title: How to convert String to int(and not to int option) in SML
body: <p>I am trying to extract integer value from a string using <code>Int.fromString</code> function
  but as we know, its specification is : <code>String -&gt; int option</code>. So the result of applying <code>Int.fromString</code> is of type <code>int option</code>. But I need the result of type <code>int</code>. Also I am sure that the extracted part is integer. How can this be done?</p>