Re: [RT] Attribute Driven Templates (Was: [RT] do me a favor, don't call them taglibs)

[Leszek Gawron]

Daniel Fagerstrom wrote:
macro(<name>,<param-name>,...,<param-name>)
-------------------------------------------
example:
<table do="macro(mytable,list,td-class)">
  <tr do="forEach($list)">
    <td class="${$class}">${item}</td>
  </tr>
</table>
We also need an evalBody as in JXTG. And maybe we should have a 
possibilty to give a name space to the macro name.
We also need:
- some script compiler directives i.e. for cache control (as in JXTG)
- template inclusion so the templates may be defined in a separate file
Named macros rock! This way we can completely eliminate the need for 
this hack:
http://cocoon.apache.org/2.1/userdocs/flow/jxtemplate.html#eval

Imagine that user wants to render a fancy table providing only a header 
rendering macro and a row template:

<tr do="macro(tableHeader,context)">
  <th>Elem1</th>
  <th>Elem2</th>
</tr>
<tr do="macro(singleRow,context)">
  <td>{context.elem1}</td>
  <td>{context.elem2}</td>
</tr>
<table do="macro(mytable,list,headerMacro,rowMacro)">
  <!-- some fancy longish code here -->
  <tr>
    <th>No.</th>
    <th do="eval($headerMacro)"/>
  </tr>
  <tr do="forEach($list)">
    <td>${index}</td>
    <td do="eval($rowMacro,context=.)"/><!-- problem here -->
  </tr>
</table>
Lovely!
Still I see one problem: as every directive is bound to some tag one 
should be able to eval the macro and strip the root element. In my case 
the output would look like this:

<tr>
  <th>No.</th>
  <tr>
    <th>Elem1</th>
    <th>Elem2</th>
  </tr>
</tr>
This would fix it: <th do="eval($headerMacro,stripRoot=true)"/>
If we used tags we would be able to introduce <jx:template> as in jxtg 
that would not show up in the output. Here we have no such possibility.

Several directives
------------------
So, how do we handle multiple directives for one element? We could 
handle the TAL example above like:

<p 
do="let(x=/a/long/path/from/the/root;if(x);content(x/txt);attributes(class=x/class)"> 
IMO this one is not that clear as the same syntax using tags. This will 
be also a lot harder to implement as we will have to create much more 
sophisticated parser. With tags, the xml syntax does 95% of parsing 
itself with only a little amount of additional coding.

<jx:let name="x" value="/a/long/path/from/the/root">
  <jx:if test="x">
    <jx:content select="x/txt">
      <jx:attribute name="class" value="x/class">
        <p>Ex Text</p>
      </jx:attribute>
    </jx:content>
  </jx:if>
<jx:let>
What hits me is how the attribute based syntax can be compact comparing 
to this monster :)

Formating?
----------
IMO most of the basic formating can be done in a special conversion 
layer as we have discussed in the convertor thread.
I understand this is completely orthogonal functionality to the one you 
described.

I have not given any detailed thought to all of the constructions above, 
just wanted to concretize what attribute driven templating could look 
like in Cocoon.

WDYT?
I am only afraid how I will explain the directive ordering to my 
developers. Moreover: how many mistakes they will make, which IMO will 
be much harder to trace comparing to old verbose syntax.

--
Leszek Gawron                                      [EMAIL PROTECTED]
Project Manager                                    MobileBox sp. z o.o.
+48 (61) 855 06 67                              http://www.mobilebox.pl
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