hi Not sure if I'm on the right track here, so as a beginner I thought I'd ask on this list. I want to declare a type 'All' that consists of the of the types 'Tinteger, Tbool, Tstring, Tarray' but I would also like to make a relationship that Tinteger and Tbool are also the type 'Simple' and that 'Tstring' and 'Tarray' are 'Composite' and that Mixed is then either Simpletype or Composite. So I can then write a function that takes a type of All and produces a list of Mixed. data All = Tinteger Int | Tbool Bool | Tstring String | Tarray [Alltypes] data Simple = Tinteger | Tbool data Composite = Tstring | Tarray data Mixed = Simple | Composite k :: All -> [Mixed] k a = case a of Simple s -> [Simple s] Composite c -> [Composite c] But this isn't valid Haskell code because I can't have multiple declarations of the same types, is there a way to specify a relationship, if so can someone point me in the right direction? Roger