JSON without the unnecessary quotes would probably work quite nicely.
A couple weeks ago I pulled my JSON stuff out of libgdx for standalone use:http://code.google.com/p/jsonbeans/
It is a tiny lib that round trips objects <-> JSON automatically. It can also parse into map/lists/strings/floats if you prefer. You can do "json.setOutputType(OutputType.minimal);" and get a JSON-like data format that only has quotes where needed. I hadn't thought about making some commas optional, I'll give that some thought. I haven't benchmarked it, but performance should be reasonable. Parsing is done in one pass using a Ragel
generated state machine, but I didn't bother to support streaming. Emitting is streamed. Some speed could be gained by using ReflectASM
for the reflection.