references

i've been reading over the docs on references, and i can't see anyway to pass around functions as references. i know how to do this easily with perl, but i cannot seem to find the correct syntax for creating a reference to a function in PHP. what i'd like to do is something like this: // X is now a reference to test() // but i dont want test() to be executed now $x =& test(); // Now, i want to execute test() with // something like this and see "Hello World" &$x(); function test() { print "Hello World"; } any and all help is appreciated. thanks a lot.