A process that is triggered, stepped for a while, then finished.

Useful to drive animations and filter other events and behaviors.

-- Set up a 1 second countdown
(startingE, startedE, starting) <-
  Course.setup (startE $> 1.0) $
    tickE $> old ->
      if old > dt then
        Right (old - dt)
      else
        Left ()

-- Prevent click events after starting the countdown
let clicks = fmap (Course.whenIdle starting) allClicks