Call from a code reference in Template Toolkit - perl

Question

I have a simple higher-order function that builds a message formatter.
use strict;
use warnings;
sub make_formatter {
my $level = shift;
return sub {
my $message = shift;
return "[$level] $message";
}
}
I use it from Perl like that:
my $component_formatter = make_formatter('ComponentError');
print $component_formatter->('Hello') . "\n";
I want to use make_formatter from a Template Toolkit template. I have tried to do the following:
use Template;
use Template::Constants;
my $template = Template->new({
# DEBUG => Template::Constants::DEBUG_ALL,
VARIABLES => {
make_formatter => make_formatter,
}
});
my $template_str = "
[% my_formatter = make_formatter('MyFormatter') %]
<h1>[% my_formatter('Sample message') %]</h1>
";
$template->process(\$template_str);
The output of this script is:
$ perl test.pl
Use of uninitialized value $level in concatenation (.) or string at test.pl line 10.
<h1>[] MyFormatter</h1>
Is it possible to call my_formatter using only Template Toolkit syntax ? Calling external Perl code that is not callable by default from Template Toolkit is not an option.

Answer 1

First let me please point out that putting use strict; use warnings; at the beginning of your script is strongly advised.
If you do that for your snippet generating the $template,
you will get a Bareword "make_formatter" not allowed while "strict subs" in use error, which should help you determine this is not a useful notation.
Now if you call make_formatter() instead, this will output <h1>[] MyFormatter</h1>. This makes sense: your function returned the sub, which is called with 'MyFormatter' in your template ( and $level is undef, as you called make_formatter with no input ).
As Mr. Haegland pointed out,
my $template = Template->new({
VARIABLES => {
make_formatter => \&make_formatter,
}
});
leads to the output I understand you want:
<h1>[MyFormatter] Sample message</h1>
\&make_formatter gives you a subroutine reference,
which in perl normally you could call using:
my $ref = \&make_formatter; $ref->( 'Input' );
This can then be called in the first line of your template,
returning another code ref, which is then called in your second line.
Hope this helps!