I doubt it's any more complicated to add S-Expressions than to change list parsing to take either [] or () and set a type flag based on which one it finds. Sema

I doubt it's any more complicated to add S-Expressions than to change list parsing to take either [] or () and set a type flag based on which one it finds. Semantically, it's not more complex either, just giving one extra piece of user-defined metadata to the actual data that's still basically a list.