I was correct before, except I conflated the word "extended" with "eliminated" in my mind: http://lambda-the-ultimate.org/node/1277#comment-51723 The most robust solution to Tim Sweeney's problem is to rethink what a "class" should be: http://www.haskell.org/haskellwiki/?title=Why_Haskell_matters&oldid=24286#Haskell_vs_OOP In Haskel, subtyping is done with Module. A "type class" is a polymorphic (relative to data type) interface, and the polymorphism is strictly parameterized for the client/consumer of the interface, i.e. the data type is known to the function that inputs the interface AT COMPILE TIME: http://www.haskell.org/~pairwise/intro/section2.html#part3 If all the functions/methods of package Engine input exclusively interfaces (i.e. Engine.IActor), then client package GearsOfWar can create a new subtype GearsOfWar.Actor which also implements the interface Engine.IActor (and perhaps even more interfaces). A problem with virtual (runtime pointer) inheritance is that it hides the subclass from the compiler. Polymorphic interfaces are missing from C++ and one can sort of hack an emulation with abstract classes, private delegates, and templates: http://lambda-the-ultimate.org/node/1277#comment-51806 In Haskell, parameterized polymorphic interfaces can be inherited, and this is knowable to the client function at compile time. Fundamental theorems tell us that any membership rule for a set can not be an absolute point, thus we should strive for typing and classing architecture which is the most granular (these are my summaries): * Russell's Paradox: there is no rule for a set that does not cause it to contain itself, thus all sets are infinitely recursive. * Liskov Substition Principle: it is an undecidable problem that subsets inherit. * Linsky Referencing: it is undecidable what something is when it is described or perceived. * Coase Theorem: there is no external reference point, any such barrier will fail. * Godel's Theorem: any formal theory, in which all arithmetic truths can be proved, is inconsistent. * 1856 Thermo Law: entire universe (a closed system, i.e. everything) trends to maximum disorder.