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How to Implement Function Currying in PHP Arrow Functions: Tips and Examples

M66 2025-06-20

How to Implement Function Currying in PHP Arrow Functions: Tips and Examples

Currying is an important concept in functional programming that transforms a function with multiple arguments into a series of functions that each accept a single argument. In PHP, we can leverage arrow functions to implement currying, which simplifies the code structure and improves code reusability.

Arrow functions, introduced in PHP 7.4, are a new syntax feature that allows functions to capture external variables and only include one expression in the function body, eliminating the need for the `return` keyword.

Understanding Currying with Code Example

Here’s an example that demonstrates how to implement function currying using PHP arrow functions:


// Define a regular addition function
$add = function($a, $b) {
    return $a + $b;
};

// Define a currying function
$curry = function($func) {
    return fn($a) => fn($b) => $func($a, $b);
};

// Call the addition function with currying
$curriedAdd = $curry($add);

// Method 1
$result = $curriedAdd(1)(2); // 3
echo $result;

// Method 2
$add2 = $curriedAdd(2); // Fix parameter a = 2
$result = $add2(3); // 5
echo $result;

// Method 3
$add5 = $curriedAdd(5); // Fix parameter a = 5
$result = $add5(6); // 11
echo $result;

In the code above, we first define a simple addition function `$add`. We then define the function `$curry`, which takes a function as a parameter and returns a curried version of that function. The curried function is implemented using an arrow function that accepts an argument `$a` and returns another function that takes a second argument `$b`, which is then passed to the original function `$func` to compute the result.

With currying, we can pass arguments in three common ways:

  1. Passing arguments sequentially, for example: $curriedAdd(1)(2), where we first pass 1, then 2, and the result is 3.
  2. Partial application, where we first pass part of the arguments and then return a new function that accepts the remaining arguments, for example: $add2 = $curriedAdd(2), where we pass 2 and then pass 3 to get 5.
  3. Fixing some parameters in advance, such as: $add5 = $curriedAdd(5), fixing parameter a to 5, and then passing 6 to get the final result of 11.

This curried approach not only makes functions more flexible but also helps us manage and reuse code more effectively, especially in function composition and callback function handling.

By using PHP arrow functions to implement currying, we can simplify the code structure and make it more readable and maintainable. However, in real-world development, it's essential to assess when to apply currying based on the specific requirements, as overusing it might lead to overly complex and hard-to-understand code.

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