use CGI::Carp qw(fatalsToBrowser set_message);
BEGIN {
    sub handle_errors {
        my $msg = shift;
        print "<h2>Error trapped by CGI::Carp</h2>\n";
        $msg = s/\n/<br />/g;
        print "<p>Message: $msg</p>\n<pre>\n";
        foreach my $key ( keys %ENV ) {
            print " $key\t $ENV{$key}\n";
        }
        print "</pre>\n";
    }
    set_message(\&handle_errors);
}

use Modern::Perl;
use CGI::Simple;
use CGI::Session;

# and so on...