Hi, I'm trying to use SYB to implement some basic relational persistance. I define a PKey datatype to represent primary keys like this: newtype PKey a = PKey a deriving (Show, Typeable, Data) I then define a sample data type like this: data User = User { id :: PKey Int, firstName :: String, lastName :: String, } deriving (Show, Typeable, Data) Finally, I try to iterate over the structure like this: test = gmapQ (gshow `ext1Q` aux) where aux :: PKey a -> String aux _ = "test" The problem is that for id gmapQ calls gshow instead of my customized version (aux). I've seen a discussion on this on haskell cafe at the following URL: http://www.opensubscriber.com/message/haskell-cafe@haskell.org/2167871.html I couldn't understand the following details: 1. Do I need to derive both Typeable and Data instances? 2. Do I need to derive them for both PKey and User or just PKey? 3. Where can I find sample code to derive these instances? Documentation shows a sample of how GHC derives Data, is that a good template to use? Also, what's a good example to derive Typeable (if in fact it needs to be done manually)? Thanks, - Slava.