Turtles Circling

to setup
  setup-circle radius number
  setup-plots
end 

to setup-circle [r n]
  clear-all
  set-default-shape turtles "circle"
  ;; turtles should be evenly spaced around the circle
  create-ordered-turtles n [
    set size 2  ;; easier to see
    fd r
    rt 90
  ]
end 

to all-circle
  circle radius
  display
end 

to circle [r]
  ask turtles [ move-along-circle r ]
  if plot? [ update-plots ]
end 

to move-along-circle [r]
  fd (pi * r / 180) * (speed / 50)
  rt speed / 50
end 

to zero-circle
  ask turtle 0
    [ pen-down
      move-along-circle radius ]
  display
end 

to draw-circle
  clear-drawing
  create-turtles 1
    [ set color gray - 3
      set size 2 * draw-radius
      set shape "circle"
      stamp
      die ]
end 


; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.