title: Haskell: What does the warning "Variable is implicitly quantified due to a context" mean?
body: <p>At this line</p>
  
  <pre><code>type SafeReturn a = Exception e =&gt; Either e a
  </code></pre>
  
  <p>I got this warning</p>
  
  <pre><code>Variable ‘e’ is implicitly quantified due to a context
  Use explicit forall syntax instead.
  </code></pre>
  
  <p>What does it mean?</p>