Use of MonadWidget

[romefeller]

If I have this function:

mainForm :: (MonadCall t m, MonadWidget t m) => m ()
mainForm = do
ck <- getCookie
...

The getCookie functon is:
cookie :: JSM Text
cookie = document ^. js (t_ "cookie") >>= fromJSValUnchecked

getCookie :: MonadWidget t m => m Text
getCookie = liftJSM cookie

But I get the error:

error:
• Could not deduce: DomBuilderSpace m ~ GhcjsDomSpace
arising from a use of ‘mainForm’
from the context: ObeliskWidget t (R FrontendRoute) m
bound by a type expected by the context:
forall t (m :: * -> *).
ObeliskWidget t (R FrontendRoute) m =>
RoutedT t (R FrontendRoute) m ()
at /home/romefeller/weivi/weivi-frontend-poc/frontend/src/Frontend.hs:(24,22)-(25,38)
or from: a ~ ()

where:

frontend_body = subRoute $ \case
FrontendRoute_Main -> mainForm

I'm unsure how to circumvent this error (I do not remember), as it seems to involve a mismatch between the expected DOM environment and what's provided by my ObeliskWidget setup. Has anyone faced a similar issue or can offer guidance on making mainForm compatible within this context?

Thanks in advance for any help or insights!

[alexfmpe]

You are seeing a type error because one can only run JSM inside the second argument of prerender as the first is statically rendered by the backend and does not have JS access.

obelisk/skeleton/frontend/src/Frontend.hs

Line 42 in 135bfd7

prerender_ blank $ liftJSM $ void

Now, cookies in particular can be fetched both on the backend and the frontend, so you want askCookies instead:

obelisk/lib/frontend/src/Obelisk/Frontend/Cookie.hs

Lines 33 to 34 in 135bfd7

	class Monad m => HasCookies m where
	askCookies :: m Cookies

[romefeller]

Thanks, @alexfmpe!