kkallio@14: con changePoller t = {Val : source t,
kkallio@14:                       Last : source t}
kkallio@14: 
kkallio@14: fun create [t ::: Type] (_ : eq t) (i : t)  =
kkallio@14:     v <- source i;
kkallio@14:     l <- source i;
kkallio@14: 
kkallio@14:     return {Val = v,
kkallio@14:             Last = l}
kkallio@14: 
kkallio@14: fun addChangeListener [t ::: Type] (_ : eq t) f pollInterval cp =
kkallio@14:     let
kkallio@14:         fun go () =
kkallio@14:             sleep pollInterval;
kkallio@14:             sample <- get cp.Val;
kkallio@14:             lst <- get cp.Last;
kkallio@14:             if sample = lst then
kkallio@14:                 go ()
kkallio@14:             else
kkallio@14:                 f sample;
kkallio@14:                 set cp.Last sample;
kkallio@14:                 go ()
kkallio@14:     in
kkallio@14:         go ()
kkallio@14:     end
kkallio@14: 
kkallio@14: fun ctl [t ::: Type] cp = cp.Val
kkallio@14: 
kkallio@14: fun value [t ::: Type] cp = signal (cp.Val)
kkallio@14: