Description:
------------
Attempting to use a function to generate the value for assignment to a class constant causes a parse error.


Reproduce code:
---------------
<?php
class MyClass {
  const good = "Blah";  // will work
  const bad = substr(0, 3, "Blah");  // results in parse error
}
?>

Actual result:
--------------
Parse error: parse error, unexpected '(', expecting ',' or ';'