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
courten...@gmail.com <mailto:courten...@gmail.com>
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