glue

scf(1);
plot2d(0,0,-1,"010"," ",[-2,-2,2,2]);
xrect(-1,1,2,2);
xarc(-0.5,0.5,2,2,0,360*64);
a=gca();
r=a.children(1);
c=a.children(2);
nc=glue([r,c]);
// a.children(1) and nc now both correspond to the
// newly created compound object,
a.children(1)
// which is then translated.
move(nc,[-1,-0.5]);