I'm currently experimenting with PPI and it can be used to visualize your program.

Using davido sample code I arranged:

use strict;
use warnings;

use PPI;
use PPI::Dumper;

# retrieve the example standalone script from DATA
my $doc;
while (<DATA>){ $doc .= $_}

my $pdom = PPI::Document->new( \$doc );

# uncomment to see the whole pdom
#PPI::Dumper->new($pdom)->print;

$pdom->find(

    sub{
        # skip white spaces, for example
        return if $_[1]->isa('PPI::Token::Whitespace');
        
        # just print top level elements
        if (
                # is a top level element
                $_[1]->parent == $pdom
        ){
            #                      PPI class       remove \n at the en
+d       starting line
            print "found TOPLEVEL ",ref $_[1]," ", $_[1]=~s/\n$//r ," 
+(line ",$_[1]->line_number,")\n";                            
        }
    }
);
__DATA__
#!/usr/bin/env perl

my $fb = fizzbuzz();
print "$_\n" for @$fb;

sub fizzbuzz {
    my ($n, $m) = (1, 100);
    my @out;
    for my $num ($n .. $m) {
        my $line = '';
        $line .= 'fizz' if $num % 3 == 0;
        $line .= 'buzz' if $num % 5 == 0;
        push @out, $line || $num;
    }
    return \@out;
}
[download]

and the output is:

found TOPLEVEL PPI::Token::Comment #!/usr/bin/env perl (line 1)
found TOPLEVEL PPI::Statement::Variable my $fb = fizzbuzz(); (line 3)
found TOPLEVEL PPI::Statement print "$_\n" for @$fb; (line 4)
found TOPLEVEL PPI::Statement::Sub sub fizzbuzz {
    my ($n, $m) = (1, 100);
    my @out;
    for my $num ($n .. $m) {
        my $line = '';
        $line .= 'fizz' if $num % 3 == 0;
        $line .= 'buzz' if $num % 5 == 0;
        push @out, $line || $num;
    }
    return \@out;
} (line 6)
[download]

L*