next so far result.

A Transducer is a function that receives one reduction function and returns another reduction function.

Transducers were initially introduced to Clojure by Rich Hickey and ported to PHP by Michael Dowling. Transducers are a powerful way to build algorithmic transformations that can be reused in a variety of situations. This article will explore its use through a series of practical examples.

Example

Before proceeding, we need to install the Transducers package through Composer.

composer require mtdowling/transducers

We will use a simple User class for the following example.

class User
{
    public $id;
    public $name;
    public $age;

    public function __construct($id, $name, $age)
    {
        $this->id = $id;
        $this->name = $name;
        $this->age = $age;
    }

    public function __toString()
    {
        return sprintf("\n%d - %s - %d", $this->id, $this->name, $this->age);
    }
}

// 示例數(shù)據(jù)
$data = [
    new User(1, "younes", 24),
    new User(2, "youssef", 26),
    new User(3, "hamza", 25),
    new User(4, "ismail", 17),
];

use Transducers as t;

$uppercase = t\map(function($user) { 
    return new User($user->id, ucfirst($user->name), $user->age); 
});

$result = t\xform($data, $uppercase);

var_dump($result);

map function is similar to the array_map function of PHP: we pass a callable function, which in this case will capitalize the username initial.

We use the xform function to apply our uppercase Transducer. It takes our data as the first parameter and the Transducer as the second parameter.

// 輸出
array(4) {
  [0]=>
  object(User)#14 (3) {
    ["id"]=>
    int(1)
    ["name"]=>
    string(6) "Younes"
    ["age"]=>
    int(24)
  }
  [1]=>
  object(User)#15 (3) {
    ["id"]=>
    int(2)
    ["name"]=>
    string(7) "Youssef"
    ["age"]=>
    int(26)
  }
  [2]=>
  object(User)#16 (3) {
    ["id"]=>
    int(3)
    ["name"]=>
    string(5) "Hamza"
    ["age"]=>
    int(25)
  }
  [3]=>
  object(User)#17 (3) {
    ["id"]=>
    int(4)
    ["name"]=>
    string(6) "Ismail"
    ["age"]=>
    int(17)
  }
}

xform Returns a value of the same type as the data parameter (in this case an array). If you strictly need to output an array, we can also use to_array.

// ...
$result = t\to_array($data, $uppercase);
// ...

We can also use to_string to convert the output to a string, or use into($target, $coll, callable $xf) to convert the output to a specific type. For more details, please see the documentation.

composer require mtdowling/transducers

class User
{
    public $id;
    public $name;
    public $age;

    public function __construct($id, $name, $age)
    {
        $this->id = $id;
        $this->name = $name;
        $this->age = $age;
    }

    public function __toString()
    {
        return sprintf("\n%d - %s - %d", $this->id, $this->name, $this->age);
    }
}

// 示例數(shù)據(jù)
$data = [
    new User(1, "younes", 24),
    new User(2, "youssef", 26),
    new User(3, "hamza", 25),
    new User(4, "ismail", 17),
];

The best part about Transducers is that we can combine multiple conversions into one Transducer. For example, let's capitalize the initial letter of the username and delete the minor.

use Transducers as t;

$uppercase = t\map(function($user) { 
    return new User($user->id, ucfirst($user->name), $user->age); 
});

$result = t\xform($data, $uppercase);

var_dump($result);

filter function is similar to the array_filter function of PHP. The comp function creates a Transducer from the Transducer list, in this case uppercase (using map) and removeMinors (using filter).

// 輸出
array(4) {
  [0]=>
  object(User)#14 (3) {
    ["id"]=>
    int(1)
    ["name"]=>
    string(6) "Younes"
    ["age"]=>
    int(24)
  }
  [1]=>
  object(User)#15 (3) {
    ["id"]=>
    int(2)
    ["name"]=>
    string(7) "Youssef"
    ["age"]=>
    int(26)
  }
  [2]=>
  object(User)#16 (3) {
    ["id"]=>
    int(3)
    ["name"]=>
    string(5) "Hamza"
    ["age"]=>
    int(25)
  }
  [3]=>
  object(User)#17 (3) {
    ["id"]=>
    int(4)
    ["name"]=>
    string(6) "Ismail"
    ["age"]=>
    int(17)
  }
}

Now we have a reusable Transducer combination that we can use at any time to reduce data based on this standard. Check the documentation for a list of available reduction functions.

Create Transducer

The reduction function receives a value as a parameter and returns an array of reduction functions that must contain three elements:

• init: Function that returns the initial value of Transducer. If no initial value is provided, it is called only on the first call.
• result:result function is used to build the final result from the call stack.
• step: This is where you write the reduction logic—you may call it zero or multiple times according to your reduction logic.

This gets very confusing without actual code, so let's take the take Transducer function as an example. It gets n items from the top of the data array.

// ...
$result = t\to_array($data, $uppercase);
// ...

use Transducers as t;

$uppercase = t\map(function($user) { 
    return new User($user->id, ucfirst($user->name), $user->age); 
});

$result = t\to_string($data, $uppercase);

var_dump($result);

The following is the source code of the take reduction function.

// 輸出
string(64) "
1 - Younes - 24
2 - Youssef - 26
3 - Hamza - 25
4 - Ismail - 17"

take function is called multiple times with result and input parameters. Each time it is called, it decrements the remaining variable and tests whether it is less than zero. In this case, we return a Reduced object instance, which represents a stop point.

Our Transducer function example will remove empty elements from the data. Using the previous explanation of how Transducer works, we can access the $input variable and decide whether to call the next step callback or simply return the value.

$uppercase = t\map(function($user) { 
    return new User($user->id, ucfirst($user->name), $user->age); 
});
$removeMinors = t\filter(function($user) { 
    return $user->age >= 18;
});

$comp = t\comp(
    $uppercase,
    $removeMinors
);

$result = t\to_string($data, $comp);

var_dump($result);

We can test this by adding some empty items to our $data variable.

// 輸出
string(48) "
1 - Younes - 24
2 - Youssef - 26
3 - Hamza - 25"

// ....
$comp = t\comp(
    $uppercase,
    $removeMinors,
    t\take(2)
);

$result = t\to_string($data, $comp);

var_dump($result);

Conclusion

In this article, we understand a new aspect of the functional programming world called Transducers. We review the purpose of Transducers, even if data conversion is easier. We also reviewed some examples to better demonstrate the value of Transducers. You now have a new tool in your developer toolbox, or at least have a better understanding of the concept of Transducer.

If you have any questions about Transducers, you can post it below!

FAQs about Transducers in PHP

What is the basic concept of Transducers in PHP?

Transducers in PHP is a data processing technology that allows you to create composable and reusable software components. They are essentially functions that accept a reducer and return a new reducer. This concept is borrowed from Clojure and JavaScript and has adapted to PHP. Transducers allow you to separate the data conversion process from the actual data source, making your code more modular and easier to maintain.

How is Transducers different from traditional PHP functions?

Traditional PHP functions usually combine the process of getting and converting data, which can make code difficult to maintain and reuse. Transducers, on the other hand, separate the two processes. This means you can create a Transducer that converts data in a specific way and then use it with any data source to make your code more flexible and reusable.

Can you provide an example of Transducer in PHP?

Of course, let's consider a simple example. Suppose you have an array of numbers and you want to add 1 to each number. You can create a Transducer that does this:

composer require mtdowling/transducers

You can then use this Transducer with any reduction function and data source.

How to use Transducers with different data sources?

Transducers are designed to be used with any data source. This is because they run at the single data item level, not at the entire data source level. Therefore, you can use Transducer with arrays, database query results, data streams from network connections, etc. The only requirement is that your data source must be able to work with the reduction function.

What are the benefits of using Transducers in PHP?

Transducers offer many benefits. They allow you to separate the data conversion process from the actual data source, making your code more modular and easier to maintain. They also allow you to create reusable software components that can be used in any data source. Finally, because Transducers operate on a single data item, they may be more efficient than traditional PHP functions when dealing with large data sets.

What are the disadvantages of using Transducers in PHP?

While Transducers provide many benefits, they may also be more complex than traditional PHP functions. This is because they involve the concepts of functional programming that may not be familiar to some PHP developers. But once you understand how Transducers work, they can be a powerful tool for writing clean, efficient and reusable code.

Can Transducers be used with PHP frameworks?

Yes, Transducers can be used with any PHP framework. They are a general data processing technology that does not depend on any specific framework features. However, some frameworks may provide their own utilities for handling Transducers, which can make them easier to use.

How to learn more about Transducers in PHP?

There are many resources available to learn Transducers in PHP. You can start by reading online articles and tutorials, such as articles on SitePoint. There are also books and online courses that cover the topic in more depth. Finally, you can try writing your own Transducers and using them in your PHP project.

Does Transducers be used in other programming languages?

Yes, the concept of Transducers originated from the Clojure programming language and has since been adopted by several other languages, including JavaScript and PHP. Each language implements Transducers in its own way, but the basic concepts are the same.

Can I use Transducers with PHP built-in array functions?

Yes, you can use Transducers with PHP's built-in array functions. However, remember that these functions may not be as efficient as using Transducer, especially when dealing with large arrays. This is because PHP's array functions usually create new arrays, and Transducer can convert data in place.

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