spek@scelia ~/scratch $ perl des.pl
display
------
sub display {
    my $num = shift;
    print "$num\n";
}


two
------
sub two {
    return one(_helper(shift));
}


three
------
sub three {
    return two(shift);
}


one
------
sub one {
    my $num = calc(shift);
    display($num);
}


calc
------
sub calc {
    my $num = shift;
    return $num ** 3;
}


_helper
------
sub _helper {
    my $num = shift;
    return ++$num;
}