T12468.hs:9:7: error:
    • Found hole: _ :: Int
    • In the expression: _
      In an equation for ‘f’: f I = _
    • Relevant bindings include f :: T a -> a (bound at T12468.hs:9:1)
      Valid substitutions include
        maxBound :: forall a. Bounded a => a
          (imported from ‘Prelude’ at T12468.hs:3:8-13
           (and originally defined in ‘GHC.Enum’))
        minBound :: forall a. Bounded a => a
          (imported from ‘Prelude’ at T12468.hs:3:8-13
           (and originally defined in ‘GHC.Enum’))
        undefined :: forall (a :: TYPE r).
                     GHC.Stack.Types.HasCallStack =>
                     a
          (imported from ‘Prelude’ at T12468.hs:3:8-13
           (and originally defined in ‘GHC.Err’))