How modify a sql-function without breaking views ?

Hi,

I'm wondering how I might modify a sql-function without breaking views
that use it.
Basically the function gets called with a parameter and fetches a SETOF
type_X where type_X is a columnlist for the function's result.
The function joins a couple of tables to make some code-columns nicely
readable and selects some columns.

Later there are a growing number of views that need all those columns
from the function and join some other tables agains it.
Nothing impressive, yet.

But what can I do if I figure I'd like to have another column in this
function result?
To add it, I had to drop the type and recreate it.
This drops the function and with it go all subsequent views down the
drain. :(