Annonymouse function in php

<?php

$add = function($x,$y){
    return $x + $y;
};

$sub = function($x,$y){
    return $x - $y;
};

$mul = function($x,$y){
    return $x * $y;
};

$div = function($x,$y){
    return $x / $y;
};

function calculate($x,$y,$fn){
    return $fn($x,$y);
}

echo calculate(100,200, $add);