ruby tree class, why does it says there is 2 arguments instead of 1 in initialize?

class Tree
attr_accessor :children, :node_name

def initialize(tree_hash={})
    tree_hash.each do |k,v|
        @node_name = k
        @children = v.map { |k,v|   Tree.new(k,v) }
    end
end

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

def visit(&block)
    block.call self
end
end

ruby_tree = Tree.new({'grandpa' => {'dad' => {'child 1' => {}, '开发者_Python百科child 2' => {} },'uncle' => {'child 3' => {}, 'child 4' => {} } } })

puts "Visiting a node"
ruby_tree.visit {|node| puts node.node_name}
puts

puts "visiting entire tree"
ruby_tree.visit_all {|node| puts node.node_name}

And the error message: (I am using ruby 1.9.2)

C:\ruby>ruby tree.rb

tree.rb:4:in `initialize': wrong number of arguments (2 for 1) (ArgumentError)

   from tree.rb:7:in `new'
   from tree.rb:7:in `block (2 levels) in initialize'
   from tree.rb:7:in `each'
   from tree.rb:7:in `map'
   from tree.rb:7:in `block in initialize'
   from tree.rb:5:in `each'
   from tree.rb:5:in `initialize'
   from tree.rb:21:in `new'
   from tree.rb:21:in `<main>'

There are 2 args in the line:

@children = v.map { |k,v|   Tree.new(k,v) }

Maybe you want to change k,v to {k => v} ?

    @children = v.map { |k,v|   Tree.new(k=>v) }

I think the initialisation is problematic though- what kind of tree are you implementing?