On Fri, Jul 25, 2003 at 08:31:26AM -0700, Hal Daume wrote:
However, once we fix this, we can see the real problem. Your Universe class has a method, distanceVector, of type:
| distanceVector :: Universe u, Floating a => u -> Vector a -> Vector a -> Vector a
And here's the problem. When 'u' is 'OrthorhombicUniverse x', it doesn't know that this 'x' is supposed to be the same as the 'a'. One way to fix this is to parameterize the Universe data type on the element, something like:
class Universe u where distanceVector :: (RealFrac a, Floating a) => u a -> (Vector a) -> (Vector a) -> (Vector a) ...
Another approach is to make Universe a multi-parameter type class: class (RealFrac a, Floating a) => Universe u a | u -> a where distanceVector :: u -> Vector a -> Vector a -> Vector a ... You need to use ghc with '-fglasgow-exts' for this. Peace, Dylan