Jesse, you want to use the is_callable($bob) . Callable is *only* available as a type hint.
http://www.php.net/manual/en/language.types.callable.php

[code]
function sparkles(Callable $func) {
$func();
return "fairy dust";
}

class Butterfly {
public function __invoke() {
echo "flutter";
}
}

$bob = new Butterfly();
echo sparkles($bob), "\n"; // flutterfairy dust

if( is_callable( $bob ) ) {
echo 'Can call $bob', "\n";
}
[/code]