T16646Fail.hs:16:5: error: [GHC-39999]
    • No instance for ‘WithDict cls meth’
        arising from a use of ‘withDict’
      Possible fix:
        add (WithDict cls meth) to the context of
          the type signature for:
            f :: forall (cls :: Constraint) meth r. meth -> (cls => r) -> r
    • In the expression: withDict @cls @meth
      In an equation for ‘f’: f = withDict @cls @meth

T16646Fail.hs:22:5: error: [GHC-39999]
    • No instance for ‘WithDict (C a) (Maybe a)’
        arising from a use of ‘withDict’
    • In the expression: withDict @(C a) @(Maybe a)
      In an equation for ‘g’: g = withDict @(C a) @(Maybe a)