[Haskell-cafe] Declaring a tuple of instances of Enums as an instance of the Enum class

[R J]

Say I've got a type "Month" declared as an instance of the "Enum" class, and a type "MonthPair" declared as a pair of months:
data Month                 =  January                           |  February                           |  March                           |  April                           |  May                           |  June                           |  July                           |  August                           |  September                           |  October                           |  November                           |  December                           deriving (Eq, Enum, Ord, Show)
type MonthPair             =  (Month, Month)                           deriving (Enum)
The "deriving" on "MonthPair" gives me the error "parse error on input 'deriving'".
Why is this error generated?  Is there a syntax error, or is there a conceptual problem with enumerating a Cartesian product, such as Month x Month?  The cardinality of the Cartesian product is finite (including the bottom values, cardinality = 1 + (12 + 1)*(12 + 1) = 170), and so the product is amenable at least to some arbitrary enumeration (such as Cantor's diagonal method).
Thanks. 

 		 	   		  
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