haskell polymorphism and lists

Question

Suppose I have the following:

class Shape a where
    draw a :: a -> IO ()

data Rectangle = Rectangle Int Int

instance Shape Rectangle where
    draw (Recta         


        

Answer 1

Consider using a single type instead of separate types and a typeclass.

data Shape = Rectangle Int Int
           | Circle Int Int

draw (Rectangle length width) = ...
draw (Circle center radius)   = ...

shapes = [Circle 5 10, Circle 20 30, Rectangle 10 15]