linear encoder to control rotary indexer??

I would like to use a linear encoder to control a haas or similar
rotary indexer. The machine is going to cut a helical pattern. I just
want the indexer to rotate X ammount for every .0001 in linear travel
in both directions. The haas indexer controler has an rs-232 port
as does some of the encoders I have seen for sale. Is it possible to
control everything from a PC? I just need to have several programs
that change the ammount of rotation per inch of linear travel. As you
can guess I have no experience building something like this. Any
suggestions would be appreciated. Thanks Brad