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From Joshua Chamas <>
Subject Re: [Maybe OT] Modular design - calling pages like a subroutine with a twist.
Date Thu, 15 Nov 2001 19:57:51 GMT
Scott Chapman wrote:
> I'm very interested in making a modular site design but haven't
> found the tools yet to allow this with the twist I'm looking for.

I'll try to show how Apache::ASP could help here.  In Apache::ASP,
scripts can be executed as subroutines, even with return values,
and I think this goes to the heart of what you need here.

I would probably break abstract headers & footers out of 
each page, to be called automatically in global.asa.  This allows
all pages to not need to know about HTML headers & footers being sent:

# global.asa
sub Script_OnStart { $Response->Include(''); }
sub Script_OnEnd   { $Response->Include(''); }

> Say I have a page that encapsulates some functionality, such as
> sending a form then validating the contents that are returned. I'd
> call that PageB.
> PageB could be more than one page or a page calling itself, etc.

Right ... PageB is just form logic/rendering, headers & footers
are called automatically via events in global.asa.

> When PageA calls PageB, as soon as PageB finishes presenting
> the form it doesn't stop but drops out the bottom and returns
> immediately to PageA.  There are commands in some of the tools
> (Mason and soon Embperl - maybe others) to force it to stop there
> but this doesn't make for the modularity I have in mind.
<% my @rv = $Response->Include('PageB', @args); %>
<!-- Rest of PageA -->

$Response->Include() just calls another page as a perl subroutine
is called with @args passed in as @_ in the script, and @rv returned
if return(@rv) is used in the script too.

> PageB then gets submitted by the user and it either calls itself
> (using conditionals to then do the data validation) or another page.
> After things are validated Ok, I'd like to have it return right back to
> PageA, just where it left off using a "Return" statement. Thus,
> PageA could call a "PageB" and have it do all it's processing then
> return, just like calling a regular subroutine.

PageA can execute PageB, and PageB can execute PageA, but this
could cause a loop, so I am not sure what you really want here,
but hope the above showed how one might achieve this.

> 2) are there any tools (preferrably perl) out there that support this
> cleanly.  I've worked with Embperl and glanced through the docs of
> Mason, AxKit and TT and didn't see anything looking like this.

The $Response->Include() mechanism is very powerful, turning pages
into subroutines, and always returns to the original caller.  
To transfer control to another page without returning, 
use $Server->Transfer().  This differs from $Response->Redirect()
in that all the globals like $Session/$Application/$Request remain
the same.  If the ASP syntax is too ugly for you, you could turn 
this into an XMLSub used like:

  <page:include file="PageB" arg1="..." arg2="..." />

where you would define:

# global.asa or or any perl module that gets loaded
sub page::include {
  my($args) = @_;
  $Response->Include($args->{'file'}, $args);

-- Josh
Joshua Chamas                           Chamas Enterprises Inc.
NodeWorks Founder                       Huntington Beach, CA  USA                1-714-625-4051

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