I want to add instance methods to a class at runtine.

$ cat testcmds.rb
module Bar
  def hello
    puts "hello called"
  end
end

class Foo
end

Foo.include(Bar)

Foo.new.hello

$ ruby testcmds.rb
testcmds.rb:10: private method `include' called for Foo:Class 
(NoMethodError)

How can I do this?