Functional programming with PHP and Haskell

With the development of the Internet, programming languages ​​​​are constantly updated and improved. Nowadays, various programming languages ​​emerge in endlessly, and two of them, PHP and Haskell, have attracted much attention among developers.

PHP is a very popular server-side scripting language used for rapid development of web applications. PHP is widely used in many fields such as web development, dynamic page generation, and server-side scripting.

Haskell is a strongly typed pure functional programming language. It has all the advantages of functional programming languages, such as concise code, easy maintenance, high code reuse rate, etc.

Although the two programming languages ​​PHP and Haskell seem to have very different styles, in fact they both support functional programming style. This article will introduce how to use PHP and Haskell for functional programming.

1. Functional programming in PHP

Functional programming in PHP is mainly implemented through anonymous functions, higher-order functions and closures.

1.1 Anonymous function

The anonymous function in PHP is a function without a function name and can be called directly through variables. Anonymous functions can be used to conveniently define some temporary functions, and are usually used as parameters of higher-order functions.

$greet = function($name) {
    echo "Hello {$name}!";
};

$greet('World');

1.2 Higher-order functions

Higher-order functions refer to functions that can take functions as parameters or return values. PHP also supports higher-order functions, and by using anonymous functions, functions can be encapsulated and called conveniently.

function apply($callback, $value) {
    return $callback($value);
}

$addThree = function($x) {
    return $x + 3;
};

echo apply($addThree, 5); // 输出 8

1.3 Closure

Closure refers to a function that can access external variables. It is usually implemented by defining an anonymous function inside the function. In PHP, you can use closures to achieve some advanced usage.

function generator($start) {
    return function() use(&$start) {
        $start++;
        return $start;
    };
}

$next = generator(0);
echo $next(); // 输出 1
echo $next(); // 输出 2

2. Functional programming in Haskell

Haskell is a purely functional programming language, and its functional programming support is far more complete and complex than PHP. This section will introduce some functional programming techniques in Haskell.

2.1 Higher-order functions

In Haskell, functions are first-class citizens, which means that functions can be passed and calculated like other values. Therefore, higher-order functions are also a major feature in Haskell.

apply :: (a -> b) -> a -> b
apply f x = f x

addThree :: Int -> Int
addThree x = x + 3

main :: IO ()
main = do
    let res = apply addThree 5
    putStrLn $ show res

2.2 Currying

Currying is a technique that converts a multi-parameter function into a function with only a single parameter. In Haskell, all functions have only one parameter. If multiple parameters are required, currying is required.

add :: Int -> Int -> Int
add x y = x + y

addCurry :: Int -> (Int -> Int)
addCurry x = (y -> x + y)

main :: IO ()
main = do
    let res1 = add 2 3
        res2 = (addCurry 2) 3
    putStrLn $ show res1
    putStrLn $ show res2

2.3 Function synthesis

Haskell often links multiple functions together to form a new function through function synthesis. Function composition improves code readability and allows us to use less code to accomplish the same task.

compose :: (b -> c) -> (a -> b) -> a -> c
compose f g x = f (g x)

addThree :: Int -> Int
addThree x = x + 3

double :: Int -> Int
double x = x * 2

main :: IO ()
main = do
    let res = compose addThree double 2
    putStrLn $ show res

3. Summary

This article introduces some basic skills of functional programming in PHP and Haskell, allowing readers to understand how to use these two programming languages ​​for functional programming. . Whether you are a PHP developer or a Haskell developer, you can learn some useful knowledge from this article. Functional programming is a trend, and good use of functional programming can effectively improve code quality and readability.

The above is the detailed content of Functional programming with PHP and Haskell. For more information, please follow other related articles on the PHP Chinese website!