Overlap9.hs:10:7:
    Couldn't match expected type ‘F a’ with actual type ‘Int’
    In the expression: length (show x)
    In an equation for ‘g’: g x = length (show x)
    Relevant bindings include
      x :: a (bound at Overlap9.hs:10:3)
      g :: a -> F a (bound at Overlap9.hs:10:1)