suggested helper function: maybeWidget

[rprije]

I find this helper function useful:

maybeWidget :: (DomBuilder t m, MonadFix m, MonadHold t m)
=> m b
-> (Dynamic t a -> m b)
-> Dynamic t (Maybe a)
-> m (Dynamic t (m b))
maybeWidget handleNothing handleJust dynMaybe =
(fmap . fmap) (maybe handleNothing handleJust) $ maybeDyn dynMaybe

It's analogous to the maybe function in that it allows a Dynamic t (Maybe a) to dynamically switch between widgets depending on whether that maybe is a Nothing or a Just. I typically use it with dyn and switchEvent from reflex-frp/reflex#49

[dfordivam]

This can also be in reflex along with Reflex.Collection APIs..

[alexfmpe]

In addition to what @dfordivam said, it might be worth adding similar helpers, like

eitherWidget :: (DomBuilder t m, MonadFix m, MonadHold t m)
            => (Dynamic t a -> m c)
            -> (Dynamic t b -> m c)
            -> Dynamic t (Either a b)
            -> m (Dynamic t (m c))
eitherWidget handleLeft handleRight dynEither =
  (fmap . fmap) (either handleLeft handleRight) $ eitherDyn dynEither

or theseWidget (if theseDyn was a thing).

Maybe it can even be derived generically (https://github.com/reflex-frp/reflex/pull/106/files/173c1bf983b8a61b17c932230ee3757c0e154add#diff-2536923df364966db0a4fb4bc1d9eb4aR44)