This module allows you to declare hierarchies of exception classes for
use in your code.  It also provides a simple exception class that it
uses as the default base class for all other exceptions.

You may choose to use another base class for your exceptions.
Regardless, the ability to declare all your exceptions at compile time
is a fairly useful trick and helps push people towards more structured
use of exceptions.

WWW: http://search.cpan.org/dist/Exception-Class/