my $tree = Branch->new(3)->add_child(
     Branch->new(1.1)->add_child(
          Leaf->new(1),
          Leaf->new(1.2)
	),
     Branch->new(2.0)->add_child(
          Leaf->new(2.1),
#         Leaf->new(2.15),
          Leaf->new(2.2),
	)
    );

my $result = $grammar->apply($tree, 'len');
print "$result\n";