T10971b.hs:4:11: error:
    • Ambiguous type variable ‘t2’ arising from a use of ‘length’
      prevents the constraint ‘(Foldable t2)’ from being solved.
      Relevant bindings include
        x :: t2 a (bound at T10971b.hs:4:6)
        f :: t2 a -> Int (bound at T10971b.hs:4:1)
      Probable fix: use a type annotation to specify what ‘t2’ should be.
      Potentially matching instances:
        instance Foldable (Either a) -- Defined in ‘Data.Foldable’
        instance Foldable Maybe -- Defined in ‘Data.Foldable’
        ...plus three others
        ...plus 29 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: length x
      In the expression: \ x -> length x
      In an equation for ‘f’: f = \ x -> length x

T10971b.hs:5:13: error:
    • Ambiguous type variable ‘t1’ arising from a use of ‘fmapDefault’
      prevents the constraint ‘(Traversable t1)’ from being solved.
      Relevant bindings include
        x :: t1 a (bound at T10971b.hs:5:8)
        g :: (a -> b) -> t1 a -> t1 b (bound at T10971b.hs:5:1)
      Probable fix: use a type annotation to specify what ‘t1’ should be.
      Potentially matching instances:
        instance Traversable (Either a) -- Defined in ‘Data.Traversable’
        instance Traversable Maybe -- Defined in ‘Data.Traversable’
        ...plus three others
        ...plus 29 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: fmapDefault f x
      In the expression: \ f x -> fmapDefault f x
      In an equation for ‘g’: g = \ f x -> fmapDefault f x

T10971b.hs:6:14: error:
    • Ambiguous type variable ‘t0’ arising from a use of ‘fmapDefault’
      prevents the constraint ‘(Traversable t0)’ from being solved.
      Relevant bindings include
        x :: t0 a (bound at T10971b.hs:6:8)
        h :: (a -> b) -> t0 a -> (t0 b, Int) (bound at T10971b.hs:6:1)
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      Potentially matching instances:
        instance Traversable (Either a) -- Defined in ‘Data.Traversable’
        instance Traversable Maybe -- Defined in ‘Data.Traversable’
        ...plus three others
        ...plus 29 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: fmapDefault f x
      In the expression: (fmapDefault f x, length x)
      In the expression: \ f x -> (fmapDefault f x, length x)

T10971b.hs:6:31: error:
    • Ambiguous type variable ‘t0’ arising from a use of ‘length’
      prevents the constraint ‘(Foldable t0)’ from being solved.
      Relevant bindings include
        x :: t0 a (bound at T10971b.hs:6:8)
        h :: (a -> b) -> t0 a -> (t0 b, Int) (bound at T10971b.hs:6:1)
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      Potentially matching instances:
        instance Foldable (Either a) -- Defined in ‘Data.Foldable’
        instance Foldable Maybe -- Defined in ‘Data.Foldable’
        ...plus three others
        ...plus 29 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: length x
      In the expression: (fmapDefault f x, length x)
      In the expression: \ f x -> (fmapDefault f x, length x)