Take for instance Pandoric Macros that allow you to peek inside the hidden state of a closure:

  # Traditional Let over Lambda
  counter = let x = 100
    () -> x += 1
  end
  counter() # 101
  
  # Pandoric Macro
  captured_x_ref = Core.getfield(counter, :x)
  println("The hidden state is: ", captured_x_ref.contents) # Outputs: 101