Description: With the loop_context_vars switch in HTML::Template you can make some useful macros. I found myself needing things like this all too often:
$tmpl->param( foos => \@foo, num_foos => scalar @foo, bars => \@bar, num_bars => scalar @bar, ... );
So I made a macro that handles this inside the template by adding a <TMPL_NUM foo> directive. Does anyone else have useful HTML::Template tricks up their sleeves?

By the way, I'm well aware that this is a great example of the serious limits of templating using HTML::Template's philosophy. This is some ugly template-ese under the hood. This is why I will probably switch over to Template::Toolkit in the not-so-distant future (at least for projects where I'm the one writing the template).

use HTML::Template;

sub tmpl_num_filter {
    s[<TMPL_NUM (\w+)>]
        for ${+shift};

my $tmpl = HTML::Template->new(
               scalarref         => \do { local $/; <DATA> },
               filter            => \&tmpl_num_filter,
               die_on_bad_params => 0,
               loop_context_vars => 1

$tmpl->param(hobbits => [
    { name => "Frodo" },
    { name => "Samwise" },
    { name => "Meriadoc" }
print $tmpl->output;

These are my <TMPL_NUM hobbits> favorite hobbits:
<ul><TMPL_LOOP hobbits>
  <li><TMPL_VAR name>