An example polygon using CIRCLE.

PERSPECTIVE
REPEAT 36 [
  POLYSTART
  CIRCLE 100
  POLYEND
  RIGHTROLL 10
]
POLYVIEW

An example polygon using ARC.

PERSPECTIVE
REPEAT 36 [
  POLYSTART
  ARC2 180 100
  RIGHT   90
  FORWARD 200
  RIGHT   90
  POLYEND
  RIGHTROLL 10
]
POLYVIEW