sweet.hs

sweet.hs

newtype L c t = L (forall e. Dict (c (t e)))

withL :: forall c t r. L c t -> (forall e. Dict (c (t e)) -> r) -> r
withL (L dict) r = r dict

functorEitherL :: L Functor Either
functorEitherL = L Dict

someFuntorEitherL :: Dynamic
someFuntorEitherL = toDyn functorEitherL

getItBack :: Dynamic -> TypeRep (L c t) -> Maybe (L c t)
getItBack (Dynamic rep a) l_t =
  case rep of
    _ | Just Type.HRefl <- Type.eqTypeRep l_t rep
        -> Just a
    _ -> Nothing

applyClass :: Dynamic -> TypeRep (L c t) ->
  (forall e. Dict (c (t e)) -> r) -> Maybe r
applyClass dyn l_t f = do
  l <- getItBack dyn l_t
  pure $ withL l f