title: Test if a list is sorted
body: <p>It is really easy to find a minimum of a list in haskell:</p>
  
  <p><code>foldl1 (min) [9,5,7,3,7,4,6,10]</code> gives me <code>3</code>. ;)</p>
  
  <p>I replaced <code>min</code> with <code>&lt;=</code> to test if a list is sorted:</p>
  
  <p><code>foldl1 (&lt;=) [9,5,7,3,7,4,6,10]</code></p>
  
  <p>I get this error message:</p>
  
  <pre><code>No instance for (Num Bool) arising from the literal `9'
  Possible fix: add an instance declaration for (Num Bool)
  In the expression: 9
  In the second argument of `foldl1', namely `[9, 5, 7, 3, ....]'
  In the expression: foldl1 (&lt;=) [9, 5, 7, 3, ....]
  </code></pre>
  
  <p>Is there a way to fix this error?</p>