2006/11/28, Slavomir Kaslev
Hello,
I have to define a couple of float2, float3, float4 Cg, HLSL style vectors in Haskell. At first I was tempted to make them instances of Num, Floating, RealFrac, etc. but some of the functions defined in those classes have no sense for vectors. One such example is signum from class Num.
There are several workarounds for this. One may come up with some meaning for vectors of such functions, for example:
instance Num Float3 where ..... signum a | a == Float3 0 0 0 = 0 | otherwise = 1
This is silly. Other option, which I prefer, is to leave such functions undefined (that is signum=undefined, not just not defining them). Is this ok? Are there any other options?
Another bugging thing is that some of the functions do have meaning for vectors but they need different signatures. For example (**) :: Floating a => a -> a -> a, for vectors should be (**) :: (Floating a, Vector v) => v -> a -> v, that is (**) applied for every component of the vector. Any workarounds for that? Those are the type signatures of +, ... you can't break them. So it won't be possible to use + to add two values of different types.
I know that I can scrap all those Num, Floating, RealFrac, etc. classes and define class Vector from scratch, but I really don't want to come up and use different names for +, -, etc. that will bloat the code.
Last question: Does haskell have something like C++ templates? For example, some time in the future I may need types like int2, short3, etc., that behave just like float2, float3, but use different types for their components. I really, really wouldn't like to copy-paste the definitions of floatn and manually change their types to intn respectfully.
Yep, you have to learn that you can parametrise a type (constructor). For exemple, realise that [1], ["hello"] and "hello" are values of different types, i.e. different list types. The first one is of type [Int], the second one is [String] and the third [Char] (so you see that String is simply [Char]). In your case, you would want to define something like: Data Float2 a = Float2 a a then, optionnaly type Float2Int = Fl2 Int Bye, thu
Cheers.
-- Slavomir Kaslev _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe