I once made a rules engine for Magic the Gathering in python. As a design problem it is quite interesting since the key thing about MtG is that the pieces of th

I once made a rules engine for Magic the Gathering in python. As a design problem it is quite interesting since the key thing about MtG is that the pieces of the game can override the game rules. After reading about CLOS a few years later it seems I reinvented some of the main ideas (like cleanly re-entrant method combinators, cleanly overriding functionality of other objects in a way that can be reverted) using python's dynamiticity (especially descriptors which let you override what obj.[accesor] means).