How can I solve this logic?

[eluser]theshiftexchange[/eluser]
[quote author="bargainph" date="1242992829"]I did this for a course manager app. In it we stored datetime ranges which is very similar.

You just need to have a callback that queries the db(assuming you have a db) if there's an event on the particular date and whether it has the same ID as the event your editing.
[/quote]

How do I give the callback the ID but?

I'm trying to keep all my $config form_valadation in a seperate file; so I'm not sure how I can reference a variable in the $config file to use in the function?