[Haskell-beginners] Multiple type numeric data

[Didier Jacquemart]

Hello,

I'm just learning Haskell and have problems with a simple calculation: 
Here is my code below :

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)

When i load this program, i get the following error for the line 3.14 * 
r * r

Couldn't match expected type Float
            against inferred type Integer
In the expression : 3.14 *r * r
...

Further, i think there's a problem with the surface function, since it's 
not typed.

Thanks for your help.
Didier.