mnwe.rb

#!/usr/bin/env ruby

module MyModule
  module MyHelper
    module_function def helpermethod
      puts "helpermethod"
    end
  end
  private_constant :MyHelper  

  def modmethod
    MyHelper.helpermethod
  end
end

class MyClass
  include MyModule  
  # include MyHelper # works (well, such is life)

  def initialize
    # modmethod    # works
    # modmethod # works          
    # helpermethod # works (*shrug*)
  end
end

myobj = MyClass.new
myobj.modmethod # works (good)
# myobj.helpermethod # fails (good)