>function store (x:number, v:vector, n:index) ...
$if cols(v)<n then return v|x;
$else
$  v=rotleft(v); v[-1]=x;
$  return v;
$endif;
$endfunction
>v=zeros(1,0); for k=1:20; v=store(k,v,10); mean(v), end;
 1
 1.5
 2
 2.5
 3
 3.5
 4
 4.5
 5
 5.5
 6.5
 7.5
 8.5
 9.5
 10.5
 11.5
 12.5
 13.5
 14.5
 15.5
>v
 [ 11  12  13  14  15  16  17  18  19  20 ]