PHP Exercises: Curry a function to take arguments in multiple calls

Last update on April 19 2025 11:49:06 (UTC/GMT +8 hours)

100. Curry a Function for Partial Application

Write a PHP program to curry a function to take arguments in multiple calls.

Sample Solution:

PHP Code:

<?php
// Licence: https://bit.ly/2CFA5XY

// Function definition for 'curry' that takes a function as a parameter
function curry($function)
{
    // Define an accumulator function using a closure
    $accumulator = function ($arguments) use ($function, &$accumulator) {
        // Return a closure that takes a variable number of arguments
        return function (...$args) use ($function, $arguments, $accumulator) {
            // Merge the accumulated arguments with the new arguments
            $arguments = array_merge($arguments, $args);

            // Use Reflection to get information about the original function
            $reflection = new ReflectionFunction($function);

            // Get the total number of required parameters for the original function
            $totalArguments = $reflection->getNumberOfRequiredParameters();

            // Check if the accumulated arguments meet the total required parameters
            if ($totalArguments <= count($arguments)) {
                // If true, call the original function with the accumulated arguments
                return $function(...$arguments);
            }

            // If not enough arguments, continue accumulating by calling the accumulator recursively
            return $accumulator($arguments);
        };
    };

    // Return the initial accumulator with an empty array of arguments
    return $accumulator([]);
}

// Create a curried version of the 'add' function using 'curry'
$curriedAdd = curry(
    function ($a, $b) {
        return $a + $b;
    }
);

// Partially apply the curried function with one argument (10)
$add10 = $curriedAdd(10);

// Call the partially applied function with another argument (15) and display the result using 'var_dump'
var_dump($add10(15)); // 25
  
?>

Explanation:

Function Definition:

The curry function is defined to take a single function as a parameter, allowing it to transform that function into a curried version.

Accumulator Closure:

Inside curry, an accumulator function is defined using a closure. This function will handle accumulating arguments over multiple calls.

Return Closure:

The accumulator returns another closure that takes a variable number of arguments (...$args). This enables it to accept additional arguments whenever called.

Argument Merging:

The accumulated arguments are combined with the new arguments using array_merge($arguments, $args).

Reflection:

The ReflectionFunction class is used to inspect the original function ($function) to determine how many required parameters it expects.

Argument Count Check:

The code checks if the number of accumulated arguments meets or exceeds the number of required parameters:
If it does, the original function is called with all accumulated arguments, and the result is returned.
If there are not enough arguments, the accumulator is called recursively to continue gathering arguments.

Initial Call:

The curry function returns the initial accumulator with an empty array of arguments ([]), preparing it for the first invocation.

Creating a Curried Function:

A curried version of an add function (which takes two parameters and returns their sum) is created using curry.

Partial Application:

The curried function is partially applied by calling it with the first argument 10, resulting in a new function ($add10) that expects one more argument.

Final Call:

The partially applied function $add10 is called with another argument (15), resulting in the sum 25, which is displayed using var_dump.

Output:

int(25)

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP script to create a curry function that transforms a multi-argument function into a series of unary functions.
Write a PHP function to implement currying so that arguments can be applied in multiple stages.
Write a PHP script to demonstrate partial application by currying a function and calling it with subsets of arguments.
Write a PHP script to convert a standard function into a curried function that accepts its parameters one at a time.

PHP Code Editor:

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