R J <[email protected]> writes: > 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'".
You can't derive instances for type aliases (as its mainly there for documentation reasons, etc.). However, pairs don't have Enum instances by default so you still can't use its instance. If you define "data MonthPair = MonthPair Month Month" then you should be able to derive Enum. -- Ivan Lazar Miljenovic [email protected] IvanMiljenovic.wordpress.com _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
