I have a class that is basically:<br /><br />data TwoLists = TL {doubleList :: [Double], intList :: [Int]}<br /><br />Almost all of the operations of this type map, fold, etc on one of the lists or the other, and then return a new instance of the type. So I am implementing to functions dFmap, and iFmap. I actually would like all of the list functions, but I don&#39;t want to reimplement them.<br /><br />So my question is, what is the haskell way of handling a type like this. Is there some sort of TwoTypeTraversable I should be deriving from? Essential is there a Haskell idiom for this situation.<br /><br />-Jonathan