title: Haskell length function error message
body: <p>As sort of "Wat" for Haskell, it's pointed out at the end of <a href="http://profsjt.blogspot.co.il/2017/10/is-haskell-right-language-for-teaching.html" rel="nofollow noreferrer">haskell for teaching</a> that</p>
  
  <pre><code>length (1,2)
  
  1
  </code></pre>
  
  <p>vs.</p>
  
  <pre><code>length (1,2,3)
  
  
  &lt;loads of error messages&gt;
  </code></pre>
  
  <p>The questions is why? And how to correct this?</p>