title: Convert Maybe String to (Maybe?) Integer
body: <p>I would like to convert a Maybe String type to an Integer.</p>
  
  <p>My actual code is:</p>
  
  <pre><code>  let rule = getParamRule args -- this is a Maybe String type
    let rule_int = read rule::Int -- I would like to convert to (Maybe) Integer
    print rule
    print rule_int
  </code></pre>
  
  <pre><code>test.hs:26:23: error:
      • Couldn't match type ‘Maybe String’ with ‘[Char]’
        Expected type: String
          Actual type: Maybe String
      • In the first argument of ‘read’, namely ‘rule’
        In the expression: read rule :: Maybe Int
        In an equation for ‘rule_int’: rule_int = read rule :: Maybe Int
  </code></pre>