As far as the name of the keyword: anyone who knows what "tail call" means will figure out "become" pretty quickly. If they don't get it from context clues, som

As far as the name of the keyword: anyone who knows what "tail call" means will figure out "become" pretty quickly. If they don't get it from context clues, someone will just have to tell them, "oh, it's a tail call", and the confusion will dissolve, because "become" is really not a bad word for what happens in a tail call. (This is obviously less important than the implementation issues kibwen handled.)