How to draw dash-dotted curves using MetaPost?

The definition of widthdots is

dashpattern(on 3 off 3)

while evenly is

dashpattern(off 2.5 on 0 off 2.5)

Thus something like

beginfig(32);
draw dashpattern(on 3 off 3 on 0 off 3) dashed evenly;
picture p;
p=currentpicture;
currentpicture:=nullpicture;
draw fullcircle scaled 1cm xscaled 3 dashed p;
endfig;
end.

taken from figure 32 in the Metapost manual will alternate dashes and dots.