John Smith
Why can polymorphic data constructors not be instantiated as a class? (not sure if I used the right terminology there)
For example,
a = [1,True]::[Show] b = "foo":a c = map show b
This would obviate the need for wrapper types
Your type signature doesn't make sense. You are confusing type classes with types. Show is a type class. As far as I see, you will need a wrapper type: data Object = forall a. Show a => Object { unObject :: a } a = [Object 1, Object True] b = Object "foo" : a c = map (show . unObject) b I have not tested this code, though. At least I can get the following list to type-check (using RankNTypes and ImpredicativeTypes extensions): [1,2,3] :: [forall a. Num a => a] but I can't use it in any way. And somehow I also can't mix data types here. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/