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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 ())
In the expression: (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)
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