Overlap9.hs:11:7:
    Could not deduce (F a ~ Int)
    from the context (Show a)
      bound by the type signature for g :: Show a => a -> F a
      at Overlap9.hs:10:6-23
    Relevant bindings include
      g :: a -> F a (bound at Overlap9.hs:11:1)
      x :: a (bound at Overlap9.hs:11:3)
    In the return type of a call of ‛length’
    In the expression: length (show x)
    In an equation for ‛g’: g x = length (show x)