patterns.hs

module Main where
type Radius = Double
type Side   = Double
data Shape =
           Point
        |  Circle    Radius
        |  Rectangle Side Side
        |  Square    Side
area Point
area (Circle r) =pi*r*r area (Rectangle w h) = w * h
area (Square s) =s*s
rev [] = []
rev (x:xs) = rev xs ++ [x]
main = do
  print (area Point)
  print (area (Circle 10))
  print (area (Rectangle 20 343535))
  print (area (Square 20))
  print (rev [42, 55, 10, 20])