rx finally gets (experimental) structured failures

Rx is my schema system for validating data in a highly extensible and portable way. It is in the same problem space as JSON Schema and Kwalify (both of which, I think, Rx exceeds), and close to RELAX NG. I wrote it last summer, and I’ve used it quite a bit since then, and I have not been unhappy with it… except for its error reporting.

As initially implemented, all it would tell me was “yeah, something wasn’t valid.” This was obviously a real pain, especially when validating complex structures or writing new, complex schemata.

Finally, as Rx and Email::MIME::Kit got intertwined and have started to sink deep down into the guts of Listbox, I knew I’d need to improve what Rx could tell me – or, more importantly, what it could tell the other folks who’d work on the project.

I’m still working on the implementation, but now, given this schema:

type: //seq
- //int
- //nil
- type: //rec
    foo: //int
    bar: //int
      type    : //arr
      contents: //int

…and this input…

- 1
- ~
- foo: 1
  bar: 2
  baz: [ 3, 4, 5, 6.2, 7 ]

…you can get this structured failure (read from bottom to top):

- type   : tag:codesimply.com,2008:rx/core/int
  error  : [ type ]
  message: found value is not an integer
- type: tag:codesimply.com,2008:rx/core/arr
  entry: 3
- type: tag:codesimply.com,2008:rx/core/rec
  entry: baz
- type: tag:codesimply.com,2008:rx/core/seq
  entry: 2
Written on April 16, 2009
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