Problems in passing a function to a subroutine

Hi,

I have a numerical integration subroutine quad and I want to use it to
perform an complex integral in my code. quad has an interface for a
function which depends only on x:

quad(func,a,b)
...
interface
  real function func(x)
  real :: x
  end func
end interface
...
end quad

However, the function to be integrated depends on many parameters, not
only on x. How can I pass it to quad? Is it better to modify the
interface in quad (and all the subroutines called by quad), or to
create a module containing func and all the modules needed by it? Have
you ever met a similar problem? Thanks

best regards

deltaquattro