[Zopexmlmethods-devel] =?iso-8859-1?Q?Interface_for_XPathMethod=3F?=

[Craeg S. <cs...@ar...>]

It seems that most processors have encapsulated
XPath expressions in a type, and have a notion of 
pre-compiling them, all except for Sablotron.

Of course, each processor has its own special type,
and we don't want to expose that to XPathMethod.

What about this for an interface:

IXPathProcessor

  def compile(expression):
     "return handle to compiled expression or expr itself"

  def evaluate(xmlString, xmlURL, xpath):
     "return pretty printed result of xpath evaluation"

Eventually, all of the processors can implement
both IXSLTProcessor and IXPathProcessor.

As a matter of fact, how about I start out implementing
only FourSuite, and simply leave the other processors
_not_ implementing IXPathProcessor for now.

Then we have to extend ProcessorChooser to understand
interfaces-- you ask "tell me the list of processors
available for XXX" where XXX is xpath, xslt, dtd, etc.

That's interesting, because now we need to know both

a) a compiletime notion of whether a particular
processor supports feature X (either yes, no, or
yes but we haven't implemented it yet)

b) a runtime notion of whether a particular processor
is currently installed

For (a) I guess we just say 
  if IXPathProcessor.isImplementedBy(processor):
     # try it...

Thoughts?

--Craeg