title: Extract data from a signal
body: <p>I have a signal like this: <code>signal1 = Signal.constant {a=4, b=3, l = []}</code><br>
  How do I extract a data from the signal?<br>
  I have tried <code>Signal.map (\x -&gt; x) signal1</code> but <code>Signal.map</code> returns another signal. </p>