use strict;
use warnings;

sub foo {
    my $bar if 0;
    $bar = @_ ? shift : 1;
    unless (*bar{CODE}) {
        my $bar_sub = sub {
            my $foo = shift;
            return $foo * (++$bar);
        };
        *bar = $bar_sub;
    }   
    my $result = bar($bar);
    $result;
}
warn "calling foo(1): 1 * 2 = " . foo(1) . "\n";
warn "calling foo():  1 * 2 = " . foo()  . "\n";
warn "calling foo():  1 * 2 = " . foo()  . "\n";
warn "calling bar(5): 3 * 5 = " . bar(5) . "\n";
warn "calling foo(3): 3 * 4 = " . foo(3) . "\n";
__END__
calling foo(1): 1 * 2 = 2
calling foo():  1 * 2 = 2
calling foo():  1 * 2 = 2
calling bar(5): 3 * 5 = 15
calling foo(3): 3 * 4 = 12