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+[[!comment format=mdwn
+ username="https://www.joachim-breitner.de/"
+ nickname="nomeata"
+ avatar="http://cdn.libravatar.org/avatar/a2112893817513537c6a2c228c04c138a2f68bba57121ab7f267de58fc5171d7"
+ subject="comment 3"
+ date="2017-05-07T03:19:14Z"
+ content="""
+Still not good, I think, as the instance `Hashable Hash` has `hash = id`, so
+```
+hash Nothing = hash () = id (hash ()) = hash (Just (hash ())
+```
+and we have a collision at type `Maybe Hash`.
+
+What would work is to do the same that `Hashable []` does, i.e. has the hash again:
+```
+    hash (Just v) = hash (val (hashValue v))
+    hash Nothing = hash (mempty :: B.ByteString)
+```
+"""]]