Re: [Haskell-beginners] Type constructors sharing a common field

If you could have a single polymorphic "age" function for all types having an age, you could never have this runtime error, because the compiler would infer which "age" we are referring to. The GHC OverloadedRecordFields extension that Michael linked seems to do what I am looking for (http://www.well-typed.com/blog/84/).