Frequently Anticipated Questions

Only for JSON?

Rx isn't only for JSON. It's just that JSON is a very good least common denomenator for common datatypes, and using JSON for the reference tests makes it very easy to implement elsewhere -- there are JSON implementations nearly oheverywhere.

Rx is all about data structures, not the mechanism you used to transport them. It doesn't know about JSON, YAML, XML, or any other way to serialize or exchange data. There are a few unfortunate exceptions, though. For example, because Perl has no native boolean type, it relies on encountering the kind of object that a JSON deserializer would create. These exceptions are always about language constraints, and never about Rx itself.

In short, Rx validates data, not JSON strings.

Why not use ... ?

There are other systems for validating simple data structures, of course. Rx was only written after the other available systems proved inadequate.

XML-centric systems like XSD and RELAX NG had a few problems, but the biggest was that they were made for validating data as represented in XML, which tends to be different than (or a subset of) the data representations found in JSON, YAML, or just in program code. Even if this wasn't a problem, there just aren't enough simple implementations of these validators.

Kwalify was designed as a schema system for YAML, but its design has portability issues. For example, it allows regular expressions, the implementation of which differ between platforms. Its implementation of "mapping merging" requires references, which are not a feature of JSON, and no system for emulating them in JSON is given. This means that a Kwalify schema might not be representable in JSON, which is a shame, since JSON is far more widely-implemented than YAML. Its Ruby implementation includes its own YAML parser, which doesn't conform to current YAML specs. There are other problems, too.

JSON Schema is fairly similar in conception to Rx, but is more complex to implement and is less straightforward to safely extend with more types. It does offer some features that Rx does not, like subclassing and references.