perl - package module alternative to template system - perl

Question

I building a web service, instead of using template system like toolkit I using package module like this:
Create pages urls, each page in independent module according to url previous create in the route,
pass as argument to every module a unique hash ref with variables for global title, footer, and all others data where is the same in each page (module).
main.pl
use strict;
use warnings;
use Handler;
my %mvs = (# my variables
username => $set{user},
titleglobal => '| web System ',
ip => $env->{REMOTE_ADDR}
.........
.........
);
for my $module_url (reverse #all_urls_names ) {
$router->add($module_url, sub {
$module_url->new(\%mvs);
})
}
In the module page, I have anothers modules who load header.pm, footer.pm but the body.pm is loaded directly in the current module page, in this case Handler.pm
Handler.pm
package Handler;
use strict;
use warnings;
use Layout::Head;
use Layout::Footer;
my $layout = sub {
my ($head, $body, $footer) = ( Head::new($mvs), thebody($mvs), Footer::new($mvs) );
return <<THE_HTML;
$head
$body
$footer
THE_HTML
};
return [ 200, [ "Content-Type" => "text/html" ], [ $layout->() ] ];
}
sub thebody{
.........
.........
}
I have done this approach having as reference the wordpress layout, all is working fine and good.
¿is this good way to building maintainable code ?
Note: I chose this way because I not want to install more modules.
(solves the given problem with the least amount of necessary code (less code to debug - obvious speedup)

Answer 1

You say that your constraint is not installing modules. But, what's the on-the-ground difference between installing prewritten modules and creating new ones?
Maybe you have issues with deployment. That's understandable. However, you can use things such as Carton to create applications. Set up everything on a system where you have the flexibility you need to deploy to a system where you don't.
With many CPAN modules you can take the libraries directly from the distribution and reuse them. If they don't use XS or need external libraries (say, like, openssl), they are able to run out of the box.
I don't particularly advise this, but it's doable. You get widely tested modules and the community support that comes with it. That's less code to debug because someone else already did the work! These things are complicated systems and you are going to have to do quite a bit of work to not only debug what you've done but discover everything else that you should have done and supported. Having reinvented a few things myself, I've learned my lesson.
Everyone eventually writes their own templating system (and everyone should as part of their life experience). That's fine. However, you should study what other systems do and how they do it so you don't repeat their mistakes. Some templating modules are small and simple and can be the basis for your explorations. Check out Text::Template for example: it's two module files and no dependencies. Going through this exercise shows you the hidden depths and complexities of what you are trying to do.
If you are making a web framework, have you looked at Mojolicious? It is a self-contained system that only requires core Perl modules (although you'll likely still need other things like a database connection and so on). It has a nice templating system. For something lighter weight (but how much lighter can you get), your approach looks like CGI::Prototype. Take a look at that.
Lastly, avoiding modules because you're anxious about installing anything might be something you just need to confront and get it over with. Almost any system is a bit scary at first and gets better after you get used it and learns how it works. You might not like CPAN (but what does "like" have to do with getting work done?), but perhaps you can get what you need from system packages already. In the end you want to get more work done. A little work at the front can save you a lot of work at the end.
We're here to help when you run into problems installing modules! :)

Answer 2

Is this good way to build maintainable code?
No.
At the heart of your system you have HTML (and, perhaps, CSS and Javascript) embedded in your Perl code. This might look like a good idea when it's just you maintaining the site, but when you get successful enough to need a separate front-end development team, you'll realise what a terrible idea it is.
Also, you are reinventing wheels. There are many great web frameworks and templating systems available on CPAN. Most of them have been used in production by lots of people over many years. They will have more features than your code and will be far better tested.
You say you're doing this because you don't want to install more modules. I urge you to reconsider this approach. Most modern Perl programming consists of plumbing together the right CPAN modules. You will be needlessly restricting the power of the language.