T10403.hs:15:7: warning: [-Wpartial-type-signatures (in -Wdefault)]
    • Found type wildcard ‘_’ standing for ‘Functor f’
      Where: ‘f’ is a rigid type variable bound by
               the inferred type of h1 :: Functor f => (a -> a1) -> f a -> H f
               at T10403.hs:17:1-41
    • In the type signature: h1 :: _ => _

T10403.hs:15:12: warning: [-Wpartial-type-signatures (in -Wdefault)]
    • Found type wildcard ‘_’ standing for ‘(a -> a1) -> f a -> H f’
      Where: ‘a1’, ‘a’, ‘f’ are rigid type variables bound by
               the inferred type of h1 :: Functor f => (a -> a1) -> f a -> H f
               at T10403.hs:17:1-41
    • In the type signature: h1 :: _ => _

T10403.hs:19:7: warning: [-Wpartial-type-signatures (in -Wdefault)]
    • Found type wildcard ‘_’ standing for ‘(a -> a1) -> f0 a -> H f0’
      Where: ‘f0’ is an ambiguous type variable
             ‘a1’, ‘a’ are rigid type variables bound by
               the inferred type of h2 :: (a -> a1) -> f0 a -> H f0
               at T10403.hs:22:1-41
    • In the type signature: h2 :: _

T10403.hs:22:15: warning: [-Wdeferred-type-errors (in -Wdefault)]
    • Ambiguous type variable ‘f0’ arising from a use of ‘fmap’
      prevents the constraint ‘(Functor f0)’ from being solved.
      Relevant bindings include
        b :: f0 a (bound at T10403.hs:22:6)
        h2 :: (a -> a1) -> f0 a -> H f0 (bound at T10403.hs:22:1)
      Probable fix: use a type annotation to specify what ‘f0’ should be.
      These potential instances exist:
        instance Functor IO -- Defined in ‘GHC.Base’
        instance Functor (B t) -- Defined at T10403.hs:10:10
        instance Functor I -- Defined at T10403.hs:6:10
        ...plus five others
        ...plus two instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the second argument of ‘(.)’, namely ‘fmap (const ())’
      In the expression: (H . fmap (const ())) (fmap f b)
      In an equation for ‘h2’: h2 f b = (H . fmap (const ())) (fmap f b)

T10403.hs:28:8: warning: [-Wdeferred-type-errors (in -Wdefault)]
    • Couldn't match type ‘f0’ with ‘B t’
      Expected: H (B t)
        Actual: H f0
        because type variable ‘t’ would escape its scope
      This (rigid, skolem) type variable is bound by
        the type signature for:
          app2 :: forall t. H (B t)
        at T10403.hs:27:1-15
    • In the expression: h2 (H . I) (B ())
      In an equation for ‘app2’: app2 = h2 (H . I) (B ())
    • Relevant bindings include
        app2 :: H (B t) (bound at T10403.hs:28:1)