Didier, here is some code that improves your one function, it will almost compile with ghc. module Main where data Figure = Carre Int Int Int | Rond (Int, Int, Integer) -- i hope Integer allows fromInteger function for r surface_carre :: Figure -> Int surface_carre (Carre x y c)= c * c surface_rond :: Figure -> Float surface_rond (Rond (x, y, r))= 3.14 * (fromInteger (r * r)) surface x = case x of Carre a b c -> surface_carre x Rond (a, b, c) -> surface_rond x a::Figure a=Carre 10 10 5 b::Figure b=Rond (20, 20, 3) main :: IO () main = do putStrLn "Test" return () Note that surface has a problem because surface_carre returns an Int and surface_rond returns a Float. These types are incompatible. I don't think there is a more general type you can use. Can you get away with just using all the same type? - iæfai On 2009-11-01, at 12:53 PM, Didier Jacquemart wrote:
data Figure = Carre Int Int Int | Rond (Int, Int, Integer) -- i hope Integer allows fromInteger function for r
surface_carre :: Figure -> Int surface_carre (Carre x y c)= c * c
surface_rond :: Figure -> Float surface_rond (Rond (x, y, r))= 3.14 * r * r
surface x = case x of Carre a b c -> surface_carre x Rond (a, b, c) -> surface_rond x a::Figure a=Carre 10 10 5 b::Figure b=Rond (20, 20, 3)