And then you can use the code I gave in the previous reply to generate the Serialize instance. I suppose this is better looking, but you may want to check the efficiency since it requires a lookup (but it's a super tiny table so it might not be all that bad). You can generate similar code with Template Haskell, eliding the lookup. 

[1] http://stackoverflow.com/questions/6000511/better-way-to-define-an-enum-in-haskell