[SOLVED] Send action from Eff in eval in Halogen?

Send action from Eff in eval in Halogen?

I'm trying to throttle a search field in purescript-halogen. What I have so far:

eval (Search search next) = do
  State st <- get

  -- clear last timeout
  liftEff' $ maybe (return unit) T.clearTimeout st.searchTimeout

  -- new timeout
  t <- liftEff' $ T.timeout 1000 $ return unit -- how to send action from here???
  modify (\(State s) -> State $ s { searchTimeout = Just t })

  pure next

I thought about saving the UI driver in a global Var and send new actions from there, but this seems very hacky to me.

Or maybe there's another way to do that?

Solution

This is the kind of thing you'll probably need to create an EventSource for. An EventSource allows you to subscribe to something somewhat like a signal/stream/event listener and then raise actions.

This isn't quite what you want, but is an example of using an EventSource to run an interval based timer: https://github.com/slamdata/slamdata/blob/2ab704302292406e838e1a6e5541aa06ad47e952/src/Notebook/Cell/Component.purs#L213-L217