Calling a function before it's defined | PHP

Question

Is there any possible way when in one file - please note, just one file. To call a function when it isn\'t defined yet, e.g.

Answer 1

I just discovered that you can call a function if it's defined later in the same file.
But if it's defined in an other file, you must include the file before calling the function.

my_func();
function my_func() {...}
--->   No problem

but

my_func();
include_once 'define_my_func.php';
--->   PHP Fatal error

It's like a conditional function as in the example 2 on the doc on user-defined functions