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

One way to do it would be with vtables:

data Shape = Shape {
  draw :: IO (),
  etc :: ...
}

rectangle :: Int -> Int -> Shape
rectangle len width = Shape {
  draw = ...,
  etc = ...
}

circle :: Int -> Int -> Shape
circle center radius = Shape {
  draw = ...,
  etc = ...
}