[Zope] DTML Syntax contd. + rant

[Martijn Faassen]

Oliver Frommel wrote:
> 
> Hi,
> 
> so why do these two pieces of code produce different results? (I thought they
> should print the same, according to the with-tag howto)
> (the second one prints the title of folder A twice)
> 
> <dtml-with A>
>   <dtml-var title><br>
>   <dtml-var "B.title">
> </dtml-with>
> 
> <dtml-with A>
>  <dtml-var title><br>
>  <dtml-with B>
>   <dtml-var title>
>  </dtml-with>
> </dtml-with>

Hm, I actually don't know. Some parts of Zope semantics are too obscure
in my opinion.. Anyway, it seems to matter if B is a Folder or a DTML
Method/DTML Document. If it's a Folder, the second works as you'd
expect, and you do get the same result as in the first. If it's not a
folder, you get the acquired title from folder A instead (this explains
the printing of the same title twice).

What I don't understand is why this occurs; perhaps this is because the
with tag only works with ObjectManagers (folders) and not with other
objects? But this isn't documented anywhere.

The bizarre thing is that this hack does give the expected (by you and
me) result with DTML Documents:

<dtml-with A>
 <dtml-in "(B,)">
  <dtml-var title>
 </dtml-in>
</dtml-with>

What the 'in' tag does there is loop through a list containing just B.
Now it does display B's title.

What also gives the same result is this:

<dtml-with A>
  <dtml-with "_.getitem('B')">
    <dtml-var title>
  </dtml-with>
</dtml-with>

This may give us a clue on what's going on. The getitem() function looks
up a name in the namespace, but does not call it. If B is called, we get
the HTML result, which does not have any 'title' property. I think. You
can verify this by checking what happens if you do:

<dtml-with "'some test string'">

</dtml-with>

I don't think it does anything; it just passes silently. If B however is
looked up using getitem(), we *do* have a reference to the object, and
the with tag does work as expected. I think this explains it, though I
wonder why *folders* don't get 'called' and return strings.

Some input on this from people more knowledgable than I am would be
appreciated. It reflects badly on DTML that something so basic takes me
such a long time figuring it out. After all I've been using DTML for
almost a year now.. And I'm not stupid. :)

Philosophical end rant:

If I ever get the time I'd be tempted to work on a DTML 'cleanup'
project. DTML is currently *far* too much like Perl and not enough like
Python. *some* easy things are very easy, but as a consequence some
other easy things become far too hard, or at least look far too
complicated. You can spell the same thing in too many ways. The
community encourages and praises additions for convenience (like the
'default' option, or the new extended &entity; syntax) but as a result
DTML loses its conceptual integrity. It becomes too big and not easy to
understand.

I understand the argument that DTML shouldn't be used for complicated
purposes, and that you should use Python. This is fine and good, but in
practice people *do* use DTML for complicated purposes. ZClasses in fact
encourage this. 

DTML should be more like Python. Luckily the Zope framework does allow
new objects to be plugged in using something else than DTML, so not all
hope is lost. :)

Feedback on this rant would be appreciated.

First-thing-I'd-get-rid-of-is-the-'_'-ly yours,

Martijn