About php7 Uniform Variable Syntax, nested functions - php

Question

I'm try to solve a task which uses new functions php7 uniform variable syntax nested () support foo()() (https://wiki.php.net/rfc/uniform_variable_syntax).
I need write function test for this code:
$sum = function($a, $b) { return $a + $b; };
test(6)(2)(3)($sum); // 11
test(3)(1)($sum); // 4
test(3)(3)('pow'); // 27
I don't found any explanation for this feature. Where can I find how to use it? I see that I must return function name in function test, but how to pass argument?

Answer 1

Thanks all for help. It's something like this:
<?php
function test($a) {
echo '<br/>';
$arr[] = $a;
return $mf = function($b) use(&$mf, &$a, &$arr) {
if(gettype($b) == 'object') {
echo(array_reduce($arr, $b));
} elseif (gettype($b) == 'string') {
if($b == 'pow') {
echo array_reduce($arr, function ($carry, $a) {
return !empty($carry) ? pow($carry, $a) : $a;
});
}
} elseif (gettype($b) == 'integer') {
$arr[] = $b;
}
return $mf;
};
}
$sum = function($a, $b) { return $a + $b; };
test(6)(2)(3)($sum); // 11
test(3)(1)($sum); // 4
test(3)(3)('pow'); // 27

Answer 2

This is more about nested recursive functions, or currying, than that rfc. That rfc just enabled the syntax that supported it.
This uses recursion until you pass a callable:
function test($var) {
$values = [$var];
$function = function($callback) use (&$values, &$function) {
if (is_callable($callback)) {
return array_reduce(array_slice($values, 1), $callback, $values[0]);
}
$values[] = $callback;
return $function;
};
return $function;
}
Because your functions expect two parameters but your nesting could have unlimited parameters, it's best to use an array and array reduce.
However, since multiplication functions like pow won't work with a null initial value, you can specify the initial value as the first passed parameter from the array.