[Xy-pic] macros

[Alex]

Hi,

I would like to define macros to reduce the amount of clutter in xy 
environments.  For example, something like

\newcommand{\XyCover}[2]{
#1*{};#2*{}**{};
?<*[@_][o]=<0.0pc>{\bullet};
?>*[@_][o]=<0.8pc>{\bigcup} **[|(2)]\dir{-};
}

\[
\xy
\XyCover{(-10,0)}{(0,10)}
\XyCover{(0,10)}{(10,0)}
\XyCover{(10,0)}{(0,-10)}
\XyCover{(0,-10)}{(-10,0)}
\endxy
\]

Can I do this sort of thing?

Many thanks,
Alex.