Arcueid used to do it that way, by parsing and expanding ssyntax at read time, rather than at compile time the way reference Arc does. It turns out that the reason why ssyntax expansion is thus deferred has to do with the way the ssyntax compose (:) and complement (~) operators work. They cannot be expanded properly by simple lexical substitution the way all other ssyntax operators can be, as they alter the structure of a sexpr that uses them, so it is impossible for the reader to do it. It has to be done once we already have the full sexprs, and that means that it becomes a step at compile time.
