I'm trying to understand parametric polymorphism and polymorphic data types. I especially want to go beyond simply using the defined polymorphic data types (lists and so forth) and see how I can make my own useful ones. As my first stab at it, it seemed like I should be able to create my own heterogeneous "list" data type -- i.e., a "list" data type that can contain elements of different types. (like, [3,'a',True], for example) But I'm a little stuck. My first try was like so: data HeteroList a b = Null | Element a (HeteroList a b) deriving (Show) ...but this of course did not work, because all elements end up having to be the same type. Then I tried data HeteroList a b = Null | Element a (HeteroList b a) deriving (Show) ...but this doesn't work because every other other element has to be the same type: Element 'a' (Element 1 (Element 'a' (Element 2 Null))) ...I could go on and embarrass myself some more, but since I'm likely widely off-base I'll just ask if somebody can point me in the right direction. -- frigidcode.com theologia.indicium.us