Isn't your rebuttal obliquely preempted by "Trying to satisfy the typecase without using an else clause would then point up the need to handle all the other pos

Isn't your rebuttal obliquely preempted by "Trying to satisfy the typecase without using an else clause would then point up the need to handle all the other possible implementations of IntSet"? More explicitly, I'm thinking that the commenter explains the advantage of TCO over your solution: "And trampoline provide you full PTC at the cost of a (local) encoding that must be followed by every single bit of software that you want to use PTC with. [...] Now why should the user have to be doing manually what the computer could automatically do a better job at? " [http://projectfortress.sun.com/Projects/Community/blog/ObjectOrientedTailRecursion#comment-5 http://projectfortress.sun.com/Projects/Community/blog/Objec...]. Your use of dynamic dispatch is better for extensibility than suggested typecase, but you're still mucking about with a trampoline that a compiler could write for you.