My guess is that it's class B : public A and class C : public A In this case it seems perfect to use type classes: class A t where do_x :: t -> Integer -> Integer -> Integer data B = ... instance A B where do_x b x y = ... data C = ... instance A C where do_x c x y = ... If you want some general "A" object, you can use existentials (or, better yet, GADTs): data A_general = forall t. A t => A_general t or data A_GADT where A_GADT :: A t => t -> A_GADT so that int foo (A v) {... v.do_x(1,2)...} becomes foo :: A_GADT -> Integer foo (A_GADT v) = ... do_x v 1 2 ... Simon Courtenage wrote:
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 mailto:courtenage@gmail.com
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