expected.txt

c.b.a.root

node.rb

#!/usr/bin/env ruby

class NodeTest
    def initialize(parent, name)
        @parent = parent
        @name = name
    end

    def add_node(name)
        self.class.new(self, name)
    end

    def name()
        @name
    end

    def parent()
        @parent
    end

    def walk()
        yield @parent.walk if @parent
        yield self
    end

    def path()
        self.walk {|node| puts node.name}
    end
end

root = node = NodeTest.new(nil, 'root')
node_names = ['a', 'b', 'c']
for nn in node_names do
    node = node.add_node(nn)
end

puts  node.path

output.txt

$ ruby test.rb 
test.rb:23:in `walk': no block given (yield) (LocalJumpError)
	from test.rb:22:in `walk'
	from test.rb:22:in `walk'
	from test.rb:22:in `walk'
	from test.rb:27:in `path'
	from test.rb:37:in `<main>'