why bother?

Just use The God's Hammer Dispatch (AKA Non-intuitive way of programming
for those who don't think in objects ;) :

fillRectangle: aRectangle basicFillStyle: aFillStyle
������ "Fill the given rectangle with the given, non-composite, fill style."
������
������ | pattern |

������ (aFillStyle isKindOf: InfiniteForm) ifTrue: [
������ ������ ^self infiniteFillRectangle: aRectangle fillStyle: aFillStyle
������ ].


=>

fillRectangle: aRectangle basicFillStyle: aFillStyle
������ "Fill the given rectangle with the given, non-composite, fill style."

������ ^ aFillStyle fillRectangle: aRectangle onCanvas: self

��

..and then after refactoring it will look exactly how Athens doing it,
because if you rename fill style with "paint" and rectangle with "shape" you will see it :)