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Re: XPattern Specification

Alan Gutierrez wrote:
> * Karl Waclawek <karl@w...> [2005-01-17 09:16]:
>> > 4. Position counters (to enable position predicates and
>> > position()
>>Especially for a streaming processor, should the goal of a pattern
>>matching language not be, to allow for flexible cooperation
>>between what the language does and what the handlers do?
>     Brings me back to my suggestion for a generic XPath binding API.
>     public interface Function {
>         public Node invoke(NodeList arguments);
>     }
>     Works for Java.
>     What works across all languages?

If one "language" needs to interact with multiple other
languages, then what we are talking about is multiple
"lanuage bindings".

>>Predicate evaluation could also be performed in the handler
>>call-backs.  So, maybe the XPattern language could provide for
>>simple attribute value matching, but leave more difficult tasks to
>>the call-back handlers, which can take advantage of a Turing
>>complete language, and which can also easliy interact with
>>application context (e.g  if our database has a record for this
>>id, return true, otherwise return false).  And there should be a
>>specified way for how the handlers return results for predicate
>     I'm of that mind set. I like this proposal.
>     I'd like to match information, then respond with Java. My
>     example, simplified.
>     <document>
>         <reverse>Alan</reverse>
>     </dcoument>
>     Transformed to:
>     <document>
>         <reverse>Alan</reverse>
>         <reversed>nalA</reversed>
>     </document>

I am using an API I have developed mostly for myself
(although open sourced). Whenever I match an element,
call-backs are made on one of these interfaces (C# with generics):

   public interface IXmlHandler<S> where S: EventStatus
     void Reset();
     void ProcessingInstruction(string target, string data, S status);
     void SkippedEntity(string name, S status);

   public interface IDocHandler<S>: IXmlHandler<S> where S: EventStatus
     void StartDocument(object context, S status);
     void EndDocument(S status);
     void StartRoot(QName name, IAttributes attributes, S status);
     void EndRoot(S status);

   public interface IElementHandler<C, N, S>: IXmlHandler<S>
       where C: XmlPathContext<C, N, S>
       where N: XmlPathNode<N, C, S>
       where S: EventStatus
     // context is valid until Deactivate is called, but attributes is only
     // valid during the call to Activate
     void Activate(C context, QName name, IAttributes attributes, S status);
     void Characters(char[] chars, int start, int length, S status);
     void IgnorableWhitespace(char[] ws, int start, int length, S status);
     // called before child is activated
     void StartChild(QName name, IAttributes attributes, S status);
     // called after child is deactivated
     void EndChild(S status);
     void Deactivate(S status);

>     I'm looking to notified of a reverse element, and to be notified
>     of the end of the reverse element, so I can insert the reversed
>     element. This isn't really node matching, but event matching.
>     + = open, - = close, () = capture, [] = emit
>     +document
>         +reverse (foo) -reverse
>        [+reversed &util::reverse($foo) -reversed]

Some events for the API above would be (matching on /document/reverse):

- Activate(..., "reverse",...)
- one or more Characters() calls
- Deactivate(...)

In the Deactivate event the handler would emit:

The handler wouldbe derived from an existing helper class, which
performs character buffering.

For that task that would be all the pattern matching language and
API support I would need. Maybe there is a danger of overengineering
in this discussion?



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