[Petal] Various things

[Jean-Michel Hiver]

Hi List,

Since it's almost a year since Petal has been written, I would like to
think with you in the future direction we want Petal to head towards.

* It doesn't do METAL macros.
* It has poor error reporting.
* It is not properly compliant with TALES...
  (but PETALES syntax is already too limited, and TALES is even more
  imited than that)
  
* the UGLY syntax is ugly, but sometimes necessary.
* caching involves writing temp files with can be a security problem.
* it can be sometimes cumbersome to write.


Let's take it point by point:


1/ It doesn't do METAL macros.

I must confess that I do not fully understand METAL macros. They seem to
be some kind of includes inside-out. Apparently the advantage is that it
is more WYSIWYG-compatible that an include statement.

Anybody has a full understanding of METAL? What steps would a METAL
implementation involve?


2/ It has poor error reporting.

Again this is a big problem. We want to support a variety of parsers
which process a file format which is not line-oriented, yet it would be
very nice to get more syntax checking and better error reporting.

Any idea on how to implement this?


3/ It is not properly compliant with TALES.

Maybe we need to make the expression parser more pluggable. What about
modifiers? Should they be inside / outside the expression parser? Should
we provide ways to redefine the Petal expression syntax?


4/ The ugly syntax is ugly

Don't know what to do about that :)


5/ Caching involves writing temp files with can be a security problem.

I know you can turn the cache off, but... Wouldn't it be better to
always do in-memory conversion and avoid potential security risks? Maybe
turn caching on only if the programmer provides a temp directory to
write to? How about we use a more formal cache module, such as
Cache::Cache?


6/ It can sometimes be cumbersome to write.

It would be nice to have more control in order to be able to extend the
TAL syntax. For example, someone on the ZPT list proposed a brilliant
idea, which was to have to extra TAL attributes:

<quote>
  Add two new TAL attributes, "repeat-define" and "repeat-condition".
  These have the same semantics as "define" and "condition", respectively,
  but when combined with a "repeat" attribute, they get executed once
  per loop iteration.  I would be able to rewrite the above example like
  this:

  <tr tal:repeat="item here/objectItems"
      tal:repeat-define="key python: item[0]; value python: item[1]"
      tal:repeat-condition="python: value.date < expiration">
    <td>...</td>
    <td>...</td>
  </tr>
</quote>


Also, I think it would be really nice to be able to define new
namespaces and operation associated with those namespaces. For example,
instead of typing:

  <a
    href="#"
    petal:content="self/description"
    petal:attributes="href     self/uri;
                      title    self/title;
                      dir      self/dir;
                      align    self/align;
                      lang     self/lang"
  >Hello</a>
  
It would be nice to be able to say:

  <a
    href="#"
    petal:content="self/description"
    attr:href="self/uri"
    attr:title="self/title"
    attr:dir="self/dir"
    attr:align="self/align"
    attr:lang="self/language"
  >Hello</a>

(There is still the problem of setting something like xml:lang since you
cannot write attr:xml:lang="self/language"...)


I must confess that as far as I'm concerned Petal is a finished product
in the sense that it provided our content management system MKDoc with a
robust templating system which was the original intention. It certainly
took some time...

As we intend to modularize and open-source other bits of our software I
might not have as much time for Petal as I had in the past because I'll
have to maintain other modules.

But it doesn't mean Petal is dead! I am commited to do bug fixes and
continue maintaining the patch / release process.

If you have any suggestions, please share. In particular any suggestion
regarding METAL support and improved error reporting, which I think are
two important features missing from Petal.

Cheers,
-- 
Building a better web - http://www.mkdoc.com/
---------------------------------------------
Jean-Michel Hiver
jhiver at mkdoc.com  - +44 (0)114 255 8097
Homepage: http://www.webmatrix.net/