This appears to be something in between of JSON and Protocol buffers. I wonder under what conditions Ion makes more sense than either of the JSON/PBuff.
One significant advantage is you can opt-in to sharing schemas - without requiring all consumers to have your schema. Like a lot of Amazon's internal data formats, Ion designed to support backwards compatible schemas as well (that is, adding additional fields does not break existing consumers).
It has isomorphic text and binary representations as part of the standard making debugging or optimized transport a config option.
The type system is significantly richer than JSON and maps well to several languages (internally Amazon uses it with C, C++, Perl, Java, Ruby, etc.).
Yes, super useful. Depends on how your application needs to use S-expressions. You could define DSLs for a very expressive and complex rules-engine with S-Expressions forming your rules. Now you can write your rules as text, pass it around and build rule evaluators of those expressions all on top of Ion.
It has isomorphic text and binary representations as part of the standard making debugging or optimized transport a config option.
The type system is significantly richer than JSON and maps well to several languages (internally Amazon uses it with C, C++, Perl, Java, Ruby, etc.).
S-Expressions.