Running programs with an occurrence at "now"

[parenthetical]

I need to run a program returning an event in a way that I can tell what the value of a possible event occurrence at "now" is, maybe even allowing an input event to have an occurrence at now.

For example with a function runE behaving like so:

runE :: (t ~ SpiderTimeline Global, m ~ SpiderHost Global)
       => (Event t a -> m (Event t b))
       -> [a]
       -> IO [Maybe b]
runE = ...

where

runE (\e -> do
        n <- now
        pure . fmap getSum $ (Sum 1 <$ n) <> (Sum <$> e))
   [1,1]

produces: [2,1].

What would be the best way to implement such a function?

[parenthetical]

Coming back to this, the following seems to do the trick!

runE :: (t ~ SpiderTimeline Global)
       => (Event t a -> PushM t (Event t b))
       -> [a]
       -> IO [Maybe b]
runE p input = runSpiderHost $ do
  let p' e =
        switchHoldPromptOnly never
        . pushAlways (const (p e))
        =<< headE e
  (inE, trigRef) <- newEventWithTriggerRef
  outE <- runHostFrame (p' inE)
  outHnd <- subscribeEvent outE
  forM input (\a -> fireEventRefAndRead trigRef a outHnd)