带两个括号的PHP函数：calc（1）（2）

JavaScript:

function calc(x) {
  return function(y) {
     return x + y;
  };
}

console.log(calc(1)(2));

This will return 3.

I tried the same with PHP:

function calc($x) {
    return function($y) { 
        return $x + $y; 
    };
}

echo calc(1)(2);

This will return 2. And I get an E_NOTICE:

E_NOTICE : type 8 -- Undefined variable: x -- at line 4

Why is the variable x undefined? Is it because that wouldn't work with PHP or am I doing something wrong?

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it's called a closure :

http://php.net/manual/en/class.closure.php

http://php.net/manual/en/functions.anonymous.php

function calc($x) {
    return function($y) use($x){ 
        return $x + $y; 
    };
}