Re: [Yaml-core] schemas and pull parsers

[Steve H. <sh...@zi...>]

Rolf wrote:
> Have you though about how operators can be expressed ? I'm thinking
> about OR, for example. Lets say we have a schema where some key can
> be either a scalar or a map, and if it is a map you want to specify its
> structure. And directives, such as 'if' ?
>

Well, I thought a little bit about the OR scenario.  Basically I would use a
sequence to provide a list of alternative types.

name: Name
type:
 - type: map
      items:
        - name: firstname
          type: scalar
        - name: lastname
          type: scalar
    - type: scalar

Pretty ugly, huh?  This would validate either of these documents:

Name: Rolf Veen
---
Name:
  firstname: clark
  lastname: evans


> A different thing is that if we finally have an event tree representing
> the schema, then we can build a validating parser even with the push
> parser, at least in Java. Code could be something like:
>
> YamlSchema schema = new YamlSchema("schema.yml");
>
> try {
>      Object graph = Yaml.load("aFile.yml", schema);
> }
> catch ( SyntaxException e) { ... }
> catch ( SchemaException e) { ... }
>
> The exceptions abort the parsing process.
>

Sure, that makes sense to me.  As new events get pushed, you adjust where you
are in the schema to do the validation.

With the pull way, it's the opposite--you basically walk the schema, deciding
what kind of data you expect, and then you pull a bit of data from the YAML
document and verify that it really conforms.

When you start supporting multiple types, as in my example above, things will
get a little tricky under either architecture.

Cheers,

Steve