Tcl (Itcl) and default parameters/arguments

Hi. I'm working in Itcl, and I'm wondering if this is possible:

itcl::class x {
public variable y;

public method a { {p1 $y} } {
puts "Value is: $p1"
}
}

That is - can I use a VARIABLE as the default value? If so, what am I doing
wrong?

Right now, I get:
% source x.tcl
% x y
y
% y configure -y 3
% y a
Value is: $y
%

Obviously, I'd like to get:
% y a
Value is: 3

Any comments? I've searched the Itcl and Tcl docs + wiki, with no "this is
impossible" or "this can be done using method xyz".

I suspect it's NOT possible, but it would be REALLY nice if it were.

Mattias
.