That's not possible, as constants are declared at compile time, while functions are executed at runtime.

Ok, if that is the case, how does the global constant MAGIC_QUOTES get defined from the code in the description?

<?php
define( 'MAGIC_QUOTES', ( (bool)get_magic_quotes_gpc() ), true );
var_dump( MAGIC_QUOTES );
?>

prints bool(true)

We are running 3 functions there (according to the docs). One to get the value being applied, another to cast to int and finally one to "define" the constant.

Just for reference, I reread the docs for global constants set using define(). http://us2.php.net/manual/en/function.define.php states:

Defines a named constant at runtime. See the section on constants for more details.

define() is just a function. which declares constants.
I was talking about class constants et al.

I don't understand why I'm being shrugged off as impossible. I'm asking for functionality similar to global constants for class constants. If you can do it for global constants, it seems only plausible that class constants should be handled in a similar fashion.
I could find many more uses for the exact same functionality if necessary, within the same applicable class even.

I've thought on this a bit more. It seems that php currently has the idea of constants set-up a bit limited in sight. While PHP has "constants"implimented correctly in the class scope, it doesn't implement it in this way on the global scope. It is silly that functionality of such a feature should change in such a drastic manner.

If you are unwilling to change the functionality of class keyword const, then you need to implement a method as to set a variable read-only within a class. Which is just completely redundant in nature and contrary to the cause.

Perhaps you could rethink how you are implementing the const keyword and revamp it to assign a member as read-only. This might even help you with implementing the visibility scopes (public, private, protected) to a class constant. Because again, it is perfectly plausible to have a constant accessible only within the scope of a single class or child classes.

Again, class constants along with the classes and functions are declared in compile time, so they can have only constant value.
Common constants are declared in runtime using define() function, which is why it may take a result of an expression.
There is nothing to be done with that unless you're willing to rewrite all the engine from scratch.

I still don't know how a suggestion can be marked bogus ;)

There is no reason to close it as the request is perfectly acceptable as a suggestion or feature request. If you don't want to "re-write the engine" to maintain consistency, then perhaps someone else will one day :)

"Common constants are declared in runtime using define() function, which
is why it may take a result of an expression."

Why not expand define() to allow setting a class specific constant that can be called as $this->class_name->some_constant ? As it stands now I have to write excess functions that will return the values of specified class variables. Adding the ability to add constants within the spoce of a single class would remove that need :)

>I still don't know how a suggestion can be marked bogus

I can show you.

>There is no reason to close it as the request is perfectly
>acceptable as a suggestion or feature request. 

A feature request for renaming PHP to XXX is perfectly valid also, but there is no point to keep it open.