Does this work for you?
data A a = A (Int,Int)
data B
data C
class A_Class a where
do_x :: a -> Int
instance A_Class (A B) where
do_x (A (a,b)) = a + b
instance A_Class (A C) where
do_x (A (a,b)) = a - b
-- > do_x ((A (1,2)) :: A B)
-- 3
-- > do_x ((A (1,2)) :: A C)
-- -1
-deech
On Mon, Jul 5, 2010 at 9:22 AM, Simon Courtenage
Hi, I am porting a C++ program to Haskell. My current task is to take a class hierarchy and produce something equivalent in Haskell, but I don't seem to be able to get a grip on how type classes and instances contribute to the solution. Can anyone enlighten me? Roughly, the class hierarchy in C++ is of the form class A { public: virtual int do_x(int,int) = 0; }; class B { public: int do_x(int x,int y) { ...} }; class C { public: int do_x(int x,int y) { ...} }; Any help would be greatly appreciated. Thanks Simon courtenage@gmail.com
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