Re: [Webmacro-devel] Revised #macro stack overflow test code

[Brian G. <br...@qu...>]

> Take an RSS news feed for example, typically these can contain up to 15 
> news items. You may only want to display five of them. As the item nodes 
> are usually under a channel node, this would be rather awkward to implement 
> with a generic tree traversal directive.

This is a good example, since it would be a common usage of any DOM
traversal in WM and is pretty simple.

Option 1: preprocess with a servlet and extract what you want.  This
is a pretty decent option.  The servlet traverses the tree and puts an
array of RssFeedElement objects, with properties like Link,
Description, etc, in the context.  Then the template traverses it with
#foreach.  

This option only works when your document is simple, like an RSS feed,
which has a relatively flat structure.  

Option 2: Introduce a context tool that knows how to flatten trees into
linear streams of SAX-like events:
begin-x
  begin-y
    z
    z  
  end-y
end-x

Now, traverse it in WM with #foreach.  You have to maintain context by
yourself, though, and this sucks even worse in WM than it does in
ordinary languages.  

Option 3: Use XPath for selection.  Use an XPath select to whittle
down the subset of the document you want, and then apply the
techniques from Option 1 or 2.  This is nice because it eliminates
nearly all of the extraneous XML and gives you something suitable for
transforming into a linear array.
  
Option 4: Some sort of traversal directive, which is going to end up
looking a lot like XSL.  Combining it with XPath could be a win.

#domtree $dom {
  #node "content" $c {
    blah $c
  }
  #node "channel" $c { 
    blah blah $c
  }
}