I used a global to control json-serialize's interpretation of lists, but
it could be an argument as well.
Please don't add global state to json.c. It's a low-level library that shouldn't rely on global state (and global state should generally be avoided in libraries). Not having global state was one of my explicit design goals for json.c
Well, it's not really "global state" in the sense I believe you're talking about, because no part of the library is maintaining any state in global variables -- it's read-only from json.c.
That said, if that's your only objection, consider that duck removed :)
João