signal_filter.elm

import Html exposing (..)
import Html.Attributes exposing (..)

import Time

currentTime : Signal Time.Time
currentTime = Time.every Time.second

main = Signal.map2
  (\time ls -> 
    div [] 
      [ text <| toString time 
      , ul [] <|
        List.map (\elt -> li [] [ text <| toString elt ]) ls
      ]
  )
  currentTime
  (filterPast ls)
  
 
-- ls = [1437923356077, 1437923356077, 1437925056077, 1437923506077]

ls = List.map (\n -> n * Time.second + 1437925514918 ) (range 100)

range n = if n == 0 then [] else n :: range (n - 1)

isPast : Float -> Signal Bool
isPast elt = Signal.map (\time -> elt <= time) currentTime


filterPast : List Float -> Signal (List Float)
filterPast ls =
  let 
    folder =
      Signal.map3 (\currentTime head tail -> 
        if currentTime >= head then
          tail
        else
          head :: tail
        )
        currentTime
  in
    List.foldl folder (Signal.constant []) (List.map Signal.constant ls)