It would make more sense to just have newSWFMorph( shape1, shape2);, but as things are now, shape2 needs to know that it's the second part of a morph. (This, because it starts writing its output as soon as it gets drawing commands - if it kept its own description of its shapes and wrote on completion this and some other things would be much easier.)
S'il conservait les descriptions de ses propres formes, et attendait leur totalité avant d'écrire, ceci et bien d'autres choses serait tellement plus simple).