T11514.hs:6:7: error:
    • Cannot instantiate unification variable ‘a0’
      with a type involving polytypes: (Show a => a -> a) -> ()
        GHC doesn't yet support impredicative polymorphism
    • In the expression: undefined
      In an equation for ‘foo’: foo = undefined
    • Relevant bindings include
        foo :: (Show a => a -> a) -> () (bound at T11514.hs:6:1)