title: Undefined data constructor "?" in Hugs intepreter
body: <p>Strange error when attempting to load file into hugs:    </p>
  
  <pre><code>Hugs&gt; :l test.hs
  ERROR "test.hs":3 - Undefined data constructor "?"
  </code></pre>
  
  <p>Full content of file (yes, one line):</p>
  
  <pre><code>test :: [a] -&gt; ([a],[a])
  </code></pre>
  
  <p>Can anyone enlighten me?</p>
  
  <hr>
  
  <p>Note: Attempting to load the same file in ghci doesn't work either, but for reasons that <em>make sense</em>:</p>
  
  <pre><code>Prelude&gt; :r
  [1 of 1] Compiling Main             ( test.hs, interpreted )
  
  test.hs:1:1:
  The type signature for ‘test’ lacks an accompanying binding
  Failed, modules loaded: none.
  </code></pre>