class Tree
    attr_accessor :children, :node_name

    def initialize(hash)
        @children = []
        hash.keys.each do |key|
            @node_name = key
            hash[key].keys.each do |keychild|
                @children << Tree.new(hash[key][keychild])
            end
        end
    end

    def visit_all(&block)
        visit &block
        children.each {|c| c.visit_all &block}
    end

    def visit(&block)
        block.call self
    end

    def to_s
        puts "Node name: " + @node_name + "\n"
        puts "Children:\n"
        children.each do |c|
            puts "\t" + c.to_s
        end
    end
end

x = {"grandpa" => { "dad" => {"child 1" => {}, "child 2" => {} }, "uncle" => {"child 3" => {}, "child 4" => {} } } }
y = Tree.new(x)
puts y.to_s


./grep.rb:27:in `+': can't convert Array into String (TypeError)
        from ./grep.rb:27:in `to_s'
        from ./grep.rb:26:in `each'
        from ./grep.rb:26:in `to_s'
        from ./grep.rb:34