gistfile1.txt

class Tree {
    has $:node;
    has $:parent;

    has @:children = [];

    BUILD ($node, @children?) { 
        $:node = $node;
        if (@children) {
            @:children = @children;
            self._fix_parent;
        }
    }

    method node { $:node }

    method parent ($parent?) {
        if ($parent) { $:parent = $parent; }
        $:parent
    }

    method depth { $:parent ? $:parent.depth + 1 : 0 }

    method traverse (&f) {
        &f.(self);
        @:children.each(-> ($c) { 
            $c.traverse(&f) 
        })
    }

    method _fix_parent { 
        @:children.each(-> ($c) { $c.parent(self) }) 
    }
}

my $t = ^Tree.new("0.0", [
    ^Tree.new("1.0", [
        ^Tree.new("1.1"),
        ^Tree.new("1.2", [
            ^Tree.new("1.2.1"),
            ^Tree.new("1.2.2"),
        ])
    ]),
    ^Tree.new("2.0", [
        ^Tree.new("2.1", [
            ^Tree.new("2.1.1", [
                ^Tree.new("2.1.1.1"),
            ]),
            ^Tree.new("2.1.2", [
                ^Tree.new("2.1.2.1"),
                ^Tree.new("2.1.2.2"),
            ])
        ])
    ]),
    ^Tree.new("3.0"),
]);

$t.traverse(-> ($c) {
   say( (".." x $c.depth), $c.node )
})