module Main where

import System (getArgs)

class Shape s where draw :: s-> String
                    draw _ = "Shape"
class Shape s=> Triangle s
class Shape s=> Circle s

data TriangleT = Triangle
instance Shape TriangleT where draw Triangle = "Triangle"
instance Triangle TriangleT 

data CircleT   = Circle
instance Shape CircleT where   draw Circle   = "Circle"
instance Circle CircleT

data ShapeT = forall s. Shape s=> Shape s
instance Shape ShapeT where 
  draw (Shape s) = draw s

main :: IO ()
main = do 
  a<- getArgs 
  let s= case (head a) of 
           "t" -> Shape Triangle; "c"-> Shape Circle

  putStrLn (draw s)

data ShapeDef = ShapeDef 
instance Shape ShapeDef where   draw _ = "Shape"  

main' :: IO ()
main' = do 
  a<- getArgs 
  let s= case (head a) of 
           "t" -> Shape Triangle; "c"-> Shape Circle; _ -> Shape ShapeDef

  putStrLn (draw s)