"Archimedes' screw"

Archimedes screw 


to main ; Screw by Yehuda Katz
cs ht
setpensize[3 3] draw 0
setpc 0 setpensize[1 1]
end

to draw :x
if :x>91[stop]
setpc(se 2.8*:x abs 2.8*ycor 0)
sp :x-36 :x-46
lt 2 fd 60
draw :x+.2
end

to procs
ed[main draw procs]
end