[Petal] TPJ article 0.1

[Jean-Michel Hiver]

Hi,

> Yes, I have read it. I think your examples are good and like that you
> give a behind-the-scenes look at how Petal operates (in fact, I'd rename
> Advanced Petal to something like Inside Petal or The Code Behind Petal;
> I think of advanced petal as more ways to use it, not how it works; the
> modifiers section would be appropriate as an Advanced Petal topic).

Ok, renamed it to "Inside Petal"


> I tried to put myself into the frame of mind of someone just coming
> across the article. As such, I think you save some of the most
> interesting info for the last (such as caching, modular architecture,
> and the other bells and whistles mentioned in the conclusion) and don't
> harp on the benefits of the TAL specs enough (you say it's a good idea
> but don't really sell the reader on why a Perl programmer should be
> implementing a spec from a Python project).

OK. I have rephrased the introduction to emphasize on the benefits of
TAL. However I am not doing a full "sales job" on the benefits of TAL as
you mentioned. Probably because:

a/ It would destroy the structure of the article.

b/ It is an article about Petal, not TAL, although they are naturally
very similar.

c/ I'll reference "At the Forge" article so that people can read about
those benefits.

> I'm a bit confused about the canonicalizer section. I get the input
> parser stuff but you say that there are two output canonicalizers. Your
> example shows what a canonicalizer does with the input. However, the
> output you show does not look like XHTML. If I understand correctly, the
> canonicalizer builds the Perl sub that eventually generates the
> page. Depending on the output canonicalizer chosen, the code gets built
> and the data gets handled a bit differently. Is that accurate? Or does
> the canonicalizer sit before the CodeGenerator?

Yes, the canonicalizer sits before the code generator.


> write Petal syntax but never really explain why. In fact, I've never
> really understood this.  Perhaps you can clarify your reasoning in the
> article?


I have reworded this section as follows:

-------------------------------- %< --------------------------------

At this point I have to confess: Petal started as just a big hack. It is
builton top of a previous twist in which I used a syntax made of XML
processing instructions as follows:
                                                                                                                                  
    <?if name="something"?>
       ... do something <?var name="foo"?> etc...
    <?end?>
                                                                                                                                  
Looks familiar huh?
                                                                                                                                  
Instead of building a module which directly converts XML events intoPerl
code, I've built a module which converts XML events into the syntax
above since the system above was already working (!).
                                                                                                                                  
I've also made this module turn an $inline_variable into an
<?var name="inline_variable"?>.
                                                                                                                                                                                                                     The Petal canonicalizer was born. It turns alternate syntaxes (TAL, inline) into the original canonical syntax, which unfortunately happens to look very ugly.
                                                                                                                                 
A neat effect is that you can use all three syntaxes at the same time,
so this is legal:
                                                                                                                                  
    <?if name="true:something"?>
      <p tal:repeat="item something">$item</p>
    <?end?>
                                                                                                                                  
However you should really stick with the standard TAL syntax as much as
possible:
                                                                                                                                  
    <p tal:condition="true:something"
       tal:repeat="item something"
       tal:content="item">Exempli Gratia</p>
                                                                                                                                  
If you want more information on the canonical syntax, see perldoc Petal

-------------------------------- %< --------------------------------


> A question about modifiers. Would it be possible to create a modifier
> library instead of a bunch of independent modules? According to the
> article, the existing syntax names the modifier based on the filename.
> What would need to change to allow Petal to install multiple modifiers
> from a single module?

It is possible indeed. You could have:

Petal::Hash::MultipleStuff::One
Petal::Hash::MultipleStuff::Two

And then have:

package Petal::Hash::MultipleStuff
use Petal::Hash;
use strict;

$Petal::Hash::MODIFIERS->{'one:'} = 'Petal::Hash::MultipleStuff::One';
$Petal::Hash::MODIFIERS->{'two:'} = 'Petal::Hash::MultipleStuff::Two';

1;

__END__

Then Petal would install multiplestuff:, which in turn would install
one: and two:.


> Other minor issues:
>  - Digital Creations is now (according to Reuven's article) the Zope
>    Corporation

Fixed.

>  - client should be plural in 1st sentence of Hello World example

Fixed.

>  - It should be I in last sentence of 1st para. of same ex?

Fixed.

>  - I've noticed in the Petal docs that you are starting to use the tal
>    namespace. Why do you revert to the petal namespace in the article?
>    That may be confusing to users who want to install and use Petal.

Fixed.

>  - In Adv Petal section, you refer to Fergal's Daly; although I suppose
>    that Fergal possesses his last name, I'm guessing you meant to put
>    that possessive after Daly.

Fixed.


> My $0.02,

They were worth more than that :)
Cheers,