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Re^3: Survey of Surveys on HTML Templating systems

by fergal (Chaplain)
on Feb 23, 2005 at 22:34 UTC ( #433883=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Survey of Surveys on HTML Templating systems
in thread Survey of Surveys on HTML Templating systems

I don't get it, from the example you gave, seamstress requires a whole load of extra Perl code as well as a HTML template.

As for a mini-language it's almost non-existent. Petal's loops are very simple

<table> <tr tal:repeat="thing user/things"> <td tal:content="thing/name">Widgets </td>: <td tal:content="thing/count">10</td> </tr> </table>
this will produce one row for every element of $h->{user}->{things}.

That's as complex as you can get with loops. You just supply an array and Petal loops over it. This forces you to prepare all your data in advance and then just pump it into the template (although you can call methods as well as doing hash lookups so it's possible to lazily produce the data only as it's needed).


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Re^4: Survey of Surveys on HTML Templating systems
by metaperl (Curate) on Feb 23, 2005 at 22:51 UTC
    I don't get it, from the example you gave, seamstress requires a whole load of extra Perl code as well as a HTML template.
    I would say that Seamstress requires a lot of Perl and nothing but id tags in the HTML (a standard thing) while in contrast Petal requires very little Perl but more programming in the XML/HTML. Looking at this another way, the learning curve for Seamstress is nothing but object-oriented Perl an object-oriented API for tree manipulation. The learning curve for Petal is Perl to the level of references and a mini-language for manipulating those references.

    Seamstress can unroll tables in two ways: using a row-oriented iterator method and it can also create tables using grid coordinates.

    here is a reference to my query about alternating table rows in Petal... it is different from how Seamstress does it.

    I have said time and again here that I do not like mini-languages. I spent enough time learning Perl and HTML so that I dont want to be concerned with hybrid technologies which are no more powerful but do require me to remember yet another set of rules and exceptions and limitations. To each his own, but keep me away from mini-languages personally.

      I think you're seriously overestimating the amount of programming involved in the templates in Petal. It's deliberately designed to stop you from doing anything more than substitutions, loops over an array and conditionals. It is not a turing complete language.

      As for the mini-language for manipulating references, the only rule for the language is / means go down another level so a/b/c is $h->{a}->{b}->{c}. It hardly deserves the name mini-language.

      Imagine a page with 20 variables. The templates look almost exactly the same for Petal and Seamstress but Seamstress also requires 40 almost identical lines of Perl to find the ids and replace them.

      This means that each ID tag has to appear twice, once in the template and once in your Perl, plenty of opportunity for typos. Lets say you decide that your template should display a field that was previously omitted. Now you have to change your template _and_ add 2 more lines of Perl to make sure it gets replaced.

      I don't like mini-languages either but I would quickly become bored writing a find line and a replace line for each datum. I'd probably decide on a convention for the id tags so that the the id taq can be interpreted as a path down into a hash of data. At which point I'd have basically invented the main part of TAL. Mini-languages are bad but I'll take a small, tight mini-language any day over lines and lines of cookie cutter coding.

        Imagine a page with 20 variables. The templates look almost exactly the same for Petal and Seamstress but Seamstress also requires 40 almost identical lines of Perl to find the ids and replace them.
        Actually, I believe your assessment is based on my slow, plodding examples which dont use the convenience methods in HTML::Element::Library. Please take a look at that library module, in particular the content_handler subroutine and then understand that the Seamstress code can be quite concise. In fact, even without looking at that, did you notice my second way of rewriting the example? I did not use the id tag from the HTML more than once in the Seamstree code. I repeat:
        # look ma, concise code! for my $content (qw(name last_login)) { $tree->look_down('tal:content' => $content) ->replace_content($hash->{user}{$content}); }
        This means that each ID tag has to appear twice, once in the template and once in your Perl, plenty of opportunity for typos.
        I have the same thing in both places: an id tag. Petal has a data structure in one place and a mini-language to drive access to the data structure in the other. Typos happen. Test suites catch them. Both frameworks have things to do in Perl and HTML.
        Lets say you decide that your template should display a field that was previously omitted. Now you have to change your template _and_ add 2 more lines of Perl to make sure it gets replaced.
        And with Petal, you have to go retrieve the field again and make sure that the access of the field syncs up with TAL specifier. We both have to do work and again you overstate the number of code lines due to lack of familarity with convenience libraries.

        And at some point, you are going to have to go into the HTML and do your mini-programming. I _never_ have to touch the HTML as long as the designer puts an id tag wherever dynamic functionality is needed.

        At which point I'd have basically invented the main part of TAL. Mini-languages are bad but I'll take a small, tight mini-language any day over lines and lines of cookie cutter coding.
        Perl is a powerful general purpose programming language offering numerous facilities for re-use: hashes, subs, modules, objects, normalized database access, etc. Writing cookie-cutter code in _any_ domain is un-necessary if you know Perl and have a background in software engineering. The codebase of Seamstress in the online website I just developed does not suffer from your proposed weakness.

        Further, when the unrolling tasks becomes more difficult, such as moving around div elements or adding 2 or 3 attributes to an element based on complex business logic, I expect the mini-language to peter out or resort to PERL tags while my end-to-end Perl approach will continue to support me even at such higher levels of dynamic HTML munging.

        At any rate, Petal and Seamstress and XML::LibXML all stress non-invasive HTML templating. And any of the 3 is hugely preferred over any other existing approaches for me.

        And don't forget: Seamstress is not alone! It has a counterpart in the Java world named XMLC. And I must thank Chris Winters, the person who initially pointed this framework out to me.

        Nice discussion. Thanks for your input!

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