Just some functional programming ideas

functional.php

<?php

//Closure Example
$add = function($x) {
	return function($y) use ($x) {
		return $x + $y;
	};
};

$addTen = $add(10);

var_dump( $result = $addTen(2) );

//A functional programming example. A Map example that uses closures.
//This allows us to create any number of array processes by composing a custom function with our map function.
function map( $fn ) {
	return function( $arr ) use ( $fn ) {
		return array_map( $fn, $arr );
	};
}
function sanitize_text_field( $string ) {
	return filter_var( $string, FILTER_SANITIZE_STRING );
}
$sanitize_array = map( 'sanitize_text_field' );

var_dump( $sanitize_array( array( '<h1>title 1</h1>', '<h1>title 2</h1>', '<h1>title 3</h1>' ) ) );

function either( $default, $value ) {
    if ( ! empty( $value ) ) {
      return $value;
    }

    return $default;  
}

$test = either('needs something', array());
var_dump($test);

//curried either
function either( $default ) {
	return function($value) use( $default ) {
		if ( ! empty( $value ) ) {
			return $value;
		}
		return $default;
	};
}

function return_error( $error_message ) {
	return new Exception( $error_message );
}

function return_false() {
	return false;
}

$maybe_false = either( return_false() );
$maybe_error = either ( return_error('something is missing') );

$test_false = $maybe_false(array());
$test_error = $maybe_error(array());
var_dump($test_false);
var_dump($test_error);

function error_check( $error_message, $value ) {
  if ( ! empty( $value ) ) {
      return $value;
    }
    
    return new Exception( $error_message );

}

function empty_check( $value ) {
  if ( ! empty( $value ) ) {
      return $value;
    }
    
    return false;

}

// Filter Example
//None Curried Either
function either( $default, $value ) {
	if ( ! empty( $value ) ) {
		return $value;
	}
	return $default;
}

//Same error function as above.
function return_error( $error_message ) {
	return new Exception( $error_message );
}

$users = array( 'John', "Bobby", 'Alex' );

function filter( $fn ) {
	return function( $arr ) use ( $fn ) {
		return array_filter( $arr, $fn );
	};
}

function get( $value ) {
	return function( $el ) use ( $value ) {
		return $el === $value;
	};
}

function get_user( $username, $users ) {
	$find = filter( get( $username ) );
	return either( return_error( 'Users not found' ), $find( $users ) );
}

var_dump( get_user( 'Bobby', $users ) );

class Wrap {
	protected $value;
	public function __construct( $value ) {
		$this->value = $value;
	}
	public static function of( $x ) {
		return new Wrap( $x );
	}
	public function map($func) {
		return static::of( call_user_func( $func, $this->value ) );
	}
}

$test = wrap::of('small world');
var_dump($test);
var_dump($test->map('ucwords'));
var_dump($test->map('strtoupper'));