title: Debugging an unresolvable thunk in GHCi
body: <p>I have an infinite loop somewhere in my program resulting in a <code>&lt;&lt;loop&gt;&gt;</code> exception when run normally.  Using GHCi, I've tracked the problem down to a thunk</p>
  
  <pre><code>f = Constructor1
    (Constructor2 A :
     (_t3::[DataType2]))
  </code></pre>
  
  <p>Attempting to sequence the thunk with <code>seq _t3 ()</code> results in GHCi hanging, so if I understand correctly the infinite loop is occurring in the reduction to Weak Head Normal Form.  Is there any way to investigate this thunk, for example to see step by step the reduction steps attempting to be used to evaluate it?</p>