[TimTheTinker]

I'm not talking about something arbitrarily extensible or compound values like vectors or lat/lon. Just a few more common data types -- primitive-like values that frequently need to be passed around.

This would probably best exist as a well-known wrapper around JSON itself.

[jitl]

there are a zillion of these "json pro" kind of things: superjson, devalue, capnweb, all with slightly different ideas about how to lower high-level semantics to json's available types. it's so easy to do this kind of thing, its a real https://xkcd.com/927/ situation.

CBOR (Concise Binary Object Representation) has JSON-like semantics with type extension support; with built in type extensions its much easier to get some agreement about registering certain magic type IDs to mean certain things. for example from a random google search for "cbor datetime" https://j-richter.github.io/CBOR/date.html; there's an IANA registry of type IDs: https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml

however, it is binary.

[akdev1l]

Amazon ION is kind of this?

Few people seem to use it outside of Amazon tho