Code to turn all defined internal functions into Closures to be able to pass them around as First Class Citizens. Not that you should do that.

Turn all internal functions into Closures

<?php

$functions = get_defined_functions();
foreach($functions['internal'] as $function) {
    $GLOBALS[$function] = function() use ($function) {
        return call_user_func_array(
            $function,
            func_get_args()
        );
    };
}

// Alternate version (PHP >= 5.4)

foreach (get_defined_functions()['internal'] as $function) {
    $GLOBALS[$function] = (new ReflectionFunction($function))->getClosure();
}