gistfile1.txt

role BinaryTree[::T] {
    has T $!value;
    has BinaryTree[T] ($.left, $.right);
 
    method replace-all(T $value) {
        $!value = $value;
        $.left.?replace-all($value);
        $.right.?replace-all($value);
    }
}
 
class IntTree does BinaryTree[Int] { }
 
my IntTree $it .= new(value => 1,
                      left  => IntTree.new(value => 2),
                      right => IntTree.new(value => 3));
 
$it.replace-all(42);
say $it.perl;