Y Combinator in Ruby

y_combinator.rb

# Define the Y combinator
module Y
  extend self
  def combinator(&generator)
      lambda do |x|
          lambda do |*args|
              generator.call(x.call(x)).call(*args)
          end
      end.call(lambda do |x|
          lambda do |*args|
              generator.call(x.call(x)).call(*args)
          end
      end)
  end
end

# Call the Y combinator, providing it with a procedure that
# accepts a recursive callback function and returns a procedure.
# The Y combinator returns the recursive function. Then call that
# function to produce a Hash object.
hash = Y.combinator do |callback|
    lambda do
        Hash.new { |h, k| h[k] = callback.call }
    end
end.call

# Now this will work:
hash['a']['b']['c']['d']['e']['f']['g'] = 1

# => {"a"=>{"b"=>{"c"=>{"d"=>{"e"=>{"f"=>{"g"=>1}}}}}}}