I have a module with a matrix type constructor:

> data (Natural r, Natural c) => Matrix r c t = Matrix [[t]] deriving (Eq)

which uses type-level naturals to provide dimension checking.

A type class for multiplication:

> class Multiply a b where
>  type Product a b
>  times :: a -> b -> Product a b

and an instance for matrix multiplication:

> instance (Natural a, Natural b, Natural c, Num t) => Multiply (Matrix a b t) (Matrix b c t) where
>  type Product (Matrix a b t) (Matrix b c t) = Matrix a c t
>  times m1 m2 = ...

All of this works really well, I get dimension checking (and inference), and lot of other goodies.

My request has to do with the following GHCi session:

*Main> let a = matrix two two [[1,1],[2,6]]
*Main> :t a
a :: Matrix Two Two Integer
*Main> :t a `times` a
a `times` a :: Product
                 (Matrix Two Two Integer) (Matrix Two Two Integer)

When a type function is fully-applied, as Product is in this case, it would be nice if GHC could simplify it prior to display.

This would result in the following output for this example:

:t a `times` a
a `times` a :: Matrix Two Two Integer

I have attached the files necessary to run this test case, although a simpler one could be constructed.