T14273.hs:7:27: warning: [-Wdeferred-type-errors (in -Wdefault)]
    • Could not deduce (Show a1) arising from a use of ‘show’
      from the context: Show a
        bound by the type signature for:
                   pleaseShow :: forall a. Show a => Bool -> a -> Maybe String
        at T14273.hs:5:1-49
      The type variable ‘a1’ is ambiguous
      These potential instances exist:
        instance (Show a, Show b) => Show (Either a b)
          -- Defined in ‘Data.Either’
        instance Show Ordering -- Defined in ‘GHC.Show’
        instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
        ...plus 24 others
        ...plus 70 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the first argument of ‘Just’, namely ‘(show _a)’
      In the expression: Just (show _a)
      In an equation for ‘pleaseShow’: pleaseShow True a = Just (show _a)

T14273.hs:7:32: warning: [-Wtyped-holes (in -Wdefault)]
    • Found hole: _a :: a1
      Where: ‘a1’ is an ambiguous type variable
      Or perhaps ‘_a’ is mis-spelled, or not in scope
    • In the first argument of ‘show’, namely ‘_a’
      In the first argument of ‘Just’, namely ‘(show _a)’
      In the expression: Just (show _a)
    • Relevant bindings include
        a :: a (bound at T14273.hs:7:17)
        pleaseShow :: Bool -> a -> Maybe String (bound at T14273.hs:6:1)
      Constraints include Show a (from T14273.hs:5:1-49)
      Valid hole fits include
        a :: a (bound at T14273.hs:7:17)
        k :: String (bound at T14273.hs:10:1)
        otherwise :: Bool
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Base’))
        False :: Bool
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Types’))
        True :: Bool
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Types’))
        LT :: Ordering
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Types’))
        EQ :: Ordering
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Types’))
        GT :: Ordering
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Types’))
        () :: () (bound at <wired into compiler>)
        pi :: forall a. Floating a => a
          with pi @Double
          (imported from ‘Prelude’ at T14273.hs:1:8-40
           (and originally defined in ‘GHC.Float’))

T14273.hs:13:10: warning: [-Wdeferred-type-errors (in -Wdefault)]
    • Ambiguous type variable ‘a0’ arising from a use of ‘show’
      prevents the constraint ‘(Show a0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘a0’ should be.
      These potential instances exist:
        instance (Show a, Show b) => Show (Either a b)
          -- Defined in ‘Data.Either’
        instance Show Ordering -- Defined in ‘GHC.Show’
        instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
        ...plus 24 others
        ...plus 70 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: show (_h ++ [])
      In an equation for ‘foo’: foo xs = show (_h ++ [])

T14273.hs:13:16: warning: [-Wtyped-holes (in -Wdefault)]
    • Found hole: _h :: [a0]
      Where: ‘a0’ is an ambiguous type variable
      Or perhaps ‘_h’ is mis-spelled, or not in scope
    • In the first argument of ‘(++)’, namely ‘_h’
      In the first argument of ‘show’, namely ‘(_h ++ [])’
      In the expression: show (_h ++ [])
    • Relevant bindings include
        xs :: [a] (bound at T14273.hs:13:5)
        foo :: [a] -> String (bound at T14273.hs:13:1)
      Valid hole fits include k :: String (defined at T14273.hs:10:1)