monad transformers - throwError in Halogen component queries -

i'm struggling achieving following goal: have api requests typed in manner return either desired value, or error when status code wasn't indicating success, or when auth token has been invalid etc: either string r.

now, don't want care when i'm evaling components queries. interested in happy path (expected errors invalid logon attempt considered happy path, want keep unexpected stuff out of it), , errors should handled uniformily , globally (sending notification bus).

for this, i've created transformer stack:

type app = readert env (exceptt string (aff appeffects)) 

now, use runui, needed provide natural transformation used hoist (unless i'm missing other possibilities):

runapp :: env -> app ~> aff appeffects runapp env app =   res <- runexceptt $ runreadert app env   case res of     right r -> pure unit     left err -> bus.write err env.bus                    -- return here? 

because we're using ~> here, we're forced retain return type, left case don't have @ hand!

how 1 tackle such requirement? reiterate - want able 'cancel' evaluation of component query when executed action encounters error, want silently , handle top.

you have exceptional case current thread can't continue, thing throw exception in aff using throwerror :: forall eff a. error -> aff eff a.