How to call a mongodb function using monk/node.js?

Tyring to implement this:

http://ift.tt/XCnTjC

to provide sequence counters for a few things.

I've got the function stored in my db, but I can't call it without an error:

var model_id = db.eval('getNextSequence("model")');

Returns:

Object # has no method 'getNextSequence'

Is this because monk doesn't support the use of db functions via eval?