Re: XML Syntax with Freemarker?

Saturday, July 31, 2010, 5:17:05 AM, Michael Cervenak Ahern wrote:

> Ok,
>
> So this is a question / comment for the floor.  A problem that has
> been bothering me with Freemarker and that is that you can't quite
> create an Freemarker template that is also a valid XML document.  If
> you are using it as a general text templating solution it is not a
> problem - so far in our project we are using it for email templates.
>
> The problem area that had caused me to initially investigate the
> project though is in the generation for providing plug points for
> customer content customization of HTML markup.  In this role, I have
> been looking at ways to reduce / catch developer and customer
> errors.  One easy way to do this is if it supported an XML markup
> notation.  One can almost do this with the square bracket notation
> if you set square brackets as the default... however, I have noticed
> that there are a couple of times where you still need to put
> directives at the top of the template which break the XML ness.
>
> So to prove my point on catching errors; just take a look at the alternative syntax page itself:
> http://freemarker.sourceforge.net/docs/dgui_misc_alternativesyntax.html
> In this example it is missing (and I belatedly starting take notes so I apologize for any omission):
> - 1 x </th>
> - 2 x </td>
> - 2 x </tr>
> - 1 x </p>
> - 2 x '/' in close element tag
> I know this was a hastily written example - and I'd spot the error
> (I hope) at runtime in the browser;

These are not errors, as the template uses HTML, not XHTML. End-tag is
optional for these elements in HTML.

> but all of those errors would have been flagged by my syntax checker
> while editing. Getting rid of the directives at the top and plopping
> this in an XML editor still leaves one syntax error with the
> placement of a [/#if].

The #if is also used properly in the example; as they are not XML
tags, but FTL tags, they don't need to nest properly with HTML tags.
(Anyway I also don't like this kind of solution, because you repeat
the condition expression, but that's another topic...)

> As such a full blown XML markup does feel in order.
>
> Anyhow this is a super long winded question, but is there any
> thoughts / plans around this?

As of plans, there is practically no chance FreeMarker will ever be
XML/HTML aware, or support an XML syntax. Like, first we had to push
out 3.0, which is much less radical and much closed to completion, and
still...

As of thoughts (if you are still interested after the "plans"
sections), I believe that a template language on the field where
FreeMarker plays, should be (X)HTML-aware, and so even spot typos in
HTML element names and like. Also it would need special flow-control
instructions for making elements conditional with keeping their
children, also there should be built-in ways to add/remove HTML
attributes, etc. But as of using XML-syntax for the templating tags,
it's IMO a PITA (and not doing that is one of the important selling
points of FreeMarker over JSP), given the ridiculously verbose syntax
of XML when used for a programming languages:

  <t:if test="${exp}">

VS

  [#if exp]

Surely using XML syntax editors could spot *some* of the typos in the
template tags too, but I'm not sure that worths all the extra typing
and the resulting visual bloat. If you only want to spot the errors in
the static parts with an XML-editor, the best thing you can do is keep
the templating constructs look like XML character-data, and that you
can almost achieve with [#...]. Just almost, because you are in
trouble if you want to make a HTML attribute conditional, or an
element name to be a variable, etc. But there are work-arounds for
those too... yeah, they are kind of awkward, but still.

> I know Freemarker will never be GXP - however GXP appears dead...
> long live Freemarker

(Frankly, I'm puzzled how still no Java template engine of this kind
appeared in so many years that mops the floor with FreeMarker. I mean,
would any of us long-time "FM admins" here design an engine now, it's
virtually impossible to do something that's not better than FM. I
really just came here (like 10 years ago?) to help writing docs and
suggest a few features that I needed (as I don't have time to write my
own engine), and look where it went... And now I will be the one who
has to have the bad conscience! :) That's why I always have this
burning desire to "beat" FM myself, but not the time/energy it
seems...)

> One thought around prototyping this once things quite down is to use
> an XSL template and a custom template cache to look for '.xftl'
> files that are transformed into standard .ftl files to rather than
> cracking open the template parser code.

That's actually the question of writing a TemplateLoader
implementation (and the XSLT, of course). Only problem with it is that
the error messages will be hard to understand, since those will refer
to the already transformed templates.

> While I'm still a ways from finding the time to do this - have there
> been any thoughts in the past/present around what such a syntax
> would look like?

Yes, I think you will find some discussion in the archives.

> Thanks in advance,
> -Mike

-- 
Best regards,
 Daniel Dekany


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