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T10403.hs:15:7: warning:
Found constraint wildcard ‘_’ standing for ‘Functor f’
In the type signature:
h1 :: _ => _
T10403.hs:15:12: warning:
• Found type wildcard ‘_’ standing for ‘(a -> b) -> f a -> H f’
Where: ‘b’ is a rigid type variable bound by
the inferred type of h1 :: Functor f => (a -> b) -> f a -> H f
at T10403.hs:17:1
‘a’ is a rigid type variable bound by
the inferred type of h1 :: Functor f => (a -> b) -> f a -> H f
at T10403.hs:17:1
‘f’ is a rigid type variable bound by
the inferred type of h1 :: Functor f => (a -> b) -> f a -> H f
at T10403.hs:17:1
• In the type signature:
h1 :: _ => _
• Relevant bindings include
h1 :: (a -> b) -> f a -> H f (bound at T10403.hs:17:1)
T10403.hs:19:7: warning:
• Found type wildcard ‘_’ standing for ‘(a -> b) -> f0 a -> H f0’
Where: ‘b’ is a rigid type variable bound by
the inferred type of h2 :: (a -> b) -> f0 a -> H f0
at T10403.hs:22:1
‘a’ is a rigid type variable bound by
the inferred type of h2 :: (a -> b) -> f0 a -> H f0
at T10403.hs:22:1
‘f0’ is an ambiguous type variable
• In the type signature:
h2 :: _
• Relevant bindings include
h2 :: (a -> b) -> f0 a -> H f0 (bound at T10403.hs:22:1)
T10403.hs:22:15: warning:
• 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 -> b) -> 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 four others
(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:
• Couldn't match type ‘f0’ with ‘B t’
because type variable ‘t’ would escape its scope
This (rigid, skolem) type variable is bound by
the type signature for:
app2 :: H (B t)
at T10403.hs:27:1-15
Expected type: H (B t)
Actual type: H f0
• 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)
T10403.hs:28:20: warning:
• Couldn't match type ‘f0’ with ‘B t’
because type variable ‘t’ would escape its scope
This (rigid, skolem) type variable is bound by
the type signature for:
app2 :: H (B t)
at T10403.hs:27:1-15
Expected type: f0 ()
Actual type: B t ()
• In the second argument of ‘h2’, namely ‘(B ())’
In the expression: h2 (H . I) (B ())
• Relevant bindings include
app2 :: H (B t) (bound at T10403.hs:28:1)
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