adam@0: type t = source bool
adam@0: 
adam@0: fun create r =
adam@0:     b <- source False;
adam@0:     spawn (sleep r.Milliseconds;
adam@0:            b <- get b;
adam@0:            if b then
adam@0:                return ()
adam@0:            else
adam@0:                r.Action);
adam@0:     return b
adam@0: 
adam@0: fun cancel b = set b True