Differentiating a vector



Hello,

I'm still quite new to Maxima, and I would like to differentiate a 
vector e.g. [x,y,x^2*y^2] wrt x or y. How would I go about doing this? 
I've tried:

Vec = [x,y, x^2*y^2];
diff(Vec,x); --> Result: 0?

Vec(x,y) = [x,y, x^2*y^2];
diff(Vec(x,y),x); --> Result: (again) 0 ???

Thanks,

- Olumide