My thanks to everyone who replied with their helpful comments. You are
right that I forgot to add the public inheritance on the C++ classes (that's
what happens when you write code in an email without passing it through a
compiler first).
I like the idea below, which is easy to understand. It seems to me, though,
that there's a lot more to the use of typeclasses than is covered in some of
the haskell textbooks, and if anyone knows of a good in-depth treatment of
this, I would be grateful for a pointer.
Thanks again to everyone who responded,
Simon
On Mon, Jul 5, 2010 at 2:28 PM, Miguel Mitrofanov
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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