[Haskell-cafe] Data declaration vs type classes

Dear haskellers, What is the difference between writing data Task = GroceryTask String | LaundryTask Int doTask :: Task -> IO () doTask (GroceryTask s) = print "Going to " ++ s doTask (LaundryTask n) = print (show n ++ " pieces washed" and class Task a where work :: a -> IO () data GroceryTask = GroceryTask String data LaundryTask = LaundryTask Int instance Task GroceryTask where .. instance Task LaundryTask where .. doTask :: Task a => a -> IO () doTask = work They seem to be similar functionality wise, except that one is on the data level and another is on the class level. How should one go about deciding to use data or class? Is there a semantic difference? Which is more appropriate here? Happy new year, Hon