title: How to serialize/deserialize a hashmap?
body: <p>I have a large hashmap containing millions of entries, and I want to persist it to disk, so that when it is read from the disk again, I don't have the overhead of inserting the key-value pairs back into the map again.</p>
  
  <p>I am trying to use the cereal library to do this, but it appears that the <a href="http://hackage.haskell.org/package/unordered-containers-0.2.1.0" rel="noreferrer">HashMap</a> datatype needs to derive Generic. Is there a way to do this?</p>