use warnings;
use strict;
{
	package Indent;
	sub new { my $c=shift; bless { i=>shift//"\t", c=>0 }, $c }
	use overload  '++' => sub { ++shift->{c} },
		'--' => sub { my $s=shift; $$s{c}=0 if --$$s{c}<0; $$s{c} },
		'""' => sub { my $s=shift; $$s{i} x $$s{c} },
		'='  => sub { my $s=shift; bless {%$s}, ref $s },
}

my $recurse; $recurse = sub {
	my ($lvl,$i) = @_ ? @_ : (0, Indent->new("foo"));
	print "<", $i++, "> Enter\n";
	$recurse->($lvl+1,$i) unless $lvl>=2;
	print "<", --$i, "> Leave\n";
};
$recurse->();

__END__

<> Enter
<foo> Enter
<foofoo> Enter
<foofoo> Leave
<foo> Leave
<> Leave