I support the suggestion of providing instance Show Unique I would also support having instance Read Unique As John says, the representation of a Unique value as a String should be completely undefined except that u == u' iff showUnique u == showUnique u' In UniForM we have a similar type to Unique which also instances (Eq,Ord,Show,Read) One advantage of instancing Show is that it makes it easier to debug programs which use Unique values. Read is more debatable, but I'm sure we use it somewhere.