T10403.hs:16:7: warning: [GHC-88464] [-Wpartial-type-signatures (in -Wdefault)]
    • Found extra-constraints wildcard standing for ‘Functor f’
      Where: ‘f’ is a rigid type variable bound by
               the inferred type of h1 :: Functor f => (a1 -> a2) -> f a1 -> H f
               at T10403.hs:18:1-41
    • In the type signature: h1 :: _ => _

T10403.hs:16:12: warning: [GHC-88464] [-Wpartial-type-signatures (in -Wdefault)]
    • Found type wildcard ‘_’ standing for ‘(a1 -> a2) -> f a1 -> H f’
      Where: ‘a2’, ‘a1’, ‘f’ are rigid type variables bound by
               the inferred type of h1 :: Functor f => (a1 -> a2) -> f a1 -> H f
               at T10403.hs:18:1-41
    • In the type signature: h1 :: _ => _

T10403.hs:20:7: warning: [GHC-88464] [-Wpartial-type-signatures (in -Wdefault)]
    • Found type wildcard ‘_’
        standing for ‘(a1 -> a2) -> f0 a1 -> H f0’
      Where: ‘f0’ is an ambiguous type variable
             ‘a2’, ‘a1’ are rigid type variables bound by
               the inferred type of h2 :: (a1 -> a2) -> f0 a1 -> H f0
               at T10403.hs:23:1-41
    • In the type signature: h2 :: _

T10403.hs:23:15: warning: [GHC-39999] [-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 a1 (bound at T10403.hs:23:6)
        h2 :: (a1 -> a2) -> f0 a1 -> H f0 (bound at T10403.hs:23:1)
      Probable fix: use a type annotation to specify what ‘f0’ should be.
      Potentially matching instances:
        instance Functor IO -- Defined in ‘GHC.Base’
        instance Functor (B t) -- Defined at T10403.hs:11:10
        ...plus 8 others
        ...plus one instance 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:29:8: warning: [GHC-46956] [-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:28:1-15
    • 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:29:1)