While the documentation suggests that the use of a constant is similar to the use of a variable, there is an exception regarding variable functions. You cannot use a constant as the function name to call a variable function.
const DEBUGME ='func';
function func($s) { echo $s. "\n"; }
DEBUGME('abc'); // results in a syntax error
$call = DEBUGME;
$call('abc'); // does the job
But you can use a constant as an argument to a function. Here's a simple workaround when you need to call a variable constant function:
function dynamic($what, $with)
{
$what($with);
}
dynamic(DEBUGME, 'abc');
This makes sense to me to hide API's and/or long (complicated) static calls.
Enjoy!