Type-safe matrix multiplication

After the long-winded discussion at Write this Scala Matrix multiplication in Haskell, I was left wondering...what would a type-safe matrix multiplication look like? So here's your challenge: either link to a Haskell implementation, or implement yourself, the following:

data Matrix ... = ...

matrixMult :: Matrix ... -> Matrix ... -> Matrix ...
matrixMult ... = ...

Where matrixMult produces a type error at compile time if you try to multiply two matricies with incompatible dimensions. Brownie points if you link to papers or books that discuss this precise topic, and/or discuss yourself how useful/useless this functionality is.