RE: [Haskell-cafe] Newbie question about tuples

with guaranteed termination, of course

Just out of curiosity (not Haskell related): I always get confused when people speak about "guaranteed termination"; what about the halting problem? In which context can one check for "guaranteed termination", as the halting problem says it's not *generally* possible? -----Original Message----- From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Jonathan Cast Sent: Friday, July 13, 2007 16:21 To: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Newbie question about tuples 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 struct Vector { T Element[N];

friend T dot(const Vector& a, const Vector& b) { T result = 0; for( int i=0; i

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 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 No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.476 / Virus Database: 269.10.4/898 - Release Date: 12/07/2007 16:08 No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.476 / Virus Database: 269.10.4/898 - Release Date: 12/07/2007 16:08