data Point = Point { x :: Double, y :: Double }
data Circle = Circle { center :: Point, radius :: Double }
data Rectangle = Rectangle { edge1 :: Point, edge2 :: Point }
                                     
class Shape a where                  
    area :: a -> Double              
                                     
instance Shape Circle where          
    area :: Circle -> Double         
    area (Circle {radius = r}) = pi * r^2 
                                     
instance Shape Rectangle where       
    area :: Rectangle -> Double   
    area (Rectangle {edge1 = Point {x = x1, y = y1}
                     , edge2 = Point {x = x2, y = y2}})
        = length * width
      where
        length = abs (x1 - x2)                                                                                                                                                 
        width = abs (y1 - y2) 
                    
main = print $ area $ Rectangle (Point 0 0) (Point 3 4)