On Friday 13 July 2007, peterv wrote:
> I'm beginning to see that my old implementation in C++ clutters my Haskell
> design.
>
> You see, in C++ I can write:
>
> // A vector is an array of fixed-length N and elements of type T
> template<typename T, int N> struct Vector
> {
> T Element[N];
>
> friend T dot(const Vector& a, const Vector& b)
> {
> T result = 0;
> for( int i=0; i<N; ++i )
> {
> result += a.Element[i] * b.Element[i];
> }
> return result;
> }
> };
>
> So basically a wrapper around a fixed-size array of any length.
> Implementations of (+), (-), dot, length, normalize, etc... then work on
> vectors of any size, without the overhead of storing the size, and with
> compile-time checking that only vectors of the same size can be used,
> etc... This also fits in nicely when creating a Matrix<T,N,M> class.
>
> I don't think Haskell has something like a "fixed-length array" or constant
> expressions that *must* be resolved at compile-time (like the N in the C++
> template)?
I'm surprised no one has posted anything on type-level programming yet. You
might google for that. And GHC 6.8 will have true type-level functions (with
guaranteed termination, of course) which will help. But I'm sure a good
google will turn up a clearer explanation than I can provide; I've never
needed or wanted to understand the type-level stuff.
Jonathan Cast
http://sourceforge.net/projects/fid-core
http://sourceforge.net/projects/fid-emacs
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
